FT-IR-cPAS—New Photoacoustic Measurement Technique for Analysis of Hot Gases: A Case Study on VOCs

Abstract

This article describes a new photoacoustic FT-IR system capable of operating at elevated temperatures. The key hardware component is an optical-readout cantilever microphone that can work up to 200 °C. All parts in contact with the sample gas were put into a heated oven, incl. the photoacoustic cell. The sensitivity of the built photoacoustic system was tested by measuring 18 different VOCs. At 100 ppm gas concentration, the univariate signal to noise ratios (1σ, measurement time 25.5 min, at highest peak, optical resolution 8 cm−1) of the spectra varied from minimally 19 for o-xylene up to 329 for butyl acetate. The sensitivity can be improved by multivariate analyses over broad wavelength ranges, which effectively co-adds the univariate sensitivities achievable at individual wavelengths. The multivariate limit of detection (3σ, 8.5 min, full useful wavelength range), i.e., the best possible inverse analytical sensitivity achievable at optimum calibration, was calculated using the SBC method and varied from 2.60 ppm for dichloromethane to 0.33 ppm for butyl acetate. Depending on the shape of the spectra, which often only contain a few sharp peaks, the multivariate analysis improved the analytical sensitivity by 2.2 to 9.2 times compared to the univariate case. Selectivity and multi component ability were tested by a SBC calibration including 5 VOCs and water. The average cross selectivities turned out to be less than 2% and the resulting inverse analytical sensitivities of the 5 interfering VOCs was increased by maximum factor of 2.2 compared to the single component sensitivities. Water subtraction using SBC gave the true analyte concentration with a variation coefficient of 3%, although the sample spectra (methyl ethyl ketone, 200 ppm) contained water from 1,400 to 100k ppm and for subtraction only one water spectra (10k ppm) was used. The developed device shows significant improvement to the current state-of-the-art measurement methods used in industrial VOC measurements.

Broadband Laser-Based Infrared Detector for Gas Chromatography

“…Another point to consider for future improvements is that our current CEPAS detector can operate only up to 50 °C, making the handling of high-boiling-point compounds difficult as they tend to stick on the walls of the cell. However, an earlier study has shown that the CEPAS detector can operate at least up to 180 °C with suitable engineering . Overall, an optimally designed CEPAS detector could improve the detection limits of GC-PAS as much as 2–3 orders of magnitude, resulting in low-pg to sub-pg LODs and thus surpassing FID performance also in terms of detection limits, not only in selectivity.…”

“…However, an earlier study has shown that the CEPAS detector can operate at least up to 180 °C with suitable engineering. 43 Overall, an optimally designed CEPAS detector could improve the detection limits of GC-PAS as much as 2−3 orders of magnitude, resulting in low-pg to sub-pg LODs and thus surpassing FID performance also in terms of detection limits, not only in selectivity.…”

Photoacoustic Spectroscopy for the Determination of Lung Cancer Biomarkers—A Preliminary Investigation

“…The screw cap valve of the Tedlar bag was used for the connection to ensure sealing. This procedure for the generation of VOC gas mixtures is established among researchers in this field [ 44 ]. After the gas transfer from the preparation bag to the sample cell, the gas in- and outlet of the cell were closed.…”

The research of temperature properties of photoacoustic spectroscopy detection for SF6 decomposition products in gas insulated switchgear

“…So there will be background absorptions to a certain extent corresponding to different lters. The background PA signal corresponding to a specic lter could be considered as a xed value when the external environment conditions stay permanent, [17][18][19][20][21] because SF 6 is the major component of measured gas.…”