title: Determination of aspartame and its degradation and epimerization products by capillary electrophoresis.
abstract: 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.
authors.affiliation: Department of Pharmaceutical Chemistry, University of Münster, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Sabah
authors.forename: G K
authors.initials: GK
authors.lastname: Scriba
mesh_terms: D001218:Aspartame / Q000032:analysis* / Q000737:chemistry; D002021:Buffers; D004355:Drug Stability; D019075:Electrophoresis, Capillary; D006863:Hydrogen-Ion Concentration; D010710:Phosphates / Q000737:chemistry; D015203:Reproducibility of Results; D012996:Solutions / Q000032:analysis; D013237:Stereoisomerism; D013549:Sweetening Agents / Q000032:analysis* / Q000737:chemistry
chemical_list: D002021:Buffers; D010710:Phosphates; D012996:Solutions; D013549:Sweetening Agents; D001218:Aspartame