Development of a Total Organic Carbon method for the quantitative determination of solubility enhancement by cyclodextrins: Application to essential oils

Formation of inclusion complexes with cyclodextrins (CDs) is known to enhance guest solubility in aqueous medium. Different techniques allow determining the evolution in solubility of individual guest compounds. However, examination of mixtures solubility encapsulated in CDs is still a challenge. This is mainly related to the difference in the response of mixture components to the applied technique or to the fact that most of the conventional methods examine the signal of an individual constituent of the mixture. Thus, applying current techniques may not reflect the behavior of the whole mixture. Here, we used for the first time Total Organic Carbon (TOC) analysis to explore and assess the efficiency of 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) to enhance the solubility of natural complex mixtures such as essential oils (EOs). Phase solubility studies were performed for eleven EOs with HP-beta-CD. The TOC method has provided good validation parameters for linearity, precision and accuracy. For further validation of the method, phase solubility studies were performed with HP-beta-CD for eugenol, as a model EO component. The eugenol solubility was determined by UV-Visible and TOC analyses in order to compare the results. Data obtained from both methods were similar (p < 0.05), thereby proving the effectiveness of the developed TOC method. Finally, the phase solubility diagrams of EOs showed that the solubilizing potential of CD increased proportionally with the decrease in EO intrinsic solubility. Results proved that TOC could be successfully applied to investigate CD/guest inclusion complexes and is expected to have a broad range of applications in the field of mixtures encapsulation. (C) 2016 Elsevier B.V. All rights reserved.