Features of quantitative and qualitative data analysis. Quantitative Analysis

Already in the course of the study, one can assume about its results, but usually these conclusions are considered preliminary, and more reliable and thorough data can only be obtained as a result of a thorough analysis.

Data analysis in social work is about integrating all the information collected and bringing it into a form suitable for explanation.

Methods for analyzing social information can be divided into two large classes in accordance with the form in which this information is presented:

- qualitative methods focused on the analysis of information presented mainly in verbal form.

- quantitative methods are mathematical in nature and represent processing techniques digital information.

Qualitative analysis is a precondition for the use of quantitative methods; it is aimed at identifying the internal structure of the data, that is, at clarifying those categories that are used to describe the sphere of reality being studied. At this stage, the final determination of the parameters (variables) necessary for a comprehensive description occurs. When there are clear descriptive categories, it is easy to move on to the simplest measurement procedure - counting. For example, if you identify a group of people who need certain help, you can calculate the number of such people in a given microdistrict.

In a qualitative analysis, there is a need to produce information compression, that is, obtain the data in a more compact form.

The main method of information compression is coding - the process of analyzing qualitative information, which includes the identification of semantic segments text or real behavior, their categorization (naming) and reorganization.

To do this, find and mark in the text itself keywords, that is, those words and expressions that carry the main semantic load directly indicate the content of the text as a whole or its individual fragment. Different types of highlighting are used: underlining with one or two lines, color marking, making notes in the margins, which can be in the nature of both additional icons and comments. For example, you can highlight those fragments where the client talks about himself. On the other hand, you can highlight everything that concerns his health; you can separate those problems that the client is able to solve himself, and those problems for which he needs outside help.

Fragments of similar content are marked in a similar way. This allows them to be easily identified and, if necessary, collected together. Then the selected fragments are searched using different headings. By analyzing the text, you can compare its individual fragments with each other, identifying similarities and differences.

The material processed in this way becomes easily visible. The main points come to the fore, as if rising above the mass of details. It becomes possible to analyze the relationships between them, identify their general structure and, on this basis, put forward some explanatory hypotheses.

When several objects are studied simultaneously (at least two) and when comparison in order to detect similarities and differences becomes the main method of analysis, the comparative method is used. The number of objects studied here is small (most often two or three), and each of them is studied in sufficient depth and comprehensively.

It is necessary to find a form of data presentation that is most convenient for analysis. The main technique here is schematization. A scheme always simplifies real relationships and coarsens the true picture. In this sense, schematization of relationships is also a compression of information. But it also involves finding a visual and easily visible form of presenting information. This purpose is served by combining data into tables or diagrams.

For ease of comparison, the material is summarized in tables. The general structure of the table is as follows: each cell represents the intersection of a row and a column. The table is convenient because it can include both quantitative and qualitative data. The point of the table is that it can be glanced at. Therefore, usually the table should fit on one sheet. The pivot table used for analysis is often drawn on a large sheet of paper. But a large table can always be divided into several parts, that is, several tables can be made from it. Most often, a row corresponds to one case, and the columns represent its various aspects (features).

Another method of concise and visual presentation of information is diagrams. There are different types of diagrams, but almost all of them are structural diagrams, in which elements are depicted with conventional figures (rectangles or ovals), and connections between them are depicted with lines or arrows. For example, using a diagram is convenient to represent the structure of any organization. Its elements are people, or more precisely, positions. If the organization is large, then larger structural elements—divisions—are selected as elements. Using the diagram, it is easy to imagine the hierarchy of relationships (the system of subordination): senior positions are located higher on the diagram, and junior ones are lower. The lines connecting the elements indicate exactly who is directly subordinate to whom.

Representation in the form of diagrams can also be used to identify the logical structure of events or text. In this case, a semantic analysis is first carried out and key events or components are outlined, and then they are presented in graphical form so that the connection between them becomes as clear as possible. It is clear that schematization leads to a coarsening of the picture due to the omission of many details. However, information is compressed and converted into a form convenient for perception and memorization.

Thus, the main techniques of qualitative analysis are coding and visual presentation of information.

Quantitative analysis includes methods for statistical description of a sample and methods for statistical inference (testing statistical hypotheses).

Quantitative (statistical) methods of analysis are widely used in scientific research in general and in the social sciences in particular. Sociologists resort to statistical methods to process the results of mass public opinion polls. Psychologists use the apparatus of mathematical statistics to create reliable diagnostic tools - tests.

All methods of quantitative analysis are usually divided into two large groups. Methods of statistical description are aimed at obtaining a quantitative characteristic of the data obtained in a specific study. Statistical inference methods allow one to correctly extend the results obtained in a specific study to the entire phenomenon as such, and to draw conclusions of a general nature. Statistical methods make it possible to identify consistent trends and build on this basis theories designed to explain them.

Science always deals with the diversity of reality, but it sees its task in discovering the order of things, some stability within the observed diversity. Statistics provide convenient methods for such analysis.

To use statistics, two basic conditions are required:

a) it is necessary to have data about a group (sample) of people;

b) this data must be presented in a formalized (codified) form.

It is necessary to take into account possible sampling error, since only individual respondents are taken for the study; there is no guarantee that they are typical representatives of the social group as a whole. Sampling error depends on two factors: the sample size and the degree of variation of the characteristic that interests the researcher. The larger the sample, the less likely it is that it will include individuals with extreme values of the variable under study. On the other hand, the lower the degree of variation of a characteristic, the generally closer each value will be to the true mean. Knowing the sample size and obtaining a measure of the dispersion of observations, it is not difficult to derive an indicator called standard error of the mean. It gives the interval within which the true population mean should lie.

Statistical inference is the process of testing hypotheses. Moreover, the initial assumption is always made that the observed differences are random in nature, that is, the sample belongs to the same general population. In statistics, this assumption is called null hypothesis.

Methodology for preparing final (qualifying) work, requirements for its content and format

The final (qualifying) work completes the training of a social work specialist at a university and shows his readiness to solve theoretical and practical problems.

The final (qualifying) work must be an independent, complete development, in which current problems of social work are analyzed, the content and technologies for solving these problems are revealed not only in theoretical, but also in practical terms at the local and regional levels. Any final (qualifying) work in social work should be a kind of social project.

The final (qualifying) work must indicate that the author has deep and comprehensive knowledge of the object and subject of research, the ability to conduct independent scientific research using the knowledge and skills acquired during the development of the main educational program;

The final (qualifying) thesis must contain a rationale for choosing a research topic, a review of published specialized literature on this issue, a presentation of the research results, specific conclusions and proposals.

The final (qualifying) work must demonstrate the author’s level of mastery of scientific research methods and scientific language, his ability to present the material briefly, logically and reasonably.

The final (qualifying) work should not mechanically repeat the graduate’s academic work (coursework, abstracts, etc.).

Conclusions, proposals and recommendations on the problems under study, put forward by the author to the bodies, organizations, institutions and services of social protection of the population, must be specific, have practical and theoretical value, and have elements of novelty.

Objectives of the thesis:

Systematization, consolidation and expansion of theoretical and practical knowledge in social work, their application in solving specific practical problems;

Development of independent work skills;

Mastering the methodology of research, generalization and logical presentation of material.

In the thesis the student must show:

Solid theoretical knowledge on the chosen topic, problematic presentation of theoretical material;

Ability to study and summarize general and specialized literature on the topic, solve practical problems, draw conclusions and suggestions;

Skills in analysis and calculations, experimentation, computer skills;

Ability to competently apply methods for assessing the social effectiveness of proposed activities.

The thesis has a clear composition: introduction, main part, consisting of several chapters, and conclusion.

The introduction indicates the topic and purpose of the thesis, substantiates the relevance of the research, its theoretical and practical significance, and names the main research methods. It provides the rationale for addressing this topic, its relevance at the moment, the significance, purpose and content of the tasks set, the object and subject of the research are formulated, and it is reported what the theoretical significance and practical value of the results obtained are.

Topics of final (qualifying) works are approved by the graduating departments. The topic must correspond to the specialty; when formulating it, it is advisable to take into account the scientific directions that have developed in the department and the possibility of providing students with qualified scientific guidance. It is desirable that the topics be relevant and have novelty, theoretical and practical significance. When formulating a topic, one must take into account the presence or absence of literature and practical materials, the student’s own work on the topic (term papers, scientific reports, etc.), the student’s interest in the chosen topic, and the student’s ability to conduct the necessary research.

Consequently, the introduction is a fairly important part of the thesis, since it predetermines the further development of the topic and contains the necessary qualification characteristics.

The relevance of the topic, importance, significance at the present time, modernity, topicality is a prerequisite for any scientific work. Justification of relevance is the initial stage of any research, characterizing the student’s professional training in how he knows how to choose a topic, formulate it, how correctly he understands it and evaluates it from the point of view of modernity, its scientific or practical significance. Coverage of relevance should not be wordy. It is enough to show the essence of the problem, to determine where the border between knowledge and ignorance about the subject of research lies.

From the formulation of the scientific problem and evidence that its part, which is the object of study of this work, has not yet received sufficient development and coverage in the scientific literature, it is logical to move on to the formulation of the purpose of the research being undertaken, as well as pointing out specific tasks that need to be solved in accordance with this purpose. Purpose of the study- what the graduate student strives for in his thesis, what he is going to accomplish, establish, why he took up the development of this topic. In accordance with the given goal, the student will have to formulate specific research objectives as certain stages of research that must be completed to achieve the goal.

In addition to the above, a mandatory element of the introduction is the formulation of the object and subject of the study, where an object is a process or phenomenon that generates a problem situation and is chosen for research, and item- something that is within the boundaries of the object. The object and subject of research are related to each other as general and specific. It is on the subject of the research that the thesis student’s main attention should be directed, since it is the subject of the research that determines the topic of the work indicated on the title page.

An obligatory element of the introduction of a scientific work is also an indication of research methods, which serve as a tool in obtaining factual material, being a necessary condition for achieving the goal set in such work.

The introduction describes other elements of the scientific process. These include, in particular, an indication of what specific material the work itself was performed on. It also provides a description of the main sources of information (official, scientific, literary, bibliographic), and also indicates the methodological basis of the study.

Main part consists of several chapters, which, in turn, are divided into paragraphs. This compositional part outlines the main theoretical principles of the thesis, analyzes the factual material, and provides statistical data. Possible illustrative material can be presented here or included in the appendix.

In the main part of the work, the student reveals the methodology and methodology of the research, using for this purpose the following methods: observation, comparison, analysis and synthesis, induction and deduction, theoretical modeling, ascent from the abstract to the concrete, and vice versa.

The content of the chapters of the main part must correspond exactly to the topic of the work and fully disclose it. The conclusions drawn by the graduate student in the study must be consistent, reasoned, and scientifically substantiated. In this case, argumentation is understood as a logical process, the essence of which is that it substantiates the truth of the expressed judgment with the help of other judgments, examples, and arguments.

Conclusion contains conclusions on the thesis. Conclusions should reflect the main content of the work, be accurate and concise. They should not be replaced by a mechanical summation of conclusions at the end of chapters that present a brief summary, but contain something new that constitutes the final results of the study. It is here that the knowledge that is new in relation to the original knowledge is contained. It is this that is brought up for discussion and evaluation by the state commission and the public in the process of defending the thesis.

If the work had practical significance, the conclusions should contain indications of where and how they can be applied in social work practice. In some cases, it becomes necessary to indicate ways to continue researching a topic, those tasks that future researchers will have to solve first. The work is completed with a list of normative materials used and a list of references used.

