Hawach To Talk About The Modified QuEChER With Extraction
Based on the introduction of the traditional QuEChERS method, HAWACH combined with the research status of different types of sample pretreatment technology in recent years briefly described the research and application of the improved QuEChERS method in pesticides multi-residue detection from extraction and purification. Hopefully, it can provide a reference for the detection of different types of substrates.
1. Optimize the extraction process
The extraction process uses an extraction solvent to extract the target substance in the matrix through liquid-liquid, liquid-solid, and other methods, and at the same time, the organic phase is separated from the aqueous phase with salt.
Choose different solvents and salts according to different characteristics of the matrix and pesticides to be tested to achieve the best extraction effect. There are two main aspects of its optimization: (1) extraction solvent, (2) buffer salt, and the salting-out process.
1.1 Selection and application of extraction solvents
The extraction solvent should not only satisfy the best extraction effect of the target compound, reduce its degradation loss, but also extract the interferences in the matrix as little as possible. Therefore, in the face of complex sample matrices, researchers used different extraction solvents to obtain better extraction results.
Stöckelhuber et al. used gas chromatography-tandem mass spectrometry to determine the residues of 9 pesticides commonly used in grapes in arthropods and gastropods in the soil under the vines using gas chromatography-tandem mass spectrometry. Comparing the extraction effects of acetonitrile and ethyl acetate, it was found that the peak area of the acetonitrile extract was much smaller than that of ethyl acetate.
Considering the toxicity of acetonitrile, ethyl acetate was selected as the extraction solvent, with PSA and anhydrous magnesium sulfate purification, the recovery rate of the 9 pesticide residues was 84% ~ 110%, the relative standard deviation was less than 18%, and the detection limit was 0.02 ~ 0.20 mg/kg (mass fraction).
When Maestroni et al. used gas chromatography-tandem mass spectrometry to determine 59 pesticide residues in grape leaves, acidified ethyl acetate was used as the extraction solvent, which has a good extraction effect for small and medium polar pesticide projects, and can greatly reduce co-extraction of interfering substances. However, this extraction solvent will have a very low recovery rate for more polar substances and is not suitable for the determination of pesticide residues with high polarity.
1.2 Selection and application of buffer salt and salting-out process
The buffered salt can ensure the stability of the target component to be tested which is sensitive to pH. The function of salting out is to promote the separation of the organic phase from the aqueous phase and the distribution of the analyte in the organic phase.
Faraji et al. found that the use of salt packs with sodium bicarbonate had the best extraction effect when detecting acetamiprid, imidacloprid, spirotetramat, and their metabolites in figs. The presence of sodium bicarbonate has little effect on the recovery rate of spirotetramat and its metabolites, but it can significantly increase the recovery rate of acetamiprid, imidacloprid, and their metabolites. This is because acetamiprid, imidacloprid, and their metabolites are alkaline compounds, and sodium bicarbonate can reduce their ionization.