TOPIC 1. Forced slaughter, the procedure for its implementation and veterinary examination of forced slaughter meat
The goal is to learn the procedure for performing forced slaughter of animals, conducting veterinary examinations of slaughter products and their use.
1. Study and understand the procedure established by the “Rules for veterinary inspection of slaughter animals and veterinary and sanitary examination of meat and meat products” for performing forced slaughter of animals, conducting veterinary examinations and using slaughter products. Prepare and give answers to test questions:
1) What is meant by forced slaughter of animals, in what cases is slaughter not considered forced and when is it prohibited to subject animals to forced slaughter?
2) The procedure for registration and carrying out forced slaughter and veterinary examination of slaughter products.
3) The procedure for sampling and preparing an accompanying document when sending material to a veterinary laboratory for bacteriological and other studies.
4) What organoleptic characteristics are used to identify carcasses obtained from animals that have died or were in an agonal state?
5) With the help of what laboratory methods research reveals meat obtained from animals that have died or were in a state of agony and what is their essence?
6) The procedure for delivering forced slaughter meat to meat processing plants for neutralization and processing.
7) The procedure for acceptance, examination of meat from forced slaughter at a meat processing plant, its neutralization and processing.
2. Execute laboratory tests samples of forced slaughter meat in order to identify the fact that meat was obtained from an animal that had died or was in a state of agony
a) Perform a peroxidase reaction.
b) Perform a reaction with formaldehyde.
c) Conduct a bacteriscopic examination of meat samples.
d) Determine the pH of meat using colorimetric and potentiometric research methods.
e) Examine meat samples by cooking test.
f) Based on the research performed, give a conclusion on the suitability or unsuitability of meat for food purposes.
The procedure for carrying out forced slaughter of animals and examination of meat in accordance with the “Rules for veterinary examination of slaughter animals and veterinary and sanitary examination of meat and meat products”
In case of forced slaughter of animals at a meat processing plant, slaughterhouse, on farms due to illness or other reasons threatening the life of the animal, as well as in cases requiring long-term, economically unjustified treatment, veterinary and sanitary examination of meat and other slaughter products is carried out in the usual manner . In addition, it is mandatory to carry out bacteriological and, if necessary, physical and chemical research, but with a mandatory cooking test to identify extraneous odors that are unusual for meat.
Forced slaughter of animals is carried out only with the permission of a veterinarian (paramedic).
Pre-slaughter holding of animals delivered to a meat processing plant for forced slaughter is not carried out.
On the reasons for the forced slaughter of animals on farms, a report must be drawn up, signed by a veterinarian. This act and the conclusion of the veterinary laboratory on the results of bacteriological examination of the carcass of a forcibly killed animal, together with a veterinary certificate, must accompany the specified carcass when delivered to the meat processing plant, where it is re-subjected to bacteriological examination.
If an animal is suspected of being poisoned by pesticides or other toxic chemicals, it is necessary to have a conclusion from a veterinary laboratory on the results of testing the meat for the presence of toxic chemicals.
Transportation of meat from forcedly slaughtered animals from farms to meat industry enterprises must be carried out in compliance with current veterinary and sanitary rules for the transportation of meat products.
In order to ensure correct examination of the meat of forcedly killed sheep, goats, pigs and calves, it must be delivered to the meat processing plant in whole carcasses, and the meat of cattle, horses and camels - in whole carcasses, half carcasses and quarters and placed in a separate refrigeration chamber. Half-carcasses and quarters are tagged to determine whether they belong to the same carcass.
Carcasses of pigs forcedly killed on farms must be delivered to the meat processing plant with their heads intact.
When delivering salted meat from animals forcedly killed on farms to a meat processing plant, each barrel must contain corned beef from one carcass.
Carcasses of animals forcedly killed en route without a pre-mortem veterinary examination, delivered to a meat processing plant without a veterinary certificate (certificate), a veterinary act on the reasons for forced slaughter and a conclusion from a veterinary laboratory on the results of a bacteriological examination, are prohibited from being accepted at the meat processing plant.
If, according to the results of examination, bacteriological and physico-chemical research, meat and other products of forced slaughter are found suitable for use as food, then they are sent for boiling, as well as for the production of meat loaves or canned goods “Goulash” and “Meat Pate”.
The release of this meat and other slaughter products in raw form, including into public catering networks (canteens, etc.), without prior disinfection by boiling is prohibited.
Note: Cases of forced slaughter do not include:
slaughter of clinically healthy animals that cannot be fattened to the required standards, are lagging in growth and development, are unproductive, barren, but have a normal body temperature; slaughter of healthy animals that are at risk of death as a result of a natural disaster (snow drifts on winter pastures, etc.), as well as those injured before slaughter at a meat processing plant, slaughterhouse, slaughterhouse; forced slaughter of livestock in meat processing plants is carried out only in a sanitary slaughterhouse.
Selection, packaging and shipment of samples to the veterinary laboratory According to the above rules of veterinary examination, depending on the expected diagnosis and the nature of pathological changes, the following are sent for bacteriological examination:
a part of the flexor or extensor muscle of the front and hind limbs of the carcass, covered with fascia at least 8 cm long, or a piece of another muscle measuring at least 8x6x6 cm;
lymph nodes - from cattle - superficial cervical or axillary and external iliac, and from pigs - superficial cervical dorsal (in the absence of pathological changes in the head and neck area) or axillary of the first rib and patellar;
spleen, kidney, liver lobe with hepatic lymph node (in the absence of a lymph node - gallbladder without bile).
When taking part of the liver, kidney, and spleen, the surface of the incisions is cauterized until a scab forms.
When examining half or quarter carcasses, a piece of muscle, lymph nodes and tubular bone are taken for analysis.
When examining meat from small animals (rabbits, nutria) and poultry, whole carcasses are sent to the laboratory.
When examining salted meat in a barrel container, samples of meat and existing lymph nodes are taken from the top, middle and bottom of the barrel, as well as, if present, tubular bone and brine.
If erysipelas is suspected, in addition to muscles, lymph nodes and internal organs, tubular bone is sent to the laboratory.
For bacteriological examination, the brain, liver lobe and kidney are sent for listeriosis.
If anthrax, emcar, or malignant edema is suspected, a lymph node of the affected organ or a lymph node that collects lymph from the site of the suspicious focus, edematous tissue, exudate, and in pigs, in addition, the mandibular lymph node, is sent for examination.
