Physical methods in analytical chemistry. Analytical chemistry - what is it? Definition, tasks and research methods

analysis method name the principles underlying the analysis of matter, that is, the type and nature of the energy that causes perturbation of the chemical particles of matter.

The analysis is based on the dependence between the recorded analytical signal on the presence or concentration of the analyte.

Analytical signal is a fixed and measurable property of an object.

AT analytical chemistry analysis methods are classified according to the nature of the property being determined and according to the method of recording the analytical signal:

1.chemical

2.physical

3.Physical and chemical

Physico-chemical methods are called instrumental or measuring, as they require the use of instruments, measuring instruments.

Consider a complete classification of chemical methods of analysis.

Chemical methods of analysis- based on energy measurement chemical reaction.

During the reaction, the parameters associated with the consumption of starting materials or the formation of reaction products change. These changes can either be observed directly (precipitate, gas, color) or measured such as reagent consumption, product mass, reaction time, etc.

By goals methods of chemical analysis are divided into two groups:

I. Qualitative analysis- is to discover individual elements(or ions) that make up the analyte.

Qualitative analysis methods are classified:

1. cation analysis

2. anion analysis

3. analysis of complex mixtures.

II.Quantitative analysis- consists in determining the quantitative content of individual constituent parts complex substance.

Quantitative chemical methods classify:

1. Gravimetric(weight) method of analysis is based on the isolation of the analyte in its pure form and its weighing.

Gravimetric methods according to the method of obtaining the reaction product are divided into:

a) chemogravimetric methods are based on measuring the mass of the product of a chemical reaction;

b) electrogravimetric methods are based on measuring the mass of the product of an electrochemical reaction;

c) thermogravimetric methods are based on measuring the mass of a substance formed during thermal exposure.

2. Volumetric methods of analysis are based on measuring the volume of a reagent consumed for interaction with a substance.

Volumetric methods, depending on the state of aggregation of the reagent, are divided into:

a) gas volumetric methods, which are based on the selective absorption of the determined component of the gas mixture and the measurement of the volume of the mixture before and after absorption;

b) liquid volumetric (titrimetric or volumetric) methods are based on measuring the volume of a liquid reagent consumed for interaction with the analyte.

Depending on the type of chemical reaction, methods of volumetric analysis are distinguished:

Protolithometry is a method based on the course of a neutralization reaction;

redoxometry - a method based on the occurrence of redox reactions;

complexometry - a method based on the course of the reaction of complexation;

· precipitation methods - methods based on the reactions of precipitation formation.

3. Kinetic methods of analysis are based on determining the dependence of the rate of a chemical reaction on the concentration of reactants.

Lecture No. 2. Stages of the analytical process

Decision analytical task carried out by performing an analysis of the substance. According to IUPAC terminology analysis [‡] called the procedure for obtaining empirically data on chemical composition substances.

Regardless of the chosen method, each analysis consists of the following stages:

1) sampling (sampling);

2) sample preparation (sample preparation);

3) measurement (definition);

4) processing and evaluation of measurement results.

Fig1. Schematic representation of the analytical process.

Sample selection

Conducting chemical analysis begins with the selection and preparation of samples for analysis. It should be noted that all stages of the analysis are interconnected. Thus, a carefully measured analytical signal does not provide correct information about the content of the analyte, if the selection or preparation of the sample for analysis is not carried out correctly. Sampling error often determines the overall accuracy of the component determination and makes it meaningless to use high-precision methods. In turn, sampling and sample preparation depend not only on the nature of the analyzed object, but also on the method of measuring the analytical signal. Sampling and sample preparation techniques and procedures are so important in chemical analysis that they are usually prescribed State standard(GOST).

Consider the basic rules for sampling:

The result can only be correct if the sample is sufficiently representative, that is, accurately reflects the composition of the material from which it was selected. The more material is selected for the sample, the more representative it is. However, a very large sample is difficult to handle and increases analysis time and cost. Thus, it is necessary to take a sample so that it is representative and not very large.

· The optimal mass of the sample is due to the heterogeneity of the analyzed object, the size of the particles from which the heterogeneity begins, and the requirements for the accuracy of the analysis.

· Lot homogeneity must be ensured to ensure representativeness of the sample. If it is not possible to form a homogeneous batch, then stratification of the batch into homogeneous parts should be used.

Take into account when taking samples state of aggregation object.

· The condition for the uniformity of sampling methods must be met: random sampling, periodic, staggered, multi-stage sampling, blind sampling, systematic sampling.