Auxiliary or additional materials that clutter the text of the main part of the work are placed in the appendix. The content of applications can be quite diverse. These, for example, can be copies of original documents (Charter, Regulations, Instructions, reports, plans, etc.), individual excerpts from instructions and rules, unpublished texts, etc. In form they can be text, tables, graphs , cards.

The appendices cannot include a bibliographic list of used literature, auxiliary indexes of all types, reference comments and notes, which are not appendices to the main text, but elements of the reference and accompanying apparatus of the work that help to use its main text.

The final qualifying work is submitted to the department in printed form. The approximate amount of work should be 2-2.5 p.l. (50-60 pages of typewritten text). Field boundaries: left - 3.5 cm; on the right - 1.5 cm, on top and bottom - 2.5 cm. Computer typing is carried out in the text version of Microsoft Word (interval 1-1.5 according to the multiplier, 12-14 font Times New Roman).

All pages of the work, including pages with tables and diagrams, are numbered sequentially in Arabic numerals, located, as a rule, above the middle of the text.

The title page of the thesis includes the full name of the organization in which the work was performed, the name of the department, the title of the essay, the code and name of the specialty, the surname and initials of the performer, surname, initials, scientific degree (position, title) of the supervisor, city and year of writing.

The titles of chapters and paragraphs are indicated in the same sequence and in the same wording in which they are given in the text of the work.

The text of the main part of the work is divided into chapters, sections, subsections, paragraphs, paragraphs.

The thesis, prepared in accordance with the requirements, must be submitted to the graduating department no later than 14 days before the defense period. The terms of the pre-defense and the terms of defense of the thesis are established by the graduating department.

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Since ancient times, people have tested the properties and suitability of food (meat, vegetables, fruits, etc.) using organoleptic properties - color, smell, taste, etc. Nowadays, a variety of chemical, physical and physicochemical methods of analysis are widely used. Until now, the Pharmacopoeia provides organoleptic properties for most drugs. However, when checking the authenticity and suitability of a drug, preference is given to the use of a variety of chemical reactions used in analytical chemistry. Analytical chemistry is divided into two parts: a) qualitative analysis b) quantitative analysis.

Qualitative analysis makes it possible to establish what chemical elements the test sample consists of, what ions, functional groups or molecules are included in its composition. When studying unknown substances, qualitative analysis always precedes quantitative analysis.

Depending on the composition of the object under study, the following are distinguished:

Analysis of inorganic substances, which includes the detection of cations and anions;

Organic matter analysis, which includes:

a) elemental analysis - detection and determination of chemical elements;

b) functional analysis - determination of functional groups consisting of several chemical elements and having certain properties;

c) molecular analysis - detection of individual chemical compounds. Thus, the main task of qualitative analysis is to detect the corresponding cations, anions, functional groups, molecules, etc. in the test sample. The main task of quantitative analysis is to determine the amount of a particular component contained in the analyzed sample. The tasks and methods of quantitative analysis are discussed in detail in the "Methodological manual on quantitative analysis for students of the Faculty of Pharmacy."

Papplication of qualitative analysis in pharmacy

Various methods of qualitative analysis are widely used to check and evaluate the quality of medicinal products. Qualitative chemical reactions in pharmaceutical analysis are used

to determine the authenticity of a medicinal substance;

for testing for purity and presence of impurities;

to identify individual ingredients in multi-substance medicinal products.

ABOUTauthentication and purity testing of pharmaceuticals

To determine the authenticity of the drug under study, analytical chemical reactions are carried out, and, if necessary, the corresponding physicochemical constants (boiling point, melting point, etc.) are measured.

The analysis of substances that are electrolytes in aqueous solutions comes down to the determination of cations and anions.

The identification of most organic medicinal substances is carried out using specific reactions, which are based on the chemical properties of the functional groups included in their composition. The main requirement for these reactions is sufficient sensitivity with respect to the ions or functional groups being determined and a high rate of their occurrence.

Purity Tests and Impurity Limits

The criterion for the purity of a medicinal substance is the absence of some impurities and a limited amount of others. Impurities can be divided into two groups: 1) impurities that negatively affect the pharmacological effect of the drug; 2) impurities that do not affect the pharmacological effect, but reduce the content of the active component in the drug. For the first group of impurities that negatively affect the pharmacological effect of the drug, the sample must be negative. The second group of impurities does not affect the pharmacological effect and may be present in the drug in small quantities. A list of indicators and standards for the content of these impurities is presented in the relevant literature.

Mmethods of qualitative analysis

Chemical methods of qualitative analysis use qualitative analytical reactions. With the help of such reactions, the desired chemical element or functional group is converted into a compound that has a number of characteristic properties: color, smell, state of aggregation. The substance that is used to carry out a qualitative analytical reaction is called a reagent or reagent. Chemical methods are characterized by high selectivity, ease of implementation, and reliability, but their sensitivity is not very high: 10-5 - 10-6 mol/l. In cases where higher sensitivity is needed, physicochemical or physical methods of analysis are used. Physical methods are based on measuring a certain physical parameter of the system, which depends on the content of the component. For example, in qualitative spectral analysis, emission spectra are used, since each chemical element has a characteristic emission spectrum. In the radiation spectrum, the inert chemical element helium was discovered first in the sun and then discovered on earth. Qualitative luminescent analysis uses luminescent emission spectra that are characteristic of an individual substance. In physicochemical methods of analysis, the corresponding chemical reaction is first performed, and then some physical method is used to study the resulting reaction product.

Using physical and physicochemical methods of analysis, both qualitative and quantitative analysis are quite often carried out. The use of these methods often requires the use of expensive equipment. Therefore, in qualitative analysis, physical and physicochemical methods of analysis are not used as often as chemical methods. When performing a qualitative chemical analysis, a certain amount of a substance is needed. Depending on the amount of substance taken for analysis, analysis methods are divided into macromethods, semi-micromethods, micromethods and ultramicromethods of analysis. For macroanalysis, 0.5 - 1.0 g of the substance or 20 - 50 ml of solution is used. The analysis is performed in ordinary test tubes, beakers, flasks, and precipitates are separated by filtration through filters, such as paper ones. In microanalysis, as a rule, from 0.01 to 0.001 g of a substance or from 0.05 to 0.5 ml of a solution are used; reactions are performed using the droplet or microcrystalscopic method. Semi-microanalysis occupies an intermediate position between macromethods and micromethods. For analysis, usually use from 0.01 to 0.1 g of dry matter or 0.5 to 5.0 ml of solution. Analytical reactions are usually carried out in conical tubes, and the solution is dosed using a dropper. The separation of solid and liquid phases is carried out using a centrifuge.

WITHmethods for performing analytical reactions

Analytical reactions are performed using the “dry” and “wet” methods. In the first case, the analyzed sample and analytical reagent are taken in a solid state and, as a rule, heated to a high temperature. Such reactions include:

1. Flame color reaction. Volatile salts of some metals on a platinum wire are introduced into that part of the burner flame that does not glow, and the color of the flame is observed in a characteristic color.

2. The reaction of the formation of “pearls” of borax Na2B4O7 or ammonium and sodium hydrogen phosphate NaNH4HPO4. A small amount of one of these salts is fused in the eye of a platinum wire until a glassy mass is formed that resembles a pearl. Then a few grains of the analyzed substance are applied to the hot pearl and brought back into the burner flame. By changing the color of pearls, they conclude that the corresponding chemical elements are present.

3. Fusion reactions with dry substances: (Na2CO3; KClО3; KNO3, etc.) to obtain specifically colored products.

Reactions that are carried out using the “dry” method are of an auxiliary nature and are used for preliminary tests. Reactions performed by the “wet” method (in solution) are basic in qualitative analysis.

Reactions that are performed in a “wet” way must be accompanied by an “external” effect:

change in the color of the solution,

formation or dissolution of a precipitate,

gas release, etc.

Hsensitivity and specificity of analytical reactions

In qualitative analysis, chemical reactions are characterized by the following parameters: a) specificity and selectivity. b) sensitivity. A specific reaction is one that can be used to determine the presence of a specific ion in the presence of other ions. An example of a specific reaction is the opening of ions by the action of a strong alkali solution when heated:

If the sample being analyzed contains ammonium ions, then when heated, ammonia gas is released, which can be easily identified by its smell or by the change in color of red litmus paper. This reaction is specific and is not interfered with by any other ions.

Little is known about specific reactions in qualitative analysis, so reactions are used that can be carried out only when the analyzed solution does not contain those ions that interfere with the desired reaction. Selective is a reaction, for which it is necessary to first remove from the solution those ions that interfere with the desired qualitative reaction. For example, the pharmacopoeial qualitative reaction to K+ ions is the effect of a solution of sodium tartrate:

If the analyzed sample contains potassium ions, then a white precipitate of acidic potassium tartrate is formed. But ions have exactly the same effect:

Consequently, ammonium ions interfere with the determination of potassium ions. Therefore, before determining potassium ions, ammonium ions must be removed. Effective performance of selective reactions is possible if ions that interfere with the determination of a given ion or substance are removed from the solution. Most often, for this purpose, the system is divided (into precipitate and solution) so that the ion that is determined and the ion that interferes with this are located in different parts of the system.

The sensitivity of a reaction (reagent) is a measure of the ability of a reagent to produce a reliably detectable analytical effect with the ion being determined. The smaller the amount of a substance that can be detected using a certain reaction, the more sensitive it is. Therefore, when choosing reactions for detecting various ions, it is necessary to know the quantitative characteristics of the sensitivity of the reactions. Quantitative characteristics of the sensitivity of a reaction are the opening minimum (the minimum that is detected), the detection limit and the dilution limit.

The smallest amount of a substance or ions that can be detected by a particular reaction under certain conditions is called the discoverable minimum. This value is very small, it is expressed in micrograms, that is, in millionths of a gram, and is denoted by the Greek letter g (gamma); 1g = 0.000001g = 10-6g.

At the suggestion of the terminology commission of IUPAC (International Union of Pure and Applied Chemistry), to characterize the smallest content that can be determined using this method, I recommend using the term definition limit. Thus, the limit of determination is the minimum content of the component at which the presence of the determined component is determined using this technique with a given confidence probability of 0.9. For example, Cmin 0.9 = 0.01 µg, means that this method determines 0.01 µg of a substance with a confidence probability of 0.9. Confidence probability is denoted by “p”, then in general the definition limit should be denoted as follows: Cmin p.

It should be remembered that the sensitivity of a reaction cannot be characterized only by the absolute amount of a substance. The concentration of ions or substances in the solution is also important. The lowest concentration of an ion or substance at which it can be detected by a given reaction is called the limiting concentration. In analytical practice, the reciprocal of the limiting concentration is used, which is called the “limiting dilution.” Quantitatively, the limiting dilution (h) is expressed by the ratio:

where V(solution) is the volume of the maximally diluted solution (in ml) containing 1 g of the substance or ions that need to be opened. For example, for the reaction to iron ions with potassium thiocyanate, the limit dilution is 1:10000. This means that when diluting a solution that contains 1 g of iron ions in a volume of 10,000 ml (10 l), detection of Fe3+ ions using this reaction is still possible.

The sensitivity of reactions largely depends on the conditions under which they are carried out (pH of solution, heating or cooling, use of non-aqueous solvents, etc.). The sensitivity of reactions is also affected by foreign ions, which in most cases are present in the analyzed solution.

Qualitative analysis of the test sample is usually carried out using the following two methods:

a) fractional analysis;

b) systematic analysis.

