Simultaneous determination of cortisol, cortisone, 6β-hydroxycortisol and 6β-hydroxycortisone by HPLC.

A specific and sensitive method based on high-performance liquid chromatography with ultraviolet absorbance detection (HPLC-UV) was developed for the simultaneous determination of urinary cortisol (F), cortisone (E), 6 beta-hydroxycortisol (6 beta-OHF) and 6 beta-hydroxycortisone (6 beta-OHE) using dexamethasone as the internal standard. The method involved solid-phase extraction of the five compounds from urine using Oasis HLB Waters cartridges with an elution solvent of ethyl acetate-diethyl ether (5 mL; 4: 1, v/v), followed by 1 mol/L of NaOH (1 mL) and 1.0% acetic acid (1 mL). Separation of the five analytes was achieved within 31 min by using a reversed-phase C18 analytical column (200 x 4.6 mm, 5 mu m, Agilent). A UV detector operated at 245 nm was used. According to the method validation, inter-run and intra-run precision was below 9.45% and accuracy ranged from 98.16 to 115.50%. The lower limits of quantitation were 5 ng/mL for four analytes. This is the first HPLC method that can simultaneously determine F, E, 6 beta-OHF and 6 beta-OHE in human urine. The assay was applied to research the ratio of (6 beta-OHF + 6 beta-OHE)/(F + E) as a non-invasive biomarker for the metabolism of tacrolimus.