Wavelength-modulated photoacoustic spectroscopy sensor for multi-gas measurement of acetone, methane, and water vapor based on a differential acoustic resonator

Precise assessment of breath acetone and methane is significant to the medical diagnosis process. A multi-gas sensing system based on wavelength-modulated differential photoacoustic spectroscopy was developed for simultaneous measurement of acetone and methane. A distributed feedback diode laser emitting in the range from 3363 to 3371 nm was employed to scan the absorption lines of acetone and methane. The cross sensitivities in terms of spectral interference among acetone, methane, and water vapor are effectively eliminated by using a linear combination method of reference spectra for accurately determining the concentration of acetone and methane. The positive effect of water vapor on photoacoustic signal resulting from the light absorption of acetone and methane was precisely evaluated. To improve the instrument performance, a differential PA cell companying with a differential amplifier circuit is experimentally demonstrated in providing a better performance of noise suppression compared with a single acoustic resonator. With a low detection limit down to 0.43 ppm and 12 ppb (integration time of 10 s) for acetone and methane, the sensor shows a great potential for medical diagnosis in simultaneous measurement of acetone and methane.