The main stages of chemical analysis. The procedure for the production of forensic chemical examination

Analytical signal as a source of information about the qualitative and quantitative composition of a substance. Classification of chemical analysis methods according to the nature of the analytical signal.

Analytical chemistry and chemical analysis. Subject and tasks of analytical chemistry. Classification of methods of chemical analysis.

LECTURE #1

Lecture plan:

1. Analytical chemistry and chemical analysis. Subject and tasks of analytical chemistry. Classification of methods of chemical analysis.

2. Analytical signal as a source of information about the qualitative and quantitative composition of a substance. Classification of chemical analysis methods according to the nature of the analytical signal.

3. Main stages of chemical analysis.

4. Principles and methods of qualitative chemical analysis.

Analytical chemistry is the science of methods for determining the chemical composition and structure of chemical systems.

Chemical system (substance) may be an individual chemical compound, a mixture of compounds, any material (plastic, wood, etc.). The composition of substances and materials has qualitative and quantitative characteristics.

Qualitative composition indicates the presence in the substance of certain chemical elements (elemental composition), functional groups (functional composition), as well as individual chemical compounds in a mixture (molecular composition).

Quantitative compound describes the quantitative content of individual constituents in a substance.

structure a chemical system is called the spatial order of the arrangement of atoms and their chemical bonds in a molecule of a substance (intramolecular structure), as well as the arrangement and relationship of molecules in a chemical system (intermolecular structure).

Summarizing the above, we can schematically depict the main characteristics of a chemical system, choosing ordinary water as an example.

Determination of the qualitative and quantitative composition of substances and their structure is carried out using chemical analysis.

Thus, analytical chemistry is a science that develops and creates methods of chemical analysis, that is, the subject of analytical chemistry as a science is the theory of chemical analysis. Analytical chemistry develops the theoretical foundations of analysis methods, determines the limits of their applicability and metrological characteristics, and offers methods for analyzing various objects. Chemical analysis is the practical application of analytical chemistry.

Depending on what aspect of the chemical system the analyst is interested in, there are qualitative, quantitative and structural analysis:

- qualitative analysis serves to determine the qualitative chemical composition and identification (identification with the standard) of substances;

- quantitative analysis serves to determine the quantitative relationships between the components of a chemical system;

- structural analysis serves to study the intra- and intermolecular structure of substances (for example, a DNA molecule is two helixes consisting of purine and pyrimidine bases arranged in a certain sequence and interconnected by hydrogen bonds).

Qualitative analysis usually precedes quantitative analysis, and structure determination is carried out, as a rule, with information about the qualitative and quantitative composition of the substance.

According to the complexity of carrying out, elemental, functional, molecular and phase analysis are distinguished:

- elemental analysis - this is the establishment of the presence and quantitative content of chemical elements in a substance, that is, the determination of its elemental composition;

- functional analysis - this is the establishment of the presence and quantitative content of functional groups in the molecules of organic compounds;

- molecular analysis - this is the establishment of the presence and quantitative content of molecules of individual chemical compounds in a substance, mixtures and materials;

- phase analysis - this is the analysis of a substance for the presence in it of separate phases that differ in their chemical and physical properties and are separated from each other by interfaces.

Depending on how much substance is handled when performing the analysis, macro-, semi-micro-, micro- and ultra-microanalysis are distinguished:

In the macro- and semi-micro method, ordinary chemical glassware is used, the system of work in both methods is identical, however, the advantage of semi-micro analysis is a much lower consumption of reagents. Micro- and ultramicroanalysis requires the use of highly sensitive reactions, special methods and equipment. In practice, semi-microanalysis is most often used in conventional chemical laboratories.

For chemical analysis, it is necessary that the substance or its constituent parts have certain chemical, physical and physico-chemical properties that make it possible to detect, measure the amount and establish the structure of this substance. Such properties are called analytical properties or analytical signal . Thus, an analytical signal is a property of a substance that depends on its nature and content in the sample, that is, an analytical signal characterizes the qualitative and quantitative composition of the analyzed substance. Depending on the nature of the analytical signal, chemical analysis methods are divided into 4 groups:

1) chemical methods are based on the use of chemical reactions (neutralization, oxidation-reduction, complexation and precipitation) in which the analyte enters. In this case, a qualitative analytical signal is a visual external effect of the reaction - a change in the color of the solution, the formation or dissolution of a precipitate, the release of a gaseous product. In quantitative determinations, the volume of the evolved gaseous product, the mass of the precipitate formed, and the volume of a reagent solution with a precisely known concentration spent on interaction with the analyte are used as an analytical signal.

2) physical methods do not use chemical reactions, but measure any physical properties (optical, electrical, magnetic, thermal, etc.) of the analyzed substance, which are a function of its composition.

3) physical and chemical methods use the change in the physical properties of the analyzed system as a result of chemical reactions. Physicochemical methods also include chromatographic methods of analysis based on the processes of sorption-desorption of a substance on a solid or liquid sorbent under dynamic conditions, and electrochemical methods (potentiometry, voltammetry, conductometry).

