iCONVERT: An Integrated Device for the UV-Assisted Determination of H₂S via Mid-Infrared Gas Sensors

Abstract

In this technical note, we describe an integrated device platform for performing in-flow gaseous conversion reactions based on ultraviolet (UV) irradiation. The system combines, using the same footprint, an integrated UV-conversion device (iCONVERT), a preconcentrator unit (iPRECON), and a new generation of mid-infrared (MIR) gas cell simultaneously serving as a photon conduit, i.e., so-called substrate-integrated hollow waveguide (iHWG) optically coupled to a compact Fourier transform-infrared (FT-IR) spectrometer. The iCONVERT is assembled from two blocks of aluminum (dimensions, 75 mm × 50 mm × 40 mm; L × W × D) containing 4 miniaturized UV-lamps (47mm × 6 mm × 47 mm each). For the present study, the iPRECON-iCONVERT-iHWG sensing platform has specifically been tailored to the determination of H2S in gaseous samples. Thereby, the quantitative UV-assisted conversion of the rather weak IR-absorber H2S into the more pronouncedly responding SO2 is used for hydrogen sulfide detection. A linear calibration model was established in the range of 7.5 to 100 ppmv achieving a limit of detection at 1.5 ppmv using 10 min of sample preconcentration (onto Molecular Sieve 5A) at a flow rate of 200 mL min(-1). When compared to a conventional UV-conversion system, the iCONVERT revealed similar performance. Considering the potential for system miniaturization using, e.g., dedicated quantum cascade lasers (QCL) in lieu of the FT-IR spectrometer, the developed sensing platform may be further evolved into a hand-held device.

Advances in Mid-Infrared Spectroscopy for Chemical Analysis

“…Furthermore, combining such sensing systems with similar miniaturized conversion or preconcentration strategies prior to spectra acquisition expands their applicability to a wide range of measurement scenarios. For example, the conversion of rather weak molecular IR absorbers such as H 2 S into a stronger IR absorber-here, SO 2 -has been demonstrated by Petruci et al (80,(147)(148)(149). The combination of a compact FTIR spectrometer with a substrate-integrated HWG has led to a LOD of 3 ppm within a continuous flow system ( Figure 5).…”

Gas-phase broadband spectroscopy using active sources: progress, status, and applications [Invited]

“…These cells have the potential to operate from the visible to the THz. In another approach, hollow mid-IR waveguides have been fabricated with interaction paths on the order of 10 cm and small sample volumes [328, 329]. Finally, resonant optical cavities can be miniaturized, including mm-scale fiber Fabry-Perot cavities formed between mirrors machined on the tips of optical fibers [330, 331].…”

Highly Sensitive H2S Sensing with Gold and Platinum Surface-Modified ZnO Nanowire ChemFETs

“…A fast and selective detection of such small concentrations is challenging. Here, standard sensing procedures often use mass spectrometry, gas chromatography, or infrared (IR) gas sensors [6][7][8]. Despite offering a reliable and selective detection technique, the instruments for these sensing approaches are bulky and expensive [7].…”