What is a Chemical Agent?
Chemical reagent is a relatively standard substance for chemical research and composition analysis, and is an important condition for scientific and technological progress. It is widely used in the synthesis, separation, qualitative and quantitative analysis of substances. In the daily work of schools, hospitals, and research institutes, chemical reagents are inseparable.
- Chinese name
- Chemical reagent
- Foreign name
- Chemical reagent
- Use
- For the synthesis and separation of substances
- Species
- 300 kinds
- Classification
- Standard, biochemical, electronic, experimental reagents
- Direction of development
- Development of supporting, standby reagents and supporting services
- Chemical reagent is a relatively standard substance for chemical research and composition analysis, and is an important condition for scientific and technological progress. It is widely used in the synthesis, separation, qualitative and quantitative analysis of substances. In the daily work of schools, hospitals, and research institutes, chemical reagents are inseparable.
Chemical reagent chemical reagent definition
- Chemical reagent
- Energy development, defense industry, scientific research and the national economy in all walks of life, but what is "chemical reagents", what does it contain, and giving it an accurate definition is still very difficult. Early chemical reagents only meant "pure chemicals used in chemical analysis and chemical tests to determine the composition or composition of a substance." Later it was expanded to "chemicals used to achieve chemical reactions", and the chemicals referred to by "chemical reagents" have already exceeded this category. Some people think that "chemicals used in scientific experiments" can be called "chemical reagents". A more comprehensive definition of chemical reagents can be: compounds or simple substances of various purity grades used in chemical tests, chemical analysis, chemical research and other tests.
Current national standards for chemical reagents
- GB / T 14305-1993 chemical reagent cyclohexane
- GB 15346-1994 Chemical reagent packaging and marking
- GB / T 15347-1994 chemical reagents ascorbic acid
- GB / T 15895-1995 chemical reagent 1,2-dichloroethane
- GB / T 15896-1995 chemical reagent formic acid
- GB / T 15897-1995 chemical reagent calcium carbonate
- GB / T 15898-1995 Chemical Reagent Cobalt Nitrate Hexahydrate (Cobalt Nitrate)
- GB / T 15899-1995 Chemical reagent Manganese sulfate monohydrate (manganese sulfate)
- GB / T 15901-1995 Chemical reagent copper chloride dihydrate (copper chloride)
- GB / T 629-1997 chemical reagent sodium hydroxide
- GB / T 1264-1997 Chemical reagent Sodium fluoride
- GB / T 640-1997 chemical reagent sodium bicarbonate
- GB / T 671-1998 chemical reagent magnesium sulfate
- GB / T 689-1998 chemical reagent pyridine
- GB / T 1401-1998 Chemical reagent Disodium ethylenediamine tetraacetate
- GB / T 1268-1998 Chemical reagent sodium thiocyanate
- GB / T 642-1999 Chemical reagent Potassium dichromate
- GB / T 649-1999 Chemical reagent Potassium bromide
- GB / T 684-1999 Chemical reagent toluene
- GB / T 1276-1999 Chemical reagent Ammonium fluoride
- GB / T 2305-2000 chemical reagent phosphorus pentoxide
- GB / T 6684-2002 Chemical reagent 30% hydrogen peroxide
- GB / T 678-2002 Chemical reagent ethanol (anhydrous ethanol)
- GB / T 12591-2002 chemical reagent ether
- GB / T 682-2002 Chemical reagent chloroform
- GB / T 679-2002 Chemical reagent ethanol (95%)
- GB / T 601-2002 Chemical reagent standard titration solution preparation
- GB / T 603-2002 Preparation of preparations and products used in chemical reagent test methods
- GB / T 602-2002 Preparation of standard solutions for the determination of impurities in chemical reagents
- GB / T 652-2003 Chemical reagent barium chloride
- GB / T 1265-2003 Chemical reagent sodium bromide
- GB / T 606-2003 General method for determination of moisture in chemical reagents Karl Fischer method
- GB / T 674-2003 Chemical reagent powdered copper oxide
- GB / T 656-2003 Chemical reagent Ammonium dichromate
- GB / T 16493-1996 Chemical reagent Trisodium citrate dihydrate (trisodium citrate)
- GB / T 16494-1996 Chemical reagent xylene
- GB / T 16496-1996 chemical reagent potassium sulfate
- GB / T 16983-1997 chemical reagent dichloromethane
- GB / T 17521-1998 Chemical reagent N, N-dimethylformamide
- GB / T 615-2006 General method for determination of boiling range of chemical reagents
- GB / T 9721-2006 General rules for molecular absorption spectrophotometry of chemical reagents (UV and visible light)
- GB / T 1263-2006 Chemical reagent Disodium hydrogen phosphate dodecahydrate (disodium hydrogen phosphate)
- GB / T 1266-2006 Chemical reagent Sodium chloride
- GB / T 617-2006 General method for determination of melting range of chemical reagents
- GB / T 9722-2006 General rules for chemical reagent gas chromatography
- GB / T 605-2006 General method for colorimetric determination of chemical reagents
- GB / T 614-2006 General method for determination of refractive index of chemical reagents
- GB / T 622-2006 Chemical reagent hydrochloric acid
- GB / T 626-2006 Chemical reagent
- GB / T 616-2006 General method for determination of boiling point of chemical reagents
- GB / T 9739-2006 General method for the determination of iron in chemical reagents
- GB / T 683-2006 Chemical reagent methanol
- GB / T 611-2006 General method for density determination of chemical reagents
- GB / T 618-2006 General method for determination of crystallization point of chemical reagents
- GB / T 673-2006 Chemical reagent Arsenic trioxide
- GB / T 609-2006 General method for determination of total nitrogen in chemical reagents
- GB / T 637-2006 Chemical reagent sodium thiosulfate pentahydrate (sodium thiosulfate)
- GB / T 672-2006 Chemical reagent Magnesium chloride hexahydrate (magnesium chloride)
- GB / T 658-2006 chemical reagent ammonium chloride
- GB / T 621-1993 chemical reagent hydrobromic acid
- GB / T 9725-2007 General Principles of Potentiometric Titration of Chemical Reagents
- GB / T 9726-2007 General rules for determination of potassium permanganate reduced by chemical reagents
- GB / T 9732-2007 Chemical reagent-General method for the determination of ammonium
- GB / T 9730-2007 General method for determination of oxalate
- GB / T 9724-2007 General rules for the determination of pH value of chemical reagents
- GB / T 9729-2007 General method for the determination of chlorides in chemical reagents
- GB / T 631-2007 Chemical reagent ammonia
- GB / T 613-2007 General method for determination of specific optical power (specific optical rotation) of chemical reagents
- GB / T 638-2007 Chemical reagent stannous chloride (II) dihydrate (stannous chloride)
- GB / T 6685-2007 Chemical reagents Hydroxylamine chloride (hydroxylamine hydrochloride)
- GB / T 625-2007 Chemical reagent sulfuric acid
- GB / T 676-2007 chemical reagent acetic acid (glacial acetic acid)
- GB / T 9731-2007 Chemical reagent-General method for determination of sulfur compounds
- GB / T 1272-2007 Chemical reagent Potassium iodide
