Determination of alkylbenzene metabolites in groundwater by solid-phase extraction and liquid chromatography–tandem mass spectrometry

Benzylsuccinate (BSA), methylbenzylsuccinate (methylBSA), and ethylbenzylsuccinate (ethylBSA) are unambiguous anaerobic biotransformation products from toluene, xylenes, and ethylbenzene decay, respectively, and may be used to indicate intrinsic bioremediation is occurring at hydrocarbon-contaminated sites. In order to improve upon current methods that detect and quantify anaerobic hydrocarbon metabolites in field samples, solid-phase extraction (SPE) and direct sample injection methods coupled with liquid chromatography–tandem mass spectrometry (LC–MS–MS) were evaluated. In laboratory studies, recoveries of authentic standards of non-deuterated or deuterated benzylsuccinates and toluates ranged from 80 to 106% with relative standard errors ranging from 2 to 4%. The method detection limits for these analytes using SPE–LC–MS–MS ranged from 0.006 to 0.029 μg/L whereas those for direct injection-LC–MS–MS ranged from 0.61 to 1.5 μg/L. Given the increased sensitivity of using SPE coupled with LC–MS–MS, this technique was then used to analyze for the presence of putative anaerobic alkylbenzene metabolites in groundwater from a hydrocarbon-contaminated site where single-well push–pull tests were conducted using deuterated aromatic hydrocarbons. Both deuterated and non-deuterated benzylsuccinates and toluates were successfully detected and quantified in field samples using this method.