Fractional analysis is used to identify desired ions in the presence of other ions. Since little is known about specific reactions that allow the detection of a particular ion in the presence of any other ions, in fractional analysis many qualitative reactions are carried out after pre-treatment of the analyzed sample with reagents that precipitate or mask ions that interfere with the analysis. A significant contribution to the theory and practice of fractional analysis was made by N.A. Tananaev. The analytical reactions used in fractional analysis are called fractional reactions.

When selecting and conducting fractional reactions, you must:

select the most specific reaction for detecting the analyzed ion;

find out from literature data or experimentally which cations, anions or other compounds interfere with the selected reaction;

establish the presence in the analyzed sample of ions that interfere with the selected reaction;

select, based on reference data, a reagent that removes or masks such ions and does not react with the analyzed ions.

As an example, consider carrying out a fractional reaction for determining Ca2+, using the most commonly used reaction for detecting Ca2+ - the reaction with ammonium oxalate (NH4)2C2O4:

Ca2++ C2O42? = CaС2O4v. The sample contains Fe2+ and Ba2+ ions, which also form water-insoluble oxalates. It is known from the literature that many ions of d-elements, as well as s2-elements (Sr2+, Ba2+), interfere with the reaction with oxalates. Iron (II) can be removed by the action of ammonia in the form of Fe(OH)2 (PR = 7.9 10-16). Under these conditions, Ca2+ ions will not precipitate, since Ca(OH)2 is a strong base, quite soluble in water. In the presence of oxalates, Fe2+ will almost completely transform into the Fe(OH)2 precipitate, and Ca2+ will react with C2O42?. To remove Ba2+, it is advisable to use the action of sulfates, given that CaSO4 is somewhat soluble in water. The technique for performing a fractional reaction for determining Ca2+ ions is as follows. An ammonia solution (to pH 8 - 9) and a (NH4)2SO4 solution are added to the test solution. The resulting precipitates of Fe(OH)3 and BaSO4 are filtered off. (NH4)2C2O4 is added to the filtrate. The appearance of a white precipitate of CaС2О4 indicates the presence of Ca2+ ions in the analyzed sample. Systematic analysis is the analysis of a mixture of ions under study by dividing them into several analytical groups. Ions of a certain analytical group are isolated from solution by the action of a group reagent. The group reagent must quantitatively precipitate the ions of the corresponding analytical group, and an excess of the group reagent must not interfere with the determination of the ions remaining in solution. The resulting precipitate must be soluble in acids or other reagents in order to determine the ions that were in the precipitate.

XChemical reagents and working with them

Chemical reagents are substances that are used for chemical reactions. According to the degree of purity and purpose, the following categories of reagents are distinguished:

1) special purity (ultra-high purification), (special purity)

2) chemically pure (“reagent grade”),

3) pure for analysis (“analytical grade”),

4) clean (“h.”),

5) technical products packaged in small containers (“technical”).

High purity reagents are prepared for special purposes; their purity can be extremely high.

The purity of reagents of different categories is regulated by GOST and technical conditions (TU), the numbers of which are indicated on the labels. These labels also indicate the content of major impurities.

Reagents are also divided depending on their composition and purpose. Based on their composition, reagents are divided into the following groups:

a) inorganic reagents,

b) organic reagents,

c) reagents labeled with radioactive isotopes, etc.

By purpose, for example, organic analytical reagents, complexones, fixals, pH indicators, primary standards, solvents for spectroscopy, etc. are distinguished. The purpose of reagents is often reflected on the labels, where a number of other information is sometimes also indicated, especially in the case of organic substances. The full rational name, name in several languages, formula, molar mass, melting point or other characteristics, as well as the batch number and release date are indicated. When working with chemicals, it is necessary to take into account their toxicity and follow safety regulations.

All work with concentrated solutions of acids, alkalis, ammonia, hydrogen sulfide, as well as organic solvents is carried out in a fume hood.

When working with acids and alkalis, you must remember the rules for handling them carefully. If they come into contact with human skin, they can cause burns, and if they come into contact with clothing, they can damage them.

When diluting concentrated sulfuric acid, you must carefully pour the acid into the water, and not vice versa.

After working in the laboratory, you must wash your hands thoroughly.

TO qualitative analysis of inorganic substances

Qualitative analysis of inorganic substances allows us to establish the qualitative composition of both individual substances and mixtures, as well as determine the authenticity of a pharmaceutical product and the presence of impurities in it. Qualitative analysis of inorganic substances is divided into cation analysis and anion analysis.

TO qualitative analysis of cations

There are several methods for the systematic analysis of cations, depending on the use of group reagents:

a) sulfide (hydrogen sulfide) method, the group reagents in which are hydrogen sulfide and ammonium sulfide (Table 1);

b) ammonium phosphate method, group reagent - mixture of (NH4)2HPO4 + NH3 (Table 2);

c) acid-base method, group reagents - acids (HCl, H2SO4), bases (NaOH, KOH, NH3 H2O) (Table 3).

Table 1 Classification by sulfide method

Group number	Group reagent
		Li+; Na+; K+; NH4+
	(NH4)2CO3 + NH3 + NH4Cl Carbonates are not soluble in water	(Mg2+); Ca2+; Sr2+; Ba2+
	(NH4)2S + NH3 + NH4Cl Sulfides do not dissolve in water, ammonia, they dissolve in HCl.	Ni2+; Co2+; Fe2+; Fe3+; Al3+; Cr3+; Mn2+; Zn2+
	H2S + HCl Sulfides do not dissolve in HCl.	Cu2+; Cd2+; Bi3+; Hg2+; As3+; As5+; Sb3+; Sb5+; Sn2+; Sn4+
	HCl Chlorides are insoluble in water and acids	Ag+; Pb2+; Hg22+

Table 2 Ammonium-phosphate classification of cations

Group number	Group reagent

	(NH4)2HPO4 + NH3. Phosphates are insoluble in water and ammonia	Mg2+; Ca2+; Sr2+; Ba2+;Mn2+; Fe2+; Fe3+; Al3+; Cr3+;Bi3+; Li+
	Phosphates dissolve in ammonia to form ammonia	Cu2+; Cd2+; Hg2+; Co2+; Ni2+; Zn2+
	HNO3. Cations are oxidized to higher oxidation states	As3+; As5+; Sb3+; Sb5+; Sn2+; Sn4+
	HCl. Chlorides are insoluble in water and acids	Ag+; Pb2+; Hg22+

Table 3 Acid - basic classification of cations

Group number	Group reagent
	No. Chlorides, sulfates and hydroxides are soluble in water
	HCl Chlorides are insoluble in water and acids.	Ag+; Pb2+; Hg22+
	H2SO4 Sulfates are insoluble in water, acids and alkalis.	Ca2+; Sr2+; Ba2+
	NaOH Hydroxides are insoluble in water and soluble in both acids and alkalis.	Zn2+; Al3+; Cr3+; Sn2+; Sn(IV); As(III); As(V);
	NaOH Hydroxides are insoluble in water, ammonia and alkalis.	Mn2+; Mg2+; Fe2+; Fe3+; Bi3+; Sb(III); Sb(V)
	NH3 Hydroxides do not dissolve in water, excess alkali, dissolve in ammonia, and form ammonia.	Cu2+; Cd2+; Ni2+; Co2+; Hg2+

In pharmaceutical practice, the acid-base method is more often used, based on the different solubility of hydroxides and some salts formed by these cations (chlorides, sulfates) (Table 3).

Systematic analysis begins with preliminary tests, which are most often carried out dry (see page 3). Then the sample is dissolved and individual cations (NH4+, Fe2+, Fe3+, etc.) are determined, for which specific qualitative reactions are known. After this, cations of groups 2–6 are precipitated in the form of hydroxides and basic salts, acting on separate portions of a solution of K2CO3 or Na2CO3, and Na+ ions (if K2CO3 were acted) and K+ (if Na2CO3 were acted) are found in the filtrate. Then, in a separate portion of the solution, the second analytical group is precipitated using a solution of hydrochloric (hydrochloric) acid. Cations of analytical group III in the form of sulfates are precipitated with a 1 M solution of sulfuric acid in the presence of ethanol, and cations of analytical groups I, III, VI remain in solution. By adding excess NaOH, the mixture under study is divided in this way: cations of groups I and IV are in solution, and cations of groups V and VI are precipitated in the form of hydroxides. Further separation of cations of groups V and VI is carried out by the action of excess ammonia. In this case, hydroxides of cations of analytical group VI form soluble ammonia, and hydroxides of analytical group V remain in the sediment.

Thus, the main task of the group analytical reagent is:

a) determination of cations of the corresponding analytical group in the analyzed solution;

b) separation of cations of a certain group from cations of other analytical groups.

Analytical properties of cations . TO cations of the first analytical group

Analytical group I of cations includes alkali metal cations K+, Na+, as well as the complex cation NH4+. These cations have low polarization ability due to their large ionic radii. The ionic radii of K+ and NH4+ are close, therefore these ions have almost the same analytical properties. Most compounds of analytical group I cations are soluble in water. Therefore, analytical group I of cations does not have a group reagent.

In solution, hydrated K+, Na+ and NH4+ ions are colorless. The color of some sodium, potassium or ammonium compounds is due to the color of the anion, for example: Na2CrO4 is yellow, and KMnO4 is red-violet.

Reactions of potassium ions K+

Effect of a mixture of tartaric acid and sodium acetate (pharmacopoeial reaction).

Potassium ions form a white crystalline precipitate of potassium hydrogen tartrate:

KCl + H2C4H4O6 + CH3COONa = KHC4H4O6v + NaCl + CH3COOH

K+ + H2C4H4O6 + CH3COO? = KHC4H4O6v + CH3COOH

The same effect is achieved by the action of the acid salt of tartaric acid (sodium hydrogen tartrate) NaHC4H4O6:

KCl + NaHC4H4O6 = KHC4H4O6v + NaCl

K+ + HC4H4O6? = KHC4H4O6v

The KHC4H4O6 precipitate dissolves in mineral acids and alkalis:

KHC4H4O6 + H+ = K+ + H2C4H4O6

KHC4H4O6 + OH? = K+ + C4H4O62? + H2O

Therefore, the analysis of potassium ions is carried out in a neutral environment. The solubility of the KHC4H4O6 precipitate increases with increasing temperature. Therefore, to form this precipitate, cool the solution with cold water.

2. Effect of sodium hexanitrocobaltate (III) Na3. Potassium ions with this reagent form a yellow crystalline precipitate of sodium potassium hexanitrocobaltate (III):

2KCl + Na3 = K2Na v + 2NaCl

2K+ + Na+ + 3? = K2Nav

The precipitate can dissolve in mineral acids to form unstable acid H3 at pH<4.

K2Na + 3H+ = 2K+ + Na+ + H3

Alkalis decompose the reagent to form a brown precipitate, Co(OH)3:

K2Na + 3KOH = Co(OH)3v + 5KNO2 + NaNO2

K2Na + 3OH? = Co(OH)3v + 2K+ + Na+ + 6NO2?

Ammonium ions interfere with the determination of potassium ions because they react similarly to potassium ions.

3. Flame coloring reaction (pharmacopoeial reaction). Potassium salts turn the colorless burner flame purple. If there are sodium ions in the solution, which color the flame yellow and mask the violet color of potassium ions, the flame should be observed through cobalt blue glass. In this case, the yellow radiation from sodium is absorbed by the blue glass. The potassium emission will be observed as purple-red.

