{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,7]],"date-time":"2026-04-07T17:13:45Z","timestamp":1775582025840,"version":"3.50.1"},"reference-count":43,"publisher":"MDPI AG","issue":"18","license":[{"start":{"date-parts":[[2023,9,20]],"date-time":"2023-09-20T00:00:00Z","timestamp":1695168000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"the Innovation Fund Denmark (IFD)","award":["0140-00011B (UP-CEMS)"],"award-info":[{"award-number":["0140-00011B (UP-CEMS)"]}]},{"name":"the Danish Agency for Institutions and Educational Grants","award":["0140-00011B (UP-CEMS)"],"award-info":[{"award-number":["0140-00011B (UP-CEMS)"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>We report on the use of quartz-enhanced photoacoustic spectroscopy (QEPAS) for multi-gas detection. Photoacoustic (PA) spectra of mixtures of water (H2O), ammonia (NH3), and methane (CH4) were measured in the mid-infrared (MIR) wavelength range using a mid-infrared (MIR) optical parametric oscillator (OPO) light source. Highly overlapping absorption spectra are a common challenge for gas spectroscopy. To mitigate this, we used a partial least-squares regression (PLS) method to estimate the mixing ratio and concentrations of the individual gasses. The concentration range explored in the analysis varies from a few parts per million (ppm) to thousands of ppm. Spectra obtained from HITRAN and experimental single-molecule reference spectra of each of the molecular species were acquired and used as training data sets. These spectra were used to generate simulated spectra of the gas mixtures (linear combinations of the reference spectra). Here, in this proof-of-concept experiment, we demonstrate that after an absolute calibration of the QEPAS cell, the PLS analyses could be used to determine concentrations of single molecular species with a relative accuracy within a few % for mixtures of H2O, NH3, and CH4 and with an absolute sensitivity of approximately 300 (\u00b150) ppm\/V, 50 (\u00b15) ppm\/V, and 5 (\u00b12) ppm\/V for water, ammonia, and methane, respectively. This demonstrates that QEPAS assisted by PLS is a powerful approach to estimate concentrations of individual gas components with considerable spectral overlap, which is a typical scenario for real-life adoptions and applications.<\/jats:p>","DOI":"10.3390\/s23187984","type":"journal-article","created":{"date-parts":[[2023,9,20]],"date-time":"2023-09-20T22:38:45Z","timestamp":1695249525000},"page":"7984","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Quartz-Enhanced Photoacoustic Spectroscopy Assisted by Partial Least-Squares Regression for Multi-Gas Measurements"],"prefix":"10.3390","volume":"23","author":[{"given":"Andreas N.","family":"Rasmussen","sequence":"first","affiliation":[{"name":"Danish Fundamental Metrology, Kogle All\u00e9 5, 2970 H\u00f8rsholm, Denmark"}]},{"given":"Benjamin L.","family":"Thomsen","sequence":"additional","affiliation":[{"name":"Danish Fundamental Metrology, Kogle All\u00e9 5, 2970 H\u00f8rsholm, Denmark"}]},{"given":"Jesper B.","family":"Christensen","sequence":"additional","affiliation":[{"name":"Danish Fundamental Metrology, Kogle All\u00e9 5, 2970 H\u00f8rsholm, Denmark"}]},{"given":"Jan C.","family":"Petersen","sequence":"additional","affiliation":[{"name":"Danish Fundamental Metrology, Kogle All\u00e9 5, 2970 H\u00f8rsholm, Denmark"}]},{"given":"Mikael","family":"Lassen","sequence":"additional","affiliation":[{"name":"Danish Fundamental Metrology, Kogle All\u00e9 5, 2970 H\u00f8rsholm, Denmark"}]}],"member":"1968","published-online":{"date-parts":[[2023,9,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"572","DOI":"10.1109\/TGRS.2010.2055874","article-title":"Backscatter 2-\u03bcm Lidar Validation for Atomospheric CO2 Differential Absorption Lidar Applications","volume":"49","author":"Refaat","year":"2011","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Feng, S., Farha, F., Li, Q., Wan, Y., Xu, Y., Zhang, T., and Ning, H. (2019). Review on Smart Gas Sensing Technology. Sensors, 19.","DOI":"10.3390\/s19173760"},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Nazemi, H., Joseph, A., Park, J., and Emadi, A. (2019). Advanced Micro- and Nano-Gas Sensor Technology: A Review. Sensors, 19.","DOI":"10.3390\/s19061285"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"227","DOI":"10.1016\/j.ijms.2004.08.010","article-title":"Applications of breath gas analysis in medicine","volume":"239","author":"Amann","year":"2004","journal-title":"Int. J. Mass Spectrom."