- GB / T 9727-2007 General method for the determination of phosphates in chemical reagents
- GB / T 10726-2007 General method for determination of metallic impurities by solvent extraction and atomic absorption spectrometry
- GB / T 9723-2007 General rule for flame atomic absorption spectrometry of chemical reagents
- GB / T 670-2007 Chemical reagent silver nitrate
- GB / T 12589-2007 Chemical reagent ethyl acetate
- GB / T 665-2007 Chemical reagent anhydrous copper sulfate (II) (copper sulfate)
- GB / T 9728-2007 General method for the determination of sulfates in chemical reagents
- GB / T 633-1994 Chemical reagent sodium nitrite
- GB / T 650-1993 Chemical reagent Potassium bromate
- GB / T 1279-2008 Chemical Reagent Ammonium Iron (III) Sulfate Dodecahydrate
- GB / T 2304-2008 chemical reagent arsenic-free zinc particles
- GB / T 9734-2008 Chemical reagent-General method for the determination of aluminum
- GB / T 9855-2008 Chemical reagent citric acid monohydrate (citric acid)
- GB / T 696-2008 chemical reagent urea (urea)
- GB / T 660-1992 chemical reagent ammonium thiocyanate
- GB / T 1291-2008 Chemical reagent Potassium hydrogen phthalate
- GB / T 10705-2008 Chemical reagent 5-sulfosalicylic acid dihydrate (5-sulfosalicylic acid)
- GB / T 9854-2008 Chemical reagent oxalic acid dihydrate (oxalic acid)
- GB / T 610-2008 General method for the determination of arsenic in chemical reagents
- GB / T 1273-2008 Chemical reagent Potassium ferric (II) hexacyanate trihydrate
- GB / T 9742-2008 General method for determination of silicates using chemical reagents
- GB / T 9741-2008 General method for determination of ignition residues of chemical reagents
- GB / T 9737-2008 General rules for determination of chemical substances liable to carbonization
- GB / T 9740-2008 General method for determination of evaporation residues of chemical reagents
- GB / T 632-2008 Chemical reagent sodium tetraborate decahydrate (sodium tetraborate)
- GB / T 2306-2008 Chemical reagent potassium hydroxide
- GB / T 639-2008 Chemical reagent anhydrous sodium carbonate
- GB / T 15894-2008 chemical reagent petroleum ether
- GB / T 1292-2008 Chemical reagent Ammonium acetate
- GB / T 686-2008 chemical reagent acetone
- GB / T 690-2008 chemical reagent benzene
- GB / T 1294-2008 Chemical reagent L (+)-tartaric acid
- GB / T 9733-2008 Chemical reagent-General method for determination of carbonyl compounds
- GB / T 9735-2008 General method for determination of heavy metals in chemical reagents
- GB / T 9736-2008 General method for determination of acidity and alkalinity of chemical reagents
- GB / T 9738-2008 General method for determination of water-insoluble matter in chemical reagents
- GB / T 15355-2008 Chemical reagent Nickel chloride hexahydrate (nickel chloride)
- GB / T 643-2008 chemical reagent potassium permanganate
- GB / T 3914-2008 General rules for anodic stripping voltammetry of chemical reagents
- GB / T 12590-2008 chemical reagent n-butanol
- GB / T 9853-2008 Chemical reagent anhydrous sodium sulfate
- GB / T 667-1995 chemical reagent zinc nitrate hexahydrate (zinc nitrate)
- GB / T 669-1994 Chemical reagent Strontium nitrate
- GB / T 685-1993 chemical reagent formaldehyde solution
- GB / T 691-1994 chemical reagent aniline
- GB / T 693-1996 Chemical reagent sodium acetate trihydrate (sodium acetate)
- GB / T 694-1995 Chemical reagent anhydrous sodium acetate
- GB / T 11547-2008 Determination of liquid chemical resistance of plastics
- GB / T 23942-2009 General rules for chemical reagent inductively coupled plasma atomic emission spectrometry
- GB / T 657-2011 Chemical Reagent Ammonium Molybdate Tetrahydrate (Ammonium Molybdate)
- GB / T 659-2011 chemical reagent ammonium nitrate
- GB / T 1281-2011 chemical reagent bromine
- GB / T 623-2011 chemical reagent perchloric acid
- GB / T 644-2011 Chemical reagent potassium hexacyanoferrate () acid (potassium ferricyanide)
- GB / T 661-2011 Chemical reagents Ammonium iron (II) sulfate hexahydrate (ammonium ferrous sulfate)
- GB / T 646-2011 chemical reagent potassium chloride
- GB / T 664-2011 Chemical reagents Ferrous sulfate heptahydrate (ferrous sulfate)
- GB / T 620-2011 chemical reagent hydrofluoric acid
- GB / T 688-2011 chemical reagent carbon tetrachloride
- GB / T 647-2011 chemical reagent potassium nitrate
- GB / T 636-2011 Chemical reagent sodium nitrate
- GB / T 677-2011 chemical reagent acetic anhydride
- GB / T 666-2011 chemical reagent zinc sulfate heptahydrate (zinc sulfate)
- GB / T 1271-2011 Chemical reagent potassium fluoride dihydrate (potassium fluoride)
- GB / T 641-2011 chemical reagent potassium persulfate (potassium persulfate)
- GB / T 655-2011 chemical reagent ammonium persulfate
- GB / T 15354-2011 Chemical reagent tributyl phosphate
- GB / T 645-2011 Chemical reagent Potassium chlorate
- GB / T 653-2011 chemical reagent barium nitrate
- GB / T 628-2011 Chemical reagent Boric acid
- GB / T 687-2011 chemical reagent glycerol
- GB / T 675-2011 chemical reagent iodine
- GB / T 651-2011 chemical reagent potassium iodate
- GB / T 1274-2011 chemical reagent potassium dihydrogen phosphate
- GB / T 648-2011 chemical reagent potassium thiocyanate
- GB / T 1288-2011 Chemical reagent potassium sodium tartrate tetrahydrate (sodium potassium tartrate)
- GB / T 1267-2011 Chemical reagent Sodium dihydrogen phosphate dihydrate (sodium dihydrogen phosphate)
- GB / T 654-2011 chemical reagent barium carbonate
- GB / T 1270-1996 chemical reagents cobalt chloride hexahydrate (cobalt chloride)
- GB / T 1278-1994 chemical reagent ammonium bifluoride
- GB / T 1282-1996 Chemical reagent phosphoric acid
- GB / T 1285-1994 chemical reagent cadmium chloride
- GB / T 1289-1994 Chemical reagent sodium oxalate
- GB / T 1396-1993 chemical reagent ammonium sulfate
- GB / T 1397-1995 Chemical reagent Potassium carbonate
- GB / T 1400-1993 chemical reagent hexamethylenetetramine
- GB / T 13353-1992 Methods for determination of chemical resistance of adhesives Metals and metals
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Chemical reagent title
- For chemical reagents, we are accustomed to many confused titles:
Content-based title
- Standard substance, standard solution, standard impurity solution, standard reference substance, standard sample, standard reagent, indicator reagent, reference substance, reference reagent, chemical reference, chemical standard, instrument standard, analytical reagent, first-class reagent, second-class reagent, Ultra-pure reagents, high-purity reagents, equivalent reagents, pharmaceutical standards, pesticide standards, spectral purity, chromatographic purity, electronic purity, steel standards, pig iron standards, coal standards, ore standards, etc ...
Chemical reagent based on application
- Chemical reagents, general reagents, analytical reagents, diagnostic reagents, teaching reagents, experimental reagents, separation tools, buffer solutions, indicator reagents, biochromins, photosensitive materials, synthetic reagents, intermediates, chemical materials, water quality analysis, residual pesticide testing, Molecular biology reagents ...
