Multi-class pesticides analysis in challenging vegetable matrices using fast 5 msec MRM with 15 msec polarity switching

Many regulatory authorities have established multi-class residual pesticides methods for the analysis of vegetables, fruits and other food stuffs. However, there is no global agreement on the provision of a target list of pesticides and this presents a risk with products moving between different regulatory requirements.
In order to eliminate this risk, food safety laboratories need to ideally screen as many compounds as possible in a single run which may reach maximum residual limits (MRL); typically 10ppb in food matrices. In this study we report the application of ultra-fast 5msec SRM with 15 msec polarity switching for the analysis of 138 pesticides, while still obtaining excellent LOQs for the majority of compound < 10 ppb.
Leek and Paprika (yellow and red) were purchased from a local Japanese grocery store, with the country of origin Japan (Leek) and New Zealand (Paprika). Sample preparation was carried out by the use of a quick, easy, cheap, effective, rugged and safe (QuEChERs) method. LCMS-8040 triple quadruple mass spectrometer (Shimadzu, Japan) was used to monitor 276 MRM transitions (two MRMs per compound). Each transition was monitored plus-minus 0.8 minutes of the target analytes retention time. The maximum loop time was 0.58 seconds and the maximum number of overlapped MRM transitions was 98 (Dwell time: 5 msec, Pause time: 1 msec).
According to the method published by the European Union Reference Laboratory (EURL) entitled "Multiresidue Method using QuEChERS followed by GC-QqQ/MS/MS and LC-QqQ/MS/MS for Fruits and Vegetables", 138 pesticides were selected as target analytes with sample pre-treatment by QuEChERs methods. Of these 138 pesticides, the EURL analysed and validated 66 pesticides by GC-QqQ and the remaining 72 pesticides by LC-QqQ. In contrast to the EURL method, in this study all 138 pesticides were analysed in a single analysis using MRM after spiking into vegetable matrices. This was achievable due to the fast dwell (5 msec) and pause times (1msec) and rapid polarity switching (15 msec) of the triple quadruple mass spectrometer. Each MRM was optimised and calibration curves constructed in the range 1 to 1000 ppb. 21 pesticides measured by GC-QqQ in the EURL method did not reach the necessary LOQ (10 ppb), but the remaining 45 pesticides achieved excellent LOQs in the range 0.08 to 10 ppb. 5 ppb and 50 ppb matrix matched standards were prepared for recovery studies. 90 % of the pesticides analysed presented excellent recoveries in the range 70 -120 % in all studied matrices.