Gries, Wolfgang, et al. Analytical and Bioanalytical Chemistry 407.12 (2015): 3417-3423.
Background: Quantitative assessment of human exposure to the ubiquitous rubber vulcanization accelerator 2-mercaptobenzothiazole (MBT), which readily migrates to the environment, has been a challenging analytical task. Human urine samples contain a variety of low-molecular weight, biotransformed species of MBT that are excreted as conjugates (glucuronides, sulfates, mercapturic acids) and collectively considered to represent total MBT. To accurately quantify total MBT, an assay with low detection limits and high specificity is needed.
Solution: 2-Mercaptobenzothiazole-d4 was used as the isotope-labeled internal standard for a high-throughput LC-MS/MS analytical method. The assay was comprised of: 1) enzymatic hydrolysis of urine samples to release total MBT from conjugates; 2) automated column-switching LC to process a large number of samples in a short time; 3) isotope-dilution quantitation with MBT-d4 to compensate for matrix effects and recovery differences; and 4) positive electrospray ionization (ESI+) monitored using the following MRM transitions: MBT (m/z 167.93 → 135.09/124.15), MBT-d4 (m/z 171.95 → 139.11/128.17).
Key Results:
Incorporation of MBT-d4 allowed for validation of a method that could be used for biomonitoring of MBT exposure:
Ultra-Sensitive: The method had a reproducible LOD and LOQ in urine of 0.4 and 1.0 μg/L, respectively.
Precision: Relative standard deviations were low over the method's analytical range (1.6-5.8%).
Observed MBT in only 1 of 28 non-exposed control samples (10.8 μg/L) while all 25 occupationally exposed workers were found to be positive (up to 6,210 μg/L), validating the performance of the assay.
LeFevre, Gregory H., et al. Environmental science & technology 50.13 (2016): 6762-6771.