Samples taken for research with an accompanying document are sent to the laboratory in a moisture-proof container, sealed or sealed. When sending samples for research to the production laboratory of the same enterprise where the samples were taken, there is no need to seal them. The accompanying document indicates the type of animal or product, its affiliation (address), what material is sent and in what quantity, the reason for sending the material for research, what changes have been established in the product, the intended diagnosis and what kind of research is required (bacteriological, physico-chemical, etc.) .d.).
Methods for identifying forced slaughter meat - sick, killed in agony or dead animals
Pathoanatomical and organoleptic examination When determining meat from a sick animal killed in an agonal state or a dead animal, the following must be taken into account external signs: the condition of the cutting site, the degree of bleeding, the presence of hypostases and the color of the lymph nodes on the section.
Condition of the stabbing site . A cut refers to the place where blood vessels are cut during the slaughter of an animal. To create the appearance of a normally slaughtered animal, owners often make cuts in the neck of dead animals, rub blood into the cut site, hang them by the hind legs for better blood drainage, etc.
There are the following differences between the intravital and postmortem incision: the intravital incision is uneven due to muscle contraction, the tissues in the area of the incision are infiltrated (soaked) with blood to a greater extent compared to those lying deeper. The cut made after the death of the animal is more even, the blood almost does not permeate the tissue, and the blood present on the surface of the tissue is easily washed off with water. The tissues in the degree of blood infiltration in the area of the incision do not differ from the tissues located deeper.
Degree of carcass bleeding . Carcasses obtained from sick animals, and especially from animals that were in an agonal state or died, are poorly or very poorly bled. The carcasses are dark red in color; the cuts reveal small and large blood vessels filled with blood. Intercostal vessels appear as dark veins. If you separate the shoulder blade from the carcass, you can find vessels filled with blood.
If you insert a strip of filter paper (10 cm long and 1.5 cm wide) into a fresh cut and leave it there for several minutes, then if bleeding is poor, not only the part of the paper that comes into contact with the meat will become saturated with blood, but also the free its end (this method is not acceptable for thawed meat), adipose tissue has a pink or reddish color.
With good bleeding, the meat is crimson or red, the fat is white or yellow, and there is no blood on the cut muscle. The vessels under the pleura and peritoneum are not translucent; the intercostal vessels look like light strands.
The color of the lymph nodes on the section. Lymph nodes when cut in carcasses of healthy animals and those that were dressed in a timely manner have a light gray or yellowish color. In the meat of animals that are seriously ill, killed in an agonal state, or dead, the lymph nodes on the cut have a lilac-pink color. In addition, depending on the disease in the lymph nodes, their enlargement will be detected, various shapes inflammatory processes, hemorrhage, necrosis, hypertrophy.
Presence of hypostases . By hypostasis we understand the postmortem and premortem redistribution (draining) of blood into the underlying parts of the body during prolonged agony. The tissues on the side of the body on which the sick animal lay are saturated with blood to a greater extent. The same is observed on paired organs (kidneys, lungs). Hypostasis should not be confused with bruising. Bruising occurs in the subcutaneous tissue as a result of disruption of the integrity of blood vessels due to bruises. They are local and superficial in nature, and hypostases are diffuse (diffused) and during hypostases, the deep layers of tissue are also infiltrated with blood. Hypostases can form not only after the death of an animal, but during life. They can form during prolonged agony, when the animal’s cardiac activity is weakened and the blood gradually stagnates in the underlying areas of the body. Thus, the detection of hypostases indicates that the meat was obtained from a dead animal that had lain uncut for a certain time, or from an animal that was in a state of prolonged agony. If the animal was in an agonal state for a short time and was slaughtered, then hypostases may be absent. Therefore, the absence of hypostases is not yet an indicator that the meat was not obtained from a dying animal.
Determining the fact that meat was obtained from animals that were in an agonal state or died is of fundamental importance, since such meat is dangerous to human health and, according to veterinary legislation, is not allowed for food and must be disposed of or destroyed.
Cooking test . Meat obtained from seriously ill, moribund or dead animals can be identified to a certain extent using an organoleptic method, the so-called cooking test. For this purpose 20 gr. chopped meat to the state of minced meat is placed in a 100 ml conical flask, pour 60 ml. distilled water, mix, cover with a watch glass, place in a boiling water bath and heat to 80-85ºС until vapor appears. Then open the lid slightly and determine the smell and condition of the broth. Broth made from the meat of seriously ill, agonizing or dead animals, as a rule, has an unpleasant or medicinal smell, it is cloudy with flakes. Conversely, broth made from the meat of healthy animals has a pleasant, specific meaty smell and is transparent. Taste testing is not recommended.
Physico-chemical research
According to the “Rules for veterinary examination of animals and veterinary and sanitary examination of meat and meat products”, in addition to pathological, organoleptic and bacteriological analysis, meat from forced slaughter, as well as if there is a suspicion that the animal was in a state of agony before slaughter or was dead, must be subjected to physico-chemical research.
Bacterioscopy . Bacterioscopic examination of fingerprint smears from the deep layers of muscles, internal organs and lymph nodes is aimed at preliminary (before obtaining the results of bacteriological examination) detection of pathogens of infectious diseases ( anthrax, emphysematous carbuncle, etc.) and contamination of meat with opportunistic microflora ( coli, Proteus, etc.).
The bacterioscopic examination technique is as follows. Pieces of muscles, internal organs or lymph nodes are cauterized with a spatula or immersed twice in alcohol and set on fire, then using sterile tweezers, a scalpel or scissors, a piece of tissue is cut out from the middle and smears are made on a glass slide. Air-dried, flamed over a burner flame and Gram-stained. The preparation is stained through filter paper with a solution of carbolic gentian violet - 2 minutes, the filter paper is removed, the paint is drained and without washing the preparation it is treated with Lugol's solution - 2 minutes, decolorized with 95% alcohol - 30 seconds, washed with water, counterstained with Pfeiffer fuchsin - 1 minute ., washed again with water, dried and microscopically examined under immersion. In fingerprint smears from the deep layers of meat, internal organs and lymph nodes of healthy animals, there is no microflora.
In case of diseases, rods or cocci are found in fingerprint smears. A complete determination of the detected microflora can be determined in a veterinary laboratory, for which they inoculate on nutrient media, obtain a pure culture and identify it.
pH determination . The pH value of meat depends on the glycogen content in it at the time of slaughter of the animal, as well as on the activity of the intramuscular enzymatic process, which is called meat ripening.
