For example, when using GC-MS analysis, in order to increase the detection sensitivity, 8 ml or more of the supernatant may be taken at sixth step, and then spin and concentrate before proceeding to the next step; for samples containing more pigments, such as green vegetables, leeks, etc., especially when using a detector that is easily contaminated such as GC-ECD, a small amount of GCB can be added in step 6, but for some pesticides such as dicofol and chlorothalonil have some losses due to their instability in the acetone medium.
F Sehenck et al. (2001) have shown that solid phase extraction can also be used for purification. After step 5, the supernatant can be taken on a prepared PSA SPE cartridge with acetone/toluene (3:1) to elute. If necessary, the supernatant can be concentrated and then passed through the column to improve the sensitivity of the test to meet the requirements of sample analysis.
Advantages of the QuEChERS method. The QuEChERS method has the following advantages:
1) High recovery rate, the recovery rate of a large number of polar and alkaline pesticide varieties is between 85% and 100% (mostly greater than 95%);
2) High accuracy (reproducibility less than 5%), corrected by internal standard method;
3) Short analysis time, and 6 pre-weighed samples can be measured within 30-40 minutes;
4) Small amount of solvent used, little pollution and the no chloride-containing solvent;
5) It is easy to operate and can be completed without high skill or training;
6) Very few glassware used;
7) The method is very strict, and the organic acid is removed during the purification process;
8) It can be completed in a small laboratory;
9) The acetonitrile is sealed immediately after it is added to the container, so that it has less chance of contact with the worker;
10) Low cost of the solvent;
11) The simple device used in the sample preparation process.