Non-contact detection of chemical warfare simulant triethyl phosphate using PM-IRRAS

Polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS) was employed to detect the chemical warfare agent (CWA) simulant triethyl phosphate (TEP) on gold, as well as on US military paint, i.e., chemical agent resistant coating (CARC). The targeted CWAs (G and V-series nerve agents) are characterized by phosphoric group vibrations present in the 1200 cm(-1) region. TEP displays two prominent peaks at 1268 cm(-1) and 1036 cm(-1) corresponding to P=O and (P)-O-C vibrations, respectively. A droplet of TEP solution in cyclohexane was deposited on gold and CARC substrates and after solvent evaporation PM-IRRAS spectra were collected in the 1200 cm(-1) region. The integrated peak area of the PO and (P)OC vibrations was used to construct calibration curves and to determine the experimental limit of detection (LoD). In the case of gold as the substrate the estimated LoD of ~0.48 μg and 1.23 μg was obtained for the P=O and (P)-O-C vibrations, respectively. In the case of CARC, a LoD of 24 μg was determined. These detection limits are at least 3 orders of magnitude lower than the typical lethal dose of G and V-series nerve agents, demonstrating potential of PM-IRRAS for non-contact detection of these CWAs.