Stability of aspartame in water: organic solvent mixtures with different dielectric constants.
In order to examine the influence of solvent composition on the stability of aspartame (N-alpha-L-aspartyl-L-phenylalanine-1-methyl ester) in solution (5 mg/mL), the degradation of aspartame was carried out in water:methanol, water:ethanol, and water:glycerine mixtures with dielectric constant values of 45, 55, and 65, respectively. The rate of disappearance of aspartame was measured by a sensitive HPLC assay. The degradation rate of aspartame increased as the dielectric constant of the solvent mixture decreased in all three solvents systems. For example, at 60 degrees C, the degradation rate constants were 4.1, 5.9, and 8.4 x 10(-3) h-1 at dielectric constant of 65, 55, and 45, respectively. From these results, it can be concluded that the stability of aspartame in aqueous solutions cannot be enhanced by the replacement of water by solvents of lower dielectric constant.
Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Canada.
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Sanyude
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Locock
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Pagliaro
D001218:Aspartame / Q000032:analysis / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002851:Chromatography, High Pressure Liquid; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D008293:Malates; D012997:Solvents; D013696:Temperature; D014867:Water
D007202:Indicators and Reagents; D008293:Malates; D012997:Solvents; D014867:Water; C030298:malic acid; D001218:Aspartame