Reactions of sodium ions Na+

1. Effect of potassium hexahydroxostibiate K. Concentrated solutions of sodium salts, when interacting with this reagent, form a white crystalline precipitate:

NaCl + K = Nav + KCl

Na+ + ? = Nav

Na is a fine crystalline precipitate that quickly settles to the bottom of the test tube and partially adheres to the walls. The precipitate is clearly visible if you tilt the test tube or pour the solution out of it. If a precipitate does not form immediately (a supersaturated solution), rub the walls of the test tube with a glass rod and cool the solution.

Features of the reaction conditions.

1. The test solution must contain a neutral or slightly alkaline environment. In an acidic environment, reagent K decomposes, resulting in the formation of a white amorphous precipitate of metaantimony acid HSbO3:

K + HCl = KCl + Hv = HSbO3v + 3H2O

This precipitate is mistaken for Na precipitate and an erroneous conclusion is made about the presence of sodium ions in the solution. Therefore, acidic solutions are first neutralized with KOH alkali.

2. Na salt noticeably dissolves in water and is capable of forming supersaturated solutions, therefore, a precipitate does not precipitate from dilute solutions or precipitates after a long time. The concentration of sodium salt in the solution should be quite high; dilute solutions are first concentrated by evaporation.

3. The reaction must be carried out in the cold, since the solubility of Na increases with increasing temperature.

4. Ammonium salts interfere with the reaction. Due to hydrolysis, aqueous solutions of ammonium salts have an acidic reaction, so reagent K in the presence of ammonium salts decomposes, as in the case of acids. Mg2+ ions also interfere with the detection of Na+ ions, since they form a crystalline precipitate with K, which can be mistaken for a crystalline precipitate of Na.

Therefore, when detecting Na+ ions using K, the following conditions should be met:

the test solution should not contain NH4+ and Mg2+ ions;

the solution must be neutral or slightly alkaline and fairly concentrated;

the reaction must be carried out in the cold.

2. Action of zinc uranyl acetate Zn(UO2)3(CH3COO)8. Sodium ions with this reagent in neutral or acetic acid solutions form a pale yellow precipitate of sodium zinc uranyl acetate:

NaCl + Zn(UO2)3(CH3COO)8 + CH3COOH + 9H2O = NaZn(UO2)3(CH3COO)9 9H2Ov + HCl

Na+ +Zn2+ +3UO22+ +8CH3COO? +CH3COOH +9H2O =NaZn(UO2)3(CH3COO)9 9H2Ov+ H+

Under a microscope, NaZn(UO2)3(CH3COO)9 9H2O crystals look like regular octahedra or tetrahedra. In this case, the detection of Na+ ions is not interfered with by K+ or NH4+ ions.

3. Flame color reaction (pharmacopoeial reaction). Sodium salts color the burner flame yellow.

Reactions of ammonium ions NH4+

1. Action of alkali (pharmacopoeial reaction). Ammonium ions react with alkali solutions (KOH, NaOH). When heated, ammonia gas is released:

NH4+ + OH? = NH3^ + H2O

This reaction is specific and quite sensitive. Other cations do not interfere with the detection of ammonium ions.

Ammonia gas can be detected in several ways:

by smell;

by the blueness of red litmus paper moistened with distilled water;

corresponding chemical reactions, for example, the reaction between ammonia and mercury(I) nitrate proceeding according to the following equation:

In this case, a reaction occurs: disproportionation of mercury(I) into mercury(II) and metallic mercury. (A disproportionation reaction is the reaction of changing the oxidation state of the atoms of an element in a compound to form two substances in which this element exhibits a higher and lower oxidation state compared to the initial oxidation state of the element in the original compound).

Filter paper moistened with a solution of mercury (I) nitrate turns black. The blackening of filter paper is caused by the release of free metallic mercury.

2. Effect of Nessler's reagent K2. Ammonium ions with Nessler's reagent (alkaline solution K2) form a red-brown amorphous precipitate of mercury (II) amide complex, which has the following formula:

This amide complex has the following name: diiododimercurammonium iodide.

NH4Cl + 2K2 + 2KOH = Iv + 5KI + KCl

NH4+ + 22? + 2OH? = Iv + 5I?

The reaction is very sensitive. At low concentrations of ammonium ions, no precipitate is formed, and the solution turns yellow. In an acidic solution, the K2 reagent is destroyed to form a red precipitate, HgI2. The reaction must be carried out in a neutral or alkaline environment. The reaction is interfered with by cations that form colored hydroxide precipitates.

Cr(OH)3, Fe(OH)3, Ni(OH)2, etc.

3.Relation of ammonium salts to heating. All ammonium salts decompose when heated. The decomposition process of ammonium salts depends on the nature of the anion.

Ammonium salts, which contain anions of volatile acids (HCl, HBr, HF, etc.), when heated, decompose into gaseous ammonia and volatile acid, for example,

NH4Cl > NH3 + HCl

But when leaving the high temperature zone, the decomposition products combine again, forming an ammonium salt:

NH3 + HCl = NH4Cl.

If the composition of ammonium salts includes anions of non-volatile acids, then upon calcination gaseous ammonia is released, and the non-volatile acid remains:

(NH4)3PO4 = 3NH3^ + H3PO4

H3PO4 = H2O^ + HPO3

(NH4)3PO4 = 3NH3^ + H2O^ + HPO3

In cases where the salt anion has oxidizing properties, ammonia is oxidized to free nitrogen or to nitrogen oxides. For example:

(NH4)2Cr2O7 = N2 + 4H2O + Cr2O3

NH4NO3 = N2O + 2H2O

Examples of the decomposition of some other ammonium salts:

NH4NO2 = N2 + 2H2O

3(NH4)2SO4 = N2 + 4NH3 + 6H2O + 3SO2

(NH4)2C2O4 = 2NH3 + H2O + CO + CO2

WITHsystematic course of analysis of a mixture of cations.Pfirst analytical group

When analyzing cations of analytical group I, ammonium ions are first determined. To do this, add an alkali solution to a small amount of the analyzed solution and heat it. When ammonium ions are present, an ammonia odor is felt. If ammonium ions are detected, they must be removed from the solution because they interfere with the determination of potassium and sodium ions. To open sodium ions, KOH or K2CO3 is added to a separate portion of the solution being analyzed and boiled to remove ammonia. Then the solution is neutralized with acetic acid (CH3COOH), cooled and opened with Na+ by the action of a solution of K or Zn(UO2)3(CH3COO)8. To determine K+ ions, ammonia is removed from the solution by the action of NaOH or Na2CO3 when the solution is boiled. Then the solution is neutralized with acetic acid and, after cooling, K+ is determined by the action of solutions of NaHC4H4O6 or Na3

Practical recommendations for analyzing a mixture of cations of analytical group I

1. Determination of ammonium ions. To 2 - 3 drops of the solution being determined, add 6 - 8 drops of NaOH solution and heat. Wet red litmus paper is brought to the opening of the test tube. If ammonium ions are detected, ammonium ions must be removed before determining potassium or sodium ions (see the following points). If there are no ammonium ions, then steps 2 and 5 do not need to be performed. Potassium ions are opened by performing steps 3 or 4. Sodium ions are opened by performing steps 6 or 7.

2. Preparation of a solution for the determination of potassium cations. To 5 drops of the test solution add 5 drops of Na2CO3 or NaOH solution. The test tube with the solution is heated until the ammonia is completely removed (the odor disappears, wet red litmus paper should not turn blue). After ammonium ions are removed, a solution of acetic acid is added dropwise to the solution until it becomes acidic (the litmus paper should turn red) and cooled.

3. Determination of potassium cations by the action of a solution of NaHC4H4O6. To 2 - 3 drops of a solution that does not contain NH4+ ions, add 3 - 4 drops of NaHC4H4O6 solution, accelerating the precipitation by rubbing a glass rod against the walls of the test tube and cooling the solution.

4. Determination of potassium cations by the action of Na3 solution. 1 drop of a solution that does not contain NH4+ ions is applied to a glass slide, and 1 drop of Na3 solution is applied next to it. The drops are mixed with a glass rod.

5. Preparation of a solution for determining sodium cations. To 5 drops of the analyzed solution add 5 drops of K2CO3 or KOH solution. The test tube is heated to completely remove ammonia. After this, add acetic acid until the reaction is neutral.

6. Determination of sodium cations. To 3 - 4 drops of a solution that does not contain NH4+ ions, add 3 - 4 drops of K solution and rub the inner walls of the test tube with a glass rod.

7. Determination of sodium cations using microcrystalline reaction. A drop of a solution that does not contain NH4+ ions is placed on a glass slide. Carefully evaporate it almost dry. A drop of Zn(UO2)3(CH3COO)8 solution is placed nearby and the drops are connected to each other with a glass rod. The formed crystals are examined under a microscope.

Table 4TOqualitative reactions of cations of the analytical group

		Reaction product and its properties
	(Pharm.) K(Sb(OH)6]	Nav; white; R. k.l.
	Zn(UO2)3(CH3COO)8 +	NaZn(UO2)3(CH3COO)9 9H2Ov; green-yellow;
	(Farm.) Flame	yellow flame color
	(Pharm.) NaHC4H4O6	KNS4N4O4v; white; R. k.sch.
	(Pharm.) Na3	K2Nav; yellow; R. k.sch.,
	(Farm.) Flame	purple flame color
	(Pharm.) NaOH heating.	NH3 > litmus test turns blue 4NH3+2Hg2(NO3)2+ H2O >NO3v+ Hgv, black NH3 + HCl >NH4Cl; White smoke
		v; brown

R. -- soluble; to. - acids; sch. - alkalis, pharm. - pharmacopoeial reaction.

TOcations of the second analytical group.ABOUTgeneral characteristics

The second analytical group of cations includes Pb2+, Ag+, Hg22+ cations. Cations of the second analytical group form insoluble halides (except for silver fluoride) sulfates, sulfides, chromates, phosphates, arsenites, arsenates, hydroxides (oxides), carbonates. This is explained by the high polarization ability of these cations.

The group reagent for analytical group II is HCl solution. When exposed to HCl, only chlorides of cations of the second analytical group are precipitated. Cations of other analytical groups remain in solution.

Cations of analytical group II are characterized by complex formation reactions, and Hg22+ ions are characterized by oxidation-reduction reactions and disproportionation reactions. Therefore, the systematic analysis of cations of analytical group II is based on the reactions of precipitation, complexation and oxidation-reduction. Most salts of analytical group II cations are colorless. Colored salts are salts that contain colored anions, such as chromates.

Rreactions of cations of the second analytical group

1. The effect of a solution of hydrochloric (hydrochloric) acid. Analytical group II cations form white precipitates with HCl.

Ag+ +Cl? = AgClv PR = 1.78 10-10

Hg22+ +2Cl? = Hg2Cl2v PR = 1.3 10-18

Pb2+ + 2Cl? = PbCl2v PR = 1.6 10-5

Chloride precipitates dissolve in excess concentrated HCl to form complex ions

AgClv + 2HCl = H2

AgClv + 2Cl? = 2?

PbCl2v + 2HCl = H2

PbCl2v + 2Cl? = 2?

In this regard, a large excess of the group reagent is not allowed.

The most soluble of the chlorides of analytical group II is lead chloride, which dissolves noticeably in hot water (at 1000C, 3.34 g of PbCl2 can be dissolved in 100 g of H2O). This is used to separate PbCl2 from other cations of this group.

Silver chloride is soluble in ammonia, unlike mercury chloride (I):

AgClv + 2NH3 = Cl

AgClv + 2NH3 = + + Cl?

This reaction is used to separate AgCl from Hg2Cl2.

If the Hg2Cl2 precipitate is exposed to an ammonia solution, it will turn black due to the formation of fine metallic mercury

Hg2Cl2v+ 2NH3 = Clv + Hgv + NH4Cl.

