Double antinode excited quartz-enhanced photoacoustic spectrophone

Abstract

A double antinode excited quartz-enhanced photoacoustic spectroscopy (DAE-QEPAS) spectrophone, employing a custom-made quartz tuning fork (QTF) and operating at the 1stt overtone resonance mode is reported. The signal phase variation along the QTF prong was investigated, and a piezoelectric transducer was introduced to compensate the phase shift between two QTF separated 1st overtone antinode points. Two sets of acoustic micro-resonators were optimized and assembled at two antinode points to improve the spectrophone performance. With the two antinodes excited by one laser source, the DAE-QEPAS spectrophone attained a sensitivity gain factor of ∼100 times and ∼3 times with respect to the 1st overtone resonances of a bare custom QTF and a standard on-beam QEPAS spectrophone, respectively. H2O was selected as the target analyte and a detection limit of ∼230 ppb was obtained by the DAE-QEPAS spectrophone for a 1 s integration time, corresponding to a normalized noise equivalent absorption coefficient of 1.73 × 10-9 cm−1·W·Hz−1/2.