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

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 C 18, even if absolute recoveries are found to be better. (C) 2004 Elsevier B.V. All rights reserved.