Competitive binding of a Tris run buffer with chiral crown ether in chiral capillary electrophoresis

In capillary electrophoresis of primary amine racemates using (+)‐(18‐crown‐6)‐tetracarboxylic acid (18C6H 4 ) as a chiral selector, chiral recognition emanates from the differences in the complex formation between 18C6H 4 and the two protonated amine enantiomers. The presence of buffer constituents such as tris(hydroxymethyl)aminomethane (Tris) or Na + , capable of forming complexes with 18C6H 4 , is thus detrimental to the chiral separation of primary amines. Such a competitive binding of buffer constituents was studied by comparing the electrophoretic mobilities of racemic analytes obtained in Tris/citric acid and triethylamine/citric acid buffers. We developed a simple fitting method to determine the competitive binding constant and applied it to the Tris buffer system. The competitive binding constant of Tris with 18C6H 4 obtained at pH 3.0 was 27 ± 4.