CO2-laser photoacoustic spectroscopy applied to low-level toxic-vapor monitoring

A CO2-laser photoacoustic detector is being developed that can detect the hazardous hydrazine-based rocket fuels and selected toxic industrial compounds at concentrations below 100 ppb in the ambient air. This paper reviews our work to develop this detector based on the principles of photoacoustic spectroscopy and classical acoustics. The low parts-per-billion level detection capability of the method to the hydrazines is demonstrated with both acoustically nonresonant and resonant photoacoustic cell designs. A flowing, resonant photoacoustic cell whose interior is coated with tetrafluoroethylene Teflon has been shown to be preferred for detecting highly adsorptive or reactive compounds. Photoacoustic spectroscopy has been demonstrated to be useful in measuring adsorption or reaction losses of low-concentration gases on surfaces.