Subject of analytical chemistry

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

Analytical chemistry - is the science of the principles, methods and means of determining chemical composition and structures 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 to create and improve its methods, determine the limits of their applicability, evaluate metrological and other characteristics, and develop methods for analyzing specific objects.

A system that provides specific analysis of certain objects using 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 technique of analysis

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

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

Method of analysis - summary principles underlying the analysis of a substance (without indicating the component and object being determined).

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

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

The analysis technique may include the following steps:

A specific analysis technique does not necessarily have to include all of the listed steps. The set of operations performed depends on the complexity of the composition of the sample being analyzed, the concentration of the analyte, the purpose of the analysis, the permissible error of the analysis result, and what analysis method is intended to be used.

Types of analysis

Depending on the purpose there are:

Depending on which components need to 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, the following are distinguished:

· 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, 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 a substance);

· radiometric(based on nuclear reactions).

Physical and physicochemical 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.

Analyticalare chemical reactions, the result of which carries certain analytical information, for example, reactions accompanied by the formation of a precipitate, the release of gas, 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 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:

Detection limit(m min, P or С 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 their joint presence can be carried out using fractional and systematic methods of analysis.

Systematic called method 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 carry out large number operations, duration, bulkiness, significant losses of detected ions, etc.

Fractionalis a method of qualitative analysis that involves detecting 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.

Elimination of the interfering influence of ions can be done in two ways

For example

· complexation

· change in pH of the environment

· redox reactions

· deposition

· 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. NH 4 + and K + ions form sparingly soluble hexanitrocobaltates, perchlorates, chloroplatinates, as well as sparingly soluble compounds with some large organic anions, for example, dipicrylamine, tetraphenyl borate, hydrogen tartrate. 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; the acidic properties of NH 4 + are more pronounced (pK a = 9.24). Not prone to complexation reactions. K + , Na + , Li + ions do not participate in redox reactions, since they have a constant and stable oxidation state, NH 4 + ions have reducing properties.

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

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

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

Related information.

1. INTRODUCTION

2. CLASSIFICATION OF METHODS

3. ANALYTICAL SIGNAL

4.3. CHEMICAL METHODS

4.8. THERMAL METHODS

5. CONCLUSION

6. LIST OF REFERENCES USED

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 analysis. Analysis is the main means of contamination control environment. Determining 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. From level chemical analysis The development of many sciences depends on the laboratory's equipment 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 partly their chemical structure. Analytical chemistry methods make it possible to answer questions about what a substance consists of and 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 estimate 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 fields of knowledge.

The method of analysis 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 a method of analysis, they mean the underlying principle, a quantitative expression of the relationship between the composition and any measured property; selected implementation techniques, including identification and elimination of interference; devices for practical implementation and methods for processing measurement results. An analysis technique is a detailed description of the analysis of a given object using the selected method.

Three functions of analytical chemistry as a field of knowledge can be distinguished:

1. solving general questions of analysis,

2. development of analytical methods,

3. solving specific analysis problems.

You can also highlight qualitative And quantitative tests. The first solves the question of which components the analyzed object includes, the second provides 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, sample decomposition, separation of components, detection (identification) and determination. There are hybrid methods that combine separation and determination. Detection and definition methods have much in common.

Highest value have methods of determination. They can be classified according to the nature of the property being measured or the method of recording the corresponding signal. Determination methods are divided into chemical , physical And biological. Chemical methods are based on chemical (including electrochemical) reactions. This also 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: accuracy 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, you need 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 sampling and preparation of the sample, the stage of chemical analysis begins, at which the component is detected or its quantity is determined. For this purpose, they measure analytical signal. In most methods, the analytical signal is the average of the measurements physical quantity at the final stage of analysis, functionally related to the content of the component being determined.

If it is necessary to detect any component, it is usually fixed appearance analytical signal - the appearance of a precipitate, color, line 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 (nonequilibrium). With 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 record the analytical signal. Kinetic masking is based on increasing the difference between the rates of reaction of the masked and analyte substances 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 component being determined is below the detection limit of the method; the components being determined are unevenly distributed in the sample; there are no standard samples for calibration of instruments; the sample is highly toxic, radioactive and expensive.

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

Concentration is an operation (process) that results in an increase in the ratio of the concentration or amount of microcomponents to the concentration or amount of macrocomponents.

Precipitation and coprecipitation.

Precipitation is typically used to separate inorganic substances. Precipitation of microcomponents with organic reagents, and especially their coprecipitation, provides a high concentration coefficient. These methods are used in combination with determination methods that are designed to obtain an analytical signal from solid samples.

