In recent years capillary electrophoresis (CE) has found increasing use in the area of drug and metabolite analysis in biological fluids. The aim of these studies was to couple the versatility of electrospray (ES)-MS and ES-MS-MS with the speed and sensitivity of CE to produce a practical method of detecting and identifying small quantities of unknown compounds in biological fluids while minimising work-up procedures.

The drugs chosen for this study were the non-steroidal anti-inflammatory drugs, aspirin, ibuprofen and flurbiprofen, all of which produce metabolites of high polarity and which are suitable for analysis by negative ionisation ES. Following a therapeutic oral dose of between100 to 600 mg to a healthy male volunteer, urine was collected and an aliquot (2ml) applied to a solid phase extraction cartridge. The eluate was evaporated to dryness, reconstituted in methanol (200µl). and aliquots (30nl) analysed directly by CE-ES-MS with simultaneous UV detection. These results are compared with HPLC methods in terms of sensitivity and speed of analysis.

Ion source cone voltage fragmentation and on-line CE-ES-MS-MS have been used to provide structural information for metabolite identification. and the latter has been employed as a method for monitoring for specific metabolite types, e.g. glucuronides.