Analytica Chimica Acta 529 (2005) 207–210 Evaluation of two different clean-up steps, to minimise ion suppression phenomena in ion trap liquid chromatography–tandem mass spectrometry for the multi-residue analysis of beta agonists in calves urine Maurizio Fiori, Cinzia Civitareale, Sabrina Mirante, Eugenia Magar` o, Gianfranco Brambilla ∗ Department of Food Safety and Animal Health, Istituto Superiore di Sanit` a, Viale Regina Elena, 299 I 00161 Rome, Italy Received 1 June 2004; received in revised form 31 August 2004; accepted 31 August 2004 Available online 1 October 2004 Abstract In an analytical strategy, the selectivity of the steps from the extraction to the detection is a key factor to assure both reliability and forensic validity to the results. The availability of MS/MS ion trap facilities could induce the risk to maximise the relevance of MS/MS technique, despite the choice of a more selective clean-up step. In this work, we reported about the evaluation of two different purification procedures, as requisite to minimise both matrix-induced ion suppression phenomena and progressive loss of sensitivity in LC–MS/MS multi-residue beta agonists routine analysis. To this purpose, calves urine extracts from SPE C18 not endcapped (NE) and molecular imprinted polymers (MIPs) columns were tested according to the following procedure: 20 blank samples were analysed and then spiked with pooled beta agonists before and after the clean-up step. Background noise and analytes signals were compared with those from pure standards injected at the same nominal spiking concentration. In such a way, both recovery factors and matrix phenomena were evaluated. Results indicate that MIPs clean-up is effective to reduce ion suppression phenomena below 10%, with no detectable loss of sensitivity after 20 runs. The same results are not achievable with conventional SPE C18, even if absolute recoveries are found to be better. © 2004 Elsevier B.V. All rights reserved. Keywords: LC–MS/MS; Ion suppression; MIPs; SPE; Beta agonists 1. Introduction In veterinary residue analysis, some innovative aspects in the last years consisted of the availability of MS n liquid chro- matography devices based on ion trap technology and of the production of molecular imprinted polymers (MIPs) columns for their selective clean-up from biological matrices [1,2]. The aim of this work was to verify if the clean-up of beta ag- onists on MIPs columns, whose imprinter molecule has been re-designed to cover a broad spectrum of potential analytes [3], could improve the overall analytical performances of an LC–MS n ion trap detector. Such devices are generally more affected by matrix interferences and consequent ion suppres- sion phenomena with respect to traditional triple quadrupole ∗ Corresponding author. Tel.: +39 06 49902764; fax: +39 06 49902544 E-mail address: g.brambi@iss.it (G. Brambilla). equipments, due to relevant differences both in principle and sources design [4]. Moreover, polar compounds such as, beta agonists are seems to be more susceptible for ion suppression in ESI mode [5]. We chose as default a minimum required performance limit (MRPL) of 0.25 ng mL -1 for each of the eight beta agonists, selected as most representative of this class, taking into account their differences in the chemical structure. 2. Materials and methods 2.1. Chemicals Clenbuterol hydrochloride (Clen), Tulobuterol (Tul), Isox- suprine (Isox) and Formoterol (Form) were all purchased 0003-2670/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2004.08.068