When the sample is treated with the QuEChERS pretreatment method, anhydrous magnesium sulfate needs to be added. The anhydrous magnesium sulfate is exothermic with water and agglomerated. The temperature of the sample will increase some heat labile pesticides such as omethoate, methamidophos. phorate and captan in degradation and reduce the recovery rate.
Therefore, usually, add dry ice before homogenizing the sample, or put the sample in the refrigerator in advance to cool to 4 ° C and then homogenized. In order to prevent the anhydrous magnesium sulfate from agglomerating with water, immediately shake the tube after the addition, or use a homogenizer to break up the bulk magnesium sulfate and the sample.
In addition, animal and plant samples with high-fat content should be placed in a refrigerator for overnight storage. For samples containing sulfides such as strontium, sight-preheating is required before extraction.
Last but not least, control the pH of the extraction solvent. Some pesticides are unstable in acidic or alkaline substrates, easily degraded, and with lower recovery rate. we found that the addition of buffer salts could greatly reduce the degree of degradation of acid-base sensitive pesticides according to related tests.
QuEChERS Operation Method Improvement
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