Near-infrared chemical imaging slope as a new method to study tablet compaction and tablet relaxation

Near-infrared chemical imaging (NIR-CI) spectra of lactose monohydrate tablets were acquired and the spectral slope from each pixel in the data hypercube was used to assess tablet compaction and relaxation. Tablets were prepared at compaction pressures of 100, 300, and 500 MPa using un-lubricated and magnesium stearate lubricated lactose monohydrate. Results show that NIR slope distribution is a function of applied compaction forces and magnesium stearate lubrication. The distribution of NIR slope values was studied using histograms and statistical parameters. The mean slope value yields a linear calibration curve that predicts tablet compaction pressure as a function of spectral slope. The NIR-CI slope measurements were also used to study tablet relaxation, which occurs as tablets release some of the stored energy from compression. The NIR-CI slope method provides a qualitative description of the relaxation process and provides quantitative information describing relaxation through time.