· One of the factors that should be taken into account when choosing a sampling method is the possibility of changing the composition of the object and the content of the determined component over time. For example, the variable composition of water in a river, a change in the concentration of components in food products etc.

MOSCOW AUTOMOTIVE AND ROAD INSTITUTE (STATE TECHNICAL UNIVERSITY)

Department of Chemistry

I approve the head. department professor

I.M. Papisov "___" ____________ 2007

A.A. LITMANOVICH, O.E. LITMANOVYCH

ANALYTICAL CHEMISTRY Part 1: Qualitative Chemical Analysis

Toolkit

for students of the second year of the specialty “Engineering protection environment”

MOSCOW 2007

Litmanovich A.A., Litmanovich O.E. Analytical Chemistry: Part 1: Qualitative Chemical Analysis: Methodological Guide / MADI

(GTU) - M., 2007. 32 p.

The main chemical laws of the qualitative analysis of inorganic compounds and their applicability for determining the composition of environmental objects are considered. The manual is intended for students of the specialty "Environmental Engineering".

© Moscow Automobile and Road Institute (state Technical University), 2008

CHAPTER 1. SUBJECT AND OBJECTIVES OF ANALYTICAL CHEMISTRY. ANALYTICAL REACTIONS

1.1. Subject and tasks of analytical chemistry

Analytical chemistry- the science of methods for studying the composition of substances. These methods determine which chemical elements, in what form and in what quantity are contained in the object under study. In analytical chemistry, two large sections are distinguished - qualitative and quantitative analysis. The tasks set by analytical chemistry are solved with the help of chemical and instrumental methods (physical, physicochemical).

AT chemical methods analysis the element to be determined is converted into a compound having such properties, with the help of which it is possible to establish the presence of this element or to measure its amount. One of the main ways to measure the amount of a formed compound is to determine the mass of a substance by weighing on an analytical balance - a gravimetric method of analysis. Methods of quantitative chemical analysis and instrumental methods of analysis will be discussed in part 2 methodological manual in analytical chemistry.

An urgent direction in the development of modern analytical chemistry is the development of methods for analyzing environmental objects, waste and waste water, gas emissions from industrial enterprises and road transport. Analytical control makes it possible to detect the excess of the content of especially harmful components in discharges and emissions, helps to identify sources of environmental pollution.

Chemical analysis is based on the fundamental laws of general and inorganic chemistry with which you are already familiar. Theoretical basis chemical analysis include: knowledge of the properties of aqueous solutions; acid-base equilibria in aqueous

solutions; redox equilibria and properties of substances; patterns of complexation reactions; conditions for the formation and dissolution of the solid phase (precipitates).

1.2. analytical reactions. Conditions and methods for their implementation

Qualitative chemical analysis is carried out using analytical reactions accompanied by noticeable external changes: for example, gas evolution, color change, formation or dissolution of a precipitate, in some cases - the appearance of a specific odor.

Basic requirements for analytical reactions:

1) High sensitivity, characterized by the value of the detection limit (Cmin) - the lowest concentration of the component in the solution sample, at which this analysis technique allows you to confidently detect this component. The absolute minimum value of the mass of a substance that can be detected by analytical reactions is from 50 to 0.001 μg (1 μg = 10–6 g).

2) Selectivity- characterized by the ability of the reagent to react with as few components (elements) as possible. In practice, they try to detect ions under conditions under which the selective reaction becomes specific, i.e. allows you to detect this ion in the presence of other ions. As examples of specific reactions(of which there are few) are as follows.

a) The interaction of ammonium salts with an excess of alkali when heated:

NH4Cl + NaOH → NH3 + NaCl + H2O . (one)

The released ammonia is easy to recognize by its characteristic odor (“ammonia”) or by a change in the color of a wet indicator paper brought to the neck of the test tube. Reaction

allows you to detect the presence of ammonium ions NH4 + in the analyzed solution.

b) Interaction of ferrous salts with potassium hexacyanoferrate (III) K3 with the formation of a precipitate of blue color(Turnbull blue, or Prussian blue). Reaction (well familiar to you on the topic "Corrosion of metals" in the course

These reactions make it possible to detect Fe2+ and Fe3+ ions in the analyzed solution.

Specific reactions are convenient in that the presence of unknown ions can be determined fractional method- in separate samples of the analyzed solution containing other ions.

3) The speed of the reaction ( high speed ) and ease of implementation.

The high reaction rate ensures the achievement of thermodynamic equilibrium in the system for a short time(practically at the rate of mixing components during reactions in solution).

