DEVELOPMENT OF A COUPLED-COLUMN LIQUID-CHROMATOGRAPHIC TANDEM MASS-SPECTROMETRIC METHOD FOR THE DIRECT DETERMINATION OF BETAMETHASONE IN URINE

Different hyphenated liquid chromatographic (LC) and mass spectrometri c (MS) techniques were investigated in,order to set-up a method for th e fast, direct analysis of betamethasone in hydrolysed and non-hydroly sed urine using large-volume sample injection. After the optimisation of the LC parameters using a traditional UV detector and of the thermo spray and mass spectrometric parameters by flow injection, urine sampl es (0.5 mi) were submitted to analysis by either LC combined with tand em mass spectrometry (MS-MS), coupled-column LC (LC-LC) combined with single quadrupole MS, and LC-LC-MS-MS. Both the three-step configurati ons (LC-MS-MS and LC-LC-MS) did not provide satisfactory results: loss of sensitivity was noted in the case of LC-MS-MS (likely due to reduc ed efficiency in the ionisation of betamethasone in the thermospray ow ing to the presence of large amounts of matrix interference), while in the case of LC-LC-MS a high chemical noise resulting in insufficient selectivity of detection was observed. On the contrary, LC-LC-MS-MS an alysis proved to meet the demand of high speed of analysis (sample thr oughput, 4.5 h(-1)), selectivity, and sensitivity (LOQ, 1 ng/ml; LOD, 0.2 ng/ml). Notwithstanding the complex analytical system adopted, the developed procedure was manageable and very robust, provided that at the beginning of each analytical session the performance of the system was controlled by checking the retention time of the analytes on the first analytical column with UV detection and by optimising vaporiser temperature of the thermospray by flow injection. (C) 1998 Elsevier Sc ience B.V. All rights reserved.