On-line coupling of solid-phase extraction with mass spectrometry for the analysis of biological samples. II. Determination of clenbuterol in urine using multiple-stage mass spectrometry in an ion-trap mass spectrometer

Solid-phase extraction (SPE) was coupled to ion-trap mass spectrometry to d etermine clenbuterol in urine. For SPE a cartridge exchanger was used and, after extraction, the eluate was directly introduced into the mass spectrom eter, For two types of cartridges, i.e. C-18 and polydivinylbenzene (PDVB), the total SPE procedure (including injection of 1 mL urine, washing, and d esorption) has been optimised, The total analysis, including SPE, elution, and detection, took 8.5 min with PDVB cartridges, while an analysis time of 11.5 min was obtained with C-18 cartridges. A considerable amount of matri x was present after extraction of urine over C-18 cartridges, resulting in significant ion suppression. With PDVB cartridges, the matrix was less prom inent, and less ion suppression was observed, For single MS, a detection li mit (LOD) of about 25 ng/mL was found with PDVB cartridges. With Cls cartri dges an LOD of only about 50 ng/mL could be obtained. Applying tandem mass spectrometry (MS/MS) did not lead to an improved LOD due to an interfering compound, However, a considerable improvement in the LOD was obtained with MS3. The selectivity and sensitivity were increased by the combination of e fficient fragmentation of clenbuterol and reduction of the noise. Detection limits of 2 and 0.5 ng/mL were obtained with C18 and PDVB cartridges, resp ectively. The ion suppression was 4 to 45% (concentration range: 250 to 1.0 ng/mL) after extraction of urine using PDVB cartridges, and up to 70% ion suppression was observed using Cls cartridges. With MS4, no further improve ment in selectivity and sensitivity was achieved, due to inefficient fragme ntation of clenbuterol and no further reduction of noise. Copyright (C) 200 0 John Wiley & Sons, Ltd.