Rapid analysis of multiclass pesticides in onion using gas chromatography-tandem mass spectrometry

Abstract

A rapid method using gas chromatography–tandem mass spectrometry (GC-MS/MS) for simultaneous identification and quantification of 170 amenable-GC pesticides including 45 of organochlorines, 45 of organophosphates, 70 of organonitrogens and 10 of pyrethroids in onion was developed. The modified buffered-QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) approach was optimized for sample preparation. Pesticides were extracted/partitioned from the samples with acetonitrile containing 0.5% acetic acid, followed by cleanup using dispersive solid phase extraction (d-SPE) with 150 mg MgSO₄, 50 mg primary secondary amine (PSA), and 50 mg alumina neutral (Al-N) and 5 mg graphitize carbon black (GCB) per mL of extract. For comparison purposes conventional GC-MS/MS experiments were performed on a DB-5 30m×0.25mm×0.25µm analytical column. LP-GC-MS/MS analysis was performed on a DB-5 10m×0.53mm×1µm analytical column connected to a 3m×0.15mm non-coated restriction capillary at the inlet end. Under the optimized conditions the analysis time was reduced to 9 min with the LP-GC-MS/MS approach which corresponds to an almost threefold gain in speed versus the conventional GC-MS/MS (33 min). The average recoveries of all analytes were between 70 and 120% with relative standard deviations (RSDs) lower than 20% (n=5) at 0.01, 0.05, and 0.1 mg kg⁻¹ spiking levels. The limits of detections (LODs) and limits of quantitation (LOQs) of all analytes were 0.003-0.005 mg kg⁻¹ and 0.01 mg kg⁻¹, respectively. These values were far below the MRLs established by the European Union (at 0.01 mg kg⁻¹), apparent from the results, the overall analytical performances were comparable for the two GC-MS/MS methods, but the LP-GC-MS/MS was high sample throughput (approximately 4-fold gain in speed vs. tradition GC-MS/MS) and cost-effective. In order to assess its applicability to the analysis of real samples, 40 onion samples previously determined using conventional GC-MS/MS and LP-GC-MS/MS. The results obtained with the compared techniques showed that 3 pesticides were detected in 4 samples.