Development of an Analytical Protocol for Forensic Identification of Chemical Warfare Agent Surrogates

Abstract

An analytical protocol for forensic identification of chemical warfare agent surrogates in various sample media is developed. This protocol can be implemented on site or in a mobile laboratory, based on a quick sample extraction procedure and a subsequent gas chromatography/mass spectrometry (GC/MS) analysis. The surrogates in this work include 2-chloroethyl ethyl sulfide (CEES), dimethyl methyl phosphonate (DMMP), 2-(butylamino) ethanethiol (BAET), pinacolyl methyl phosphonate (PMP), and diethyl phosphoramidate (DEPA) that are simulants of mustard gas, sarin, VX (O-Ethyl S-2-diisopropylaminoethyl methylphosphonothiolate), soman, and tabun, respectively. The target analytes in headspace or air sample are sampled by the solid phase microextraction (SPME) fibers and all surrogates are easily detected by GC/MS analysis. The neat vapor is also directly analyzed by a portable MS through a membrane inlet but only the more volatile CEES and DMMP are detectable and correctly identified. The stability of surrogates in acetone is monitored in the preparation of standard solution. All surrogates are relatively stable in acetone with the exception of BAET, which is found to degrade quickly in water and other organic solvents (e.g., acetone, methanol, ethanol, hexane). Extraction of water and soil samples is also investigated in this study. In analyzing water sample spiked with the surrogates, it is found that SPME does not offer any advantage over direct aqueous injection into the GC/MS. CEES readily hydrolyzes in water to form 2-(ethylthio)-ethanol. Soil samples are extracted by acetone and the raw extracts are analyzed without any concentration, and all surrogates are detectable at 5–10 ppm level for CEES, DMMP, and DEPA. An actual case study is carried out using SPME to detect the presence of surrogate vapor inside a laboratory refrigerator in which they are stored.