Mixed Chiral Stationary Phase Research Articles

Novel bovine serum album and β-cyclodextrin-based mixed chiral stationary phase for the enantioseparation in capillary electrochromatography

A capillary was co-immobilized with mixed β-cyclodextrin and bovine serum album by chemical covalent coupling as the chiral stationary phase for the enantioseparation of proton-pump inhibitors in capillary electrochromatography. The chromatographic parameters including buffer concentration, pH value, organic modifier, and applied voltage were optimized. The separation performance of the developed column was evaluated by enantioseparating omeprazole, lansoprazole, pantoprazole, and esomeprazole with extremely high resolutions of 5.21, 7.11, 6.39, and 4.75, respectively. Moreover, the mixed chiral stationary phase exhibited a broader range and could separate more than 10 chiral analytes compared to the single-selector column. The relative standard deviations of the day-to-day and column-to-column repeatability were less than 4%, demonstrating excellent stability of the fabricated column. An open tubular capillary immobilized with the bovine serum album and β-cyclodextrin as the chiral stationary phase is a promising prospect for separating chiral drugs in capillary electrochromatography because of the combination of the enantioselectivities of both individual selectors.

CHIRAL GAS CHROMATOGRAPHY IN THE RESOLUTION OF ENANTIOMERS INVOLVED IN FRUIT FLAVOURS

This work addresses the use of chiral gas chromatography in resolving optically active stereoisomers and racemates found in fruit flavours. It presents the types of chiral selectors applied to terpene-derived metal coordination compounds, polysiloxane-linked α-amino acid and mixed chiral stationary phases, and focuses on derivatized cyclodextrins, the most popular chiral stationary phases presently used in chromatographic analysis. Knowledge about the techniques involved in chiral recognition and enantiomer identification in the fruit flavour field is given along with examples from the latest studies.

(S)‐(–)‐α,α‐Di(2‐naphthyl)‐2‐pyrrolidinemethanol, a useful tool to study the recognition mechanism in chiral ligand‐exchange chromatography

A dynamic coating of the RP-18 carbon chain layers with the new chiral selector (S)-(-)-alpha,alpha-di(2-naphthyl)-2-pyrrolidinemethanol allowed the formation of a mixed chiral stationary phase that has been used in the separation of a selected set of amino acid racemates. Both a representative model and classification structure-property relationship studies have been performed in order to study the contribution of hydrophobic, bulky and electron-donating groups in the side chain of the chiral selector to the mechanism of chiral recognition.

Enantioseparation of Chiral Organochlorines on Permethylated - and -Cyclodextrin, as well as 1:1 Mixtures of Them

Gas chromatography columns coated with 10% permethylated beta- and gamma-cyclodextrin in 85% dimethyl-15% diphenyl polysiloxane (beta- and gamma-PMCD, respectively) and 1:1 mixures are prepared and tested with regard to the enantioseparation of chiral chloropesticides. On the columns with the individual O-methylated cyclodextrins (O-tCDs), the enantiomers of aaeeee-hexachlorocyclohexane (alpha-HCH), e-aeee-1,3,4,5,6-pentachlorocyclohex-1-ene (beta-PCCH), and e-aaee-1,3,4,5,6-pentachlorocyclohex-1-ene (gamma-PCCH), cis- and trans-chlordane, and cis-heptachlor epoxide are separated on both columns, with the exception of the latter being separated only on beta-PMCD. On the column coated with 5% beta- and 5% gamma-PMCD, the resulting separation factor (a) is virtually 1/2 of the arithmetric mean of the elution-dependent separation factors on the individual O-tCDs. In case of reversed elution order on beta- and gamma-PMCD, the enantiomers are not resolved on the mixed columns as is the case with cis-chlordane. Likewise, the lower resolution of the gamma-PCCH enantiomers on the mixed columns prove the reversed elution order on beta- and gamma-PMCD without having enantioenriched standards available. On the column coated with 5% beta- and 5% gamma-PMCD, similar retention times to those observed on both 10% beta-PMCD and 10% gamma-PMCD are obtained. On the column coated with 10% beta- and 10% gamma-PMCD, significantly longer retention times are obtained compared with the columns that contain a total of 10% chiral stationary phase (CSP). This indicates that a relevant part of the interaction of the analytes with the chiral selector is non-enantioselective and, thus, only delays the elution of both enantiomers. Moreover, these non-enantioselective interactions prevent a direct comparison of CSPs with different amounts of the chiral selector. However, this is possible by using mixed phases of two CSPs with similar properties. Using this system, it is demonstrated that for the organochlorine compounds studied, no higher separation factor is observed on the mixed CSPs than on the individual O-tCD with the higher separation factor. Estimations allow a prediction that enantioseparations of organohalogen compounds can be achieved on columns coated with as little as 1% of the CSP.

