{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T02:52:04Z","timestamp":1760237524495,"version":"build-2065373602"},"reference-count":26,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2020,5,21]],"date-time":"2020-05-21T00:00:00Z","timestamp":1590019200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Infrared attenuated total reflection (ATR) spectroscopy is a common laboratory technique for the analysis of highly absorbing liquids and solids. However, in a process environment, maintaining a sufficient sample exchange and cleaning of the sensitive surface of the element is a crucial issue. An important industrial application is the measurement of isocyanate concentrations. Isocyanates are necessary for the fabrication of polyurethane materials and are among the chemicals with the highest production volume worldwide. For process applications, narrowband photometers or MEMS spectrometers are more appropriate than the use of bulky FTIR instruments frequently encountered in a laboratory environment. Toluene diisocyanate (TDI) and hexamethylene diisocyanate (HDI) concentrations are measured with a planar ATR photometer setup. Using a miniature Fabry\u2013Perot interferometer (FPI), trace concentrations below 100 ppm (m\/m) are detected. By employing an ATR element of the cylindrical shape, sensors can be realized with a smooth surface ideally suited for an automatic cleaning system in a process environment. A laboratory setup with sapphire tubes as ATR elements for incorporation in a liquid flow system is described. Reflection and transmission configurations were investigated. Measurements with acetonitrile as a less toxic substitute showed that with cylindrical ATR sensors\u2019 detection limits for isocyanate concentrations below 100 ppm (m\/m) are feasible.<\/jats:p>","DOI":"10.3390\/s20102917","type":"journal-article","created":{"date-parts":[[2020,5,21]],"date-time":"2020-05-21T11:31:18Z","timestamp":1590060678000},"page":"2917","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Cylindrical IR-ATR Sensors for Process Analytics"],"prefix":"10.3390","volume":"20","author":[{"given":"Armin","family":"Lambrecht","sequence":"first","affiliation":[{"name":"Fraunhofer IPM, Heidenhofstr. 8, D-79110 Freiburg, Germany"}]},{"given":"Carsten","family":"Bolwien","sequence":"additional","affiliation":[{"name":"Fraunhofer IPM, Heidenhofstr. 8, D-79110 Freiburg, Germany"}]},{"given":"Jochen","family":"Erb","sequence":"additional","affiliation":[{"name":"Fraunhofer IPM, Heidenhofstr. 8, D-79110 Freiburg, Germany"}]},{"given":"Hendrik","family":"Fuhr","sequence":"additional","affiliation":[{"name":"Fraunhofer IPM, Heidenhofstr. 8, D-79110 Freiburg, Germany"}]},{"given":"Gerd","family":"Sulz","sequence":"additional","affiliation":[{"name":"Fraunhofer IPM, Heidenhofstr. 8, D-79110 Freiburg, Germany"}]}],"member":"1968","published-online":{"date-parts":[[2020,5,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"851","DOI":"10.1364\/JOSA.55.000851","article-title":"Electric Field Strengths at Totally Reflecting Interfaces","volume":"55","author":"Harrick","year":"1965","journal-title":"J. Opt. Soc. Am."},{"key":"ref_2","unstructured":"Harrick, N.J. (1967). Internal Reflection Spectroscopy, Interscience Publ."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"434","DOI":"10.1366\/0003702011951948","article-title":"Multivariate Calibration for the Determination of Analytes in Urine Using Mid-Infrared Attenuated Total Reflection Spectroscopy","volume":"55","author":"Heise","year":"2001","journal-title":"Appl. Spectrosc."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"729","DOI":"10.1366\/000370206777887071","article-title":"Continuous glucose monitoring by means of fiber-based, mid-infrared laser spectroscopy","volume":"60","author":"Lambrecht","year":"2006","journal-title":"Appl. Spectrosc."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"142","DOI":"10.1007\/s12393-019-09191-2","article-title":"Mid-infrared (MIR) Spectroscopy for Quality Analysis of Liquid Foods","volume":"11","author":"Su","year":"2019","journal-title":"Food Eng. Rev."},{"key":"ref_6","unstructured":"Anton Paar (2020, March 16). Carbo 520 Optical. Available online: https:\/\/www.anton-paar.com\/us-en\/products\/details\/carbo-520-optical\/."},{"key":"ref_7","unstructured":"Centec (2020, March 16). CARBOTEC NIR. Available online: https:\/\/www.centec.de\/sensors\/electronics-semiconductor\/carbotec-nir\/."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1038\/srep02525","article-title":"Determination of Chlorinated Hydrocarbons in Water Using Highly Sensitive Mid-Infrared Sensor Technology","volume":"3","author":"Lu","year":"2013","journal-title":"Sci. Rep."