Analysis of twenty phenolic compounds in human urine: hydrochloric acid hydrolysis, solid-phase extraction based on K2CO3-treated silica, and gas chromatography tandem mass spectrometry

This study developed a new method for the analysis of 20 phenolic compounds in human urine. The urine samples were prepared by hydrochloric acid (HCl) hydrolysis, liquid–liquid extraction (LLE), and solid-phase extraction (SPE) cleanup. We found that HCl hydrolysis is of similar effectiveness to, and much cheaper than, the traditional enzymatic method. Vanillic acid was co-eluted with butyl paraben and interfered with the determination of butyl paraben in urine. K2CO3-treated-silica-gel SPE was designed to efficiently eliminate interference from the endogenous organic acids (especially vanillic acid) in urine. After derivatization, the samples were analyzed by large-volume-injection gas chromatography–tandem mass spectrometry (LVI-GC–MS–MS). Good linearity (R2 ≥ 0.996) was established in the range 0.1–100 ng mL−1 for all analytes. Method detection limits (MDLs) were 0.7–9.8 pg mL−1. Intraday (n = 5) and interday (n = 5 days) validation was performed, with satisfactory accuracy (recovery: 70–126 % and 73–107 %, respectively) and precision (RSD ≤ 19 %) at two levels (low: 0.1 and 0.5 ng mL−1; high: 5 and 10 ng mL−1). The method was used in a population study and achieved more than 85 % detection for most analytes; mean analyte concentrations were in the range 0.01–185 ng mL−1. The method is suitable for the analysis of multiple phenolic metabolites in human urine.