Β-cyclodextrin Column Research Articles

Enantiomeric Separation of Substituted Quinuclidines and Aza-Norbornanes By HPLC Using an Acetylated β-Cyclodextrin Bonded Stationary Phase

Abstract A method for the HPLC enantiomeric separation of substituted azabicycles (quinuclidines and aza-norbornanes) has been developed, after borane complexation with borane-THF, using an acetylated β-cyclodextrin column. the procedure is relatively simple and has been applied to the determination of the enantiomeric purity of several synthetic compounds of potential pharmaceutical interest.

Effects of mobile phase composition on the reversed-phase separation of dipeptides and tripeptides with cyclodextrin-bonded-phase columns

The effects of mobile phase composition on the reversed-phase separation of several dipeptides and tripeptides with a γ-cyclodextrin-bonded-phase column have been studied. The addition of organic modifier ( i.e. methanol) into the aqueous buffer (pH 4.65) mobile phase causes a minimum capacity factor value to be observed for each peptide. This is interpreted to result from two retention mechanisms involved in the separation. The adsorption process causes the retention time to decrease as the water content in the mobile phase is increased. The inclusion process acts in the opposite fashion. The presence of Cu(II) salt in the mobile phase allows further modifications of separation selectivity. This is because the peptide conformation changes upon Cu(II) complexation which in turn alter the hydrophobicity and/or inclusion stability of the peptide. The effects of mobile phase pH (3.6–5.6) and ionic strength (0.001–0.06) were not significant in the present application. Studies with a β-cyclodextrin column show similar results.

Liquid chromatographic retention behaviour and separation of chlorophenols on a β-cyclodextrin bonded-phase column. Part III. Diaromatic chlorophenols

The liquid chromatographic retention behaviour of 16 diaromatic phenols and chlorophenols (PCB metabolic analogues) on a β-cyclodextrin bonded-phase column was investigated with respect to mobile-phase composition, pH, temperature, and ionic strength. The mechanistic aspects of retention of these compounds on the β-cyclodextrin column were studied and compared to other reversed-phase columns. Comparison is also made to the liquid chromatographic retention behaviour and separation of monoaromatic chlorophenols on the same column. The size, shape, and spatial geometry of each substrate appears to affect retention and selectivity. Most of the evidence suggests that inclusion complex formation, which involves hydrophobic interactions with the interior of the cavity and/or van der Waals interactions of the chlorine substituents with the backbone of the cavity, provides the physical basis for the resolution of these positional isomers. Under certain chromatographic conditions, however, it appears that, for certain congeners, all or part of the molecule is excluded from the cyclodextrin cavity; in such cases a normal-phase or mixed chromatographic mechanism is postulated based on the interaction of the substrates with the secondary hydroxyls on the periphery of the cyclodextrin moieties. The gradient–elution separation of 14 out of 16 of this type of compound on a single chromatogram is also reported and discussed. Keywords: biphenylols, chlorobiphenylols, biphenyldiols, liquid chromatographic retention behaviour, gradient-elution separation, β-cyclodextrin bonded-phase column.

( S)-2-Hydroxyprophyl-β-cyclodextrin, a new chiral stationary phase for reversed-phase liquid chromatography

( S)-2- and ( R,S)-2-hydroxypropyl-β-cyclodextrin have been bonded to silica gel and evaluated as stationary phases for reversed-phase liquid chromatography. Stationary phases also were prepared on two silicas having different pore sizes and surface areas. Dissimilarities were observed in enantiomeric selectivities between these columns and also between these and the native β-cyclodextrin columns. With the exception of compounds 5 and 10, all other racemates reported here which have been successfully resolved on the new phases are enantiomers which have not been previously reported as separated on the β-cyclodextrin stationary phase. In some cases, there also differences in enantioselectivities observed between the ( S)- and the ( R,S)-hydroxypropyl-β-cyclodextrin phases on the same silica. The results are discussed in terms of the retention mechanism and compared to results reported earlier for β-cyclodextrin columns.

Determination of drug enantiomers in biological samples by coupled column liquid chromatography and liquid chromatography-mass spectrometry

Liquid chromatography-mass spectrometry (LC-MS) and coupled column chromatagraphy can be used to overcome problems likely to occur in direct separation and determination of drug enantiomers in biological samples. This is exemplified here with the direct separation and determination of terbutaline in human plasma at the nmol/l level. A β-cyclodextrin column with an aqueous mobile phase was used for chiral separation. For coupled column chromatography, the concentration of each enantiomer was calculated from the enantiomeric area ratio and the racemate concentration. A deuterium-labelled internal standard was used in the LC-MS experiments.

