Back at the beginning of the 16th century. an important truth was established: medicinal properties each plant is determined by its chemical composition, that is, the presence in it of certain substances that have a certain effect on the human body. As a result of the analysis of numerous facts, it was possible to identify certain pharmacological properties and a spectrum of therapeutic action of many groups of chemical compounds called active ingredients... The most important of them are alkaloids, cardiac glycosides, triterpene glycosides (saponins), flavonoids (and other phenolic compounds), coumarins, quinones, xangones, sesquiterpene lactones, lignans, amino acids, polysaccharides and some other compounds. Of the 70 groups of natural compounds known now, we are often interested in only a few groups with biological activity. This limits our choices and thus speeds up the search for the natural chemicals we need. For example, antiviral activity possess only a few groups of flavonoids, xanthones, alkaloids, terpenoids and alcohols; antineoplastic- some alkaloids, cyanides, triterpene ketones, diterpenoids, polysaccharides, phenolic compounds, etc. Polyphenolic compounds are characterized by hypotensive, antispasmodic, antiulcer, choleretic and bactericidal activity. Many classes of chemical compounds and individual chemical substances have a strictly defined and rather limited spectrum of biomedical activity. Others, usually very extensive classes, such as alkaloids, have a very wide, varied spectrum of action. Such compounds deserve a versatile medical and biological study, and above all in the directions of interest to us and recommended. The advances in analytical chemistry have made it possible to develop simple and fast methods (express methods) for identifying chemical compounds and individual chemical substances in the classes (groups) we need. As a result of this, the method of mass chemical analysis, otherwise called chemical screening (from the English word screening - sifting, sorting through a sieve), arose and was widely introduced into the practice of prospecting work. It is often practiced to find the desired chemical compounds by analyzing all plants in the area under study.
For the first time on a large scale chemical screening method when looking for new medicinal plants PS Massagetov, the head of the Central Asian expeditions of the All-Union Scientific Research Chemical-Pharmaceutical Institute (VNIHFI), began to use it. A survey of more than 1,400 plant species allowed Academician A.P. Orekhov and his students by 19G0 to describe about 100 new alkaloids and organize in the USSR the production of those that are necessary for medical purposes and the fight against agricultural pests. The Institute of Chemistry of Plant Substances of the Academy of Sciences of the Uzbek SSR examined about 4000 species of plants, identified 415 alkaloids, and for the first time established the structure of 206 of them. The VILR expeditions examined 1498 plant species of the Caucasus, 1026 species of the Far East, many plants of Central Asia, Siberia, and the European part of the USSR. In the Far East alone, 417 alkaloid-bearing plants have been found, including the semi-shrub securinega containing the new alkaloid securinine, a strychnine-like agent. By the end of 1967, the structure of 4349 alkaloids had been described and established worldwide. The next stage of the search is in-depth comprehensive assessment of pharmacological, chemotherapeutic and antitumor activity isolated individual substances or total preparations containing them. It should be noted that in the country as a whole and on a global scale, chemical research is significantly ahead of the possibilities of deep medical and biological testing of new chemical compounds identified in plants. At present, the structure of 12,000 individual compounds isolated from plants has been established; unfortunately, many of them have not yet been subjected to biomedical studies. Of all the classes of chemical compounds, the alkaloids are undoubtedly the most important; 100 of them are recommended as important medicines, for example, atropine, berberine, codeine, cocaine, caffeine, morphine, papaverine, pilocarpine, platifillin, reserpine, salsolin, secuurenine, strychnine, quinine, cytisine, ephedrine, etc. Most of these drugs are obtained from the result of searches based on chemical screening. However, the one-sided development of this method is alarming, in many institutes and laboratories reduced to the search for only alkaloid plants.It should not be forgotten that, in addition to alkaloids, new biologically active plant substances belonging to other classes of chemical compounds are discovered every year. If until 1956 the structure of only 2669 natural compounds from plants that did not belong to alkaloids was known, then in the next 5 years (1957-1961), another 1754 individual organic substances were found in plants. Now the number of chemical substances with an established structure reaches 7000, which, together with alkaloids, is over 12,000 plant substances. Chemical screening slowly emerges from the "alkaloid period". Of the 70 groups and classes of plant substances currently known (Karrer et. Al., 1977), it is carried out only in 10 classes of compounds, because there are no reliable and fast express methods for determining the presence of other compounds in plant raw materials. The involvement of new classes of biologically active compounds in chemical screening is an important reserve for increasing the rate and efficiency of the search for new drugs from plants. It is very important to develop methods for quickly searching for individual chemicals, for example, berberine, rutin, ascorbic acid, morphine, cytisine, etc. Secondary compounds, or the so-called substances of specific biosynthesis, are of the greatest interest in the creation of new medicinal preparations. Many of them have a wide spectrum of biological activity. For example, alkaloids are approved for use in medical practice as analeptics, analgesics, sedatives, antihypertensives, expectorants, choleretic, antispasmodic, uterine, central nervous system tonic and adrenaline-like drugs. Flavonoids are able to strengthen the walls of capillaries, lower the tone of intestinal smooth muscles, stimulate the secretion of bile, increase the detoxifying function of the liver, some of them have antispasmodic, cardiotonic and antitumor effects. Many polyphenolic compounds are used as antihypertensive, antispasmodic, antiulcer, choleretic and antibacterial agents. Antitumor activity was noted in cyanides (for example, contained in peach seeds, etc.), triterpene ketones, diterpenoids, polysaccharides, alkaloids, phenolic and other compounds. More and more drugs are created from cardiac glycosides, amino acids, alcohols, coumarins. polysaccharides, aldehydes, sesquiterpene lactones, steroid compounds. Often medical use find long-known chemical substances, in which only recently it was possible to detect one or another medico-biological activity and to develop a rational method for the manufacture of drugs. Chemical screening allows not only to outline new promising objects for study, but also: 
The chemical composition of each plant organ also varies considerably in different phases of its development. The maximum content of some substances is observed in budding phase, others - in full flowering phase, third - during fruiting etc. For example, the alkaloid triacanthin is contained in significant quantities only in the blossoming leaves of the trichoid gledichia, while in other phases of development it is practically absent in all organs of this plant. Thus, it is easy to calculate that to identify, for example, only a complete list of alkaloid plants in the flora of the USSR, numbering about 20,000 species, it is necessary to do at least 160,000 analyzes (20,000 species X 4 organs X 2 phases of development), which will require about 8000 days of work of 1 laboratory assistant-analyst. Approximately the same amount of time must be spent to determine the presence or absence of flavonoids, coumarins, cardiac glycosides, tannins, polysaccharides, triterpene glycosides and every other class of chemical compounds in all plants of the flora of the USSR, if analyzes are carried out without preliminary culling of plants for one reason or another. In addition, the same organs in the same phase of plant development in one region may have the necessary active substances, and in another region they may not. In addition to geographical and environmental factors (the influence of temperature, humidity, insolation, etc.), the presence of this plant special chemical races, completely indistinguishable by morphological characteristics. All this greatly complicates the task and, it would seem, makes the prospects for the completion of a preliminary chemical assessment of the flora of the USSR, and even more so of the entire globe, very remote. However, knowledge of certain patterns can greatly simplify this work. First, it is not at all necessary to examine all organs at all stages of development. It is enough to analyze each organ in the optimal phase, when it contains the largest amount of the investigated substance. For example, previous studies have established that leaves and stems are richest in alkaloids during the budding phase, the bark - during the spring sap flow, and flowers - in the phase of their full blooming. Fruits and seeds, however, may contain different alkaloids and in different quantities in a mature and immature state, and therefore, if possible, they should be examined twice. Knowledge of these regularities greatly simplifies the work on the preliminary chemical assessment of plants. Complete examination of all types- the method is effective, but still it is a blind job! Is it possible, without carrying out even the simplest chemical analysis, to distinguish groups of plants, presumably containing one or another class of chemical compounds, from those obviously not containing these substances? In other words, is it possible to determine the chemical composition of plants by eye? As will be discussed in the next section of our brochure, in general terms, we can answer this question in the affirmative. The properties of all plant organisms and the internal structures inherent in individual species are determined by the multifaceted, constantly changing environmental influences. The influence of factors such as climate, soil, as well as the cycle of substances and energy is significant. Traditionally, to identify the properties of medicinal products or food products, the proportions of substances that can be isolated analytically are determined. But these separately taken substances cannot cover all the intrinsic properties, for example, of medicinal and aromatic plants. Therefore, such descriptions of individual properties of plants cannot satisfy all our needs. An exhaustive description of the properties of herbal medicinal preparations, including biological activity, requires a comprehensive, comprehensive study. There are a number of techniques that allow you to identify the quality and quantity of biologically active substances in the composition of the plant, as well as the places of their accumulation.
