Some Special Problems Arise in the application of QuEChERS
One special problem is that the extraction of acetonitrile, produces certain heat when anhydrous magnesium sulfate is added. In some ways, the heat can increase the extraction rate or raise extraction efficiency. But on the other side, too much heat will lead to the loss of pesticide residues that are thermally unstable or volatile.
To reconcile these conflicts in the practical application, we have proved that QuEChERS has good recovery for hundreds of pesticides and different analytes. The heat may cause potential degradation to a minority of pesticides, yet the acidic environment can help these pesticides keep stable. When using frozen samples, the temperature can be very moderate after extraction.
Another problem is that in all multi-pesticide residues analysis, some kinds of pesticides such as captan and folpet, can not get efficient, persistent, and stable recovery. On the whole, the acidic environment can reduce the loss of these pesticide residues, but the analytes can be easily degraded in the non-acid samples.
This problem sometimes arises before the samples are extracted. In fact, the above-mentioned pesticides are not suitable for liquid and gas chromatographic analysis. We must strictly control the correlated conditions and use analyte protectants to get high-quality detection results.