Application of Hadamard transformation to chiral separation by capillary electrophoresis

Hadamard transform capillary electrophoresis, which is a sensitive detection method using multiple sample injection, was applied to the separation of glutamic acid enantiomers labeled with fluorescein isothiocyanate (FITC). A capillary was filled with a sample solution containing FITC-labeled D,L-glutamic acids, cyclodextrin, and buffer components. The sample was injected by an optically gated sample injection method, in which an intense laser beam was focused onto the capillary to convert fluorescent analyte ions to nonfluorescent ones by photodegradation. To form analyte plug, a shutter placed in the pathway of the laser beam was closed for a constant time period. In the presence of cyclodextrin, enatiomers of FITC-labeled glutamic acid could be injected by the optically gated sample injection method. Two cyclodextrins, β- and γ-cyclodextrins, were employed as chiral selectors in the capillary electrophoretic separations. For the separation of FITC-labeled glutamic acid enantiomers, γ-cyclodextrin shows a better resolution than β-cyclodextrin. The optimum concentration of γ-cyclodextrin was found to be 10 mM. Multiple sample injection was accomplished by closing or opening the shutter according to a sequence based on a Hadamard matrix. When the resulting electropherogram was transformed by the inverse Hadamard matrix, The S/N ratio in the transformed result was enhanced with no degradation in the resolution, compared to that in the electropherogram obtained by a single injection method. As a result, Hadamard transform capillary electrophoresis allows a significant improvement in the S/N ratios for FITC-labeled glutamic acid enantiomers. Therefore, the present method will be applicable to the separation and sensitive detection of enantiomers labeled with FITC.