Pesticide enrichment factors and matrix effects on the determination of multiclass pesticides in tomato samples by single-drop microextraction (SDME) coupled with gas chromatography and comparison study between SDME and acetone-partition extraction procedure

In this study a single-drop microextraction (SDME) method was extended for the determination of multiclass pesticides (metribuzin, vinclozolin, fosthiazate, procymidone, fludioxonil, kresoxim-methyl, fenhexamid, iprodione, bifenthrin, lambda-cyhalothrin, indoxacarb and azoxystrobin) in tomatoes and validated in comparison with a robust solvent extraction method in order to estimate the feasibility of SDME in more complicated determinations in terms of extraction efficiency, pesticides chromatographic stability and chromatographic induced matrix effects in pesticide residue analysis in food samples. Both sample preparation methods: (i) a single-drop microextraction method (SDME) developed recently in our laboratory, and (ii) a modified acetone-partition extraction procedure (APE) method that is being applied today for routine analysis of fruits and vegetables in many laboratories of pesticide residues analysis, were validated under ISO 17025 norms and SANCO Guide recommendations. For all pesticides studied, with the exception of pyrethroids, SDME exhibited good analytical characteristics by reporting from similar to 138 times lower LODs as compared with APE. The enrichment factors of the SDME procedure applied in tomato extracts ranged from 0.7 for bifenthrin to 812 for fenhexamid whereas, the concentration factors for the whole SDME studied ranged from <0.1 for bifenthrin and lambda-cyhalothrin to 52 for fenhexamid. Relative recoveries ranged from 67 to 90% for SDME and from 90 to 120% for APE. Matrix effects assessment performed for both methods studied indicated that matrix matched standards should be used for quantitation purposes. However, the estimation of the gas chromatographic matrix effects by SDME indicated that SDME is a more selective sample preparation method than APE.