Physical and physico-chemical methods are often combined under the general name instrumental methods of analysis, since analytical instruments and apparatuses are used for analysis, recording physical properties or their change.

Unlike chemical methods, instrumental methods of analysis make it possible to simultaneously establish the qualitative and quantitative composition of substances quickly and fairly accurately. Examples of a qualitative analytical signal in physical and physicochemical methods are the wavelength of electromagnetic radiation absorbed or emitted by a substance in spectroscopy (λ), retention parameters in chromatography (retention time t R), half-wave potential in polarography ( E 1/2), and the quantitative analytical signal is the intensity of absorption or emission of electromagnetic radiation (optical density BUT), the area of the chromatographic peak (spot) ( S), the magnitude of the diffusion current ( ID).

4) biological methods used for the analysis of biologically active substances. For example, antibiotics are analyzed for their ability to stop the growth of microorganisms, and cardiac glycosides are analyzed for their ability to stop an isolated frog heart.

Thus, the primary task of analytical chemistry is the discovery and comprehensive study of the analytical properties (determination of the analytical signal) of substances in order to determine their relationship with the composition and structure of the analyzed chemical systems and, on this basis, to create a specific chemical analysis technique.

In the course of any analysis, the following main stages can be distinguished:

1) sampling for analysis (sampling) and its transfer into a solution (dissolution);

2) separation and concentration;

3) analysis (final definition);

4) processing of the obtained results.

1) Sampling. There are 3 types of samples:

a) general (primary) sample- obtained from a large mass of the analyzed sample by uniform selection of a substance from different parts throughout the entire volume of the sample. The mass of the general sample is several tens of grams and its main property is representativeness. Sample representativeness- this is the correspondence of the composition of the sample to the average composition of the analyzed sample. To obtain a representative sample, it is necessary to thoroughly mix the substances taken for analysis from different parts of the sample (liquid and gaseous) or grind in a mortar until a homogeneous mass (solid).

b) laboratory (average) sample is necessary for conducting a comprehensive complete analysis of the sample and its mass corresponds to the selected methods of analysis. A laboratory sample is obtained from a general sample by reducing its size by the method quartering or using automatic samplers. When quartering, the sample is laid out in a uniform layer in the form of a square and divided by diagonals into four triangles. Two opposite parts are discarded, and the other two are combined, crushed again and quartered again. The laboratory sample thus obtained weighing several grams is placed in a dark glass jar with a ground-in lid to prevent external influences. Part of the laboratory sample is intended for arbitration analysis.

in) analytical sample (sample for analysis) needed for a single definition. An analytical sample is obtained from a laboratory sample by taking an accurate sample on an analytical balance. An approximate sample weight for analysis is calculated in advance, based on the approximate content of the analyte in the sample and the method of determination.

When dissolving a sample, they try to transfer all its components into the solution without loss. In this case, it is most convenient to use water, as well as acidic or alkaline aqueous solutions, aqueous solutions of complexing agents.

To dissolve organic compounds, non-aqueous solvents are often used - alcohols, ketones, ethers, aromatic and aliphatic hydrocarbons, organochlorines, etc.

2) Separation and concentration. Since many analyzed samples are mixtures of compounds that can interfere with the determination of each other, their preliminary separation by chemical (precipitation, coprecipitation), physical (distillation) and physicochemical (chromatography, extraction) methods is necessary. The same methods (plus evaporation) can be used to concentrate individual components to reduce their detection limit (increase sensitivity). As a result of concentration, an increase in the concentration of the analyzed component in the solution is achieved, which is characterized by the concentration coefficient K conc:

where: FROM ref and V ref - concentration and volume of the initial (diluted) solution;

FROM con and V con - concentration and volume of the final (concentrated) solution

3) Conducting an analysis is carried out according to the available standard certified methods, depending on the task of chemical analysis.

4) Processing of the received results includes the generalization of the observations made, the determination of the correctness and reproducibility of the data obtained, the calculation of the results of the analysis, the assessment of the reliability of the results obtained by the methods of mathematical statistics.

Forensic chemical examination is a forensic chemical department of the bureau of forensic medical examinations, and it is carried out to isolate, identify and determine the amount (or exclusion) of poisonous, narcotic and potent substances and their decay products in human organs and tissues. Pharmaceuticals, food, drink, tobacco products, the human environment and objects are also subject to research.

To detect and identify the presence of chemical and medicinal substances, forensic chemical examination uses preliminary methods: color reaction, thin layer chromatography, enzyme immunoassay. Confirmatory methods are also used: spectrophotometry in the visible, ultraviolet and infrared regions, atomic absorption spectrophotometry, gas-liquid chromatography, chromatography-mass spectrometry.