When performing analytical reactions, it is necessary to remember what determines the shift in the equilibrium of the reaction in the right direction and its flow to a large depth of transformation. For reactions occurring in aqueous solutions of electrolytes, the shift in thermodynamic equilibrium is affected by the concentration of ions of the same name, the pH of the medium, and the temperature. In particular, temperature depends the value of equilibrium constants - constants

dissociation for weak electrolytes and solubility products (PR) for sparingly soluble salts, bases

These factors determine the depth of the reaction, the yield of the product and the accuracy of the determination of the analyte (or the very possibility of detecting a certain ion at a small amount and concentration of the analyte).

The sensitivity of some reactions increases in an aqueous organic solution, for example, when acetone or ethanol is added to an aqueous solution. For example, in an aqueous ethanol solution, the solubility of CaSO4 is much lower than in an aqueous solution (the SP value is lower), which makes it possible to unambiguously detect the presence of Ca2+ ions in the analyzed solution at much lower concentrations than in an aqueous solution, and also to most completely free the solution from these ions (precipitation with H2 SO4 ) to continue the analysis of the solution.

In qualitative chemical analysis, a rational sequence is developed in the separation and detection of ions - a systematic course (scheme) of analysis. In this case, ions are separated from the mixture in groups, based on their equal relation to the action of certain group reagents.

One portion of the analyzed solution is used, from which groups of ions are sequentially isolated in the form of precipitation and solutions, in which individual ions are then detected . The use of group reagents makes it possible to decompose the complex problem of qualitative analysis into a number of simpler ones. The ratio of ions to the action of certain

group reagents is the basis analytical classification of ions.

1.3. preliminary analysis an aqueous solution containing a mixture of salts, by color, smell, pH value

The presence of a color in a clear solution proposed for analysis may indicate the presence of one or several ions at once (Table 1). The intensity of the color depends on the concentration of the ion in the sample, and the color itself can change if

metal cations form more stable complex ions than complex cations with H2O molecules as ligands, for which the color of the solution is indicated in Table. one .

pH measurement of the proposed solution ( if the solution is prepared in water, and not in a solution of alkali or acid) also

Aqueous solutions of some salts may have specific odors depending on the pH of the solution due to the formation of unstable (decomposing) or volatile compounds. By adding NaOH solutions to the sample solution or

strong acid (HCl, H2 SO4 ), you can gently smell the solution (Table 3).

Table 3

The reason for the smell (see Table 3) is the well-known property of reactions in electrolyte solutions - the displacement of weak acids or bases (often aqueous solutions of gaseous substances) from their salts by strong acids and bases, respectively.

CHAPTER 2. QUALITATIVE CHEMICAL ANALYSIS OF CATIONS

2.1. Acid-base method for classifying cations by analytical groups

The simplest and least “harmful” acid-base (basic) method of qualitative analysis is based on the ratio of cations to acids and bases. The classification of cations is carried out according to the following criteria:

a) solubility of chlorides, sulfates and hydroxides; b) basic or amphoteric character of hydroxides;

c) the ability to form stable complex compounds with ammonia (NH3) - ammoniates (i.e. amino complexes).

All cations are divided into six analytical groups using 4 reagents: 2M HCl solution, 1M H2SO4 solution, 2M NaOH solution and concentrated aqueous ammonia solution

NH4 OH (15-17%) (Table 4).

Table 4 Classification of cations by analytical groups

Obviously, the above list of cations is far from complete and includes the cations most frequently encountered in practice in the analyzed samples. In addition, there are other principles of classification by analytic groups.

2.2. Intragroup analysis of cations and analytical reactions for their detection

2.2.1. First group (Ag+ , Pb2+ )

Test solution containing Ag+, Pb2+ cations

↓ + 2M HCl solution + C 2 H5 OH (to reduce the solubility of PbCl2)

If PC > PR, are formed white precipitates of a mixture of chlorides,

which are separated from the solution (the solution is not analyzed):

Ag+ + Cl– ↔ AgCl↓ and Pb2+ + 2Cl– ↔ PbCl2 ↓ (3)

Obviously, at low concentrations of precipitated cations, the concentration of Cl– anions should be relatively high

↓ To sediment part + H2 O (distilled) + boiling

↓ To the 2nd part of the sediment of the mixture of chlorides + 30%

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

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

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

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

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

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

Physical Methods analyzes are based on the measurement of some physical property of substances, which is a function of composition. For example, refractometry is based on measuring the relative refractive indices of light. In an activation assay, the activity of isotopes, etc. is measured. Often, a chemical reaction is preliminarily carried out during the assay, and the concentration of the resulting product is determined by physical properties, for example, by 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 determines tungsten in granites and slates, antimony, tin and lead in rocks and phosphates; atomic absorption method - magnesium and silicon in silicates; X-ray fluorescent - vanadium in ilmenite, magnesite, alumina; mass spectrometric - manganese in the lunar regolith; neutron activation - iron, zinc, antimony, silver, cobalt, selenium and scandium in oil; method of isotopic dilution - cobalt in silicate rocks.

