Qualification of Solid Raw Materials Using near Infrared Spectroscopy

Abstract

In order to get a final product which always has the same properties, it is very important to understand and control the manufacturing process but it also implies that the starting materials must be perfect. Perfection does not exist and so it is necessary to determine the purity of the material or to be sure it is always the same from batch to batch. Near infrared (NIR) spectroscopy is known for its good ability to identify compounds as it is mentioned in a lot of publications. For the quantification of solids, the problem becomes harder involving reference techniques which are very often less precise and accurate than NIR measurement. However, in the case of moisture, gravimetric technique is sufficiently precise to get a good calibration. The main advantage of the quantification is the power of the methods to predict the results ‘you want to have’. Its drawback is that when a parameter not included in the calibration set is modified, it may have an impact on the global evaluation. Another approach for raw materials is the qualification combining both the identification technique and send quantitative information. Qualification is based on the construction of clusters in a multidimensional space assuming that we use a number of different batches representative of the whole required variability to be measured. These different approaches will be illustrated with examples of compounds used in the photographic industry.