Subject of Analytical Chemistry

There are various definitions of the concept of "analytical chemistry", for example:

Analytical chemistry - it is the science of the principles, methods and means of determining chemical composition and structure of substances.

Analytical chemistry - This scientific discipline, which develops and applies methods, instruments and general approaches to obtain information about the composition and nature of matter in space and time(definition adopted by the Federation of European Chemical Societies in 1993).

The task of analytical chemistry is the creation and improvement of its methods, the determination of the limits of their applicability, the assessment of metrological and other characteristics, the development of methods for analyzing specific objects.

A system that provides a specific analysis of certain objects using the methods recommended by analytical chemistry is called analytical service.

The main task of the pharmaceutical analytical service is to control the quality of medicines produced by the chemical-pharmaceutical industry and prepared in pharmacies. Such control is carried out in analytical laboratories of chemical and pharmaceutical plants, control and analytical laboratories and in pharmacies.

Principle, method and methodology of analysis

Analysis- a set of actions, the purpose of which is to obtain information about the chemical composition of the object.

Principle of analysis - a phenomenon that is used to obtain analytical information.

Analysis method - summary principles underlying the analysis of a substance (without specifying the component and object being determined).

Analysis Method - detailed description performing an analysis of a given object using the selected method, which provides the specified characteristics of correctness and reproducibility.

Several different analysis methods may have the same principle. The same method of analysis can be based on many various techniques analysis.

The analysis methodology may include the following steps:

A particular analysis technique does not have to include all of the above steps. The set of operations performed depends on the complexity of the composition of the analyzed sample, the concentration of the analyte, the goals of the analysis, the permissible error of the analysis result, and on which analysis method is supposed to be used.

Types of analysis

Depending on the purpose, there are:

Depending on which components should be detected or determined, the analysis can be:

· isotopic(individual isotopes);

· elemental(elemental composition of the compound);

· structural-group /functional/(functional groups);

· molecular(individual chemical compounds characterized by a certain molecular weight);

· phase(individual phases in an inhomogeneous object).

Depending on the mass or volume of the analyzed sample, there are:

· macroanalysis(> 0.1 g / 10 - 10 3 ml);

· semi-microanalysis(0.01 - 0.1 g / 10 -1 - 10 ml),

· microanalysis (< 0,01 г / 10 -2 – 1 мл);

· submicroanalysis(10 -4 – 10 -3 g /< 10 -2 мл);

· ultramicroanalysis (< 10 -4 г / < 10 -3 мл).

Methods of analytical chemistry

Depending on the nature of the property being measured (the nature of the process underlying the method) or the method of recording the analytical signal, the determination methods are:

Physical methods of analysis, in turn, are:

· spectroscopic(based on the interaction of matter with electromagnetic radiation);

· electrometric (electrochemical)(based on the use of processes occurring in an electrochemical cell);

· thermometric(based on the thermal effect on the substance);

· radiometric(based on nuclear reaction).

Physical and physico-chemical methods of analysis are often combined under the general name " instrumental methods of analysis».

CHAPTER 2

2.1. Analytical reactions

Chemical methods for detecting substances are based on analytical reactions.

Analyticalcall chemical reactions, the result of which carries certain analytical information, for example, reactions accompanied by precipitation, gas evolution, the appearance of an odor, a change in color, the formation of characteristic crystals.

The most important characteristics of analytical reactions are selectivity and detection limit. Depending on the selectivity(the number of substances that enter into a given reaction or interact with a given reagent) analytical reactions and the reagents that cause them are:

Limit of detection(m min , P or C min , P) - smallest mass or concentration of a substance, which with a given confidence probability P can be distinguished from the signal of the control experiment(See Chapter 10 for more details).

2.2. Systematic and fractional analysis

Detection of elements in the joint presence can be carried out by fractional and systematic methods of analysis.

Systematic called a method of qualitative analysis based on the separation of a mixture of ions using group reagents into groups and subgroups and the subsequent detection of ions within these subgroups using selective reactions.

The name of systematic methods is determined by the group reagents used. Known systematic methods of analysis:

· hydrogen sulfide,

· acid-base,

· ammonium phosphate.

Each systematic method of analysis has its own group analytical classification. The disadvantage of all systematic methods of analysis is the need to a large number operations, duration, bulkiness, significant loss of detectable ions, etc.

Fractionalcalled a qualitative analysis method that involves the detection of each ion in the presence of others using specific reactions or carrying out reactions under conditions that exclude the influence of other ions.

Typically ion detection fractional method carried out according to the following scheme - first, the influence of interfering ions is eliminated, then the desired ion is detected using a selective reaction.

The elimination of the interfering effect of ions can be carried out in two ways.

For example

· complex formation

· pH change

· redox reactions

· precipitation

· extraction

2.3. general characteristics, classification and methods for detecting cations

According to acid-base classification cations, depending on their relationship to solutions of HCl, H 2 SO 4 , NaOH (or KOH) and NH 3, are divided into 6 groups. Each of the groups, with the exception of the first, has its own group reagent.

First analytical group of cations

The first analytical group of cations includes cations K + , Na + , NH 4 + , Li + . They do not have a group reagent. Ions NH 4 + and K + form sparingly soluble hexanitrocobaltates, perchlorates, chloroplatinates, as well as sparingly soluble compounds with some large organic anions, for example, dipicrylamine, tetraphenylborate, hydrotartrate. Aqueous solutions of salts of group I cations, with the exception of salts formed by colored anions, are colorless.

Hydrated ions K + , Na + , Li + are very weak acids, acidic properties are more pronounced in NH 4 + (рК a = 9.24). Not prone to complex formation reactions. Ions K + , Na + , Li + do not participate in redox reactions, since they have a constant and stable oxidation state, NH 4 + ions have reducing properties.