Source-based title
- Imported reagents, natural extracts, extracts, dry powders, extracts ...
Chemical reagents based on custom
- Chemicals, fine chemicals, pharmaceuticals, cold reagents, special reagents, first-class reagents, second-class reagents, third-class reagents, small-variety reagents ...
Chemical reagent
- Inorganic reagents, organic reagents, isotopes and labeled compounds, biochemical reagents, amino acids and their derivatives, proteins and peptides, nucleotides and their derivatives, monosaccharides and polysaccharides, enzymes and coenzymes, antibiotics, vitamins, dyes and pigments, culture Base, chromatography medium, electrophoresis medium, biological buffer ...
Classification of chemical reagents
- The categories of chemical reagents are basically divided according to use or discipline. Many new categories were added in the 1980s abroad. Germany's E. Merck company is divided into 20 categories, 88 categories. The United States Baker (JTBaker) company has 75 major categories, 124 sub-categories. With the development of science and technology, the variety of chemical reagents has become more and more numerous, and the classification of categories has become more and more detailed, and the varieties have become serialized and matched.
Chemical reagent quality index
- Chemical reagents are of various quality levels and numerous varieties, and are particularly chaotic. Generally, there are 225 varieties of conventional varieties (a class of reagents), which are essential varieties. They are basically produced complementaryly in China's chemical reagent bases in Beijing, Tianjin, Shanghai, Xi'an, Chengdu, Guangzhou, and Shenyang. The second-class reagents are used in almost all fields and are also a must-have variety for manufacturers. There are about 1,800 to 2,000 varieties. Such reagents have a large demand and are widely used. There are about 3,000 to 6,000 varieties of the three types of reagents, and most of their application fields are related to the national reagents and the people's livelihood, such as chemical reagents, metallurgy, power, food, medicine and other industries.
- In our country, there are 225 kinds of chemical reagents represented by three grades of excellent purity, analytical purity and chemical purity, in accordance with the national standards of the People's Republic of China and the standards issued by the former Ministry of Chemical Industry. These 225 kinds of chemical reagents stipulate the basis of the content of chemical reagents in China in a standard form. The determination of the content of other chemicals is based on this, and the content is determined by measurement. Therefore, the quality of these chemicals is very important. At the same time, these 225 chemical reagents have become basic varieties due to their wide range of uses. These 225 varieties have been marked in the chemical reagent catalog. In addition, there are special reagents, the production volume is very small, almost on-demand production, and the quantity is generally specified by the user.
Chemical reagent common quality levels
- Excellent grade (GR, green label): The main component content is very high and the purity is high, which is suitable for accurate analysis and research work, and some can be used as reference materials.
- Analytical purity (AR, red label): high content of main components, high purity, low interference impurities, suitable for industrial analysis and chemical experiments. Equivalent to foreign ACS level (American Chemical Society standard)
- Chemical purity (CP, blue label): high content of main components, high purity, interference impurities, suitable for chemical experiments and synthetic preparation.
- Experimental pure (LR, yellow label): high content of main ingredients, poor purity, no choice of impurity content, only suitable for general chemical experiments and synthetic preparation.
- Indicators and stains (ID or SR, purple label): Specific sensitivity is required.
- Designated grade (ZD): Chemical reagents customized for specific users according to the quality control indicators required by users.
- Electronic purity (MOS): It is suitable for the production of electronic products, and the content of electrical impurities is extremely low.
- Equivalent reagents (3N, 4N, 5N): The main component content is 99.9%, 99.99%, or 99.999% or more.
- Spectral purity: The purity of the main ingredients is 99.99%
- Level description:
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- Superior PureGR
- For microorganisms FMB
- Analytical Pure-AR
- IndustrialTECH
- Chemically pureCP
- PracticePRACT
- ExperimentalLR
- SynthesisFS
- Biochemical Grade-BC
- IndicatorIND
- High performance liquid chromatography- HPLC
- Gas chromatography- GC
- Biological StainingBS
- Liquid chromatography-LC
- BaselinePT
- For chromatographyFCP
- Atomic absorption AAS
- TLC-TLC
- Infrared absorptionIR
- Spectral puritySP
- Nuclear magnetic resonanceNMR
- Spectral PureUV
- Fluorescence AnalysisFIA
- SynthesisSYN
- Inorganic analytical reagents are commonly used inorganic chemicals for chemical analysis. Its purity is higher than that of industrial products with less impurities.
- Organic reagents for inorganic analysis are special organic compounds such as precipitants, extractants, chelating agents, and indicators for the determination, separation, and enrichment of elements in the analysis of inorganic substances, rather than general solvents. , Organic acids and organic bases. These organic reagents must have good sensitivity and selectivity. With the development of analytical chemistry and the chemical industry, such reagents with better sensitivity and selectivity will be developed, such as those that have complexing ability to some metals (such as alkali metals, alkaline earth metals) and ammonium ions that have appeared since 1967. This is the case for Crown ethers.
- Primary standards are compounds with high purity, few impurities, good stability, and constant chemical composition. Among the standard reagents, there are classifications such as volume analysis, pH measurement, and calorific value measurement. There is a distinction between primary benchmarks and working benchmarks in each category. All the first benchmarks must be verified by the National Academy of Metrology, and the production unit uses the first benchmark as the measurement standard for the work benchmark product. The standard reagents for commercial operations mainly refer to the capacity analysis work standards in the capacity analysis category [content range: 99.95% to 100.05% (weight titration)]. Generally used for calibration of titrants.
- Standard substances are chemicals used for comparison in chemical analysis, instrument analysis, or chemicals used to calibrate instruments. Its chemical composition, content, physical and chemical properties, and impurities must be known and meet the regulations or be recognized.
- Reagents Micro-analytical reagents are suitable for micro-analytical reagents where the permitted amount of the substance to be determined is only one percent (a weight of about 1 to 15 mg and a volume of about 0.01 to 2 ml).
- Organic analytical standards are chemical reagents used for comparison when determining the composition and structure of organic compounds. Its composition must be precisely known. Can also be used for microanalysis.
- Pesticide analytical standards (Pesticide analytical standards) are suitable for gas chromatography analysis of pesticides or determination of pesticide residues for comparison. Its content requires accuracy. There are solutions prepared from a small amount of a single pesticide, or mixed solutions prepared from multiple pesticides.
- Refractive index liquid is a high-purity stable liquid whose refractive index is known. It is used to determine the refractive index of crystalline substances and minerals. The refractive index of each package is marked on the outside.
- A normal solution is an aqueous solution containing one gram of equivalent solute in one liter of solution, which means a solution with a concentration of 1N. Indicators Indicators are substances that can change their color due to the presence of certain substances. It is mainly used to indicate the end of titration in volume analysis. Generally it can be divided into acid-base indicator, redox indicator, adsorption indicator and so on. In addition to analysis, indicators can also be used to test the presence of certain harmful and toxic substances in gases or solutions.
- Test paper is a small piece of dry paper impregnated with an indicator or reagent solution. It is used to test the presence of a compound, element or ion in the solution. It is also used for medical diagnosis. Instrumental analysis reagent
- Instrumental analytical reagents are reagents used in the process of sample analysis using special instruments designed according to the principles of physics, chemistry, or physical chemistry. Atomic Absorption Spectroscopy Standards
- Atomic absorption spectroscopy standards are reagents used as standards when analyzing samples using atomic absorption spectroscopy.
