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 sectors of the national economy. Mineral exploration is based to varying degrees on the results of analysis. Analysis is the main means of monitoring environmental pollution. 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. The development of many sciences depends on the level of chemical analysis and 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. It is sometimes possible to estimate the spatial arrangement of 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 developing the theoretical foundations of methods, establishing the limits of their applicability, assessing metrological and other characteristics, and 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.

Determination methods are of greatest importance. 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 physico-chemical. Physical methods are based on physical phenomena and processes, biological methods are based 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 measurements of a 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 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 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

Chemical detection and determination methods 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 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 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 is the best way to solve 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 of 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 of electromagnetic radiation with matter. 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 consequence of chemical reactions. To a lesser extent, methods based on the release or absorption of heat as a result of physical processes are used. 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, "Higher School", 1999.

4. “Fundamentals of analytical chemistry. Book 2", Moscow, "Higher School", 1999.

4.2. CHROMATOGRAPHIC METHODS

4.3. CHEMICAL METHODS

4.4. ELECTROCHEMICAL METHODS

4.5. SPECTROSCOPIC METHODS

4.6. MASS SPECTROMETRIC METHODS

4.7. ANALYSIS METHODS BASED ON RADIOACTIVITY

4.8. THERMAL METHODS

4.9. BIOLOGICAL ANALYSIS 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 sectors of the national economy. Mineral exploration is based to varying degrees on the results of analysis. Analysis is the main means of monitoring environmental pollution. 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. The development of many sciences depends on the level of chemical analysis and 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. It is sometimes possible to estimate the spatial arrangement of 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 developing the theoretical foundations of methods, establishing the limits of their applicability, assessing metrological and other characteristics, and 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.

Determination methods are of greatest importance. 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 physico-chemical. Physical methods are based on physical phenomena and processes, biological methods are based 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 measurements of a 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 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 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).

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

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

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, the analysis involves a chemical reaction first, and the concentration of the resulting product is determined by physical properties, for example, the intensity of absorption of light radiation by the 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, and a high level of 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.

Of great practical importance are methods based on the study of the emission and absorption of electromagnetic radiation in various regions of the 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), the thermal effects of reactions (thermometric titration), as well as the separation of ions in a magnetic field (mass spectrometry) are being successfully developed.

Classification of methods of qualitative analysis.

Subject and tasks of analytical chemistry.

Analytical chemistry is the science of methods for qualitative and quantitative research into the composition of substances (or mixtures thereof). The task of analytical chemistry is to develop the theory of chemical and physicochemical methods of analysis and operations in scientific research.

Analytical chemistry consists of two main sections: qualitative analysis consists in “opening”, i.e. detection of individual elements (or ions) that make up the analyte. Quantitative Analysis consists in determining the quantitative content of individual components of a complex substance.

The practical importance of analytical chemistry is great. Using chemical methods. analysis discovered laws: constancy of composition, multiple ratios, atomic masses of elements, chemical equivalents were determined, formulas of many compounds were established.

Analytical chemistry contributes to the development of natural sciences - geochemistry, geology, mineralogy, physics, biology, technological disciplines, medicine. Chemical analysis is the basis of modern chemical-technological control of all industries in which raw materials, products and production waste are analyzed. Based on the results of the analysis, the flow of the technological process and the quality of the product are judged. Chemical and physical-chemical methods of analysis form the basis for establishing state standards for all manufactured products.

The role of analytical chemistry in organizing environmental monitoring is great. This is monitoring of contamination of surface waters, soils with heavy metals, pesticides, petroleum products, and radionuclides. One of the tasks of monitoring is to create criteria that establish the limits of possible environmental damage. For example MPC - maximum permissible concentration- this is such a concentration, when exposed to the human body, periodically or throughout life, directly or indirectly through environmental systems, no diseases or changes in health status occur, detectable by modern methods immediately or in long-term periods of life. For each chem. substances have their own MPC value.

Classification of methods of qualitative analysis.

When studying a new compound, they first determine what elements (or ions) it consists of, and then the quantitative ratios in which they are found. Therefore, qualitative analysis usually precedes quantitative analysis.

All analytical methods are based on obtaining and measuring analytical signal, those. any manifestation of the chemical or physical properties of a substance that can be used to establish the qualitative composition of the analyzed object or to quantify the components it contains. The analyzed object can be an individual connection in any aggregate state. a mixture of compounds, a natural object (soil, ore, mineral, air, water), industrial products and food. Before analysis, sampling, grinding, sifting, averaging, etc. are carried out. An object prepared for analysis is called sample or sample.

Depending on the task at hand, a method is chosen. Analytical methods of qualitative analysis are divided into: 1) “dry” analysis and 2) “wet” analysis.

