PARENT SESSION
PS12 - Applications of LC-MS in Environmental Analysis
Sunday, 17 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P129) Positive and negative voltage switching micro-LC-MS/MS analysis of pharmaceuticals in aqueous samples.

Miao, Xiu-Sheng^*,1, Metcalfe, Chris¹, ¹ Water Quality Centre, Trent University, Peterborough, Ontario, Canada

ABSTRACT- When LC-MS (or MS/MS) is applied to analyze pharmaceuticals, some analytes are suitable for analysis in positive-ion mode, while some are suitable for analysis in negative-ion mode, due to their differences in molecular structures and behavior in an ionization source. Therefore, they are usually analyzed separately in positive- and negative-ion modes. In this work, atorvastatin, novobiocin and roxithromycin were studied using postive and negative voltage switching micro-LC-ES-MS/MS with a triple quadrupole mass spectrometer, Quattro LC (Micromass, UK). Atorvastatin and roxithromycin were suitable for analysis in ES positive-ion mode, while novobiocin was suitable for analysis in ES negative-ion mode. With positive and negative voltage switching, the three analytes were analyzed with one injection, and the run time was cut in half without any reduction in sensitivity, compared to analyses using positive- and negative-ion modes separately. The second aim of this work was to determine the feasibility of micro-LC-ES-MS/MS in positive and negative voltage switching mode for the determination of the pharmaceuticals in aqueous samples. Solid-phase extraction (SPE) was applied to enrich the analytes from aqueous samples of surface water and sewage treatment plant effluents, and a microbore LC column (100x1.0 mm) was chosen for chromatographic separation. The mobile phase solvents were acetonitrile and 10 mM aqueous ammonium acetate, and a flow rate of 0.1 mL/min was used for chromatographic separation. The injection volume was 1 mL, and the analytes were quantified in time scheduled multiple reaction monitoring mode. By performing positive and negative voltage switching, the micro-LC-ES-MS/MS could analyze the three analytes with a 4-minute run, with instrumental detection limits 1-3 pg. This analytical method, combined with SPE, was successfully applied to the determination of trace levels of the above pharmaceuticals in aqueous samples.

Key words: Micro-LC-MS/MS, positive and negative voltage switching, pharmaceutical, aqueous sample