The main tasks of forensic chemical examination are associated with the following:

1) by solving issues by judicial and investigative authorities, the solution of which is impossible without special knowledge of the field of toxicological chemistry. Toxicological (forensic) chemistry is a scientific method by which the forensic authorities can more correctly and more objectively resolve some of the issues that arise in the practice of their activities;

2) with the provision of all possible assistance to public health in order to prevent poisoning by various chemicals that are used in industry, agriculture, medicine and everyday life. This preventive health care is most often provided by medical institutions, in particular, forensic medical institutions.

Forensic chemical examination can be both basic and additional examination. The main examination is carried out in the presence of a decision, which is issued by the inquirer, investigator, prosecutor or judge, determined by the court or the person who deals with the case of administrative offenses.

An additional examination is carried out during the examination of a corpse or a living person upon submission of a written referral from a forensic medical expert or is determined by a decision of the person who ordered the examination.

Items of forensic chemical examination are either seized in their entirety, or scrapings are made from them. The material for examination is packed in such a way as to protect it from contamination by foreign impurities. Liquid materials are sent for examination in clean glassware with a ground stopper. Solids are wrapped in clean paper.

The forensic chemical laboratory, together with the object of study, must receive the following supporting documents:

1) an accompanying relation containing information about to whom, for what purpose and what exactly is sent;

2) a decision of the forensic chemical examination of evidence, which should contain preliminary information about the circumstances of the case, issues to be resolved, the listed objects of research to be sent;

3) an extract from the act of forensic examinations of a corpse, which must contain information about the main results of the autopsy, and the purpose of the forensic chemical examinations;

4) a copy of the medical record of an inpatient or outpatient in case of providing medical assistance to the victim;

5) in case of repeated examinations - a copy of the expert's opinion or an act on the primary forensic chemical examination.

The main forensic chemical examination clarifies the following questions:

the composition and name of the substance presented;

homogeneity of the composition of the studied object and sample;

the relation of the object submitted for examination to certain substances: narcotic, potent, poisonous, explosive, etc.;

if there is a substance, then finding out its name and quantity;

The entire set of these tasks is solved by independent experts. Chemical laboratories conduct tests of any objects. Special laboratories are equipped for forensic chemical examinations, in which all the necessary tools and tools are collected. The course and results of all examinations carried out are recorded in the journal. After completing all the procedures, the laboratory staff draws up the conclusion of the examination.

The conclusion of the examination is a legal document that has evidentiary value. An expert opinion can be provided in court in the event of further litigation. Forensic science has an important role to play in establishing the truth in a trial. At the end of the forensic chemical examination, the experts issue a conclusion that has an evidentiary character in legal proceedings.

When making an opinion, experts can only use the materials provided to them. Russian legislation guarantees the independence of an expert in drawing up an opinion from the investigator and the court.

The law warns about the criminal liability of an expert who gives deliberately false conclusions, which minimizes the possibility of an unfair attitude of experts in relation to forensic chemical research.

Such an examination, as a forensic chemical examination, in one case from its beginning to end must be carried out by the forces of one chemical expert, who was entrusted with its implementation and for which he is responsible. Moreover, all the main operations for the isolation of certain substances, their qualitative detection and their quantitative determination, are carried out personally by an expert chemist.

The opinion of an expert or a commission of experts is recommended, in accordance with the stages of research, to be formed from the following parts: introductory part, research part and conclusions.

Information about the assignment by the head of the SEU of the production of a forensic examination to an expert (experts), an explanation of the rights and obligations, a warning about criminal liability for giving a knowingly false conclusion under Article 307 of the Criminal Code of the Russian Federation (hereinafter referred to as the Criminal Code) or about administrative liability under Article 17.9 of the Code of the Russian Federation on administrative offenses, and, if necessary, for the disclosure of preliminary investigation data under Article 310 of the Criminal Code of the Russian Federation, it is recommended to indicate before the introductory part of the conclusion.

The introductory part states:

the name of the forensic institution (s);

number of the conclusion, type of forensic examination, its type (primary, additional, repeated, complex, commission); on what (criminal, civil or other) case it was produced; grounds for the production of a forensic examination (decree or determination, when and by whom it was issued);

the date of receipt of materials for forensic examination in the SEU and the date

signing the conclusion;

information about the expert: last name, first name, patronymic, education, specialty (general by education and expert), work experience in that expert

specialty, in which the forensic examination is carried out, academic degree and academic title, position held;

questions put before an expert or a commission of experts. In this case, the questions are given in the wording that is given in the resolution (determination) on the appointment of a forensic examination. If the wording of the question requires clarification, but the expert understands its content, then after verbatim quotation, it can be indicated how the expert understands the task, guided by special knowledge. If there are several questions, the expert can group them in a sequence that provides the most appropriate order for conducting research. In addition, the question raised at the initiative of the expert (Article 204 of the Code of Criminal Procedure, 77 of the Code of Civil Procedure, 86 of the APC) is given after the questions contained in the resolution (definition);

objects of research and case materials submitted to the expert for the production of a forensic examination, the method of their delivery, the type and condition of the packaging;

information about the applications submitted by the expert, the results of their consideration;

the circumstances of the case that are important for giving an opinion;

information about the participants in the process who were present during the forensic examination (surname, initials, procedural status);

· reference materials and normative documents (with a full indication of their details), which the expert was guided by when resolving the issues raised.

