Quartz-enhanced photoacoustic detection of trace impurities in hydrogen: spectrophone design and CO sensing

In this work, the use of Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) for the detection of CO impurities in hydrogen was demonstrated. Due to the high speed of sound in hydrogen, the geometry of the spectrophone was specifically selected to ensure efficient sound wave amplification. Therefore, a QEPAS spectrophone was designed by exploiting a custom quartz tuning fork operating at first overtone mode (∼44,0 kHz) in combination with compact resonator tubes. The spectrophone was integrated into a QEPAS sensor for CO trace detection at 2193.36 cm−1 in a hydrogen matrix. The QEPAS sensor was calibrated using certified mixtures, returning a detection limit of 1.5 ppm for 10 s. Furthermore, pressure-dependent measurements enabled the determination of the effective V-T relaxation rate of CO in hydrogen, which was found to be 438 ± 80 s−1 Torr−1.