手性有序无机介孔硅用作气相色谱固定相

手性介孔材料在手性分离、不对称催化、手性传感等领域具有广泛的应用价值。手性有序无机介孔硅是一类介孔结构高度有序、不含有机成分的手性材料。该文采用D-苯丙氨酸为手性源合成手性有序无机介孔硅(COIMS),将其用聚硅氧烷(OV-1701)稀释后用作固定相制备毛细管气相色谱手性柱,并对该手性柱的分离性能进行了考察,8种手性化合物在该手性柱上得到了拆分。COIMS柱对直链烷烃、醇的分离也表现出良好的选择性。该柱还具有分析时间短、在较高温度下测定稳定等优点,其具有开发成高温手性固定相的潜力。     

Permethylated cyclodextrins in the GC separation of racemic mixtures of volatiles: Part 1

The chromatographic separation of racemic mixtures of volatile compounds by 2,3,6-trimethyl-α-, β- and γ-cyclodextrins is discussed. Columns were prepared by mixing the derivatized cyclodextrin with OV-1701 or hydroxy-terminated OV-1701 (OV-1701-OH) following Schurig's method [1]. About 130 racemates with widely differing structures were used to test the performances of 2,3,6-permethylated-α, β- and, γ-cyclodextrins mixed with the polysiloxane polymers in different ratios. The influence of the different types of cyclodextrin on racemate separation is shown, and some phenomena which might be helpful in the elucidation of the chromatographic behavior involved are also described. The influence both of the percentage of cyclodextrin in the polysiloxane, and of the operating conditions (carrier gas, flow rate, and temperature) in the separation of flavor and fragrance racemates is also evaluated.     

Enantiomer separations by capillary GC on modified gyclodextrins

Three new chiral selectors, 6-tert-butyldimethylsilyl-2,3-diethyl-a-cyclodextrin, 6-tert-butyldimethylsilyl-2,3-diethyl- and dipropyl-β-cyclodextrin (TBDE-α-CD, TBDE-β-CD, TBDP-β-CD) were synthesized and tested as chiral stationary phases in capillary gas chromatography. TBDE-β-CD in particular showed a high enan-tioselectivity for test chiral compounds due to good solubility in a polar polysiloxane (OV-1701). Enantioselectivity obtained with TBDE-β-CD was compared with that of 6-tert-butyldimethylsilyl-2,3-di-O-methyl-β-cyclodextrin (TBDM-β-CD). Better enantiose-lectivity was obtained with TBDE-P-CD than with TBDM-β-CD for the test chiral compounds studied. This is probably due to greater effect of the increased hydrophobicity of TBDE-β-CD which favors inclusion of the analytes than the effect of increased steric hindrance. With TBDP-β-CD the less polar lactones are well separated due most likely to increased hydrophobicity of the propyl groups while the more polar are not well resolved. For TBDP-β-CD it is likely that the unfavorable steric hindrance is predominant over the favorable hydrophobicity of the propyl groups, thus hindering the formation of inclusion complexes of the alcohols with TBDP-β-CD. TBDE-α-CD was also a valuable chiral selector for the separation of small chiral molecules such as simple secondary alcohols and nitro-substituted alcohols.     

A β-cyclodextrin covalent organic framework used as a chiral stationary phase for chiral separation in gas chromatography

Chiral covalent organic frameworks(CCOFs) featuring chirality, stability, and good porosity have attracted a considerable amount of attention due to their important applications, such as asymmetric catalysis, chiral separation, and chiral recognition. In this study, a β-cyclodextrin(β-CD) covalent organic framework(β-CD-COF) diluted with polysiloxane OV-1701 was explored as a novel chiral stationary phase(CSP) for gas chromatography(GC) separation of racemates. The β-CD-COF coated capillary colu...     

