Combination of Sorption Tube Sampling and Thermal Desorption with Hollow Waveguide FT-IR Spectroscopy for Atmospheric Trace Gas Analysis:  Determination of Atmospheric Ethene at the Lower ppb Level

Abstract

The determination of organic trace gases in the ambient environment at the lower ppb level is demonstrated based on a novel technique combining sorption tube sampling on Molsieve and Carbosieve S-III, thermal desorption, and detection of the trace analyte by hollow waveguide Fourier transform infrared (HWG-FT-IR) spectroscopy. While ethene concentrations of approximately 5 ppm can be directly observed using HWG-FT-IR, enrichment factors of up to 5000 were achieved by sorption tube sampling and thermal desorption. Detection limits of approximately 1 ppb are reported. Efficient enrichment by the sampling tube is achieved due to the favorable internal volume ( approximately 0.4 cm(3) at a length of 470 mm) of the hollow waveguide serving as a miniaturized gas cell. This new method was validated for ethene by thermodesorption-cryofocusing-GC-FID as the reference method. Analytical performance has been compared for standard gas mixtures and for ethene measurements in urban air. Finally, ethene data from a sampling campaign at two alpine sites in Tyrol/Austria are presented.

Optoelectronic Capillary Sensors in Microfluidic and Point-of-Care Instrumentation

“…The selectivity of sensors can be achieved by physical processing of the sample in the capillary head, for example by heating [85–86]. In one sensor using that principle, the set of parameters from which the fingerprint of a liquid is selected was indirectly monitored by measurements of light propagation.…”

“…The heater, made by thick-film technology, had a width of 1.5 mm, and its heating power was 3 W. The temperature in the box where the head was placed was stabilized at 22 °C. This box was also used for removing vaporized liquid from the capillary as suggested in [86]. …”

iHWG-μNIR: a miniaturised near-infrared gas sensor based on substrate-integrated hollow waveguides coupled to a micro-NIR-spectrophotometer

“…12 Additionally, highly compact gas cells may be realized, which can be coupled to a variety of broador narrow-band light sources and detectors. HWGs have frequently been used to determine gaseous species in the infrared region of the spectra, such as carbon monoxide and nitric oxide, 13 methane, carbon dioxide and chloroethane, 14 benzene, toluene and xylenes, 15 ethane, 16 as well as in the near infrared region, such as methane. 17 Recently, a new generation of HWG structures was introduced by Mizaikoff et al, the socalled substrate-integrated hollow waveguide (iHWG).…”

Near-Infrared Hollow Waveguide Gas Sensors

“…The utilization of hollow-core waveguides provides the distinct advantage of combining a compact gas cell with an efficient radiation guide for the measurement of small gas volumes. Gas-sensing applications utilizing infrared HWGs have already been reported in the early 1990s 5,6 and have since been coupled to both Fourier transform infrared (FT-IR) spectrometers [7][8][9][10] and laser light sources. 11,12 The first approaches to using a silver/silver halide coating on the interior of hollow waveguides were reported by Croitoru 13 and his group at Tel Aviv University in 1992.…”