In-line moisture measurement during granulation with a four-wavelength near infrared sensor: An evaluation of particle size and binder effects

Factors affecting in-line near infrared (NIR) moisture measurement with a four-wavelength sensor were evaluated (choice of binder used in granulation liquid and the increase in particle size). An entire NIR spectrum is not necessary for the measurement of water, and often the use of only a few NIR wavelengths around the water band enables reliable and high-speed detection of moisture. Glass ballotini and microcrystalline cellulose (MCC) were used as model test materials. The binders studied were poly[1-(2-oxo-1-pyrrolidinyl)ethylene] (PVP) and gelatin. Full off-line NIR spectra of test materials at different levels of binder solutions were measured. The major spectral features for both the binders were bands around 1700 nm (first overtones CH related stretches) and 2200 nm (combination bands). Gelatin also had an NH band around 1500 nm (first overtones of NH stretches) and combination bands at about 2050 nm. Particle size effects were observed as an increase in spectra baseline. All these factors should be considered when choosing NIR wavelengths used for detection of water with a fixed wavelength set-up. A robust calibration model enables the development of in-process control of wet granulation processes.