Analysis of twenty phenolic compounds in human urine: hydrochloric acid hydrolysis, solid-phase extraction based on K^sub 2^CO3-treated silica, and gas chromatography tandem mass spectrometry

Issue Title: Direct Optical Detection (pp. 3881-4034) 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. K^sub 2^CO3-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 (R ^sup 2^[greater than or equal to]0.996) was established in the range 0.1-100 ng mL^sup -1^ for all analytes. Method detection limits (MDLs) were 0.7-9.8 pg mL^sup -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[less than or equal to]19 %) at two levels (low: 0.1 and 0.5 ng mL^sup -1^; high: 5 and 10 ng mL^sup -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^sup -1^. The method is suitable for the analysis of multiple phenolic metabolites in human urine.