Cyclodextrin derivatives for the GC separation of racemic mixtures of volatile compounds. Part VI: The influence of the diluting phase on the enantioselectivity of 2,6-Di-O-methyl-3-O-pentyl-β-cyclodextrin

As a continuation of previous studies on the use of cyclodextrin derivatives (CD) for the separation of volatile compounds by capillary GC, the influence of diluting phases other than OV-1701 or OV-1701-OH has been investigated. 2,6-Di-O-methyl-3-O-pentyl-β-cyclodextrin (2,6-DiMe-3-Pe-β-CD) was taken as the reference CD derivative, because of the large number of volatile racemates it is able to separate; OV-1701 or OV-1701-OH was chosen as the reference diluting phase. The performance of a column coated with a 0.15 μm film of 10 % 2,6-DiMe-3-Pe-β-CD in OV-1701 was compared with that of analogous columns coated with films of the same thickness containing the same percentage of the CD derivative diluted with stationary phases of different polarity, i.e. PS-086, PS-347.5, and OV-225. Resolution values and separation factors of thirty racemates were used to evaluate the effect of different diluting phases on column performance.     

Characterization,evaluation and in-situ cross-linking of new polar phases in capillary gas chromatography

Summary The possibilities of OV-1701 and RSL-310, two new stationary phases, have been evaluated for capillary gas chromatography in fused silica columns. OV-1701 is a cyanopropylphenyldimethyl polysiloxane of moderate polarity possessing excellent chromatographic characteristics. The phase exhibits high coating and chromatographic efficiencies, high temperature stability and is suitable for cross-linking. RSL-310 is a polar liquid stationary phase yet to be permanently bonded in a capillary column. The selectivity of both phases extends the applicability of fused silica columns.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Molecular modelling experiments on chiral recognition in GC with specially derivatized cyclodextrins as selectors

The results of gas chromatographic enantiomeric separations of selected non-polar and polar test solutes (limonene and 1-phenylethanol) using two different derivatives of β-cyclodextrin, permethyl-β-CD and 2,3-dimethyl-tert-butyldimethylsilyl-β-CD (PMCD and TBCD) are interpreted in combination with the conclusions from molecular modelling calculations based on docking experiments. A comparison of the two selectors which were used as solution in a polysiloxane matrix (OV 1701) indicated that the less flexible TBCD which is blocked on one side by the bulky tert-butyldimethylsilyl groups seems to possess advantages for certain chiral separations, especially of the non-polar type. The special properties of TBCD as selector are also demonstrated by chiral separations of other compounds.     

Direct enantiomer separation of chiral γ-lactones from food and beverages by multidimensional gas chromatography

Chiral γ-lactones from the raw flavor extract of strawberries and some commercially available fruit-containing food and beverages were stereoanalyzed directly by multidimensional gas chromatography (MDGC) employing heart-cutting techniques from DB-1701 as the preseparation column onto heptakis (3-O-acetyl-2,6-di-O-pentyl)-β-cyclodextrin as the chiral stationary phase.     

Determination of Enantiomer Ratios of Bornane Congeners in Biological Samples Using Heart-Cut Multidimensional Gas Chromatography

The enantiomeric ratios of the chlorinated bornanes, 2-exo, 5,5,9,9,10, 10-heptachlorobornane (B[20030]-(022)), 2-endo,3-exo,5-endo,6-exo,8, 8,10,10-octachlorobornane (B[12012]-(202), Parlar No. 26), 2-exo,3-endo,6-endo,8,9,10,10-heptachlorobornane (B[21001]-(112)), 2,2,5,5,9,9, 10,10-octachlorobornane (B[30030]-(022), Parlar No. 38), 2-endo,3-exo,5-endo6-exo,8,8,9,10,10-nonachlorobornane (B[12012]-(212), Parlar No. 50), and 2,2,5,5,8,9,9,10,10-nonachlorobornane (B[30030]-(122), Parlar No. 62) were determined in a hake liver (Merluccius merluccius) and in two whitebeaked dolphin blubber (Lagenorynchus albirostris) samples. The analysis was performed by heart-cut multidimensional gas chromatography using an electron capture detector (ECD). Ultra 2 (5%-phenyl-95%-methylsilicone) was used as stationary phase in the first column and enantioselectivity was obtained in the second column with a phase consisting of a mixture of OV-1701 and heptakis(2,3,6-O-tert- butyldimethylsilyl)-β-cyclodextrin (10 : 1). All reference standards were also tested on the enantioselective column alone. The comparison of the two systems showed that deviations of ±0.12 from the racemic enantiomer ratio can be observed for the single column due to co-eluting impurities which are present in the reference standards. In most of the heart-cut chromatograms of the biota samples about 15 peaks could be found, showing the importance of a multidimensional separation system for an interference-free quantification by ECD. In all biological samples a significant deviation from the racemic enantiomer ratio was found for B[30030]-(022) (Parlar No. 38) and for B[30030]-(122) (Parlar No. 62). This indicates that an enantioselective disposition of the congeners occurs. In addition, considerations are presented concerning the relationship between congener structure and enantiomeric disposition.     