- For chromatography chromatography reagents are reagents and materials used in analytical methods such as gas chromatography, liquid chromatography, gas-liquid chromatography, thin-layer chromatography, and column chromatography, and include fixed solutions, supports, and solvents.
- For electron microscopy reagents are reagents such as fixatives, embedding agents, and staining agents used in research work using electron microscopes in fields such as biology and medicine.
- Solvent for NMR spectroscopy Solvent for NMR spectroscopy is mainly a deuterated solvent (also known as deuterated reagent or deuterated reagent), which is a solvent in which hydrogen in the organic solvent structure is replaced by deuterium (deuterium) . In nuclear magnetic resonance analysis, the deuterated solvent can not show peaks, and it does not interfere with the analysis of the hydrogen spectrum of the sample.
- For polarography reagents refer to the reagents required for quantitative and qualitative analysis by polarography.
- Spectral purity Spectral purity (Spectrography) reagent usually refers to a reagent with higher purity analyzed by emission spectroscopy.
- Spectrophotometric pure reagent refers to the solution used in the spectrophotometric method, which has a certain wavelength transmittance for qualitative and quantitative analysis.
- Biochemical reagent (Biochemical reagent) refers to biological materials or organic compounds related to life science research, as well as reagents for clinical diagnosis and medical research. Due to the wide range and rapid development of life sciences, this kind of reagent has a wide variety and complex properties.
Chemical reagent other levels
- In addition, there are still more than 20 levels.
- AAS Atomic Absorption Spectroscopy, BC Biochemical Reagent, BP British Pharmacopoeia, BR Biological Reagent, BS Biological Stain, CR Chemical Reagent, EP Special Pure, FCP Chromatography, FMP Microscope, FS Synthesis, GC Gas Chromatography, GR Premium Pure reagents, HPLC high-pressure liquid chromatography, ID indicator, IR infrared absorption spectroscopy, MAR microanalytical reagents, NMR nuclear magnetic resonance spectroscopy, OAS organic analysis standards, PA analysis, Pract practice, PT reference reagents, Puris special purity, Purum Pure, SP spectrally pure, Tech industrial, TLC thin layer chromatography, UP ultra-pure, USP United States Pharmacopoeia, UV ultraviolet spectrophotometrically pure, JX teaching reagents ... MI pharmaceutical grade, I industrial grade, F food grade, M cosmetic grade, S solid, L liquid, E fine, C crude ...
- Obviously, the quality standards of these chemical reagents are generally divided into the above quality levels, which is far from meeting the needs of scientific research and production.
Chemical reagents
- Chemical reagents are affected by external factors such as temperature, light irradiation, air and moisture during storage, transportation and sales, and are prone to deliquescent, mycin, discoloration, polymerization, oxidation, volatilization, sublimation and decomposition. Changes that render it useless. Therefore, reasonable packaging, appropriate storage conditions and transportation methods should be used to ensure that the chemical reagents do not deteriorate during storage, transportation and sales. Some special requirements for storage and transportation should be handled in accordance with special requirements. Some chemical reagents have a certain shelf life, so be careful when using them.
- The validity of chemical reagents varies greatly with the chemical properties of the chemicals. In general, chemically stable substances have a longer shelf life and simpler storage conditions.
Principles for judging the stability of chemical reagents
- To determine the stability of a substance, the following principles can be followed:
- Inorganic compounds can be used for a long time as long as they are properly stored and intact. However, those materials that are easily oxidized and deliquescent can only be stored for a short period of time (1 to 5 years) under conditions of protection from light, shade and dryness, depending on whether the packaging and storage conditions meet the requirements.
- Organic small molecular weight compounds are generally more volatile, and the tightness of the packaging is better, which can be stored for a long time. However, it is susceptible to oxidation, thermal decomposition, easy polymerization, and photosensitive materials.
- Organic polymers, especially life materials such as oils, polysaccharides, proteins, enzymes, and peptides, are extremely vulnerable to the effects of microorganisms, temperature, and light, and lose their activity, or deteriorate and deteriorate. Therefore, they must be stored in a refrigerated (freezing) state for a long time. Shorter.
- Reference materials, standard materials and high-purity materials should be stored in strict accordance with the storage regulations in principle to ensure that the packaging is intact and protected from the impact of the chemical environment, and the storage time should not be too long. Generally, the reference substance must be used within the validity period.
- The stability of most chemicals is relatively good, and the specific situation should be determined by actual use requirements. If the analysis data is generally understood, or the analysis results have no specific accuracy requirements, such as general teaching experiments, the general requirements for the quality level of chemical reagents can be made. However, the factory laboratory data is used to guide production, and the quality indicators of chemical reagents must not be vague. In general, chemical reagents used in general synthetic preparations can be used in most cases. However, the research and the synthesis of some special chemicals, in some cases, the quality of the raw materials is very strict and requires strict control.
- In actual use, people are always accustomed to judging the validity of chemical reagents by the date of production, but this is not true. For example, in a college or university, I have seen warehouse managers clean up all chemical reagents that have been in the factory for more than 2 years and prepare to destroy them, on the grounds that they have expired. Not to mention the huge waste of money, the destruction of hazardous chemicals alone is enough. What's more, it is not allowed for commercial companies to take over in order to prevent merchants from "deceiving people". Later, it was said that these large quantities of chemical reagents were "deeply buried".
- In short, the effectiveness of chemical reagents must first make basic judgments based on the physical and chemical properties of the chemical reagents, then make an apparent observation of the preservation status of the chemical reagents, and then draw conclusions on whether they can be used according to specific needs.
Classification of chemical reagents
Chemical Reagents in China
- The rational classification of chemical reagents is far from meeting the needs of scientific research and production due to the drafting of national standards, and it has seriously hindered the production of chemical reagents in China. With the existing 227 national standards and industry standards alone, it is difficult to give a quality specification for such a large number of chemical reagents; we also cannot give all the chemicals to a national quality standard. When it comes to reagents, the first thing people think of is analytical or chemical purity. Even when people buy, regardless of their use, they do nt buy it. This is also the reason why many varieties that do not have national standards, but somehow give the product a red AR label. It is because in actual use, many cases do not require true "analytical purity". The illegal manufacturers intentionally put the "analytical purity" label on industrial products to confuse the purity level. Although most cases do not cause quality accidents, However, it seriously interfered with the production and use of true standard materials, analytical grades.
- Furthermore, since the number of conventional chemicals is huge, but only 225 varieties are classified as excellent, analytical or chemical, what's the need?
Difference between Chinese and international chemical reagents
- Internationally, there is an increasing tendency to mark the grade and purity of chemical reagents according to the main content of the chemical, physical constants, etc. It is generally believed that when the main content, boiling point, melting point, density, refractive index, and even UV, IR, and NMR spectra are known, the purity and scope of application of a substance can be completely determined. This is the main difference between the contents of chemical reagent labels in China and foreign chemical reagent labels.
- In fact, the so-called chemical reagents are the reagents used in chemical experiments; that is, the chemical reagents required for chemical experiments. The division of chemical purity and grade can be determined according to the quality standards and scope of application of chemical agents.
Chemical reagent classification
- According to this, chemical reagents are divided into four categories: standard reagents, biochemical reagents, electronic reagents, and experimental reagents.
- The classification principle of the level 1 standard not only clarifies the quality standards, but also takes into account the scope of application of the chemical reagent.
- The level 2 standard is a further division based on the level 1 classification. It is a further definition and limitation of the level 1 standard.
