QEPAS spectrophones: design, optimization, and performance

The impact of design parameters of a spectrophone for quartz-enhanced photoacoustic spectroscopy on its performance was investigated. The microresonator of spectrophone is optimized based on an experimental study. The results show that a 4.4 mm-long tube with 0.6 mm inner diameter yields the highest signal-to-noise ratio, which is similar to 30 times higher than that of a bare QTF at gas pressures between 400 and 800 Torr. The optimized configuration demonstrates a normalized noise-equivalent absorption coefficient (1 sigma) of 3.3x10(-9) cm(-1)W/Hz(1/2) for C2H2 detection at atmospheric pressure. The effect of the changing carrier gas composition is studied. A side-by-side sensitivity comparison between QEPAS and conventional photoacoustic spectroscopy technique is reported.