Optimisation and validation of a GC-MS/MS method for the analysis of methyl salicylate in hair and skin samples for use in human-volunteer decontamination studies

Methyl salicylate has a long history of use as a chemical warfare agent simulant for volatile lipophilic compounds such as sulphur mustard. An improved isotope dilution GC-MS/MS method was developed, optimised and validated for the analysis of methyl salicylate in human skin and hair samples, for use in emergency decontamination volunteer studies. Following derivatisation, quantification was measured on a triple quadrupole mass spectrometer, set to EI mode and conducting multiple reaction monitoring of target ions. The mass transitions were 209 -> 179 and 213 -> 161 for quantitation of methyl salicylate and methyl salicylate D4, respectively whereas qualifier ion transitions used to verify identity were 209 -> 169 and 213 -> 89. The method achieved excellent coefficient of determination (R-2 > 0.9968 to 0.9999) over the range of 0.5-5000 ng/ml and the LOD and LOQ were 0.05 ng/ml and 0.5 ng/ml. The method was further validated for accuracy (infra-day and inter-day average 100.28% to 102.03% and 99.48% to 102.33%, respectively) and precision (infra-day RSD 1.43% to 2.35%, inter-day RSD 1.91% to 2.97%) at three concentrations (25, 250 and 2500 ng/ml). The validated method was successfully used to identify methyl salicylate in samples of human skin generated during volunteer studies of emergency decontamination systems and in hair of staff conducting these studies.