Sample pretreatment operation method

Sample pretreatment method

Sample pretreatment should include all operations before injection, except for steps such as weighing, dissolution, and dilution. The sample needs to:

① Filtering;

② Extraction;

③ Derivatization (pre column derivatization);

④ Liquid chromatography (low-pressure column chromatography);

Some samples cannot be analyzed for injection after pre-treatment and require derivatization to enable some components without UV absorption or fluorescence to be detected by UV and fluorescence detectors after derivatization. This not only improves sensitivity but also improves separation (quality change). Sample pretreatment can also bring some problems, such as sample loss, sample contamination, incomplete derivatization reactions, or the generation of multiple reactants. Derivative reactions often affect the accuracy of experiments or introduce errors throughout the entire sample pretreatment process.

The sample solution used for liquid chromatography analysis must be uniform and free of particles, as particles can damage the injector and block the column head. The processed sample should be aligned with the light and shaken before being prepared for column loading, and the sample solution should be checked for particles. As long as particles, turbidity, or emulsification are visible, they should be filtered, and the filter membrane should be able to retain 0.15 μ Particles above m may cause contamination during the sample filtration process, resulting in a decrease in the content of sample components due to filtration and adsorption, and errors caused by the volatilization of sample solvents.

The purpose of extraction is to separate the analyzed components from the co soluble sample medium, or to reduce the damage of substances (such as proteins) and interferences to the column. Organic solvent extraction is generally used, which requires the solvent used for extraction to have low toxicity, good volatility, few impurities, good solubility of the test sample, and immiscibility with water.

Commonly used solvents include ether, ethyl acetate, dichloromethane, chloroform, benzene, or two or more mixed solvents. After extraction, the sample can generally be directly injected, sometimes requiring concentration or blowing dry concentration, and then dissolved and injected with a fixed volume of liquid or mobile phase. This increases the sample concentration, improves sensitivity, and avoids interference from solvent peaks on the sample peaks. In extraction, the solubility of sample molecules should be considered. In addition to lipophilic and water-soluble components, there are also water-soluble salts made from lipophilic components. The extraction method is as follows:

Water soluble samples

(1) Extraction method for acidic components and generated salts:

After the impurities are extracted by organic solvent and base note to acidity, organic solvent is added for extraction or sample injection, or it is dried under N2 flow, and the sample is injected after being dissolved by appropriate solvent.

(2) Extraction method for alkaline components and generated salts:

After the impurities are extracted by organic solvent and adjusted to alkalinity, the organic solvent is added for extraction or sample injection, or it is dried under N2 flow, and the sample is injected after being dissolved by appropriate solvent.