The detection of cations of the I analytical group is carried out according to the following scheme

The detection of K + , Na + , Li + interfere with the cations of p- and d-elements, which are removed by precipitating them (NH 4) 2 CO 3 . The detection of K + is interfered with by NH 4 +, which is removed by calcining the dry residue or binding with formaldehyde:

4 NH 4 + + 6CHOH + 4OH - ® (CH 2) 6 N 4 + 10H 2 O

Similar information.

1. INTRODUCTION

2. CLASSIFICATION OF METHODS

3. ANALYTICAL SIGNAL

4.3. CHEMICAL METHODS

4.8. THERMAL METHODS

5. CONCLUSION

6. LIST OF USED LITERATURE

INTRODUCTION

Chemical analysis serves as a means of monitoring production and product quality in a number of industries National economy. Mineral exploration is based to varying degrees on the results of the analysis. Analysis is the main means of controlling contamination environment. Finding out the chemical composition of soils, fertilizers, feed and agricultural products is important for the normal functioning of the agro-industrial complex. Chemical analysis is indispensable in medical diagnostics and biotechnology. The development of many sciences depends on the level of chemical analysis, the equipment of the laboratory with methods, instruments and reagents.

The scientific basis of chemical analysis is analytical chemistry, a science that has been a part, and sometimes the main part, of chemistry for centuries.

Analytical chemistry is the science of determining the chemical composition of substances and, in part, their chemical structure. Methods of analytical chemistry allow answering questions about what a substance consists of, what components are included in its composition. These methods often make it possible to find out in what form a given component is present in a substance, for example, to determine the oxidation state of an element. Sometimes it is possible to evaluate spatial arrangement components.

When developing methods, you often have to borrow ideas from related fields of science and adapt them to your goals. The task of analytical chemistry includes the development theoretical foundations methods, establishing the limits of their applicability, assessing metrological and other characteristics, creating methods for analyzing various objects.

Methods and means of analysis are constantly changing: new approaches are involved, new principles and phenomena are used, often from distant areas of knowledge.

The analysis method is understood as a fairly universal and theoretically justified method for determining the composition, regardless of the component being determined and the object being analyzed. When they talk about the method of analysis, they mean the underlying principle, the quantitative expression of the relationship between the composition and any measured property; selected implementation techniques, including interference detection and elimination; devices for practical implementation and methods for processing measurement results. Analysis methodology is a detailed description of the analysis of a given object using the selected method.

There are three functions of analytical chemistry as a field of knowledge:

1. solution of general issues of analysis,

2. development of analytical methods,

3. solution of specific problems of analysis.

It can also be distinguished qualitative And quantitative analyses. The first decides the question of what components the analyzed object includes, the second gives information about the quantitative content of all or individual components.

2. CLASSIFICATION OF METHODS

All existing methods of analytical chemistry can be divided into methods of sampling, decomposition of samples, separation of components, detection (identification) and determination. There are hybrid methods that combine separation and definition. Detection and definition methods have much in common.

Highest value have definition methods. They can be classified according to the nature of the measured property or the way the corresponding signal is registered. Methods of determination are divided into chemical , physical And biological. Chemical methods are based on chemical (including electrochemical) reactions. This includes methods called physicochemical. Physical methods are based on physical phenomena and processes, biological - on the phenomenon of life.

The main requirements for analytical chemistry methods are: correctness and good reproducibility of results, low detection limit of the required components, selectivity, rapidity, ease of analysis, and the possibility of its automation.

When choosing an analysis method, it is necessary to clearly know the purpose of the analysis, the tasks that need to be solved, and evaluate the advantages and disadvantages of the available analysis methods.

3. ANALYTICAL SIGNAL

After the selection and preparation of the sample, the stage of chemical analysis begins, at which the component is detected or its amount is determined. For this purpose, they measure analytical signal. In most methods, the analytical signal is the average of measurements physical quantity at the final stage of the analysis, functionally related to the content of the analyte.

If it is necessary to detect any component, it is usually fixed appearance analytical signal - the appearance of a precipitate, color, lines in the spectrum, etc. The appearance of an analytical signal must be reliably recorded. When determining the amount of a component, it is measured magnitude analytical signal - sediment mass, current strength, spectrum line intensity, etc.

4. METHODS OF ANALYTICAL CHEMISTRY

4.1. METHODS OF MASKING, SEPARATION AND CONCENTRATION

Masking.

Masking is the inhibition or complete suppression of a chemical reaction in the presence of substances that can change its direction or speed. In this case, no new phase is formed. There are two types of masking - thermodynamic (equilibrium) and kinetic (non-equilibrium). In thermodynamic masking, conditions are created under which the conditional reaction constant is reduced to such an extent that the reaction proceeds insignificantly. The concentration of the masked component becomes insufficient to reliably fix the analytical signal. Kinetic masking is based on increasing the difference between the reaction rates of the masked and the analyte with the same reagent.

Separation and concentration.

The need for separation and concentration may be due to the following factors: the sample contains components that interfere with the determination; the concentration of the analyte is below the detection limit of the method; the components to be determined are unevenly distributed in the sample; there are no standard samples for calibrating instruments; the sample is highly toxic, radioactive and expensive.

Separation- this is an operation (process), as a result of which the components that make up the initial mixture are separated from one another.

concentration- this is an operation (process), as a result of which the ratio of the concentration or amount of microcomponents to the concentration or amount of the macrocomponent increases.

Precipitation and co-precipitation.

Precipitation is generally used to separate inorganic substances. Precipitation of microcomponents by organic reagents, and especially their co-precipitation, provide a high concentration factor. These methods are used in combination with methods of determination that are designed to obtain an analytical signal from solid samples.

Separation by precipitation is based on the different solubility of the compounds, predominantly in aqueous solutions.

Co-precipitation is the distribution of a microcomponent between a solution and a precipitate.

Extraction.

Extraction is a physicochemical process of distributing a substance between two phases, most often between two immiscible liquids. It is also a process of mass transfer with chemical reactions.

