Why does sample preparation determine the success or failure of an experiment?

The chemical composition of food is very complex. It not only contains macromolecular organic compounds such as protein, sugar, fat, vitamins, and organic pesticides introduced due to pollution, but also contains various inorganic elements such as potassium, sodium, calcium, and iron. These components often exist in a complex bonded or complexed state through various forces. When a method is used to determine the content of a certain component, the presence of other components often interferes with the determination.

Therefore, sample pretreatment often determines the success or failure of the experiment, so what should be done in this situation? Do you know how to deal with it?

In order to ensure the smooth operation of the analysis and get accurate results, the force between the components in the sample must be destroyed before the determination, so that the measured components free, while excluding interfering components; in addition, some measured trace components, such as contaminants, pesticides, aflatoxins, etc., due to the small content, it is difficult to detect, in order to accurately measure their content, the sample must be enriched or concentrated before the determination.

These operations are collectively referred to as sample pretreatment, which is an important part of the food composition analysis process and is directly related to the success or failure of the analysis test. Only a few foods, such as beverages, beer, liquor, etc., in the determination of its trace element content without pretreatment, directly with the atomic absorption spectrophotometer can be determined.

Why do samples need to be pre-treated?

1、 To make the measured components separated from the complex sample and made into the form of solution for easy determination.
2、 Remove the matrix substances that interfere with the analysis and determination.
3、 If the concentration of the measured component is low, it also needs to be concentrated and enriched.
4、 If the measured component is difficult to detect by the selected analytical method, it needs to be quantitatively transformed into another easily detectable compound by sample derivatization.

Are there still requirements for sample pre-treatment?

1, whether the sample should be pretreated, how to pretreatment, sampling what method, should be considered according to the characteristics of the sample, the requirements of the test and the performance of the analytical instrument used.

2, should try not to use or use less pretreatment, in order to reduce the operating steps, speed up the analysis, but also to reduce the adverse effects of the pretreatment process, such as the introduction of contamination, the loss of substances to be measured.

3, decomposition method when processing samples, decomposition must be complete, can not cause the loss of the measured components, the recovery of the components to be measured should be high enough.

4, the sample can not be contaminated, can not introduce the components to be measured and interfere with the determination of the substance.

5, the consumption of reagents should be as little as possible, the method is simple and easy to use, fast, less pollution of the environment and personnel.

When the measured component in the sample is free - the solution is prepared by the dissolution method.

When the measured component in the sample is in the bound state - the decomposition method is used to prepare the solution.