Chemical reagents

DEEP CLEARED WATER: MODERN TECHNOLOGIES OF PRODUCTION AND APPLICATIONS

Obtaining not just clean, but deeply purified water is dictated by the needs of many industries, instrument making and medicine. The variety of areas of application of deep purification water requires a careful selection of its individual parameters for each specific application. What cleaning technologies exist today? Let's try to figure it out.

Depending on the method of obtaining or cleaning, there are several types of water with a minimum amount of impurities:

Osmotic water (or water purified by reverse osmosis)

This technology is borrowed from nature and refers to membrane methods of water purification. Its principle is quite simple: water, like through a sieve, is forced through a semi-permeable membrane made of a porous thin-film composite. The pore diameter (0.0001 micron) is large enough to allow water molecules to pass through, but small for ions and dissolved impurities to pass through. In terms of purification quality, membrane systems are among the most effective, especially for organic and biological impurities: here it reaches almost 97–99.9% for any type of pollution.

Deionized (or demineralized) water

In the process of deionization (demineralization), water is passed through two layers of ion exchange material to more effectively remove all dissolved salts. Simultaneously or sequentially, cation exchange resins containing hydrogen ions H+ and anion exchange resins containing OH– hydroxyl ions are used. Since all salts soluble in water consist of cations and anions, treatment of water with cation and anion exchange resins completely replaces cations and anions in the salts present in the treated water with hydrogen and hydroxyl ions, i.e. water. Thus, in the volume limited by ion-exchange membranes, there is a very significant decrease in the concentration of impurity salts.

Distilled water

The distillation method is based on the evaporation of the water to be treated, followed by the condensation of the steam. Such water is almost completely purified from mineral salts, organic and other impurities dissolved in it. The technology is simple, but energy intensive.

Bi-distilled and high resistance water

Single-distilled water is not chemically pure enough. The purest is bidistilled water, which is often called "high-resistance". Obtaining demineralized water of this quality - namely, such water is necessary in microelectronics - is a complex task, requiring a comprehensive and thoughtful approach to choosing a desalination technique. It is for this reason that modern systems for obtaining high-purity water use several qualitatively different stages of purification: ultrafiltration, two-stage osmosis, ion exchange (mixed action filters), electrodeionization, etc.

Thus, today there are at least four technologies for obtaining water with a minimum amount of impurities. All these technologies differ from each other in terms of cost, energy intensity, and the degree of purity of the resulting water. But it would be incorrect to give preference to only one of the technologies. Obviously, water for pharmaceutical purposes has completely different requirements than, for example, water for diluting heat transfer fluids, making solutions for accumulators, for steam turbines or for swimming pools. And the production of electrolytes, microelectronics, electroplating, analytical and research laboratories impose their own requirements on the quality of the water used. That is why when choosing the type of water with a minimum amount of impurities , the technological process in which it will be used is very important. After all, the process itself will not least depend on the quality of the water used in it.

KOVACH REAGENT FOR THE DETERMINATION OF INDOL-POSITIVE BACTERIA

Kovac's reagent determination of indole buy from 100 grams The study of the enzymatic activity of microorganisms is a common way to determine both general and specific enzymes characteristic of certain species.

The ability of microorganisms to act on a known substrate is a good marker of the presence of one or another enzyme in them. An indicator of enzyme activity can be a change in the physical state of the substrate (liquefaction of gelatin), acidification of the nutrient medium (Hiss media with carbohydrates), or the formation of certain metabolic products (indole, hydrogen sulfide, ammonia), etc.

Determination of the presence of indole is a key test for the differentiation of Enterobacteriaceae. Escherichia coli (E. coli), isolated from human samples, is capable of producing indole in 90.1-98.6% of cases, bacteria from the genera Citrobacter and Enterobacter do not form indole.

In 1928, the Hungarian-Swiss chemist Erwin Kovacs proposed using a solution containing 4-dimethylaminobenzaldehyde, amyl alcohol and hydrochloric acid to detect indole.

Indole-positive microorganisms are able to break down L-tryptophan contained in peptone nutrient media to indole, pyruvic acid and ammonia. The indole, in turn, reacts with the 4-dimethylaminobenzaldehyde contained in the Kovacs reagent to form a highly visible red complex.

