Evaluation of an automated thermospray liquid chromatography-mass spectrometry system for quantitative use in...

An automated thermospray liquid chromatography-mass spectrometry system is described, including an autosampler and a gradient liquid chromatography system controlled from the mass spectrometer data system. The performance and reliability of the equipment during unattended operation were evaluated by repeated injections of standard solutions of some antiasthmatic drugs, using deuterium-labelled analogues as internal standards. High sensitivity and reproducibility were achieved during a 19-hour run, incorporating gradient elution and a total of 54 injections. The relative standard deviation of the peak area measurement of the internal standards was in the range of 6.5-8.2%. The corticosteroid budesonide can be routinely measured in plasma down to 0.1 nmol/l. Direct injection of a small plasma volume into the thermospray liquid chromatography-mass spectrometry system could be used to monitor drug plasma levels during a toxicity study in dogs.