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

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

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

In the theoretical fundamentals of analytical occupies a significant place, including statistical. processing results. Analytical theory also includes the doctrine of selection and preparation, of drawing up an analysis scheme and the choice of methods, principles and ways of automating analysis, the use of computers, and the foundations of national economies. using the results of chem. analysis. A feature of the analytical is the study of not general, but individual, specific. sv-in and characteristics of objects, which ensures the selectivity of many others. analyte methods. Thanks to close ties with the achievements of physics, mathematics, biology, etc. areas of technology (this is especially true of methods of analysis) analytical transformation. into a discipline at the intersection of sciences.

Almost all determination methods are based on the dependence of c.-l. measurable properties in-in from their composition. Therefore, an important direction of the analytical is the search and study of such dependencies in order to use them to solve the analyte. tasks. At the same time, it is almost always necessary to find the level of connection between St. and the composition, develop ways to register St. Islands (analytical signal), eliminate interference from other components, eliminate the interfering influence of decomp. factors (eg, fluctuations of t-ry). The value of the analyte. the signal is converted into units characterizing the number or components. Measured to be, for example, mass, volume, light absorption.

Much attention is paid to the theory of methods of analysis. Theory of chem. and partially physical.-chemical. methods is based on ideas about several fundamentals. types of chem. p-tions, widely used in the analysis (acid-base, redox.,), and several important processes (-,). Attention to these issues is due to the history of the development of analytical and practical. the significance of the respective methods. Since, however, the proportion of chem. methods decreases, and the share of fiz.-chem. and physical methods is growing, the improvement of the theory of methods of the last two groups and the integration of theoretical. Aspects of Individual Methods in General Analytic Theory.

History of development. Tests of materials were carried out in ancient times, for example. investigated to establish their suitability for melting, decomp. products - to determine the content of Au and Ag in them. Alchemists 14th-16th centuries for the first time applied and performed a huge amount of experiments. works on the study of St-in in-in, laying the foundation for chem. analysis methods. In the 16-17 centuries. (period ) new chem. ways of detecting in-in, based on p-tions in the solution (for example, the discovery of Ag + by the formation of a precipitate with Cl -). R. Boyle, who introduced the concept of "chemical analysis", is considered the founder of scientific analytical.

Until the 1st floor. 19th century analytical was osn. section. During this period, many were opened. chem. elements, the constituent parts of certain natures are distinguished. in-in, established and multiple relations, . T. Bergman developed a systematic scheme. analysis, introduced H 2 S as an analyte. , proposed methods of analysis in a flame to obtain pearls, etc. In the 19th century systematic qualities. the analysis was improved by G. Rose and K. Fresenius. The same century was marked by huge successes in the development of quantities. analysis. Titrimetric was created. method (F. Decroisil, J. Gay-Lussac), significantly improved gravimetric. analysis, methods developed. Of great importance was the development of methods org. compounds (Yu. Liebig). In con. 19th century there was an analytical theory, which was based on the doctrine of chem. in solutions with participation (ch. arr. W. Ostwald). By this time, methods of analysis in aqueous solutions occupied a predominant place in the analytical.

In the 20th century methods of microanalysis org. compounds (F. Pregl). Polarographic was proposed. method (J. Geyrovsky, 1922). Appeared a lot of fiz.-chem. and physical methods, eg. mass spectrometric, x-ray, nuclear physics. Of great importance was the discovery (M.S. Tsvet, 1903) and then the creation of its various variants, in particular, distribution. (A. Martin and R. Sint, 1941).

In Russia and the USSR, the works of N.A. Menshutkin (his textbook on analytics went through 16 editions). M.A. Ilyinsky, and especially L.A. Chugaev put into practice org. 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 the action of org. analytical., in the development of photometric methods. analysis, atomic absorption., in the analytical of individual elements, especially rare and platinum, and a number of objects - in-in high purity, mineral raw materials, and .

