A trace analysis method based on HPLC-MS/MS for the simultaneous determination of residues of the two isomers of pyrisoxazole in tomato fruit and soil

Abstract

A simple, sensitive and accurate method for the simultaneous determination of residues of the two isomers of pyrisoxazole in tomato fruit and soil was established using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). All samples were extracted by using acetonitrile and the tomato fruit samples were additionally dehydrated by adding anhydrous sodium sulfate (Na₂SO₄). The extract was then cleaned up by using a GX-274 automated SPE system equipped with a Supelclean™ ENVI™-18 SPE tube. Separation was carried out on a XBridge™ C18 column using a mobile phase of methanol–0.1% aqueous formic acid solution at a flow rate of 0.6 mL min⁻¹. Quantification was achieved by MS/MS detection applying the multiple reaction monitoring (MRM) model while electrospray ionization (ESI) was operated in the positive ion mode. MRM analysis was conducted by monitoring the precursor ion to product ion transitions from m/z 289.1 to 120.2 (for both the isomers of pyrisoxazole). The method showed satisfactory linearity for both isomers of pyrisoxazole in the concentration range of 10–500 μg L⁻¹, with correlation coefficients higher than 0.998 in all cases. For the two isomers of pyrisoxazole, the limits of detection (LODs) were below 0.8 μg kg⁻¹, and the limits of quantification (LOQs) were below 2.8 μg kg⁻¹. According to the results of the recovery assay, the method presented satisfactory accuracy with a mean recovery of 80.0–91.5% and satisfactory precision with all RSD values below 8.5% at the three concentration levels (10, 100 and 1000 μg kg⁻¹) for the two isomers of pyrisoxazole in the two matrices. With the established method, 30 real samples (15 samples of tomato fruit and 15 samples of soil) were analyzed. The two isomers of pyrisoxazole were not detected in all samples.