Immediately after slaughter, the reaction of the environment in the muscles is slightly alkaline or neutral - equal to - 7. Within a day, the pH of meat from healthy animals, as a result of the breakdown of glycogen to lactic acid, decreases to 5.6-5.8. In the meat of sick or killed animals in an agonal state, such a sharp decrease in pH does not occur, since the muscles of such animals contain less glycogen (used during illness as an energy substance), and, consequently, less lactic acid is formed and the pH is less acidic, i.e. .e. higher.
Meat from sick and overworked animals is in the range of 6.3-6.5, and agonizing or dead animals are 6.6 and higher, it approaches neutral - 7. It should be emphasized that meat must be aged for at least 24 hours before examination.
The indicated pH values do not have an absolute meaning, they are indicative, auxiliary in nature, since the pH value depends not only on the amount of glycogen in the muscles, but also on the temperature at which the meat was stored and the time elapsed after the slaughter of the animal.
pH is determined by colorometric or potentiometric methods.
Colorimetric method. To determine pH, a Michaelis apparatus is used, which consists of a standard set of colored liquids in sealed test tubes, a comparator (stand) with six test tube sockets and a set of indicators in vials.
First, an aqueous extract (extract) is prepared from muscle tissue in a ratio of 1:4 - one part by weight of muscle and 4 parts of distilled water. To do this, weigh 20 grams. muscle tissue (without fat and connective tissue) is finely chopped with scissors, ground with a pestle in a porcelain mortar, to which a little water is added from a total amount of 80 ml. The contents of the mortar are transferred to a flat-bottomed flask, the mortar and pestle are washed with the remaining amount of water, which is poured into the same flask. The contents of the flask are shaken for 3 minutes, then for 2 minutes. stand and again for 2 minutes. shaken. The extract is filtered through 3 layers of gauze and then through a paper filter.
First, the pH is approximately determined to select the desired indicator. To do this, pour 1-2 ml into a porcelain cup, extract and add 1-2 drops of a universal indicator. The color of the liquid obtained by adding the indicator is compared with the color scale available in the kit. When the environment is acidic, further research use the indicator paranitrophenol; if it is neutral or alkaline, use metanitrophenol. Test tubes of the same diameter made of colorless glass are inserted into the comparator sockets and filled as follows: 5 ml is poured into the first, second and third test tubes of the first row, 5 ml of distilled water is added to the first and third, and 4 ml of water is added to the second. and 1 ml of indicator, 7 ml of water is poured into test tube 5 (middle of the second row), standard sealed test tubes with colored liquid are inserted into the fourth and sixth sockets, selecting them so that the color of the contents in one of them is the same as the color of the middle middle row test tubes. The pH of the extract under study corresponds to the figure indicated on the standard test tube. If the color shade of the liquid in the test tube with the extract under study is intermediate between two standards, then take the average value between the indicators of these two standard test tubes. When using a micro-Michaelis apparatus, the number of reaction components is reduced by 10 times.
Potentiometric method. This method is more accurate, but difficult to implement because it requires constant adjustment of the potentiometer using standard buffer solutions. A detailed description of determining pH by this method is available in the instructions supplied with devices of various designs, and the pH value can be determined using potentiometers both in extracts and directly in muscles.
Peroxidase reaction. The essence of the reaction is that the peroxidase enzyme found in meat decomposes hydrogen peroxide to form atomic oxygen, which oxidizes benzidine. This produces paraquinone diimide, which, when combined with unoxidized benzidine, produces a blue-green compound that turns brown. During this reaction, peroxidase activity is important. In the meat of healthy animals it is very active; in the meat of sick animals and those killed in an agonal state, its activity is significantly reduced.
The activity of peroxidase, like any enzyme, depends on the pH of the medium, although complete correspondence between the benzidine reaction and pH is not observed.
Reaction progress: 2 ml of meat extract (at a concentration of 1:4) is poured into a test tube, 5 drops of a 0.2% alcohol solution of benzidine are added and two drops of a 1% hydrogen peroxide solution are added.
The extract from the meat of healthy animals acquires a blue-green color, turning into brownish-brown after a few minutes (positive reaction). In an extract from the meat of a sick animal or an animal killed in an agonal state, the blue-green color does not appear, and the extract immediately acquires a brown-brown color (negative reaction).
Formol test (test with formalin). In case of severe diseases, even during the life of the animal, significant quantities of intermediate and final products of protein metabolism - polypeptides, peptides, amino acids, etc. - accumulate in the muscles.
The essence of this reaction is the precipitation of these products with formaldehyde. To perform the test, an aqueous extract from meat is required in a 1:1 ratio.
To prepare an extract (1:1), a meat sample is freed from fat and connective tissue and 10 grams are weighed. Then the sample is placed in a mortar, thoroughly crushed with curved scissors, and 10 ml is added. physiological solution and 10 drops of 0.1 N. sodium hydroxide solution. The meat is ground with a pestle. The resulting slurry is transferred using scissors or a glass rod into a flask and heated to boiling to precipitate the proteins. The flask is cooled under running cold water, after which its contents are neutralized by adding 5 drops of a 5% oxalic acid solution and filtered through filter paper. If the extract remains cloudy after filtering, it is filtered a second time or centrifuged. If you need to get a larger amount of extract, take 2-3 times more meat and, accordingly, 2-3 times more other components.
Industrially produced formalin has an acidic environment, so it is first neutralized with 0.1 N. sodium hydroxide solution using an indicator consisting of an equal mixture of 0.2% aqueous solutions of neutralrot and methylene blue until the color changes from violet to green.
Reaction progress: 2 ml of extract is poured into a test tube and 1 ml of neutralized formaldehyde is added. The extract obtained from the meat of an animal killed in agony, seriously ill or dead turns into a dense jelly-like clot. When extracted from the meat of a sick animal, flakes fall out. The extract from the meat of a healthy animal remains liquid and transparent or becomes slightly cloudy.
Sanitary assessment of meat
According to the “Rules for veterinary inspection of slaughter animals and veterinary and sanitary examination of meat and meat products,” meat is considered to be obtained from a healthy animal if there are good organoleptic characteristics of the carcass and the absence of pathogenic microbes.
The organoleptic characteristics of the broth during the cooking test (color, transparency, smell) correspond to fresh meat.
The meat of sick animals, as well as those killed in a state of agony, has insufficient or poor bleeding, lilac-pink or bluish coloration of the lymph nodes. There may be pathogenic microflora in the meat. When you try cooking, the broth is cloudy and with flakes it may have an extraneous odor that is not typical for meat. Additional indicators in this case, there may also be a negative reaction to peroxidase, pH - 6.6 and higher, and for cattle meat, in addition, positive reactions: formol and with a solution of copper sulfate, accompanied by the formation of flakes or a jelly-like clot in the extract. Moreover, before determining the pH, setting up the reaction with peroxidase, formol and with a solution of copper sulfate, the meat must be subjected to maturation for at least 20-24 hours.
