The novel combination of dynamic vapour sorption gravimetric analysis and near infra-red spectroscopy as a hyphenated technique

The novel combination of an environmental controlled gas flow microbalance (Dynamic Vapour Sorption, Surface Measurement Systems, UK) with a NIR spectrometer (Foss NIR Systems) is described. The study follows the gravimetric changes and the spectroscopic changes in the amorphous and crystalline states of lactose at 298 K. NIR spectra and gravimetric water sorption were recorded simultaneously for the same sample. Differentiation of the amorphous and crystalline states of lactose was possible from the evaluation of peak intensity and shifts in the known fingerprint regions of the NIR spectra, i.e. 1350-1510 and 1825-1975 nm which correspond to water changes, and 2075-2160 nm which tends to illustrate changes in the organic/structural backbone character. Gravimetric analysis confirmed that the amorphous lactose crystallised, as weight changes can be linked to structural changes. The combined technique maintains the high performance of the DVS microbalance for gravimetric analysis but also provides a preset, regulated and controllable environment for studies using NIR spectroscopy probes, which was previously not possible. The results obtained agree with accepted data, and therefore provide validation for the hyphenation technique. The use of the combined DVS-NIR instrument has indicated two new pieces of information, firstly the amorphous form loses some water before the crystallisation is detectable. This indicates that water desorption may precede crystallisation, rather than the other way around, and secondly, the sample has completed crystallisation before water desorption has ended. (C) 2000 Elsevier Science B.V. All rights reserved.