Cantilever-enhanced photoacoustic detection of hydrogen sulfide (H2S) using NIR telecom laser sources near 1.6 µm

Abstract

concentrations as low as 500 pptv manifesting in the characteristic odor of rotten eggs can already be detected by the human olfactory sense, the total loss of olfactory sensation starts at 150-200 ppmv [3]. Because of the wide occurrence of H 2 S in industrial processes and its often negative impact on process stabilities and product quality, its concentration needs to be tightly monitored. Furthermore, safety considerations and legal concentration limits also necessitate the accurate determination of H 2 S levels. In practice, concentrations ranging from sub-ppm levels at low pressures to several per cents at atmospheric conditions need to be monitored. Due to such diverse requirements, H 2 S analyzers based on different measurement technologies have been developed and are in industrial use. Apart from spectroscopic techniques based on absorption measurements, a range of other analytical techniques such as pulsed UV fluorescence [4], sulfur chemiluminescence [5], colorimetry employing a lead acetate tape [6], flame photometry as detector in gas chromatography [7] as well as electrochemical detection techniques ranging from potentiometric, galvanic, coulometric and amperometric detection [8] is frequently employed. It is interesting to note that in the petrochemical industry the lead acetate tape method is still in frequent use. Also, gas chromatographic methods are popular as they can be used to detect several components almost simultaneously, but this technique requires preparation and extraction of the sample gas leading to a time-consuming measurement. A general drawback of nonspectroscopic techniques is the fact that they do not allow for direct measurements. This, however, also applies to H 2 S detection based on UV fluorescence as this technique requires sample combustion as well as detection by chemoluminescence, where addition of reagents is required.Most of the spectroscopic techniques are based on the detection of the absorption spectrum of the molecules in Abstract Sensitive detection of hydrogen sulfide (H 2 S) at different pressure levels using a cantilever-enhanced photoacoustic detector in combination with a telecom NIR L-band laser source is reported. Amplitude and wavelength modulation schemes for photoacoustic signal generation are compared. A detection limit (3σ) of 8 ppmv was achieved for amplitude modulation mode with a 50-s averaging time for the H 2 S absorption near 1.6 µm. As compared to simulated spectra, the cantilever-enhanced photoacoustic detection approach in combination with the sufficiently stable and narrow bandwidth NIR laser is able to reproduce the rotationally resolved H 2 S spectrum at low pressures of 300 mbar.

Trace Ammonia Detection Based on Near-Infrared Fiber-Optic Cantilever-Enhanced Photoacoustic Spectroscopy

“…A detection limit of 9 ppb was achieved with an integration time of 10 s. If the microphone noise is higher than the acoustic noise caused by the environment, the sensitivity of the gas detection system based on PAS can be effectively improved by increasing the sensitivity of acoustic sensors. Therefore, various high-sensitivity acoustic sensors have been proposed in recent years, such as quartz tuning fork [9][10][11], fiber-optic acoustic sensor [12][13][14][15], and optical cantilever [16][17][18]. Wu et al developed a quartz-enhanced PAS (QEPAS) based NH 3 gas detection system.…”

“…A distributed feedback (DFB) diode laser boosted by an EDFA combined with a quartz tuning fork was used for trace NH 3 detection. Experiments showed that the detection limit could reach 52 ppb [18]. Ma et al reported a sensitive QEPAS based NH 3 sensor [20].…”

Implementation of a quantum cascade laser-based gas sensor prototype for sub-ppmv H2S measurements in a petrochemical process gas stream

“…Despite a variety of online monitoring options for gaseous hydrogen sulfide, its reliable quantitative and selective determination still remains challenging in the field of chemical sensors [1–3]. …”

Off-beam quartz-enhanced photoacoustic spectroscopy-based sensor for hydrogen sulfide trace gas detection using a mode-hop-free external cavity quantum cascade laser

“…In practice, concentrations ranging from sub-ppmv levels at low pressures to several per cents at atmospheric conditions need to be monitored. Despite a variety of online monitoring options for gaseous H 2 S, its reliable quantitative and selective determination still remains challenging in the field of chemical sensors [3][4][5].…”

“…In practice, concentrations ranging from sub-ppmv levels at low pressures to several per cents at atmospheric conditions need to be monitored. Despite a variety of online monitoring options for gaseous H 2 S, its reliable quantitative and selective determination still remains challenging in the field of chemical sensors [3][4][5].In the field of laser spectroscopy, the constant improvement of quantum cascade lasers (QCLs) has led to their application as reliable sources of coherent light ranging from the mid-infrared (MIR) to the terahertz spectral region for sensitive detection of molecular species on their fundamental vibrational, respectively, rotational bands [6][7][8][9]. Due to their tailorable emission wavelength, high output power, compactness, narrow spectral linewidth, and wavelength tuneability, QCLs are optimal choices for spectroscopic applications.…”