Optimization of separation and detection conditions for the multiresidue analysis of pesticides in grapes by comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry

A comprehensive GC×GC–TOFMS method was optimized for multiresidue analysis of pesticides using a combination of a non-polar (RTX-5MS, 10 m × 0.18 mm × 0.2 μm) and a polar capillary column (TR-50MS, 1 m × 0.1 mm × 0.1 μm), connected in series through a dual stage thermal modulator. The method resolved the co-elution problems as observed in full scan one-dimensional GC–MS analysis and allowed chromatographic separation of 51 pesticides within 24 min run time with library-searchable mass spectrometric confirmation. Four pesticides, viz. chlorpyrifos-methyl, vinclozoline, parathion-methyl and heptachlor could be baseline separated on GC×GC, which were otherwise closely eluting and interfering each other's detection in 1D GC–MS run. Similarly, it could be possible to separate myclobutanil, buprofezin, flusilazole and oxyfluorfen on GC×GC. Although in 1D GC–MS, these closely eluting compounds could be identified through deconvolution algorithm and ‘peak-find’ option of the Chromatof® software but the spectral purity significantly improved on GC×GC analysis. Thorough optimization was accomplished for the oven temperature programming, ion source temperature and GC×GC parameters like modulation period, duration of hot pulses, modulation-offset temperature, acquisition rate, etc. to achieve best possible separation of the test compounds. The limit of detection significantly improved by 2–12 times on GC×GC–TOFMS against GC–TOFMS because of sharper and narrower peak shapes. The method was tested for grape matrix after preparing the samples using previously described method and recoveries of the entire test pesticides were within 70–110% at 10 ng/g level of fortification. GC×GC–TOFMS was found to be an excellent technique for library-based screening of pesticides with high accuracy and sensitivity.