Luminescence microscopic analysis It is based on the fact that biologically active substances contained in a plant give a bright colored glow in a luminescent microscope, and different chemical substances are characterized by different colors. So, alkaloids give a yellow color, and glycosides - orange. This method is mainly used to identify places of accumulation of active substances in plant tissues, and the intensity of the luminescence indicates a greater or lesser concentration of these substances. Phytochemical analysis is designed to identify a qualitative and quantitative indicator of the content of active substances in easthenia. Chemical reactions are used to determine the quality. The amount of active substances in a plant is the main indicator of its good quality, therefore, their volumetric analysis is also carried out using chemical methods. For the study of plants containing active substances such as alkaloids, coumarins,
glavones, which require not a simple summary analysis, but also their separation into components, are called chromatographic analysis. Chromatographic analysis method was first introduced in 1903 by a botanist
Color, and since then its various options have been developed, which have an independent
meaning. This method of separating a mixture of g-ceetv into components is based on the distinction in their physical and chemical properties. Photographically, with the help of panorama chromatography, it is possible to make visible internal structure plants, see the lines, shapes and colors of the plant. Such paintings, obtained from aqueous extracts, are retained on silvery-nitrate filter paper and reproduced. The method of interpreting chromatograms is being successfully developed. This technique is supported by data obtained using other already known proven techniques.
On the basis of circulating chromo diagrams, the development of a panoramic chromatography method is continuing to determine the quality of a plant by the presence of nutrients concentrated in it. The results obtained using this method should be supported by the data of the analysis of the level of acidity of the plant, the interaction of enzymes contained in its composition, etc. , storage and at the stage of direct receipt of dosage forms in order to increase the content of valuable active substances in it.
Updated: 2019-07-09 22:27:53
Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.
Introduction
1. Analysis of soils
2. Analysis of plants
3. Analysis of fertilizers
Conclusion
Bibliography
Introduction
Agronomic chemistry studies Ch. arr. nitrogen and mineral nutrition s.-kh. plants in order to increase yields and improve production. Thus, a. NS. examines the composition of the agricultural. plants, soil, fertilizers and the processes of their mutual influence. Likewise, she studies the processes of making fertilizers and substances used for pest control, and also develops methods of chemical. analysis of agronomic objects: soil, plants and products obtained from them, etc. The microbiological processes of the soil are especially significant. In this area, a. NS. comes into contact with soil science and general agriculture. On the other hand, as well. NS. relies on plant physiology and comes into contact with it, since a. NS. studies the processes occurring during germination, nutrition, maturation of seeds, etc., and uses the methods of water, sand and soil crops. In their research, agronomists-chemists, using Ch. arr. chem. methods, of which physicochemical methods have recently been especially widely used, at the same time must master the technique of artificial cultures and bacteriological research methods. Due to the complexity and variety of tasks a. x., some groups of questions previously included in a. x., have become independent disciplines.
This applies to chemistry, which studies the chemical composition of plants, mainly agricultural crops. and technical, as well as to biological chemistry and biological physics, which study the processes of a living cell.
1 . Analysissoils
Features of the soil as an object of chemical research and indicators of the chemical state of soils
Soil is a complex subject of research. The complexity of studying the chemical state of soils is due to the peculiarities of their chemical properties and is associated with the need to obtain information that adequately reflects the properties of soils and provides the most rational solution to both theoretical issues of soil science and issues of practical use of soils. A wide range of indicators is used to quantitatively describe the chemical state of soils. It includes indicators determined during the analysis of almost any objects and developed specifically for soil research (exchange and hydrolytic acidity, indicators of the group and fractional composition of humus, the degree of saturation of soils with bases, etc.)
The peculiarities of soil as a chemical system are heterogeneity, polychemism, dispersion, heterogeneity, change and dynamics of properties, buffering capacity, as well as the need to optimize soil properties.
Polychemism of soils... In soils, the same chemical element can be a part of various compounds: readily soluble salts, complex aluminosilicates, organomineral substances. These components have different properties, which, in particular, determine the ability of a chemical element to pass from solid to liquid phases of soil, migrate in the soil profile and in the landscape, be consumed by plants, etc. Therefore, in the chemical analysis of soils, not only the total content of chemical elements is determined, but also indicators characterizing the composition and content of individual chemical compounds or groups of compounds with similar properties.
Soil heterogeneity. In the composition of the soil, solid, liquid, and gas phases are distinguished. When studying the chemical state of the soil and its individual components, indicators are determined that characterize not only the soil as a whole, but also its individual phases. Developed by mathematical models, allowing to assess the relationship between the levels of partial pressure of carbon dioxide in the soil air, pH, carbonate alkalinity and calcium concentration in the soil solution.
Polydispersity of soils. The solid phases of the soil consist of particles of various sizes from grains of sand to colloidal particles with a diameter of several micrometers. They are not the same in composition and have different properties. In special studies of the genesis of soils, indicators of the chemical composition and other properties of individual granulometric fractions are determined. The dispersion of soils is associated with their ability to ion exchange, which in turn is characterized by a specific set of indicators - the capacity of cation and anion exchange, the composition of exchangeable cations, etc. Many chemical and physical properties soil.
Acid-base and redox properties of soils. The composition of soils includes components that exhibit properties acids and bases, oxidizing and reducing agents. At solving various theoretical and applied problems soil science, agrochemistry, land reclamation determine the indicators, characterizing the acidity and alkalinity of soils, their redox state.
Inhomogeneity, variability, dynamics, buffering of chemical properties of soils. Soil properties are not the same even within the same genetic horizon. When researching soil profile formation processes are assessed chemical properties of individual elements of the organization of soil masses. Soil properties vary in space, change in time and at the same time the soil has the ability resist changing their properties, that is, they show buffering. Indicators and methods for characterizing variability have been developed, dynamics, buffering properties of soils.
Changing soil properties. Various processes continuously occur in soils that lead to changes in the chemical properties of soils. Practical application is found for indicators characterizing the direction, severity, speed of processes occurring in soils; the dynamics of changes in the properties of soils and their regimes are investigated. The variability of the composition of soils. Different types and even types and varieties of soils can have such different properties that not only different analytical methods are used for their chemical characterization, but also different sets of indicators. So, in podzolic, soddy-podzolic, gray forest soils, the pH of water and salt suspensions, exchangeable and hydrolytic acidity are determined, exchange bases are displaced from the soil aqueous solutions salts. When analyzing saline soils, the pH of only aqueous suspensions is determined, and instead of acidity indicators, total, carbonate and other types of alkalinity are determined. The listed features of soils largely determine the fundamental foundations of methods for studying the chemical state of soils, the nomenclature and classification of indicators of the chemical properties of soils and chemical soil processes.
System of indicators of the chemical state of soils
Group 1... Indicators of properties of soils and soil components
Subgroups:
1. Indicators of the composition of soils and soil components;
2. Indicators of the mobility of chemical elements in soils;
3. Indicators of acid-base properties of soils;
4. Indicators of ion-exchange and colloidal-chemical properties of soils;
5. Indicators of the redox properties of soils;
6. Indicators of catalytic properties of soils;
Group 2... Indicators of chemical soil processes
Subgroups:
1. Indicators of the direction and severity of the process;
2. Indicators of the speed of the process.
Principles for Determining and Interpreting Indicator Levels
The results of the analysis of soils contain information on the properties of soils and soil processes and, on this basis, allow solving the problem facing the researcher. Methods for interpreting the levels of indicators depend on the methods of their determination. These methods can be divided into two groups. The methods of the first group make it possible to assess its properties without changing the chemical state of the soil. The second group consists of methods based on the chemical treatment of the analyzed soil sample. The purpose of this treatment is to reproduce chemical equilibria, which are carried out in real soil, or to knowingly violate the relationships that have developed in soils and extract from the soil a component, the amount of which makes it possible to assess the chemical property of the soil or the process taking place in it. This stage of the analytical process - chemical treatment of a sample of soil - reflects the main feature of the research method and determines the methods of interpreting the levels of most of the determined indicators.
