A robust LC-MS/MS assay with online cleanup for measurement of serum testosterone

Accurate measurement of low levels of testosterone is critical for diagnosis and treatment of androgen disorders. The very low concentrations of testosterone in children, females, and males with androgen suppression therapies necessitate the use of mass spectrometry-based methods. We aimed to develop a liquid chromatography with tandem mass spectrometry method with simplified sample preparation and online solid-phase extraction cleanup to achieve enhanced precision, accuracy, robustness, and cost-effectiveness. The assay was linear from 10 to 20 000 pg/mL with an analytical recovery of 93-104%. The total coefficient of variation was 2.5, 1.9, and 1.7% at concentration levels of 348, 5432, and 10 848 pg/mL, respectively. No significant carryover was observed from samples with concentrations up to 20 000 pg/mL. No significant interference was observed from androstenedione, dehydroepiandrosterone, epi-testosterone, and estriol. Comparison with CDC Hormone Standardization program (HoSt) reference samples with defined values (n = 40) showed a Deming regression slope of 0.963, intercept of 28.06 pg/mL, standard error of estimate was 66.9, a correlation coefficient of 0.9996, and a mean bias of -0.6%. The method met the accuracy criteria by the CDC HoSt program. In addition, we achieved >12 000 injections on a single analytical column without significant performance deterioration due to the specific online solid-phase extraction settings.

Photolysis of Low-Brominated Diphenyl Ethers and Their Reactive Oxygen Species-Related Reaction Mechanisms in an Aqueous System

To date, no report was concerned with participation of reactive oxygen species in waters during photolysis of low-brominated diphenyl ethers (LBDEs). Herein, we found that electron spin resonance (ESR) signals rapidly increased with increasing irradiation time in the solution of LBDEs and 4-oxo-TMP solutions. But this phenomenon did not occur in the presence of NaN₃ (¹O₂ quencher) demonstrating generation of ¹O₂ in process of LBDEs photolysis. The indirect photolytic contribution rate for BDE-47 and BDE-28 was 18.8% and 17.3% via ¹O₂, and 4.9% and 6.6% via ·OH, respectively. Both D₂O and NaN₃ experiments proved that the indirect photolysis of LBDEs was primarily attributable to ¹O₂. The bimolecular reaction rate constants of ¹O₂ with BDE-47 and BDE-28 were 3.12 and 3.64 × 10⁶ M^-1 s^-1, respectively. The rate constants for BDE-47 and BDE-28 (9.01 and 17.52 × 10⁻³ min^-1), added to isopropyl alcohol, were very close to those (9.65 and 18.42 × 10⁻³ min^-1) in water, proving the less indirect photolytic contribution of ·OH in water. This is the first comprehensive investigation examining the indirect photolysis of LBDEs in aqueous solution.

Fast liquid chromatographic-tandem mass spectrometric method using mixed-mode phase chromatography and solid phase extraction for the determination of 12 mono-hydroxylated brominated diphenyl ethers in human serum

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are formed from the oxidative metabolism of polybrominated diphenyl ethers (PBDEs) in humans, rats and mice, but their quantitation in human blood and other matrices with liquid chromatography-mass spectrometric techniques has been a challenge. In this study, a novel analytical method was developed and validated using only 250 μL of human serum for the quantitation of twelve OH-PBDEs, fully chromatographically separated in a 15 min analytical run. This method includes two novel approaches: an enzymatic hydrolysis procedure and a chromatographic separation using a mixed mode chromatography column. The enzymatic hydrolysis (EH) was found critical for 4'-OH-BDE17, which was not detectable without it. For the sample clean up, a solid phase extraction protocol was developed and validated for the extraction of the 12 congeners from human serum. In addition, for the first time baseline resolution of two components was achieved that correspond to a single peak previously identified as 6'-OH-BDE99. The method was validated for linearity, accuracy, precision, matrix effects, limit of quantification, limit of detection, sample stability and overall efficiency. Recoveries (absolute and relative) ranged from 66 to 130% with relative standard deviations <21% for all analytes. Limit of detection and quantitation ranged from 4 to 90 pg mL(-1) and 6-120 pg mL(-1), respectively, with no carry over effects. This method was applied in ten commercially available human serum samples from the general US population. The mean values of the congeners detected in all samples are 4'-OH-BDE17 (34.2 pg mL(-1)), 4-OH-BDE42 (33.9 pg mL(-1)), 5-OH-BDE47 (17.5 pg mL(-1)) and 4'-OH-BDE49 (12.4 pg mL(-1)).