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"2070","DOI":"10.1039\/C3AN01457F","article-title":"Broadband spectroscopy with external cavity quantum cascade lasers beyond conventional absorption measurements","volume":"139","author":"Lambrecht","year":"2014","journal-title":"Analyst"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"5916506","DOI":"10.1155\/2019\/5916506","article-title":"Partial Least Squares (PLS) Integrated Fourier Transform Infrared (FTIR) Approach for Prediction of Moisture in Transformer Oil and Lubricating Oil","volume":"2019","author":"Sim","year":"2019","journal-title":"J. Spectrosc."},{"key":"ref_11","unstructured":"Helmdach, L., Feth, M.P., Minnich, C., and Ulrich, J. (2020, May 20). Application of ATR-MIR Spectroscopy in the Pilot Plant-Scope and Limitations Using the Example of Paracetamol Crystallizations. Available online: http:\/\/www.sciencedirect.com\/science\/article\/pii\/S0255270113000913#."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"648","DOI":"10.1080\/03602551003664909","article-title":"In-Line Monitoring of SBR Emulsion Polymerization Using ATR-FTIR Spectroscopy","volume":"49","author":"Li","year":"2010","journal-title":"Polym. Plast. Technol. Eng."},{"key":"ref_13","unstructured":"Specac Ltd. (2020, March 17). Golden Gate | Versatile ATR Accessory. Available online: https:\/\/www.specac.com\/en\/products\/ftir-acc\/atr\/atr\/golden-gate."},{"key":"ref_14","unstructured":"Hellma GmbH (2020, May 20). DPR 207\/DMD 270 ATR Small Diameter Probe. Available online: https:\/\/www.hellma.com\/en\/process-analytics\/process-probes\/ir-products\/."},{"key":"ref_15","unstructured":"Art Photonics GmbH (2020, March 17). Fiber Optic ATR-Probes. Available online: https:\/\/artphotonics.com\/product\/fiber-optic-atr-probes\/."},{"key":"ref_16","unstructured":"IFS GmbH (2020, March 17). MIR Fiber Probes with Diamond ATR FTIR Technology. Available online: https:\/\/ifs-aachen.de\/."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"627","DOI":"10.1002\/ceat.201500334","article-title":"Mid-Infrared Spectroscopy for Monitoring of Anaerobic Digestion Processes-Prospects and Challenges","volume":"39","author":"Eccleston","year":"2016","journal-title":"Chem. Eng. Technol."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"127847","DOI":"10.1016\/j.snb.2020.127847","article-title":"A pocket-sized 3D-printed attenuated total reflection-infrared filtometer combined with functionalized silica films for nitrate sensing in water","volume":"310","author":"Baumgartner","year":"2020","journal-title":"Sens. Actuators B Chem."},{"key":"ref_19","first-page":"U316","article-title":"Am Slepski. Real-time monitoring of isocyanate chemistry using a fiber-optic FTIR probe","volume":"221","author":"Thomson","year":"2001","journal-title":"Abstr. Pap. Am. Chem. Soc."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"217","DOI":"10.1016\/j.vibspec.2006.07.004","article-title":"In situ monitoring of an isocyanate reaction by fiber-optic FT-IR\/ATR-spectroscopy","volume":"43","author":"Friebe","year":"2007","journal-title":"Vib. Spectrosc."},{"key":"ref_21","unstructured":"The National Institute for Occupational Safety and Health (2020, March 17). Toluene Diisocyanate (TDI) and Toluenediamine (TDA): Evidence of Carcinogenicity: Current Intelligence Bulletin 53. DHHS (NIOSH) Publication Number 90\u2013101, Available online: https:\/\/www.cdc.gov\/niosh\/docs\/90-101\/default.html."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"16","DOI":"10.1515\/teme-2014-0036","article-title":"ATR-Photometer zur Bestimmung der Isocyanatkonzentration in Prozessanwendungen","volume":"82","author":"Theuer","year":"2015","journal-title":"tm-Tech. Mess."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"221","DOI":"10.1109\/PROC.1966.4634","article-title":"Statistics of atomic frequency standards","volume":"54","author":"Allan","year":"1966","journal-title":"Proc. IEEE"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"131","DOI":"10.1007\/BF00425997","article-title":"The limits of signal averaging in atmospheric trace-gas monitoring by tunable diode-laser absorption-spectroscopy (Tdlas)","volume":"57","author":"Werle","year":"1993","journal-title":"Appl. Phys. B-Photophysics Laser Chem."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"065501","DOI":"10.1088\/0957-0233\/26\/6\/065501","article-title":"MIR-ATR sensor for process monitoring","volume":"26","author":"Geoerg","year":"2015","journal-title":"Meas. Sci. Technol."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"39","DOI":"10.1016\/j.jms.2019.01.001","article-title":"Real-time liquid-phase organic reaction monitoring with mid-infrared attenuated total reflectance dual frequency comb spectroscopy","volume":"356","author":"Herman","year":"2019","journal-title":"J. Mol. 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