Dry analysis carried out with solids. It is divided into pyrochemical and grinding methods.

Pyrochemical (Greek - fire) type of analysis is carried out by heating the test sample in the flame of a gas or alcohol burner, performed in two ways: obtaining colored “pearls” or coloring the burner flame.

1. “Pearls”(French - pearls) are formed when salts NaNH 4 PO 4 ∙ 4 H 2 O, Na 2 B 4 O 7 ∙ 10 H 2 O - borax) or metal oxides are dissolved in a melt. By observing the color of the resulting glass pearls, the presence of certain elements in the sample is established. So, for example, chromium compounds make pearl green, cobalt - blue, manganese - violet-amethyst, etc.

2. Flame coloring- volatile salts of many metals, when introduced into the non-luminous part of the flame, color it in different colors, for example, sodium - intensely yellow, potassium - violet, barium - green, calcium - red, etc. These types of analysis are used in preliminary tests and as an “express” method.

Analysis by rubbing method. (1898 Flavitsky). The test sample is ground in a porcelain mortar with an equal amount of solid reagent. The color of the resulting compound is used to determine the presence of the ion being determined. The method is used in preliminary tests and “express” analysis in the field for the analysis of ores and minerals.

2.Wet analysis - This is the analysis of a sample dissolved in some solvent. The solvent most often used is water, acids or alkalis.

According to the method of conducting, methods of qualitative analysis are divided into fractional and systematic. Fractional Analysis Method- this is the determination of ions using specific reactions in any sequence. It is used in agrochemical, factory and food laboratories, when the composition of the test sample is known and it is only necessary to check the absence of impurities or during preliminary tests. Systematic analysis - This is an analysis in a strictly defined sequence, in which each ion is detected only after interfering ions have been detected and removed.

Depending on the amount of substance taken for analysis, as well as on the technique of performing operations, methods are divided into:

- macroanalysis - carried out in relatively large quantities of the substance (1-10 g). The analysis is performed in aqueous solutions and in test tubes.

- microanalysis - examines very small quantities of a substance (0.05 - 0.5 g). It is performed either on a strip of paper, a watch glass with a drop of solution (droplet analysis) or on a glass slide in a drop of solution, crystals are obtained, according to the shape of which the substance is determined under a microscope (microcrystalscopic).

Basic concepts of analytical chemistry.

Analytical reactions - These are reactions accompanied by a clearly visible external effect:

1) precipitation or dissolution of sediment;

2) change in the color of the solution;

3) gas release.

In addition, two more requirements are imposed on analytical reactions: irreversibility and sufficient reaction rate.

Substances under the influence of which analytical reactions occur are called reagents or reagents. All chem. reagents are divided into groups:

1) by chemical composition (carbonates, hydroxides, sulfides, etc.)

2) according to the degree of purification of the main component.

Conditions for performing chem. analysis:

1. Reaction medium

2. Temperature

3. Concentration of the ion being determined.

Wednesday. Acidic, alkaline, neutral.

Temperature. Most chem. reactions are performed at room conditions “in the cold”, or sometimes it is necessary to cool under the tap. Many reactions occur when heated.

Concentration- this is the amount of a substance contained in a certain weight or volume of a solution. A reaction and reagent capable of causing a noticeable external effect characteristic of it even at a negligible concentration of the substance being determined are called sensitive.

The sensitivity of analytical reactions is characterized by:

1) extreme dilution;

2) maximum concentration;

3) a minimum volume of an extremely dilute solution;

4) detection limit (opening minimum);

5) sensitivity indicator.

Limit dilution Vlim – the maximum volume of solution in which one gram of a given substance can be detected (in more than 50 experiments out of 100 experiments) using a given analytical reaction. The dilution limit is expressed in ml/g.

For example, when copper ions react with ammonia in an aqueous solution

Cu 2+ + 4NH 3 = 2+ ¯bright blue complex

The limiting dilution of the copper ion is (Vlim = 2.5 10 5 mg/l), i.e. Copper ions can be opened by this reaction in a solution containing 1 g of copper in 250,000 ml of water. In a solution containing less than 1 g of copper (II) in 250,000 ml of water, these cations cannot be detected by the above reaction.

Limit concentration Сlim (Cmin) – the lowest concentration at which the analyte can be detected in solution by a given analytical reaction. Expressed in g/ml.

The maximum concentration and maximum dilution are related by the relation: Clim = 1 / V lim

For example, potassium ions in an aqueous solution are opened using sodium hexanitrocobaltate (III)

2K + + Na 3 [ Co(NO 2) 6 ] ® NaK 2 [ Co(NO 2) 6 ] ¯ + 2Na +

The limiting concentration of K + ions for this analytical reaction is C lim = 10 -5 g/ml, i.e. Potassium ion cannot be opened by this reaction if its content is less than 10 -5 g in 1 ml of the analyzed solution.

