Evaluation of segregation of free falling pharmaceutical powders using near-infrared reflectance spectroscopy-NIRS

Control of powder flow is very important in many industrial processes. Segregation is a problem that arises during powder flows. In the pharmaceutical industry, the variation of drug content in tablets may increase as a consequence of segregation. Intermolecular forces, particle size and different constituents in powdered mixtures may influence segregation, therefore, particle size and chemical constituent analysis are important in segregation studies. Near-Infrared Reflectance Spectroscopy (NIRS) has been applied as a potential online system for the detection of particle size changes and segregation during powder flow. Near-Infrared Reflectance Spectra are characterized by offsets and slopes of baselines. Both offsets and slopes are highly related to the particle size although offsets depend on the number of particles that reflect. The offset and slopes of the spectra provides information on the variation of the particle size and number of particles. In this work, three samples of lactose characterized by particle size by sieving were analyzed by NIRS. Two modes of sampling were utilized: static lactose and dynamic lactose falling through a vertical pipe. Spectra taken by dynamic mode showed a large distribution of offsets, explained by the variation in particle concentration during free fall. NIR spectra after eliminating offsets show two flow regimes during free fall. The first regime shows low apparent absorbance and the second regime shows constant apparent absorbance. Also, the samples with a larger particle size show less variation in variation in particle size. Spectra of mixtures falling freely also show that when lactose has a greater particle size, the segregation in chemical constituents is minimized. The results obtained indicate that after further development, the method developed could be used to monitor powder flows in industrial processes.