DETECTION OF THIAZIDE-BASED DIURETICS IN EQUINE URINE BY LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY

Thiazide-based diuretics are included in the list of banned drugs in t he horse-racing industry. One effect of their misuse is increased urin e flow, contributing to dilution of other doping agents. Their determi nation is essential in ensuring compliance to horse-racing regulation. This study evaluates the feasibility of using liquid chromatography/m ass spectrometry (LC/MS) with electrospray and atmospheric pressure ch emical ionization interfaces to analyze thiazidic diuretics in equine urine samples. Existing LC and gas chromatography/MS methods are limit ed in their applicability to thiazide analysis. Sample preparation, an alyte extraction, chromatographic separation, ion-source collision ind uced dissociation, solvent composition, ionization mode, and ion polar ity are discussed. The practicality of LC/MS for this analysis is demo nstrated with actual equine administration samples collected at specif ied time intervals. Detection limits were 270 ng/mL for chlorothiazide , 131 ng/mL for hydrochlorothiazide, and 384 ng/mL for trichlormethiaz ide.