Detailed introduction of chemical analysis


Posted June 26, 2021 by Bonnibelle

Chemical analysis refers to the method of determining the chemical composition or composition of a substance.

 
Chemical analysis refers to the method of determining the chemical composition or composition of a substance.

According to the nature of the analyte, it can be divided into inorganic analysis and organic analysis. According to the requirements of analysis, it can be divided into qualitative analysis and quantitative analysis. According to the number of analyte samples, it can be divided into constant analysis, semi-micro analysis, micro analysis and ultra-micro analysis.



Research history

In the 19th century when the knowledge of inorganic chemistry was gradually systematized, Jö; ns Jakob Berzelius (Jö; ns Jakob Berzelius) analyzed the invention and use of the balance to make the measured experimental data closer to the true value, so that any law has a conclusive The facts proved. Beritzius introduced many new methods, new reagents, and new instruments to analytical chemistry for the determination of atomic weight, bringing the accuracy of quantitative analysis to a new height. Later, people respected him as the father of analytical chemistry.

In terms of qualitative analysis, in 1829, the German chemist Hoinrich Rose wrote a "Analytical Chemistry Course", and proposed a systematic qualitative analysis method for the first time, which is basically the same as the current general analysis method. By the end of the 18th century, the various forms and principles of acid-base titration were basically determined. As for an important part of analytical chemistry, spectral analysis began with Newton. Newton began to study spectroscopy in 1666 and published his first paper "A New Theory of Light and Color" in 1672.



Application

Industrial raw materials, semi-finished products, finished products, agricultural soils, fertilizers, feeds, and transportation fuels, lubricants, etc., require chemical analysis in the process of research, trial production, production or use.



Classification

Chemical analysis can be divided into titration analysis (titrimetry) and gravimetry (gravimetry) according to its operating methods.

Titration analysis

According to the concentration and volume of the standard solution consumed by the titration and the measurement relationship between the test substance and the standard solution, the content of the test substance is obtained. This analysis is called titration analysis, also called volume analysis (volumetry). Utilize the four major balances of solution: acid-base (ionization) balance, redox balance, complexation (coordination) balance, precipitation and dissolution balance.

Titration analysis can be divided into:

Acid-base titration: measure the acid-base degree and acid-base content of various acids and bases;
Oxidation-reduction titration method: measuring substances with redox properties;
Complexometric titration: measuring the content of metal ions;
Precipitation titration: measure halogen and silver.
Gravimetric analysis

Through appropriate methods such as precipitation, volatilization, electrolysis, etc., the component to be tested is transformed into another pure, chemically composed fixed compound to be separated from other components in the sample, and then its mass is weighed according to the mass obtained. Calculate the content of the component to be measured, such an analysis method is called gravimetric analysis. The gravimetric method is suitable for constant analysis with a component content of more than 1%. It is characterized by high accuracy. Therefore, this method is often used for arbitration analysis, but the operation is troublesome and time-consuming. [2]

The basic operations of gravimetric analysis include: sample dissolution, precipitation, filtration, washing, drying, and burning.

Dissolution of the sample
The method of dissolving or decomposing the sample depends on the nature of the sample and the component to be tested. It should be ensured that all the components to be tested are dissolved. During the dissolution process, the components to be tested must not be lost (including redox). The added reagents will not interfere with subsequent analysis.

The precipitation of the sample
The requirement of gravimetric analysis for precipitation is to be as complete and pure as possible. In order to meet this requirement, different precipitation conditions should be selected according to different types of precipitation, such as the order of adding reagents, the amount and concentration of reagents added, and the speed of reagent addition. , The volume of the solution, the temperature, the time of precipitation aging, etc. during precipitation. It must be carried out in accordance with the prescribed operating procedures, otherwise serious errors will occur.

Filtration and washing technology
The purpose of filtration is to separate the precipitate from the mother liquor, separate it from the excess precipitant, coexisting components or other impurities, and obtain a pure precipitate by washing. For the precipitate that needs to be burned, filter paper is often used. For the precipitate that can be weighed only after drying, it is often filtered by an ancient crucible. Filtration and washing must be completed at one time without interruption, and precipitation must not be lost during the entire operation.



Related extensions

Instrumental analysis method: The analysis method based on the physical and physicochemical properties of substances is called physical and physicochemical analysis. This type of method requires a more special instrument, usually called an instrumental analysis method. The main instrumental analysis methods are as follows:

Optical analysis method
An analytical method based on the optical properties of substances. Mainly include: molecular spectroscopy, spectroscopic analysis, molecular fluorescence and phosphorescence analysis; atomic spectroscopy, such as atomic emission spectroscopy, atomic absorption spectroscopy.

Electrochemical analysis method
An analytical method established based on the electrochemical properties of substances. Mainly include potential analysis method, polarography and voltammetry analysis method, electric weight and coulomb analysis method, conductance analysis method.

Chromatographic analysis
A separation and determination method based on the difference in adsorption capacity, partition coefficient or other affinity of substances in two phases (stationary phase and mobile phase). The biggest feature of this analysis method is that it integrates separation and determination. It is an efficient, fast and sensitive analysis method for multi-component substances. Mainly include gas chromatography, liquid chromatography.



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Last Updated June 26, 2021