The QuEChERS method is essentially the derivation and further development of solid phase extraction technology and matrix solid phase dispersion technology. The core of the method is that it proposes a new mode of extracting pesticides by adding a single solvent (acetonitrile) to the class of protective agents; and replacing the commonly used anhydrous sodium sulfate with anhydrous magnesium sulfate with a stronger water absorption function; using PSA (N -Propylethylenediamine) and GCB (graphitized carbon black) purification to remove fatty acids, organic acids and pigments. Compared with other extraction chromatography fillers such as Florisil, neutral alumina, etc., PSA has less adsorption and higher recovery rate for some pesticides.
The basic steps of the QuEChERS method are as follows:
1. Take 15ml of acetonitrile solution containing 1% acetic acid into a 50 ml Teflon tube containing 6g of anhydrous magnesium sulfate and 1.5g of anhydrous sodium acetate;
2. Add the internal standard, shake and mix;
3. Add 15g crushing sample into the centrifuge tube;
4. Shake for 1 min immediately, mix the anhydrous magnesium sulfate with the sample, and make the sample into a paste;
5. Centrifuge the tube at 3700 r/min for 3 min, the organic solvent is separated from the sample;
6. 1ml of the supernatant is taken in a centrifuge tube containing 0.3 g of anhydrous magnesium sulfate and 50mg of PSA, and vortex mixing;
7. 3700 r/min is centrifuged for 3 min;
8. Take the supernatant to analyze.
1. Take 15ml of acetonitrile solution containing 1% acetic acid into a 50 ml Teflon tube containing 6g of anhydrous magnesium sulfate and 1.5g of anhydrous sodium acetate;
2. Add the internal standard, shake and mix;
3. Add 15g crushing sample into the centrifuge tube;
4. Shake for 1 min immediately, mix the anhydrous magnesium sulfate with the sample, and make the sample into a paste;
5. Centrifuge the tube at 3700 r/min for 3 min, the organic solvent is separated from the sample;
6. 1ml of the supernatant is taken in a centrifuge tube containing 0.3 g of anhydrous magnesium sulfate and 50mg of PSA, and vortex mixing;
7. 3700 r/min is centrifuged for 3 min;
8. Take the supernatant to analyze.
The above is the principle of solid phase dispersion of the matrix: the sample is treated by centrifugal purification to remove most of the impurity interference, which is also the most widely used program. In actual operation, it can also be changed according to the specific situation.
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