Sabah S, Scriba G K
Department of Pharmaceutical Chemistry, University of Münster, Germany.
J Pharm Biomed Anal. 1998 Feb;16(6):1089-96. doi: 10.1016/s0731-7085(97)00054-x.
Two capillary zone electrophoretic assays using run buffers of pH 9.35 and pH 2.70 have been developed for the determination of aspartame (alpha-L-Asp-L-PheOMe) and its potential degradation products including Phe, PheOMe, 5-benzyl-3,6-dioxo-2-piperazineacetic acid (DKP), the dipeptides Asp-Phe and Phe-Asp, as well as the isomeric beta-aspartame (beta-L-Asp-L-PheOMe). As an uncharged species at pH 2.7 DKP could not be determined. Between pH 2.0 and 3.5 the resolution of the diastereomers of aspartame and beta-aspartame was investigated. While the resolution of the epimeric beta-isomers exhibited a plateau between pH 2.3 and 2.7, resolution of the aspartame diastereomers peaked at pH 3.0. Using salicylic acid and Phe-Gly as internal standards at pH 9.35 and 2.70, respectively, linear calibration curves were obtained for a concentration range between 5 micrograms ml-1 and 1 mg ml-1. The R.S.D. for intraday and interday analysis ranged from 1.0 to 3.6% and 1.5% to 9.1%, respectively. The capillary electrophoresis assays were applied to analyze aspartame solutions heated to 70 degrees C. In agreement with the literature data aspartame was found to be less stable at pH 7 compared to pH 3. In contrast to aspartame itself, an approximate 20% epimerization of beta-aspartame was observed in the incubation mixtures.