In everyday laboratory practice, the Kovacs reagent is used to confirm the presence of E. coli and many other pathogens.

Store this reagent in a dark and cool place.

NESSLER REAGENT - MAIN PROPERTIES AND APPLICATIONS

In 1868, the German chemist Julius Nessler (J. Nessler, 1827-1905) suggested using a complex compound of hydroiodic acid HI, potassium, and mercury to carry out some specific qualitative analytical reactions. Today we know this substance under the name Nessler's reagent.

The full name of the reagent is potassium tetraiodomercurate (II) (K2[HgI4].). But you can often find a simplified name - potassium tetraiodomercurate.

To prepare the Nessler reagent, a saturated solution of HgCl2 is added to an aqueous solution of KI until a red precipitate forms, then solid KOH is added and a little saturated solution of HgCl2 is added to the resulting solution, diluted with water, allowed to settle, and the clear liquid is drained. The use of HgI2 instead of HgCl2 increases the sensitivity of the reagent.

The reagent is usually used in the form of an aqueous alkaline solution of potassium tetraiodomercuroate dihydrate (K2HgI4*KOH or K2HgI4*NaOH depending on the type of alkaline medium).

Properties of Nessler's reagent

In dry form, the reagent is a powdery substance of small pale yellow water-soluble crystals. Toxic. combustible

On sale, an aqueous solution is more common - a pale yellow liquid that decomposes under the influence of light and when heated.

Application

Nessler's reagent is used in analytical chemistry.

Since the substance is extremely sensitive to ammonium salts, it is very often used to analyze the quality of drinking or natural water. With its help, a microscopic amount (about 0.001% by volume) of ammonia can be determined by a colorimetric or photometric method.

Nessler's reagent is also used in thin layer and paper chromatography for the detection of hydroxyamino acids.

Another feature of the reagent is the ability to form a black precipitate of mercury in metallic form when interacting with alcohols or aldehydes. This property is used to detect such substances.

Precautionary measures

Since Nessler's reagent contains mercury, it is dangerous to humans. Causes chemical burns on contact with skin and mucous membranes, may corrode skin and cause serious injury!

When working with the reagent, you should use specialized personal protective equipment (including gloves, overalls, goggles and a respirator). Work must be carried out in a fume hood; as a last resort in a room with an exhaust hood.

Nessler's reagent should be stored in a hermetically sealed dark glass container in a cool room or refrigerator.

FOLIN-CHOCALTEU REAGENT FOR DETERMINATION OF THE CONTENT OF PHENOLIC COMPOUNDS AND QUANTITATIVE DETERMINATION OF PROTEIN

The Folin-Ciocalteu reagent is a mixture of sodium tungstic and molybdate solutions, to which phosphoric acid, hydrochloric acid and, after boiling, lithium sulfate, and a few drops of bromine water are added successively.

This reagent was developed by the Swedish physiologist and chemist Folin (OKO Folin) and the Romanian biochemist V. Ciocalteu, and is used in the quantitative determination of the content of phenol compounds in raw materials and finished products.

Also, the reagent is used for the quantitative determination of protein content according to the Lowry method. Note that the determination of protein by the Folin-Ciocalteu reagent is carried out rather quickly and does not require preliminary destruction of the material under study.

The method for the quantitative determination of protein is based on measuring the concentration of colored products resulting from a combination of two chemical reactions: the biuret reaction for a peptide bond and the interaction of the Folin-Ciocalteu reagent with aromatic amino acids. Proposed by Lowry in 1951.

The method for determining the total content of phenolic compounds by the colorimetric method using the Folin-Ciocalteu reagent is based on the fact that the phosphotungstic and phosphomolybdic acids contained in it, when reduced with phenolic compounds in an alkaline medium, form a blue complex (tungsten blue), the color intensity of which is proportional to the amount of phenolic compounds.

FISHER REAGENT FOR DETERMINATION OF THE QUANTITY OF WATER IN VARIOUS COMPOUNDS

Many methods have been proposed for the determination of water as an impurity in organic compounds. One of the most common is the titration with Fisher's reagent.

