“…Liquid chromatography (Agilent 1200 HPLC system; Agilent, Waldbronn, Germany) and tandem mass spectrometry (ABI 3200 Qtrap; ABI, Foster City, CA, USA) (liquid chromatography–mass spectrometry/mass spectrometry) was used to detect the concentrations of cortisol, cortisone, DHEA, testosterone, and progesterone in plasma. [ 5 6 ] The method showed good linearity ( R 2 > 0.99) in the range of 0.03–500 ng/mL, and the limit-of-quantitation were 0.1, 0.4, 0.6, 0.1, and 0.1 ng/mL for cortisol, cortisone, DHEA, testosterone, and progesterone, respectively. The coefficients of variation for intra-day and inter-day (n = 5) assays were less than 15%.…”