1,3-Diphenylguanidine (DPG), 1,3-di-o-tolylguanidine (DTG), and 1,2,3-triphenylguanidine (TPG) are rubber additives widely present in the indoor environment. Nevertheless, little is known about their human exposure. We developed a method for the quantification of DPG, DTG, and TPG in human urine, using high-performance liquid chromatography-tandem mass spectrometry. The quantitative analysis of target analytes at parts-per-trillion levels in urine was optimized using hydrophilic-lipophilic balanced solid-phase extraction and isotopic dilution. The method limits of detection and quantification were in the range of 0.002-0.02 and 0.005-0.05 ng/mL, respectively. The recoveries of all analytes in human urine fortified at 1, 5, 10, and 20 ng/mL concentrations were in the range of 75.3-111%, with standard deviations of 0.7-4%. The repeated measurement of similarly fortified human urine yielded intra-day and inter-day variations of 0.47-3.90 and 0.66-3.76%, respectively. The validated method was applied in the measurement of DPG, DTG, and TPG in real human urine samples, which revealed the occurrence of DPG in children's urine samples (n = 15) with a detection frequency of 73% and at a median concentration of 0.05 ng/mL. DPG was found in 20% of adults' urine samples (n = 20).

This paper describes a methodology for simultaneous determination of 19 steroid hormones, viz. estrone, estradiol, estriol, testosterone, 5α-dihydrotestosterone, androstenedione, androstenediol, dehydroepiandrosterone, progesterone, pregnenolone, 17α-OH-progesterone, 17α-OH-pregnenolone, cortisone, cortisol, 11-deoxycortisol, 11-deoxycorticosterone, 11-dehydrocorticosterone, aldosterone, and corticosterone, in 500-µL of urine or serum/plasma. The method was optimized using isotopically labeled internal standards and liquid-liquid extraction followed by detection using liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-MS/MS). Dansylation of estrogens significantly improved their sensitivities (~11- to 23-fold) and chromatographic separation. The respective limit of detection (LOD) and limit of quantification (LOQ) of all analytes were 0.04–0.28 and 0.14–0.92 ng/mL in human urine, and 0.11–0.35 and 0.38–1.18 ng/mL in human serum/plasma. Recoveries of all analytes (except for progesterone) fortified at 10, 20, and 200 ng/mL in urine and serum were 80–120%, with standard deviations ranging from 0 to 17.3%. Repeated analysis of similarly fortified urine and serum samples yielded intra-day and inter-day variations of 0–21.7% and 0.16–11.5%, respectively. All analytes except cortisone exhibited weak matrix effects in urine and serum (−13.9–18.2%). The method was further validated through the analysis of the National Institute of Standards and Technology (NIST) plasma Standard Reference Material (SRM1950) with certified concentrations for cortisol, progesterone, and testosterone (coefficient of variation: 3–11%). The developed method was applied in the analysis of urine samples from 20 volunteers, which revealed the occurrence of 16 analytes with detection frequencies (DFs) > 80%. Furthermore, 15 analytes were found in plasma SRM1950, indicating the feasibility of our method in the analysis of steroid hormones in urine and serum/plasma. This method will facilitate analysis of steroid hormones in population-based biomonitoring studies.