Development of a PM IRRAS device for the detection of persistent chemical warfare agents
LE3 .A278 2013
Bachelor of Science
Polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) was evaluated as a method for detection of the persistent chemical warfare agent (CWA) simulant, 11-mercaptoundecyl phosphoric acid (phosphothiol) deposited via self-assembly on gold. Targeted CWAs (G and V- series nerve agents) are characterized by phosphoric group vibrations present in the 1000 cm-1 – 1200 cm-1 region. The phosphothiol displays a characteristic peak at 1030 cm-1 which was used to determine the limit of detection (LoD) of this CWA simulant with a modified Lambert’s Law plot. First, the PM IRRAS spectra were simulated using the determined optical constants of phosphothiol and Fresnel equations. The predicted LoD was 16 ng. Next, the PM IRRAS experiments were done using an improved method. The main developments made to the method were: (a) the use of a single Photoelastic Modulator setting of 1400 cm-1; (b) the use of gold slides in place of expensive BaF2 prisms for collection of the calibration spectra; (c) and a simplified method for data processing. The experimental LoD was 21 ng. Both the simulated and experimental values for the LoD of phosphothiol on gold were lower than the median lethal dose and lowest observable adverse effect level for VX, demonstrating an excellent potential of PM IRRAS for non-contact detection of CWAs. The agreement between the simulated and experimental LoD demonstrates the utility of simulations in experimental planning and prediction of LoD for CWAs. This is of particular importance for this work because it avoids unnecessary exposure to dangerous CWAs during experiments.
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