Continuous monitoring of chemical warfare agents in vapor using a Fourier transform infra-red spectroscopy instrument with multi pass gas cell, mercury cadmium telluride detector and rolling background algorithm

Identification and quantification method for chemical warfare agents (CWAs) was developed using a continuous and standalone type hazardous gas detection instrument (MKS AIRGARD (R) Air Analyzer), Fourier transform infra-red (FT-IR) spectroscopy system which uses a multi pass gas cell, a Stirling-cooled mercury cadmium telluride detector, and advanced data processing including an exponentially weighted moving background and chemical identification algorithm. Although FT-IR spectrum of sarin vapor prepared in ambient air included absorbance bands of carbon dioxide and water remaining due to incomplete background correction, characteristic absorbance bands were clearly observed in the fingerprint region (700-1400 cm(-1)) and around 2950 cm(-1). n-Hexane was used not only as dissolving solvent for volatile CWAs but also as an interfering field matrix compound. The instrument provided a GB alarm against n-hexane (1320 mg/m(3)) vapor containing dilute sarin (more than 0.44 mg/m(3)). The height of the band peak at 1021 cm(-1) increased proportionally with the concentration. Vapors of soman, tabun, cyclohexylsarin, VX and RVX, which were prepared in ambient air, provided correct alarms, and showed FT-IR spectra similar to that of sarin. The vapors of sulfur mustard, nitrogen mustard 3, Lewisite 1, cyanogen chloride and phosgene provided correct alarms with characteristic FT-IR features, which are different from those of nerve agents. The vapors of volatile CWAs except for VX and RVX provided correct alarm even in the presence of high level of n-hexane. The vapors of unregistered CWAs and mixture vapor of nerve agents were also examined.