About The History And Development Of The QuEChERS Method
Due to the variety of targets, large structural differences, and low target content, the detection of pesticide residue method requires being accurate, rapid, sensitive, simple and low cost. The QuEChERS method is more and more widely used in pesticide residue detection, as it is green and quick. The method was developed by the National Association of Analytical Chemists in January 2007.
The US Department of Agriculture scientists first introduced it in 2003. Researched by the US Department of Agriculture’s Agricultural Research Service Center, the material is not placed in the SPF column but directly added to the sample. After a thorough validation of more than 200 pesticides, the improved method was officially adopted in January 2007 as the official method of the American Association of Analytical Chemists.
The method is characterized by extracting with a buffered salt of acetonitrile (1% acetic acid solution), leaching the target into an organic phase, and then salting out with anhydrous magnesium sulfate, and the anhydrous magnesium sulfate has the function of absorbing water, with the better effect of salting-out. It should be noted that the salt pack should not be added too fast, because the salt pack will saturate the water underneath, and the salt pack will generate heat and agglomerate, which will decompose sensitive pesticides.
The organic phase and the aqueous phase are separated by centrifugation, and then an aliquot is separated from the organic liquid layer and further purified by dispersive SPE. The main function of the dispersed SPE is through non-polar interaction and polar interaction. The ionic interaction selectively retains the matrix interference component for purification purposes.
Take primary secondary ammonia (PSA) in a dispersed solid phase extractant to remove fatty acids, graphitize carbon black, to remove planar macromolecules (such as pigments, oils, fats, non-polar compounds) and reduce the amount of residual water in the extract with anhydrous magnesium sulfate. After mixing and centrifuging, the supernatant is taken for analysis.
Sample preparation technology and instrumental analysis technology
If only the chromatographic instrument is used for qualitative and quantitative analysis, it must be fully purified in the pre-treatment. For example, conventional techniques can achieve better results, however, the entire pre-processing process is cumbersome and the processing steps are complicated. The more steps, the more the target loss, the more errors. For some pesticides, the recovery is not ideal, a large amount of organic solvent is used, and the work efficiency is not high, and the operator’s health is at risk.
If a simpler pre-processing technique, such as the QuEChERS method, is used, the whole process is very simple, with fewer steps, and only two centrifugations are required. It not only saves organic solvents but also improves work efficiency. The safety of the inspectors is guaranteed. However, the purification effect is not ideal, and a large number of co-extracted materials are highly interfering. At this time, it requires late instrument analysis with strong anti-interference ability, high sensitivity, and low detection limits.
If it is a chromatographic instrument, the target is enough to be covered by the co-existing interference, and the detection requirements are not met. At this time, the use of chromatography-tandem multi-stage mass spectrometry meets this requirement. The simple and easy pre-processing, and the fast economy has become a trend. QuEChERS method + MS / MS, LS-MS / MS mode with high specificity and high sensitivity, will inevitably become the mainstream detection method.