When performing an additional or repeated forensic examination, the introductory part shall indicate information about the primary forensic examination or previous forensic examinations: the surname, initials of the expert, the name of the expert institution (or the expert’s place of work), the number and date of the conclusion, conclusions, as well as the grounds and motives for its appointment contained in the resolution (determination).

The research part of the conclusion sets out the content and results of the research:

· the results of the inspection of the objects submitted for examination, the actions carried out with material evidence (disassembly, assembly, etc.);

the results of investigative actions (examinations, experiments, etc.), if they are used as initial data in the conduct of research; research process (separately for each stage) and its results. It is also indicated what specific physical evidence and documents were damaged or used (destroyed) in the course of the forensic examination;

applied methods, research methods, special software. In the case of using standard expert methods and expert research schemes set out in methodological publications, a reference is made to them and full information about their publication is indicated; in the case of the use of automated programs or software systems, data on the institution that developed them are given;

the purpose and conditions for performing an expert experiment, obtaining experimental samples;

Each question resolved by the expert must correspond to a specific section of the research part. If it is necessary to conduct a joint study on several closely related issues, the content of the studies is presented in one section.

During the production of an additional forensic examination, the expert has the right to refer to the study conducted in the previous examination.

During the production of a repeated forensic examination, the research part of the conclusion indicates the reasons for the discrepancy between the conclusions and the conclusions of the primary examination, if any.

In the production of a commission forensic examination by experts of one specialty, each of them conducts research in full and they jointly analyze the results.

In the production of a comprehensive forensic examination by experts of different specialties, each of them conducts research within the limits of their special knowledge. In the research part of the conclusion, it is separately indicated which studies and to what extent each expert (experts) conducted and signed by him (them).

A general assessment of the research results is given at the end of the research part of the conclusion (synthesizing section) with a detailed motivation for the judgments substantiating the conclusion on the issue being addressed. If it was not possible to give answers to some of the questions posed, the expert indicates the reasons for this in the research part.

The "Conclusions" section contains answers to the questions posed to the expert or the commission of experts. The sequence of their presentation is determined by the sequence of questions. For each of the questions posed, an answer is given on the merits or it is indicated that it is impossible to solve it.

Conclusions about the circumstances, on which the expert was not asked questions, but which were established by him in the course of research, are stated, as a rule, at the end of the section.

If the expert cannot formulate a conclusion without a detailed description of the results of the studies set out in the research part and containing an exhaustive answer to the question posed, a reference to the research part of the conclusion is allowed.

The conclusions are presented in a clear, clear language that does not allow for various interpretations, and should be understandable to persons who do not have special knowledge.

The conclusion is certified by the seal of the institution that organizes the work of the commission.

Materials illustrating the conclusion (applications) are drawn up and signed by the expert who conducted the research, and certified by the seal of the institution where they were performed.

The procedure for the production of forensic chemical examinations is provided for by the "Rules for forensic chemical examination of material evidence in forensic chemical departments of forensic medical laboratories of health authorities" (1957).

In accordance with these Rules, a forensic chemical examination of physical evidence is carried out at the request of the bodies of inquiry, investigation and court (also on the directions of forensic experts and, less often, medical institutions) in the forensic chemical departments of forensic medicine. Qing Laboratories Bureau of Forensic Medical Examination. The following provisions give an idea of the basic rules for conducting a forensic chemical examination.

1. The expert chemist must have firm confidence that the object under study is the one that was sent for analysis with these accompanying documents and that the object did not undergo any changes on the way to the laboratory, with the exception of natural processes, occurring in most objects of forensic chemical research (cadaveric material and other objects of biological origin):

a) before starting any forensic chemical analysis of ex-
Perth chemist must first of all familiarize himself in detail with
documents presented in the case, carefully compare the inscriptions
si on banks and closures with the data indicated in the accompanying
documents, check the integrity of the closures and seals
and the correspondence of the inscriptions on the seals to those indicated in the accompanying
driving documents;

b) after that, it is necessary to make an external inspection of the package
forging, and then inspect the objects of study. At autopsy
recent expert chemist must be careful that
so as not to damage the container of objects, not to bring parts into the object
printing and packaging, do not lose the objects of study. All their
observations obtained during the inspection of material evidence
and in their further study, he wrote down in detail
puts it in a work journal; c) the contents of each closure must be described in detail and weighed (solid objects) or measured (liquid objects). When describing, they note: appearance, morphological composition, color, smell, conservation of the object, the presence of foreign inclusions with their characteristics (crystals, seeds, plant parts, etc.). The latter are selected and examined separately or, if necessary, sent to a specialist in another field (for example, a pharmacognostic). If the object of study is preserved with pure alcohol (which is allowed, except in cases where the question is raised about the production of a forensic chemical study for the presence of alcohols and nitrites), a control sample of alcohol must be delivered to the laboratory in the amount that was consumed for conservation. If a control sample of a preservative is not sent or an unacceptable method of preservation is used, for example, glycerin, formalin, phenol and other substances, it is necessary to note in the act of forensic chemical examination the incorrectness of preservation and the possibility of its influence on the results of the examination.

