Abstract:

An analysis method based on gas chromatography-time-of-flight mass spectrometry (GC-TOF-MS) with single acquisition was established for the simultaneous rapid screening and accurate confirmation of 197 pesticide residues in edible vegetable oil. First, a standard library of the 197 pesticides was established. The library contained GC-TOF-MS information such as retention time, accurate mass measurements of quantitative and quantitative ions, and ratio of the qualitative ion. According to the European Union regulation (SANTE/11945/2015), the standard for qualitative determination by HRMS was determined; that is, each compound was confirmed by at least two ions. Second, the instrument conditions and sample pretreatment conditions for the determination of different pesticides were optimized. The following observations were made: the extraction efficiency of acetonitrile was better than that of acetonitrile containing 0.1% formic acid because pesticide recovery in the former case was in the range of 70%-120%; C18 and PSA adsorbents exerted a better purification effect than did the other two purification materials (C18 and Z-Sep adsorbent or PRiME HLB column), thus ensuring good recovery of the target compounds; most pesticides showed a matrix enhancement effect, necessitating the use of a matrix-matched external calibration method for quantitation. Finally, based on the above findings, the experimental procedure was established. The edible vegetable oil samples were ultrasonically extracted with acetonitrile, and the resultant solution was subjected ot fat removal by freezing at -20 ℃ for 2 h. The supernatant (1.0 mL) was cleaned-up by dispersive solid phase extraction using 50 mg C18 and 50 mg PSA powder. The compounds were separated on an HP-5MS UI capillary column (30 m×0.25 mm×0.25 μm) and ionized using an electron impact ion source. Qualitative and quantitative detection of the pesticides was completed in full scan mode. The retention time, mass accuracy, and qualitative ion matching ratio were used for qualitative screening, while the peak areas of the quantitative ion were used for quantification. The limits of quantification (LOQs) of 174 pesticides were 0.01 mg/kg, and the LOQs of the other 23 pesticides ranged from 0.025 to 0.1 mg/kg. The linear ranges were LOQs to 200 μg/L for 196 pesticides, and from 2 to 100 μg/L for biphenyl, with the correlation coefficients being greater than 0.99. The recoveries of 156 pesticides were in the range of 70% to 120% at three spiked levels (0.1, 0.25, and 0.5 mg/kg), accounting for 79% of the total pesticides. The proposed method was successfully applied to the determination of pesticide residues in 23 edible vegetable oil samples. Chlorpyrifos was detected in all six peanut oil samples. Bromopropylate, fenpropathrin, oxadiazon, permethrin, tebufenpyrad, cyproconazole and pirimiphos-methyl were detected in a fourth-grade rapeseed oil sample. The results demonstrate that the developed method is accurate, reliable, and time-saving. It can be used for the high-throughput screening and quantitative determination of pesticide residues in edible vegetable oil.

Key words: gas chromatography-time-of-flight mass spectrometry (GC-TOF-MS), pesticide residues, vegetable oil