What are the common methods of analytical chemistry? First of all, chemical analysis refers to the method of determining the chemical composition or composition of a substance.
According to the nature of the analyzed substance, it can be divided into inorganic analysis and organic analysis.
According to the requirements of the analysis, it can be divided into qualitative analysis and quantitative analysis. According to the quantity of the analyzed substance sample, it can be divided into constant analysis, semi-micro analysis, micro analysis and ultra-micro analysis.
Classification: Chemical analysis can be divided into titration analysis (titrimetry) and gravimetric analysis (gravimetry) according to its different operation methods.
Titration analysis: According to the concentration and volume of the standard solution consumed by titration and the chemical reaction measurement relationship between the measured substance and the standard solution, the content of the measured substance is obtained. This analysis is called titration analysis, also known as volume analysis (volumetry). Use the four major balances of the 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 pH and acid-base content of various acids and bases;
Oxidation-reduction titration: measuring substances with oxidation-reduction properties;
Complexometric titration: measuring the content of metal ions;
Precipitation titration: Determination of halogen and silver.
Gravimetric analysis
Through appropriate methods such as precipitation, volatilization, electrolysis, etc., the component to be measured is converted into another pure, chemically composed, fixed compound and separated from other components in the sample, and then its mass is weighed. The content of the component to be tested is calculated according to the mass obtained by weighing, and such an analysis method is called gravimetric analysis.
Gravimetric analysis is suitable for the constant analysis of components whose content is greater 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.
The basic operations of gravimetric analysis include: sample dissolution, precipitation, filtration, washing, drying and burning steps.
Dissolution of the sample
The method of dissolving or decomposing the sample depends on the nature of the sample and the components to be tested, and should ensure that all components to be tested are dissolved. During the dissolution process, the components to be tested must not be lost (including redox) and the added reagents will not interfere with subsequent analysis.
2. 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, the speed of adding reagents, the volume of solution during precipitation, temperature, precipitation aging time, etc. It must be carried out in accordance with the prescribed operating procedures, otherwise serious errors will occur.
3. Filtration and Washing Technology
The purpose of filtration is to separate the precipitate from the mother liquor, separate it from excess precipitant, coexisting components or other impurities, and obtain pure precipitate through washing. For precipitates that need to be burned, filter paper is often used. For precipitates that can be weighed only after drying, they are often filtered using a Gooch crucible. Filtration and washing must be completed at one time without interruption, and the sediment must not be lost during the entire operation.