Minimum volume of extremely diluted solution Vmin– the smallest volume of the analyzed solution required to detect the discovered substance by a given analytical reaction. Expressed in ml.

Detection limit (opening minimum) m– the smallest mass of the analyte that can be unambiguously discovered by a given an. reaction in a minimal volume of extremely dilute solution. Expressed in µg (1 µg = 10 -6 g).

m = C lim V min × 10 6 = V min × 10 6 / V lim

Sensitivity index analytical reaction is determined

pС lim = - log C lim = - log(1/Vlim) = log V lim

An. the reaction is more sensitive, the smaller its opening minimum, the minimum volume of the extremely diluted solution, and the greater the maximum dilution.

The detection limit depends on:

1. Concentrations of the test solution and reagent.

2. Duration of the course of an. reactions.

3. Method of observing the external effect (visually or using a device)

4. Compliance with the conditions for fulfillment of an. Reactions (t, pH, amount of reagent, its purity)

5. Presence and removal of impurities, foreign ions

6. Individual characteristics of an analytical chemist (accuracy, visual acuity, ability to distinguish colors).

Types of analytical reactions (reagents):

Specific- reactions that allow the determination of a given ion or substance in the presence of any other ions or substances.

For example: NH4 + + OH - = NH 3 (odor) + H 2 O

Fe 3+ + CNS - = Fe(CNS) 3 ¯

blood red

Selective- reactions allow you to selectively open several ions at once with the same external effect. The fewer ions a given reagent opens, the higher its selectivity.

For example:

NH 4 + + Na 3 = NH 4 Na

K + + Na 3 = NaK 2

Group reactions (reagents) allow you to detect a whole group of ions or some compounds.

For example: group II cations - group reagent (NH4)2CO3

CaCI 2 + (NH 4) 2 CO 3 = CaCO 3 + 2 NH 4 CI

BaCI 2 + (NH 4) 2 CO 3 = BaCO 3 + 2 NH 4 CI

SrCI 2 + (NH 4) 2 CO 3 = SrCO 3 + 2 NH 4 CI

In theoretical the fundamentals of analytical occupies a significant place, including statistical. processing of results. Analytical theory also includes the doctrine of selection and preparation, the drawing up of an analysis scheme and the choice of methods, the principles and ways of automating analysis, the use of computers, as well as the fundamentals of national economies. use of chemical results. analysis. The peculiarity of the analytical one is the study of not general, but individual, specific ones. holy and characteristics of objects, which ensures the selectivity of the plural. analyte methods. Thanks to close connections with the achievements of physics, mathematics, biology and so on. fields of technology (this especially concerns methods of analysis) analytical transformation. into a discipline at the intersection of sciences.

Almost all determination methods are based on the dependence of s.l. the measurable properties of substances depend on their composition. Therefore, an important area of ​​analytical research is the search and study of such dependencies in order to use them to solve analytes. tasks. In this case, it is almost always necessary to find the level of connection between the property and the composition, develop methods for registering the property (analytical signal), eliminate interference from other components, eliminate the interfering influence of various components. factors (eg temperature fluctuations). The size of the analyte. the signal is converted into units that characterize the number or components. Be measured, for example, mass, volume, light absorption.

Much attention is paid to the theory of analysis methods. Theory chem. and partly physical-chemical. methods is based on ideas about several basic. types of chem. p-tions widely used in analysis (acid-base, oxidation-reduction,) and several important processes (-,). Attention to these issues is due to the history of the development of analytical and practical science. the significance of the corresponding methods. Since, however, the share of chemical methods is decreasing, and the share of physical-chemical. and physical methods is growing, improving the theory of methods of the last two groups and integrating theoretical ones is becoming of great importance. aspects of individual methods in general analytical theory.

History of development. Testing of materials was carried out in ancient times, for example. examined to determine their suitability for smelting, decomp. products - to determine the content of Au and Ag in them. Alchemists 14-16 centuries. for the first time applied and carried out a huge amount of experiments. works on the study of holy waters, laying the foundation for chemistry. methods of analysis. In the 16th-17th centuries. (period) new chemicals appeared. methods for detecting substances based on the solutions in the solution (for example, the discovery of Ag + by the formation of a precipitate with Cl -). R. Boyle is considered the founder of scientific analytical science, who introduced the concept of “chemical analysis.”

