| Title: | FT-IR-cPAS--new photoacoustic measurement technique for analysis of hot gases: a case study on VOCs |
| Author(s): | Hirschmann CB; Koivikko NS; Raittila J; Tenhunen J; Ojala S; Rahkamaa-Tolonen K; Marbach R; Hirschmann S; Keiski RL; |
| Address: | "Photonic Devices and Measurement Solutions, VTT Technical Research Centre of Finland, Kaitovayla 1, FI-90570 Oulu, Finland. christian.hirschmann@vtt.fi" |
| ISSN/ISBN: | 1424-8220 (Electronic) 1424-8220 (Linking) |
| 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 degrees 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 (1sigma, 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 (3sigma, 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" |
| Keywords: | "Calibration Gases/*chemistry Photoacoustic Techniques/*instrumentation/*methods Spectroscopy, Fourier Transform Infrared/*instrumentation/*methods Temperature Volatile Organic Compounds/chemistry elevated temperature measurement photoacoustic spectroscopy;" |
| Notes: | "MedlineHirschmann, Christian Bernd Koivikko, Niina Susanna Raittila, Jussi Tenhunen, Jussi Ojala, Satu Rahkamaa-Tolonen, Katariina Marbach, Ralf Hirschmann, Sarah Keiski, Riitta Liisa eng Research Support, Non-U.S. Gov't Switzerland 2011/12/14 Sensors (Basel). 2011; 11(5):5270-89. doi: 10.3390/s110505270. Epub 2011 May 16" |