Extraction methods are suitable for concentration, extraction of microcomponents or macrocomponents, individual and group isolation of components in the analysis of various industrial and natural objects. The method is simple and fast to perform, provides high efficiency of separation and concentration, and is compatible with various methods of determination. Extraction allows you to study the state of substances in solution under various conditions, to determine the physico-chemical characteristics.

Sorption.

Sorption is well used for separation and concentration of substances. Sorption methods usually provide good separation selectivity and high values ​​of concentration factors.

Sorption- the process of absorption of gases, vapors and dissolved substances by solid or liquid absorbers on a solid carrier (sorbents).

Electrolytic separation and cementation.

The most common method of electoral separation, in which the separated or concentrated substance is isolated on solid electrodes in the elemental state or in the form of some kind of compound. Electrolytic isolation (electrolysis) based on the deposition of a substance by electric current at a controlled potential. The most common variant of cathodic deposition of metals. The electrode material can be carbon, platinum, silver, copper, tungsten, etc.

electrophoresis is based on differences in the speeds of movement of particles of different charges, shapes and sizes in an electric field. The speed of movement depends on the charge, field strength and particle radius. There are two types of electrophoresis: frontal (simple) and zone (on a carrier). In the first case, a small volume of a solution containing the components to be separated is placed in a tube with an electrolyte solution. In the second case, the movement occurs in a stabilizing medium that keeps the particles in place after the electric field is turned off.

Method grouting consists in the reduction of components (usually small amounts) on metals with sufficiently negative potentials or almagamas of electronegative metals. During cementation, two processes occur simultaneously: cathodic (separation of the component) and anodic (dissolution of the cementing metal).

Evaporation methods.

Methods distillation based on the different volatility of substances. The substance passes from a liquid state to a gaseous state, and then condenses, forming again a liquid or sometimes a solid phase.

Simple distillation (evaporation)– single-stage separation and concentration process. Evaporation removes substances that are in the form of ready-made volatile compounds. These can be macrocomponents and microcomponents, the distillation of the latter is used less frequently.

Sublimation (sublimation)- transfer of a substance from a solid state to a gaseous state and its subsequent precipitation in a solid form (bypassing the liquid phase). Separation by sublimation is usually resorted to if the components to be separated are difficult to melt or are difficult to dissolve.

Controlled crystallization.

When a solution, melt or gas is cooled, solid phase nuclei are formed - crystallization, which can be uncontrolled (bulk) and controlled. With uncontrolled crystallization, crystals arise spontaneously throughout the volume. With controlled crystallization, the process is set by external conditions (temperature, direction of phase movement, etc.).

There are two types of controlled crystallization: directional crystallization(in a given direction) and zone melting(movement of a liquid zone in a solid body in a certain direction).

With directional crystallization, one interface appears between a solid and a liquid - the crystallization front. There are two boundaries in zone melting: the crystallization front and the melting front.

4.2. CHROMATOGRAPHIC METHODS

Chromatography is the most commonly used analytical method. The latest chromatographic methods can determine gaseous, liquid and solid substances with molecular weights from units to 10 6 . These can be hydrogen isotopes, metal ions, synthetic polymers, proteins, etc. Chromatography has provided extensive information on the structure and properties of many classes of organic compounds.

Chromatography- This is a physico-chemical method of separation of substances, based on the distribution of components between two phases - stationary and mobile. The stationary phase (stationary) is usually a solid (often referred to as a sorbent) or a liquid film deposited on a solid. The mobile phase is a liquid or gas flowing through the stationary phase.

The method allows separating a multicomponent mixture, identifying the components and determining its quantitative composition.

Chromatographic methods are classified according to the following criteria:

a) according to the state of aggregation of the mixture, in which it is separated into components - gas, liquid and gas-liquid chromatography;

b) according to the separation mechanism - adsorption, distribution, ion-exchange, sedimentary, redox, adsorption-complexation chromatography;

c) according to the form of the chromatographic process - column, capillary, planar (paper, thin-layer and membrane).

4.3. CHEMICAL METHODS

At the core chemical methods detection and definition are chemical reactions of three types: acid-base, redox and complexation. Sometimes they are accompanied by a change in the aggregate state of the components. The most important among chemical methods are gravimetric and titrimetric. These analytical methods are called classical. The criteria for the suitability of a chemical reaction as the basis of an analytical method in most cases are completeness and high speed.

gravimetric methods.

Gravimetric analysis consists in isolating a substance in its pure form and weighing it. Most often, such isolation is carried out by precipitation. A less commonly determined component is isolated as a volatile compound (distillation methods). In some cases, gravimetry The best way solution of an analytical problem. This is an absolute (reference) method.

The disadvantage of gravimetric methods is the duration of the determination, especially in serial analyzes of a large number of samples, as well as non-selectivity - precipitating reagents, with a few exceptions, are rarely specific. Therefore, preliminary separations are often necessary.

Mass is the analytical signal in gravimetry.

titrimetric methods.

The titrimetric method of quantitative chemical analysis is a method based on measuring the amount of reagent B spent on the reaction with the component A being determined. In practice, it is most convenient to add the reagent in the form of a solution of exactly known concentration. In this version, titration is the process of continuously adding a controlled amount of a reagent solution of exactly known concentration (titran) to a solution of the component to be determined.

In titrimetry, three titration methods are used: forward, reverse, and substituent titration.

direct titration- this is the titration of a solution of the analyte A directly with a solution of titran B. It is used if the reaction between A and B proceeds quickly.

Back titration consists in adding to the analyte A an excess of a precisely known amount of standard solution B and, after completion of the reaction between them, titration of the remaining amount of B with a solution of titran B'. This method is used in cases where the reaction between A and B is not fast enough, or there is no suitable indicator to fix the reaction equivalence point.