The method was developed in 1935 by the German chemist Karl Fischer. The fundamental principle of "Fischer water determination" is based on the Bunsen reaction between iodine, sulfur dioxide and water. K. Fischer discovered that the use of an excess of sulfur dioxide, methanol as a solvent, and pyridine as a base (to buffer the solution) can be used to determine water in non-polar solvents.

This method is one of the most sensitive and makes it possible to determine even a small amount of water in organic liquids, for example, in petroleum products. In this case, the reagent simultaneously acts as an indicator.

The most important advantage of Karl Fischer titrations over thermal titrations (weight loss on ignition) is its specificity for water. Loss on ignition shows the total content of all volatile components.

Two-component Fischer reagents are stable during storage and give a high titration rate. The Fischer reagent used for titration is a solution of iodine, sulfur dioxide and pyridine, most often in methanol. Sometimes methanol is replaced with methyl cellosolve, dioxane, or glacial acetic acid.

Fisher's reagent is also used to determine water, both hygroscopic and crystallization in inorganic substances, although interfering compounds are more common here than in the analysis of organic substances. Strong oxidizing and reducing agents that react with iodine or iodide interfere with the determination.

Fischer's reagent cannot be used to determine water in ketones or aldehydes or in the presence of small amounts of these substances in the analyzed solvents. To remove aldehydes and ketones, a 2% pyridine solution of hydrogen cyanide is added, under the action of which aldehydes and ketones are converted into cyanohydrins.

It was proposed to use Fisher's reagent for the determination of hydroxy acids, acid anhydrides, carbonyl derivatives and water of hydration in salts.

Currently, two versions of the method are used: coulometric and volumetric (volumetric)

Volumetric titration is reduced to the addition of an iodine-containing titrant. The reaction of iodine with water also requires an alcohol (or equivalent) and an organic base, which can be contained both in the titrant and in the reagent for the titration cell.

Depending on the composition, Fisher's reagents are single-component and two-component.

One-component Fisher's reagent (titrant) contains all reactants: iodine, imidazole, alcohol, sulfur dioxide. In this case, only the reaction medium is needed in the titration cell: alcohol, chloroform, etc.

In two-component Fischer reagents - the distribution of interacting substances between the titrant and the solvent. The first reagent (titrant) is an alcoholic solution of iodine, and the second (solvent) is an alcoholic solution of SO2 with imidazole or pyridine.

One-component Fisher reagents are not stable and the titer may change by 0.5 mg during a year of storage in a sealed bottle. Two-component Fischer reagents are stable during storage and give a high titration rate due to the excess SO2 content in the solvent.

The popularity of Karl Fischer titration is due to the following advantages:

- high accuracy and reproducibility;

- water selectivity;

- small quantities of required samples;

- simple method of sample preparation;

- short analysis time;

- practically unlimited measuring range;

- suitable for the analysis of solids, liquids, gases;

- independence from the presence of other volatile substances.

Important to remember:

1. Fisher's reagent is unstable to light and moisture. It must be standardized before each use.

2. The operating pH range for Fischer water determination is between 5 and 8, otherwise highly acidic or basic compounds should be buffered.

3. Poorly soluble compounds in methanol (for example, fats, hydrocarbons) should be dissolved in higher alcohols or chloroform, formamide additions are also possible (for polar substances).

4. Avoid titration of substances that can react with the components of the Fischer reagent (for example, aldehydes and ketones, strong acids and bases, oxidizing and reducing agents, compounds that react with the components of the Fischer reagent to form water).

WIES REAGENT FOR DETERMINATION OF IODINE NUMBER

Not a single modern food production can exist and develop without a constant improvement in the quality of products and control of their safety. High competition, growing customer requirements, constant monitoring by government agencies and public organizations require full compliance of goods with state standards, specifications and other industry standards.

Edible fats and oils are used in the manufacture of a wide range of food products. Factory laboratories of confectionery, dairy, fat-and-oil and meat processing enterprises regularly perform a large number of various physical and chemical analyzes aimed at controlling the composition and quality of both ingredients and finished products.