Sample solvent effects in an apparent chiral high-performance liquid chromatographic separation on β-cyclodextrin

The effect of sample solvent on chromatographic peak shape using a β-cyclodextrin column has been investigated. Sample solvents ranging in polarity from hexane to mobile phase (water-methanol-0.5 M pH 4.5 borate buffer, 600:400:1) were used with assessments of column efficiency made by calculating theoretical plates as N 5 σ , N 4 σ and N SYS. Best agreement with observed peak shape resulted from use of N 5 σ especially in the narrow polarity span from 40 to 100% methanol. No chiral separation was obtained on the cyclodextrin column for the aminoalkylindole compounds investigated, although one possessed a naphthaldehyde substituent which should have promoted such separation.

Improvement in the fluorimetric detection of 5-methoxypsoralen by using β-cyclodextrin in the mobile phase and a cross-linked β-cyclodextrin column

In liquid chromatography with a cross-linked β-cyclodextrin column, the addition of 10 −2 M β-cyclodextrin to the methanol/water (25:75) mobile phase produces a 6-fold increase in the fluorescence signal of 5-methoxypsoralen (5-MOP), an important skin photosensitizer. An inclusion compound is formed between 5-MOP and β-cyclodextrin. For 20-μl injections, the limit of detection is 2.25×10 −9 M 5-MOP; calibration plots are linear in the range 10 −3–10 −8 M.

High-performance liquid chromatographic separation of peptide and amino acid stereoisomers

Several high-performance liquid chromatographic (HPLC) methods are described for separation of peptide stereoisomers which are not well resolved by traditional reversed-phase chromatography. These chiral HPLC methods include investigations with a β-cyclodextrin column, a Pirkle d-Phenyl Glycine column and a Chiral-Pak WH column. A method based on derivatization of dipeptides with a chiral reagent, N-acetyl- l-cysteine and o-phthalaldehyde, is also discussed. A series of linear and cyclic dipeptides and modified amino acids were chromatographed on the four systems. Resolution varied for the four different systems depending on the types of compounds that were chromatographed.

High-performance liquid chromatographic determination of mepyramine maleate, pheniramine maleate and phenylpropanolamine hydrochloride in tablets and drops.

HPLC with a chemically bonded β-cyclodextrin (Cyclobond I) column was used for the separation and determination of mepyramine maleate, pheniramine maleate and phenylpropanolamine hydrochloride in dosage forms. The intact compounds were separated and determined in standard mixtures and in selected pharmaceutical dosage forms. All three active ingredients in tablets and oral drops can be separated by HPLC; caffeine in timed-release tablets was determined by spectrophotometry after TLC separation from interfering components.

High Performance Liquid Chromato-Graphy Separations of Nitrosamines. II. Acyclic Nitrosamines

Abstract The separation of acyclic nitrosamines by HPLC using a β-cyclodextrin bonded silien gel column and a C18 reversed phase column was evaluated. Four groups of nitrosamines were used to evaluate the utility of both columns: (1.) methylmethyl-, methylethyl-, methylpropyl and methylbutyl-; (2.) ethylmethyl-, ethylethyl-, and ethylpropyl-; (3.) propylmethyl-, propylpropyl-, and propylbutyl-; and (4.) butylmethyl-, butylethyl-, butylpropyl-, and butylbutyl nitrosamines. The results show that both columns performed well in separating the nitrosamines in each group, with the C18 column requiring a higher percentage of organic modifier (methanol) than the β-cyclodextrin column. The β-cyclodextrin column was superior in separating all the E to Z isomers of short chain alkyl nitrosamines, while the C18 column was superior in separating long alkyl chain nitrosamines and their E and Z isomers. It, was also found that, the longer the alkyl chain the longer the retention time, while nitrosamines having the same number of carbons, for example ethylbutyl-and propylpropyleluted at virtually the same time, using both columns.

Improved Cyclodextrin Chiral Phases: A Comparison and Review

Abstract Cyclodextrin chiral phases have been shown to be widely applicable for the separation of enantiomers, diastereomers, structural isomers and routine compounds. Two innovations have recently occured in this field. First, the efficiency and selectivity of the β-cyclodextrin column has been improved. Second, compatable TLC plates which produce separations analogous to the columns have been developed. These results are discussed subsequent to a brief review of published work. In addition, the mechanism of separation on cyclodextrin bonded media, solvent effects, temperature effects and structural effects on chiral separations are considered.