2. After reviewing the accompanying documents, registration, inspection, description and study of the objects of research, production of preliminary samples, the chemical expert is obliged to draw up an accurate and detailed research plan. If there are indications of the purpose of the forensic chemical examination of material evidence, first of all, a study is carried out for the substances mentioned in the documents. However, often from the case materials, external examination of objects, preliminary samples and preliminary data, it is necessary to expand the study, which is also the responsibility of an expert chemist.
3. Forensic chemical examination of physical evidence should be started on the day of their receipt due to the possibility of decomposition of certain chemicals (hydrocyanic acid, atropine, cocaine, etc.) during storage of the object. In the registration and work logs, the date of receipt of material evidence by the laboratory and the date of the beginning and end of the forensic chemical investigation are noted.
4. For the production of a forensic chemical examination, only a part of the delivered material is spent, for example, 1/3 of it. The second part of the material can be used (if necessary) for a verification study or quantitative determination by the expert chemist himself. The last part is sent to the institution that sent the material for forensic chemical research or is stored in accordance with the order of the Minister of Health of the USSR No. 166 (Appendix No. 4).

When small amounts of material (for example, up to 100 g of the internal organs of a corpse) enter the laboratory, the expert chemist has the right to use it completely, about which the person who sent the material to the laboratory is informed.

If poisoning is suspected, if biological material is sent for analysis, the following are examined separately: 1) stomach with contents; 2) small intestine with contents; 3) large intestine; 4) liver with gallbladder; 5) kidney with urine; 6) lungs, spleen, heart and blood; 7) the brain and part of the spinal cord.

Combining biological material for analysis into two samples: 1) organs of the gastrointestinal tract; 2) parenchymal organs - possible only in exceptional cases.

5. Forensic chemical examination in one case from beginning to end is carried out by one expert chemist, who is entrusted with its implementation and for which he is responsible. In this case, all the main operations associated with the isolation of certain substances, their qualitative detection and their quantitative determination, the expert chemist performs personally.
6. Each forensic chemical study is conducted as a quantitative study, into which it can be converted at any stage of the analysis. Objects for all studies are taken by weight, and the distillates, filtrates, etc. obtained during the analysis are measured.
7. When choosing methods for isolating various chemicals from objects of study of biological origin, as well as methods for qualitative detection and quantification, the expert chemist must choose those that have been tested and sufficiently studied in relation to chemical-toxicological analysis, by virtue of what the results of the study can serve as convincing evidence of the presence of certain substances. When conducting a forensic chemical study, only those methods and reactions are used that the expert chemist got acquainted with earlier, mastered them, knows all the conditions for their production, can take into account all the errors that are possible in their application. One cannot learn from forensic chemical research, but only what has been studied can be applied to it.

Wherever possible, it is necessary to carry out several different reactions so that the coincidence of their results eliminates the possibility of error.

Specific assistance in the choice of methods for isolating, detecting and determining a number of chemicals is provided by methodological letters published by the Chief Forensic Expert of the USSR Ministry of Health, which are compiled after a comprehensive check of the method on forensic chemical material.

It is advisable, when choosing methods for detecting chemical substances, to stop the choice on those reactions whose products could be preserved for presentation to the bodies of inquiry; investigation and trial as corpus delicti (material evidence). In some cases, it is extremely useful to compare the result of a particular reaction with the results of a reaction carried out with a known substance.

8. With positive results of a forensic chemical study for the presence of atropine, strychnine, nicotine and some other substances, the chemical detection reactions of which are not specific enough, the study should be supplemented by a pharmacological test on animals. The latter in the simplest cases, such as, for example, applying a substance to the back of a frog with suspicion of strychnine or nicotine, introducing a substance into the eye of a cat with suspicion of atropine, is carried out by an expert chemist, and in more complex cases by a pharmacologist.
9. Quantitative determination is carried out in all cases when it is possible and when there are appropriate methods of determination. The amounts of the found substances are related to 100 g of the investigated object and expressed in weight units.