Iodine number is an important indicator of lipid composition

One of the most important parameters of lipids is their fatty acid composition, which is determined by gas chromatography or wet chemistry methods. In this way, the qualitative and quantitative fatty acid composition, the amount of trans-isomers, as well as the iodine number of fat are determined.

The iodine number allows you to judge the degree of unsaturation of the fatty acids that make up the fat. The higher the content of unsaturated fatty acids, the higher the value of the iodine number.

The main advantages of determining the iodine number using the Wijs reagent

It should be noted that the determination of the iodine number by the chromatographic method has several significant drawbacks. The first is a large spread of the obtained values on different devices. At the same time, the determination of the iodine number using the Wijs reagent (a solution of iodine monochloride ICl in an organic solvent) makes it possible to obtain accurate values regardless of the equipment used.

The second disadvantage of the chromatographic method is its high cost and complexity. In addition, not all laboratories can afford to buy and operate a chromatograph. The cost of equipment for titrimetric determination is much lower, and the speed of analysis is many times faster.

The third important point is that the arbitration method recognizes the determination of the iodine number with the help of the Wijs reagent. The data obtained on the chromatograph, in the event of any disputes and proceedings, cannot serve as the basis for making a decision.

Griess reagent - a mixture of 1-naphthylamine, sulfanilic acid and tartaric acid.

Griess reagent is a laboratory indicator used in analytical chemistry to study the metabolic processes associated with the reduction of nitrates, as well as to determine the content of nitrites in products, soil, groundwater, drinking and domestic water. Another area of application of the Griess reagent is the study of nitrifying microbes.

The compound is named after the German chemist JP Griess (1829-1888), who proposed it for the photometric determination of nitrites, nitrous acid, and some types of organic substances that release nitrous acid when heated.

Griess reagent is a mixture of sulfanilic acid, alpha-naphthylamine and tartaric acid. In the presence of nitrous acid, a solution of the reagent components forms a colored compound suitable for quantitative colorimetric determination.

The sensitivity of determining the amount of nitrite by the Griess method is 0.002 mg/l. The measurement range is from 0.1 to 15 µg.

Preparation of the Griess reagent in the laboratory

In laboratory practice, several methods are used to obtain the Griess reagent. The first is the manufacture of the reagent from scratch. For this, solutions of sulfanilic acid and alpha-naphthylamine are prepared in advance, which are then mixed in equal volumes.

The second method - the manufacture of a reagent from a dry powder - is less time consuming and is currently the most common. All that is needed is to take a certain amount of dry Griess reagent and dissolve it in distilled water.

A fresh solution should not have color and can be stored in a refrigerator in a hermetically sealed dark glass container for no more than two days.

Safety regulations

Griess reagent belongs to substances of hazard class 2-3. The compound is toxic, in contact with the skin and mucous membranes causes a chemical burn.

It is allowed to prepare the reagent, as well as conduct analyzes with it, in a ventilated room with general supply and exhaust and local ventilation, using protective equipment: rubber gloves, overalls, gas masks or goggles and respirators.

HEMATOXYLIN - HISTOLOGICAL DYE IN MICROSCOPIC TECHNOLOGY

The widespread use of hematoxylin in microscopic technology is due to its remarkable properties as a dye of plant origin. The uniqueness of origin and distinctive natural properties allow us to speak about the indispensability of the properties of this product in scientific research and laboratory diagnostics.

Hematoxylin is a dye of plant origin, which is found in the form of a glycoside in the sap of the log tree (Haematoxylon campechianum), which grows in India and America. The homeland of this tree is Southern Mexico, the Campeche region. Kampesh extract containing hematoxylin was originally used for dyeing fabrics in the textile industry. Hematoxylin has been used as a histological stain since the middle of the 19th century. Hematoxylin, introduced into microtechnology by Waldeyer in 1882, marked the beginning of the development of the most valuable staining methods. The first recipe for alum hematoxylin was proposed by Behmer in 1865. And in the 20th century it became the main dye used to stain cell nuclei.