Preparation of soil samples from the investigated areas
Soil samples should be taken using cores with a diameter of about 10 mm to a depth of 10-20 cm. It is better to pre-sterilize the cores in boiling water (100 0 С). For soil analysis, mixed soil samples are taken to the depth of the cultivated layer. As a rule, it is sufficient to draw up one mixed sample for a plot of up to 2 ha. A mixed sample is made up of 15-20 individual soil samples taken evenly over the entire area of the site. Samples for soil analysis are not taken immediately after the introduction of mineral and organic fertilizers, lime. Each mixed sample weighing 500 g is packed in a cloth or polyethylene bag and marked.
Soil preparation for agrochemical analysis
Preparation of an analytical sample is a critical operation that ensures the reliability of the results obtained. Carelessness and errors in sample preparation and average sampling are not compensated for by subsequent high-quality analytical work. Soil samples taken in the field or in a growing house are pre-dried in air at room temperature. Storage of raw samples leads to significant changes in their properties and composition, especially as a result of enzymatic and microbiological processes. On the contrary, thermal overheating is accompanied by a change in the mobility and solubility of many compounds.
If there are many samples, then drying is carried out in cabinets with forced ventilation. Determination of nitrates, nitrites, absorbed ammonium, water-soluble forms of potassium, phosphorus, etc. carried out on the day of sampling at their natural humidity. The rest of the determinations are carried out in air-dry samples. Dry samples are ground in a soil mill or in a porcelain mortar with a rubber tipped pestle. The ground and dried sample is passed through a sieve with a hole diameter of 2-3 mm. Rubbing and sieving is carried out until all of the sample taken passes through the sieve. Only fragments of stones, large roots and foreign inclusions are allowed to be discarded. Samples are stored in closed craft bags in a chemical-free room. A sample of soil for analysis is taken by the "average sample" method. For this, the sieved sample is scattered in a thin layer (about 0.5 cm) on a sheet of paper in the form of a square and divided into small squares with a spatula with a side of 2-2.5 cm. Part of the sample is taken from each square with a spatula.
The main agrochemical indicators of soil analysis, without which no land cultivation can do, are the content of humus, mobile forms of phosphorus, nitrogen and potassium, soil acidity, the content of calcium, magnesium, as well as trace elements, including heavy metals. Modern methods of analysis make it possible to determine 15-20 elements in one sample. Phosphorus belongs to macronutrients. According to the availability of mobile phosphates, soils are distinguished with a very low content - less than mg., Low - less than 8 mg., Medium - 8 - 15 mg. and high - more than 15 mg. phosphates per 100 g of soil. Potassium. For this element, gradations have been developed for the content of mobile forms in the soil: very low - up to 4 mg, low - 4-8 mg, medium - 8-12 mg, increased - 12-17 mg, high - more than 17 mg. exchangeable potassium per 100 g of soil. Soil acidity - characterizes the content of hydrogen protons in the soil. This indicator is expressed by the pH value.
Soil acidity affects plants not only through the direct effect of toxic hydrogen protons and aluminum ions on plant roots, but also through the nature of the intake of nutrients. Aluminum cations can bind with phosphoric acid, transforming phosphorus into a form inaccessible to plants.
The negative effect of low acidity is reflected in the soil itself. When hydrogen protons are displaced from the soil absorbing complex (AUC) of calcium and magnesium cations, which stabilize the soil structure, the soil granules are destroyed and the soil structure is lost.
Distinguish between actual and potential soil acidity. The actual acidity of the soil is due to the excess of the concentration of hydrogen protons over hydroxyl ions in the soil solution. Potential soil acidity includes hydrogen protons bound to AUC. To judge the potential acidity of the soil, the pH of the salt extract (pH KCl) is determined. Depending on the pH value of KCl, soil acidity is distinguished: up to 4 - very strongly acidic, 4.1-4.5 - strongly acidic, 4.6-5.0 - moderately acidic, 5.1-5.5 - slightly acidic, 5.6- 6.0 is close to neutral and 6.0 is neutral.
Soil analysis for heavy metals and radiation analysis are classified as rare analyzes.
Receiving water solution soil.
Solutions of substances contained in the soil are obtained in many ways, which in principle can be divided into two groups: - obtaining a soil solution; - obtaining an aqueous extract from the soil. In the first case, unbound or weakly bound soil moisture is obtained - the one that is contained between the soil particles and in the soil capillaries. This is a weakly saturated solution, but its chemical composition is relevant for a plant, since it is this moisture that washes the roots of plants and it is in it that the exchange of chemicals takes place. In the second case, soluble chemical compounds associated with its particles are washed out from the soil. The output of salt into the water extract depends on the ratio of soil and solution and increases with an increase in the temperature of the extraction solution (up to certain limits, since too high a temperature can destroy any substances or transfer them to a different state) and an increase in the volume of the solution and the degree of soil fineness ( to certain limits, since too fine dusty particles can make it difficult or impossible to extract and filter the solution).
The soil solution is obtained using a number of tools: pressure, centrifugation, displacement of liquid by immiscible solution, vacuum filtration method and lysimetric method.
Pressing is carried out with a soil sample taken from the field in laboratory conditions... The more solution needed, the larger the sample should be, or the higher the applied pressure, or both.
Centrifugation is carried out at 60 rpm for a long time. The method is ineffective and is suitable for soil samples with a moisture content close to the total possible moisture content of a given soil. For overdried soil, this method is not applicable.
The displacement of soil moisture by a substance that does not mix with the soil solution makes it possible to obtain virtually all soil moisture, including capillary moisture, without the use of sophisticated equipment. Alcohol or glycerin is used as a displacing fluid. The inconvenience is that these substances, in addition to their high density, have a good extracting ability with respect to some compounds (for example, alcohol easily extracts soil organic matter), therefore, overestimated indicators of the content of a number of substances can be obtained in comparison with their actual content in the soil solution. The method is not suitable for all soil types.
In the vacuum filtration method, a vacuum is created above the sample with the help of a vacuum, which exceeds the tension level of the soil moisture. In this case, capillary moisture is not extracted, since the tensile forces in the capillary are higher than the tensile forces of the surface of the free liquid.
The lysimetric method is used in the field. The lysimetric method allows not so much to assess the gravitational moisture (that is, moisture capable of moving through the soil layers due to the force of gravity - with the exception of capillary moisture), as to compare the content and migration of chemical elements of the soil solution. Free soil moisture is filtered through the soil horizon by gravitational forces to the sampler located on the soil surface.
To get a more complete picture of the chemical composition of the soil, prepare a soil extract. To obtain it, a soil sample is crushed, passed through a sieve with cells with a diameter of 1 mm, water is added in a mass ratio of 1 part of soil to 5 parts of bidistilled (purified from any impurities, degassed and deionized) water, pH 6.6 - 6.8, temperature 20 0 C. Degassing is carried out in order to free water from admixtures of dissolved gaseous carbon dioxide, which, when combined with some substances, gives an insoluble precipitate, reducing the accuracy of the experiment. Impurities of other gases can also have a negative impact on the results of the experiment.
For more accurate weighing of the sample, one should take into account its natural humidity, field (for a freshly taken sample) or hygroscopic (for a dried and stored sample). Determined as a percentage of the mass of the sample, its moisture content is converted into mass and added to the required mass. The weighed portion is placed in a dry flask with a volume of 500-750 ml, water is added. The flask with the soil sample and water is tightly stopped and shaken for two to three minutes. Next, the resulting solution is filtered through an ash-free folded paper filter. It is important that there are no volatile acid vapors in the room (it is preferable to work under draft, where acid solutions are not stored). Before filtering, the solution with the soil is shaken well so that the small particles of soil close the largest pores of the filter and the filtrate is more transparent. Approximately 10 ml of the initial filtrate is discarded as it contains impurities from the filter. Filtration of the rest of the primary filtrate is repeated several times. The work on determining the content of chemicals in the aqueous extract begins immediately after its receipt, since over time chemical processes occur that change the alkalinity of the solution, its oxidizability, etc. Already the filtration rate can show the relative total content of salts in the solution. If the water extract is rich in salts, then the filtration will take place quickly and the solution will turn out to be transparent, since the salts prevent the peptization of soil colloids. If the solution is poor in salts, filtration will be slow and not very high quality. In this case, it makes sense to filter the solution several times, despite the low speed, because with additional filtration, the quality of the water extract increases due to a decrease in the content of soil particles in it.
