Improving the performance of hollow waveguide-based infrared gas sensors via tailored chemometrics

Abstract

The use of chemometrics in order to improve the molecular selectivity of infrared (IR) spectra has been evaluated using classic least squares (CLS), partial least squares (PLS), science-based calibration (SBC), and multivariate curve resolution-alternate least squares (MCR-ALS) techniques for improving the discriminatory and quantitative performance of infrared hollow waveguide gas sensors. Spectra of mixtures of isobutylene, methane, carbon dioxide, butane, and cyclopropane were recorded, analyzed, and validated for optimizing the prediction of associated concentrations. PLS, CLS, and SBC provided equivalent results in the absence of interferences. After addition of the spectral characteristics of water by humidifying the sample mixtures, CLS and SBC results were similar to those obtained by PLS only if the water spectrum was included in the calibration model. In the presence of an unknown interferant, CLS revealed errors up to six times higher than those obtained by PLS. However, SBC provided similar results compared to PLS by adding a measured noise matrix to the model. Using MCR-ALS provided an excellent estimation of the spectra of the unknown interference. Furthermore, this method also provided a qualitative and quantitative estimation of the components of an unknown set of samples. In summary, using the most suitable chemometrics approach could improve the selectivity and quality of the calibration model derived for a sensor system, and may avoid the need to analyze expensive calibration data sets. The results obtained in the present study demonstrated that (1) if all sample components of the system are known, CLS provides a sufficiently accurate solution; (2) the selection between PLS and SBC methods depends on whether it is easier to measure a calibration data set or a noise matrix; and (3) MCR-ALS appears to be the most suitable method for detecting interferences within a sample. However, the latter approach requires the most extensive calculations and may thus result in limited temporal resolution, if the concentration of a component should be continuously monitored.

Broadband Laser-Based Infrared Detector for Gas Chromatography

“…In most cases, this is possible even in the case of simultaneously eluted compounds. Chemometrics offer tools for such purpose, one of which is CLS, allowing multicomponent analysis based on a spectral library . In Figures and , we give examples of the usefulness of CLS in identifying and quantifying multiple compounds simultaneously.…”

“…Photoacoustic spectroscopy is not the only potential laser-based infrared detection method for GC. As an alternative approach, hollow optical waveguides, ,, including hollow-core photonic crystal fibers, offer an efficient way of minimizing the sample volume. Additionally, miniaturization of optical cavities could make cavity-enhanced absorption spectroscopic techniques a tempting detection method for GC.…”

iHWG-MOX: A Hybrid Breath Analysis System via the Combination of Substrate-Integrated Hollow Waveguide Infrared Spectroscopy with Metal Oxide Gas Sensors

“…In contrast to equally robust industrial process monitoring systems (e.g., by Horiba), which enable monitoring high gas flows in harsh environments, iHWGs may also be used to analyze exceedingly small flows and, thus, minute sample volumes. This results in rapid sample transient times and, correspondingly, an improved time resolution. ,, iHWGs have nowadays evolved into a key component for a variety of gas sensing scenarios that readily combine with a wide variety of light sources. ,− To detect even traces of gas molecules, a compact combination of iHWGs with a new generation of miniaturized preconcentration devices was demonstrated for enriching and/or converting VOCs relevant in exhaled breath analysis and environmental and safety/security monitoring scenarios. ,, …”