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1806","DOI":"10.1364\/OE.25.001806","article-title":"Photo-acoustic sensor for detection of oil contamination in compressed air systems","volume":"25","author":"Lassen","year":"2017","journal-title":"Opt. Express"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"2821","DOI":"10.1063\/1.1145562","article-title":"Trace gas detection with cavity ring down spectroscopy","volume":"66","author":"Jongma","year":"1995","journal-title":"Rev. Sci. Instrum."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Wilson, A. (2018). Application of electronic-nose technologies and VOC-biomarkers for the noninvasive early diagnosis of gastrointestinal diseases. Sensors, 18.","DOI":"10.3390\/s18082613"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1908385","DOI":"10.1002\/adma.201908385","article-title":"Trace-level, multi-gas detection for food quality assessment based on decorated silicon transistor arrays","volume":"32","author":"Yuan","year":"2020","journal-title":"Adv. Mater."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"106950","DOI":"10.1016\/j.optlaseng.2022.106950","article-title":"A sensitive carbon monoxide sensor for industrial process control based on laser absorption spectroscopy with a 2.3 \u03bcm distributed feedback laser","volume":"152","author":"Lewen","year":"2022","journal-title":"Opt. Lasers Eng."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"C68","DOI":"10.1364\/AO.419942","article-title":"Methane leak detection by tunable laser spectroscopy and mid-infrared imaging","volume":"60","author":"Strahl","year":"2021","journal-title":"Appl. Opt."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1295","DOI":"10.1364\/OL.452085","article-title":"Acoustic microresonator based in-plane quartz-enhanced photoacoustic spectroscopy sensor with a line interaction mode","volume":"47","author":"Lang","year":"2022","journal-title":"Opt. Lett."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"250","DOI":"10.1364\/AO.58.000250","article-title":"Versatile photoacoustic spectrometer based on a mid-infrared pulsed optical parametric oscillator","volume":"58","author":"Lamard","year":"2019","journal-title":"Appl. Opt."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"11035","DOI":"10.1021\/acs.analchem.0c00075","article-title":"Partial Least-Squares Regression as a Tool to Retrieve Gas Concentrations in Mixtures Detected Using Quartz-Enhanced Photoacoustic Spectroscopy","volume":"92","author":"Zifarelli","year":"2020","journal-title":"Anal. Chem."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"101","DOI":"10.1016\/S0143-8166(01)00092-6","article-title":"Near- and mid-infrared laser-optical sensors for gas analysis","volume":"37","author":"Werle","year":"2002","journal-title":"Opt. Lasers Eng."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"133","DOI":"10.1108\/SR-09-2014-696","article-title":"Detecting gases with light: A review of optical gas sensor technologies","volume":"35","author":"Bogue","year":"2015","journal-title":"Sens. Rev."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"012004","DOI":"10.1088\/0957-0233\/24\/1\/012004","article-title":"Optical gas sensing: A review","volume":"24","author":"Hodgkinson","year":"2013","journal-title":"Meas. Sci. Technol."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"586","DOI":"10.1364\/AOP.8.000586","article-title":"Photoacoustics: A historical review","volume":"8","author":"Manohar","year":"2016","journal-title":"Adv. Opt. Photon."