A chiral porous organic cage for molecular recognition using gas chromatography

Molecular organic cages as shape-persistent organic molecules with permanent and accessible cavities have attracted a lot of interest because of their importance as host-guest systems. Herein, we report a chiral porous organic cage (POC) CC9 diluted with a polysiloxane OV-1701 to fabricate a CC9-coated capillary column, which was used for the high-resolution gas chromatographic separation of organic compounds, including positional isomers and racemates. On the CC9-coated capillary column, a large number of racemic compounds such as chiral alcohols, esters, ethers and epoxides can be resolved without derivatization. By comparing the chiral recognition ability of the CC9-coated column with the commercially available β-DEX 120 column and the POC CC3-R coated column recently reported by our group, the CC9-coated column offered good resolution during the separation of some racemates, that were not separated using the β-DEX 120 column or POC CC3-R coated column. Therefore, the CC9-coated column can be complementary to the β-DEX 120 column and CC3-R coated column. The results indicated that the CC9-coated column exhibited great potential for application in the separation of positional isomers and enantiomers with great selectivity, high resolution and good reproducibility.     

Extending the scope of enantiomer separation on diluted methylated β-cyclodextrin derivatives by high-resolution gas chromatography

High-resolution open-tubular columns coated with solutions of heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (Phase I) or heptakis(2,6-di-O-methyl-3-O-trifluoroacetyl)-β-cyclodextrin (Phase II) in moderately polar polysiloxanes such as OV-1701 (5% cyanopropyl/7% phenyl/88% methylpolysiloxane) and OV-225 (25% cyanopropyl/50% phenyl/25% methylpolysiloxane) are used for the gas chromatographic enantiomer separation of volatiles belonging to different classes of compounds. No derivatization procedures are necessary for most of the resolved chiral molecules. The chiral stationary phases can be operated between 25 and 190°C for extended periods of time. The enantiomer separation of saturated, unfunctionalized hydrocarbons clearly demonstrates the importance of molecular inclusion in chiral recognition using cyclodextrins for this class of compounds. The different, and in some cases complementary, selectivity of the Phases I and II is demonstrated.     

Thermal Decomposition of Toxaphene Congeners by High Resolution Gas Chromatographic Phases

Some toxaphene congeners are thermally unstable under commonly used gas chromatographic temperature conditions. The thermal stability of the 22 commercially available congeners has been studied at four different heating rates on four stationary phases Ultra 2 (5%-diphenyl-95%-dimethylpolysiloxane), a liquid crystalline phase (N,N′-bis(p-butoxy-benzylidene)-α,α′-bis-p-toluidine), Rtx-2330 (90%-biscyanopropyl-10%-phenylcyanopropyl-polysiloxane), and heptakis-(2,3,6-O-t-butyldimethylsilyl)-β-cyclodextrin (TBDMS-CD) diluted in OV-1701-OH. A substantial degradation of the congeners Parlar 39, 42, 50, 56, 58, and 62 could be observed on the cyanopropyl polysiloxane stationary phase. Furthermore, the applied temperature program and stationary phase had an influence on the signal areas. These factors are important for a quantitative analysis.     