10. A detailed record is kept of all the operations, reactions, and results of observations in the working journal of an expert chemist. All data and calculations are recorded here. related to quantitative definitions. An expert chemist has no right to keep anything in his memory, write down the data and calculations for a forensic chemical study on separate sheets of paper. He is obliged, at the request of the court or in case of any doubts about the correctness of the study, to submit not only an act of forensic chemical examination, drawn up on the basis of entries in the work log. but also a journal with all the draft entries in it.
11. From the moment of receipt of material evidence, the expert chemist is responsible for their protection:

a) from criminal encroachments by persons interested in substituting research objects, destroying them, introducing any poisonous or potent substances into them. To prevent such cases, the forensic chemical department of the forensic laboratory at the end of the work must be locked and sealed by an expert chemist. In the laboratory where the forensic chemical research is carried out, unauthorized persons do not have the right to be and work with poisonous and potent substances should not be carried out. Material evidence throughout the entire time of the study must also be kept in a locked room. At the end of the examination with material evidence, they proceed in accordance with the rules for the storage and destruction of material evidence in forensic laboratories;

b) from getting into the objects of study of the substances sought
with parts of the seal or capping, with reagents or utensils. For
to prevent the ingress of the desired substances with foreign
the object must be carefully opened packages and caps
with material evidence and present special requirements
attitude to reagents used in forensic chemical
analysis, and to chemical glassware. Chemist, not relying on service
living staff, when using chemical glassware and
devices for the production of forensic chemical analysis of the
wives must personally verify their cleanliness. This is especially
important because in most cases
an expert chemist has to detect microquantities of those
or other desired substances and apply micro- and semi-micro-
methods of analysis;

c) from mixing different objects of research between
yourself. To avoid mixing, it is desirable to simultaneously
to exhaust only one, maximum two analyzes. In the last
tea, it is necessary not to group identical operations side by side,
related to various analyses. To avoid possible
errors must be made on all cups, flasks, glasses
appropriate inscriptions (for example, put the number of the expert
tyses).

12. Despite the fact that one should always strive not to delay the results of a forensic chemical examination, it is important to remember that unreasonable haste can cause irreparable harm and mislead the entire investigation. Hence the need to carefully consider the results of a forensic chemical study, to review, where necessary, the relevant literature, to evaluate certain reactions and methods, sometimes even to re-examine before a conclusion is given on a forensic - chemical analysis.
13. Forensic chemical examination of material evidence (as well as any other examination of material evidence) is very responsible. Therefore, at all stages of the production of research (expertise), they are drawn up by appropriate documents. So, at the first stage - the receipt of material evidence by the laboratory for the production of research - it is necessary that, together with the material evidence and the accompanying document, a decision of the bodies of inquiry or investigation on the appointment of a forensic chemical examination of material evidence be delivered to the laboratory or court order. Without such a document, the forensic laboratory cannot accept physical evidence for examination. The decision, which sets out the circumstances of the case, lists the subjects to be investigated and clearly formulates the questions that need to be resolved, is the main document that guides the entire study, sets certain tasks for the expert chemist, and determines the plan of the entire analysis.

Other accompanying documents also serve to guide the forensic chemical research. The protocol of inspection of the scene of the incident and the seizure of material evidence, an extract from the medical history, an act of a forensic medical examination of a corpse, and other documents are important.

There have been cases when only the availability of these documents allowed an expert chemist to apply a special research methodology or expand the boundaries of forensic chemical analysis and thereby help the bodies of inquiry, investigation and court.

Of the numerous practical examples, one can be cited, when a forensic chemical study of children's clothes contaminated with some kind of yellow substance, and the contents from under the nails of two children, it was possible with a positive result to test for the presence of para-nitro-aniline, as a rule, not included in the circle of forensic chemical research. The correct direction of the forensic chemical analysis was helped by the investigator, who reported that the powder with which, according to his assumption, the children's clothes were stained, was brought from the factory, and the children "powdered" with this powder looked "black" in a few minutes ( cyanosis).

According to the "Rules", the forensic laboratory has the right to request missing documents if they are not sent, and even delay the study.

The reason for the high requirements for the execution of a "referral" for examination lies in the exceptional value of material evidence for the bodies of inquiry, investigation and court, often in their uniqueness.

At the same time, if the bodies of inquiry, investigation or court did not sufficiently ensure the correct direction of the research, did not clearly formulate their questions, unproductive expenditure of valuable material evidence is possible.

Prof. A. V. Stepanov, in the first edition of his manual on forensic chemistry, cited an example when an investigator sent an expert chemist to analyze water with a proposal to “make an analysis”. The chemist conscientiously examined the water for the presence of toxic substances, as well as contaminants, used up material evidence, but could not foresee the investigator's question: "Does the water contain traces of blood"?

The second stage is documentation in the production process and the third stage is the writing of a forensic chemical examination report. All physical evidence and documents submitted for examination are first of all registered in a certain form, provided for by the rules of forensic chemical research.

Registration is carried out in a special book, the pages of which are numbered, and the book itself is laced, sealed and signed by the head of the bureau of forensic medical examination.

The registration book makes it possible to ensure strict accounting of material evidence, helps the expert chemist to quickly navigate responses to requests for examinations, and also to draw up reports.

Each examination necessarily ends with the drawing up of an act (conclusion) of a forensic chemical examination. The main written source for drawing up the act is the workbook of an expert chemist, in which all entries related to the study of material evidence are made daily (a sample of a substance for a particular type of study, basic operations, results of qualitative reactions, quantitative data definitions, calculations, etc.).

