Simultaneous measurement of aldosterone and cortisol by high-performance liquid chromatography-tandem mass spectrometry: application to dehydration-rehydration studies.

Aldosterone and cortisol are useful biomarkers of dehydration and stress, respectively. The aim of this study was to develop an HPLC-tandem mass spectrometric method for the simultaneous measurement of aldosterone and cortisol in human plasma that could be applied to the study of athletes undergoing exercise and rehydration. Samples were prepared and analysed using an on-line sample preparation/HPLC system coupled to a triple quadrupole tandem-mass spectrometer. Samples (200 microL) were pre-treated and extracted on Hysphere C18 HD cartridges (7 microm, Spark Holland). Chromatography was performed on a Sunfire C18 analytical column (50 mm x 3.0 mm, 3 microm, Waters) under isocratic conditions at a flow rate of 0.3 mL/min. The mobile phase consisted of 35% acetonitrile/water. Mass spectrometric detection was by selected reaction monitoring using negative electrospray ionization conditions. The assay had an analytical range of 25-500 pg/mL and 25-500 ng/mL for aldosterone and cortisol, respectively (r(2)>0.992, n=22). Inter-day accuracy and imprecision for quality control samples was 99.4-106% and <16%, respectively (n=10). In a study of nine human subjects, both aldosterone and cortisol concentrations reflected the expected physiological responses to dehydration, rehydration and exercise when measured by this method. The reported method is suitable to facilitate the study of athletes undergoing dehydration and rehydration protocols.