Why Particle Size Changes NIR Response
NIR measurements depend on the interaction between light and the sample surface or bulk material. Fine particles, coarse particles, and mixed particle sizes scatter light differently, so two samples with the same chemistry may produce different spectral shapes if their physical structure is different.
Smaller particles often increase light scattering and may create stronger or more uniform spectral responses. Coarser or uneven particles can create variable contact with the analyser window, inconsistent reflectance, and less repeatable measurements.
This is especially important for powders, grains, minerals, soils, food ingredients, polymers, and blended materials. Calibration models should include representative particle size variation, or samples should be prepared consistently before measurement. Grinding, mixing, cup presentation, and repeated scans can help improve repeatability where appropriate.
Assessing NIR for Variable Particle Samples
For more detail on the method, review PAS’s overview of Near Infrared Spectroscopy technology. To compare suitable instruments, explore PAS’s NIR analysers through Portable Analytical Solutions, or get in touch to discuss particle size, sample preparation, and measurement requirements.