- The level 3 standard is mainly for comparison with the original old standard, or to indicate a more accurate purpose.
- After the level 1 or level 2 is determined, the quality index of a chemical reagent and the application purpose to which this quality index can be applied are also determined.
- Therefore, the author recommends that the quality standards of "standard reagents", which are the standards and standards for analysis and inspection, be published to clear national standards. The quality indicators of the remaining "biochemical reagents, electronic reagents, and experimental reagents" can be determined by the market in accordance with enterprise standards or increasingly updated process requirements. In this way, our chemical reagent industry can get out of the old "stuck" old frame and develop Flourish!
- Standard reagent BZ: In accordance with international norms and technical requirements, it is explicitly used as a reference material for analysis and arbitration.
- Biochemical reagent SH: formulated for biochemical testing and biochemical synthesis.
- Electronic reagent DZ: Generally refers to chemicals and materials used in the electronic information industry, mainly including chemicals for integrated circuits and discrete devices, supporting chemicals for printed circuit boards, chemicals for surface assembly, and chemicals for display devices.
- Experimental reagent SY: "Synthetic reagent" determined according to "main content". Experimental reagents are used in chemical laboratories to synthesize, prepare and isolate common reagents that can meet the requirements of synthetic processes.
Chemical reagent chemical reagent label
- The quality index of chemical reagents determines the applicable scope of chemical reagents. Therefore, the author recommends that a national standard for "chemical reagent labeling" should be published and approved, and a standard specification index of chemical reagents in the standard will be used to describe Standardized production and reasonable use are of great significance.
- "Chemical reagent label" carrying information:
- Registered trademark: A trademark that clearly indicates the manufacturer's registration.
- Quality standards: Quality standards are displayed in both color and Chinese pinyin codes. The color display area is the manufacturer's information area at the bottom of the label; Chinese pinyin codes (such as BZ, SH, DZ, SY) are marked in prominent positions.
- Chinese name and type: The product names are based on the "Inorganic Chemical Substance System Naming Principles" and "Organic Chemical Substance System Naming Principles" promulgated by the Chinese Chemical Society in 1982, taking into account the long-term common names and trade names. And give as accurately as possible the type or dosage form that can describe the chemical reagent, such as: aqueous solution, alcohol solution, powder, block, stick, paste, and even particle size such as 200 mesh.
- English name: The product name is based on "Inorganic Chemical Substance System Naming Principles" and "Organic Chemical Substance System Naming Principles" promulgated by IUPAC in 1982, taking into account the long-term common names and trade names.
- CAS registration number: It consists of 9 digits in square brackets and is divided into three parts by hyphens. For example, [58-08-2] is the CAS registration number of caffeine.
- Molecular formula = molecular weight: Correctly write the molecular formula, that is, the molecular formula, and calculate the molecular weight accurately according to the international atomic weight published in 1968. If NaOH = 40.10.
- Content of main component: The mass percentage content of the chemical reagent determined according to the molecular method stipulated by national standards or enterprise standards. Such as 99.9%.
- Packing amount: The solid substance gives the mass packing amount of the chemical reagent, such as 1g, 5g, 10g, 25g, 100g, 250g, 500g, 1000g and so on. The volume of the chemical reagent is given by liquid or gas, such as 1ml, 5ml, 10ml, 25ml, 100ml, 250ml, 500ml, 1000ml and so on.
- Appearance: Use simple and accurate words to describe the physical state of the chemical reagent such as color, odor, and physical state.
- Physical constants: The measured values of physical constants such as "melting point, boiling point, density, viscosity, optical rotation, refractive index, and solubility" are given in order.
- Characteristic spectrum: give characteristic absorption peaks such as "ultraviolet, infrared and nuclear magnetic spectrum".
- Interference impurity content: Give the mass percentage content of the main impurities, especially the accurate measurement value of the mass percentage content of the main interference impurities.
- Dangerous Goods Rule Number: Dangerous goods must be marked with the Dangerous Goods Rule number. Production batch number: Give the production batch number to facilitate traceability.
Development Characteristics of Chemical Reagents Abroad
Development of chemical reagents towards supporting, standby reagents and supporting services
- The benefit of matching comes from improving the service for the convenience of users. In the foreign market, almost all conventional experiments and test items in industry, agriculture, health, environmental protection, scientific research, and teaching have set of test strips, supporting solutions, pre-filled chromatography columns, pre-coated sheets, various reference standards, and special applications. Tools and easy-to-use small instruments. The foreign market already has special auxiliary reagents for combinatorial chemistry, such as the basic modules of peptides: p-amino acids, Fmos (fluorenylmethoxycarbyl) -amino acids and other amino acid auxiliary reagents; the basic modules of organic synthesis: acid chloride, alcohol, Phenols, aldehydes, amines, carboxylic acids, ketones, etc .; and matching reagents customized according to user requirements. Most reagent companies, for the convenience of users, also sell small instruments, safety supplies, various map data (chemical structure, infrared, ultraviolet, emission spectrum, chromatography, etc.) often used in laboratory work, compound safety data, various Analysis of test method data, etc., a considerable part of which is published on CD-Rom discs.
- Many reagent companies not only sell tangible products, but also carry out technical consulting services, providing a wide range of technical services, such as: analysis testing, product intermediate scale-up tests, product process design, and drafting environmental protection schemes.
Chemical reagents attach great importance to scientific research and development
- Each reagent company has its own research and development department. Most companies also cooperate with universities, scientific research units, well-known scientists or other companies to develop, and even merge companies with certain technical expertise to enhance the company's development and competitiveness. They do not hesitate to invest heavily in scientific research and development in order to occupy an advantageous position in the rapid technological advancement and fierce market competition. Taking Merck KGaA as an example, from 1994 to 1998, the proportion of funds they invested in scientific research and development each year accounted for 9.56%, 9.O%, 8.18%, 9.76%, and 10.05%. During the same period, Merck (Darm. ): 43.52%, 43.94%, 45.29%, 47.0% and 46.95%.
Continuous progress in chemical reagent production, management and process technology
- Most companies' factories have obtained ISO 9001, ISO 9002, GMP or FDA quality management certifications. Attention is paid to process, industrial hygiene, and environmental protection at the production site. In recent years, with the continuous expansion of the variety of supply markets, many more complex process technologies have been widely adopted. The use of computer-aided production, technology, and management has become very common. Most reagent companies have established their own websites on the Internet. In addition to reporting the company's history, institutional structure, business scope, and catalogues, they are mainly online shopping, and continuously (about every week) release the current status of the company's operations. , Technical achievements, foreign cooperation, planning guidelines, etc. Their annual investment in fixed assets is huge. Take Merck KGaA as an example. From 1994 to 1998, the proportion of fixed asset investment in sales was 7.2%, 8.4%, 7.4%, 6.7%, 7.7% (eg: 1998 (Equivalent to 624 million marks, equivalent to RMB 2.8 billion).
Chemical reagent alliance and cooperation are a trend
- The types of chemical reagents are extremely complicated, and the services are wide, covering almost all economic and technological fields. It is impossible for any company to capture the entire business of reagents, and the characteristics of reagent sales are that the more varieties it operates, the more sales it will increase. The greater the amount of opportunity, the greater the probability of profit. Therefore, 20 years ago, there was a tendency for small companies to move closer to large companies, large companies to merge small companies, or to operate jointly. It is the Sigma-A1drich company that can supply the most varieties in the world. Their advantages in varieties are almost irreplaceable. This is indeed the result of joint operations.
