Evidence for multiple retention mechanisms

Synthesis and characterization of beta-cyclodextrin inclusion complex containing di(8-hydroxyquinoline) magnesium

The beta-cyclodextrin (beta-CD) inclusion complex containing di(8-hydroxyquinoline)magnesium was prepared. The product was characterized by NMR, IR, differential thermal thermogravimetric analysis (DT-TGA), spectrofluorimetry, and elemental analysis, indicating the formation of inclusion complex in which the quinoline rings of the guest were encapsulated within the beta-CD cavities. The Job's method provided 2:1 stoichiometry for the inclusion complex between beta-CD and di(8-hydroxyquinoline)magnesium. The association constant calculated with the modified Benesi-Hildebrand equation at 25 degrees C was determined. And the mean association constant was 3577 (L/mol)2, R.S.D. was 2.58%. The thermal stability and solubility of di(8-hydroxyquinoline)magnesium were improved when forming inclusion complex.

Rapid determination of complex mixtures by dual-column gas chromatography with a novel stationary phase combination and spectrometric detection

Fast GC separations of a broad range of analytes are demonstrated using a capillary column coated with a novel immobilized ionic liquid (IIL) stationary phase. Both completely cross-linked and partially cross-linked columns were evaluated, yielding approximately 1600 and approximately 2000 theoretical plates per meter, respectively. Enhanced separation is demonstrated using a dual-column ensemble comprised of an IIL column, a commercially coated Rtx-1 column, and a pneumatic valve connecting the inlet to the junction point between the two columns. Enhanced separation of 20 components, with two sets of co-eluting peaks is shown in approximately 150 s, while sacrificing only a length of time equivalent to the sum of the stop flow pulses, or about 15.5 s. A novel application of a band trajectory model that shows band position as a function of analysis time as analytes move through the column ensemble is employed to determine pulse application times. The model predicts component retention times within a few seconds. Another method of selectivity enhancement of the IIL stationary phase-coated columns is demonstrated using a differential mobility spectrometer (DMS) that provides a second dimension separation based on ion mobility in a high-frequency electrical field. The DMS is able to separate all but one set of co-eluting components from the IIL column. The separation of 13 components found in the headspace above U.S. currency is demonstrated using the IIL column in a dual-column ensemble as well as with the DMS.

Cyclodextrins: a versatile tool in separation science

Cyclodextrins have been used extensively in separation science because they have been shown to discriminate between positional isomers, functional groups, homologues and enantiomers. This property makes them one of the most useful agents for a wide variety of separations. The main goal of this review is a discussion of somewhat more exotic applications of cyclodextrins to separation methods. Techniques examined in detail include gel electrophoresis, isotachophoresis, isoelectric focusing, preparative scale electrophoretic techniques, thin-layer chromatography, electrochemically modulated liquid chromatography, use of monolithic media in liquid chromatography, microdialysis, separation on hollow fibers, foam flotation enrichment, solid- and liquid-phase extractions, countercurrent chromatography, separation through liquid and composite membranes, and cyclodextrin applications in molecularly imprinted polymers. Since a lot of attention has been paid to use of cyclodextrins in capillary electrophoresis, liquid, gas and supercritical fluid chromatography, these techniques will be only briefly discussed. The second goal of this review is a discussion of a scaling-up the analytical separations to semi-preparative or preparative techniques. It was found that despite a need for large scale separations in the industry, development of these techniques has been somewhat lagging behind development of miniaturized analytical separations. It is hoped that the focus on areas outside more traditional separation applications might stimulate further research.