Journal of Chromatography A, 1000 (2003) 299���309 www.elsevier.com/locate/chroma M ulti-residue screening of pesticides in vegetables, fruits and baby food by stir bar sorptive extraction���thermal desorption���capillary gas chromatography���mass spectrometry a,b,c , b *, Pat Sandra Bart Tienpont , Frank Davida a Research Institute for Chromatography, Kennedypark 20, B-8500 Kortrijk, Belgium b Laboratory of Organic Chemistry, University of Ghent, Krijgslaan 281 S4, B-9000 Ghent, Belgium c Department of Chemistry, CENSSUS, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa Abstract The performance of stir bar sorptive extraction (SBSE) for the enrichment of pesticides from vegetables, fruits and baby food samples is discussed. After extraction with methanol, an aliquot is diluted with water and SBSE is performed for 60 min. By applying a new thermal desorption unit (TDU), fully automated and unattended desorption of 98 stir bars is feasible, making SBSE very cost-effective. The presence of pesticide residues is elucidated with the retention time locked gas chromatography���mass spectroscopy method (RTL-capillary GC���MS). With SBSE���RTL-capillary GC���MS operated in the scan mode, more than 300 pesticides can be monitored in vegetables, fruits and baby food. The multi-residue method (MRM) described provides detectabilities from the mg/kg (ppm) to the sub-mg/kg (ppb) level, thereby complying with the maximum residue levels (MRLs) set by regulatory organizations for pesticides in different matrices. Several examples, i.e. pesticide residues in lettuce, pears, grapes and baby food, illustrate the potential of SBSE���RTL-capillary GC���MS. ��� 2003 Elsevier Science B.V. All rights reserved. Keywords: Stir bar sorptive extraction Retention time locking Vegetables Fruit Baby food Multi-residue analysis Pesticides 1 . Introduction one pesticide, e.g. chlormequat, or selective residue methods (sMRMs), i.e. the determination of a rela- In recent years, regulatory agencies have empha- tively small number of chemically related com- sized more and more the need for the development pounds, e.g. N-methylcarbamate insecticides, are and use of analytical methods able to determine, in intensively applied for pesticide residue determi- food products, as many residues as possible from the nations in a large number of samples, the pesticide many insecticides, fungicides and other compounds treatment history of which is known. The use of applied in agricultural practice. At present, single SRM and sMRM methods will continue, but the residue methods (SRMs), i.e. the determination of development and use of multi-residue methods (MRMs), i.e. the determination of as many pesticides as possible with only one sample preparation method *Corresponding author. Research Institute for Chromatography, and one chromatographic technique, is needed to Kennedypark 20, B-8500 Kortrijk, Belgium. Tel.: 132-56-204- analyze samples with an unknown or doubtful pes- 031 fax: 132-56-204-859. E-mail address: pat.sandra@richrom.com (P. Sandra). ticide treatment history. 0021-9673/03/$ ��� see front matter ��� 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0021-9673(03)00508-9

300 P. Sandra et al. / J. Chromatogr. A 1000 (2003) 299���309 A single chromatographic technique cannot liquid extraction. The principles and applications of monitor the currently used 800 and almost 600 sorptive extraction have recently been reviewed [9]. superceded pesticides (herbicides, fungicides, insec- Solid-phase microextraction (SPME) [10] and stir ticides, araricides, nematicides, growth regulators, bar sorptive extraction [11] on polydimethylsiloxane synergists, etc.) as listed in The Pesticide Manual (PDMS) as extraction medium have been applied for [1], and the application of both GC and HPLC is the determination of pesticides in aqueous food mandatory. Half of the currently used pesticides are, samples such as drinking water, fruit juices, bever- however, amenable to capillary GC analysis and by ages, etc. Yang et al. [12] applied SPME for the replacing the classical selective detection methods by determination of pesticide residues in fruit juice and the universal and specific mass spectrometer, many Boyd-Boland et al. [13] used SPME for the analysis classes of pesticides can be analyzed in a single run. of pesticide residues in water samples. In both cases, Moreover, the need for confirmation of positive PDMS was selected as being the best sorbent. SBSE samples by a secondary technique becomes obsolete followed by thermal desorption or liquid desorption and the MS has the sensitivity required for residue was used by Sandra et al. [14] for the analysis of analysis. dicarboximide fungicides in wines. The main differ- A variety of capillary GC���MS-based multi-residue ence between SPME and SBSE is the much larger methods have been developed. For example, working quantity of PDMS used in the latter, resulting in very group 4 of the Technical Committee (TC 275) of the high recoveries. European Committee for Standardization (CEN) For multi-residue analysis by capillary GC���MS, provides information on five multi-residue methods important improvements have been made in recent for non-fatty foods (EN 1528:1996) [2]. All methods years. Through the features of electronic pneumatic require extraction with organic solvents such as control (EPC), retention time locked libraries (RTLs) acetone [3���5] acetonitrile [6] and ethylacetate [7] for GC-amenable pesticides and endocrine disrupters with the exception of Ref. [7], they all require can be constructed, and by linking the locked partitioning into a solvent mixture, and further clean- retention times to the mass spectral data, hardly any up by column chromatography or gel permeation pesticide that is in the library can escape detection chromatography (GPC) is advised. The multi-residue and elucidation [15,16]. The Agilent RTL-MS library capillary GC���MS method that was applied in our presently comprises 567 substances. We recently laboratory until the application of the Twister de- evaluated SBSE as a sample preparation technique scribed in this contribution is a method used by the for the enrichment of pesticides from aqueous ma- laboratories of the Dutch Inspectorate for Health trices (water and beverages) and came to the conclu- Protection [7]. This method is similar to the Luke sion that more than 400 pesticides in the RTL-MS method [3], but the extraction procedures have been library can be enriched with recoveries complying miniaturized to reduce solvent consumption. Recent- with the required limits of quantification (LOQs) set ly, Fillion described the analysis of 191 GC-amen- by regulatory organizations, e.g. the 0.1 mg/l (ppb) able pesticides in fruit and vegetables by capillary norm for drinking water. The list of pesticides GC���MS. The sample preparation comprises extrac- amenable to SBSE enrichment and RTL-capillary tion with 150 mL acetonitrile, a salting-out step, GC���MS analysis for solid food samples is somewhat clean-up by solid-phase extraction on octadecyl and smaller (i.e. ca. 350 pesticides) because of matrix on aminopropyl silica and a concentration step [8]. effects in solid samples. The complete pesticide lists In the present era of ������green chemistry������, extraction for both aqueous (Tables 1���4) and food samples with large quantities of toxic solvents is difficult to (Tables 3 and 4) can be found on the website justify for multi-residue determinations of pesticides www.richrom.com/html/ric The lists ]appnotes.html. in foodstuffs and solventless sample preparation contain the locked retention times, four qualifier ions techniques should be favored. for MS confirmation, the log P values and the Solventless sample preparation techniques based theoretical SBSE recoveries on Twisters of 24 and on sorptive extraction have been demonstrated to be 116 mL. The maximum residue levels (MRLs) set by good and environmentally friendly alternatives to the European Community (Directives 645/2000 and