Chemical analysis is mainly suitable for components with constant or semi-trace analyte content, while instrumental analysis is mainly used for the analysis of trace or even trace components.

The accuracy of chemical analysis is very good, but the precision is not good, that is, the content of constant or semi-trace components can be accurately determined, but the effect of trace components is poor or even impossible to detect, and the error range is small, which usually requires control within +-0. 1%. The analytical accuracy of the instrument is poor, but the precision is good. It can determine trace components qualitatively or quantitatively, but the error range is large, above +- 1%.

For example, if the content of a component to be detected is 10%, the detection error is relatively large within +- 1%, that is, the detection rate is 9%- 1 1%, and the required error is +-0. 1%, that is, the detection rate is. For the component with the content of 0. 1%, the error of +- 1% is completely acceptable, that is, 0.09%-0.1%is detected without the required error of +-0. 1%.

For example, it is required to detect calcium and magnesium ions in water, and the content of these ions is high, which also requires accurate detection. If water is to be treated to remove calcium and magnesium ions, ammonium carbonate should be added and boiled. If the error is within 0.65438 0%, ammonium carbonate can be ignored more or less, but if the error is within 65438 0%, the amount of ammonium carbonate is too much.

To detect an organic pollutant in water, such as DDT, the content of this substance in water is usually very small, and the upper limit of the content in drinking water is very low. The accuracy of chemical analysis is not enough and there is no suitable method. It is more convenient to analyze with instruments, and the results can meet the requirements.

In a word, chemical analysis and instrumental analysis are two important branches of analytical chemistry, both of which are indispensable and complement each other.