Separation by precipitation is based on the different solubilities of compounds, mainly in aqueous solutions.

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

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 a variety of industrial and natural objects. The method is simple and fast to perform, provides high separation and concentration efficiency, and is compatible with various determination methods. Extraction allows you to study the state of substances in solution under various conditions and determine physicochemical characteristics.

Sorption.

Sorption is well used for separating and concentrating substances. Sorption methods usually provide good separation selectivity and high concentration coefficients.

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 is electrolysis, in which the separated or concentrated substance is isolated on solid electrodes in an elemental state or in the form of some kind of compound. Electrolytic separation (electrolysis) based on the deposition of a substance by electric current at a controlled potential. The most common option is cathodic metal deposition. 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 radius of the particles. There are two options for electrophoresis: frontal (simple) and zone (on a carrier). In the first case, a small volume of solution containing the components to be separated is placed in a tube with an electrolyte solution. In the second case, movement occurs in a stabilizing environment, which holds the particles in place after the electric field is turned off.

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

Evaporation methods.

Methods distillation based on different volatility of substances. A substance changes from a liquid to a gaseous state and then condenses to form a liquid or sometimes a solid phase again.

Simple distillation (evaporation)– single-step separation and concentration process. Evaporation removes substances that are in the form of ready-made volatile compounds. These can be macrocomponents and microcomponents; 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 solid form (bypassing the liquid phase). Separation by sublimation is resorted to, as a rule, if the components being separated are difficult to melt or difficult to dissolve.

Controlled crystallization.

When a solution, melt or gas is cooled, the formation of nuclei of the solid phase occurs - crystallization, which can be uncontrolled (volumetric) and controlled. With uncontrolled crystallization, crystals arise spontaneously throughout the entire 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 in a certain direction).

With directional crystallization, one interface appears between a solid and a liquid—the crystallization front. In zone melting there are two boundaries: 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 a molecular weight from units to 10 6. These can be hydrogen isotopes, metal ions, synthetic polymers, proteins, etc. Using chromatography, extensive information has been obtained on the structure and properties of organic compounds of many classes.

Chromatography is a physicochemical method for the separation of substances, based on the distribution of components between two phases - stationary and mobile. The stationary phase is usually a solid substance (often called a sorbent) or a liquid film deposited on a solid substance. The mobile phase is a liquid or gas flowing through the stationary phase.

The method allows you to separate a multicomponent mixture, identify components and determine its quantitative composition.

Chromatographic methods are classified according to the following criteria:

a) according to the aggregate state 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, sedimentation, redox, adsorption - complexing 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 determination are based on three types of chemical reactions: acid-base, redox and complexation. Sometimes they are accompanied by a change in the state of aggregation of the components. The most important among chemical methods are gravimetric and titrimetric. These analytical methods are called classic. 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 involves isolating a substance in its pure form and weighing it. Most often, such isolation is carried out by precipitation. Less commonly, the component being determined is isolated in the form of a volatile compound (distillation methods). In some cases, gravimetry - The best way solving an analytical problem. This is the absolute (reference) method.

The disadvantage of gravimetric methods is the duration of 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.

The analytical signal in gravimetry is mass.

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 determined component A. In practice, it is most convenient to add the reagent in the form of a solution of a precisely known concentration. In this embodiment, titration is the process of continuously adding a controlled amount of a reagent solution of precisely known concentration (titran) to a solution of the component being determined.

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

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

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

Titration by substituent consists of titrating with titrant B not a determined amount of substance A, but an equivalent amount of substituent A’ resulting from a previously carried out reaction between the determined substance A and some reagent. This titration method is usually used in cases where direct titration is not possible.

Kinetic methods.

Kinetic methods are based on the use of the dependence of the rate of a chemical reaction on the concentration of 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 value proportional to it.

The reaction underlying the kinetic method is called indicator. A substance, by the change in concentration of which the speed of the indicator process is judged, is an indicator.

Biochemical methods.

Among modern methods In chemical analysis, biochemical methods occupy an important place. Biochemical methods include methods based on the use of processes occurring with the participation of 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 are 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 detected 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 surface of the electrode or in the near-electrode space. Any electrical parameter (potential, current, resistance, etc.), functionally related to the concentration of the analyzed solution and amenable to correct measurement, can serve as an analytical signal.

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

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

There are different 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 recorded experimentally in the form of absorption of radiation, 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 is to identify and determine the structure of organic compounds. It is advisable to carry out molecular analysis of complex mixtures of organic compounds after their chromatographic separation.