Mercury amide chloride Cl, which is formed in this reaction, can be considered as ammonium chloride NH4Cl, in which two hydrogen atoms are replaced by one doubly charged mercury ion. This reaction is used to determine Hg22+ and separate it from other cations during analysis.

2. Action of alkalis.

Lead cations with alkalis form a white precipitate Pb(OH)2.

Pb2+ + 2OH? = Pb(OH)2v

Lead hydroxide has amphoteric properties, therefore it dissolves in both nitric acid and excess alkali:

Pb(OH)2v+ 2HNO3 = Pb(NO3)2+ 2H2O

Pb(OH)2v+ 2H+ = Pb2+ + 2H2O

Pb(OH)2v+ 2NaOH = Na2

Pb(OH)2v+ 2OH? = 2?

Silver cations with alkalis form a white precipitate of silver hydroxide AgOH, which quickly decomposes to form silver oxide:

Ag+ + OH? = AgOHv

2AgOHv= Ag2Ov + H2O

Mercury (I) cations, when interacting with alkalis, form a black precipitate of mercury (I) oxide:

Hg22+ + 2OH? = Hg2Ov + H2O

All oxides and hydroxides of cations of the second analytical group are soluble in nitric acid.

Ag2O + 2HNO3 = 2AgNO3 + H2O

Hg2O+2HNO3 = Hg2(NO3)2 + H2O

Pb(OH)2 + 2HNO3 = Pb(NO3)2 + 2H2O

3. Effect of potassium iodide solution.

Analytical group II cations form colored, poorly soluble iodides:

Ag+ + I? = AgIv yellow

Pb2+ + 2I? = PbI2v golden yellow color

Hg22+ + 2I? = Hg2I2v green.

Lead iodide is soluble in hot water acidified with acetic acid. Mercury (I) iodide Hg2I2 reacts with excess reagent:

Hg2I2v+ 2I? = 2? + Hgv

4. Effect of ammonia solution.

Silver cations form a white precipitate of silver hydroxide with ammonia solution, which quickly turns brown as the hydroxide turns into oxide. The precipitate is soluble in excess ammonia:

Ag+ + NH3 + H2O = AgOHv + NH4+

2AgOHv = Ag2Ov + H2O

Ag2Ov + 4NH3 + H2O = 2+ + 2OH?

In an acidic environment, the ammonia complex of silver is destroyed:

2H+ = Ag+ + 2NH4+

It is also destroyed by the action of iodide ions with the formation of a silver iodide precipitate:

I? = AgIv+ 2NH3

Mercury (I) cations with ammonia solution form the ammonia complex of mercury (II) and metallic mercury. For example, with Hg2(NO3)2 the reaction proceeds in accordance with the equation

Lead cations form white hydroxide with ammonia solution, which does not dissolve in excess of the reagent:

Pb2+ + 2NH3 + 2H2O = Pb(OH)2v+ 2NH4+

5. Action of chromates.

Cations of analytical group II form colored precipitates under the action of K2CrO4 or Na2CrO4:

2Ag+ + CrO42? = Ag2CrO4v brick red;

Hg22+ + CrO42? = Hg2CrO4v red;

Рb2+ + CrO42? = PbCrO4 v yellow.

Silver chromate dissolves easily in ammonia solution:

Ag2CrO4v+ 4NH3 = 2+ + CrO42?.

Lead chromate precipitate is soluble in potassium and sodium hydroxides:

PbCrO4v + 4OH? = 2? + CrO42?.

Chromate precipitates are soluble in nitric acid:

2Ag2CrO4v+ 4HNO3 = 4AgNO3+ Н2Cr2O7 + H2O

6. Action of carbonates.

Silver cations form a white precipitate with carbonate anions:

2Ag+ + CO32? = Ag2CO3v

Silver carbonate is soluble in nitric acid and ammonia solution:

Ag2CO3v+ 4NH3 = 2+ + CO32?

Ag2CO3v+ 2H+ = 2Ag+ + H2O + CO2^

Mercury (I) cations form a yellow precipitate with carbonate anions:

Hg22+ + CO32? = Hg2CO3v

Mercury (I) carbonate is unstable and decomposes:

Hg2CO3v = HgOv+ Hgv + CO2^

Lead cations form a white precipitate of the main salt:

2Pb(NO3)2 + 3Na2CO3 + 2H2O = (PbOH)2CO3v + 2NaHCO3 + 4NaNO3

2Pb2+ + 3CO32? + 2H2O = (PbOH)2CO3v + 2HCO3?

The precipitate of lead salt is soluble in acids and alkalis:

(PbOH)2CO3 v+ 4H+ = 2Pb2+ + CO2 ^+ 3H2O

(PbOH)2CO3v+ 6OH? = 22? + CO32?

7. Action of sulfates.

Analytical group II cations form poorly soluble white compounds:

2Ag+ + SO42? = Ag2SO4v

Hg22+ + SO42? = Hg2SO4v

Pb2+ + SO42? = PbSO4v

Lead sulfate is soluble in alkalis and 30% ammonium acetate solution:

PbSO4v + 4OH? = 2? + SO42?

PbSO4v + 2CH3COONH4 = Pb(CH3COO)2 + (NH4)2SO4.

This feature is used in the systematic analysis of cations of analytical groups I - VI.

The effect of some reagents on cations of analytical group II is presented in Table 5.

Table 5 Effect of some reagents on cations of analytical group II



AgCl, white precipitate, soluble in NH3.	Hg2Cl2, white precipitate that decomposes under the action of NH3. on Hg and HgNH2Cl.	PbCl2, a white solid, dissolves in hot water.
Ag2S, a black precipitate, dissolves in NH3.	HgS + Hg. Black sediment, dissolves in aqua regia.	PbS, a black precipitate, dissolves in HNO3.
Ag2O, brown precipitate, soluble in NH3 or HNO3.	Hg2O, black precipitate, soluble in HNO3.	Pb(OH)2, white precipitate, soluble in HNO3.
AgI, a yellow precipitate, is insoluble in NH3.	Hg2I2, a green precipitate, dissolves in excess reagent.	PbI2, a golden yellow precipitate, dissolves in hot water, excess reagent and CH3COOH.
Ag2SO4, a white precipitate, precipitates from concentrated solutions and dissolves in hot water.	Hg2SO4, a white precipitate, dissolves in aqua regia.	PbSO4, white precipitate, soluble in alkalis and 30% ammonium acetate solution.

Thus, the second analytical group includes the cations Ag+, Hg22+, Pb2+. When salts of analytical group II cations interact with HCl, white precipitates of AgCl, Hg2Cl2, PbCl2 are formed, which are sparingly soluble in water and acids. Precipitates of AgCl and Hg2Cl2 turn black due to decomposition and release of free metals (silver or mercury). AgCl dissolves in excess NH3 to form a colorless, water-soluble complex compound Cl. This complex compound decomposes under the action of nitric acid to form AgCl, which precipitates, and NH4NO3. This reaction is used to separate Ag+ from other group II cations. AgCl also dissolves markedly in excess chlorides to form type M complexes

Hg2Cl2, when interacting with an ammonia solution, forms Cl and metallic mercury, as a result of which the precipitate turns black. The PbCl2 precipitate is slightly soluble in cold water and soluble in hot water. This property is used to separate Pb2+ from other group II cations.

WITHsystematic course of analysis of cations of the 2nd analytical group

When analyzing cations of analytical group II, mercury (I) is first discovered by reaction with copper metal. The group reagent (HCl solution) precipitates cations of analytical group II in the form of chlorides. The Pb2+ ion is not completely deposited. The chloride precipitate is treated with hot water and quickly filtered. Lead ions are discovered in the filtrate. If they are found, the precipitate is washed several times with hot water until the reaction to Cl ions is negative. (sample with addition of AgNO3). After PbCl2 is separated, the precipitate is treated with an ammonia solution. Silver chloride dissolves to form silver ammonia Cl, and the mercuric chloride precipitate turns into a black mixture of NH2HgCl and Hg. Instant blackening of the sediment indicates the presence of Hg22+. Silver ions are discovered in the filtrate: when nitric acid is added, the formation of a white precipitate indicates the presence of silver ions in the mixture: Cl + 2HNO3 = AgClv + 2NH4NO3 The precipitate dissolves in the ammonia solution.

TO cations of the third analytical group. general characteristics

Analytical group III of cations includes cations of alkaline earth metals: Ba2+, Sr2+, Ca2+, which belong to the main subgroup of the second group of the periodic table of D.I. Mendeleev. Most salts of these cations are slightly soluble in water: sulfates, carbonates, chromates, oxalates, phosphates. For analytical group III cations, oxidation-reduction reactions are not typical, since they have a constant oxidation state. Cations of this analytical group are colorless; most of their salts are colorless. Analytical group III cations form colored compounds only with colored anions, for example: the yellow color of BaCrO4 is due to the corresponding color of CrO42? ions.

The group reagent for analytical group III cations is a solution of sulfuric acid. To ensure complete precipitation of BaSO4, SrSO4 and CaSO4, ethyl alcohol is added to the solution. Cations of IV - VI analytical groups are not precipitated by sulfuric acid.

Rreactions of cations of analytical group III

1. Effect of sulfuric acid solution. Cations Ba2+, Sr2+, Ca2+ under the action of a solution of sulfuric acid form white precipitates of sulfates:

Ba2+ + SO42? = BaSO4v PR = 1.1 10-10

Sr2+ + SO42? = SrSO4v PR = 3.2 10-7

Ca2+ + SO42? = CaSO4v PR = 2.5 10-5

The solubility of strontium and calcium sulfates is quite high, therefore, to reduce their solubility under the action of a group reagent, ethyl alcohol is added to the solution. Sulfates do not dissolve in acids and alkalis. CaSO4 is soluble in concentrated solutions of (NH4)2SO4:

CaSO4 + (NH4)2SO4 = (NH4)2

СaSO4 + SO42? = 2?

This property is used to separate Ca2+ ions from Sr2+ when they are simultaneously present.

2. Action of gypsum water. Gypsum water (saturated CaSO4 solution) precipitates Ba2+ and Sr2+ ions in the form of sulfates:

BaCl2 + CaSO4 = BaSO4v + CaCl2

SrCl2 + CaSO4 = SrSO4v + CaCl2

The solubility product of BaSO4 is small, so the precipitate forms quickly. The SrSO4 precipitate forms slowly in the form of clouding of the solution, since the solubility product of SrSO4 is greater than the solubility product of BaSO4, and, accordingly, the solubility of SrSO4 is greater.

3. Action of carbonates. Carbonate anions precipitate Ba2+, Sr2+, Ca2+ ions in the form of white crystalline sediments:

Ba2+ + CO32? = BaCO3v PR = 4.0 10-10

Sr2+ + CO32? = SrCO3v PR = 1.1 10 -10

Ca2+ + CO32? = CaCO3v PR = 3.8 10-9

Precipitates are soluble in mineral acids (HCl, HNO3) and acetic acid, for example:

BaCO3 + 2H+ = Ba2+ + H2O + CO2^ BaCO3 + 2CH3COOH = Ba2+ + 2CH3COO?+ H2O + CO2^

4. Action of chromates. Chromate anions form yellow precipitates with Ba2+ and Sr2+ ions:

Ba2+ +СrO42? = BaCrO4v PR =1.2 10-10

Sr2+ + СrO42? = SrСrO4v PR =3.6 10-5

They are soluble in strong acids (HCl, HNO3)

2BaCrO4 + 2H+ = 2Ba2+ + Cr2O72? + H2O

Strontium chromate, unlike barium chromate, is soluble in acetic acid. This difference in the properties of the chromates is used to detect and separate Ba2+ ions. In the presence of Ca2+, Sr2+ and Ba2+ ions in an acetic acid medium, only a BaCrO4 precipitate is formed under the action of a K2CrO4 solution.

