Analytical reagent

Analytical reagents are a class of chemical reagents used for analytical testing. They provide molecules, ions or free radicals in qualitative or quantitative analysis, and their reaction products are precipitated or colored compounds or fluorescent substances. Indicators, titrants, and instrumental analysis reagents are also such. The most important feature of the analytical reagent is its sensitivity and selectivity. Even if the amount of the substance to be tested is extremely small or the concentration of the ion is small, the reagent can be used for identification or quantitative determination. For example, when the concentration of magnesium ions is 1.2 mg/l, precipitation is caused by the addition of reagents such as disodium hydrogen phosphate and ammonium chloride. Selective reagents and group reagents must be used in analytical chemistry. Selective reagents are reagents that react only with a limited number of chemicals, such as silver nitrate, a selective precipitation reagent for chlorides and bromides. The organic selective reagent can form a chelate with a metal ion, such as chrome azurol S, 1-(2-pyridylazo)-2-naphthol (PAN), 4-(2-pyridylazo)-. Hydroquinone (PAR) and the like can be used as selective reagents for different metal ions under different conditions. The group reagent is a reagent that can separate many ions at the same time. Some reagents, under certain conditions, with or without other ions, react only with the substance or ion generating characteristics. These reagents are called special effects agents. The specificity is determined by the product. The size of the ions, the charge density, and the electronic arrangement of the reagents and reactive ions must meet certain conditions, otherwise no reaction will occur. Most inorganic analytical reagents have good selectivity; most organic analytical reagents have good specific effects. There are many reagents for analysis of organic functional groups, such as bromocresol green, ninhydrin, benzoquinone, 2,4-dinitrophenylhydrazine, semicarbazide, etc. for qualitatively and quantitatively determining organic acids, aldehydes, ketones and the like. [Classification] (1) Chemical analysis reagent: A test item used for chemical reaction analysis. 1) Reference Reagent: A pure compound that is used directly to formulate or calibrate a standard solution in a volumetric analysis. 2) Indicator: A reagent for indicating the end point of the titration, a pH indicator, a redox indicator, an adsorption indicator, a metal indicator, a fluorescent indicator, and the like. (2) Instrumental analysis reagent: a high purity compound dedicated to instrumental analysis. 1) Spectral Pure Reagent: A spectrally pure compound, often expressed in SP, for reagents for spectroscopic analysis. 2) Chromatographic reagents: reagents for gas chromatograph analysis and for liquid chromatograph analysis. 3) Deuterated reagent: A reagent dedicated to the analysis of nuclear resonance instruments. [Purification of Organic Analytical Reagents] Organic reagents are widely used in analytical chemistry, mainly in solvents, precipitants, complexing agents, indicators, color developers, and surfactants. In order to adapt to various analytical needs, it is sometimes necessary to purify a certain reagent, liquid organic reagents are often purified by distillation, and solid materials are purified by crystallization or sublimation. A substance having a high vapor pressure, that is, an organic reagent which has a low boiling point and does not decompose at a boiling temperature, is usually subjected to atmospheric distillation; for a substance which is difficult to be volatilized and slightly soluble in water, an organic reagent which has a higher boiling point or a boiling temperature is decomposed. Vacuum distillation or steam distillation can be employed. Purification of organic reagents by distillation is a common purification method in the laboratory. The commonly used distillation apparatus generally comprises a distiller, a condenser and a receiver. The auxiliary part also has a heater, a thermometer, a liquid pipe, a cork and the like.