Enhancement of photoacoustic spectroscopy with sorption enrichment for ppt-level benzene detection

Abstract

A real time trace gas detector for benzene is demonstrated. The measurement system takes an advantage of modest enrichment through short adsorption periods to reach a ppt-level detection limit with a sampling cycle of 90 s, which includes sample adsorption, desorption and a spectroscopic measurement. Benzene is collected on Tenax TA sorbent for 30 s and then detected from the enriched samples with photoacoustic spectroscopy. A high sensitivity is achieved using cantilever-enhanced photoacoustic spectroscopy and a continuous-wave quantum cascade laser emitting at the wavelength 14.8 μm, which corresponds to the absorption wavelength of the strongest benzene infrared band. We reach a detection limit of 150 ppt of benzene, over one sampling cycle. Interference from humidity and other common petrochemicals is evaluated.

A laser-based sensor for selective detection of benzene, acetylene, and carbon dioxide in the fingerprint region

“…The selected wavelength range, however, has some spectral overlap between benzene, acetylene, and carbon dioxide. Although the band has been targeted previously for benzene detection [29,[32][33][34]43], spectral interference from CO 2 was not addressed, which can be signi cant at trace benzene concentrations. In this work, a multi-dimensional linear regression (MLR) algorithm, discussed in Section 2.2, is implemented to simultaneously measure benzene, acetylene, and CO 2 .…”

“…Recently, Ayache et al used the same QCL technology to develop their own benzene sensor that probed the same band ( 4 ) using quartz-enhanced photoacoustic spectroscopy (QEPAS) [33]; they successfully achieved a detection limit of 4 ppb at 2 minutes of averaging time. Shortly after, Karhu and Hieta improved their CEPAS sensor [32] by adding an adsorption enrichment stage, where benzene was collected on a sorbent and then detected from the enriched samples using photoacoustic spectroscopy [34]. This enrichment ppt in 200 minutes in their previous study [32]).…”

“…Furthermore, photoacoustic detection elements are typically impacted when operating in harsh environments, e.g., by temperature variations, mechanical vibration, external acoustic noise, and humidity [7]. Indeed, as water-vapor affects the relaxation time of detected molecules, the previously discussed PAS-based benzene sensors [32][33][34] were found to be heavily affected by the relative humidity. Thus, it was concluded that it might be necessary to measure the relative humidity of the measured sample and apply a correction to the measured benzene concentration accordingly [32, 33] [34].…”