Monitoring powder blending by NIR spectroscopy

A strategy is proposed for the monitoring of powder blending. Samples are taken throughout the blender vessel and scanned by diffuse reflectance spectroscopy in the NIR range. The NIR spectra are first subjected to the Standard Normal Variate transformation (SNV). The first approach consists of overlaying the transformed spectra taken from different locations at each time. To quantify the differences between the spectra, the standard deviation spectrum at each time is calculated and the mean standard deviation value is plotted as a function of time. This plot indicates the time at which the blend is most homogeneous. Each individual spectrum can be compared with the mixture spectrum, which is an approximation of the spectrum of a true homogeneous sample. For that purpose several approaches, i.e. determination of the dissimilarity, Principal Component Analysis, are proposed. As an alternative approach to monitoring the blending the use of SIMPLISMA is recommended.Dedicated to Professor Dr. h.c. mult. J.F.K. Huber on the occasion of his 70th birthday