- The new domestic trend is to achieve the effects of integration, alliance, and joint operation through the establishment of an e-commerce platform. E-commerce platforms such as Avatar Chemicals and China Reagent that specialize in reagent trading have emerged. This is a good integration of domestic reagent resources. The way. Because it conforms to the development model of online sales, it is believed that this will be the main trend of reagent management in the future.
Journal of Chemical Reagents
- "Chemical Reagent" is a Chinese core periodical published at home and abroad. Founded in 1979, it was sponsored by China Analytical Testing Association, Sinopharm Group Chemical Reagent Co., Ltd., and Beijing Guohua Fine Test Consulting Co., Ltd., and was organized by the National Chemical Reagent Information Station. "Chemical Reagent" reports and introduces the latest research progress, theoretical knowledge, scientific research results, technical experience, new product synthesis, separation, purification, and various analytical and testing technologies in chemical reagents, fine chemicals, special chemicals and related fields, Analytical instruments, industry trends, etc., reflect the level of development at home and abroad in a timely manner.
- Main columns: research reports and briefings, monographs and reviews, analysis and test research, reagent introduction, instrument introduction, experience exchange, production and purification technology, dynamics and information, etc.
- Won the first prize of The Sixth National Excellent Journal of Petroleum and Chemical Industry in 2006. Won the first prize of the Fifth National Excellent Journal of Petroleum and Chemical Industry. Awarded the third prize of the first National Excellent Science and Technology Periodical Award for three consecutive times. Excellent journals of the Ministry of Chemical Industry were awarded the third prize of the Ministry of Chemical Industry's scientific and technological progress. ) ", A thousand kinds of journals mainly extracted by American Chemical Abstracts (CA), and source journals of the comprehensive evaluation database of Chinese academic journals.
- Issue No .: CN 11-2135 / TQ ISSN 0258-3283
- Advertising business license: Jingdong Industry and Commerce Guangzi No. 0262
- Post office subscription codes across the country: 2-444
- Foreign General Distribution: China International Book Trading Corporation
- Foreign code: M591
- Pricing: 12 yuan / period, 144 yuan / year
- Address: 160 Dongsi South Street, Dongcheng District, Beijing
- Postcode: 100010
Chemical Reagent Safe Use of Chemical Reagent
- 1. Flammable and explosive chemical reagents
- Generally, chemical reagents with a flash point below 25 ° C are included as flammable chemical reagents. Most of them are highly volatile liquids and can be burned when exposed to open flames. The lower the flash point, the easier it is to burn. Common flash points below -4 ° C are petroleum, ethyl chloride, condensed ethane, diethyl ether, gasoline, carbon dioxide, propylene, benzene, ethyl acetate, and acetic acid.
- Never use open flame when using Easy Chemicals. Heat can not be directly heated by a heater. Generally, it is not heated in a water bath. Such chemical reagents should be stored in a cool and ventilated place. When placed in a refrigerator, be sure to use an explosion-proof refrigerator. In the accident that burned the entire laboratory, in places where such chemical reagents are used in large quantities, good ventilation should be maintained at all times. Explosion-proof electrical appliances must be used, and there must be no open flames on the scene.
- Flammable reagents can also explode during fierce combustion. Some solid chemical reagents such as nitrocellulose, picric acid, trinitrotoluene, trinitrobenzene, azide or overlapping compounds, cholate, etc., are explosive in themselves. When exposed to heat or open flames, they are extremely easy to burn or decompose and explode. Never use direct heat when using these chemical reagents. When using these chemical reagents, be careful not to have open flames around.
- There is also a class of solid chemical reagents that can react violently when exposed to water, emit a lot of heat, and can also explode. Such chemical reagents include metal potassium, sodium, lithium, calcium, aluminum hydride, calcium carbide, etc. When using these chemical reagents, it is necessary to avoid direct contact with water.
- There are also some solid chemical agents that can undergo strong oxidation upon contact. Such as yellow phosphorus; also some contact with oxidants or heat, impact or friction in the air can cause sharp combustion and even explosion. Such as phosphorus sulfide, red phosphorus magnesium powder, zinc powder, aluminum powder, sap, etc. When using these chemical reagents, we must pay attention to the ambient temperature should not be too high (generally do not exceed 30 , preferably 20 Below) Do not contact with strong oxidants.
- When experimenters using flammable chemical reagents, it is better to wear necessary protective equipment, and it is best to wear protective glasses.
- 2. Toxic Chemical Reagent
- General chemical reagents are toxic to the human body. Be sure to avoid a large amount of inhalation when using them. After using the performance reagents, wash your hands, face, and bath in a timely manner, and change the work clothes. Chemical reagents, which are called highly toxic chemical reagents in biological tests with a dead weight (LD50) below 50mg / kg, such as: potassium cyanide, sodium cyanide and other cyanides, arsenic trioxide and some arsenides, mercury dichloride And some mercury salts, sulfuric acid, dimethyl and so on. It is important to understand its LD50 when using unclear chemical reagents. For some commonly used highly toxic chemical reagents, it is necessary to understand the first-aid treatment methods when these chemical reagents are poisoned. The highly toxic chemical reagents must be kept by a special person, and the amount used must be strictly controlled.
- 3 Corrosive chemicals
- Any chemical reagents should be cleaned in time when they touch the skin, mucous membranes, eyes, and respiratory organs, especially those that are highly corrosive to the skin, mucous membranes, eyes, and respiratory organs (whether liquid or solid), such as: Acids and bases, phosphorus trichloride, phosphorus oxychloride, bromine, phenol, hydrazine, etc. It is also important to avoid touching the skin, mucous membranes, eyes, and respiratory organs. Before use, be sure to understand the first aid treatment methods in contact with these corrosive chemical agents. Such as acid splashed on the skin should be washed with dilute lye and so on.
- 4 Strongly oxidizing chemical reagent
- Strongly oxidizing chemical reagents are peroxides or oxyacids and salts containing strong oxidizing power. Such as: peroxy acid, nitric acid, potassium nitrate, perchloric acid and its salts, double complex acid and its salts, permanganic acid and its salts, benzoic acid, perrhenic acid, phosphorus pentoxide and so on. Strongly oxidizing chemical reagents can release oxygen to explode under appropriate conditions, and form explosive mixtures with organic materials such as magnesium, aluminum, zinc powder, sulfur and other flammable materials. Some water may also explode. When using such strong oxidizing chemicals When the reagent is used, the ambient temperature should not be higher than 30 ° C, the ventilation should be good, and it should not be used (heated) with organic or reducing substances.
- 5. Radiochemical reagent
- When using such chemical reagents, be sure to take protective measures in accordance with the method of use of radioactive materials.
Distillation and rectification of chemical reagents
- In chemical analysis, instrumental analysis, inorganic preparation, organic synthesis, and other scientific experiments, we often encounter that the chemical reagents used are not pure enough, or the chemical reagents of the required purity are not available, which requires us to conduct our own research in the laboratory. Existing chemical reagents are purified to obtain chemical reagents of the required purity. The following Apollo reagent editor briefly introduces the distillation and rectification methods.
- Distillation and rectification [2]
- Distillation and rectification is a widely used purification method. Purification is based on the difference in the distribution of mixed components between liquid and vapor in a liquid mixture. It is the first choice for the purification of volatile and semi-volatile chemical reagents.
