Keratin adducts in human hair prove exposure to sulfur mustard in a real case of poisoning and indicate exposure to sesquimustard and O-lost in vitro.

We herein present the development and application of a forensic mass spectrometry-based procedure simultaneously targeting hard keratins from human hair adducted with sulfur mustard (SM) and its structural analogues sesquimustard (Q) and O-lost (T). These alkylating chemicals represent blister agents banned by the Chemical Weapons Convention (CWC). The procedure was applied to an authentic hair sample of an SM-poisoned patient and thus allowed for the first time the proof of exposure to SM based on keratin adducts in a real case of poisoning. Whereas adducts of SM were detected, those of Q and T were not found. Contact of SM, Q and T with hair induced the alkylation of side chains of glutamic acid (E*) residues in diverse hard keratins (adduct formation). For analysis hair proteins were subjected to lysis to make them soluble and subsequently to proteolysis with pepsin to generate adducted peptides. Micro liquid chromatography-electrospray ionization high-resolution tandem-mass spectrometry (µLC-ESI MS/HR MS) allowed the detection of the three biomarker peptides AE*IRSDL, FKTIE*EL and LE*TKLQF. The characteristic alkyl-chain hydroxyethylthioethyl (HETE) was attached by SM, hydroxyethylthioethylthioethyl (HETETE) derived from Q and the hydroxyethylthioethyloxyethylthioethyl (HETEOETE)-moiety originated from exposure to T. Accordingly, we herein present an extended and improved forensic method for the biomedical verification of hair exposure to blister agents. Due to the currently growing threat by chemical warfare agents we also included some general toxicological and bioanalytical remarks of SM poisoning helpful not only for physicians and toxicologists.