EXPERIMENTAL IMPROVEMENTS IN RECORDING GAS-PHASE PHOTOACOUSTIC SPECTRA

By adjusting several factors affecting the sensitivity of photoacoustic detection, we have constructed a general-purpose intracavity dye laser photoacoustic spectrometer with a detection limit of 4 × 10-10/cm (2:1 signal-to-noise level). This permits small signals, such as the 4-0 and 5-0 O-H stretching bands of phenol, to be recorded in the gas phase at room temperature. It is found that the photoacoustic signal-to-noise ratio can be significantly enhanced by (1) reducing the effects of window absorption through the use of simple acoustic baffles and (2) the addition of a heavy rare gas as a sound carrier, changing the speed of sound and enabling a mechanical light chopper to modulate the light at an acoustic resonance frequency of the gas cell. © 1990 American Chemical Society.