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

The need to analyze complex mixtures of org. compounds led to intensive development, edges allows you to analyze the most complex mixtures containing several. tens and even hundreds. Analytical in means. contributed to the mastery of energy, the study of space and the ocean, the development of electronics, and progress. Sciences.

Subject of study. An important role is played by the development of the theory of selection of analyzed materials; Usually, sampling issues are resolved jointly with specialists in the studied substances (for example, with geologists, metallurgists). Analytical develops methods of decomposition - fusion, etc., to-rye should provide a complete "opening" of the sample and prevent the loss of the determined components and contamination from the outside. The tasks of the analytical include the development of techniques for such general operations of analysis as the measurement of volumes, calcination.

One of the tasks of analytical chemistry is to determine the directions of development of the analyte. instrumentation, the creation of new circuits and instrument designs (which most often serves as the final stage in the 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 devices. In this regard, the analytical studies the problems of calibration, manufacture and use of comparison samples (including ) and other media in ensuring the correctness of the analysis. Creatures. the place is occupied by the processing of the results of the analysis, including with the use of a computer. For the conditions of analysis, information theory is used, mat. utility theory, pattern recognition theory, and other branches of mathematics. Computers are used not only for processing results, but also for controlling instruments, accounting for interference, calibration,; there are analytes. tasks that can be solved only with the help of a computer, for example. org. connections using art theory. intelligence (see Automated analysis).

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

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

Analytical chemistry is a section that allows you to control the production and quality of products in various sectors of the economy. Exploration of natural resources is based on the results of these studies. Methods of analytical chemistry are used to control the degree of environmental pollution.

Practical significance

Analysis is the main option for determining the chemical composition of feed, fertilizers, soils, agricultural products, which is important for the normal functioning of the agro-industrial sector.

Qualitative and quantitative chemistry are indispensable in biotechnology and medical diagnostics. The efficiency and effectiveness of many scientific fields depends on the degree of equipment of research laboratories.

Theoretical basis

Analytical chemistry is a science that allows you to determine the composition and chemical structure of matter. Her methods help answer questions related not only to the constituent parts of a substance, but also to their quantitative ratio. With their help, you can understand in what form a particular component is in the substance under study. In some cases, they can be used to determine the spatial arrangement of composite components.

When thinking over methods, information is often borrowed from related fields of science, it is adapted to a specific area of ​​research. What questions does analytical chemistry solve? Methods of analysis make it possible to develop theoretical foundations, establish the boundaries of their use, evaluate metrological and other characteristics, and create methods for analyzing various objects. They are constantly updated, modernized, becoming more versatile and efficient.

When talking about the method of analysis, they assume the principle that is put in the expression of the quantitative relationship between the property being determined and the composition. Selected methods of conducting, including the identification and elimination of interference, devices for practical activities and options for processing the measurements taken.

Functions of Analytical Chemistry

There are three main areas of knowledge:

• solution of general questions of analysis;
• creation of analytical methods;
• working out specific tasks.

Modern analytical chemistry is a combination of qualitative and quantitative analysis. The first section deals with the issue of the components included in the analyzed object. The second gives information about the quantitative content of one or more parts of the substance.

Classification of methods

They are divided into the following groups: sampling, decomposition of samples, separation of components, identification and determination of them. There are also hybrid methods that combine separation and definition.

Methods of determination are of the greatest importance. They are divided according to the nature of the analyzed property and the variant of registration of a certain signal. Problems in analytical chemistry often involve the calculation of certain components based on chemical reactions. To carry out such calculations, a solid mathematical foundation is required.

Among the main requirements that apply to the methods of analytical chemistry, we highlight:

• correctness and excellent reproducibility of the results obtained;
• low limit of determination of specific components;
• express;
• selectivity;
• simplicity;
• experiment automation.

When choosing an analysis method, it is important to clearly know the purpose and objectives of the study, to evaluate the main advantages and disadvantages of the available methods.

The chemical method of analytical chemistry is based on the qualitative reactions characteristic of certain compounds.

Analytical signal

After sampling and sample preparation are completed, the chemical analysis stage is carried out. It is associated with the detection of components in a mixture, the determination of its quantitative content.

Analytical chemistry is a science in which there are many methods, one of them is the signal. An analytical signal is the average of several measurements of a physical quantity at the last stage of analysis, which is functionally related to the content of the desired component. If it is necessary to detect a certain element, they use an analytical signal: sediment, color, line in the spectrum. Determining the amount of the component is associated with the mass of the deposit, the intensity of the spectral lines, and the magnitude of the current.