5. Action of oxalates. Oxalate ions (oxalic acid salts H2C2O4) form white crystalline precipitates:

Ba2+ + C2O42? = BaC2O4v PR = 1.1 10-7

Sr2+ + C2O42? = SrC2O4v PR = 1.6 10-7

Ca2+ + C2O42? = CaC2O4v PR = 2.3 10-9

Precipitates are soluble in strong acids, but insoluble in dilute acetic acid:

BaC2O4 + 2H+ = Ba2+ + H2C2O4

This reaction can be used to open calcium ions. barium and strontium ions interfere.

6. Flame color reaction. Barium salts color the colorless flame of a gas burner yellow-green; and strontium and calcium salts are red.

7. Microcrystalloscopic reaction to Ca2+. Calcium ions with a solution of sulfuric acid form characteristic gypsum crystals CaSO4 2H2O. Under a microscope, they are easily distinguished from small crystals of BaSO4 and SrSO4. Such research allows the discovery of calcium in the presence of strontium and barium.

8. Effect of sodium rhodizonate. With cations of analytical group III, sodium rhodizonate forms colored compounds under various conditions. This feature makes it possible to detect calcium, strontium and barium ions without first separating them. With calcium ions in an alkaline environment (NaOH), sodium rhodizonate forms a purple precipitate of basic calcium rhodizonate. The sensitivity of the reaction is 1 µg.

Sodium rhodizonate

With strontium ions, sodium rhodizonate forms a brown-colored strontium rhodizonate precipitate in a neutral environment:

The reaction is carried out using the drop method. On filter paper, when solutions of strontium salts and sodium rhodizonate react, a red-brown color is formed, which disappears when a drop of HCl is added (dissolution of the precipitate).

The reaction with sodium rhodizonate is not interfered with by the presence of K2CrO4 (different from Ba2+). This property makes it possible to detect Sr2+ in the presence of Ba2+ (calcium cations give this reaction only in an alkaline medium). In the presence of chromic acid salts, Ba2+ binds to form a BaCrO4 precipitate, which does not react with sodium rhodizonate. The sensitivity of the reaction is 7 µg. Sodium rhodizonate forms a red precipitate of barium rhodizonate with barium salts. When a drop of a neutral solution of barium salt and a solution of sodium rhodizonate is applied to filter paper, a red-brown spot of barium rhodizonate precipitate appears.

When a drop of HCl is added, the stain turns red due to the transition of barium rhodizonate to barium hydrorodizonate:

In the presence of K2CrO4, barium rhodizonate is not formed (binding of Ba2+ into the BaCrO4 precipitate). The reaction is specific for Ba2+. The formation reaction of strontium rhodizonate, unlike Ba2+, takes place in the presence of potassium chromate. The reaction can be used to determine Ba2+ and Sr2+ in their total presence. A drop of a solution that contains a mixture of Ba2+ and Sr2+ ions is applied to paper and a drop of sodium rhodizonate solution is added. The appearance of a red-brown color, which turns red when a drop of HC1 is added, indicates the presence of Ba2+. If the color disappears when HC1 is added, then only Sr2+ ions are present in the solution. In the presence of Ba2+ ions, Sr2+ ions are determined as follows: a drop of a solution of potassium chromate, a drop of a solution of the mixture being analyzed, and a drop of a solution of sodium rhodizonate are applied to paper. The appearance of a brown-red color of the spot indicates the presence of Sr2+, since BaCrO4 was formed with potassium chromate, which does not react with sodium rhodizonate. The sensitivity of the reaction is 0.25 μg. The effect of some reagents on analytical group III cations is given in Table. 6.

Methods of qualitative analysis

In qualitative analysis, the characteristic chemical or physical properties of that substance are used to determine the composition of the substance under study. There is absolutely no need to isolate the discoverable elements in their pure form in order to detect their presence in the analyzed substance. However, the isolation of pure metals, nonmetals and their compounds is sometimes used in qualitative analysis to identify them, although this method of analysis is very difficult. To detect individual elements, simpler and more convenient methods of analysis are used, based on chemical reactions characteristic of the ions of these elements and occurring under strictly defined conditions.

An analytical sign of the presence of the desired element in the analyzed compound is the release of a gas with a specific odor; in the other, the formation of a precipitate characterized by a certain color.

Reactions occurring between solids and gases. Analytical reactions can occur not only in solutions, but between solid and also gaseous substances.

An example of a reaction between solids is the reaction of the release of metallic mercury when its dry salts are heated with sodium carbonate. The formation of white smoke when ammonia gas reacts with hydrogen chloride can serve as an example of an analytical reaction involving gaseous substances.

Reactions used in qualitative analysis can be divided into the following groups.

1. Precipitation reactions accompanied by the formation of precipitation of various colors. For example:

CaC2O4 - white

Fe43 - blue,

CuS - brown - yellow

HgI2 - red

MnS - nude - pink

PbI2 - golden

The resulting precipitates may differ in a certain crystalline structure, solubility in acids, alkalis, ammonia, etc.

2. Reactions accompanied by the formation of gases with a known odor, solubility, etc.

3. Reactions accompanied by the formation of weak electrolytes. Among such reactions, as a result of which are formed: CH3COOH, H2F2, NH4OH, HgCl2, Hg(CN)2, Fe(SCN)3, etc. Reactions of the same type can be considered reactions of acid-base interaction, accompanied by the formation of neutral water molecules, reactions of the formation of gases and poorly soluble precipitates in water, and complexation reactions.

4. Reactions of acid-base interaction, accompanied by the transfer of protons.

5. Complexation reactions accompanied by the addition of various legends - ions and molecules - to the atoms of the complexing agent.

6. Complexation reactions associated with acid-base interaction

7. Oxidation - reduction reactions, accompanied by the transfer of electrons.

8. Oxidation-reduction reactions associated with acid-base interaction.

9. Oxidation - reduction reactions associated with complex formation.

10. Oxidation - reduction reactions, accompanied by the formation of precipitation.

11. Ion exchange reactions occurring on cation exchangers or anion exchangers.

12. Catalytic reactions used in kinetic methods of analysis

Wet and dry analysis

Reactions used in qualitative chemical analysis are most often carried out in solutions. The analyte is first dissolved, and then the resulting solution is treated with appropriate reagents.

To dissolve the substance being analyzed, distilled water, acetic and mineral acids, aqua regia, aqueous ammonia, organic solvents, etc. are used. The purity of the solvents used is important to obtain correct results.

The substance transferred into solution is subjected to systematic chemical analysis. A systematic analysis consists of a series of preliminary tests and sequential reactions.

Chemical analysis of test substances in solutions is called wet analysis.

In some cases, substances are analyzed dry, without transferring them into solution. Most often, such an analysis comes down to testing the ability of a substance to color a colorless burner flame in a characteristic color or impart a certain color to the melt (the so-called pearl) obtained by heating the substance with sodium tetraborate (borax) or sodium phosphate ("phosphorus salt") in a platinum ear. wire.

Chemical and physical method of qualitative analysis.

Chemical methods of analysis. Methods for determining the composition of substances based on the use of their chemical properties are called chemical methods of analysis.

Chemical methods of analysis are widely used in practice. However, they have a number of disadvantages. Thus, to determine the composition of a given substance, it is sometimes necessary to first separate the component being determined from foreign impurities and isolate it in its pure form. Isolating substances in their pure form is often a very difficult and sometimes impossible task. In addition, to determine small amounts of impurities (less than 10-4%) contained in the analyzed substance, it is sometimes necessary to take large samples.

Physical methods of analysis. The presence of a particular chemical element in a sample can be detected without resorting to chemical reactions, based directly on the study of the physical properties of the substance under study, for example, the coloring of a colorless burner flame in characteristic colors by volatile compounds of certain chemical elements.

Methods of analysis that can be used to determine the composition of the substance under study without resorting to chemical reactions are called physical methods of analysis. Physical methods of analysis include methods based on the study of optical, electrical, magnetic, thermal and other physical properties of the substances being analyzed.

The most widely used physical methods of analysis include the following.

Spectral qualitative analysis. Spectral analysis is based on the observation of emission spectra (emission or emission spectra) of the elements that make up the substance being analyzed.

Luminescent (fluorescent) qualitative analysis. Luminescent analysis is based on the observation of luminescence (emission of light) of analytes caused by the action of ultraviolet rays. The method is used to analyze natural organic compounds, minerals, medications, a number of elements, etc.

To excite the glow, the substance under study or its solution is irradiated with ultraviolet rays. In this case, the atoms of the substance, having absorbed a certain amount of energy, go into an excited state. This state is characterized by a greater supply of energy than the normal state of matter. When a substance transitions from an excited to a normal state, luminescence occurs due to excess energy.

Luminescence that decays very quickly after cessation of irradiation is called fluorescence.

By observing the nature of the luminescent glow and measuring the intensity or brightness of the luminescence of a compound or its solutions, one can judge the composition of the substance under study.

In some cases, determinations are made based on the study of fluorescence resulting from the interaction of the substance being determined with certain reagents. Luminescent indicators are also known, used to determine the reaction of the environment by changes in the fluorescence of the solution. Luminescent indicators are used in the study of colored media.

X-ray diffraction analysis. Using X-rays, it is possible to determine the sizes of atoms (or ions) and their relative positions in the molecules of the sample under study, i.e., it is possible to determine the structure of the crystal lattice, the composition of the substance and sometimes the presence of impurities in it. The method does not require chemical treatment of the substance or large quantities.

Mass spectrometric analysis. The method is based on the determination of individual ionized particles that are deflected by an electromagnetic field to a greater or lesser extent depending on the ratio of their mass to charge (for more details, see book 2).

Physical methods of analysis, having a number of advantages over chemical ones, in some cases make it possible to solve problems that cannot be resolved by methods of chemical analysis; Using physical methods, it is possible to separate elements that are difficult to separate by chemical methods, as well as to continuously and automatically record readings. Very often, physical methods of analysis are used along with chemical ones, which makes it possible to use the advantages of both methods. The combination of methods is especially important when determining minute amounts (traces) of impurities in analyzed objects.

Macro, semi-micro and micro methods

Analysis of large and small quantities of the test substance. In the past, chemists used large quantities of the substance under study for analysis. In order to determine the composition of a substance, samples of several tens of grams were taken and dissolved in a large volume of liquid. This required chemical containers of appropriate capacity.

Currently, chemists make do with small quantities of substances in analytical practice. Depending on the amount of the analyte, the volume of solutions used for analysis, and mainly on the experimental technique used, analysis methods are divided into macro-, semi-micro- and micromethods.

When performing an analysis using the macromethod, to carry out the reaction, take several milliliters of a solution containing at least 0.1 g of the substance, and add at least 1 ml of the reagent solution to the test solution. Reactions are carried out in test tubes. During precipitation, voluminous sediments are obtained, which are separated by filtration through funnels with paper filters.

Droplet analysis

Technique for carrying out reactions in droplet analysis. The so-called drop analysis, introduced into analytical practice by N. A. Tananaev, has acquired great importance in analytical chemistry.

When working with this method, the phenomena of capillarity and adsorption are of great importance, with the help of which it is possible to open and separate various ions when they are present together. In droplet analysis, individual reactions are carried out on porcelain or glass plates or on filter paper. In this case, a drop of the test solution and a drop of the reagent that causes characteristic coloring or the formation of crystals are applied to the plate or paper.

