Dispersive microextraction based on "magnetic water" coupled to gas chromatography/mass spectrometry for the fast determination of organophosphorus pesticides in cold-pressed vegetable oils.

This article presents a novel application of dispersive microextraction based on "magnetic water" (m-water) for the purification of organophosphorus pesticides (methamidophos, omethoate, monocrotophos) from cold-pressed vegetable oils. In the present study, a trace amount of water (extractant) was adsorbed on bare Fe₃O₄ by hydrophilic interaction to form m-water. Rapid extraction can be achieved while the m-water is dispersed in the sample solution with the aid of a vigorous vortex. After extraction, the analyte-adsorbed m-water can be readily isolated from the sample solution by a magnet, which could greatly simplify the operation and reduce the whole pretreatment time. Several parameters affecting the extraction efficiency were investigated, and under the optimized conditions, a simple and effective method for pesticide analysis was established by coupling with gas chromatography/mass spectrometry (GC/MS). The linearity range of the proposed method was 2-100 ng/g with satisfactory correlation coefficients (R) of 0.9997-0.9998, and the limits of quantification (LOQ) for the target compounds were in the range of 0.70-1.27 ng/g. In addition, the reproducibility was obtained by evaluating the intra- and interday precisions with relative standard deviations (RSDs) less than 7.2% and 6.5%, respectively. Finally, the established "magnetic water" microextraction method was successfully applied for the determination of pesticide residues in several kinds of cold-pressed vegetable oils.