Cyclodextrin derivatives in the GC separation of racemic mixtures of volatile compounds,part V: Heptakis 2,6-dimethyl-3-pentyl-β-cyclodextrins

This paper describes an evaluation of the chromatographic performance of columns coated with amorphous cyclodextrin (CD) derivatives, in particular 2,3,6-tripentyl-β-CD (2,3,6-TriPe-β-CD), 2,6-dipentyl-3-methyl-β-CD (2,6-DiPe-3-Me-β-CD), and 2,6-dimethyl-3-pentyl-β-CD (2,6-DiMe-3-Pe-β-CD), all diluted in polysiloxane (OV-1701 or OV-1701-OH), for the separation of the enantiomers of volatile compounds. 2,6-DiMe-3-Pe-β-CD in OV-1701 offers performance comparable with (or better than) that of the other two CDs, and without their drawbacks (inconsistency of results, as described previously). This article compares the separating ability of 2,6-DiMe-3-Pe-β-CD and 2,3,6-TriMe-β-CD, and describes the influence of the CD derivative to polysiloxane ratio, the minimum operating temperatures of the columns, and the reproducibility and consistency of performance of columns coated with the former CD derivative diluted in polysiloxane.     

Synthesis of siloxane stationary phases for capillary gas chromatography and supercritical fluid chromatography

A comparison is made between dichlorosilanes and cyclic siloxanes as starting materials in the synthesis of stationary phases for capillary gas chromatography (CGC) and supercritical fluid chromatography (SFC). Siloxanes containing one or more of the side groups methyl, vinyl, phenyl, and cyanoethyl in various ratios were synthesized and compared. These phases were characterized by chromatographic (gel permeation, GPC), spectroscopic (IR, ¹H NMR, ²⁹Si NMR), and thermal (DSC) methods. Coated fused silica columns were evaluated with respect to polarity, crosslinkability with several free-radical initiators, and thermal stability. A new liquid phase, 7% cyanoethyl, 7% phenyl, 1% vinyl methyl polysiloxane is shown to be more polar than OV-1701, more temperature stable, easily crosslinked and suitable for use in supercritical fluid chromatography.     

Optimization of the surface modification process of cross‐linked polythiol‐coated chiral stationary phases synthesized by a two‐step thiol‐ene click reaction

A new platform technology for the preparation of stable chiral stationary phases was successfully optimized. The chiral selector tert‐butylcarbamoylquinine was firstly covalently connected to the polymer poly(3‐mercaptopropyl)methylsiloxane by thiol‐ene click reaction. Secondly, the quinine carbamate functionalized polysiloxane conjugate was coated onto the surface of vinyl modified silica particles and cross‐linked via thiol‐ene click reaction. The amount of polysiloxane, chiral selector, radical initiator, reaction solvent (chloroform and methanol), reaction time, and pore size of the supporting silica particles were varied and systematically optimized in terms of achievable plate numbers while maintaining simultaneously enantioselectivity. The optimization was based on elemental analysis data, chromatographic results, and H/u‐curves (Van Deemter) of the resultant chiral stationary phases. The results suggest that better chromatographic efficiency (higher plate numbers) at equal enantioselectivity can be achieved with methanol (a poor solvent for the polysiloxane that is dispersed rather than dissolved) and a lower film thickness of quinine carbamate functionalized polysiloxane. In this study, chiral stationary phases based on 100 Å silica slightly outperformed 200 Å silica particles (each 5 μm). The optimized two step material exhibited significantly reduced mass transfer resistance compared to the one step material and equal performance as a brush‐type chiral stationary phase.     

Gas chromatographic – mass spectrometric analysis of compounds generated upon thermal degradation of some stationary phases in gas chromatography – Part II

The applicability of capillary columns for gas chromatography is often limited by stationary phase degradation at elevated temperatures. In order to achieve a better understanding of column thermostability, column bleed products have been analyzed qualitatively by gas chromatography-mass spectrometry (GC-MS). Three silicone stationary phases were studied: SE-52, SE-54, and OV-1701. Each of these was immobilized in the columns. The proportion of cyclics containing diphenyl in column bleed from SE-52 reflected to a large extent the composition of the polymer, while for SE-54 the proportion of such cyclics was unexpectedly high. The polar moiety of OV-1701, the cyanopropyl(phenyl)siloxy unit, was found to exert a highly destabilizing effect on the polymer, and the thermal degradation products consisted mainly of cyclosiloxanes containing this unit.     

