Thermospray liquid chromatography-mass spectrometry of corticosteroids

A high-performance liquid chromatographic method was developed for thermospray mass spectrometric analysis of steroidal hormones. Using a Nova-Pak C18 reversed-phase column and isocratic elution with a solvent comprised of 25 mM ammonium formate in 30% acetonitrile, corticosteroids were separated within 10 min. This solvent also permitted ultraviolet absorbance detection down to 220 nm with low-nanogram sensitivity. The use of acetonitrile was favourable for thermospray mass spectrometric analysis because mass spectra were obtained with a pseudomolecular ion as the base peak. A combination of liquid chromatography, ultraviolet absorbance detection and thermospray mass spectrometry provided a sensitive and reliable method for unequivocal confirmation of the presence of steroidal drugs in equine urine.