Substituent titration consists in titration with titrant B not of a determined amount of substance A, but of an equivalent amount of substituent A ', resulting from a preliminary reaction between a determined substance A and some reagent. This method of titration is usually used in cases where it is impossible to carry out direct titration.

Kinetic methods.

Kinetic methods are based on the dependence of the rate of a chemical reaction on the concentration of the reactants, and in the case of catalytic reactions, on the concentration of the catalyst. The analytical signal in kinetic methods is the rate of the process or a quantity proportional to it.

The reaction underlying the kinetic method is called indicator. A substance whose change in concentration is used to judge the rate of an indicator process is indicator.

biochemical methods.

Among modern methods chemical analysis an important place is occupied by biochemical methods. Biochemical methods include methods based on the use of processes involving biological components (enzymes, antibodies, etc.). In this case, the analytical signal is most often either the initial rate of the process or the final concentration of one of the reaction products, determined by any instrumental method.

Enzymatic Methods based on the use of reactions catalyzed by enzymes - biological catalysts, characterized by high activity and selectivity of action.

Immunochemical methods analyzes are based on the specific binding of the determined compound - antigen by the corresponding antibodies. The immunochemical reaction in solution between antibodies and antigens is a complex process that occurs in several stages.

4.4. ELECTROCHEMICAL METHODS

Electrochemical methods of analysis and research are based on the study and use of processes occurring on the electrode surface or in the near-electrode space. Any electrical parameter (potential, current strength, resistance, etc.) that is functionally related to the concentration of the analyzed solution and can be correctly measured can serve as an analytical signal.

There are direct and indirect electrochemical methods. In direct methods, the dependence of the current strength (potential, etc.) on the concentration of the analyte is used. In indirect methods, the current strength (potential, etc.) is measured in order to find the end point of the titration of the analyte with a suitable titrant, i.e. use the dependence of the measured parameter on the volume of the titrant.

For any kind of electrochemical measurements, an electrochemical circuit or an electrochemical cell is required, the component of which is the analyzed solution.

There are various ways to classify electrochemical methods, from very simple to very complex, involving consideration of the details of the electrode processes.

4.5. SPECTROSCOPIC METHODS

Spectroscopic methods of analysis include physical methods based on the interaction electromagnetic radiation with substance. This interaction leads to various energy transitions, which are registered experimentally in the form of radiation absorption, reflection and scattering of electromagnetic radiation.

4.6. MASS SPECTROMETRIC METHODS

The mass spectrometric method of analysis is based on the ionization of atoms and molecules of the emitted substance and the subsequent separation of the resulting ions in space or time.

The most important application of mass spectrometry has been to identify and establish the structure of organic compounds. Molecular analysis of complex mixtures of organic compounds should be carried out after their chromatographic separation.

4.7. METHODS OF ANALYSIS BASED ON RADIOACTIVITY

Methods of analysis based on radioactivity arose in the era of the development of nuclear physics, radiochemistry, and atomic technology, and are now successfully used in various analyzes, including in industry and the geological service. These methods are very numerous and varied. Four main groups can be distinguished: radioactive analysis; isotope dilution methods and other radiotracer methods; methods based on the absorption and scattering of radiation; purely radiometric methods. The most widespread radioactive method. This method appeared after the discovery of artificial radioactivity and is based on the formation of radioactive isotopes of the element being determined by irradiating the sample with nuclear or g-particles and recording the artificial radioactivity obtained during activation.

4.8. THERMAL METHODS

Thermal methods of analysis are based on the interaction of matter with thermal energy. Thermal effects, which are the cause or effect, are most widely used in analytical chemistry. chemical reactions. To a lesser extent, methods based on the release or absorption of heat as a result of physical processes. These are processes associated with the transition of a substance from one modification to another, with a change in the state of aggregation and other changes in intermolecular interaction, for example, occurring during dissolution or dilution. The table shows the most common methods of thermal analysis.

Thermal methods are successfully used for the analysis of metallurgical materials, minerals, silicates, as well as polymers, for the phase analysis of soils, and for determining the moisture content in samples.

4.9. BIOLOGICAL METHODS OF ANALYSIS

Biological methods of analysis are based on the fact that for vital activity - growth, reproduction and, in general, the normal functioning of living beings, an environment of a strictly defined chemical composition is necessary. When this composition changes, for example, when a component is excluded from the medium or an additional (determined) compound is introduced, the body, after some time, sometimes almost immediately, gives an appropriate response signal. Establishing a connection between the nature or intensity of the body's response signal and the amount of a component introduced into the environment or excluded from the environment serves to detect and determine it.

Analytical indicators in biological methods are various living organisms, their organs and tissues, physiological functions, etc. Microorganisms, invertebrates, vertebrates, as well as plants can act as indicator organisms.

5. CONCLUSION

The significance of analytical chemistry is determined by the need of society for analytical results, in establishing the qualitative and quantitative composition of substances, the level of development of society, the social need for the results of analysis, as well as the level of development of analytical chemistry itself.

A quote from N.A. Menshutkin’s textbook on analytical chemistry, 1897: “Having presented the entire course of classes in analytical chemistry in the form of problems, the solution of which is left to the student, we must point out that for such a solution of problems, analytical chemistry will give a strictly defined path. This certainty (systematic solving problems of analytical chemistry) is of great pedagogical importance. At the same time, the student learns to apply the properties of compounds to solving problems, derive reaction conditions, and combine them. This whole series of mental processes can be expressed as follows: analytical chemistry teaches chemical thinking. The achievement of the latter seems to be the most important for practical studies in analytical chemistry.

