Photometric detection of cyclodextrins in liquid chromatography by using iodine generated electrochemically in-situ

A method has been developed for photometric detection of cyclodextrins (CD) in liquid chromatography using iodine (I-2) generated electrochemically in-situ. Iodide ion in the mobile phase was electrochemically oxidized to I-2 which was subsequently reacted with I-, in an electrochemical flow cell, forming I-3 . The absorbance of I-3 was found to be greatly enhanced when CD were present in the mobile phase. The absorbance enhancement was caused by the change in the mole fraction of I-3, because of the inclusion reaction of I-3 with CD. On the basis of this phenomenon, CD were detected by means of a photodiode-array UV-visible detector positioned downstream of the electrochemical flow cell. The signals were found to be linearly dependent on CD concentration. Because the formation constants of I-3 with CD decrease in the order alpha-CD >beta-CD >gamma-CD, alpha-CD was most detectable by the method. Detection limits were 1.0 mu mol L-1 for alpha- CD, 65 mu mol L-1 for monoG1-beta-CD, 100 mu mol L-1 for beta- CD, and 200 mu mol L-1 stop for gamma-CD.