Selectivity of Terahertz Gas-Phase Spectroscopy.

Analytical potential of terahertz (THz) spectroscopy is assessed by comparing selectivity for a set of eight environmentally important gases over THz and infrared (IR) optical frequencies. Selectivity coefficients are determined over selected spectral regions for acetaldehyde, acetonitrile, ethanol, water, methanol, ammonia, propionaldehyde, and propionitrile. These selectivity coefficients quantify the magnitude of the net analyte signal for each test compound relative to the other seven. In addition to the THz spectral range (2-125 cm(-1)), selectivity coefficients are determined for the following IR regions 600-1300, 1300-2000, 2600-3100, 3100-4000, and 4000-6500 cm(-1). Highest selectivity is afforded over the THz frequencies for six of the eight test compounds and THz selectivity coefficients for the other two gases (water and acetonitrile) are acceptable for environmental measurements.