If, according to the results of examination, bacteriological and physical-chemical studies, meat and other products of forced slaughter are found suitable for use as food, then they are sent for boiling, according to the regime established by Privila, as well as for the production of meat loaves or canned goods “Goulash” and “ Meat pate."
The release of this meat and other slaughter products in raw form, including into public catering networks (canteens, etc.) without prior disinfection by inspection is prohibited.
Procedure for processing meat and meat products subject to disinfection
According to the Veterinary Sanitary Expertise Rules, meat and meat products of forced slaughter are disinfected by boiling pieces weighing no more than 2 kg, up to 8 cm thick in open boilers for 3 hours, in closed boilers at an excess steam pressure of 0.5 MPa for 2.5 hours.
Meat is considered disinfected if the temperature inside the piece reaches at least 80ºC; When cut, the color of pork becomes white-gray, and the meat of other types of animals becomes gray, without signs of a bloody tint; the juice flowing from the cut surface of a piece of boiled meat is colorless.
At meat processing plants equipped with electric or gas ovens or with canning shops, meat subject to disinfection by boiling is allowed to be sent for the production of meat loaves. When processing meat into meat loaves, the weight of the latter should be no more than 2.5 kg. Bread baking should be carried out at a temperature not lower than 120ºС for 2-2.5 hours, and the temperature inside the product by the end of the baking process should not be lower than 85ºС.
Meat that meets the requirements for raw materials for canned food – “Goulash” and “Meat Pate” – is allowed for the production of canned food.
Physicochemical research as a branch of analytical chemistry has found wide application in every sphere of human activity. They allow you to study the properties of the substance of interest, determining the quantitative composition of the components in the sample.
Substance research
Scientific research is the cognition of an object or phenomenon in order to obtain a system of concepts and knowledge. According to the principle of action, the methods used are classified into:
- empirical;
- organizational;
- interpretative;
- methods of qualitative and quantitative analysis.
Empirical research methods reflect the object under study from the external manifestations and include observation, measurement, experiment, and comparison. Empirical study is based on reliable facts and does not involve the creation of artificial situations for analysis.
Organizational methods - comparative, longitudinal, comprehensive. The first involves comparing the states of an object obtained at different times and under different conditions. Longitudinal - observation of the object of study over a long period of time. Comprehensive is a combination of longitudinal and comparative methods.
Interpretive methods - genetic and structural. The genetic variant involves studying the development of an object from the moment of its origin. The structural method studies and describes the structure of an object.
Analytical chemistry deals with methods of qualitative and quantitative analysis. Chemical studies are aimed at determining the composition of the object of study.
Quantitative analysis methods
Using quantitative analysis in analytical chemistry, the composition is determined chemical compounds. Almost all methods used are based on studying the dependence of chemical and physical properties substances from its composition.
Quantitative analysis can be general, complete or partial. Total determines the amount of all known substances in the object being studied, regardless of whether they are present in the composition or not. A complete analysis is distinguished by finding quantitative composition substances contained in the sample. The partial version determines the content of only the components of interest in this study chemicals.
Depending on the method of analysis, three groups of methods are distinguished: chemical, physical and physicochemical. All of them are based on changes in physical or chemical properties substances.
Chemical research
This method is aimed at identifying substances in various quantitatively occurring chemical reactions. The latter have external manifestations (color change, release of gas, heat, sediment). This method is widely used in many sectors of life. modern society. A chemical research laboratory is a must in the pharmaceutical, petrochemical, construction industries and many others.
Three types of chemical research can be distinguished. Gravimetry, or gravimetric analysis, is based on changes in the quantitative characteristics of the test substance in a sample. This option is simple and gives accurate results, but is labor intensive. With this type of chemical research methods, the required substance is isolated from the general composition in the form of a sediment or gas. Then it is brought into a solid insoluble phase, filtered, washed, and dried. After these procedures, the component is weighed.
Titrimetry is a volumetric analysis. The study of chemical substances occurs by measuring the volume of the reagent that reacts with the substance being studied. Its concentration is known in advance. The volume of the reagent is measured when the equivalence point is reached. Gas analysis determines the volume of gas released or absorbed.
In addition, research is often used chemical models. That is, an analogue of the object being studied is created, which is more convenient to study.
Physical research
Unlike chemical research, which is based on carrying out appropriate reactions, physical methods of analysis are based on the same properties of substances. To carry them out, special devices are required. The essence of the method is to measure changes in the characteristics of a substance caused by the action of radiation. The main methods of carrying out physical research are refractometry, polarimetry, fluorimetry.
Refractometry is carried out using a refractometer. The essence of the method comes down to studying the refraction of light passing from one medium to another. The change in angle depends on the properties of the components of the medium. Therefore, it becomes possible to identify the composition of the medium and its structure.
Polarimetry is which uses the ability of certain substances to rotate the plane of vibration of linearly polarized light.
For fluorimetry, lasers and mercury lamps are used, which create monochromatic radiation. Some substances are capable of fluorescence (absorbing and releasing absorbed radiation). Based on the fluorescence intensity, a conclusion is made about the quantitative determination of the substance.
Physico-chemical research
Physicochemical research methods record changes in the physical properties of a substance under the influence of various chemical reactions. They are based on direct dependence physical characteristics of the object under study from its chemical composition. These methods require the use of some measuring instruments. As a rule, observations are made of thermal conductivity, electrical conductivity, light absorption, boiling and melting points.
Physicochemical studies of the substance have become widespread due to the high accuracy and speed of obtaining results. IN modern world Due to development, the methods have become difficult to apply. Physico-chemical methods are used in the food industry, agriculture, and forensics.
One of the main differences between physicochemical methods and chemical ones is that the end of the reaction (equivalence point) is found using measuring instruments, and not visually.
The main methods of physicochemical research are considered to be spectral, electrochemical, thermal and chromatographic methods.
Spectral methods for analyzing substances
Spectral analysis methods are based on the interaction of an object with electromagnetic radiation. The absorption, reflection, and dispersion of the latter are studied. Another name for the method is optical. It is a combination of qualitative and quantitative research. Spectral analysis allows you to evaluate chemical composition, structure of components, magnetic field and other characteristics of the substance.