LIST OF USED LITERATURE

1. K.M. Olshanova, S.K. Piskareva, K.M. Barashkov "Analytical Chemistry", Moscow, "Chemistry", 1980

2. "Analytical chemistry. Chemical methods of analysis”, Moscow, “Chemistry”, 1993

3. “Fundamentals of Analytical Chemistry. Book 1", Moscow, " graduate School", 1999

4. “Fundamentals of Analytical Chemistry. Book 2, Moscow, Higher School, 1999

The study of substances is a rather complex and interesting matter. Indeed, in their pure form, they are almost never found in nature. Most often, these are mixtures of complex composition, in which the separation of components requires certain efforts, skills and equipment.

After separation, it is equally important to correctly determine the belonging of a substance to a particular class, that is, to identify it. Determine the boiling and melting points, calculate the molecular weight, check for radioactivity, and so on, in general, investigate. For this, they are used different ways, including physico-chemical methods of analysis. They are quite diverse and require the use, as a rule, of special equipment. about them and will be discussed further.

Physical and chemical methods of analysis: a general concept

What are these methods of identifying compounds? These are methods based on the direct dependence of all the physical properties of a substance on its structural chemical composition. Since these indicators are strictly individual for each compound, physicochemical research methods are extremely effective and give a 100% result in determining the composition and other indicators.

So, such properties of a substance can be taken as a basis, such as:

• the ability to absorb light;
• thermal conductivity;
• electrical conductivity;
• boiling temperature;
• melting and other parameters.

Physical and chemical methods studies differ significantly from purely chemical methods substance identification. As a result of their work, there is no reaction, that is, the transformation of a substance, both reversible and irreversible. As a rule, the compounds remain intact both in terms of mass and composition.

Features of these research methods

There are several main features characteristic of such methods for determining substances.

1. The research sample does not need to be cleaned of impurities before the procedure, since the equipment does not require this.
2. Physicochemical methods of analysis have a high degree of sensitivity, as well as increased selectivity. Therefore, a very small amount of the test sample is needed for analysis, which makes these methods very convenient and efficient. Even if it is required to determine an element that is contained in the total wet weight in negligible amounts, this is not an obstacle for the indicated methods.
3. The analysis takes only a few minutes, so another feature is the short duration, or rapidity.
4. The research methods under consideration do not require the use of expensive indicators.

It is obvious that the advantages and features are sufficient to make physicochemical research methods universal and in demand in almost all studies, regardless of the field of activity.

Classification

There are several features on the basis of which the considered methods are classified. However, we will give the most general system, which unites and embraces all the main methods of research related directly to physical and chemical ones.

1. Electrochemical research methods. They are subdivided on the basis of the measured parameter into:

• potentiometry;
• voltammetry;
• polarography;
• oscillometry;
• conductometry;
• electrogravimetry;
• coulometry;
• amperometry;
• dielkometry;
• high frequency conductometry.

2. Spectral. Include:

• optical;
• X-ray photoelectron spectroscopy;
• electromagnetic and nuclear magnetic resonance.

3. Thermal. Subdivided into:

• thermal;
• thermogravimetry;
• calorimetry;
• enthalpymetry;
• delatometry.

4. Chromatographic methods, which are:

• gas;
• sedimentary;
• gel-penetrating;
• exchange;
• liquid.

It is also possible to divide physicochemical methods of analysis into two large groups. The first are those that result in destruction, that is, the complete or partial destruction of a substance or element. The second is non-destructive, preserving the integrity of the test sample.

Practical application of such methods

The areas of use of the considered methods of work are quite diverse, but all of them, of course, in one way or another, relate to science or technology. In general, several basic examples can be given, from which it will become clear why such methods are needed.

1. Control over the flow of complex technological processes in production. In these cases, the equipment is necessary for contactless control and tracking of all structural links of the working chain. The same devices will fix malfunctions and malfunctions and give an accurate quantitative and qualitative report on corrective and preventive measures.
2. Carrying out chemical practical work for the purpose of qualitative and quantitative determination of the yield of the reaction product.
3. The study of a sample of a substance in order to establish its exact elemental composition.
4. Determination of the quantity and quality of impurities in the total mass of the sample.
5. Accurate analysis of intermediate, main and side participants of the reaction.
6. A detailed account of the structure of matter and the properties it exhibits.
7. Discovery of new elements and obtaining data characterizing their properties.
8. Practical confirmation of theoretical data obtained empirically.
9. Analytical work with high purity substances used in various branches of technology.
10. Titration of solutions without the use of indicators, which gives a more accurate result and has a completely simple control, thanks to the operation of the apparatus. That is, the influence of the human factor is reduced to zero.
11. The main physicochemical methods of analysis make it possible to study the composition of:

• minerals;
• mineral;
• silicates;
• meteorites and foreign bodies;
• metals and non-metals;
• alloys;
• organic and inorganic substances;
• single crystals;
• rare and trace elements.

Areas of use of methods

• nuclear power;
• physics;
• chemistry;
• radio electronics;
• laser technology;
• space research and others.

The classification of physicochemical methods of analysis only confirms how comprehensive, accurate and versatile they are for use in research.

Electrochemical methods

The basis of these methods is reactions in aqueous solutions and on electrodes under the action of an electric current, that is, in other words, electrolysis. Accordingly, the type of energy that is used in these methods of analysis is the flow of electrons.

These methods have their own classification of physico-chemical methods of analysis. This group includes the following species.

1. Electrical weight analysis. According to the results of electrolysis, a mass of substances is removed from the electrodes, which is then weighed and analyzed. So get data on the mass of compounds. One of the varieties of such works is the method of internal electrolysis.
2. Polarography. The basis is the measurement of current strength. It is this indicator that will be directly proportional to the concentration of the desired ions in the solution. Amperometric titration of solutions is a variation of the considered polarographic method.
3. Coulometry is based on Faraday's law. The amount of electricity spent on the process is measured, from which they then proceed to the calculation of ions in solution.
4. Potentiometry - based on the measurement of the electrode potentials of the participants in the process.

All the processes considered are physicochemical methods for the quantitative analysis of substances. Using electrochemical research methods, mixtures are separated into constituent components, the amount of copper, lead, nickel and other metals is determined.

