Rapid, simultaneous and nanomolar determination of pyroglutamic acid and cis-/trans-urocanic acid in human stratum corneum by hydrophilic interaction liquid chromatography (HILIC)–electrospray ionization tandem mass spectrometry

A rapid, sensitive and specific hydrophilic interaction liquid chromatography coupled to tandem mass spectrometric (HILIC–MS/MS) method for the simultaneous determination of pyroglutamic acid, cis- and trans-urocanic acid in human skin stratum corneum (SC) were developed and validated. This method was carried out without derivatization or addition of ion-pair additives in mobile phase. The analytes were extracted by PBS buffer solution and analyzed using an electrospray positive ionization mass spectrometry in the multiple reaction monitoring (MRM) mode. Chromatographic separation was performed on an AQUITY UPLC amide column using gradient elution with the mobile phase of water and acetonitrile. The standard curves were linear over the concentration range of 1.0–250 ng/mL with a correlation coefficient higher than 0.999 with an LLOQ of 0.5 ng/mL. The lower limits of detection (LLOD) of these analytes were lower than 0.2 ng/mL. The intra- and inter-day precisions were measured to be below 7.7% and accuracies were within the range of 94.3–102.6%. The validated method was successfully applied to determine the level of pyroglutamic acid and cis-/trans-urocanic acid in the SC samples from forearm and forehead region of 19 human volunteers.