The essence of the method is to determine the resonant frequencies at which a substance reacts to light. They are strictly individual for each component. Using a spectroscope, you can see lines in the spectrum and identify the constituent substances. The intensity of the spectral lines gives an idea of quantitative characteristics. The classification of spectral methods is based on the type of spectrum and the purpose of the study.
The emission method allows one to study emission spectra and provides information about the composition of a substance. To obtain data, it is subjected to an electric arc discharge. A variation of this method is flame photometry. Absorption spectra are studied using the absorption method. The above options refer to the qualitative analysis of the substance.
Quantitative spectral analysis compares the intensity of the spectral line of the object under study and a substance of known concentration. Such methods include atomic absorption, atomic fluorescence and luminescence analyses, turbidimetry, and nephelometry.
Fundamentals of electrochemical analysis of substances
Electrochemical analysis uses electrolysis to examine a substance. Reactions are carried out in an aqueous solution on electrodes. One of the available characteristics is subject to measurement. The research is carried out in an electrochemical cell. This is a vessel in which electrolytes (substances with ionic conductivity), electrodes (substances with electronic conductivity). Electrodes and electrolytes interact with each other. In this case, the current is supplied from the outside.
Classification of electrochemical methods
Electrochemical methods are classified based on the phenomena on which physical and chemical studies are based. These are methods with and without the application of extraneous potential.
Conductometry is an analytical method that measures electrical conductivity G. Conductometry analysis typically uses alternating current. Conductometric titration is a more common research method. The production of portable conductometers used for chemical studies of water is based on this method.
When carrying out potentiometry, the EMF of a reversible galvanic cell is measured. The coulometry method determines the amount of electricity consumed during electrolysis. Voltammetry studies the dependence of the current on the applied potential.
Thermal methods for analyzing substances
Thermal analysis is aimed at determining changes in the physical properties of a substance under the influence of temperature. These research methods are performed over a short period of time and with a small amount of the sample being studied.
Thermogravimetry is one of the methods of thermal analysis, which accounts for the registration of changes in the mass of an object under the influence of temperature. This method considered one of the most accurate.
In addition, thermal research methods include calorimetry, which determines the heat capacity of a substance, and enthalpimetry, based on the study of heat capacity. They also include dilatometry, which records the change in the volume of a sample under the influence of temperature.
Chromatographic methods for analyzing substances
The chromatography method is a method of separating substances. There are many main ones: gas, distribution, redox, sediment, ion exchange.
The components in the test sample are separated between the mobile and stationary phases. In the first case we're talking about about liquids or gases. The stationary phase is a sorbent - a solid substance. The components of the sample move in the mobile phase along the stationary phase. The speed and time of passage of components through the last phase is used to judge their physical properties.
Application of physical and chemical research methods
The most important area of physicochemical methods is sanitary-chemical and forensic chemical research. They have some differences. In the first case, accepted hygienic standards are used to evaluate the analysis. They are established by ministries. Sanitary-chemical research is carried out in the manner established by the epidemiological service. The process uses media models that mimic the properties of food products. They also reproduce the operating conditions of the sample.
Forensic chemical research is aimed at the quantitative detection of narcotic, potent substances and poisons in the human body, food products, and medications. The examination is carried out according to a court order.
The vast majority of information about substances, their properties and chemical transformations was obtained through chemical or physicochemical experiments. Therefore, the main method used by chemists should be considered chemical experiment.
The traditions of experimental chemistry have evolved over centuries. Even when chemistry was not an exact science, in ancient times and in the Middle Ages, scientists and artisans, sometimes by accident, and sometimes purposefully, discovered ways to obtain and purify many substances that were used in economic activities: metals, acids, alkalis, dyes and etc. Alchemists contributed greatly to the accumulation of such information (see Alchemy).
Thanks to this, already early XIX V. chemists were well versed in the basics of experimental art, especially the methods of purifying all kinds of liquids and solids, which allowed them to accomplish a lot most important discoveries. And yet, chemistry began to become a science in the modern sense of the word, an exact science, only in the 19th century, when the law of multiple ratios was discovered and atomic-molecular science was developed. Since that time, chemical experiment began to include not only the study of the transformations of substances and methods of their isolation, but also the measurement of various quantitative characteristics.
A modern chemical experiment involves many different measurements. Both the equipment for conducting experiments and chemical glassware have changed. In a modern laboratory you will not find homemade retorts - they have been replaced by standard glass equipment produced by industry and adapted specifically for performing a particular chemical procedure. Working methods have also become standard, which in our time no longer has to be reinvented by every chemist. A description of the best of them, proven by many years of experience, can be found in textbooks and manuals.
Methods for studying matter have become not only more universal, but also much more diverse. An increasingly important role in the work of a chemist is played by physical and physicochemical research methods designed to isolate and purify compounds, as well as to establish their composition and structure.
The classical technique of purifying substances was extremely labor intensive. There are cases where chemists spent years of work isolating an individual compound from a mixture. Thus, salts of rare earth elements could be isolated in pure form only after thousands of fractional crystallizations. But even after this, the purity of the substance could not always be guaranteed.
Modern chromatography methods make it possible to quickly separate a substance from impurities (preparative chromatography) and check its chemical identity (analytical chromatography). In addition, classical but highly improved methods of distillation, extraction and crystallization are widely used to purify substances, as well as such effective modern methods, such as electrophoresis, zone melting, etc.
The task that confronts a synthetic chemist after isolating a pure substance - to establish the composition and structure of its molecules - relates to a large extent to analytical chemistry. With the traditional working technique, it was also very labor-intensive. Almost the only measurement method previously used was elemental analysis, which allows one to establish the simplest formula of a compound.
To determine the true molecular as well as structural formula it was often necessary to study the reactions of a substance with various reagents; isolate the products of these reactions in individual form, in turn establishing their structure. And so on - until, based on these transformations, the structure of the unknown substance became obvious. Therefore, establishing the structural formula of a complex organic compound often took a lot of time, and such work was considered complete if it ended with a counter synthesis - the production of a new substance in accordance with the formula established for it.
This classic method was extremely useful for the development of chemistry in general. Nowadays it is rarely used. As a rule, an isolated unknown substance, after elemental analysis, is studied using mass spectrometry, spectral analysis in the visible, ultraviolet and infrared ranges, as well as nuclear magnetic resonance. For a reasonable derivation of a structural formula, the use of a whole complex of methods is required, and their data usually complement each other. But in a number of cases, conventional methods do not give an unambiguous result, and one has to resort to direct methods of determining the structure, for example, X-ray diffraction analysis.