Methods for the quantitative analysis of extracts or any other solutions obtained in the course of soil analysis.
In most cases, the interpretation of soil analysis results does not depend on the measurement method. In the chemical analysis of soils, almost any of the methods available to analysts can be used. In this case, either the directly sought-for value of the indicator is measured, or the value functionally related to it. The main sections of chem. analysis of soils: gross, or elemental, analysis - allows you to find out the total content of C, N, Si, Al, Fe, Ca, Mg, P, S, K, Na, Mn, Ti and other elements in the soil; analysis of water extract (the basis for the study of saline soils) - gives an idea of the content of water-soluble substances in the soil (sulfates, chlorides and carbonates of calcium, magnesium, sodium, etc.); determination of the absorptive capacity of the soil; identification of soil nutrient supply - the amount of readily soluble (mobile), assimilated by plants compounds of nitrogen, phosphorus, potassium, etc. is established. Much attention is paid to the study of the fractional composition of soil organic matter, forms of compounds of the main soil components, including trace elements.
In the laboratory practice of soil analysis, classical chemical and instrumental methods are used. The most accurate results can be obtained using classical chemical methods. The relative determination error is 0.1-0.2%. The error of most instrumental methods is much higher - 2-5%
Among the instrumental methods in soil analysis, electrochemical and spectroscopic ones are most widely used. Among the electrochemical methods, potentiometric, conductometric, coulometric and voltammetric methods are used, including all modern varieties of polarography.
To assess the soil, the results of the analyzes are compared with the optimal levels of the content of elements experimentally established for a given type of soil and tested in working conditions, or with the data available in the literature on the provision of soils with macro- and microelements, or with the maximum permissible concentration of the studied elements in the soil. After that, a conclusion is made about the condition of the soil, recommendations are given on its use, the doses of ameliorants, mineral and organic fertilizers for the planned harvest are calculated.
When choosing a measurement method, the features of the chemical properties of the analyzed soil, the nature of the indicator, the required accuracy of determining its level, the possibilities of measurement methods and the feasibility of the required measurements under the conditions of the experiment are taken into account. In turn, the measurement accuracy is determined by the purpose of the study and the natural variability of the studied property. Accuracy is a collective characteristic of a method that evaluates the correctness and reproducibility of the analysis results obtained.
The ratio of the levels of some chemical elements in soils.
Different levels of content and different chemical properties of elements do not always make it advisable to use the same measurement method to quantify the entire required set of elements.
In elemental (gross) analysis of soils, methods with different detection limits are used. To determine chemical elements, the content of which exceeds tenths of a percent, it is possible to use classical methods of chemical analysis - gravimetric and titrimetric.
Different properties of chemical elements, different levels of their content, the need to determine different indicators of the chemical state of an element in soil make it necessary to use measurement methods with different detection limits.
Soil acidity
The determination of soil response is one of the most common analyzes in both theoretical and applied research. The most complete picture of the acidic and basic properties of soils is formed with the simultaneous measurement of several indicators, including titratable acidity or alkalinity - the capacity factor and pH - the intensity factor. The capacity factor characterizes the total content of acids or bases in soils, the buffering capacity of soils, the stability of the reaction in time and in relation to external influences depend on it. The intensity factor characterizes the strength of the instantaneous action of acids or bases on the soil and plants; the flow of minerals into plants in a given period of time depends on it. This allows a more correct assessment of soil acidity, since in this case the total amount of hydrogen and aluminum ions present in the soil in free and absorbed states is taken into account. Actual acidity (pH) is determined potentiometrically. Potential acidity is determined by converting hydrogen and aluminum ions into solution when treating the soil with an excess of neutral salts (KCl):
The amount of free hydrochloric acid formed is judged on the exchangeable acidity of the soil. Some of the H + ions remain in the absorbed state (the strong HCl formed as a result of p-iris completely dissociates and the excess of free H + in the solution prevents their complete displacement from the PPC). The less mobile part of H + ions can be transferred into solution only with further soil treatment with solutions of hydrolytically alkaline salts (CH 3 COONa).
The hydrolytic acidity of the soil is judged by the amount of free acetic acid formed. In this case, hydrogen ions most completely pass into the solution (are displaced from the PPC), since the resulting acetic acid firmly binds hydrogen ions and the reaction shifts to the right up to the complete displacement of hydrogen ions from the PPC. The value of hydrolytic acidity is equal to the difference between the results obtained with soil treatment with CH 3 COONa and KCl. In practice, the result obtained by treating the soil with CH 3 COONa is taken as the value of hydrolytic acidity.
The acidity of the soil is determined not only by hydrogen ions, but also by aluminum:
Aluminum hydroxide precipitates, and the system is practically no different from the one that contains only absorbed hydrogen ions. But even if AlCl% remains in solution, then during titration
АlСl 3 + 3 NaOH = А (ОН) 3 + 3 NaCl
which is equivalent to a reaction
3 НСl + 3 NaOH = 3 NaCl + 3 Н 2 O. The absorbed aluminum ions are also displaced when the soil is treated with a CH 3 COONa solution. In this case, all of the displaced aluminum passes into the precipitate in the form of hydroxide.
According to the degree of acidity, determined in the salt extract 0.1N. KKCl potentiometrically, soils are divided into:
Determination of pH, exchangeable acidity and mobilealuminum according to Sokolov
Determination of exchangeable acidity is based on the displacement of 1.0 N hydrogen and aluminum ions from PPC. KKCl solution:
The resulting acid is titrated with alkali and the exchangeable acidity is calculated due to the sum of hydrogen and aluminum ions. Al is precipitated with 3.5% NaF solution.
Repeated titration of the solution allows you to determine the acidity due only to hydrogen ions.
The difference between the data of the first and second titration is used to calculate the aluminum content in the soil.
Analysis progress
1. On a technical balance, take a weighed portion of 40 g of air-dry soil using the average sample method.
2. Transfer the sample to a conical flask with a capacity of 150-300 ml.
3. Add 100 ml 1.0 N from the burette. KCl (pH 5.6-6.0).
4. Shake on a rotator for 1 hour or shake for 15 minutes. and leave overnight.
5. Filter through a funnel with dry pleated paper, discarding the first portion of the filtrate.
6. In the filtrate, determine the pH value potentiometrically.
7. To determine exchangeable acidity, pipette 25 ml of the filtrate into a 100 ml Erlenmeyer flask.
8. Boil the filtrate on a burner or hot plate for 5 minutes. on hourglass to remove carbon dioxide.
9. Add 2 drops of phenolphthalein to the filtrate and titrate with a hot solution of 0.01 or 0.02 N. alkali solution (KOH or NaOH) to a stable pink color - 1st titration.
10. In another Erlenmeyer flask, take 25 ml of the filtrate with a pipette, boil for 5 minutes, cool in a water bath to room temperature.
11.Pipette 1.5 ml of 3.5% sodium fluoride solution into the cooled filtrate, mix.
12. Add 2 drops of phenolphthalein and titrate with 0.01 or 0.02 N. alkali solution until slightly pink color - 2nd titration.
Calculation
1. Exchangeable acidity due to hydrogen and aluminum ions (according to the results of the 1st titration) in meq per 100 g of dry soil:
where: P - dilution 100/25 = 4; H is the weight of the soil in grams; K is the coefficient of soil moisture; ml KOH - the amount of alkali used for titration; n. KOH - alkali normality.
2 Calculation of acidity due to hydrogen ions is the same, but according to the results of the second titration, after the deposition of aluminum.
* When determining these indicators in moist soil, the percentage of moisture is simultaneously determined.
Reagents
1. Solution 1 n. KCl, 74.6 g of chemically pure grade. Dissolve KCl in 400-500 ml of distilled water, transfer to a 1 L volumetric flask and bring to the mark. The pH of the reagent should be 5.6-6.0 (check before starting the analysis - if necessary, set the desired pH value by adding a 10% KOH solution)
2. 0.01 or 0.02 n. a KOH or NaOH solution is prepared from a weighed portion of the reagent or fixanal.
