Application of comprehensive two-dimensional gas chromatography with nitrogen-selective detection for the analysis of fungicide residues in vegetable samples

Abstract

Comprehensive two-dimensional gas chromatography (GCxGC) with nitrogen-phosphorus detection (NPD) has been investigated for the separation and quantitation of fungicides in vegetable samples. The detector gas flows (H2, N2 and air) were adjusted to achieve maximum response of signal whilst minimizing peak width. The comparison of different column sets and selection of the temperature program were carried out with a mixture of nine N-containing standard fungicides, eight of which were chlorinated. The results from GCxGC-NPD and GCxGC with micro electron-capture detection (μECD) were compared. External calibrations of fungicides were performed over a concentration range from 1 to 1000 μg L-1. The peak area calibration curves generally had regression coefficients of R2 > 0.9980, however for iprodione which was observed to undergo on-column degradation, an R2 of 0.990 was found. The limit of detection (LOD) and limit of quantitation (LOQ) were less than about 74 and 246 ng L-1, respectively. The intra-day and inter-day RSD values were measured for solutions of concentration 0.100, 0.500 and 1.50 mg L-1. For the 0.500 mg L-1 solution, intra- and inter-day precision of peak area and peak height for most of the pesticides were about 2% and 8%, respectively. Excellent linearity was observed for these standards, from 0.001 to 25.00 mg L-1. The standard mixture peak positions were identified by using GCxGC with quadrupole mass spectrometry (qMS). To illustrate the potential and the versatility of both GCxGC-NPD and GCxGC-μECD, the method was applied to determination of fungicides in a vegetable extract. Decomposition of one fungicide standard (iprodione) during chromatography elution was readily observed in the two-dimensional (2D) GCxGC plot as a diagonal ridge response in the 2D chromatogram between the degrading compound and the decomposition product. © 2006 Elsevier B.V. All rights reserved.