Comparison of solid-state NMR and isothermal microcalorimetry in the assessment of the amorphous component of lactose

The aim of this study was to evaluate the use of solid-state nuclear magnetic resonance (NMR) in the assessment of the degree of disorder of processed lactose. The results obtained from C-13 cross-polarisation/magic angle spinning NMR were compared with those obtained from isothermal heat-conductive microcalorimetry, in which the heat flow during crystallisation of the amorphous lactose in the samples was recorded. A series of lactose mixtures was prepared and studied. In agreement with earlier studies, the microcalorimetric analyses resulted in a linear relationship between heat flow and the nominal crystallinity of the lactose mixtures. Mathematical models established from NMR spectra accurately predicted results even when the lactose mixture contained an additional component, acetylsalicylic acid. The results obtained by microcalorimetry and solid-state NMR were in agreement. Both methods were very sensitive and could detect as low as 0.5% amorphous lactose in a mixture. In addition, solid-state NMR has the advantage of being able to provide structural information about a sample containing several different components. (C) 1998 Published by Elsevier Science B.V. All rights reserved.