Analysis of pesticide residues in lettuce by large volume–difficult matrix introduction–gas chromatography–time of flight–mass spectrometry (LV-DMI-GC-TOF-MS)

Abstract

A multi-residue method is described that eliminates the need for a clean-up step and thus allows the rapid determination of pesticides in crude extracts of lettuce. Samples were extracted with a mixture of ethyl acetate, Na₂SO₄ and NaHCO₃ and the crude extracts analysed directly using large volume–difficult matrix introduction (LV-DMI) in combination with gas chromatography–time of flight–mass spectrometry (GC-TOF-MS). The LV-DMI procedure described was evaluated for the analysis of dimethoate, pyrimethanil, chlorothalonil, vinclozolin, furalaxyl and oxadixyl. Satisfactory response was obtained at the lowest calibrated level (LCL) of 0.0025 µg ml⁻¹, with good linearity over the range 0.0025–0.5 µg ml⁻¹ (0.005–1.0 mg kg⁻¹ equivalent). Average recoveries between 73 and 118% were obtained at the 0.01–0.5 mg kg⁻¹ levels with RSD values ≤13%.