Sequential Injection/Mid-Infrared Spectroscopic Analysis of an Acetone- Butanol-Ethanol Fermentation: Analyte Cross-Correlation Effects Mustafa Kansiz Institute of Analytical Chemistry, Vienna University of Technology, Vienna, Austria and School of Chemistry, Centre for Green Chemistry, Monash University, Melbourne, Victoria, Australia K. Christian Schuster Institute of Analytical Chemistry, Vienna University of Technology, Vienna, Austria Don McNaughton School of Chemistry, Centre for Green Chemistry, Monash University, Melbourne, Victoria, Australia Bernhard Lendl Institute of Analytical Chemistry, Vienna University of Technology, Vienna, Austria Abstract: Mid-infrared spectroscopy together with sequential injection analysis (SIA) and partial least squares (PLS) regression analysis was used to monitor acetone- butanol-ethanol (ABE) fermentations under different fermentation conditions. Five analytes were simultaneously predicted (acetone, acetate, butyrate, n-butanol, and glucose). In order to compare the overall model prediction ability, a relative average Received 4 September 2004, Accepted 28 July 2005 This paper was by special invitation as a contribution to a special issue of the journal entitled “Quantitative Vibrational Spectrometry in the 21st Century.” This special issue was organized by Professor Miguel de la Guardia, Professor of Analytical Chemistry at Valencia University, Spain. Address correspondence to B. Lendl, Institute of Analytical Chemistry, Vienna University of Technology, Getreidemarkt 9/151, Vienna A-1060, Austria. E-mail: blendl@mail.zserv.tuwien.ac.at Spectroscopy Letters, 38: 677–702, 2005 Copyright # Taylor & Francis, Inc. ISSN 0038-7010 print/1532-2289 online DOI: 10.1080/00387010500315801 677