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

Abstract

A method has been developed for photometric detection of cyclodextrins (CD) in liquid chromatography using iodine (I2) generated electrochemically in-situ. Iodide ion in the mobile phase was electrochemically oxidized to I2 which was subsequently reacted with I-, in an electrochemical flow cell, forming I3-. The absorbance of I3- 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 I3-, because of the inclusion reaction of I3- 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 I3- 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 micromol L(-1) for alpha-CD, 65 micromol L(-1) for monoG1-beta-CD, 100 micromol L(-1) for beta-CD, and 200 micromol L(-1) for gamma-CD.

Host–Guest Inclusion Complexation of α-Cyclodextrin and Triiodide Examined Using UV–Vis Spectrophotometry

“…The host–guest inclusion complexation of α-CD and triiodide, assuming 1:1 stoichiometry ( vide infra , to be confirmed through the analysis), is given by the following reaction and equilibrium expression: This complexation equilibrium is coupled to reaction through the I 3 – guest species. The binding of I 3 – by α-CD (according to reaction ) causes iodine to be converted into triiodide (according to reaction ) and increases the overall concentration of I 3 – in solution (as “free” I 3 – and “complexed” α-CD·I 3 – ). , This is demonstrated by the spectra in Figure where [I – ] 0 = 100 × [I 2 ] 0 . At first glance, the spectrum appears to represent just triiodide (compare Figures and ).…”

“…The binding of I 3 − by α-CD (according to reaction 4) causes iodine to be converted into triiodide (according to reaction 1) and increases the overall concen- ). 15,16 This is demonstrated by the spectra in Figure 2 where [I − ] 0 = 100 × [I 2 ] 0 . At first glance, the spectrum appears to represent just triiodide (compare Figures 1 and 2).…”

Quantitative analysis of natural cyclodextrins by high-performance liquid chromatography with pulsed amperometric detection: Application to cell permeation study

“…In most cases, the separation of natural CDs has been carried out by HPLC with reversed-phase columns [4,[8][9][10][12][13][14][15], while few applications with normal phase [2,25] and anion exchange [11] chromatography have been described. Furthermore, solid-phase extraction [5,8,10], ultrafiltration [9,12] and centrifugation [13,14] have been used as the pretreatment methods of biological samples containing natural CDs.…”

“…With CE-fluorescence methods, linear ranges of 0.21-63 mM ␣-CD, 5.2-1600 M ␤-CD and 18-6100 M ␥-CD have been obtained by using 2,6-ANS as the fluorescent complexing reagent [18] and linear ranges of 0.12-14 mM ␣-CD, 50-1800 M ␤-CD and 15-10,000 M ␥-CD by using 8,1-ANS as the fluorescent complexing reagent [29]. With HPLC-spectroscopic methods, linear ranges of 3-500 M ␣-CD, 100-2500 M ␤-CD and 200-5000 M ␥-CD have been obtained by using electrochemically created iodine as the colorimetric complexing agent [15].…”

“…In contrast to the direct detection methods, the use of photometric or fluorescence-based detection of CDs requires a complexation reaction with a specific UV-vis-absorptive of fluorescent reagent prior to the detection [13][14][15][16][17][18][19][20][21][22][23]. In general, with these indirect methods, sensitivities up to micromolar levels have been obtained.…”