Determination of the end point of a chemical synthesis process using on-line measured mid-infrared spectra

The orthogonal projection approach (OPA), principal component analysis (PCA), and multivariate curve resolution alternating least-squares (MCR-ALS) are applied to detect the end point of an organic synthetic process monitored on-line by mid-infrared spectroscopy. The OPA dissimilarity criterion and the PCA plot are useful to follow the changes in the on-line measured spectra and to detect regions where a steady state of the synthesis is obtained. MCR-ALS is applied to obtain semi-quantitative information during the synthesis by analyzing the steady-state regions simultaneously. The concentrations of the components in the different steady-state regions are calculated with respect to their concentration in a reference steady-state region, chosen from the OPA dissimilarity and PCA plots.