Characterisation of lactose in the liquid and solid state using nuclear magnetic resonance and other methods : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University

Abstract

The anomeric composition of lactose is studied using polarimetry, gas liquid chromatography and a variety of nuclear magnetic resonance (NMR) methods and the results compared. As a result reliable characterisation based on solution methods is obtained. The measurement of the spectrum of nuclear spin-lattice relaxation times (T1) of lactose powders demonstrate significant differences between crystalline and amorphous species and between the different crystalline forms of lactose. These differences form the basis of a new characterisation methodology of powdered lactose ẁhere measurements are performed in the solid state. The use of linear multiexponential curve fitting algorithms (NNLS and Contin) to deduce the "relaxation spectrum" from the multiexponential decay curve (obtained using a low-cost wideline NMR machine) allows for the reliable interpretation of noisy and drift-affected inversion recovery data. The absence of spin-diffusion between crystalline and amorphous species enables the determination of the relative weight fractions of several lactose species in a mixed powder sample with a simple correlation to the relative intensities of relaxation time components of the T1 spectrum. The T1 values of amorphous lactoseareshown to be sensitive to moisture content and the glass transition process. The quantitative results gained from using the T1 method to characterise lactose can be applied to improve the functionality of lactose and lactose-containing powders.