Verification of Exposure to Organophosphates: Detection of an Unknown Cholinesterase Inhibitor

Verification of exposure to nerve agents is relevant because the health risks of even low level exposures have not yet been fully explored. Within this context it is important to verify non-exposure in order to re-assure worried military personnel or citizens. Phosphylated butyrylcholinesterase is one of the most important biomarker to verify an exposure to nerve agents. Nerve agent adducts can be analyzed with LC-MS/MS by detection of a phosphylated nonapeptide that is derived after digestion of butyrylcholinesterase with pepsin. For a sensitive analysis (low degree of BuChE inhibition) the identity of the cholinesterase inhibitor has to be known in order to operate the LC-MS/MS instrument in the most sensitive SRM mode. In practice the identity of the cholinesterase inhibitor will not be known beforehand and the number of possible organophosphates is larger than thousand. However, the number of possible molecular masses of relevant organophosphates is approximately 170. By smart selection of these masses the number of MRM transitions that have to be acquired can even be reduced to 34 transitions, when all nerve agents from the OPCW schedule 1 list need to be screened. Furthermore, a generic method will be presented that is based on the conversion of the phosphyl moiety conjugated to BuChE. After digestion of BuChE the phosphyl group is eliminated from the peptide unde