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The use of vibrational spectroscopy as a tool for in-line process monitoring

Process control is a multidisciplinary field that encompasses a combination of analytical and process chemistry, process engineering and multivariate data analysis. Process analytical techniques (PAT) involve monitoring and control of chemical and physical processes in order to obtain products with desired properties, to improve manufacturing efficiency and reduce process costs. PAT have been utilized in various industrial branches to gain a deeper understanding of particular process stages, identify crucial control parameters, ensure the product quality by optimal design and determine the process disturbances. Conventional monitoring procedures typically involve the analysis of samples taken out of the laboratory reactor and thereby do not provide information in real time. In-line techniques based on vibrational (Infrared and Raman) spectroscopy can provide a direct insight into the mixture composition or the reaction progress at a given time and offer a non-invasive, non-destructive and real-time monitoring of physical and chemical transformations during laboratory and industrial processes. The most frequently applied in-line vibrational spectroscopic techniques are attenuated total reflectance middle infrared spectroscopy (ATR- MIR), near infrared spectroscopy (NIR) and Raman spectroscopy. Such techniques enable in situ real- time monitoring of the production processes by using different types of in-line optical immersion probes which reduce exposure to hazardous materials, sample degradation and contamination or equilibrium perturbations of the investigated system. Owing to these advantages, in-line vibrational spectroscopic techniques have been successfully used for different industrial tasks, especially in pharmaceutical and food industry. The analysis of characteristic in-line infrared and Raman bands facilitates the monitoring of various processes such as crystallization, polymorphic transitions, wet granulation, dissolution, polymer extrusion and chemical reactions. However, the obtained data are usually complex and difficult to interpret. Hence, the in- line spectra are often further processed by employing multivariate data analysis methods, such as principal components analysis (PCA), partial least squares (PLS) and indirect hard modeling (IHM). In this article main applications and future perspectives of in-line vibrational spectroscopic techniques for process monitoring are given.

Process analytical technology, in-line vibrational spectroscopy, process monitoring, multivariate data analysis

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