Analytica Chimica Acta 696 (2011) 77–83 Contents lists available at ScienceDirect Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca Feasibility of capillary liquid chromatography–microchip-atmospheric pressure photoionization–mass spectrometry for pesticide analysis in tomato Anneli Kruve a,b , Markus Haapala c , Ville Saarela d , Sami Franssila d , Risto Kostiainen c , Tapio Kotiaho b,c , Raimo A. Ketola e,∗ a Institute of Chemistry, University of Tartu, Jakobi 2, 51014 Tartu, Estonia b Department of Chemistry, Laboratory of Analytical Chemistry, P.O. Box 55, FI-00014 University of Helsinki, Finland c Division of Pharmaceutical Chemistry, Faculty of Pharmacy, P.O. Box 56, FI-00014 University of Helsinki, Finland d Department of Materials Science and Engineering, Aalto University School of Chemical Technology, P.O. Box 16200, FI-00076 AALTO, Finland e Centre for Drug Research, Faculty of Pharmacy, P.O. Box 56, FI-00014 University of Helsinki, Finland article info Article history: Received 8 February 2011 Received in revised form 5 April 2011 Accepted 7 April 2011 Available online 16 April 2011 Keywords: Pesticide analysis Carbamate pesticide Tomato Liquid chromatography Mass spectrometry Heated nebulizer microchip Atmospheric pressure photoionization abstract A new and sensitive analytical method, using capillary liquid chromatography (capLC) with a microfab- ricated heated nebulizer chip for atmospheric pressure photoionization and tandem mass spectrometry (APPI–MS/MS), was developed for the analysis of selected carbamate pesticides in a tomato matrix. The performance of the instrumental method was evaluated, using seven pesticides, namely oxamyl, methomyl, aldicarb, carbofuran, pirimicarb, thiocarb, and ditalimfos. The limits of detection achieved with the capLC–APPI–MS/MS method in the positive ion mode were low, ranging from 0.25 ng mL -1 for pirimicarb to 5 ng mL -1 for oxamyl and methomyl, corresponding to 5 and 0.25 g kg -1 for tomato sam- ples, respectively, which are clearly below the maximum residue limits for them in fruits and vegetables. The repeatability of the instrumental method ranged from 2.9 to 13.9% (RSD) at a low (0.05 g mL -1 ) concentration level. An adequate linearity (r 2 = 0.984–0.999) at a concentration range from 0.005 to 5.0 g mL -1 was observed for all pesticides. The results obtained show that the capLC–APPI–MS/MS method developed could be used for the analysis of selected pesticides from tomato. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Pesticides are widely used in agriculture to fight weeds, moulds, and pests, thereby increasing productivity. Besides this positive effect pesticides pose a health-risk to consumers [1]. Because carbamate pesticides are increasingly used in agriculture as a replacement of organochlorine pesticides they were selected as tar- get analytes in this study. Regulations, e.g., SANCO/825/00 [2], have been developed to monitor concentration of pesticide residues in many products, including fruits and vegetables. The maximum residue limits (MRL), allowed for the pesticides in fruits and veg- etables, range from 0.05 to 5.00 mg kg -1 depending on a pesticide and a fruit/vegetable. In a tomato matrix the MRLs range from 0.02 mg kg -1 for aldicarb, carbofuran, methomyl, and oxamyl, to 0.2 mg kg -1 for methiocarb, and to 1 mg kg -1 for pirimicarb [3]. Gas chromatography (GC) in combination with different detectors, such as an electron capture detector (ECD), a nitrogen–phosphorus detector (NPD), and mass spectrometry (MS), have been used for a long time in pesticide analyses [4]. Most of the ∗ Corresponding author. Tel.: +358 9 19159194; fax: +358 9 19159556. E-mail address: raimo.ketola@helsinki.fi (R.A. Ketola). pesticides used nowadays are polar and thermally labile, therefore conventional liquid chromatography (LC) coupled with MS is nowa- days extensively used in pesticide analyses [4]. For example, the QuEChERS method [5], which involves a simple and rapid extrac- tion of pesticides from various matrices, is totally compatible with an LC/MS analysis. Electrospray ionization (ESI), being highly efficient in ionization of polar compounds, has been most frequently used to connect LC with MS in pesticide analyses [6]. However, ESI is prone to matrix effects [7] and is markedly less effective for analyzing less polar compounds [8]. Atmospheric pressure chemical ionization (APCI) [9] and atmospheric pressure photoionization (APPI) [10] are often beneficial overcoming these difficulties. In APPI the eluent is vapor- ized by a heated nebulizer, and a dopant (e.g., toluene, anisole, or acetone), often used in APPI to induce efficient ionization, is ion- ized by photons emitted by the photoionization lamp [11]. This produces radical cations of the dopant, which either ionize the ana- lyte molecules through a charge transfer or react with the solvent, producing protonated solvent molecules. These protonated solvent molecules are capable of ionizing analyte molecules through a pro- ton transfer [12,13]. Nowadays, APPI is increasingly used in LC–MS analyses in various application fields, such as pharmaceutical, bio- chemical, and environmental applications [14–16]. In addition to 0003-2670/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2011.04.006