The work journal, as well as the registration book of examinations in the department, is a numbered, laced, sealed and signed by the head of the forensic medical examination bureau. It is issued to each expert chemist against receipt, and after use it is deposited in the office of the bureau. All entries related to the examination of material evidence and the production of a forensic chemical study are made only in this journal; it is unacceptable to do them on any separate sheets, in drafts, etc.

The legal document of the forensic chemical examination carried out is the act of the forensic chemical examination. The act is written in a book of acts, designed in the same way as a work journal, issued to each expert chemist.

The act is drawn up in a certain form. It has the heading: “Act No. ... of the forensic chemical examination of material evidence in the case of ...” and consists of three parts: introduction, descriptive part and conclusion. The introduction and descriptive part constitute the protocol of the examination. In the descriptive part includes sections: "External examination" and "Chemical research" (where necessary, chemical research is preceded by "Study under a microscope").

In the introduction, according to the Rules of Forensic Chemical Research and the Code of Criminal Procedure of the RSFSR (Article 191), it is indicated:

1) the time (beginning and end) of the examination;
2) the basis for the performance of the examination (the decision on the appointment of a forensic chemical examination, indicating the name of the investigator and the date), the number and date of the accompanying document;
3) the place where the expert examination was carried out (name of the forensic laboratory);
4) who performed the examination (last name, first name, patronymic, education, specialty, degree, title and qualification category, position of an expert chemist);
5) what material evidence and in what case were subjected to expert examination;
6) who was present during the performance of the expert examination;
7) the purpose of the examination or the questions raised for the resolution of the examination (the latter are given verbatim, as presented by representatives of the investigative and judicial authorities);
8) under the heading “Circumstances of the case”, the content of the case materials is summarized.

The section “External examination” describes in detail material evidence: packaging, inscriptions on jars, flasks, boxes, boxes, morphological composition of objects, weight, color, smell, reaction to litmus and other indicators, conservation,

The section "Chemical Research" provides a detailed description of the methods used, the technique for examining material evidence and the results of the research.

When describing the “Chemical Research”, the amount of the object, mineralizate, distillate, extraction, etc., spent on each operation, is noted. The entire course of forensic chemical analysis is described in detail: methods for isolating and detecting toxic and potent substances and the phenomena observed in this case (color, sediment, crystal formation, etc.). Describing the results of the study, the expert chemist should not allow the expressions in the act of forensic chemical examination: “A positive reaction was obtained”, “The result of the reaction is negative”, “Testing with hydrochloric acid showed the presence of silver salts”, etc., and also should not refer to the author of a particular method, give formulas and equations of reactions. The quantitative determination of toxic and potent substances should be presented in such a way that the described methodology and calculation make it possible to judge the reliability of the results of the determination.

In the conclusion, based on the description of the forensic chemical study, the found substances are first listed with an indication of their quantities, then the substances not found, and finally, the answers to the questions (within the competence of the expert chemist) posed by the bodies of inquiry, investigation and court.

In order to assist the forensic authorities and the forensic medical expert in concluding the act of the forensic chemical examination, speaking about the substances found by the study and their quantities, as well as about the substances not found during the analysis, the expert chemist must simultaneously give an assessment of the results obtained, based on the resolving capabilities of the applied methods of analysis and the characteristics of material evidence and chemicals found or not found by the analysis 1 .

If, in the process of work, an expert chemist establishes circumstances that are relevant to the case, but on which he was not asked questions, he indicates this in the conclusion (Article 191 of the Code of Criminal Procedure of the RSFSR).

Questions that lie outside the competence of an expert chemist are not answered in the final part of the act of forensic chemical examination. In the accompanying document to the act of forensic chemical examination, in such cases, these questions are listed and indicated (if possible) in the competence of which specialist may be the answers to them.

The act of forensic chemical examination of material evidence is signed by the expert chemist who carried out the examination.

The typewritten text of the act (copy) and the accompanying document are sent to the institution or person that sent the material evidence to the laboratory for research.

The use of pre-prepared forms, for example, a questionnaire type, for the preparation of acts of forensic chemical examination of material evidence is strictly prohibited.

An expert chemist should always remember the great responsibility that he bears for the answers in the act of a forensic chemical examination. A careless, insufficiently accurate conclusion of an expert can lead to a distortion of the direction of the case and, instead of helping the accused, the bodies of inquiry, the court, the investigation or the medical institution, cause irreparable or difficult to correct harm.

Prof. A. V. Stepanov quite rightly pointed out that any forensic chemical research is essentially a scientific research and differs from a purely scientific research only by a smaller breadth of conclusions relating only to a particular particular case 2 . The conclusion on the act of a forensic chemical examination is therefore a scientific conclusion on the issues posed to the expert chemist and requires him to apply all his theoretical knowledge, practical experience, the ability to strictly discuss and convincingly substantiate the data obtained during the examination.