When performing the reaction on filter paper, the capillary adsorption properties of the paper are used. The liquid is absorbed by the paper, and the resulting colored compound is adsorbed onto a small area of the paper, resulting in an increased sensitivity of the reaction.

Microcrystalloscopic analysis

The microcrystalloscopic method of analysis is based on the detection of cations and anions through a reaction that results in the formation of a compound with a characteristic crystal shape.

Previously, this method was used in qualitative microchemical analysis. Currently it is also used in droplet analysis.

A microscope is used to examine the formed crystals in microcrystalloscopic analysis.

Crystals of a characteristic shape are used when working with pure substances by adding a drop of a solution or a crystal of a reagent to a drop of the test substance placed on a glass slide. After some time, clearly visible crystals of a certain shape and color appear.

Powder grinding method

To detect certain elements, the method of grinding a powdered analyte with a solid reagent in a porcelain plate is sometimes used. The element being opened is detected by the formation of characteristic compounds that differ in color or smell.

Analysis methods based on heating and fusion of matter

Pyrochemical analysis. For the analysis of substances, methods based on heating the test solid or its fusion with appropriate reagents are also used. When heated, some substances melt at a certain temperature, others sublimate, and on the cold walls of the device precipitation characteristic of each substance appears; some compounds decompose when heated, releasing gaseous products, etc.

When the analyte is heated in a mixture with the appropriate reagents, reactions occur that are accompanied by a change in color, the release of gaseous products, and the formation of metals.

Spectral qualitative analysis

In addition to the above-described method of observing with the naked eye the coloring of a colorless flame when a platinum wire with an analyzed substance is introduced into it, other methods of studying light emitted by hot vapors or gases are currently widely used. These methods are based on the use of special optical instruments, the description of which is given in the physics course. In this kind of spectral devices, light with different wavelengths emitted by a sample of a substance heated in a flame is decomposed into a spectrum.

Depending on the method of observing the spectrum, spectral instruments are called spectroscopes, with the help of which the spectrum is visually observed, or spectrographs, in which the spectra are photographed.

Chromatographic method analysis

The method is based on the selective absorption (adsorption) of individual components of the analyzed mixture by various adsorbents. Adsorbents are solids on the surface of which the adsorbed substance is absorbed.

The essence of the chromatographic method of analysis is briefly as follows. A solution of a mixture of substances to be separated is passed through a glass tube (adsorption column) filled with an adsorbent.

Kinetic methods of analysis

Methods of analysis based on measuring the reaction rate and using its value to determine the concentration are combined under the general name of kinetic methods of analysis (K. B. Yatsimirsky).

Qualitative detection of cations and anions by kinetic methods is performed quite quickly and relatively simply, without the use of complex instruments.

Every living organism, including bacteria and viruses, has unique genes that are part of the DNA or RNA structure in a certain sequence. During a PCR study, genetic material is copied many times under the influence of DNA polymerase and special temperature cycles.

There are two main polymerase chain reaction methods:

The classical method is the isolation of the genetic material of the pathogen by electrophoresis;
Real-time PCR.

The technique consists of three main stages:

Preparation of the test sample;
DNA amplification;
Detection (identification) of the genetic material of the suspected pathogen.

To conduct the study, the PCR laboratory must be divided into 3 zones, each stage of the reaction is carried out strictly in the room intended for it. Each zone must be equipped with the necessary equipment, dispensers, consumables, and protective clothing used only in this room.

After registration and labeling of the samples, DNA or RNA of the pathogen is isolated from the test material in the sample preparation room by exposure to a certain temperature and special reagents. Then the process of amplification begins - creating numerous copies of a unique DNA fragment. It consists of 3 main stages:

DNA denaturation - under the influence of high temperature (95 degrees), the DNA double helix unwinds into 2 chains.
Primer annealing – special synthetic compounds (primers) that are identical to the genetic information at the ends of the desired nucleic acid fragments are attached to the ends of DNA chains. The temperature required to attach the primer is individual for a particular case and ranges from 50 to 65 degrees Celsius.
Using the enzyme DNA polymerase, a similar DNA section (amplicon) is completed between two primers at 70–72 degrees. Special substances added to the test tube are used as “building materials”.

Amplification cycles are repeated several times, therefore, the isolated DNA is copied many times, which simplifies the process of its identification. Identification can be carried out visually after electrophoresis of amplification products in an agarose gel, or automatically using the real-time technique.

When researching using the PCR method in “real time”, amplification and detection occur simultaneously in special devices. This method is the most preferable, since the study is carried out in closed test tubes, reducing the risk of contamination and, consequently, the issuance of false positive results.

Pros and cons of the method

The study takes only a few hours, in contrast to lengthy classical microbiological methods;
High specificity from 95% to 100%, because the required DNA fragment is unique for each specific microorganism;
The method is highly sensitive; a pathogen can be detected even if it is represented by only one cell in the sample being studied;
The pathogen can be identified using both qualitative and quantitative methods. This is very important when isolating opportunistic microorganisms that do not cause disease in small quantities;
Possibility to determine the genotype of the pathogen (hepatitis C, HIV infection). This is necessary for rational treatment and prognosis of possible complications;
The ability to identify a genetic predisposition to the disease, thereby preventing its development;
Almost any source of infection can be identified; modern techniques also make it possible to identify the total microflora in the test sample, for example, the vaginal biocenosis.

The possibility of obtaining both a false-positive and a false-negative sample in case of non-compliance with the rules of sample collection or errors during the study;
High cost of analysis.

Application

Almost any sample can be examined using the PCR method (blood, urine, cerebrospinal fluid, scrapings from the cervical canal and urethra, hair follicles, semen, etc.). This technique is widely used to diagnose STDs (gonorrhea, chlamydia, ureaplasmosis, mycoplasmosis, trichomoniasis). With its help, you can identify pathogens of tuberculosis, diphtheria, pneumonia, viral hepatitis, HIV infection, toxoplasmosis, cytomegalovirus and herpetic infections, salmonellosis, etc.

Polymerase chain reaction is used to establish paternity by comparing the DNA of the parent and child, identifying genetic abnormalities and the body's hereditary predisposition to various diseases.

Preparing for the test

It is recommended to donate blood strictly on an empty stomach.
Before taking a smear from the urethra or cervical canal, you should abstain from sexual activity for three days; the test must be taken no earlier than a month after the end of the course of antibiotic therapy, otherwise the result may be false positive. The PCR method detects the DNA of even a dead pathogen, so it is better to conduct the study after complete cell renewal.
Urine should be collected in a sterile container.

The answer will most often be ready in a couple of days, depending on the capabilities of the laboratory.

Decoding the results

When using a qualitative methodology, there can only be 2 answer options: positive or negative. A positive result indicates the presence of the isolated microorganism in the sample, a negative result indicates its absence.

The quantitative result must be assessed by the attending physician; an individual approach is applied in each specific case. The specialist, taking into account the received answer, decides on the need for treatment, dosage of drugs, and clarifies the form and stage of the disease.

When determining the genetic profile (predisposition to thrombophilia, breast cancer), after deciphering the result, the doctor can assess the degree of risk of developing the disease, as well as prescribe a special diet and preventive measures.

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Polymerase chain reaction - information for patients

Polymerase chain reaction (PCR) is a complex laboratory method widely used in medicine and other branches of science. At one time, PCR diagnostics became a big breakthrough in science. We can say that this is one of the most important discoveries of the 20th century in medicine. For the discovery of the method, Keri Mullis, a biochemist, received the Nobel Prize in 1993.

For a long time, infections have exacted a bitter toll from humanity. The plague alone claimed hundreds of thousands of lives in the Middle Ages. In the successful fight against epidemics, accurate and timely diagnosis is important.

PCR tests are usually carried out in a laboratory at the clinic. Despite the fact that the PCR test for infection is quite expensive, the price is compensated by its high accuracy. To establish an accurate diagnosis, it is enough to do the analysis once. If other methods are used, additional or repeat tests may be required.

How is testing for infectious diseases performed?

The most common methods used to diagnose infections are serological and cultural methods. In the first case, antibodies to the infectious agent are determined in the blood serum. In the second case, biological material obtained from a sick person is used to inoculate a special environment favorable for the growth of pathogen colonies. In both cases, diagnosis can take days or even weeks.

PCR examination can be carried out with any biological materials obtained from a sick person. Blood and other biological, physiological and pathological fluids and media can serve as samples. You can do PCR of urine or stool.

Most often, the PCR method is used to determine viral and atypical infections, since they may not be amenable to conventional diagnosis due to the characteristics of the pathological process they cause. In order to diagnose these infections, time is required during which the body begins to produce antibodies, which are determined by serological methods. However, in some cases this is unacceptable.

Using PCR, the human immunodeficiency virus can be determined within days or weeks, as accurately as possible, without the seronegative window period characteristic of other methods. (The seronegative window is the period from the moment of infection during which the body has not yet begun to produce a sufficient amount of antibodies for detection).

The in vitro PCR method means laboratory determination of infection in samples isolated from the patient.

To carry out a polymerase chain reaction, a set of special reagents is required.

The test material is added to test tubes with reagents. The tubes are placed in a special device - a PCR amplifier. It serves to amplify (increase the number) of the desired DNA or RNA fragments. The PCR amplifier runs in cyclic mode. Each cycle, if the DNA or RNA sequence of the pathogen is present in the samples, copies of fragments of these nucleic acids accumulate in the solution. Both the presence of the pathogen and its quantity in the samples can be determined.

Types of PCR

Analysis by PCR method - qualitative gives the following result:

PCR - negative, the desired pathogen was not detected in the samples;
PCR is positive; sequences characteristic of a particular pathogen were found in the samples.

When the PCR result is positive, this indicates with 95% accuracy the presence of a diagnosable infection. The accuracy of PCR kits used for diagnostics reaches 100%.

5% of erroneous results usually depend on the human factor. Thus, violations of the rules for storing reagents and research techniques can significantly reduce the accuracy of analyzes.

Quantitative PCR analysis determines the concept of viral load. In this case, it is possible to determine how many sets of pathogen DNA were contained in the samples obtained from the patient. The more, the more severe the infection. You can also determine the success of treatment by reducing the viral load.

Submission of biomaterial for PCR

PCR tests are carried out in the clinic, usually in the morning. During your visit to the doctor, you will be told what you need to donate: blood, urine, smear or scraping. PCR is capable of identifying pathogens regardless of the degree of contamination of the material.

In theory, for a positive analysis, the presence of only one pathogen in the samples is sufficient. In practice, they are trying to create more favorable conditions. There are some rules for this:

if you are taking a smear or scraping from the genitals, you should abstain from sexual intercourse 3 days before the test;
You should not wash yourself or douche with antibacterial agents on the eve of the test;
3 hours before taking a smear from the urethra, you should be patient and not urinate.

In the case where a patient donates blood, these rules may not be followed.

Research results

PCR results are usually ready within 24 hours after testing. Qualitative analysis looks simple. PCR decoding is not required, since usually the pathogen is indicated in the first column, and the result in the second. For example, like this:

(PCR) Ureaplasma urealiticum

(PCR) Herpes simplex

The method indicated in parentheses is PCR. Making an interpretation is not difficult. The patient from the example was diagnosed with cytomegalovirus (CMV) and herpes using a qualitative PCR method. Ureaplasma and chlamydia: no infectious agents were detected.