Physicochemical methods are used not only in synthetic chemistry. They are no less important when studying the kinetics of chemical reactions, as well as their mechanisms. The main task of any experiment to study the rate of a reaction is to accurately measure the time-varying, and usually very small, concentration of the reactant. To solve this problem, depending on the nature of the substance, you can use chromatographic methods, various types of spectral analysis, and electrochemical methods (see Analytical chemistry).
The perfection of technology has reached such high level, that it became possible to accurately determine the rate of even “instantaneous”, as previously believed, reactions, for example, the formation of water molecules from hydrogen cations and anions. With an initial concentration of both ions equal to 1 mol/l, the time of this reaction is several hundred billionths of a second.
Physicochemical research methods are specially adapted for the detection of short-lived intermediate particles formed during chemical reactions. For this purpose, devices are equipped with either high-speed recording devices or attachments that ensure operation at very low temperatures. These methods successfully record the spectra of particles whose lifespan under normal conditions is measured in thousandths of a second, for example, free radicals.
In addition to experimental methods, calculations are widely used in modern chemistry. Thus, the thermodynamic calculation of a reacting mixture of substances makes it possible to accurately predict its equilibrium composition (see Chemical equilibrium).
Molecule-based calculations quantum mechanics and quantum chemistry have become generally accepted and in many cases indispensable. These methods rely on highly complex mathematical apparatus and require the use of the most advanced electronic computers- COMPUTER. They allow you to create models electronic structure molecules that explain the observable, measurable properties of unstable molecules or intermediate particles formed during reactions.
Methods for studying substances developed by chemists and physical chemists are useful not only in chemistry, but also in related sciences: physics, biology, geology. Neither industry nor agriculture, neither medicine nor criminology. Physico-chemical instruments occupy a place of honor in spacecraft, with the help of which the near-Earth space and neighboring planets are explored.
Therefore, knowledge of the basics of chemistry is necessary for every person, regardless of his profession, and the further development of its methods is one of the most important directions of the scientific and technological revolution.
Lecture 9. Basics of quantitative analysis.
1. Classification of methods chemical analysis.
2. Types of gravimetric determinations.
3. General characteristics gravimetric method of analysis.
4. Volumetric titrimetric method of analysis.
5. Calculations in titrimetric analysis.
6. Methods of titrimetric analysis.
D.Z. according to school Pustovalova pp. 181-218.
Classification of methods of chemical analysis.
Number And honest A liz – Col.a. - a set of chemical, physicochemical and physical methods for determining the quantitative ratio of the components that make up the substance being analyzed.
Quantitative analysis methods:
1) chemical (gravimetry, titrimetry, gas analysis);
2) physicochemical method (photometry, electrochemical, chromatographic analysis);
3) physical-spectral: luminescent, etc.
Along with the qualitative analysis of Col. A. is one of the main branches of analytical chemistry. Based on the amount of substance taken for analysis, macro-, semi-micro, micro- and ultra-micro methods of analysis are distinguished. In macromethods, the sample weight is usually >100 mg, solution volume > 10 ml; in ultramicromethods - 1-10 -1, respectively mg and 10 -3 -10 -6 ml(see also Microchemical analysis, Ultramicrochemical analysis) . Depending on the object of study, a distinction is made between inorganic and organic CA, which in turn is divided into elemental, functional, and molecular analysis. Elemental analysis allows you to determine the content of elements (ions), functional analysis - the content of functional (reactive) atoms and groups in the analyzed object. Molecular K. a. involves the analysis of individual chemical compounds characterized by a certain molecular weight. The so-called phase analysis is of great importance - a set of methods for separating and analyzing individual structural (phase) components of heterogeneous systems. In addition to specificity and sensitivity (see Qualitative analysis), important characteristic methods of K. a. - accuracy, that is, the value of the relative error of determination; accuracy and sensitivity in CA. expressed as a percentage.
To the classical chemical methods of CA. include: gravimetric analysis, based on precise measurement of the mass of the substance being determined, and volumetric analysis. The latter includes titrimetric volumetric analysis - methods for measuring the volume of a reagent solution consumed in the reaction with the analyte, and gas volumetric analysis - methods for measuring the volume of analyzed gaseous products (see Titrimetric analysis, Gas analysis) .
Along with classical chemical methods, physical and physicochemical (instrumental) methods of CA are widely used, based on the measurement of optical, electrical, adsorption, catalytic and other characteristics of the analyzed substances, depending on their quantity (concentration). Typically, these methods are divided into the following groups: electrochemical (conductometry, polarography, potentiometry, etc.); spectral or optical (emission and absorption spectral analysis, photometry, colorimetry, nephelometry, luminescent analysis, etc.); X-ray (absorption and emission X-ray spectral analysis, X-ray phase analysis, etc.); chromatographic (liquid, gas, gas-liquid chromatography, etc.); radiometric (activation analysis, etc.); mass spectrometric. The listed methods, while inferior to chemical methods in accuracy, are significantly superior to them in sensitivity, selectivity, and speed of execution. Accuracy of chemical methods of CA. is usually in the range of 0.005-0.1%; errors in determination by instrumental methods are 5-10%, and sometimes significantly more. Sensitivity of some methods K. a. is given below (%):
Volume................................................. ......10 -1
Gravimetric........................................ 10 -2
Emission spectral........................10 -4
Absorption X-ray spectral...... 10 -4
Mass spectrometric........................10 -4
Coulometric......................................... 10 -5
Luminescent........................................ 10 -6 -10 -5
Photometric colorimetric......... 10 -7 -10 -4
Polarographic........................................10 -8 -10 -6
Activation................................................10 -9 -10 -8
When using physical and physicochemical methods, K. a. As a rule, microquantities of substances are required. The analysis can in some cases be performed without destroying the sample; Sometimes continuous and automatic recording of results is also possible. These methods are used to analyze high-purity substances, evaluate product yields, study the properties and structure of substances, etc. See also Electrochemical methods of analysis, Spectral analysis, Chromatography, Kinetic methods of analysis, Nephelometry, Colorimetry, Activation analysis.
1) chemical methods of analysis:
Gravimetric– is based on determining the mass of a substance isolated in pure form or in the form of a compound of known composition.
positive side “+” - gives the result of high strength,
negative side“-” - very labor-intensive work.
Titrimetric -(volumetric) - based on an accurate measurement of the reagent spent on the reaction with a certain component. The reagent is taken in the form of a solution of a certain concentration (titrated solution).
High speed of analysis;
Less accurate result compared to gravimetry.
