Development and Validation of an Analytical Method for Simultaneous Quantitation of Individual Xylene Isomers in...

Xylenes are ubiquitous in the environment due to their widespread use in a variety of products and industries, including cleaning agents, paint thinners, printing, and plastic production, demonstrating the potential for exposure in humans. Because of limited data on xylenes, we are investigating the toxicity of xylenes, mixed in a specific isomeric ratio, in rodent models. The goal of this study was to develop and validate a method to quantitate individual xylene isomers (p-, m-, and o-xylene) in rodent blood in support of toxicity studies. The method used internal standard calibration with isotopically labeled analytes for an analysis by headspace gas chromatography-mass spectrometry following removal of moisture with anhydrous calcium chloride to allow separation of individual isomers. In male Sprague Dawley rat blood, the method was linear (r ≥ 0.99) over the range of 5 - 1500 ng/mL, accurate (mean relative error (RE) ≤ 15.3%), and precise (relative standard deviation (RSD) ≤ 10.8%). Low limits of detection were achieved, at 1.0, 2.3, and 1.0 ng/mL for p-, m-, and o-xylene, respectively. The method was evaluated in male and female Hsd:Sprague Dawley^® SD^® rat blood and male and female B6C3F1/N mouse blood, the strains used in toxicology studies, with RE ≤ ±13.5% and RSD ≤ 10.6%. All isomers were stable for at least 62 days in blood when stored frozen. The results presented here demonstrate this method can accurately and precisely quantitate p-, m-, and o-xylene in a single analytical run in rat and mice blood samples following exposure to individual xylene isomers. The method could be easily adapted to other biological matrices, including human matrices.