A Modified Method Using Static Head-Space Gas Chromatography for Determining the Stability Constants of 1-Alkanol/.ALPHA.-Cyclodextrin Complexation

Abstract

The stability constant is of fundamental importance in understanding interactions in guest/cyclodextrin (CD) systems. The stability constant has been determined using spectroscopic methods such as absorption spectroscopy and fluorescence spectroscopy.1) It is difficult, however, to determine directly the stability constant by these spectroscopic methods if the guest has no chromophoric groups. Alkanols other than aromatic alkanol are the best known example of such a case. We previously proposed new methods using static headspace gas chromatography (SHSGC) for determining the stability constant of the CD complex, called the "direct SHSGC method, 2) " the "indirect (competitive) SHSGC method, 3) " the "solubility SHSGC method, 4) " and the "simultaneous SHSGC method. 5,6) " These methods have been successfully applied to the determination of the stability constants for the CD complexes including the alkanol/a-CD system. However, the conventional SHSGC methods require the calibration curve to evaluate the concentration of free guest in the presence of CD. In this study, the use of Henry's law constant of guest instead of using the calibration curve was adopted for evaluating the concentration of free guest. This must bring the shortening of experimental time required for the determination of the stability constant.Herein, we report a modification of the direct SHSGC method (modified SHSGC method) for determination of the stability constants of 1-alkanol/a-CD inclusion complexes. ExperimentalMaterials The a-CD used for the host was from Nihon Shokuhin Kako Co., Ltd. (Tokyo, Japan) and was used after drying in a vacuum. 1-Alkanols used for the guest of reagent grade were purchased from Tokyo Kasei Kogyo Co., Ltd. and used without further purification. Water for injection (Japanese Phamacopoeia) was obtained from Ohtsuka Pharmacy Co., Ltd. (Tokyo).Procedures The SHSGC technique used was the same as described previously.2) Briefly, sample solutions (15 ml) containing various concentrations of a-CD and a fixed concentration of 1-alkanol in water were pipetted into 32.6 ml head-space vials, and sealed using silicone septa and aluminum foils. The vials were then thermostated at 25Ϯ0.1°C and shaken for 24 h prior to analysis. This time period was found to be sufficient for attaining equilibrium. After equilibrium was established, 1-alkanol vapor from above the solution was drawn out from the vial using a gas-tight syringe. This sample was then analyzed by gas chromatography (GC, Shimadzu Co., GC-

Characterization of Cyclodextrin/Volatile Inclusion Complexes: A Review

“… CD: cyclodextrin; CRYSMEB: low methylated-β-cyclodextrin; RAMEB: randomly methylated-β-cyclodextrin; HP-β-CD: 2-hydroxypropyl-β-cyclodextrin; SBE-β-CD: sulfobutylether-β-cyclodextrin. a [ 2 ], b [ 45 ], c [ 53 ], d [ 51 ], e [ 54 ], f [ 55 ], g [ 43 ], h [ 49 ], i [ 56 ], j [ 57 ], k [ 44 ], l [ 58 ], m [ 47 ], n [ 50 ], o [ 17 ], p [ 52 ], q [ 49 ], r [ 59 ], s [ 60 ]. …”

Solubilisation of chlorinated solvents by cyclodextrin derivativesA study by static headspace gas chromatography and molecular modelling

“…There are few references in literature in which HSGC is used for determining stability constants of different compounds with CDs [28][29][30][31][32][33] and especially for VOCs [15][16][17]. The stability constants for the inclusion of VOCs with ␣-CD, ␤-CD, HPBCD, CRYSMEB and RAMEB in aqueous solution were determined at 30 • C.…”

Gas–liquid partitioning of halogenated volatile organic compounds in aqueous cyclodextrin solutions

“…Published studies on VOC-CD binding employed various gas chromatographic (vapor + liquid) equilibrium measurement techniques as headspace gas chromatography (HSGC) [3][4][5][6], phase ratio variation (PRV) [7], equilibrium partitioning in closed system (EPICS) [8], and inert gas stripping (IGS) [9]. These studies further differ in the strategy through which the extent of binding as a function of the reactants' concentrations is examined as well as in the fact whether the explicit calibration of gas chromatographic response is needed.…”

“…These studies further differ in the strategy through which the extent of binding as a function of the reactants' concentrations is examined as well as in the fact whether the explicit calibration of gas chromatographic response is needed. The studies have dealt with a number of VOCs, involving alkan-1-ols [4,5], alkanes [6], cycloalkanes [6], alkylbenzenes [3,6,9], and some sulfur or chlorine derivatives [8,10].…”