Modification and re-validation of the ethyl acetate-based multi-residue method for pesticides in produce

Abstract

The ethyl acetate-based multi-residue method for determination of pesticide residues in produce has been modified for gas chromatographic (GC) analysis by implementation of dispersive solid-phase extraction (using primary-secondary amine and graphitized carbon black) and large-volume (20 μL) injection. The same extract, before clean-up and after a change of solvent, was also analyzed by liquid chromatography with tandem mass spectrometry (LC-MS-MS). All aspects related to sample preparation were re-assessed with regard to ease and speed of the analysis. The principle of the extraction procedure (solvent, salt) was not changed, to avoid the possibility invalidating data acquired over past decades. The modifications were made with techniques currently commonly applied in routine laboratories, GC-MS and LC-MS-MS, in mind. The modified method enables processing (from homogenization until final extracts for both GC and LC) of 30 samples per eight hours per person. Limits of quantification (LOQs) of 0.01 mg kg −1 were achieved with both GC-MS (full-scan acquisition, 10 mg matrix equivalent injected) and LC-MS-MS (2 mg injected) for most of the pesticides. Validation data for 341 pesticides and degradation products are presented. A compilation of analytical quality-control data for pesticides routinely analyzed by GC-MS (135 compounds) and LC-MS-MS (136 compounds) in over 100 different matrices, obtained over a period of 15 months, are also presented and discussed. At the 0.05 mg kg −1 level acceptable recoveries were obtained for 93% (GC-MS) and 92% (LC-MS-MS) of pesticide-matrix combinations.

Current mass spectrometry strategies for the analysis of pesticides and their metabolites in food and water matrices

“…It is generally acknowledged that this ''matrix effect'' depends on the solvent chemistry (i.e., organic solvent composition, pH modifier and concentration, etc. ), pesticide chromatographic behavior, the pre-treatment/clean-up method, the pesticide ionization potential and the type of the MS analyzer and detector geometries used (Díez et al, 2006;Marín et al, 2006;Soler, James, & Pico, 2007;Soler & Pico, 2007;Gilbert-López et al, 2007a,b;Hernardo et al, 2007;Mol et al, 2007;Payá et al, 2007;Kruves et al, 2008;Kmellar et al, 2008;Romero-González, Garrido Frenich, & Martínez Vidal, 2008;Esparza, Moyano, & Galceran, 2009;Marín et al, 2009;Nanita, Pentz, & Bramble, 2009;Radišic' et al, 2009;Stahnke, Reemtsma, & Alder, 2009;Wang & Leung, 2009). An interesting strategy to compensate for matrix effects has been proposed recently for the determination of 140 pesticides in food by LC-QqQ-MS/MS (Stahnke, Reemtsma, & Alder, 2009).…”

“…In the development of large-scale multi-residue methods, a compromise is required that will provide acceptable recoveries for the largest number of analytes and, for this purpose, solvents of medium polarity are commonly selected for SE. Among these solvents, acetonitrile (Kovalczuk et al, 2006;Hengel & Miller, 2007, 2008Caboni et al, 2008;Sarais et al, 2008) ethyl acetate, used in conjunction with anhydrous sodium sulfate (Goto et al, 2006b;Banerjee et al, 2007;Mol et al, 2007;Pan, Xia, & Liang, 2008;Schurek et al, 2008a), methanol (García-Reyes, Stahnke, Reemtsma, & Alder, 2009), acetone (Kuster, López de Alda, & Barceló, 2006;Grimalt et al, 2007), and dichloromethane (Venkateswarlu et al, 2007;Tokman et al, 2009) or mixtures of solvents Pang et al, 2006b) are suitable universal solvents for SE. The SE treatment is occasionally performed with ultrasonication to increase the extraction yield and increase the speed of the procedure (Pan, Xia, & Liang, 2008).…”

“…Finally, on-line automated SPE extraction procedures hyphenated to LC-MS (Marín et al, 2006;Perreau et al, 2007;Pirard et al, 2007) or GG-MS (Planas et al, 2006) systems have been tested, aiming to minimize the time and cost of the sample preparation step. In some cases of fatty samples, gel-permeation chromatography (GPC) and/or GPC followed by SPE (Ballesteros, Sánchez, & H s e l p m a s r e t a W s e d i c i t s e p 0 0 3 -1 Greulich, & Alder, 2008 171 pesticides Fruits, vegetables, Botitsi et al, 2007 136 pesticides Fruit and Mol et al, 2007 187 pesticides Fruit and (Continued) Díez et al, 2006;Fernández Moreno et al, 2006;Garrido Frenich et al, 2006;Guardia-Rubio et al, 2006Pang et al, 2006a;Zhang et al, 2006;Huang et al, 2007;Liu et al, 2007;Van der Lee et al, 2008) or counter-current chromatography (CCC) (Goto et al, 2006a) are required for better clean up. Dispersive SPE (DSPE) or matrix-solid-phase dispersion (MSPD) involves treatment of the sample with a sorbent material either directly or after SE (Banerjee et al, 2007;Mol et al, 2007;Plaza Bolaños, Garrido Frenich, & Martínez Vidal, 2007;Kruves et al, 2008;Ramos et al, 2008;Patil et al, 2009;Radišic' et al, 2009).…”

“…The SE treatment is occasionally performed with ultrasonication to increase the extraction yield and increase the speed of the procedure (Pan, Xia, & Liang, 2008). Extraction conditions, in particular pH, must usually be adjusted to facilitate analyte extraction using formic acid Mol et al, 2008) acetic acid (Poulsen et al, 2007), buffers (Mol et al, 2007;Nanita, Pentz, & Bramble, 2009;Esparza, Moyano, & Galceran, 2009), monobasic sodium carbonate (Pihlström et al, 2007;Taylor et al, 2008), and sodium hydroxide (Dreassi et al, 2007). In a recent study, acetonitrile, methanol, and acetone, all buffered with formic acid, were compared for a generic SE method for the LC-MS determination of 136 multi-class pesticides in different food matrices; overall, acetonitrile was deemed the best compromise (Mol et al, 2008).…”

“…Detection, confirmation, and quantification of residues of multi-class pesticides and transformation products in processed foods of plant origin (Botitsi, Economou, & Tsipi, 2007) and in wines (Economou et al, 2009) were accomplished by LC-QqQ-MS which used a peak width of 0.2 Da FWHM for the first quadrupole (Q1) to reduce the background signal from isobaric compounds that resulted in the enhancement of the overall sensitivity. A total of 136 pesticides in 100 food matrices have been monitored by LC-QqQ-MS acquiring one transition for each compound (Mol et al, 2007) while 171 pesticides and metabolites in different fruit and vegetable matrices were monitored in a single chromatographic run (with one or two transitions acquired per compound) without sacrificing sensitivity and reproducibility . Another study reported the analysis of 160 pesticide residues in fruit and vegetable samples with LC-QqQ-MS in a single chromatographic run (Kmellar et al, 2008).…”