Until 1st half. 19th century analytical was the main section. During this period, many were discovered. chem. elements, the components of certain nature are identified. in-in, multiple relations are established, . T. Bergman developed a systematic scheme. analysis, introduced H 2 S as an analyte. , proposed flame analysis methods for obtaining pearls, etc. In the 19th century systematic qualities the analysis was improved by G. Rose and K. Fresenius. This same century was marked by enormous successes in the development of quantities. analysis. A titrimetric test was created. method (F. Decroisille, J. Gay-Lussac), gravimetric significantly improved. analysis, methods developed. The development of organizational methods was of great importance. connections (J. Liebig). In con. 19th century An analytical theory developed, based on the doctrine of chemistry. in districts with participation (chief sample V. Ostwald). By this time, methods of analysis in aqueous solutions occupied a predominant place in analytical research.

In the 20th century methods for microanalysis of org. connections (F. Pregl). Polarographic was proposed. method (Ya. Heyrovsky, 1922). Many physical and chemical and physical methods, eg. mass spectrometry, X-ray, nuclear physics. The discovery (M.S. Tsvet, 1903) and then the creation of its various variants, in particular the distribution, were of great importance. (A. Martin and R. Sint, 1941).

In Russia and the USSR, the works of N.A. were of great importance for the development of analytical science. Menshutkin (his textbook on analytical went through 16 editions). M.A. Ilyinsky, and especially L.A. Chugaev introduced org into practice. analyte (late 19th - early 20th centuries), N.A. Tananaev developed the drip method of qualities. analysis (simultaneously with F. Feigl, 20s of the 20th century). In 1938, N.A. Izmailov and M.S. Schreiber first described. In the 1940s Plasma sources have been proposed for atomic emission analysis. Soviet scientists also made a great contribution to the study of its analyte. use (I.P. Alimarin, A.K. BabkoKh in the theory of action of organic analytes, in the development of methods of photometric analysis, atomic absorption, in the analytical analysis of individual elements, especially rare and platinum, and a number of objects - in high purity, mineral raw materials, etc.

The requirements of practice have always stimulated the development of analytical science. So, in the 40-70s. 20th century In connection with the need to analyze nuclear, semiconductor and other materials of high purity, such sensitive methods as spark mass spectrometry, chemical spectral analysis, and voltammetry were created, providing the determination of up to 10 -7 - 10 -8% of impurities in pure in-wah, i.e. 1 part of impurity per 10-1000 billion parts of base. in-va. For the development of ferrous steel, especially in connection with the transition to high-speed converter steel production, rapid analysis has become crucial. The use of the so-called Quantometer-photoelectric. devices for multi-element optical spectral or X-ray analysis allows analysis to be carried out during melting in several minutes. minutes.

The need to analyze complex mixtures of org. compounds has led to intensive development, which makes it possible to analyze complex mixtures containing several. tens and even hundreds. Analytical means. contributed to the mastery of energy, the study of space and the ocean, the development of electronics, and progress. Sci.

Subject of study. An important role is played by the development of the theory of selection of analyzed materials; Typically, sampling issues are resolved jointly with specialists in the fields being studied (for example, geologists, metallurgists). Analytical develops methods of decomposition - fusion, etc., which should ensure complete “opening” of the sample and prevent loss of the determined components and contamination from the outside. Analytical tasks include the development of techniques for such general analytical operations as volume measurement and calcination.

One of the tasks of analytical chemistry is to determine the directions of development of analytes. instrumentation, the creation of new circuits and designs of devices (which most often serves as the final stage of development of an analysis method), as well as the synthesis of new analytes. reagents.

For quantities. analysis are very important metrological. characteristics of methods and instruments. In this regard, analytical studies the problems of calibration, production and use of comparison samples (including) and other means to ensure the correctness of the analysis. Creatures Processing of analysis results, including using a computer, takes place. For the conditions of analysis, information theory and math are used. utility theory, pattern recognition theory and other branches of mathematics. Computers are used not only for processing results, but also for controlling instruments, taking into account interference, calibration, ; there are analytes. tasks that can only be solved with the help of a computer, for example. org. connections using art theory. intelligence (see Automated analysis).

Methods of determination - basic. group of analytical methods. The basis of quantity methods. analysis lies the dependence of k.-l. a measurable property, most often physical, from the composition of the sample. This dependence must be described in a certain and known way.

A variety of methods are needed for analysis, as each has its own advantages and limitations. Yes, he is extremely sensitive. radioactivation and mass spectral methods require complex and expensive equipment. Simple, accessible and very sensitive. kinetic methods do not always provide the required reproducibility of results. When evaluating and comparing methods, when choosing them for solving specific problems, many are taken into account. factors: metrological parameters, scope of possible use, availability of equipment, analyst qualifications, traditions, etc. The most important among these factors are metrological. parameters, such as detection limit or range (number), in which the method gives reliable results, and the accuracy of the method, i.e. accuracy and reproducibility of results. In some cases, “multicomponent” methods are of great importance, allowing one to determine a large number of components at once, for example. atomic emission and x-ray