Mixed chiral stationary phase containing modified resorcinarene and β-cyclodextrin selectors bonded to a polysiloxane for enantioselective gas chromatography

Both a resorcinarene with pendant l-valine diamide groups (used as hydrogen-bonding selector) and a permethylated β-cyclodextrin (used as inclusion-type selector) were chemically bonded to poly(hydromethyl)dimethylsiloxane in a one-pot reaction via Pt-catalyzed alkene hydrosilylation. This novel mixed chiral stationary phase (mixCSP) named Chirasil-Calixval-Dex resembles a combination of the known chiral stationary phases (CSPs) Chirasil-Calixval and Chirasil-Dex and it was used successfully in enantioselective gas chromatography toward a unified enantioselective GC separation system. It is demonstrated that Chirasil-Calixval-Dex retains the individual enantioselectivites of the single components. Thus the enantiomers of apolar hydrocarbons as well as polar amino acid derivatives can be separated with the mixed CSP.

Development of an efficient GLC system with a mixed chiral stationary phase and its application to the separation of optical isomers

AbstractIn order to overcome the limitations of the methodology for the separation of enantiomers in GLC analysis, we successfully developed a novel GLC column named ‘Chiramix’, coated with a mixture of two chiral stationary phases, heptakis‐(2,6‐di‐O‐methyl‐3‐O‐pentyl)‐β‐cyclodextrin (2,6‐Me‐3‐Pe‐β‐CD) and octakis‐(2,6‐di‐O‐methyl‐3‐O‐trifluoroacetyl)‐γ‐cyclodextrin (2,6‐Me‐3‐TFAc‐γ‐CD). It was proved that the ‘Chiramix’ column is greatly superior to those with a single chiral phase for separating enantiomers of compounds with various functional groups. As a successful example, this was applied to the analysis of multicomponent systems, such as peach flavours, and the enantiomeric purities of several components of monoterpene hydrocarbons, alcohols, ketones and lactones were determined exactly and simultaneously. Copyright © 2001 John Wiley & Sons, Ltd.

Gas chromatographic enantiomer separation on single and mixed cyclodextrin derivative chiral stationary phases

Capillary gas chromatographic enantiomer separation of some polar compounds, including α-phenylethylamine, styrene oxide, pyrethroid insecticides and other carboxylates, was investigated on modified cyclodextrin (CD) chiral stationary phases. The chiral stationary phases studied included permethylated β-CD (PMBCD), heptakis (2,6-di-O-butyl-3-O-butyryl)-β-CD (DBBBCD), heptakis (2,6-di-O-nonyl-3-O-trifluoroacetyl)-β-CD (DNTBCD), the mixture of PMBCD and DBBBCD, and the mixture of PMBCD and DNTBCD. On the mixed chiral stationary phases containing the mixtures of derivatized cyclodextrins, enantiomer separation was improved significantly for some compounds as compared to the single cyclodextrin derivative chiral stationary phases, and synergistic effects were observed for some compounds on the mixed cyclodextrin derivative chiral stationary phases.

Evaluation of a chiral stationary phase based on mixed immobilized proteins

The preparation of a new chiral stationary phase (CSP) based on mixed immobilized human serum albumin (HSA) and α 1-acid glycoprotein (AGP) is reported. Enantiomeric separations of basic, acidic and neutral compounds on this AGP-HSA CSP were compared to those obtained on a HSA CSP and on a AGP CSP. The results show that the new CSP has a wider range of applications than the initial CSPs. For two compounds, the enantioselectivity on the mixed CSP was higher than on the HSA CSP.