Real time quantitation of a chemical reaction by fiber optic near-infraredspectroscopy

In this paper, a quantitative method for following the progression of an in dustrially significant reaction using chemometrics, fiber-optic near-infrar ed (NIR) spectroscopy, and a single fiber transmission probe is reported. T his method is based on a calibration for the reaction developed by sampling aliquots of a typical reaction for off-line HPLC analysis immediately afte r acquiring a spectrum. A comparison of HPLC peak areas to the spectra was used to develop a calibration for monitoring realtime product formation. A partial least squares (PLS) calibration model was developed from the charac teristic reaction data and was applied to a 30-g-scale reaction. The model successfully predicted the formation of the product. An advantageous featur e of this method is that although the product contained a specific absorban ce in the NIR, by-product generation during the reaction could also be moni tored by NIR. Based on the PLS model generated from both the product and by -product, the product concentration can be predicted directly from the spec tral data with a correlation greater than 0.9, and required only a single P LS factor. (C) 1999 Elsevier Science B.V. All rights reserved.