In the act of the forensic chemical examination and the conclusion, the material of the study must be stated with the utmost clarity and in such a way that the second person who may be entrusted with verifying the results of the first study experimentally, as well as on the basis of the case materials (re-examination), following the indicated in the act of examination through, could come to the same conclusions. The act must be written neatly, all corrections, inscribed and crossed out places must be specified and sealed with the signature of an expert chemist. If possible, permanent preparations or micrographs of the obtained crystals, raids (for example, in the Marsh tube), reaction products (for example, Prussian blue) should be attached to the act of forensic chemical examination, confirming the correctness of the conclusions. Documents accompanying physical evidence to the laboratory are stored in the department until the end of the study in a safe or a lockable cabinet, which is sealed at the end of the work. Material evidence during the production of the study is stored in a closet, and perishable evidence is stored in a refrigerator, which are locked and sealed. Upon completion of the study, the documents, together with the act of forensic chemical examination and accompanying documents, are transferred to the bureau of forensic medical examination.

In the course of any analysis, the following main stages can be distinguished:

1) sampling for analysis (sampling) and its transfer into a solution (dissolution);

2) separation and concentration;

3) analysis (final definition);

4) processing of the obtained results.

1) Sampling. There are 3 types of samples:

To dissolve organic compounds, non-aqueous solvents are often used - alcohols, ketones, ethers, aromatic and aliphatic hydrocarbons, organochlorines, etc.

where: FROM ref and V ref - concentration and volume of the initial (diluted) solution;

FROM con and V con - concentration and volume of the final (concentrated) solution

3) Conducting an analysis is carried out according to the available standard certified methods, depending on the task of chemical analysis.

Documentation is drawn up in accordance with the criminal procedure legislation and the order of the Ministry of Health of the Russian Federation.

Each expert has a working journal, where he enters all the data on the research being carried out. For each completed examination, an “Act of Forensic Chemical Research” (“Expert Conclusion”) is drawn up. The act is drawn up in two copies: one is sent to the person who appointed the examination, the second is stored in the archive of the Agricultural Organization. The act must be signed by an expert, stamped and the date of completion of registration.

The act is drawn up personally by the expert who conducted the study, on his own behalf in a certain form. The act consists of the following sections: an introductory part, a description of the objects of research, a research part (chemical research) and a conclusion (conclusions).

In the introductory part, they indicate: on the basis of which documents the examination was carried out, the department in which the study was carried out, position, full name. expert, work experience, category, list the received objects, indicate full name. of the deceased (injured), note the date of the beginning and end of the study, list the issues to be resolved. Then they state the circumstances of the case, give information from the documents received.

The act must be signed by an expert, stamped, dated.

Precautions must be applied to ensure confidentiality in the SHO (issue of information and documentation only to an authorized person).

Poison. General characteristics of the toxic effect. Formation of the toxic effect as a factor in the interaction of poison, organism and environment. The concept of "poison", "poisoning"

Among the variety of issues resolved by chemical-toxicological analysis, the question of the presence (and definition) of a chemical substance or compound in the object of study, which toxicology considers as a "poison", is most often resolved. This is necessary to establish the cause of poisoning, death.

The definition of "poison" goes beyond chemistry. This concept is medical and is given by toxicology.

Poison or poisonous substance , in toxicology, is conventionally called such a chemical substance (or compound), which, when introduced into the body in small quantities, and acting on it chemically or physico-chemically, under certain conditions, can lead to illness or death.

Poisoning or intoxication , in toxicology is called a violation of body functions under the influence of a toxic substance, which can result in a health disorder or even death.

The concept of "poison" in toxicology is conditional and much narrower than in biology. Everyone is well aware that toxic substances can be introduced into the human body (animal, plant) not only for the purpose of poisoning, but also as medicines (barbiturates, alkaloids, etc.). Poisons can be formed in the body during certain diseases and conditions (metabolic disorders, infection), they can be constantly produced by the body (hormones that act as poisons in large doses) or accumulate in organs during human life (mercury, arsenic, copper, lead and etc.)

There are no absolute poisons in nature, that is, there are no chemicals that can lead to poisoning under any conditions. In order for this or that substance to become a poison when it is available, certain and very diverse conditions must be created.

The toxic effect of a chemical depends on:

a) its dose (toxic);

b) physical and chemical properties;

c) conditions of use (path of administration, presence and quality of food in the stomach);

d) the state of the human body (gender, age, disease, weight, genetic factors, etc.)

Other substances with which the poison is introduced into the body are also important. At the same time, the effect of poisons in the presence of other substances can be enhanced - synergism is manifested (for example, barbiturates, alkaloids together with alcohol), or weakened.

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The main stages of chemical analysis. The procedure for the production of forensic chemical examination

Poison. General characteristics of the toxic effect. Formation of the toxic effect as a factor in the interaction of poison, organism and environment. The concept of "poison", "poisoning"

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