Spectral

It is based on the processes of electromagnetic radiation. There is also a classification of the methods used.

1. Flame photometry. To do this, the test substance is sprayed into an open flame. Many metal cations give a color of a certain color, so their identification is possible in this way. Basically, these are substances such as: alkali and alkaline earth metals, copper, gallium, thallium, indium, manganese, lead and even phosphorus.
2. Absorption spectroscopy. Includes two types: spectrophotometry and colorimetry. The basis is the determination of the spectrum absorbed by the substance. It operates both in the visible and in the hot (infrared) part of the radiation.
3. Turbidimetry.
4. Nephelometry.
5. Luminescent analysis.
6. Refractometry and polarometry.

Obviously, all the considered methods in this group are methods of qualitative analysis of a substance.

Emission analysis

This causes the emission or absorption of electromagnetic waves. According to this indicator, one can judge the qualitative composition of the substance, that is, what specific elements are included in the composition of the research sample.

Chromatographic

Physicochemical studies are often carried out in different environments. In this case, very convenient and effective methods become chromatographic. They are divided into the following types.

1. Adsorption liquid. At the heart of the different ability of the components to adsorption.
2. Gas chromatography. Also based on adsorption capacity, only for gases and substances in the vapor state. Used in mass production of compounds in similar states of aggregation when the product comes out in a mixture to be separated.
3. Partition chromatography.
4. Redox.
5. Ion exchange.
6. Paper.
7. Thin layer.
8. Sedimentary.
9. Adsorption-complexing.

Thermal

Physical and chemical studies also involve the use of methods based on the heat of formation or decay of substances. Such methods also have their own classification.

1. Thermal analysis.
2. Thermogravimetry.
3. Calorimetry.
4. Enthalpometry.
5. Dilatometry.

All these methods allow you to determine the amount of heat, mechanical properties, enthalpies of substances. Based on these indicators, the composition of the compounds is quantified.

Methods of analytical chemistry

This section of chemistry has its own characteristics, because the main task facing analysts is the qualitative determination of the composition of a substance, their identification and quantitative accounting. In this regard, analytical methods of analysis are divided into:

• chemical;
• biological;
• physical and chemical.

Since we are interested in the latter, we will consider which of them are used to determine substances.

The main varieties of physicochemical methods in analytical chemistry

1. Spectroscopic - all the same as those discussed above.
2. Mass spectral - based on the action of electrical and magnetic field free radicals, particles or ions. The physicochemical analysis laboratory assistant provides the combined effect of the indicated force fields, and the particles are separated into separate ionic flows according to the ratio of charge and mass.
3. radioactive methods.
4. Electrochemical.
5. Biochemical.
6. Thermal.

What do such processing methods allow us to learn about substances and molecules? First, the isotopic composition. And also: reaction products, the content of certain particles in especially pure substances, the masses of the desired compounds and other things useful for scientists.

Thus, the methods of analytical chemistry are important ways obtaining information about ions, particles, compounds, substances and their analysis.

PHYSICO-CHEMICAL ANALYSIS, studies the relationship between the composition and St. you macroscopic. systems made up of several initial in-in (components). Physical and chemical analysis is characterized by the representation of these dependencies graphically, in the form of a composition-property diagram; apply also tables of numerical data and analyte. records. Since the properties of a system depend not only on its composition, but also on other factors that determine the state of the system - pressure, t-ry, degree of dispersion, gravitational strengths. and electromagnet. fields, as well as the time of observation, then in a general form they talk about the diagrams of the equilibrium factor - St., or about the physical-chemical. (chemical) diagrams. In these diagrams, all chem. processes that occur in systems when the c.-l. balance factor, such as the formation and decay of chemical. Comm., the appearance and disappearance of solid and (or) liquid solutions, etc., are expressed as geom. changes in the complex of lines, surfaces and points, which forms a diagram. Therefore, the analysis of the geometry of the diagrams makes it possible to draw conclusions about the corresponding processes in the system.

Two basic principles of physicochemical analysis were formulated by N.S. Kurnakov. According to the correspondence principle, each set of phases that are in equilibrium in a given system in accordance with the phase rule corresponds to a certain geom on the diagram. image. Based on this principle, N.S. Kurnakov defined physicochemical analysis as a geome. chemical research method. transformations.

The second main the principle of physico-chemical analysis, called. principle of continuity, the following is formulated. way: with a continuous change in the parameters that determine the state of the system, the properties of its individual phases change continuously. St.-va systems as a whole also change continuously, but on condition that new phases do not arise and old ones do not disappear; if the number of phases changes, then the properties of the system also change, and, as a rule, abruptly.

The third principle of physicochemical analysis was proposed by Ya.G. Goroshchenko. He claims that any set of components, regardless of their number and physical. sv-in, can make up a system (the principle of compatibility). It follows from it that the diagram of any system contains all the elements of particular systems (subsystems) of which it is composed. IN common system translation elements of private systems are combined with geom. images for chem. diagram, arising as a display of processes occurring with the participation of all components of the overall system.

One of the main directions of the theory of physico-chemical analysis is the study of the topology of chemical. diagrams. The advantage of physicochemical analysis as a research method is that it does not require isolation of the chemical product. interaction of components from the reaction mixture, as a result of which the method allows you to explore the chemical. transformations in solutions, alloys (especially metallic ones), glasses, etc. objects, which are practically impossible to study using the classical. preparative-synthetic. methods. Physical and chemical analysis was widely used in the study of complex formation in solutions in order to determine the composition and determine the stability of chemical. connections. Schedule composition - sv-in usually has one extremum, as a rule, a maximum. In simple cases, the maximum corresponds to the molar ratio of the components of the system, representing the stoichiometry of the complex compound. In the general case, the extremum points on the curves (or surfaces) of St.-in, as well as the inflection points, do not correspond to the composition of the chemical compounds formed in the system. Comm., but in the limit, when the degree of dissociation of chemical. conn. is equal to zero, the continuous curve of the dependence of St-va on the composition breaks up into two branches intersecting at a singular point, the abscissa of which corresponds to the composition of the chemical. connections.