Chemical properties of hematoxylin

Hematoxylin is a colorless or slightly colored crystals of a sweet taste, acquiring a reddish-yellow color under the action of light, as well as in air. Hematoxylin is slightly soluble in cold water, but soluble in hot water (especially in the presence of borax), ethyl alcohol, glycerin, and poorly soluble in diethyl ether. With alkalis, it gives solutions of a purple color, which quickly changes to bluish-violet, and then to brown. Diluted acids have no effect on hematoxylin. It has the properties of an acid-base indicator. The gross formula of hematoxylin is C16H14O6 CAS 517-28-2, and the most common synonyms are: Haematoxylin, Hematoxylin, Natural Black 1, CI 75290, hydroxybrazilin, oxybrazilin.

Application

By itself, hematoxylin does not represent a pigment, but during the oxidation of hematoxylin it extremely easily forms the pigment hematein, which in turn gives various products of deeper oxidation that are not applicable for staining. All recipes for the preparation of hematoxylin for staining preparations are aimed at converting hematoxylin to hematein. But neither hematoxylin nor hematein are able to give color without mordants, with which they form salt-like compounds - varnishes. Salts of aluminum, iron, copper, chromium, molybdenum, vanadium are used as mordants. The most common mordants are aluminum compounds (in the form of ammonium alum or potassium alum) or iron (ferric chloride or iron ammonium alum). Other mordants are used much less frequently and include chromic alum and phosphotungstic acid.

Hematoxylin solutions

There are numerous ways to prepare color solutions from hematoxylin, although the essence of all these methods is one thing - its oxidation.

Methods with iron hematoxylin

There are two methods of staining with iron hematoxylin - regressive and progressive. The first is based on overstaining and subsequent differentiation by washing in an appropriate liquid; at the same time, iron salts are introduced into the dye solution or the sections are treated with them before staining. The liquid used for differentiation should be thoroughly washed after the end of the procedure. If it is not washed out, it continues to act after reaching the desired degree of differentiation and may spoil the color.

The progressive method uses acidic solutions or excess iron salts to avoid overstaining.

Iron haematoxylin staining methods typically include:

Broussy's iron hematoxylin.

Weigert's iron hematoxylin.

Iron hematoxylin according to Yasvoin.

Iron hematoxylin according to Rego.

Iron trioxyhematein according to Hansen.

Staining with iron chloride hematoxylin according to Hekvist.

Alum hematoxylin methods

Complexes of hematoxylin with aluminum salts are usually prepared using double ammonium aluminum sulfate or aluminum-ammonium alum. Such complexes are commonly referred to as alum hematoxylin. Sometimes potassium or sodium alum is used instead of ammonium, and the staining results do not change. Since the coloring agent is hematein, and aluminum salts, unlike ferric salts, are not oxidizing agents, solutions of alum hematoxylin must be oxidized or allowed to “ripen” before use. Hematein is slowly formed by passing air bubbles through hematoxylin solutions (it may take 3-4 weeks to obtain homogeneous results), while keeping the solutions in open vessels for several weeks; hematein is also formed in a solid dye stored in an open vessel in a humid atmosphere. Most chemical oxidizing agents, such as peroxides, iodates, permanganates, perchlorates, mercuric oxide, and ferric salts, oxidize hematoxylin immediately, although some act when heated.

The selectivity of staining nuclei with alum hematoxylin increases in the presence of an excess of aluminum salts or even in acidic solutions.

Staining methods with alum hematoxylins usually include:

Mayer's sour gemalun.

· Double staining with hemalan-eosin.

· Alum hematoxylin but Erlihu.

Staining with Delafield's hematoxylin.

Staining with alum hematoxylin according to Hansen.

Alum hematoxylin by Carazzi.

The following methods are also widely used:

Technique for staining sections with differentiation

· Technique of staining with hematoxylin-eosin on a glass slide.

· Method for staining paraffin sections with hematoxylin-eosin according to the Bemer method.

Technique of staining with hematoxylin-eosin

Repeated attempts have been made to find a cheaper and more convenient replacement for hematoxylin for use in microscopic technology. It was proposed to use such natural dyes as blueberry juice, black currant juice, synthetic dyes (anthocyanin BB, phenocyanin TC, gallein, brazilin, alizarin blue S, celestine blue). However, none of these substitutes has been able to completely replace hematoxylin at present. In many ways, therefore, today, hematoxylin is indispensable in scientific research and laboratory diagnostics.