3. 3.5% solution of sodium fluoride, prepared in distilled water without CO 2 (boil distilled water, evaporating to 1/3 of the original volume).
Methods for determining priority pollutants in soils
Separately, in view of the urgency and importance of the problem, mention should be made of the need to analyze heavy metals in soils. Revealing of soil pollution with heavy metals is carried out by direct methods of sampling soil samples in the studied territories and their chemical analysis. A number of indirect methods are also used: visual assessment of the state of phytogenesis, analysis of the distribution and behavior of species - indicators among plants, invertebrates and microorganisms. It is recommended to take samples of soils and vegetation along the radius from the source of pollution, taking into account the prevailing winds along the route 25-30 km long. The distance from the pollution source to reveal the pollution halo can vary from hundreds of meters to tens of kilometers. Determining the toxicity level of heavy metals is not easy. This level will not be the same for soils with different textures and organic matter content. The proposed MPC for mercury - 25 mg / kg, arsenic - 12-15, cadmium - 20 mg / kg. Some destructive concentrations of a number of heavy metals in plants (g / million) have been established: lead - 10, mercury - 0.04, chromium - 2, cadmium - 3, zinc and manganese - 300, copper - 150, cobalt - 5, molybdenum and nickel - 3, vanadium - 2. Cadmium... In solutions of acidic soils, it is present in the forms Cd 2+, CdCl +, CdSO 4, alkaline soils - Cd 2+, CdCl +, CdSO 4, CdHCO 3. Cadmium ions (Cd 2+) make up 80-90% of the total amount in solution, except for those soils that are contaminated with chlorides and sulfates. In this case, 50% of the total amount of cadmium is CdCl + and CdSO 4. Cadmium is prone to active bioconcentration, which leads in a short time to its excess in bioavailable concentrations. Thus, cadmium, in comparison with other heavy metals, is the most potent soil toxicant. Cadmium does not form its own minerals, but is present in the form of impurities, most of it in soils is represented by exchangeable forms (56-84%). Cadmium practically does not bind with humic substances. Lead. Soils are characterized by less soluble and less mobile forms of lead in comparison with cadmium. The content of this element in the water-soluble form is 1.4%, in the exchangeable form - 10% of the gross; more than 8% of lead is associated with organic matter, most of this amount is fulvates. 79% of lead is associated with the mineral component of the soil. Concentrations of lead in soils of background regions of the world are 1-80 mg / kg. The results of many years of world research have shown an average lead content in soils of 16 mg / kg. Mercury. Mercury is the most toxic element in natural ecosystems. The Hg 2+ ion can be present in the form of individual organomercury compounds (methyl-, phenyl-, ethylmercury, etc.). The Hg 2+ and Hg + ions can be bound to minerals as part of their crystal lattice. At low pH values of the soil suspension, most of the mercury is sorbed by organic matter, and as the pH increases, the amount of mercury bound to soil minerals increases.
Lead and cadmium
To determine the content of lead and cadmium in objects of the natural environment at the background level, the method of atomic absorption spectrophotometry (AAS) is most widely used. The AAS method is based on the atomization of the analyte transferred into solution in a graphite cell in an inert gas atmosphere and the absorption of the resonance line of the emission spectrum of the hollow cathode lamp of the corresponding metal. The absorption of lead is measured at a wavelength of 283.3 nm, cadmium at a wavelength of 228.8 nm. The analyzed solution goes through the stages of drying, ashing and atomization in a graphite cell using high-temperature heating by electric current in an inert gas flow. The absorption of the resonance line of the emission spectrum of the lamp with a hollow cathode of the corresponding element is proportional to the content of this element in the sample. With electrothermal atomization in a graphite cuvette, the detection limit for lead is 0.25 ng / ml, cadmium is 0.02 ng / ml.
Solid soil samples are transferred to a solution as follows: 5 g of air-dry soil is placed in a quartz cup, 50 ml of concentrated nitric acid is poured, carefully evaporated to a volume of approximately 10 ml, 2 ml of 1N. nitric acid solution. The sample is cooled and filtered. The filtrate is diluted to 50 ml with bidistilled water in a volumetric flask. An aliquot of the sample 20 μl is introduced into a graphite cuvette with a micropipette and the concentration of the element is measured.
Mercury
The most selective and highly sensitive method for determining the mercury content in various natural objects is the cold vapor atomic absorption method. Soil samples are mineralized and dissolved with a mixture of sulfuric and nitric acids. The resulting solutions are analyzed by atomic absorption. The mercury in solution is reduced to metallic mercury and, with the aid of an aerator, mercury vapor is fed directly into the cell of the atomic absorption spectrophotometer. The detection limit is 4 μg / kg.
Measurements are carried out as follows: the equipment is brought into operation, the microprocessor is turned on, a dissolved sample of 100 ml is poured into the sample, then 5 ml of a 10% tin chloride solution is added and the aerator with a plug on the thin section is immediately inserted. The maximum reading of the spectrophotometer is recorded, according to which the concentration is calculated.
2. Plant analysis
Analysis of plants allows you to solve the following problems.
1. To investigate the transformation of macro- and microelements in the soil-plant-fertilizer system under different modes of plant cultivation.
2. Determine the content of the main biocomponents in plant objects and feed: proteins, fats, carbohydrates, vitamins, alkaloids and the compliance of their content with the accepted norms and standards.
3. Assess the measure of the suitability of plants for the consumer (nitrates, heavy metals, alkaloids, toxicants).
Selection plant sample
The selection of a plant sample is a crucial stage of work, it requires certain skills and experience. Errors in sampling and preparation for analysis are not compensated for by high-quality analytical processing of the collected material. The basis in the selection of samples of plants in agro- and biocenoses is the method of the average sample. In order for the average sample to reflect the status of the entire set of plants, take into account the macro- and microrelief, hydrothermal conditions, the uniformity and density of plants, and their biological characteristics.
Plant samples are taken in dry weather, in the morning, after the dew has dried. When studying metabolic processes in plants in dynamics, these hours are observed throughout the growing season.
Distinguish between crops of continuous sowing: wheat, oats, barley, cereals, grasses, etc. and row crops: potatoes, corn, beets, etc.
For solid sowing crops, 5-6 plots with a size of 0.25-1.00 m 2 are allocated evenly on the experimental plot, the plants from the plot are mowed at a height of 3-5 cm. The total volume of material taken is a combined sample. After carefully averaging this sample, take an average 1 kg sample. The average sample is weighed, and then the botanical composition is analyzed, weeds and diseased plants are taken into account, which are excluded from the sample.
Plants are divided into organs with weight accounting in the sample of leaves, stems, ears, flowers, ears. Young plants do not differentiate by organs and are fixed entirely. For row crops, especially high-stalk crops such as corn, sunflower, etc. the combined sample is made up of 10-20 medium-sized plants taken along the diagonal of the plot or alternately in non-adjacent rows.
When selecting root crops, 10-20 medium-sized plants are dug up, cleaned of soil, dried, weighed, the aboveground organs are separated and the roots are weighed.
The average sample is made taking into account the size of tubers, ears, baskets, etc. To do this, the material is sorted visually into large, medium, small and, accordingly, the fractional participation of the fraction is an average sample. In high-stemmed crops, the sample can be averaged due to the longitudinal dissection of the entire plant from top to bottom.
The criterion for assessing the correct sampling is the convergence of the results of chemical analysis in parallel determinations. The rate of chemical reactions in plant samples taken during the active growing season is much higher than in many analyzed objects. Due to the work of enzymes, biochemical processes continue, as a result of which the decomposition of substances such as starch, proteins, organic acids and especially vitamins occurs. The task of the researcher is to minimize the time from taking a sample to analyzing or fixing plant material. A decrease in the rate of reactions can be achieved by working with fresh plants in the cold in a climatic chamber (+ 4 ° C), as well as short storage in a household refrigerator. In fresh plant material at natural humidity, water-soluble forms of proteins, carbohydrates, enzymes, potassium, phosphorus are determined, and the content of nitrates and nitrites is determined. With a small margin of error, these determinations can be carried out in plant samples after freeze drying.
