Melting behaviour of D-sucrose, D-glucose and D-fructose

The melting behaviour of D-sucrose, D-glucose and D-fructose was studied. The melting peaks were determined with DSC and the start of decomposition was studied with TG at different rates of heating. In addition, melting points were determined with a melting point apparatus. The samples were identified as D-sucrose, alpha-D-glucopyranose and beta-D-fructopyranose by powder diffraction measurements. There were differences in melting between the different samples of the same sugar and the rate of heating had a remarkable effect on the melting behaviour. For example, T-o, DeltaH(f) and T-i (initial temperature of decomposition) at a 1degreesC min(-1) rate of heating were 184.5degreesC, 126.6 J g(-1) and 171.3degreesC for D-sucrose, 146.5degreesC, 185.4 J g(-1) and 152.0degreesC for D-glucose and 112.7degreesC, 154.1 J g(-1) and 113.9degreesC for D-fructose. The same parameters at 10degreesC min(-1) rate of heating were 188.9degreesC, 134.4 J g(-1) and 189.2degreesC for D-sucrose, 155.2degreesC, 194.3 J g(-1) and 170.3degreesC for D-glucose and 125.7degreesC, 176.7 J g(-1) and 136.8degreesC D-fructose. At slow rates of heating, there were substantial differences between the different samples of the same sugar. The melting point determination is a sensitive method for the characterization of crystal quality but it cannot be used alone for the identification of sugar samples in all cases. Therefore, the melting point method should be validated for different sugars. (C) 2004 Elsevier Ltd. All rights reserved.