Optimisation and Validation of a UHPLC-MS/MS Assay Using Timed Post-Column Ammonium Fluoride Infusion for Sensitive Serum Steroids Quantitation

Steroid metabolomics has potential for identifying biomarkers and improving disease diagnosis. However, poor ionisation efficiency and low circulating concentrations of some steroids limit the broader clinical applications. Here, we developed a ultra-high-performance liquid chromatography - tandem mass spectrometry (UHPLC-MS/MS) assay for quantitation of 18 steroids in serum encompassing the mineralocorticoid, glucocorticoid and androgen biosynthesis pathways, including both classic and 11-oxygenated androgens. Steroid extraction from 100 μL of serum was performed using supported liquid extraction with ethyl acetate elution. Ionisation efficiency of steroids was investigated using formic acid in the mobile phase and post-column infusion of ammonium fluoride. Ammonium fluoride enhanced the signal intensity of 3-keto-Δ4 steroids up to ninefold, however A-ring reduced steroids exhibited greater ionisation with formic acid. Thus, to optimise sensitivity, a timed post-column infusion of 2 mmol/L ammonium fluoride was employed during chromatographic separation. The lower limits of quantitation ranged from 0.04 to 2.1 nmol/L. Accuracy ranged from 82 to 113% and intra- and inter-assay imprecision was <10% and <13%, respectively. The assay was applied to analyse morning serum steroid concentrations in healthy individuals (55 women, 44 men; age-matched). Serum progesterone, 11-deoxycorticosterone, dehydroepiandrosterone and androstenedione were significantly higher in women; in contrast, testosterone and 5α-dihydrotestosterone were higher in men. In summary, we have successfully developed and validated a UHPLC-MS/MS assay for multi-steroid profiling ad applied it to healthy individuals of both sexes.