Trace analysis of γ-cyclodextrin in a sample of β-cyclodextrin by capillary electrophoresis

A new capillary electrophoretic method for trace analysis of γ-cyclodextrin, γ-CD, in a sample of β-CD has been developed, building on our recent work in which the tetraphenylborate ion, Ph4B−, was found to bind to γ-CD three orders of magnitude more strongly than to β-CD. The method involves measurement of the change of net electrophoretic mobility of Ph4B− and its CD complexes in a background electrolyte containing a fixed concentration of β-CD. Good linearity was found between 1/Δμ and 1/Cγ, where Δμ is the difference in the mobility of Ph4B− in the β-CD solution at a given and at zero concentration of γ-CD, and Cγ the γ-CD concentration. The limit of detection for γ-CD in a β-CD sample was found to be 0.020% (w/w), and high precision and accuracy were obtained.