Optimization of a multi‐residue screening method for the determination of 85 pesticides in selected food matrices by stir bar sorptive extraction and thermal desorption GC‐MS

Abstract

A multi-residue method to determine 85 pesticides, including organochlorine pesticides, carbamates, organophosphorus pesticides, and pyrethroids, in vegetables, fruit, and green tea, has been developed. The method is based on stir bar sorptive extraction (SBSE) coupled to thermal desorption (TD) and retention time locked (RTL) GC-MS operating in the scan mode. Samples are extracted with methanol and diluted with water prior to SBSE. Dilution of the methanol extract before SBSE was optimized to obtain high sensitivity and to minimize adsorption onto the glass wall of the extraction vessel as well as to minimize sample matrix effects (particularly for the pesticides with high log K(o,w) values). The optimized method consists of a dual SBSE extraction performed simultaneously on respectively a twofold and a fivefold diluted methanol extract. After extraction, the two stir bars are placed in a single glass thermal desorption liner and are simultaneously desorbed. The method showed good linearity (r2 > 0.9900) and high sensitivity (limit of detection: < 5 microg kg(-1)) for most of the target pesticides. The method was applied to the determination of pesticides at low microg kg(-1) in tomato, cucumber, green soybeans, spinach, grapes, and green tea.

HPLC‐method for determination of permethrin enantiomers using chiral β‐cyclodextrin‐based stationary phase

“…40 Furthermore, 3-phenoxybenzoic acid, 3-(4 0 -hydroxyphenoxy) benzyl alcohol and 3-(4 0 -hydroxyphenoxy)-benzoic acid may also be present. 3,33,40 It was not the purpose of this work to identify these. The UV spectra of the dominant degradation products are very similar to all four trans-and cis-enantiomers.…”

“…It is approved by the Food and Drug Administration for treatment of headlice 3 and lately are used for therapy of opportunistic infections in HIV infected patients. 4 Permethrin is an ester of the dichloro-analogue of chrysanthemic acid and 3-phenoxybenzyl alcohol.…”

Automation of solid‐phase microextraction

“…For GC analysis, the loaded stirrer bars are inserted into thermal desorption tubes/ liners, which can be automatically loaded and removed from a GC injection port fitted with a thermal desorption unit and a temperature programmable injector [64,67]. However, the user needs to manually transfer the stirrer bar into the sample vial and from the sample vial to the liner tray [64].…”

Fast Gas Chromatography and Its Use in Pesticide Residues Analysis

“…Solid-phase microextraction (SPME), stir bar sorptive extraction (SBSE) and microextraction with packed sorbents (MEPS) are examples that are used for sample preparation of pesticide residues containing food matrices (Chen et al, 2010). It was shown by several authors (Ochiai et al, 2005, Barriada-Pereira et al, 2010, that using SBSE technique allows batch sample preparation, for example 60 samples on one stir-plate, (typically in minutes (up to 60 min)), high recovery and extremely low LODs at sub ng.l -1 . Whereas SPE and MSPD need a concentration step, SPME and SBSE allow carrying out the extraction and concentration step in a single step.…”