Methods of masking, concentration, separation

Masking is the inhibition or complete suppression of a chemical reaction in the presence of those substances that can change its speed or direction. There are two types of masking: equilibrium (thermodynamic) and non-equilibrium (kinetic). For the first case, conditions are created under which the reaction constant decreases so much that the process proceeds insignificantly. The concentration of the masked component will be insufficient for reliable fixation of the analytical signal. Kinetic masking is based on the growth of the difference between the velocities of the analyte and the masked substance with a constant reagent.

Carrying out concentration and separation is due to certain factors:

• there are components in the sample that interfere with the determination;
• the concentration of the analyte does not exceed the lower limit of detection;
• the detected components are unevenly distributed in the sample;
• the sample is radioactive or toxic.

Separation is the process by which the components present in the original mixture can be separated from each other.

Concentration is an operation due to which the ratio of the number of small elements to the number of macrocomponents increases.

Precipitation is suitable for separating several. Use it in combination with methods of determination designed to obtain an analytical signal from solid samples. The division is based on the different solubility of substances used in aqueous solutions.

Extraction

The Department of Analytical Chemistry involves laboratory research related to extraction. By it is meant the physicochemical process of the distribution of a substance between immiscible liquids. Extraction is also called the process of mass transfer during chemical reactions. Such research methods are suitable for extracting, concentrating macro- and microcomponents, as well as for group and individual isolation in the analysis of various natural and industrial objects. These techniques are simple and fast to perform, guarantee excellent concentration and separation efficiency, and are fully compatible with a variety of detection methods. Thanks to extraction, it is possible to consider the state of a component in solution under different conditions, as well as to reveal its physicochemical characteristics.

Sorption

It is used for concentration and separation of substances. Sorption technologies provide good selectivity of mixture separation. This is the process of absorption of vapors, liquids, gases by sorbents (solid-based absorbers).

Carburation and electrowinning

What else does analytical chemistry do? The textbook contains information about the method of electrodischarge, in which a concentrated or separated substance is deposited on solid electrodes in the form of a simple substance or as part of a compound.

Electrolysis is based on the precipitation of a specific substance using an electric current. The most common option is cathodic deposition of low-activity metals. The material for the electrode can be platinum, carbon, copper, silver, tungsten.

electrophoresis

It is based on differences in the speeds of movement of particles of different charges in an electric field with a change in tension, particle size. Currently, two forms of electrophoresis are distinguished in analytical chemistry: simple (frontal) and on a carrier (zone). The first option is suitable for a small volume of solution that contains the components to be separated. It is placed in a tube where there are solutions. Analytical chemistry explains all the processes that occur at the cathode and anode. In zone electrophoresis, the movement of particles is carried out in a stabilizing medium that keeps them in place after the current is turned off.

The carburizing method consists in the restoration of constituent parts on metals that have a significant negative potential. In such a case, two processes occur at once: cathodic (with the release of the component) and anode (the cementing metal dissolves).

Evaporation

Distillation relies on the varying volatility of chemicals. There is a transition from a liquid form to a gaseous state, then it condenses, again turning into a liquid phase.

With simple distillation, a single-stage separation process proceeds, followed by concentration of the substance. In the case of evaporation, those substances that are present in volatile form are removed. For example, among them there may be macro- and micro-components. Sublimation (sublimation) involves the transfer of a substance from a solid phase to a gas, bypassing the liquid form. A similar technique is used in cases where the substances to be separated are poorly soluble in water or melt poorly.

Conclusion

In analytical chemistry, there are many ways to isolate one substance from a mixture, to identify its presence in the sample under study. Chromatography is one of the most used analytical methods. It allows you to detect liquid, gaseous, solid substances having a molecular weight from 1 to 106 a. e. m. Thanks to chromatography, it is possible to obtain complete information about the properties and structure of organic substances of various classes. The method is based on the distribution of components between the mobile and stationary phases. Stationary is a solid substance (sorbent) or a liquid film that is deposited on a solid substance.

The mobile phase is a gas or liquid that flows through the stationary part. Thanks to this technology, it is possible to identify individual components, carry out the quantitative composition of the mixture, and separate it into components.

In addition to chromatography, gravimetric, titrimetric, and kinetic methods are used in qualitative and quantitative analysis. All of them are based on the physical and chemical properties of substances, allow the researcher to detect certain compounds in the sample, and to calculate their quantitative content. Analytical chemistry can rightfully be considered one of the most important branches of science.