Capillary Zone Electrophoresis Separation of Amino Acid Enantiomers as Dansylated Derivatives Through Control of Electroosmotic Flow

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D,L-Amino acid enantiomers are separated by capillary zone electrophoresis (CZE) as 5-dimethylamino- 1-naphthalene sulfonyl (dansyl) derivatives using a Cu2+-L-aspartyl-L-phenylalanine methyl ester (aspartame) complex as a chiral selector in the buffer. Only partial enantiomeric resolution is obtained for several dansyl-D,L-amino acids and for the most favorable cases resolution approaches about 1.4. Increasing Mg2+, Cd2+, or Zn2+ concentration in a 10 mM NH4OAc, 2.5 mM Cu2+, 5.0 mM aspartame, pH = 7.40 buffer increases dansyl-D,L-amino acid migration time, increases migration time difference between the D-enantiomer, which appears first in the electropherogram, and the L-enantiomer, and resolves the enantiomers of most dansyl-D,L-amino acids with resolution values in the range of 1.4 to > 5.0 depending on the derivative and buffer conditions. An increase in the buffer divalent cation concentration reduces the electroosmotic flow (EOF) while the electrophoretic mobilities of the dansyl-D,L-amino acid enantiomers do not undergo significant change as the divalent cation concentration increases. The improved resolution between the dansyl-D,L-amino acid enantiomers is due to the reduced EOF and small differences in the ternary complex formed between the dansyl-D,L-amino acid enantiomers and the Cu2+-aspartame complex. †nee, B. Chanthawat.