- First, the principle of distillation
- The main purpose of distillation is to separate volatile and semi-volatile impurities from chemical reagents containing impurities or to evaporate the volatile and semi-volatile bodies, leaving non-volatile and hardly volatile impurities behind. The saturation vapor pressure change of a substance at different temperatures is the basis of distillation separation. In general, if the vapor pressures of the two components in the liquid mixture are significantly different, more volatile and semi-volatile components in the vapor phase can be enriched. Two phasesliquid phase and vapor phasecan be recovered separately, with volatile and semi-volatile components being enriched in the gas phase and non-volatile components being enriched in the liquid phase.
- With the exception of hydrocarbon mixtures and a few other examples, Raoult's and Dalton's laws can be used in ideal mixture systems, and mixture solutions often do not follow the ideal vapor-liquid phase behavior. Applying these two laws can get the specific volatility (aAB) of the two components of a binary system: aAB = (YA / YB) / (XA / XB) = P0A / P0B where YA and YB are in equilibrium Molar fractions of components A and B in the gas phase, XA and XB are the molar fractions of components A and B in the liquid phase at equilibrium, respectively, and POA and POB are the vapor pressures of components A and B at equilibrium, respectively, both obeying Raouilt's law . As aAB increases, so does the degree of enrichment.
- Second, simple distillation
- The simplest distillation device is shown in Figure-1. When a liquid sample is heated and transformed into steam, some of it is condensed and returned to the original distillation flask, while the rest is condensed and transferred to the collection container. Since the distillation is continuous, the composition that escapes and is kept in the liquid is slowly changing. As a method of purifying chemical reagents, simple distillation can only separate impurities with a large difference in boiling point, such as impurities with a boiling point different from the body by more than 50 ° C. To remove impurities whose boiling point is less than 50 ° C from the main body, the distillation method described below is used.
- The simple atmospheric distillation device is mainly composed of a distillation flask with a side tube, a thermometer, a condenser, a collector and a heating device. When installing, the mercury ball of the thermometer should be inserted slightly lower than the side tube. The side tube of the distillation flask is connected to the condenser in a horizontal type, and the lower port of the condenser is connected to the collector (Figure-1). When using a distillation device, choose a heating device based on the boiling point of the chemical test being distilled: When the boiling point of the distilled liquid is below 80 ° C, use a hot water bath to heat it; when the boiling point of the liquid is above 100 ° C, use direct fire on an asbestos net or use Oil bath heating; when the liquid temperature is above 200 ° C, use a metal bath for heating.
- When distilling liquids with a boiling point above 150 ° C, an air condenser can be used. In order for the distillation to proceed smoothly, zeolite must be added to the flask after the liquid has been charged into the flask and before heating. Because the inner surface of the flask is smooth, it is prone to overheating and sudden boiling, which prevents the distillation from proceeding smoothly. When adding new zeolite, you must wait for the liquid in the flask to cool to room temperature before adding it, otherwise there is a danger of sudden boiling. Zeolite can only be used once. When the liquid is cooled, the original zeolite added will lose its effect, so when the distillation is continued, new zeolite must be added. In atmospheric distillation, substances that are porous, non-fragile, and do not chemically react with the distilled substance can be used as zeolites. Commonly used zeolites are plain fired clay or broken porcelain pieces cut into 1 to 2 mm.
- After the distillation unit is installed, heating can begin. When the contents of the distillation flask began to boil, the temperature rose sharply. When the temperature rises to 1 ° C above and below the boiling point of the substance to be distilled, the heating intensity of the heater is adjusted to a level of one drop per second. At this time, the temperature of the heating bath should be maintained at about 20 ° C higher than the boiling point of the substance in the distillation flask. When distilling a substance with a higher boiling point, when the steam does not reach the side tube, it is cooled by the outside air and refluxed, so that it cannot be distilled out. At this time, you can use a small flame to evenly heat the underside of the side tube, but to avoid overheating, so that the thermometer does not indicate the correct boiling point, you can also properly heat the unheated part of the distillation flask. In the distillation operation, the following points should be noted:
- (1) Control the heating temperature. If a heating bath is used, the temperature of the heating bath should be a few degrees higher than the boiling point of the distilled liquid, otherwise it is difficult to distill the distillate. The more the heating bath temperature is higher than the boiling point of the distilled liquid, the faster the distillation speed. However, the temperature of the heating bath should not be too high. Otherwise, the vapor pressure of the distillation bottle and the condenser will exceed atmospheric pressure, which may cause accidents, especially when distilling low-boiling substances. Generally, the temperature of the heating bath must not be higher than the boiling point of the distilled material by 30 ° C.
- (2) When distilling high-boiling substances, it is easy to be condensed, and often the steam is condensed before it reaches the side tube of the distillation flask and drips back into the distillation flask. Therefore, short-necked distillation flasks or insulation measures should be used to ensure the smooth progress of the distillation.
- (3) Before distillation, the boiling point and saturated vapor pressure of the chemical reagent and its impurities must be known to determine when (that is, at what temperature) to collect the pure chemical reagent.
- (4) Round bottom flasks should be used for distillation flasks.
- Chemical reagents with a boiling point of 40-150 ° C can be simply distilled at normal pressure. For chemical reagents with a boiling point above 150 ° C, or chemical reagents with a boiling point below 150 ° C, but thermally unstable and thermally decomposable, vacuum distillation and steam distillation can be used, which will be briefly introduced below.
- 1. A simple device for vacuum distillation. The entire system consists of a Claisen distillation flask, a condenser tube, a collector, a suction (vacuum pump) device, and an interface. When installing a vacuum distillation device, attention should be paid to whether the device is sealed. The stopper must be a good quality stopper slightly larger than the diameter of the flask. The choice of stopper material should be based on the nature of the vapor in the liquid sample. If steam does not cause erosion to the rubber stopper, it is easy to keep the seal with the rubber stopper. It is also easy to keep the seal when using a good quality scrub. After the installation of the unit is completed, the vacuum distillation unit must be sealed for inspection before commencing distillation. The inspection method is to confirm the sealing of the device through the change of the pressure measurement value of the system. If the pressure value does not change, it means that the device does not leak air, and then the vacuum distillation operation can be performed. During distillation under reduced pressure, a capillary can be inserted into the distillation flask to prevent bumping. The upper end of the capillary is sealed and the lower end is open. After checking and confirming that the distillation device is airtight, add the chemical reagents to be purified into the flask, the amount is half of the flask capacity, and then draw the system to a reduced pressure state and start heating. The depth of the flask immersed in the heating bath, the liquid level of the substance to be distilled in the flask must be lower than the liquid level of the heating bath. Especially when distilling high-boiling substances, the flask should be as deep as possible. When distillation under reduced pressure, foam often occurs due to the presence of low-boiling solvents, and it is necessary to distill these low-boiling solvents under low vacuum conditions at the beginning of distillation, and then slowly increase the vacuum. The degree of vacuum depends on the vapor pressure of the liquid sample in the device. The cooling effect before distillation must be good, otherwise it is difficult to increase the vacuum of the system.
- The relationship between pressure and boiling point can be approximated by the following formula: logP = A + (B / T)
- Where P is the vapor pressure, T is the absolute temperature, and A and B are constants. In actual operation, you can refer to the relevant pressure boiling point diagram. When the distillation components are distilled at the desired boiling point, or when the distillation process needs to be interrupted, the heating should be stopped, the heating bath should be removed, and after cooling, the vacuum of the system should be slowly relieved, and air should be allowed to enter the device to return to normal pressure. Shut off the vacuum pump .
