Improvements in identification and quantitation of pesticide residues in food by LC-QTOF using sequential mass window acquisition (SWATH®)

Abstract

The efficiency of a data independent acquisition by the sequential window acquisition of all theoretical fragment ions (SWATH®) in high resolution accurate mass spectrometry was evaluated for pesticide residue analysis. Selection of various mass range windows over 100–950 Da was studied to produce MS/MS spectra with selectivity improvement. The number of mass windows selected was restricted to ten to avoid excessive scanning MS/MS time that can produce a very low number of points per chromatographic peak. The SWATH workflow was demonstrated to be effective in reducing the number of interferents in the MS/MS spectrum allowing compliance with the ion ratio (±30%) of the intensity of the precursor vs. fragment ion and mass errors ≤ 5 ppm in all cases studied. Two applications of this methodology were investigated: (a) baby foods, focusing on the analysis of 15 LC-amenable pesticides for which the European legislation establishes strict MRL levels (0.003 mg kg⁻¹) and (b) eggs, evaluating the presence of fipronil, fipronil sulfone, fipronil desulfinyl and fipronil sulfide. This last application was in line with the interest due to the recent rapid alert on the presence of fipronil in eggs (RASFF Portal in the EU, July 2017). The analytical approaches proposed yielded a very good linearity in the range of 0.003–0.200 mg kg⁻¹ (baby food) and 0.001–0.250 mg kg⁻¹ (eggs), and reproducibility < 20% allowing conclusive identification and reliable quantification of selected analytes at the EU MRL levels. The evaluation of the identification and quantitation capabilities of the instrument was performed through the analysis of real samples and a Proficiency Test (PT) sample for both baby foods and eggs.