Determination of pharmaceuticals in aqueous samples using positive and negative voltage switching microbore liquid chromatography/electrospray ionization tandem mass spectrometry.

Analytical methods were developed for atorvastatin, novobiocin and roxithromycin using microbore liquid chromatography/electrospray ionization tandem mass spectrometry (microbore LC/ESI-MS/MS) in positive and negative voltage switching mode. Atorvastatin and roxithromycin require the positive-ion mode, whereas the negative-ion mode is required for the determination of novobiocin. Using the positive and negative voltage switching function, the three analytes were determined with one injection, and the time required was half that required using separately run positive- and negative-ion modes, without any reduction in sensitivity. A microbore LC column (100 x 1.0 mm i.d.) was chosen for chromatographic separation with mobile phase solvents acetonitrile and 10 mM aqueous ammonium acetate. The flow-rate was 0.1 ml min(-1) and the injection volume was 1 micro l. The analytes were quantified in the multiple reaction monitoring mode with external standards. By switching the positive and negative voltage, the three analytes were determined with a 4 min chromatographic run and with instrumental detection limits of 1-3 pg. This analytical method, using a microbore LC column combined with solid-phase extraction, was applied successfully to the determination of trace levels of the above pharmaceuticals in aqueous samples. Atorvastatin was detected in a sewage treatment plant final effluent. Copyright 2003 John Wiley & Sons, Ltd.