- Steam distillation is a common method for separating and purifying organics in samples, especially when there are a lot of resinous impurities in the samples. The composition of the sample to be processed should have the following conditions: insoluble or almost insoluble in water, long-term coexistence with water during boiling without chemical change, and a vapor pressure of more than 10mmHg at about 100 .
- Steam distillation is another technique for thermally sensitive sample preparation and purification. It can also be used for liquid samples with poor heat transfer. Local overheating will directly cause heating. Steam distillation can be accomplished by continuously passing steam through the sample mixture in the vessel. Sometimes users add water directly into the flask for the same purpose. Steam carries highly volatile components in the gas phase and the concentration of such volatile materials in the steam mixture is related to their vapor pressure in the steam mixture.
- This technique is very gentle, and the material that is distilled during the distillation process does not heat up to a temperature higher than that of steam at all. At the end of the process, steam and separation materials are condensed. Generally, they are immiscible and can be separated into two phases. Sometimes analytical chemists must use additional sample preparation techniques, such as liquid-liquid extraction to completely separate the aqueous and organic layers.
- 2. A simple device for water vapor distillation, A is a water vapor generator, and glass tube B is a liquid level gauge. It can be seen that the height of the internal water surface occurs. Usually the water volume is 75% of the container volume. If it is too full, the water will be flushed to the flask when boiling. The safety glass tube C is inserted almost to the bottom of the generator A. When the pressure in the container is too high, water can rise along the glass tube to adjust the internal pressure. If the system becomes clogged, water will be sprayed from the upper opening of the tube. At this time, you should check whether the lower end of the steam duct in the round bottom flask is blocked. The distillation part usually uses a 500-ml long-necked round bottom flask. In order to prevent the liquid in the bottle from splashing into the condensate tube due to splashing, the position of the flask was tilted 45 degrees in the direction of the generator. The liquid sample in the bottle should not exceed 1/3 of its volume. The end of the steam introduction pipe E should be bent so that it is perpendicular to the center of the bottom of the bottle and extends close to the bottom of the bottle. The inner diameter of the steam outlet pipe F (bending angle of about 30 degrees) is preferably larger than that of the pipe E. One end is inserted into a double-hole wooden plug to expose about 5 mm, and the other end is connected to the condenser pipe. The distillate enters the receiver H through the pipe. The periphery of the receiver can be cooled with a cold water bath.
- A T-shaped tube should be installed between the water vapor generator and the long-necked round bottom flask, and a spring clip G should be connected to the lower end of the T-shaped tube in order to remove the condensation in time to block the water droplets.
- For steam distillation, first place the sample solution in D. Heat the steam generator until it is close to boiling, then tighten G to make the steam evenly enter the round bottom flask. In order to prevent the steam from condensing in D and accumulating too much, if necessary, an asbestos net can be placed under D and heated with a small fire. The heating rate must be controlled so that all the steam can condense in the condensing pipe. If the substance that is volatilized with water vapor has a high melting point and it is easy to precipitate solids after condensation, the flow rate of the condensed water should be reduced to keep it liquid after condensation. If solids have precipitated and are close to clogging, the circulation of cooling water can be temporarily stopped, and even the cooling water needs to be temporarily removed to allow the material to melt and flow into the receiver with the water. It must be noted that when cooling water is re-introduced into the condenser jacket, it must be carefully and slowly flowed in to prevent the condenser tube from bursting due to sudden cooling. In case the condenser tube is blocked, stop the distillation immediately and try to clear it. For example, use a glass rod to scoop out the blocked material or use hot water to melt it out in a condenser jacket.
- When the distillation needs to be interrupted or the distillation is completed, the spring clamp G must be opened to let the atmosphere pass, and then the heating is stopped, otherwise the liquid in D will be sucked back into A. During the distillation process, if you find that the water level in the safety tube C rises rapidly, it means that a blockage has occurred in the system. At this time, you should immediately open the spring clamp G and then remove the heat source. After removing the blockage, continue steam distillation.
- Three. Distillation
- Rectification is a fractional distillation using a fractionation column. During the rectification process, after the rectified chemical is boiled in a distillation flask, the steam evaporates from the round bottom flask into the fractionation column, and is partially condensed into liquid in the fractionation column. Because this liquid contains a lot of low-boiling components, its boiling point is lower than that of the liquid in the distillation flask. When another part of the steam in the distillation flask rises to the fractionation column, it exchanges heat with these already condensed liquids to make it boil again, and the rising steam itself is partially condensed. Therefore, a new one is generated. The liquid-vapor equilibrium results in an increase in low-boiling components in the vapor. When this new steam rises in the fractionation column, it is condensed into a liquid, and then it is boiled by heat exchange with another rising steam. As the rising steam continually condenses and evaporates in the fractionation column, each condensation and evaporation causes the low-boiling components in the steam to continuously increase. Therefore, the rising process of steam in the fractionation column is similar to the simple distillation after repeated many times, so that the low-boiling components in the steam are gradually increased. It can be seen that the fractionation column is a key device in the fractionation process. If an appropriate fractionation column is selected, the vapor obtained from the top of the fractionation column after condensation can be a pure low-boiling point component or a low-boiling point component. The main component of the effluent.
- The fractionation capacity and efficiency of a fractionation column are represented by "theoretical plate value" and "theoretical plate equivalent height (HETP)", respectively. A theoretical plate value is equivalent to a simple distillation. Fractionation columns with the same fractionation capacity are not necessarily equal in length. For example: A and B fractionation columns have theoretical plate values of 20, the height of A is 60 cm, and the height of B is 20 cm. Obviously, the theoretical plate equivalent heights of the two are different. Because the theoretical plate height is:
- HETP = fractionating column height / theoretical plate number
- Therefore, the theoretical plate equivalent height of the fractionation column A is 3 cm, and the theoretical plate equivalent height of the fractionation column B is 1 cm. It can be seen from this example that the lower the theoretical plate equivalent height of the fractionation column, the higher the fractionation efficiency per unit length.
- When performing the rectification operation, the fractionation column is mainly selected according to the boiling point difference between the main body and the impurities in the chemical reagent being rectified and the high and low range of the boiling point. If the boiling point difference between the two components is above 100 ° C, a fractionation column may not be used; if the boiling point difference is around 25 ° C, an ordinary fractionation column may be selected; if the boiling point difference is around 10 ° C, a fine fractionation column is required , Such as microgroove fractionation columns. The heating source used in the rectification process must be stable to ensure a stable heating temperature. Only with strict control and constant heating can the required reflux ratio be maintained. If the heating is too fast, flooding will occur and the fractionation efficiency will be too poor. If the heating is too slow, the fractionation column can only function as reflux condensation, and nothing can be distilled at all. In addition, during the rectification, the reflux and distillate need a proper ratio, that is, the reflux ratio should be appropriate, and its value is roughly equal to the theoretical plate value of the fractionation column, so that the rectification process can proceed normally.
- Fourth, the practical application of distillation and rectification
- Distillation and rectification are mainly used for liquids or chemical reagents that can be heated to become liquids, especially for the purification of organic chemical reagents. Before distillation or rectification, some chemical reagents can sometimes be added to chemically react with impurities in the chemical reagents to be purified, resulting in substances with higher boiling points (or lower), which are easier to remove during distillation or rectification.
- During distillation or rectification, the first and last remaining fractions are often removed. The more the two ends are removed, the higher the purity of the obtained chemical reagent, but the lower the yield.