Depending on the type of reactions occurring during the titration process, the following are distinguished: methods:
Acid-base titration methods,
Reductive titration method,
Deposition method
Complexation.
2) Physico-chemical method- based on the measurement of absorption, transmission, and scattering of light by the solution being determined.
Most photometric methods use assessment of the color intensity of the solution visually or using appropriate instruments.
It is used for a specific component that is part of the analyte in very small quantities;
The accuracy of the method is lower than in gravimetry and titrimetry.
Electrochemical methods- electrogravimetric analysis, conductometry, potentiometry and polarography.
Chromatographic method- based on the use of the phenomenon of selective adsorption of a solution of a substance and ions various substances or adsorbents: Al 2 O 3, silica gel, starch, talc,
permutide, synthetic resins and other substances.
Application: both in quantitative analysis and qualitative analysis, especially widely used for the determination of substances and ions.
Analysis of a substance can be carried out to determine its qualitative or quantitative composition. In accordance with this, a distinction is made between qualitative and quantitative analysis.
Qualitative analysis makes it possible to establish what chemical elements the analyzed substance consists of and what ions, groups of atoms or molecules are included in its composition. When studying the composition of an unknown substance qualitative analysis always precedes the quantitative one, since the choice of method for quantitative determination of the constituent parts of the analyzed substance depends on the data obtained from its qualitative analysis.
Qualitative chemical analysis is mostly based on the transformation of the analyte into some new compound that has characteristic properties: color, a certain physical state, crystalline or amorphous structure, specific odor, etc. The chemical transformation that occurs is called a qualitative analytical reaction, and the substances that cause this transformation are called reagents (reagents).
When analyzing a mixture of several substances that are similar in chemical properties, they are first separated and only then characteristic reactions into individual substances (or ions), so qualitative analysis covers not only individual ion detection reactions, but also methods for their separation.
Quantitative analysis allows you to establish quantitative relationships between parts of this connection or mixtures of substances. Unlike qualitative analysis, quantitative analysis makes it possible to determine the content of individual components of the analyte or the total content of the analyte in the product under study.
Methods of qualitative and quantitative analysis that make it possible to determine the content of individual elements in the analyzed substance are called elements of analysis; functional groups- functional analysis; individual chemical compounds characterized by a certain molecular weight - molecular analysis.
A set of various chemical, physical and physicochemical methods for separating and determining individual structural (phase) components of heterogeneous systems that differ in properties and physical structure and limited from each other by interfaces is called phase analysis.
Methods of qualitative analysis
In qualitative analysis, the characteristic chemical or physical properties of that substance are used to determine the composition of the substance under study. There is absolutely no need to isolate the discoverable elements in their pure form in order to detect their presence in the analyzed substance. However, the isolation of pure metals, nonmetals and their compounds is sometimes used in qualitative analysis to identify them, although this method of analysis is very difficult. To detect individual elements, simpler and more convenient methods of analysis are used, based on chemical reactions characteristic of the ions of these elements and occurring under strictly defined conditions.
An analytical sign of the presence of the desired element in the analyzed compound is the release of a gas with a specific odor; in the other, the formation of a precipitate characterized by a certain color.
Reactions occurring between solids and gases. Analytical reactions can occur not only in solutions, but between solid and also gaseous substances.
An example of a reaction between solids is the reaction of the release of metallic mercury when its dry salts are heated with sodium carbonate. The formation of white smoke when ammonia gas reacts with hydrogen chloride can serve as an example of an analytical reaction involving gaseous substances.
Reactions used in qualitative analysis can be divided into the following groups.
1. Precipitation reactions accompanied by the formation of precipitation of various colors. For example:
CaC2O4 - white
Fe43 - blue,
CuS - brown - yellow
HgI2 - red
MnS - nude - pink
PbI2 - golden
The resulting precipitates may differ in a certain crystalline structure, solubility in acids, alkalis, ammonia, etc.
2. Reactions accompanied by the formation of gases with a known odor, solubility, etc.
3. Reactions accompanied by the formation of weak electrolytes. Among such reactions, as a result of which are formed: CH3COOH, H2F2, NH4OH, HgCl2, Hg(CN)2, Fe(SCN)3, etc. Reactions of the same type can be considered reactions of acid-base interaction, accompanied by the formation of neutral water molecules, reactions of the formation of gases and poorly soluble precipitates in water, and complexation reactions.
4. Reactions of acid-base interaction, accompanied by the transfer of protons.
5. Complexation reactions accompanied by the addition of various legends - ions and molecules - to the atoms of the complexing agent.
6. Complexation reactions associated with acid-base interaction
7. Oxidation - reduction reactions, accompanied by the transfer of electrons.
8. Oxidation-reduction reactions associated with acid-base interaction.
9. Oxidation - reduction reactions associated with complex formation.
10. Oxidation - reduction reactions, accompanied by the formation of precipitation.
11. Ion exchange reactions occurring on cation exchangers or anion exchangers.
12. Catalytic reactions used in kinetic methods of analysis
Wet and dry analysis
Reactions used in qualitative chemical analysis are most often carried out in solutions. The analyte is first dissolved, and then the resulting solution is treated with appropriate reagents.
To dissolve the analyzed substance, use distilled water, acetic and mineral acids, aqua regia, aqueous solution ammonia, organic solvents, etc. The purity of the solvents used is important to obtain correct results.
The substance transferred into solution is subjected to systematic chemical analysis. A systematic analysis consists of a series of preliminary tests and sequential reactions.
Chemical analysis of test substances in solutions is called wet analysis.
In some cases, substances are analyzed dry, without transferring them into solution. Most often, such an analysis comes down to testing the ability of a substance to color a colorless burner flame in a characteristic color or impart a certain color to the melt (the so-called pearl) obtained by heating the substance with sodium tetraborate (borax) or sodium phosphate ("phosphorus salt") in a platinum ear. wire.
Chemical and physical method of qualitative analysis.
Chemical methods of analysis. Methods for determining the composition of substances based on the use of their chemical properties are called chemical methods of analysis.
Chemical methods of analysis are widely used in practice. However, they have a number of disadvantages. Thus, to determine the composition of a given substance, it is sometimes necessary to first separate the component being determined from foreign impurities and isolate it in its pure form. Isolating substances in their pure form is often a very difficult and sometimes impossible task. In addition, to determine small amounts of impurities (less than 10-4%) contained in the analyzed substance, it is sometimes necessary to take large samples.