Diagrams composition - sv-in are the basis of the analyte. methods (colorimetry, potentiometry, etc.). For use to. - l. Holy Island in analyt. purposes, it is desirable that there be an additive dependence of the values ​​of this property on the composition. Therefore, great importance is given to the rational choice of properties (in particular, direct or reverse, for example, electrical conductivity or electrical resistance), as well as the choice of a method for expressing the concentration of system components (massmolar, volume, equivalent fractions or percentages). In modern In physico-chemical analysis, the number of used St. in the system is many tens. In principle, you can use any sv-in, to-swarm m. b. measured or calculated. For example, when solving the theoretical issues, in particular in the derivation of decomp. types of diagrams, use k.-l. thermodynamic potential, to-ry not m. b. measured directly. When choosing St. Islands, it is necessary to take into account both the possible accuracy of determining its values, and its sensitivity to what is happening in the chemical system. transformations. For example, the density of the v-va m. b. determined with great accuracy, but it is insensitive to the formation of chemical. Comm., while the hardness is sensitive to chemical. interaction in the system, but the accuracy of its determination is low. Physical and chemical analysis is characterized by a parallel study and comparison of the results of determining several. St., for example. electrical conductivity, hardness.

Among the chem. diagrams, a special place is occupied by melting (fusibility) diagrams, p-diagrams, vapor pressure diagrams, to-rye are variants of the state diagram. On such diagrams, any point, regardless of whether it is located on the c.-l. lines or lines of the diagram or not, describes the state of the system. The state diagram is the basis of the diagram of any property, since the value of each of the properties in the system generally depends on the composition, and on the t-ry, and on the pressure, i.e. from all equilibrium factors , the ratio between which gives the state diagram . Increasingly, diagrams are being explored and used in practice, showing the dependence of the state of the system simultaneously on the two most important equilibrium factors - pressure and t-ry. These diagrams are referred to as p-T-x diagrams (x is the molar fraction of the component). Even for a binary system, the construction of a p-T-x-diagram requires the use of spaces, a coordinate system, therefore, the composition-sv-diagram for binary and more complex systems is built and studied, as a rule, at constant pressure, t-re, etc. ext. factors. The complexity of building a chem. diagrams required the development of appropriate methods graphic. Images.

F physical-chemical analysis contributed to the solution of many. theoretical problems of chemistry, in particular, the creation of a theory of the structure of chemical. conn. variable composition (see Nonstoichiometry). Physical and chemical analysis is the basis for the creation of new and modification of known materials - alloys, semiconductors, glasses, ceramics, etc. by, for example, doping. On physico-chemical analysis and fiz.-chem. many technologies are based on diagrams. processes associated, in particular, with crystallization, rectification, extraction, etc., i.e., with phase separation. Such diagrams indicate, in particular, the conditions for isolating the compound, growing single crystals. T. called the method of residual concentrations allows you to explore the district of deposition of chemical. conn. as a result of interaction in r-ra. According to this method, the composition of the solid phases -products of the district - is determined by the difference between the content of the reacting components in a series of initial mixtures and in the corresponding equilibrium p-pas at the end of the interaction. At the same time, a diagram is constructed of the dependence of the equilibrium concentrations of the reacting components in the solution on the ratio between them in the initial mixtures. In parallel, they usually change the pH, the electrical conductivity of solutions, the absorption of light by a suspension, etc. St. Islands.

In the classic The physicochemical analysis of the system was studied only in the equilibrium state. Approaching equilibrium often takes a long time or is generally difficult to achieve, therefore, for practical purposes. using the method, it is necessary to study systems in a non-equilibrium state, in particular, in the process of approaching equilibrium. Strictly speaking, systems are considered nonequilibrium, in which metastaoils participate. modifications in-in capable of existing for an arbitrarily long time. Tech. the use of materials in a non-equilibrium state, e.g. glassy metal. alloys, composite materials, glassy semiconductors, has led to the need to study composition-composition diagrams for obviously non-equilibrium systems.

Physico-chemical analysis proved to be fruitful for the study and synthesis of new Comm. as a result of irreversible p-tions in non-equilibrium systems. The study of systems in the process of transition to an equilibrium state makes it possible to establish the existence of not only the final products of the p-tion, but also the intermediate ones. in-in, as well as the resulting unstable in-in. Kinetic factor, i.e., the rate of transformation (the rate of approach to equilibrium), is now considered on an equal footing with other criteria and other saints. On the Holy Islands of the system is significantly influenced by its dispersion - mol.-dispersed distribution of components (submicroscopic. state), the state of colloidal dissolution, etc., up to single-crystal. states. Diagrams composition - structure - degree of dispersion - sv-in determine the features of modern. studies in physico-chemical analysis.

The development of computers has led to the fact that the role of the analyte in physicochemical analysis has significantly increased. forms of expression of the dependencies of St. in the system on its composition. This facilitates the storage of information (modern computer systems allow the collection and storage of reference material on chemical diagrams and in graphical form) and, in particular, mat. processing of results, which was previously used in the main. only in the study of complex formation in solutions. To a certain extent, the use of modern calculates, the technique allows you to overcome the limitations of physico-chemical analysis, which lies in the fact that it establishes which chem. transformations take place in the system, but does not answer questions related to the cause and mechanism of these transformations. Calculation methods allow you to extract additional. information from chem. diagrams, eg. determine the degree of dissociation of chemical. conn. in the melt based on the analysis of the curvature of the liquidus line for binary systems or the change in the free energy of the system during the exchange of salts, based on the shape of the liquidus isotherms for ternary reciprocal systems. Attracting diff. theories of solids, models of liquids and states of gas mixtures, along with a generalization of experiments. data, allows you to get physical. diagrams (or their elements) by calculation.

