On-line coupling of solid-phase extraction with mass spectrometry for the analysis of biological samples I. Determination of clenbuterol in urine

The potential of the direct coupling of solid-phase extraction (SPE) with m ass spectrometry (MS) for the analysis of biological samples is demonstrate d. For SPE a cartridge exchanger is used and the eluate is directly introdu ced into the mass spectrometer. This system has been investigated for the d etermination of clenbuterol in urine. With mixed-mode cartridges, a conside rable ion suppression has been obtained. The mass spectrum at the elution t ime of clenbuterol is dominated by that of creatinine and adduct formation of clenbuterol and creatinine has been observed. The whole procedure includ ing injection of 1 ml urine, washing and desorption has been developed with cartridges containing 8-mu m C-18-bonded silica. If only a single MS step is used, the selectivity and, therefore, the sensitivity are insufficient. The detection limit is about 100 ng/ml. However, with atmospheric pressure chemical ionisation and the tandem MS mode the detection limit has been dec reased to about 2 ng/ml and the ion suppression is only about 10%. For the electrospray ionisation the detection limit is about 10-times higher and th e ion suppression is less favourable. The repeatability for the SPE-MS-MS p rocedure was 6.5% at 10 ng/ml(n=5) and the difference between the response factors at 10 ng/ml and 100 ng/ml was only 2.5%. The MS behaviour of clenbu terol and the matrix under the present conditions is discussed. (C) 1999 El sevier Science B.V. All rights reserved.