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 microg ml(-1), with good linearity over the range 0.0025-0.5 microg 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 < or = 13%.

Evaluation of the QuEChERS sample preparation approach for the analysis of pesticide residues in olives

“…Since then, Atas/GL Science developed an automated DSI device compatible with their Optic PTV, and marketed it as difficult matrix injection (DMI) [26,27]. Recently, the company has revised their automated approach with a second generation product.…”

Ruggedness and other performance characteristics of low-pressure gas chromatography–mass spectrometry for the fast analysis of multiple pesticide residues in food crops

“…Direct sample introduction (DSI) technique (or its automated version called difficult matrix injection) would significantly improve ruggedness because the root cause of the problems-non-volatile matrix components-is being removed after each injection [29][30][31]. Another possibility may involve the use of analyte protectants [28], which are compounds that strongly interacts with the active sites in the GC system, thus reducing losses and analyte tailing and effectively compensating for both matrix-induced response enhancement and diminishment effects even in long GC sequences of matrix injections [32].…”

Quantitative gas chromatography/time‐of‐flight mass spectrometry: a review

“…Large volume DMI-GC/TOFMS has been used to analyze pesticide residues in lettuce (Patel et al, 2003). The DMI-GC/TOFMS system consisted of an ATAS programmable injector, FOCUS automated sample processor with a Direct Thermal Desorption device, an Agilent 6890 GC and a LECO Pegasus III timeof-flight mass spectrometer.…”