Rapid determination of hydrogen sulfide-related metabolites in human urine by UHPLC-ESI-MS/MS with fluorinated ion-pairing reagents.

Although primarily considered as a toxic gas, hydrogen sulfide is naturally produced in humans from the amino acid cysteine in low quantities and is commonly referred to as the "third gaseous signaling molecule". There is a need to establish reliable biomarkers for exposure to hydrogen sulfide in human matrices not only at toxic levels but also at trace levels. Herein, we report optimized analytical methods for the direct determination of three compounds related to hydrogen sulfide metabolism in human urine without sample preparation; namely, trimethylsulfonium, thiosulfate, and cystine. The methods were based on ion-pair ultra-high performance liquid chromatography (UHPLC) with an anionic fluorinated acid or a cationic fluoroalkylamine, a member of a new generation of ion-pairing reagents, and detection by the electrospray ionization tandem mass spectrometry (ESI-MS/MS). Rapid chromatographic separation was achieved in 2-3 min with limits of detection of 0.1, 2.5, and 50 nmol L-1 (nM) for trimethylsulfonium, cystine, and thiosulfate, respectively. Isotopically labeled internal standards were used for each analyte to account for matrix effects and qualifier ions were employed to ensure selectivity. The method was validated for recovery (generally within 80-120%) and repeatability (RSD% 1.0-10%), and applied to investigate the normal concentrations of the three analytes in forty morning first-pass urine samples of healthy volunteers.