4.7. ANALYSIS METHODS BASED ON RADIOACTIVITY

Analysis methods based on radioactivity arose during the era of the development of nuclear physics, radiochemistry, and nuclear technology and are successfully used today in conducting 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 and other radiotracer methods; methods based on absorption and scattering of radiation; purely radiometric methods. The most widespread radioactivation 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 a sample with nuclear or g-particles and recording the artificial radioactivity obtained during activation.

4.8. THERMAL METHODS

Thermal analysis methods are based on the interaction of a substance with thermal energy. The greatest application in analytical chemistry is thermal effects, which are the cause or effect of 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 thermal analysis methods.

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

4.9. BIOLOGICAL ANALYSIS METHODS

Biological methods of analysis are based on the fact that for life activity - growth, reproduction and generally normal functioning of living beings, an environment of a strictly defined chemical composition is necessary. When this composition changes, for example, when any component is excluded from the environment or an additional (detectable) compound is introduced, the body sends an appropriate response signal after some time, sometimes almost immediately. 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, and plants can act as indicator organisms.

5. CONCLUSION

The importance of analytical chemistry is determined by the need of society for analytical results, to establish 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.

Quote from the textbook on analytical chemistry by N.A. Menshutkin, published in 1897: “Having presented the entire course of classes in analytical chemistry in the form of problems, the solution of which is provided to the student, we must point out that for such a solution of problems, analytical chemistry will provide a strictly defined path. This certainty (systematic solution of analytical chemistry problems) is of great pedagogical importance. The student learns to apply the properties of compounds to solve problems, derive reaction conditions, and combine them. This entire series of mental processes can be expressed this way: analytical chemistry teaches you to think chemically. Achieving the latter seems to be the most important for practical studies in analytical chemistry.”

LIST OF REFERENCES USED

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. After all, they are almost never found in nature in their pure form. 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 whether a substance belongs to a particular class, that is, to identify it. Determine boiling and melting points, calculate molecular weight, test for radioactivity, and so on, in general, research. For this purpose they are used different ways, including physicochemical methods of analysis. They are quite diverse and usually require the use of special equipment. About them and we'll talk further.

Physico-chemical methods of analysis: general concept

What are these methods for identifying compounds? These are methods that are based on the direct dependence of all 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 100% results in determining the composition and other indicators.

Thus, the following properties of a substance can be taken as a basis:

• light absorption ability;
• thermal conductivity;
• electrical conductivity;
• boiling temperature;
• melting and other parameters.

Physicochemical research methods have a significant difference from purely chemical methods identification of substances. As a result of their work, a reaction does not occur, that is, the transformation of a substance, either reversible or irreversible. As a rule, the compounds remain intact both in 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 high degree sensitivity, as well as increased selectivity. Therefore, a very small amount of the test sample is required for analysis, which makes these methods very convenient and effective. Even if it is necessary to determine an element that is contained in the total wet mass in negligible quantities, this is not an obstacle for the indicated methods.
3. The analysis takes only a few minutes, so another feature is its short duration, or expressiveness.
4. The research methods under consideration do not require the use of expensive indicators.

Obviously, the advantages and features are enough to make physicochemical research methods universal and in demand in almost all studies, regardless of the field of activity.

Classification

Several characteristics can be identified on the basis of which the methods under consideration are classified. However, we will present the most general system that unites and covers all the main methods of research related directly to physicochemical ones.

1. Electrochemical research methods. Based on the measured parameter, they are divided into:

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

2. Spectral. Include:

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

3. Thermal. Divided into:

• thermal;
• thermogravimetry;
• calorimetry;
• enthalpimetry;
• 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, 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 methods of work under consideration are quite diverse, but all of them, of course, relate to science or technology in one way or another. In general, we can give several basic examples, from which it will become clear why exactly such methods are needed.

1. Control over the course of complex technological processes in production. In these cases, equipment is necessary for contactless control and tracking of all structural links in the work chain. These same instruments will record problems and malfunctions and provide 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. Examination of a sample of a substance to determine 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 secondary participants in the reaction.
6. A detailed report on the structure of a substance 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 fields of technology.
10. Titration of solutions without the use of indicators, which gives a more accurate result and has completely simple control, thanks to the operation of the device. That is, the influence of the human factor is reduced to zero.
11. Basic 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 universal they are for use in research.

Electrochemical methods

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

These methods have their own classification of physicochemical methods of analysis. This group includes the following species.

1. Electrical gravimetric analysis. Based on the results of electrolysis, a mass of substances is removed from the electrodes, which is then weighed and analyzed. This is how data on the mass of compounds is obtained. One of the varieties of such work is the method of internal electrolysis.
2. Polarography. It is based on measuring 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 calculate the ions in the solution.
4. Potentiometry - based on measuring the electrode potentials of the participants in the process.

