Abstract
Combining the merits of non-contact measurement and high sensitivity, the quartz-enhanced photothermal spectroscopy (QEPTS) technique is suitable for measuring acid gases such as hydrogen chloride (HCl). In this invited paper, we report, for the first time, on an ultra-highly sensitive HCl sensor based on the QEPTS technique. A continuous wave, distributed feedback (CW-DFB) fiber-coupled diode laser with emission wavelength of 1.74 µm was used as the excitation source. A certified mixture of 500 ppm HCl:N2 was adapted as the analyte. Wavelength modulation spectroscopy was used to simplify the data processing. The wavelength modulation depth was optimized. The relationships between the second harmonic (2f) amplitude of HCl-QEPTS signal and the laser power as well as HCl concentration were investigated. An Allan variance analysis was performed to prove that this sensor had good stability and high sensitivity. The proposed HCl-QEPTS sensor can achieve a minimum detection limit (MDL) of ~17 parts per billion (ppb) with an integration time of 130 s. Further improvement of such an HCl-QEPTS sensor performance was proposed.
Highlights
A certified mixture of 500 ppm hydrogen chloride (HCl):N2 was adapted as the analyte
It can be observed that the HCl-quartzenhanced photothermal spectroscopy (QEPTS) signal amplitude first increased, and decreased with an increase in modulation depth
We demonstrate, for the first time, an ultra-highly sensitive QEPTS sensor for HCl detection
Summary
Hydrogen chloride (HCl) is an essential gas used in chemical production which performs key roles in various important fields, for example, semiconductor manufacturing, biofuel combustion, and plasma etching [1,2]. The sources of atmospheric HCl are primarily incineration plants, accidental emission, and medical waste [3,4,5]. Considering that HCl is toxic, corrosive, and harmful to human health and the environment, there is significant demand for the detection of HCl gas concentration levels [6,7]. To continuously monitor and control concentration levels, sensors for HCl need to provide real-time data, fast response, and have a sensitive detection ability at low parts per million (ppm) and parts per billion (ppb) levels [5]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