In fixed air-dry samples, all macronutrients are determined, i.e. ash composition of plants, total content of proteins, carbohydrates, fats, fiber, pectin substances. Drying plant samples to an absolutely dry weight for analysis is unacceptable, since the solubility and physicochemical properties of many organic compounds are disturbed, and irreversible denaturation of proteins occurs. When analyzing the technological properties of any objects, drying at a temperature of no more than 30 ° C is allowed. Elevated temperatures change the properties of protein-carbohydrate complexes in plants and distort the determination results.
Fixation of plant material
The preservation of organic and ash substances in plant samples in quantities close to their natural state is carried out due to fixation. Temperature fixation and freeze drying are used. In the first case, the stabilization of the composition of plants is carried out due to inactivation of enzymes, in the second - due to sublimation, while the plant enzymes remain in an active state, proteins do not denature. Temperature fixation of plant material is carried out in a drying oven. The plant material is placed in kraft paper bags and loaded into an oven preheated to 105-110 ° C. After loading, maintain a temperature of 90-95 ° C for 10-20 minutes, depending on the properties of the plant material. With this temperature treatment due to water vapor, plant enzymes are inactivated. At the end of the fixation, the plant material should be moist and lethargic, while it should retain its color. Further drying of the sample is carried out with air access in open bags at a temperature of 50-60 ° C for 3-4 hours. The specified temperature and time intervals should not be exceeded. Prolonged heating at high temperatures leads to thermal decomposition of many nitrogen-containing substances and caramelization of plant carbohydrates. Plant samples with a high water content - roots, fruits, berries, etc. divided into segments so that the peripheral and central parts of the fetus are included in the analysis. The set of segments for the sample is made up of segments of large, medium and small fruits or tubers in their respective proportions in the harvest. Segments of the medium sample are crushed and fixed in enameled cuvettes. If the samples are bulky, then the aerial part of the plants is crushed immediately before fixation and quickly closed in bags. If the samples are supposed to contain only a set of chemical elements, they can be dried rather than fixed at room temperature. It is better to dry the plant material in a thermostat at a temperature of 40-60 0 С, since at room temperature the mass can rot and be contaminated with dust particles from the atmosphere. Samples of grain and seeds are not subjected to temperature fixation, but they are dried at a temperature not exceeding 30 ° C. Lyophilization of plant material (drying by sublimation) is based on the evaporation of ice bypassing the liquid phase. Drying of the material during lyophilization is carried out as follows: the selected plant material is frozen to a solid state, filling the sample with liquid nitrogen. Then the sample is placed in a lyophilizer, where it is dried at low temperature and under vacuum conditions. In this case, moisture is absorbed by a special desiccant (reagent), which is used as silica gel, calcium chloride, etc. Freeze drying inhibits enzymatic processes, but the enzymes themselves are preserved.
Grinding of plant samples and their storage.
Grinding of plants is carried out in an air-dry state. The grinding speed increases if the samples are pre-dried in a thermostat. The absence of hygroscopic moisture in them is determined visually: fragile stems and leaves that break easily in hands are the most suitable material for grinding
For grinding bulk samples weighing more than 30 g, laboratory mills are used, for grinding small samples, household coffee grinders are used. In very small quantities, plant samples are ground in a porcelain mortar and then passed through a sieve. The crushed material is sieved through a sieve. The hole diameter depends on the specific analysis: from 1 mm to 0.25 mm. Part of the material that has not passed through the sieve is re-ground in a mill or in a mortar. "Discarding" of plant material is not allowed as this changes the composition of the average sample. With a large volume of ground samples, the volume can be reduced by going from an average laboratory sample to an average analytical one, the weight of the latter is 10-50 g, and for grain at least 100 g. Selection is made by quartering. Spread the laboratory sample evenly on paper or glass in a circle or square. The spatula is divided into small squares (1-3 cm) or segments. Material from non-adjacent squares is taken into an analytical sample.
Determination of various substances in plant material
Determination of water-soluble forms of carbohydrates
The content of carbohydrates and their diversity are determined by the plant species, developmental phase and abiotic environmental factors and vary widely. There are quantitative methods for the determination of monosaccharides: chemical, polarimetric. The determination of polysaccharides in plants is carried out by the same methods, but, first, the oxygen bond (-O-) of these compounds is destroyed in the process of acid hydrolysis. One of the main methods of determination, the Bertrand method, is based on the extraction of soluble carbohydrates from plant material with hot distilled water. In one part of the filtrate, monosaccharides are determined, in the other - after hydrolysis with hydrochloric acid - di- and trisaccharides, which decompose to glucose
Determination of potassium, phosphorus, nitrogen is based on the reactions of hydrolysis and oxidation of organic substances of plants with strong oxidants (a mixture of sulfuric and chloric to-t). The main oxidizing agent is perchloric acid (HClO 4). Nitrogen-free organic substances are oxidized to water and carbon dioxide, releasing ash elements in the form of oxides. Nitrogen-containing organic compounds are hydrolyzed and oxidized to water and carbon dioxide, release nitrogen in the form of ammonia, which is immediately bound by sulfuric acid. Thus, the solution contains ash elements in the form of oxides and nitrogen in the form of ammonium sulfate and ammonium salt of perchloric acid. The method eliminates the loss of nitrogen, phosphorus and potassium in the form of their oxides, since the plant matter is exposed at a temperature of 332 ° C. This is the boiling point of sulfuric acid; perchloric acid has a much lower boiling point - 121 ° C.
Definitioncontent of nitrates and nitrites... Plants accumulate nitrates and nitrites in large quantities. These compounds are toxic to humans and animals, especially nitrites, the toxicity of which is 10 times higher than nitrates. Nitrites in humans and animals convert the ferrous iron of hemoglobin to ferric iron. The resulting methaemoglobin is unable to carry oxygen. Strict control over the content of nitrates and nitrites in crop products is required. A number of methods have been developed to determine the content of nitrates in plants. The most widespread is the ionometric express method. Nitrates are extracted with a solution of potassium alum with subsequent measurement of the concentration of nitrates in the solution using an ion-selective electrode. The sensitivity of the method is 6 mg / dm 3. The limit of determination of nitrates in a dry sample is 300 ml -1, in a wet sample - 24-30 ml -1. Let us dwell in more detail on the analysis of total nitrogen in plants.
Determination of total nitrogen according to Kbeldal
A higher nitrogen content is observed in generative organs, especially in grain, and its concentration is lower in leaves, stems, roots, roots, and very little in straw. Total nitrogen in a plant is represented by two forms: protein nitrogen and nitrogen of non-protein compounds. The latter includes nitrogen, which is part of amides, free amino acids, nitrates and ammonia.
The protein content in plants is determined by the amount of protein nitrogen. The protein nitrogen content (in percent) is multiplied by a factor of 6.25 in the analysis of vegetative organs and root crops and by 5.7 in the analysis of grain. The share of non-protein forms of nitrogen accounts for 10-30% of the total nitrogen in vegetative organs, and not more than 10% in grain. The content of non-protein nitrogen by the end of the growing season decreases, therefore, in production conditions, its share is neglected. In this case, the total nitrogen (in percent) is determined and its content is converted to protein. This indicator is called "crude protein" or protein. Method principle... A sample of plant material is ashed in a Kjeldahl flask with concentrated sulfuric acid in the presence of one of the catalysts (metal selenium, hydrogen peroxide, perchloric acid, etc.). The ashing temperature is 332 ° C. In the process of hydrolysis and oxidation of organic matter, nitrogen in the flask remains in solution in the form of ammonium sulfate.
The ammonia is distilled off in a Kjeldahl apparatus when the solution is heated and boiled.
In an acidic environment, there is no hydrolytic dissociation of ammonium sulfate, the partial pressure of ammonia is zero. In an alkaline medium, the equilibrium is shifted, and ammonia is formed in the solution, which easily evaporates when heated.
2NH 4 OH = 2NH 3 * 2H 2 0.
Ammonia is not lost, but passes through the refrigerator first in the form of a gas, and then, condensing, drops into the receiver with titrated sulfuric acid and binds with it, again forming ammonium sulfate:
2NH 3 + H 2 SO 4 = (NH 4) 2 S0 4.
An excess of acid, not associated with ammonia, is titrated with an alkali of a precisely established normality using a combined indicator or methylroth.