Gas Chromatographic Enantiomer Separation of Atropisomeric PCBs Using Modified Cyclodextrins as Chiral Phases

Columns containing different types of cyclodextrin derivatives have been evaluated for chiral gas chromatographic separation of atropisomeric PCBs, o,p´‐DDT and o,p´‐DDD. Separation was attempted on columns containing mixed chiral selectors, and the performance of two closely related selectors was also examined. The cyclodextrins were: permethylated‐β‐CD (PM‐β‐CD), heptakis(2,3‐di‐O‐methyl‐6‐O‐tert‐butyldimethylsilyl)‐β‐CD (2,3‐M‐6‐TBDMS‐β‐CD), heptakis(2,3‐di‐O‐methyl‐6‐O‐tert‐hexyldimethylsilyl)‐β‐CD (2,3‐M‐6‐THDMS‐β‐CD), and heptakis(2,3‐di‐O‐ethyl‐6‐O‐tert‐hexyldimethylsilyl)‐β‐cyclodextrin (2,3‐E‐6‐THDMS‐β‐CD). The cyclodextrins were dissolved in OV‐1701 or in a dimethylsiloxane/silarylene copolymer containing 5% phenyl in the backbone. The application of mixed chiral selectors led to improved separations, however; at most eleven PCB congeners were separated on a single column. Chiral resolution of o,p´‐DDD was achieved. The use of a dimethylsiloxane/silarylene copolymer as a matrix for the cyclodextrins is a promising approach. With such a matrix, blocking of the CD cavities by silicone substituent groups can be avoided, and a reasonable CD solubility can be provided. The selectivity of heptakis(2,3‐di‐O‐ethyl‐6‐O‐tert‐hexyldimethylsilyl)‐β‐CD and heptakis(2,3‐di‐O‐methyl‐6‐O‐tert‐hexyldimethylsilyl)‐β‐CD was quite different, the former selector could separate four congeners, while the latter separated ten congeners.     

6-tert-Butyldimethylsilyl-2,3-dimethyl-α-, β-, and γ-cyclodextrins,dissolved in polysiloxanes,as chiral selectors for gas chromatography. Influence of selector concentration and polysiloxane matrix polarity on enantioselectivity

The enantioselectivity of three chiral selectors, 6-t-butyldimethyl-silyl-2,3-dimethyl-α-, β- and γ-cyclodextrin (TB-α-CD, TB-β-CD, TB-γ-CD), are compared and discussed for a range of chiral test compounds. TB-β-CD in particular offers high enantioselectivity for a variety of chiral compounds and has the special property of excellent solubility in different alkylpolysiloxanes, including the weakly polar variety, because of its weak self-association. To investigate the influence of the polarity of polysiloxane matrices this selector can be used at a wide range of concentrations in the most suitable polysiloxane matrices and at low separation temperatures without impairment of resolution by peak broadening and symmetry distortion.     

Investigation on chiral capillary columns and their application in separation of enantiomers

Six chiral diamide stationary phases (CSPs), namely N-(3-carbobenzoxypropionyl)-L-Val-tert-butylamide (CSP-1), N-undecenoyl-L-Val-S-α-phenylethylamide (CSP-2), N-undecenoyl-L-Val-R-α-phenylethylamide (CSP-3), OV-225-L-Val-tert-butylamide (CSP-4), XE-60-L-Val-tert-butylamide (CSP-5) and polycyanoethyl vinyl siloxane-L-Val-tert-butylamide (CSP-6), were inves-tigated and CSP-6 was crosslinked within narrow bore (70 μm) fused silica capillary columns. Theseparation of amino acid enantiomers on this narrow bore column by gas chromatography (GC) isillustrated.     

手性离子液体和纤维素三(3,5-二甲基苯基氨基甲酸酯)混合气相色谱手性固定相研究

合成了手性离子液体[C7H17NO] [(CF3SO2)2]-和纤维素三(3,5-二甲基苯基氨基甲酸酯),将其混合作为气相色谱固定相。研究结果表明:该混合固定相麦氏常数的平均极性值为760;在容量因子大于2的前提下,新型柱的塔板数可达1680块/m;其对手性化合物、特别是对氨基酸类具有良好的分离效果。有10对氨基酸的分离因子大于1.10,展示了该类色谱柱良好的手性应用前景。