Ion suppression effects were observed during the determination of clenbuterol in urine with solid-phase extraction/multiple-stage ion-trap mass spectrometry (SPE/MS(3)), despite the use of atmospheric pressure chemical ionisation. During SPE, a polymeric stationary phase (polydivinylbenzene) was applied. Post-cartridge infusion of analyte to the SPE eluate after the extraction of blank urine was performed to obtain a profile of the suppression. Single and multiple-stage MS were performed to provide insight in the suppressing compounds. The ion suppression was mainly ascribed to two m/z values, but still no identification of the compounds was achieved from the multiple-stage MS data. No ionisable and non-ionisable complexes and/or precipitation of clenbuterol with matrix compounds were observed. A concentration dependence of the percentage of suppression was observed. Up to 70% of the signal was suppressed upon post-cartridge infusion of 0.22 microg/mL (at 5 microL/min) clenbuterol into the eluate, and this decreased to about 4% at infusion of 22 microg/mL clenbuterol. Molecularly imprinted polymers were used to enhance the selectivity of the extraction. Although matrix components were still present after extraction, no interference of these compounds with the analyte was observed. However, the bleeding of the imprint from the polymer (brombuterol) caused significant ion suppression.

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To determine sub-ppb levels of drugs in biological samples, selective, sensitive and rapid analytical techniques are required. This work shows the possibilities for high-throughput analysis of solid-phase microextraction (SPME) directly coupled to an ion-trap mass spectrometer equipped with an atmospheric pressure chemical ionisation source. As no chromatographic separation is performed, the SPME procedure is the time-limiting step. Direct immersion SPME under non-equilibrium conditions permits the determination of lidocaine in urine within 10 min. After a 5 min sorption time with a 100 microm polydimethylsiloxane-coated fibre, the extraction yield of lidocaine from urine is about 7%. When applying 4 min desorption, using a mixture of ammonium acetate buffer (pH 4.5) and acetonitrile (85 + 15 v/v), about 10% of the analyte is retained on the fibre. An extra cleaning step of the fibre is therefore used to prevent carry-over. By use of tandem MS, no matrix interference is observed. The detection limit for lidocaine is about 0.4 ng ml(-1) and the intraday and interday reproducibility are within 14% over a concentration range of 2-45 ng ml(1).