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"4461","DOI":"10.1364\/OL.37.004461","article-title":"Part-per-trillion level SF6 detection using a quartz enhanced photoacoustic spectroscopy-based sensor with single-mode fiber-coupled quantum cascade laser excitation","volume":"37","author":"Spagnolo","year":"2012","journal-title":"Opt. Lett."},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Palzer, S. (2020). Photoacoustic-Based Gas Sensing: A Review. Sensors, 20.","DOI":"10.3390\/s20092745"},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Popa, C. (2019). Ethylene Measurements from Sweet Fruits Flowers Using Photoacoustic Spectroscopy. Molecules, 24.","DOI":"10.3390\/molecules24061144"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"129851","DOI":"10.1016\/j.jhazmat.2022.129851","article-title":"Detection of gaseous nerve agent simulants with broadband photoacoustic spectroscopy","volume":"440","author":"Mikkonen","year":"2022","journal-title":"J. Hazard. Mater."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"8266","DOI":"10.1364\/AO.55.008266","article-title":"All-optical detection of acoustic pressure waves with applications in photoacoustic spectroscopy","volume":"55","author":"Westergaard","year":"2016","journal-title":"Appl. Opt."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1902","DOI":"10.1364\/OL.27.001902","article-title":"Quartz-enhanced photoacoustic spectroscopy","volume":"27","author":"Kosterev","year":"2002","journal-title":"Opt. Lett."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"118118","DOI":"10.1016\/j.fuel.2020.118118","article-title":"Quartz-enhanced photoacoustic spectroscopy for hydrocarbon trace gas detection and petroleum exploration","volume":"277","author":"Sampaolo","year":"2020","journal-title":"Fuel"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"1848","DOI":"10.1038\/s41598-018-20087-9","article-title":"Sub-parts-per-trillion level sensitivity in trace gas detection by cantilever-enhanced photo-acoustic spectroscopy","volume":"8","author":"Tomberg","year":"2018","journal-title":"Sci. Rep."},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Christensen, J.B., H\u00f8gstedt, L., Friis, S.M.M., Lai, J.-Y., Chou, M.-H., Balslev-Harder, D., Petersen, J.C., and Lassen, M. (2020). Intrinsic spectral resolution limitations of QEPAS sensors for fast and broad wavelength tuning. Sensors, 20.","DOI":"10.3390\/s20174725"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"4118","DOI":"10.1364\/OL.41.004118","article-title":"Off-axis quartz-enhanced photoacoustic spectroscopy using a pulsed nanosecond mid-infrared optical parametric oscillator","volume":"41","author":"Lassen","year":"2016","journal-title":"Opt. Lett."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"159","DOI":"10.1007\/s00340-019-7260-6","article-title":"Mid-infrared sensing of CO at saturated absorption conditions using intracavity quartz-enhanced photoacoustic spectroscopy","volume":"125","author":"Hayden","year":"2019","journal-title":"Appl. Phys. B"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"011106","DOI":"10.1063\/1.5013612","article-title":"Recent advances in quartz enhanced photoacoustic sensing","volume":"5","author":"Patimisco","year":"2018","journal-title":"Appl. Phys. Rev."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"100479","DOI":"10.1016\/j.pacs.2023.100479","article-title":"Quartz-enhanced photoacoustic spectroscopy (QEPAS) and Beat Frequency-QEPAS techniques for air pollutants detection: A comparison in terms of sensitivity and acquisition time","volume":"31","author":"Li","year":"2023","journal-title":"Photoacoustics"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"415","DOI":"10.1119\/1.2711826","article-title":"Introduction to the quartz tuning fork","volume":"75","author":"Friedt","year":"2007","journal-title":"Am. J. Phys."