Corona Charged Aerosol Detector in studying retention and β-cyclodextrin complex stability using RP-HPLC

Binding between cyclodextrin (CD) cavity and guest molecule in Reversed Phase High-Performance Liquid Chromatography (RP-HPLC) is dynamic process. In general, increasing CD concentration is inducing inclusion complex formation, leading to reduction of analyte's retention time. Consequently, the shortness in retention time is a measure of complex stability in HPLC. However, under certain experimental conditions, the retention of some analytes could be prolonged even when concentration of CD in the mobile phase is increased. In order to reveal the cause of this unexpected retention behavior, the present study was carried on. The model mixture consisted of risperidone, olanzapine and their related impurities, while beta-CD was selected among CDs, as in the previous study. In order to achieve fast equilibrium between free analyte and beta-CD-analyte complex, beta-CD was not added to the mobile phase, but only to the sample. Detection was performed with Corona Charged Aerosol Detector (CAD), suitable for nonchromophoric beta-CD. When analyzing olanzapine impurity B-beta-CD sample, three peaks were detected, namely free beta-CD, beta-CD-analyte complex and free analyte. The complex stability constant was calculated employing a modification of the Benesi-Hildebrandt equation and CAD has proven to be useful in complex stability constants assessment if retention of free analyte and beta-CD-analyte complex is distinguished. For all other analytes only two peaks could be detected, because free analyte and formed complex are eluting at the same retention time. Under such circumstances, the authors proposed the methodology for calculating stability constants and confirmed its applicability to studied model mixture. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

In RP-HPLC, the binding between CD cavity and guest molecule is a dynamic process. The stability of the complex can be measured by the reduction in analyte's retention time. It was found that under certain conditions, the retention time of some analytes may be prolonged.