Physical methods of analysis. The presence of one or another chemical element can be detected in a sample without resorting to chemical reactions, based directly on the study of the physical properties of the substance under study, for example, the coloring of a colorless burner flame in characteristic colors by volatile compounds of certain chemical elements.
Analysis methods that can be used to determine the composition of the substance under study without resorting to chemical reactions are called physical methods of analysis. Physical methods of analysis include methods based on the study of optical, electrical, magnetic, thermal and other physical properties of the substances being analyzed.
The most widely used physical methods of analysis include the following.
Spectral qualitative analysis. Spectral analysis is based on the observation of emission spectra (emission or emission spectra) of the elements that make up the substance being analyzed.
Luminescent (fluorescent) qualitative analysis. Luminescent analysis is based on the observation of luminescence (emission of light) of analytes caused by the action of ultraviolet rays. The method is used to analyze natural organic compounds, minerals, medications, a number of elements, etc.
To excite the glow, the substance under study or its solution is irradiated with ultraviolet rays. In this case, the atoms of the substance, having absorbed a certain amount of energy, go into an excited state. This condition is characterized large supply energy than the normal state of matter. When a substance transitions from an excited to a normal state, luminescence occurs due to excess energy.
Luminescence that decays very quickly after cessation of irradiation is called fluorescence.
By observing the nature of the luminescent glow and measuring the intensity or brightness of the luminescence of a compound or its solutions, one can judge the composition of the substance under study.
In some cases, determinations are made based on the study of fluorescence resulting from the interaction of the substance being determined with certain reagents. Luminescent indicators are also known, used to determine the reaction of the environment by changes in the fluorescence of the solution. Luminescent indicators are used in the study of colored media.
X-ray diffraction analysis. Using X-rays, you can determine the sizes of atoms (or ions) and their relative position in the molecules of the sample under study, i.e. it turns out to be possible to determine the structure of the crystal lattice, the composition of the substance and sometimes the presence of impurities in it. The method does not require chemical treatment of the substance or large quantities.
Mass spectrometric analysis. The method is based on the determination of individual ionized particles rejected electromagnetic field to a greater or lesser extent depending on the ratio of their mass to charge (for more details, see book 2).
Physical methods of analysis, having a number of advantages over chemical ones, in some cases make it possible to solve problems that cannot be resolved by methods of chemical analysis; Using physical methods, it is possible to separate elements that are difficult to separate by chemical methods, as well as to continuously and automatically record readings. Very often, physical methods of analysis are used along with chemical ones, which makes it possible to use the advantages of both methods. The combination of methods is especially important when determining minute amounts (traces) of impurities in analyzed objects.
Macro, semi-micro and micro methods
Analysis of large and small quantities of the test substance. In the past, chemists used for analysis large quantities test substance. In order to determine the composition of a substance, samples of several tens of grams were taken and dissolved in a large volume of liquid. This required chemical containers of appropriate capacity.
Currently, chemists make do with small quantities of substances in analytical practice. Depending on the amount of the analyte, the volume of solutions used for analysis, and mainly on the experimental technique used, analysis methods are divided into macro-, semi-micro- and micromethods.
When performing an analysis using the macromethod, to carry out the reaction, take several milliliters of a solution containing at least 0.1 g of the substance, and add at least 1 ml of the reagent solution to the test solution. Reactions are carried out in test tubes. During precipitation, voluminous sediments are obtained, which are separated by filtration through funnels with paper filters.
Droplet analysis
Technique for carrying out reactions in droplet analysis. The so-called drop analysis, introduced into analytical practice by N. A. Tananaev, has acquired great importance in analytical chemistry.
When working with this method great value have the phenomena of capillarity and adsorption, with the help of which it is possible to open and separate different ions when they are present together. In droplet analysis, individual reactions are carried out on porcelain or glass plates or on filter paper. In this case, a drop of the test solution and a drop of the reagent that causes characteristic coloring or the formation of crystals are applied to the plate or paper.
When performing the reaction on filter paper, the capillary adsorption properties of the paper are used. The liquid is absorbed by the paper, and the resulting colored compound is adsorbed onto a small area of the paper, resulting in an increased sensitivity of the reaction.
Microcrystalloscopic analysis
The microcrystalloscopic method of analysis is based on the detection of cations and anions through a reaction that results in the formation of a compound with a characteristic crystal shape.
Previously, this method was used in qualitative microchemical analysis. Currently it is also used in droplet analysis.
A microscope is used to examine the formed crystals in microcrystalloscopic analysis.
Crystals of a characteristic shape are used when working with pure substances by adding a drop of a solution or a crystal of a reagent to a drop of the test substance placed on a glass slide. After some time, clearly visible crystals of a certain shape and color appear.
Powder grinding method
To detect certain elements, the method of grinding a powdered analyte with a solid reagent in a porcelain plate is sometimes used. The element being opened is detected by the formation of characteristic compounds that differ in color or smell.
Analysis methods based on heating and fusion of matter
Pyrochemical analysis. For the analysis of substances, methods based on heating the test solid or its fusion with appropriate reagents are also used. When heated, some substances melt at a certain temperature, others sublimate, and on the cold walls of the device precipitation characteristic of each substance appears; some compounds decompose when heated, releasing gaseous products, etc.
When the analyte is heated in a mixture with appropriate reagents, reactions occur that are accompanied by a change in color, the release of gaseous products, and the formation of metals.
Spectral qualitative analysis
In addition to the method described above for observing with the naked eye the coloring of a colorless flame when a platinum wire with an analyzed substance is introduced into it, other methods of studying light emitted by incandescent vapors or gases are currently widely used. These methods are based on the use of special optical instruments, the description of which is given in the physics course. In this kind of spectral devices, light with different wavelengths emitted by a sample of a substance heated in a flame is decomposed into a spectrum.
Depending on the method of observing the spectrum, spectral instruments are called spectroscopes, with the help of which the spectrum is visually observed, or spectrographs, in which the spectra are photographed.
Chromatographic method analysis
The method is based on the selective absorption (adsorption) of individual components of the analyzed mixture by various adsorbents. Adsorbents are called solids, on the surface of which the adsorbed substance is absorbed.
The essence of the chromatographic method of analysis is briefly as follows. A solution of a mixture of substances to be separated is passed through a glass tube (adsorption column) filled with an adsorbent.
Kinetic methods of analysis
Methods of analysis based on measuring the reaction rate and using its value to determine the concentration are combined under the general name of kinetic methods of analysis (K. B. Yatsimirsky).
Qualitative detection of cations and anions by kinetic methods is performed quite quickly and relatively simply, without the use of complex instruments.
