Variability of Magnesium Stearate
The objective of this study is to investigate the variability in physiochemical and spectral properties of commercially available vegetable grade Magnesium Stearate (MgSt) samples, and to assess the correlation between physiochemical properties and near-infrared (NIR) and Raman spectroscopic features to determine if fast spectral measurements could be used for physical and chemical evaluation. Thirteen MgSt samples of nine manufacturer grades were obtained from three suppliers. The chemical composition was examined using gas chromatography and loss on drying. The physical characteristics were examined on three levels: solid state, particle and bulk level. Comparing the largest to the smallest test values of 13 samples, the variation of the properties ranged from 7 to 335%, with majority of them varying by more than 100% of the smallest value. The samples could be categorized into four groups based on solid state properties: 1) monohydrate, 2) dihydrate, 3) mixture of mono and dihydrate and 4) anhydrous form. SEM images revealed two morphological types: thin, flat and plate-like crystal habit vs. irregular crystal habit. The overall variability was mapped using Principal Component Analysis (PCA). The greatest variation was due to different manufacturers and perhaps manufacturing methods and starting materials. Based on correlations to physiochemical properties of MgSt, NIR and Raman spectra showed potential as a rapid technique for evaluating the differences in excipient properties.