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"64","DOI":"10.1007\/s00340-020-7409-3","article-title":"Molecular relaxation effects on vibrational water vapor photoacoustic spectroscopy in air","volume":"126","author":"Lang","year":"2020","journal-title":"Appl. Phys. B"},{"key":"ref_33","doi-asserted-by":"crossref","unstructured":"Elefante, A., Menduni, G., Rossmadl, H., Mackowiak, V., Giglio, M., Sampaolo, A., Patimisco, P., Passaro, V., and Spagnolo, V. (2020). Environmental Monitoring of Methane with Quartz-Enhanced Photoacoustic Spectroscopy Exploiting an Electronic Hygrometer to Compensate the H2O Influence on the Sensor Signal. Sensors, 20.","DOI":"10.3390\/s20102935"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"100371","DOI":"10.1016\/j.pacs.2022.100371","article-title":"An algorithmic approach to compute the effect of non-radiative relaxation processes in photoacoustic spectroscopy","volume":"26","author":"Jobst","year":"2022","journal-title":"Photoacoustics"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"301","DOI":"10.1007\/s00340-006-2369-9","article-title":"Influence of molecular relaxation dynamics on quartz-enhanced photoacoustic detection of CO2 at \u03bb= 2 \u03bcm","volume":"85","author":"Wysocki","year":"2006","journal-title":"Appl. Phys. B"},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Yin, X., Dong, L., Zheng, H., Liu, X., Wu, H., Yang, Y., Ma, W., Zhang, L., Yin, W., and Xiao, L. (2016). Impact of humidity on quartz-enhanced photoacoustic spectroscopy based CO detection using a near-IR telecommunication diode laser. Sensors, 16.","DOI":"10.3390\/s16020162"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"109","DOI":"10.1016\/S0169-7439(01)00155-1","article-title":"PLS-regression: A basic tool of chemometrics","volume":"58","author":"Wold","year":"2001","journal-title":"Chemom. Intell. Lab. Syst."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"100349","DOI":"10.1016\/j.pacs.2022.100349","article-title":"High-concentration methane and ethane QEPAS detection employing partial least squares regression to filter out energy relaxation dependence on gas matrix composition","volume":"26","author":"Menduni","year":"2022","journal-title":"Photoacoustics"},{"key":"ref_39","doi-asserted-by":"crossref","unstructured":"Loh, A., and Wolff, M. (2020). Multivariate Analysis of Photoacoustic Spectra for the Detection of Short-Chained Hydrocarbon Isotopologues. Molecules, 25.","DOI":"10.3390\/molecules25092266"},{"key":"ref_40","doi-asserted-by":"crossref","unstructured":"Zifarelli, A., Patimisco, P., Sampaolo, A., Giglio, M., Menduni, G., Elefante, A., Vittorio, V., Tittel K., F., and Spagnolo, V. (2020, January 1\u20136). Partial least squares regression as novel tool for gas mixtures analysis in quartz-enhanced photoacoustic spectroscopy. Proceedings of the SPIE, Quantum Sensing and Nano Electronics and Photonics XVII, San Francisco, CA, USA.","DOI":"10.1117\/12.2545766"},{"key":"ref_41","first-page":"2825","article-title":"Scikit-learn: Machine Learning in Python","volume":"12","author":"Pedregosa","year":"2011","journal-title":"JMLR"},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"5726","DOI":"10.1364\/AO.53.005726","article-title":"Sellmeier and thermo-optic dispersion formulas for the extraordinary ray of 5 mol.% MgO-doped congruent LiNbO3 in the visible, infrared, and terahertz regions","volume":"53","author":"Umemura","year":"2014","journal-title":"Appl. Opt."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"3259","DOI":"10.1016\/j.saa.2003.11.032","article-title":"Ammonia monitoring at trace level using photoacoustic spectroscopy in industrial and environmental applications","volume":"60","author":"Schilt","year":"2004","journal-title":"Spectrochim. Acta Part A Mol. Biomol. Spectrosc."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/23\/18\/7984\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T20:54:15Z","timestamp":1760129655000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/23\/18\/7984"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2023,9,20]]},"references-count":43,"journal-issue":{"issue":"18","published-online":{"date-parts":[[2023,9]]}},"alternative-id":["s23187984"],"URL":"https:\/\/doi.org\/10.3390\/s23187984","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2023,9,20]]}}}