All the processes considered are physical and chemical methods for the quantitative analysis of substances. Using electrochemical research methods, mixtures are separated into their component components and 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 certain color, so their identification is possible in this way. These are mainly 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 acts in both the visible and hot (infrared) parts of radiation.
3. Turbidimetry.
4. Nephelometry.
5. Luminescent analysis.
6. Refractometry and polarometry.

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

Emission analysis

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

Chromatographic

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

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

Thermal

Physicochemical research also involves the use of methods based on the heat of formation or decomposition of substances. Such methods also have their own classification.

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

All these methods make it possible to determine the amount of heat, mechanical properties, and enthalpy of substances. Based on these indicators, the composition of the compounds is quantitatively determined.

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;
• physico-chemical.

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

The main types 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 to free radicals, particles or ions. Physico-chemical analysis laboratory assistants provide the combined effect of the designated force fields, and the particles are separated into separate ion flows according to the ratio of charge and mass.
3. Radioactive methods.
4. Electrochemical.
5. Biochemical.
6. Thermal.

What can we learn about substances and molecules from such processing methods? Firstly, the isotopic composition. And also: reaction products, the content of certain particles in especially pure substances, the masses of the sought 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.

PHYSICAL AND CHEMICAL ANALYSIS, studies the relationships between composition and macroscopic properties. systems made up of several initial substances (components). Physicochemical analysis is characterized by the presentation of these dependencies graphically, in the form of a composition-property diagram; Tables of numerical data and analytes are also used. records. Because the properties of a system depend not only on its composition, but also on other factors that determine the state of the system - pressure, temperature, degree of dispersion, gravitational strength. and electromagnetic

fields, as well as observation time, then in a general form we talk about diagrams of the equilibrium factor - St., or about physical-chemical. (chemical) diagrams. In these diagrams, all chem. processes occurring in systems when changes in conditions occur. equilibrium factors, such as the formation and decay of chemicals. connection, the appearance and disappearance of solid and (or) liquid solutions, etc., are expressed as geom. changes in a complex of lines, surfaces and points that form a diagram. Therefore, analysis of the geometry of the diagrams allows one to draw conclusions about the corresponding processes in the system.

Two main the principles of physicochemical analysis were formulated by N.S. Kurnakov. According to the principle of correspondence, 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 geom. chemical research method transformations.

The third principle of physicochemical analysis was proposed by Ya.G. Goroschenko. He claims that any set of components, regardless of their number and physical-chemical. St., can form a system (compatibility principle). It follows from it that the diagram of any system contains all the elements of the particular systems (subsystems) from which it is composed. IN common system

broadcast elements of private systems are combined with geo. images in chemistry 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 physical and chemical analysis is the study of chemical topology. diagrams. The advantage of physicochemical analysis as a research method is that it does not require the isolation of a chemical product. interaction of components from the reaction mixture, as a result of which the method allows one to study chemical transformations in solutions, alloys (especially metal), glasses, etc. objects, which are almost impossible to study using classical methods. preparative-synthetic methods. Physicochemical analysis has been widely used in the study of complex formation in solutions in order to determine the composition and determine the stability of chemicals. connections. The composition-st. graph usually has one extremum, usually 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 points of extrema on the curves (or surfaces) of the properties, as well as the points of inflection, do not correspond to the composition of the chemicals formed in the system. conn., but in the limit when the degree of dissociation of the chemical. conn. is equal to zero, the continuous curve of the dependence of the chemical on the composition breaks down into two branches intersecting at a singular point, the abscissa corresponds to the composition of the chemical. connections.high, molar, volumetric, equivalent fractions or percentages). In modern In physicochemical analysis, the number of systems used is many tens. In principle, you can use any sacred property, whatever it may be. measured or calculated. For example, when solving a theoretical

questions, in particular when deducing decomposition. types of diagrams, use k.-l. thermodynamic

potential, which cannot be measured directly. When choosing a property, it is necessary to take into account both the possible accuracy of determining its values ​​and its sensitivity to chemical events occurring in the system. transformations. For example, the density of a substance may be determined with great accuracy, but it is insensitive to the formation of chemicals. comp., while hardness reacts sensitively to chemical. interaction in the system, but the accuracy of its determination is low. Physicochemical analysis is characterized by parallel research and comparison of the results of determining several. sv-v, eg. electrical conductivity, hardness. isico-chemical analysis contributed to the decision of many. theoretical problems of chemistry, in particular, the creation of a theory of chemical structure.

conn. variable composition (see Nonstoichiometry). Physico-chemical analysis is the basis for creating new and modifying known materials - alloys, semiconductors, glasses, ceramics, etc. by, for example, doping. On physical-chemical analysis and physical-chemical. 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 compounds and growing single crystals. T. called the method of residual concentrations makes it possible to study chemical deposition systems. conn. as a result of interaction. in districts. According to this method, the composition of solid phases - the products of the solution - is determined by the difference between the content of the reacting components in the series of initial mixtures and in the corresponding equilibrium solutions at the end of the interaction.