Quantitative analysis gives a numerical result, usually in IU/ml. This means that in 1 ml of the test sample a certain number of copies of DNA or RNA of the pathogen was detected, in international units. Depending on the size, the severity of the infection is determined. Usually, blood is tested to determine the viral load, since during illness viruses circulate freely in the blood.

Where can I get PCR done?

It is important to get tested in a well-established clinic. Although the method is very accurate, its results are affected by adherence to the study protocol. You should not look for a clinic based on the results of queries in a search engine, such as: PCR Moscow, where to do it or PCR Stavropol clinic. As a rule, your doctor recommends where it is best to do a PCR test.

If the PCR result is positive, it is necessary to repeat the test in another laboratory. This will eliminate human error.

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Additions were made to the IVF program under compulsory medical insurance in 2018.

The number of women who have turned to ART without a permanent partner is increasing every year.

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Diagnosis of hepatitis C using PCR testing

Polymerase chain reaction (PCR) is increasingly being used in clinical practice to determine the causes of various viral diseases, including the diagnosis of viral hepatitis C.

Advice from hepatologists

In 2012, there was a breakthrough in the treatment of hepatitis C. New direct-acting antiviral drugs were developed, which with a 97% probability of completely eliminating the disease. From this point on, hepatitis C is officially considered a completely curable disease in the medical community. In the Russian Federation and CIS countries, drugs are represented by the brands sofosbuvir, daclatasvir and ledipasvir. There are a lot of fakes on the market at the moment. Medicines of proper quality can only be purchased from companies that have licenses and appropriate documentation.

PCR in its various modifications is actively used for its diagnosis. Using PCR for hepatitis C, it is possible to determine the presence of hepatitis C virus RNA in the patient’s blood and accurately make a diagnosis.

Analysis Variations

The PCR technique became available to doctors several decades ago. It is based on multiple copies of a certain fragment of viral or bacterial RNA or DNA, followed by detection (recognition of this fragment) in the patient’s blood serum.

At the same time, there are two fundamentally different methods of PCR research: quantitative and qualitative.

The qualitative method only allows us to answer the question: is there genetic material of a certain virus in the biological material (blood serum, saliva, seminal fluid, etc.)?

The quantitative method, in turn, makes it possible to determine the amount of this genetic material, which is necessary in some cases to determine the stage of the disease or assess the effectiveness of therapy.

Qualitative PCR option for disease

The use of a qualitative version of PCR analysis for this disease makes it possible to detect the presence of hepatitis C viral RNA in biological fluids (blood serum, saliva, etc.) of the patient. In this case, the result of the analysis can only be of two types: positive or negative. In this case, its correct decoding is very important.

a positive result when determining hepatitis C viral RNA tells the doctor that the biological fluid being tested contains RNA of this virus. Accordingly, the patient is infected with it, and, therefore, a diagnosis of viral hepatitis C is possible. However, it is always worth remembering the possibility of false positive test results;
a negative result of PCR analysis indicates the absence of hepatitis C virus RNA in the biological fluid being tested, or the content of RNA molecules in the test fluid was too low and was below the sensitivity limit of the PCR method. A negative test result may not always indicate the absence of the virus in the blood. The possibility of false negative test results should always be considered by the attending physician.

With the development of an acute form of hepatitis C disease, conducting a high-quality PCR study makes it possible to establish the fact of the disease within 1-3 weeks after the virus enters the human body.

False negative results may result from:

penetration of polluting substances into biological material (blood);
the use of Heparin to prevent blood clotting in vitro or its use by the patient;
penetration into the test material of substances from the environment that block enzymes used in PCR.

Quantitative PCR option

The use of quantitative PCR analysis makes it possible to determine not only the very presence of the virus in the blood, but also the number of viral particles in any biological fluid (the so-called viral load). Using this type of PCR, you can determine the number of copies of hepatitis C virus RNA that circulate in a certain volume.

The result of this type of PCR is expressed in numerical values, where the unit of measurement is international units per milliliter - IU/ml.

This type of PCR diagnosis is used on certain days of treatment for viral hepatitis C. The first determination of the viral load occurs when a sick person is admitted to the hospital. Subsequently, the analysis is carried out at the 1st, 4th, 12th and 24th weeks from the start of drug use. Already in the 12th week you can tell whether the therapy is effective or not.

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There is no need to specially prepare the patient for the study. It is recommended not to smoke on the day of the test. Blood from a vein is used as the test material.

After quantitative PCR has been carried out, it is necessary to decipher the results obtained. The concept of “norm” does not exist in such cases. To decipher, a specially developed gradation of indicators is used:

test result: not detected - hepatitis C viral RNA was not detected in the patient’s venous blood (negative result), or it is contained in a very low amount, which does not allow the method to determine it (<40 ME/мл – порог чувствительности количественного ПЦР);
research result:<8*10 5 МE/мл – положительный результат теста. Такой уровень вирусной нагрузки очень низкий. Является показателем эффективности терапии и благополучного течения заболевания;
test result: >8*10 5 IU/ml – positive test result. The load level is very high. Poor prognosis for the course of the disease and the need for correction or replacement of medications used.

It is important to remember that the resulting level of viral load does not reflect the severity of the pathology and the degree of liver destruction. For this, there are other methods of biochemical research. To correctly select treatment methods, it is necessary to know the genotype of the hepatitis C virus.

A high level of concentration of viral particles in biological fluids, and especially in the blood, is associated with a high risk of transmission of the virus through sexual contact or during pregnancy from mother to fetus.
The number of viral particles is a reflection of the effectiveness of the drugs used and allows for rational selection of drugs and doses used.

Ultrasensitive PCR diagnostic method

Today, you can undergo the so-called ultra PCR to determine the hepatitis C virus. This method is completely called PCR with hybridization-fluorescence research in real time.

When is ultra PCR indicated:

In cases of suspected viral hepatitis C in patients with latent forms of the disease.
In cases where the patient has antibodies to the hepatitis C virus, but not confirmed by PCR diagnostics.
To assess the effectiveness of the treatment and confirm the fact of recovery.
As a screening technique for early detection of disease in people in the population.

To conduct the study, as a rule, the patient's venous blood is used. The sensitivity of the ultra method is less than 10 IU/l, which is several times higher than that of standard quantitative and qualitative PCR diagnostic options. Ultra PCR is prescribed by an infectious disease specialist or hepatologist.

The decisive stage in making a diagnosis and evaluating treatment is the correct interpretation of the results obtained using the ultra PCR method. It is always worth remembering that there is a small chance of getting false negatives and false positives.

To eliminate such situations, it is necessary to prevent contamination of blood samples and laboratory materials. By using ultra PCR it is possible to avoid situations that lead to false negative results and thereby complicate diagnosis.

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What is the difference between qualitative and quantitative PCR?

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Please tell me which PCR smear test for STDs is more informative: qualitative or semi-quantitative? How are they different from each other?

In general, there are 2 types of PCR - qualitative (yes/no) and quantitative. Quantitative requires different equipment, much more expensive, and is used mainly for HIV and hepatitis.

Semi-quantitative analysis, in a certain sense, is an inadequate surrogate for quantitative analysis; it is not necessary to do it:

This is not a quantitative analysis

It is usually more expensive

When diagnosing an STD, the number of microorganisms does not matter.

This is usually a separate study.

Special media are used, usually imported, most often MYCOPLASMA DUO + antibiogram SIR (BIORAD, France) or MYCOPLASMA IST (BioMerrier), but it is more expensive. The cost of detection is about $10 for both infections.

It makes sense to do PCR only in the sense of diagnosing mycoplasmas that are not detected by culture - M.genitalium.

It is also possible as a cheap option for identifying all mycoplasmas in general - usually called Mycoplasma spp. (i.e. all species of the genus Mycoplasma). However, non-pathogenic ones are also determined, so a negative answer is of great value.

What is the name of the diagnosis if one elementary or reticular body of the main forms of chlamydia is detected? The question is similar regarding the detection of one or more pairs of gonococci, as well as one Trichomonas cell. Thank you for your attention and the discussion you started. Best regards, Vladimir.

How are you going to find ONE elemental or reticular body?

With light microscopy, this is impossible; with immunofluorescence, there are criteria for issuing a response - usually these are 5-10 objects with a characteristic glow, depending on the set.

With PCR and ELISA for antigens, the question is generally inadequate.

The sensitivity of most Russian PCR kits is about 1000 genocopies per ml of sample.

The answer is similar - how to do this?

Regarding Trichomonas, options are possible, but still ONE cell is casuistry, and you can always check the result using another method, the same PCR, by the way.

For gonorrhea, this is impossible - using a Gram-stained smear, the diagnosis of gonorrhea can only be made in acute gonorrhea in men (and in America this is also only a presumptive diagnosis), and one pair of gonococci can be found VERY RARE. All other cases are “Gram-negative intracellular diplococci.”

When sowing, you get a COLONY of gonococci, which you must identify (now this is not a problem).

For PCR, see above.

Gonococcus is determined by microscopy of Gram-stained smears;

Trichomonas microscopy of a native smear;

Chlamydia - PCR or culture on special media;

Mycoplasmas - inoculated on special media

So? It's enough? Do antibody levels play a role in diagnosing STDs?

Bacterial culture with subsequent identification of colonies using modern kits for differentiating Neisseria. Unfortunately, this is rarely done anywhere. In HPT, as a rule, identification on sugars is not carried out, although it should be.

Bacterioscopy (acute gonorrhea in men)

Microscopy of the native drug and its modifications

Culture for Trichomonas

Microscopy of stained smears (use only if typical forms are detected, and not “scraps of Trichomonas”)

Sowing on a cage. cultures or embryos (difficult)

The only possible benefit can be assumed for ascending chlamydial infection or Reiter's syndrome.

Often in the CIS they lead to multiple treatments “until the titer disappears”

As a method of monitoring cure - absolutely not!

I think STD screening will switch to nucleic acid amplification methods (the same PCR)

For chlamydia this is already the case, for gonorrhea this is increasingly the case.

Compared to a background or virological study, PCR is simpler and faster for both the clinician and the laboratory, and therefore more reliable.

The background study will remain a reference method. This is my forecast.

Do you think there is at least one adult person on Earth who has “encountered” one or another subspecies of chlamydia more than once during his life? What, however, with most of the other potentially pathogenic microflora? In the overwhelming majority of cases, such meetings (usually in low titers) end tragically for this microflora. 🙂 Much less often as a carrier (usually temporary), and even less often as a disease.

And the second question, what do you think: why, over many millennia of human coexistence with at least the same Chlamydia trachomatis, when chlamydia (this is not a reservation, because they are often treated specifically for the bacterial agent that was detected using PCR 😎) They just didn’t treat it, but, in general, their coexistence was not known, did not everyone get chlamydia? After all, in the history of mankind there were quite a few periods when polygamous sexual relationships were the norm.

This is often where “persistence” comes from. Venereologists refuse to believe the results - “you don’t find anything, here in our smears.” (Interestingly, the KVD statistics and ours for Trichomonas and gonorrhea are approximately the same. Well, where is “what’s in the smears”?) And so on, and etc.

But let’s not forget the question from dear ksena: “Good afternoon!

Please tell me which PCR smear test for STDs is more informative: qualitative or semi-quantitative? How are they different from each other?"

This question, in my opinion, is from the area of interest in human knowledge. And knowledge has no boundaries. Over time, the question of pathological molecules (prion proteins), then about the tension in torsion fields at the atomic level, etc., will be interesting, and then attention will turn to the macrocosm. There will be questions from astrology about the influence of planets on our health. His Majesty EXPERIENCE. But for this question I am very grateful. All the best, with respect to everyone present, Vladimir.