Analysis progress
1. On an analytical balance, take a sample of plant material? 0.3-0.5 ± 0 0001 g using a test tube (by the difference between the weight of the test tube with the sample and the weight of the test tube with material residues) and putting a rubber tube 12- length on the end of the test tube. 15 cm, carefully lower the sample to the bottom of the Kjeldahl flask. Pour 10-12 ml of concentrated sulfuric acid (d = 1.84) into the flask with a small cylinder. Uniform ashing of plant material begins already at room temperature, so it is better to leave acid-filled weighed portions overnight.
2. Put the flasks on an electric stove and carry out gradual combustion, first over low heat (put asbestos), then over high, periodically gently shaking. When the solution becomes homogeneous, add the catalyst (a few crystals of selenium or a few drops of hydrogen peroxide) and continue burning until the solution is completely discolored.
Catalysts... The use of catalysts contributes to an increase in the boiling point of sulfuric acid and an acceleration of ashing. Various modifications of the Kjeldahl method use metallic mercury and selenium, potassium sulfate, copper sulfate, and hydrogen peroxide. It is not recommended to use perchloric acid as a catalyst for combustion alone or in a mixture with sulfuric acid. The rate of oxidation of the material is ensured in this case not due to an increase in temperature, but due to the rapid evolution of oxygen, which is accompanied by losses of nitrogen during ashing.
3. Distillation of ammonia... After the end of combustion, the Kjeldahl flask is cooled and distilled water is carefully poured into it along the walls, the contents are mixed and the neck of the flask is rinsed. The first portion of water is poured up to the neck and quantitatively transferred into a 1 liter round-bottomed flask. The Kjeldahl flask is washed another 5-6 times with small portions of hot distilled water, each time pouring the washing water into a stripping flask. Fill the stripping flask with wash water to 2/3 of the volume and add 2-3 drops of phenolphthalein. A small amount of water makes it difficult for vaporization during distillation, and a large amount can cause the transfer of boiling water to the refrigerator.
4. In a conical flask or beaker with a capacity of 300-400 ml (receiver) pour from a burette 25-30 ml 0.1 N. H 2 SO 4 (with an accurately established titer), add 2-3 drops of methylroth indicator or Groak's reagent (purple color). The tip of the condenser tube is immersed in acid. The stripping flask is placed on the heater and connected to the refrigerator, checking the tightness of the connection. For the destruction of ammonium sulfate and ammonia stripping, a 40% alkali solution is used, taken in such a volume that is four times the volume of concentrated sulfuric acid taken during the combustion of the sample
The essence of agronomic chemistry. Soil features, system of indicators of chemical composition, principles of determination and interpretation. Methods for determining priority pollutants. Analysis of plants. Determination of types and forms of mineral fertilizers.
term paper, added 03/25/2009
Fertilizer classification methods. Features of storage and handling of mineral fertilizers, requirements for their quality. Mandatory labeling of mineral fertilizers. Calculation of doses of mineral fertilizers for the active substance. Fertilization technique.
tutorial, added 06/15/2010
Monitoring, soil classification. Method for determining hygroscopic soil moisture, exchangeable acidity. Determination of total alkalinity and alkalinity due to carbonate ions. Complexometric determination of the gross iron content in soils.
task added on 11/09/2010
Methods for the determination of iron in soils: atomic absorption and complexometric. The ratio of groups of iron compounds in different soils. Methods for the determination of mobile forms of iron using ammonium thiocyanate. Standard solutions for analysis.
test, added 12/08/2010
Substances, mainly salts, which contain nutrients necessary for plants. Nitrogen, phosphorus and potash fertilizers. The value and use of all factors that determine the high effect of fertilizers, taking into account agrometeorological conditions.
abstract added on 12/24/2013
Composition and properties of basic nitrogen fertilizers. Potash fertilizers, their characteristics. Highland, lowland and transitional peat. The importance of the production of mineral fertilizers in the country's economy. Technological process production. Environmental protection.
term paper, added 12/16/2015
A review of the development of the method for the determination of nitrogen in steel. Characteristics of the liquid metal nitrogen analyzer system of the multi-lab nitris system. Features of the Nitris Probe Tip Immersed in Liquid Steel. Analysis of the stages of the nitrogen measurement cycle.
test, added 05/03/2015
abstract, added 01/23/2010
general characteristics mineral fertilizers. Technological scheme for the production of ammonium nitrate at JSC "Acron". Drawing up material and heat balance... Determination of the temperature of the process, the final concentration of nitrate; product properties.
practice report, added 08/30/2015
Features of measuring the composition of substances and materials. Detailed description of the techniques for determining the unknown concentration in instrumental methods of analysis. Generalized interpretation of physical and chemical analysis as an independent scientific discipline.
FEDERAL EDUCATION AGENCY
VORONEZH STATE UNIVERSITY
INFORMATION AND ANALYTICAL SUPPORT OF ENVIRONMENTAL ACTIVITIES IN AGRICULTURE
Study guide for universities
Compiled by L.I. Brekhova L.D. Stakhurlova D.I. Shcheglov A.I. Thunderman
VORONEZH - 2009
Approved by the Scientific and Methodological Council of the Faculty of Biology and Soil Science - Protocol No. 10 of June 4, 2009.
Reviewer, Doctor of Biological Sciences, Professor L.A. Yablonskikh
The teaching aid was prepared at the Department of Soil Science and Land Management, Faculty of Biology and Soil Science, Voronezh State University.
For the specialty: 020701 - Soil science
A deficiency or excess of any chemical element causes disruption of the normal course of biochemical and physiological processes in plants, which ultimately changes the yield and quality of crop production. Therefore, the determination of the chemical composition of plants and indicators of product quality makes it possible to identify unfavorable environmental conditions growth of both cultural and natural vegetation. In this regard, the chemical analysis of plant material is an integral part of environmental protection activities.
A practical guide for information and analytical support of environmental protection in agriculture compiled in accordance with the program of laboratory studies on "Biogeocenology", "Analysis of plants" and "Environmental activity in agriculture" for the 4th and 5th year students of the soil department of the biosoil faculty of Voronezh State University.
TECHNIQUE FOR TAKING PLANT SAMPLES AND PREPARING THEM FOR ANALYSIS
Sampling of plants is a very crucial moment in the effectiveness of diagnostics of plant nutrition and assessment of their availability of soil resources.
The entire area of the studied crop is visually divided into several sections, depending on its size and the state of the plants. If in the sowing areas with clearly worse plants are highlighted, then these areas are marked on the field map, it is ascertained whether the poor condition of the plants is a consequence of an ento- or phyto-disease, local deterioration of soil properties or other growth conditions. If all these factors do not explain the reasons poor condition plants, it can be assumed that their nutrition is disturbed. This is verified by plant diagnostic methods. Take pro
from the sites with the worst and the best plants and the soil under them and by their analysis, they find out the reasons for the deterioration of the plants and the level of their nutrition.
If, due to the condition of the plants, the sowing is not uniform, then when sampling, it should be ensured that the samples correspond to the average condition of the plants in this section of the field. Plants with roots are taken from each selected array along two diagonals. They are used: a) to take into account the increase in mass and the course of organ formation - the future structure of the crop and b) for chemical diagnostics.
In the early phases (with two or three leaves), the sample should contain at least 100 plants per hectare. Later, for cereals, flax, buckwheat, peas and others - at least 25 - 30 plants per hectare. In large plants (adult corn, cabbage, etc.), the lower healthy leaves are taken from at least 50 plants. To take into account the accumulation in phases and the removal by the crop, the entire aerial part of the plant is taken into the analysis.
Have tree species - fruit, berry, grape, ornamental and forest - due to the peculiarities of their age changes, the frequency of fruiting, etc. taking samples is somewhat more difficult than that of field crops. The following age groups are distinguished: seedlings, wild birds, grafted two-year-olds, seedlings, young and fruiting (beginning to bear fruit, in full and in dying fruiting) trees. In seedlings, in the first month of their growth, the entire plant is included in the sample, followed by its division into organs: leaves, stems and roots. In the second and next months, fully formed leaves are selected, usually the first two after the youngest, counting from the top. In two-year-old game, the first two formed leaves are also taken, counting from the top of the growth shoot. From grafted two-year-olds and seedlings, as well as from adults, the average leaves of growth shoots are taken.
Have berries - gooseberries, currants and others - are selected from the shoots of the current growth of 3-4 leaves from 20 bushes so that in the sample
there were at least 60 - 80 leaves. Adult leaves are taken from strawberries in the same amount.