Historical essay. Main the idea of ​​physicochemical analysis was put forward by M.V. Lomonosov (1752), the first attempts to establish education in the chemical system. Comm., based on the dependence of its St. on the composition, belong to the beginning. 19th century All R . 19th century works by P.P. Anosov (1831), G.K. Sorby (1864), D.K. Chernov (1869) laid the foundations for metallurgy; DI. Mendeleev was the first to carry out geom. analysis of diagrams composition - St. in the example of the study of hydrates of sulfuric acid. The works of V.F. Alekseev on the mutual solubility of liquids, D.P. Konovalova - on the elasticity of a pair of solutions (see Konovalov's laws), I.F. Schroeder - on the temperature dependence of solubility (see Pasmicity). At the turn of the 19th-20th centuries. In connection with the needs of technology, the rapid development of physicochemical analysis began (A. Le Chatelier, J. van't Hoff, F. Osmond, W. Roberts-Austen, J. Van Laar, and others). The fundamental theoretical and experiment. works of modern physical and chemical analysis belong to N.S. Kurnakov. They combined the study of alloys and homogeneous solutions into one direction and proposed the term "physico-chemical analysis" (1913). Studies of complex formation in solutions with the works of I.I. Ostromyslensky (1911), P. Job (1928) and the development of methods for determining the composition of chemical. conn. and constants r about shchenko Ya.G., Physico-chemical analysis of homogeneous and heterogeneous systems, K., 1978; Chernogorenko V.B., Pryadko L.F., "Journal of inorg. chemistry", 1982, vol. 27, no. 6, p. 1527-30; Glazov V.M., "Izv. AN SSSR. Ser. inorganic materials", 1984, v. 20, no. 6, p. 925-36; Fedorov P.I., Fedorov P.P., Dr about D.V., Physical and chemical analysis of anhydrous salt systems, M., 1987. P.I. Fedorov.

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Any method of analysis uses a certain analytical signal, which, under given conditions, is given by specific elementary objects (atoms, molecules, ions) that make up the substances under study.

An analytical signal provides both qualitative and quantitative information. For example, if precipitation reactions are used for analysis, qualitative information is obtained from the appearance or absence of a precipitate. Quantitative information is obtained from the weight of the sediment. When a substance emits light under certain conditions, qualitative information is obtained by the appearance of a signal (light emission) at a wavelength corresponding to the characteristic color, and quantitative information is obtained from the intensity of light radiation.

According to the origin of the analytical signal, methods of analytical chemistry can be classified into chemical, physical, and physicochemical methods.

IN chemical methods carry out a chemical reaction and measure either the mass of the product obtained - gravimetric (weight) methods, or the volume of the reagent used for interaction with the substance - titrimetric, gas volumetric (volumetric) methods.

Gas volumemetry (gas volumetric analysis) is based on the selective absorption of the constituent parts of a gas mixture in vessels filled with one or another absorber, followed by measurement of the decrease in gas volume using a burette. So, carbon dioxide is absorbed by a solution of potassium hydroxide, oxygen - by a solution of pyrogallol, carbon monoxide - by an ammonia solution of copper chloride. Gas volumemetry refers to express methods of analysis. It is widely used for the determination of carbonates in g.p. and minerals.

Chemical methods of analysis are widely used for the analysis of ores, rocks, minerals and other materials in the determination of components in them with a content of tenths to several tens of percent. Chemical analysis methods are characterized by high accuracy (analysis error is usually tenths of a percent). However, these methods are gradually being replaced by more rapid physicochemical and physical methods of analysis.

Physical Methods analyzes are based on the measurement of some physical property of substances, which is a function of composition. For example, refractometry is based on measuring the relative refractive indices of light. In an activation assay, the activity of isotopes, etc. is measured. Often, a chemical reaction is preliminarily carried out during the assay, and the concentration of the resulting product is determined by physical properties, for example, according to the intensity of absorption of light radiation by a colored reaction product. Such methods of analysis are called physicochemical.

Physical methods of analysis are characterized by high productivity, low limits of detection of elements, objectivity of analysis results, high level automation. Physical methods of analysis are used in the analysis of rocks and minerals. For example, the atomic emission method determines tungsten in granites and slates, antimony, tin and lead in rocks and phosphates; atomic absorption method - magnesium and silicon in silicates; X-ray fluorescent - vanadium in ilmenite, magnesite, alumina; mass spectrometric - manganese in the lunar regolith; neutron activation - iron, zinc, antimony, silver, cobalt, selenium and scandium in oil; method of isotopic dilution - cobalt in silicate rocks.

Physical and physico-chemical methods are sometimes called instrumental, since these methods require the use of tools (equipment) specially adapted for carrying out the main stages of analysis and recording its results.

Physical and chemical methods analysis may include chemical transformations of the analyte, dissolution of the sample, concentration of the analyzed component, masking of interfering substances, and others. Unlike "classical" chemical methods of analysis, where the mass of a substance or its volume serves as an analytical signal, physicochemical methods of analysis use radiation intensity, current strength, electrical conductivity, and potential difference as an analytical signal.

Important practical value have methods based on the study of the emission and absorption of electromagnetic radiation in various areas spectrum. These include spectroscopy (for example, luminescent analysis, spectral analysis, nephelometry and turbidimetry, and others). Important physicochemical methods of analysis include electrochemical methods that use the measurement of the electrical properties of a substance (coulometry, potentiometry, etc.), as well as chromatography (for example, gas chromatography, liquid chromatography, ion-exchange chromatography, thin layer chromatography). Methods based on measuring the rates of chemical reactions (kinetic methods of analysis), thermal effects of reactions (thermometric titration), as well as on the separation of ions in a magnetic field (mass spectrometry) are successfully developed.