Analysis of Composition, Molecular Weight, and Water Content Variations in Sodium Alginate Using Solid-State NMR Spectroscopy

Solid-state nuclear magnetic resonance (SSNMR) spectroscopy has become more prevalent in the pharmaceutical industry due to its nondestructive nature and the wealth of information it can provide on a wide variety of solid samples. In this study, SSNMR spectra and relaxation times were used to analyze differences in monomer composition, molecular weight (MW), and water content among various sodium alginate samples. Differences in structure could be determined via spectral deconvolution of SSNMR spectra, and differences in intrinsic viscosity, MW, and water content were found to correlate to SSNMR relaxation times. The technique was found to be selective and sensitive enough to detect these changes in sodium alginate even when diluted with another excipient and compressed into a tablet. (C) 2011 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:3441-3452, 2011