Atmospheric pressure glow discharge desorption mass spectrometry for rapid screening of pesticides in food Matthias Conradin Jecklin, Gerardo Gamez, David Touboul and Renato Zenobi * Department of Chemistry and Applied Biosciences, ETH Zu ¨ rich, CH-8093 Zu ¨ rich, Switzerland Received 23 April 2008; Revised 7 July 2008; Accepted 10 July 2008 Flowing afterglow atmospheric pressure glow discharge tandem mass spectrometry (APGD-MS/MS) is used for the analysis of trace amounts of pesticides in fruit juices and on fruit peel. The APGD source was rebuilt after Andrade et al. (Andrade et al., Anal. Chem. 2008; 80: 2646–2653; 2654–2663) and mounted onto a hybrid quadrupole time-of-flight mass spectrometer. Apple, cranberry, grape and orange juices as well as fruit peel and salad leafs were spiked with aqueous solutions containing trace amounts of the pesticides alachlor, atrazine, carbendazim, carbofuran, dinoseb, isoproturon, metola- chlor, metolcarb, propoxur and simazine. Best limits of determination (LODs) of pesticides in the fruit juices were achieved for metolcarb (1 mg/L in apple juice), carbofuran and dinoseb (2 mg/L in apple juice); for the analysis of apple skin best LODs were 10 pg/cm 2 of atrazine, metolcarb and propoxur which corresponds to an estimated concentration of 0.01 mg/kg apple, taking into account the surface area and the weight of the apple. The measured LODs were within or below the allowed maximum residue levels (MRLs) decreed by the European Union (1–500 mg/kg for pesticides in fruit juice and 0.01–5 mg/kg for apple skin). No sample pretreatment (extraction, pre-concentration, chro- matographic separation) was necessary to analyze these pesticides by direct desorption/ionization using APGD-MS and to identify them using MS/MS. This makes APGD-MS a powerful high- throughput tool for the investigation of very low amounts of pesticides in fruit juices and on fruit peel/vegetable skin. Copyright # 2008 John Wiley & Sons, Ltd. Pesticides are widely used worldwide to control pests of crops and eliminate unwanted parasites. Around 860 active substances belonging to more than 100 substance classes are components of current pesticide products. 1 As a con- sequence of their use, some foods can contain residues of such compounds, which can eventually reach the consumers and present possible hazards for human health. Food safety control and pesticide residue determination are therefore of obvious importance to modern society. The European Union (EU) has set new stringent directives for pesticides in fruits and vegetables in order to minimize exposure of the population. 2 The established maximum residue levels (MRLs) or tolerances for pesticides in foods range from tens and hundreds of ppb (mg/kg) up to ppm (mg/kg) concentrations depending on their biological activity and/ or on how demanding their analysis is. Sensitive and reliable analytical methods are required to monitor pesticide residues in foods. Extraction, purification and concentration steps before the pesticide analysis are expensive and time-consuming, especially when a large batch of samples must be analyzed. Conventionally, pesticides are analyzed by combining a separation step (usually gas chromatography (GC) or liquid chromatog- raphy (LC)) with mass spectrometry (MS), preferably tandem mass spectrometry (MS/MS). Whether such residue analysis is better performed by GC/MS or LC/MS/MS has been thoroughly investigated and reviewed by Alder et al. 3 In recent years, LC/MS/MS using multiple reaction monitoring (MRM) has been more widely used for monitoring and quantifying pesticides in food. 4 The limits of determination (LODs) of pesticide residues in food using standard LC/MS/ MS are in the ppb range, between 0.1 and 1.0 ng/mL, 3 or between 0.4 and 2.0 mg/kg, 4 to give some typical examples. The disadvantage of such an approach is, however, that quite extensive sample pretreatment prior to LC/MS/MS analysis is required. Another disadvantage of an LC/MS/ MS approach is that matrix effects can compromise a reliable analysis. To avoid such effects, solid-phase extraction (SPE) and solid-phase microextraction (SPME) have also been thoroughly investigated. 5–8 Mass spectrometric analysis using desorption/ionization at atmospheric pressure has become a very active field of research and several new techniques have been introduced, e.g. desorption electrospray ionization (DESI), 9 desorption atmospheric pressure chemical ionization (DAPCI), 10 and ’direct analysis in real time’ (DART). 11 Some efforts have been made by the group of Cooks 12 using DESI combined with a portable mass spectrometer to directly analyze pesticides on fruit leaves. They were able to detecte 10 ng of atrazine and alachlor desorbed/ionized directly on a paper surface. RAPID COMMUNICATIONS IN MASS SPECTROMETRY Rapid Commun. Mass Spectrom. 2008; 22: 2791–2798 Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/rcm.3677 *Correspondence to: R. Zenobi, Department of Chemistry and Applied Biosciences, ETH Zu ¨ rich, CH-8093 Zu ¨ rich, Switzerland. E-mail: zenobi@org.chem.ethz.ch Contract/grant sponsor: Novartis Institute for BioMedical Research. Copyright # 2008 John Wiley & Sons, Ltd.