Physicochemical analysis turned out to be fruitful for the research and synthesis of new compounds. as a result of irreversible reactions in nonequilibrium 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 solution, but also 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 principles. The properties of the system are significantly influenced by its dispersion - molecular-disperse distribution of components (submicroscopic state), state of colloidal dissolution, etc., up to monocrystalline. condition. Diagrams composition - structure - degree of dispersion - properties determine the features of modern technology. studies in physical and chemical analysis.

The development of computers has led to the fact that the role of analytes in physicochemical analysis has significantly increased. forms of expression of the dependences of the system on its composition. This makes it easier to store information (modern computer systems make it possible to collect and store reference material on chemical diagrams and in graphical form) and, in particular, math. processing of results, which was previously used mainly. only when studying complex formation in solutions. To a certain extent, the use of modern calculates, the technique allows one to overcome the limitations of physico-chemical analysis, which lies in the fact that it establishes which chemicals. transformations take place in the system, but does not answer questions related to the cause and mechanism of these transformations. Calculation methods make it possible to extract additional information from chem. diagrams, e.g. determine the degree of dissociation of a chemical. conn. in the melt based on an analysis of the curvature of the liquidus line for binary systems or the change in the free energy of the system during salt exchange, based on the shape of the liquidus surface isotherms for ternary reciprocal systems. Attracting various theories of solids, models of liquids and states of gas mixtures, along with a generalization of experiments. data, allows you to obtain physical-chemical. diagrams (or their elements) by calculation.

Historical sketch. Basic the idea of ​​physicochemical analysis was expressed by M.V. Lomonosov (1752), the first attempts to establish education in the chemical system. connection, based on the dependence of its properties on the composition, belong to the beginning. 19th century All R . 19th century works of P.P. Anosova (1831), G.K. Sorby (1864), D.K. Chernov (1869) laid the foundations of metallurgy; DI. Mendeleev was the first to carry out geomechanics. analysis of diagrams of composition - properties using the example of studying sulfuric acid hydrates. The works of V.F. belong to the same period. Alekseeva on the mutual pH-resistance of liquids, D.P. Konovalov - on the elasticity of steam solutions (see Konovalov’s laws), I.F. Schroeder - about the temperature dependence of p-permeability (see Pasm-permeability). 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-Osten, J. Van Laar, etc.). Fundamental theoretical and experiment. works of modern physical and chemical analysis belong to N.S. Kurnakov. He combined the study of alloys and homogeneous solutions into one direction and proposed the term “physicochemical 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 chemicals. 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 inorganic chemistry", 1982, v. 27, no. 6, p. 1527-30;

Glazov V.M., "Izvestia of the USSR Academy of Sciences. Ser. inorganic materials", 1984, v. 20, no. 6, p. 925-36; Fedorov P.I., Fedorov P.P., Drobot D.V., Physico-chemical analysis of anhydrous salt systems, M., 1987. P.I. Fedorov.

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

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

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

Chemical methods of analysis are widely used for the analysis of ores, rocks, minerals and other materials to determine components in them with contents from tenths to several tens of percent. Chemical methods of analysis are characterized by high accuracy (the 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 any physical property of substances, which is a function of composition. For example, refractometry is based on measuring the relative refractive indices of light. In activation analysis, the activity of isotopes, etc. is measured. Often in the analysis, a chemical reaction is carried out first, and the concentration of the resulting product is determined by physical properties, for example, by 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 detection limits 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 is used to determine tungsten in granites and shales, antimony, tin and lead in rocks and phosphates; atomic absorption method - magnesium and silicon in silicates; X-ray fluorescence - vanadium in ilmenite, magnesite, alumina; mass spectrometric - manganese in lunar regolith; neutron activation - iron, zinc, antimony, silver, cobalt, selenium and scandium in oil; by isotope dilution method - cobalt in silicate rocks.

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

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

Important practical significance have methods based on the study of the emission and absorption of electromagnetic radiation in various areas spectrum These include spectroscopy (e.g. luminescence 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), the thermal effects of reactions (thermometric titration), as well as the separation of ions in a magnetic field (mass spectrometry) are being successfully developed.