The general requirement is the unification of the sampling technique, processing and storage of samples: taking strictly the same parts from all plants according to their tier, age, location on the plant, absence of disease, etc. It also matters whether the leaves were in direct sunlight or in the shade, and in all cases, leaves of the same placement in relation to sunlight, preferably in light, should be selected.
When analyzing the root system, the middle laboratory sample is carefully washed in a tap water, rinsed in distilled water and dried with filter paper.
A laboratory sample of grain or seeds is taken from many places (bag, box, machine) with a probe, then it is spread evenly on paper in the form of a rectangle, divided into four parts and material is taken from two opposite parts to the required amount for analysis.
One of important points in the preparation of plant material for analysis, it is correct fixing it, if the analyzes are not supposed to be carried out in fresh material.
For the chemical assessment of plant material by the total content of nutrients (N, P, K, Ca, Mg, Fe, etc.), plant samples are dried to an air-dry state in a drying cabinet at a temperature
temperature 50 - 60 ° or in air.
In analyzes, based on the results of which conclusions about the state of living plants will be drawn, fresh material should be used, since wilting causes a significant change in the composition of the substance or a decrease in its amount and even the disappearance of substances contained in
living plants. For example, cellulose is not affected by degradation, but starch, proteins, organic acids and especially vitamins are degraded after several hours of wilting. This forces the experimenter to carry out analyzes in fresh material in a very short time, which is not always possible to do. Therefore, the fixation of plant material is often used, the purpose of which is to stabilize unstable plant substances. In this case, enzyme inactivation is of decisive importance. Various methods of plant fixation are used, depending on the tasks of the experiment.
Steam fixation. This type of fixation of plant material is used when there is no need to determine water-soluble compounds (cell sap, carbohydrates, potassium, etc.). During the processing of raw plant material, such a strong autolysis can occur that the composition of the final product sometimes differs significantly from the composition of the starting material.
In practice, steam fixation is carried out as follows: inside a water bath is suspended metal grid, the top of the bath is covered with a dense non-combustible material and the water is heated to a violent release of steam. After that, fresh plant material is placed on the net inside the bath. Fixation time 15 - 20 min. Then the plants are dried
are kept in a thermostat at a temperature of 60 °.
Temperature fixation. The plant material is placed in kraft paper bags, and juicy fruits and shredded vegetables are loosely placed in enamel or aluminum cuvettes. The material is kept for 10 - 20 minutes at a temperature of 90 - 95 °. This inactivates most of the enzymes. After that, the leafy mass and fruits that have lost turgor are dried in a drying cabinet at a temperature of 60 ° with or without ventilation.
When using this method of fixing plants, it must be remembered that prolonged drying of plant material at a temperature
A temperature of 80 ° and above leads to losses and changes in substances due to chemical transformations (thermal decomposition of some substances, caramelization of carbohydrates, etc.), as well as due to the volatility of ammonium salts and some organic compounds. In addition, the temperature of the raw plant material cannot reach the ambient temperature (drying cabinet) until the water evaporates and until all the heat input has ceased to be converted into latent heat of vaporization.
Rapid and careful drying of the plant sample in some cases is also considered an acceptable and acceptable method of fixation. When this process is carried out skilfully, the deviations in the composition of the dry matter can be small. In this case, denaturation of proteins and inactivation of enzymes occurs. As a rule, drying is carried out in drying ovens (thermostats) or special drying chambers. The material is dried much faster and more reliably if heated air circulates through the cabinet (chamber). The most suitable temperature for drying
sewing from 50 to 60 °.
Dried material stays better in the dark and cold. Since many substances contained in plants are capable of self-oxidation even in a dry state, it is recommended to store the dried material in tightly closing vessels (flasks with a ground stopper, desiccators, etc.), filled to the top with the material so that there is not much air left in the vessels.
Freezing the material. Plant material is very well preserved at temperatures from -20 to -30 °, provided that freezing occurs quickly enough (no more than 1 hour). The advantage of storing plant material in a frozen state is due to both the effect of cooling and dehydration of the material due to the transition of water to a solid state. It should be borne in mind that when freezing
The enzymes are inactivated only temporarily, and after thawing, enzymatic transformations can occur in the plant material.
Treatment of plants with organic solvents. As a
All fixing substances can be used boiling alcohol, acetone, ether, etc. Fixation of plant material in this way is carried out by lowering it into an appropriate solvent. However, with this method, not only the fixation of plant material occurs, but also the extraction of a number of substances. Therefore, such fixation can be applied only when it is known in advance that the substances to be determined are not recovered by the given solvent.
The plant samples dried after fixation are crushed with scissors and then in a mill. The crushed material is sieved through a sieve with a hole diameter of 1 mm. At the same time, nothing is thrown out of the sample, since by removing part of the material that did not pass through the sieve from the first sieving, we thereby change the quality of the average sample. Large particles are passed through the mill and sieve again. Grind the rest on a sieve in a mortar.
An analytical sample is taken from the laboratory average prepared in this way. To do this, the plant material, distributed in a thin even layer on a sheet of glossy paper, is divided diagonally into four parts. Then the two opposite triangles are removed, and the remaining mass is again distributed in a thin layer over the entire sheet of paper. Again diagonals are drawn and again two opposite triangles are removed. This is done until the amount of substance required for the analytical sample remains on the sheet. The selected analytical sample is transferred to glass jar with a ground stopper. In this state, it can be stored indefinitely. The weight of an analytical sample depends on the amount and method of research and ranges from 50 to several hundred grams of plant material.
All analyzes of plant material should be carried out with two samples taken in parallel. Only close results can confirm the correctness of the work done.
Plants should be handled in a dry and clean laboratory that does not contain ammonia vapors, volatile acids and other compounds that can affect the quality of the sample.
The results of analyzes can be calculated both for air-dry and absolutely dry sample of the substance. In the air-dry state, the amount of water in the material is in equilibrium with the water vapor in the air. This water is called hygroscopic, and its amount depends both on the plant and on the state of the air: the more humid the air, the more hygroscopic water in the plant material. To convert the data to dry matter, it is necessary to determine the amount of hygroscopic moisture in the sample.
DETERMINATION OF DRY SUBSTANCE AND HYGROSCOPIC MOISTURE IN AIR-DRY MATERIAL
In chemical analysis, the quantitative content of a particular component is calculated on a dry matter basis. Therefore, before the analysis, the amount of moisture in the material is determined and thereby the amount of absolutely dry matter in it is found.
Analysis progress. An analytical sample of the substance is spread in a thin layer on a sheet of glossy paper. Then, with a spatula, from different places of the substance distributed on the sheet, small pinches of it are taken into a glass bottle pre-dried to constant weight. The sample should be about 5 g. The batch together with the sample are weighed on an analytical balance and placed in a thermostat, the temperature inside of which is maintained at 100-1050. For the first time in a thermostat, an open weighing bottle is kept for 4-6 hours. After this time, the weighing bottle from the thermostat is transferred to a desiccator for cooling, after 20-30
minutes the weighing bottle is weighed. After that, the bottle is opened and placed back in a thermostat (at the same temperature) for 2 hours. Drying, cooling and weighing are repeated until the weighing bottle reaches a constant weight (the difference between the last two weighings must be less than 0.0003 g).
The percentage of water is calculated using the formula:
where: x is the percentage of water; c - weighed amount of plant material before drying, g; в1 - weighed amount of plant material after drying.
Equipment and utensils:
1) thermostat;
2) glass bottles.
Results recording form
Weighing bottle with |
Weighing bottle with |
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hinge on |
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weighed up to |
Weight up to |
Weighing according to |
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after dry- |
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drying out |
drying out |
after vysu- |
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sewing, g |
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DETERMINATION OF "RAW" ASH BY THE METHOD OF DRY ASHING
Ash is the residue obtained after the combustion and calcination of organic matter. When burned, carbon, hydrogen, nitrogen and partially oxygen evaporate and only non-volatile oxides remain.
The content and composition of the ash elements of plants depends on the species, growth and development of plants, and especially on the soil-climatic and agrotechnical conditions of their cultivation. The concentration of ash elements differs significantly in different tissues and organs of plants. Thus, the ash content in the leaves and herbaceous organs of plants is much higher than in the seeds. There is more ash in the leaves than in the stems,
