An amylopectin tris(phenylcarbamate) chiral stationary phase for high performance liquid chromatography

Amylopectin tris(phenylcarbamate) has been evaluated as a chiral stationary phase for HPLC; the influence on its cptical resolving capabilities of mobile phase composition and nature of the alcohol used as modifier has been studied. Separation and resolution of twelve arylalcohol racemates were examined. In most instances, the stationary phase exhibited high optical resolving capacity.     

Column packing for gas chromatography containing immobilized poly(ethylene glycol) stationary phase

Summary Carbowax 20M poly(ethylene glycol) stationary phase was immobilized on Chromosorb W by cross-linking with pluriisocyanate. The properties of the prepared packing material were investigated. Column efficiencies of 10,960 and 7,510 theoretical plates/meter were obtained for n-pentadecane and 1-heptanol, respectively.     

Separation mechanism of chiral compounds in chiral stationary phase liquid chromatography

In this paper, the concept of reversed- or normal-phase chiral stationary phase liquid chromatography has been put forward according to the polar strength of mobile and stationary phases. The statistical model developed in HPLC has been used to investigate the separation mechanism of D- and L-enantiomer in chiral stationary phase liquid chromatography. It has been observed that the variation of capacity factor of enantiomers with mobile phase composition in both reversed-phase and normal-phase chiral stationary phase liquid chromatography can be described by the fundamental elution equation lnk' = a + blnC_b + _cC_b. The effect of mobile phase composition on the selectivity of enantiomers D and L in normal-phase chiral stationary phase liquid chromatography can be described by the equation lnα = Δa + ΔblnC_b, but in reversed-phase chiral stationary phase liquid chromatography the selectivity is almost independant of the mobile phase composition.     

Chromatographic evaluation of poly (trans-1,2-cyclohexanediyl-bis acrylamide) as a chiral stationary phase for HPLC

Chiral stationary phases (CSPs) based on polymeric (R,R)- or (S,S)-1,2-diaminocyclohexane (DACH) derivatives are synthesized. When bonded to 5 microm porous spherical silica gel, the poly (trans-1,2-cyclohexanediyl-bis acrylamide) based poly-cyclic amine polymer (P-CAP) stationary phases is proved to be effective chiral stationary phases that could be used in the normal-phase mode, polar organic mode and with halogenated solvents mobile phases, if desired. Since these are entirely synthetic CSPs, the elution order of all enantiomers can be reversed between the (R,R) P-CAP and (S,S) P-CAP columns. Because of the high loading of chiral selectors, the columns exhibit very high sample capacities. Thus, P-CAP columns are useful for preparative and semi-preparative enantiomeric separations. The application of these CSPs and optimization of their separations are discussed.     

A crosslinked chiral stationary phase for the separation of enantiomers by gas and supercritical fluid chromatography

Crosslinking experiments for the chiral stationary phase OV-225-L-Val-t-butylamide within both fused silica and glass capillary columns have been carried out. Amino acid enantiomers were separated on crosslinked columns by both GC and SFC methods. In SFC, the a values of amino acid enantiomers are independent of the density of the mobile phase, and they are hig her than those obtained by GC for the tested enantiomers with the same column due to the lower column temperature used in SFC.     

Cyclodextrin carbamates as novel chiral stationary phases for capillary gas chromatography

The following carbamate derivatives of cyclodextrins (CDs) were prepared as novel chiral stationary phases for capillary gas chromatography: hexakis(2,6-di-O-pentyl)-α-cyclodextrin hexa(3-n-propyl, 3-isopropyl, and 3-phenylcarbamate), heptakis-(2,6-di-O-pentyl)-β-cyclodextrin hepta(3-n-propyl, 3-isopropyl, and 3-phenylcarbamate), and octakis(2,6-di-O-pentyl)-γ-cyclodextrin octa(3-n-propyl, 3-isopropyl, and 3-isopropyl, and 3-phenylcarbamate). Metal capillary columns coated with these stationary phases resolved many kinds of racemic mixture. In general, they were especially effective towards polar compounds such as free alcohols, amines, and epoxides. The types of sample which were effectively resolved depended on the cavity size of the CD: α-CD derivatives were specifically effective toward compounds having linear alkyl chains, and β-CD derivatives toward compounds with phenyl groups. The results indicate that chiral separation with the cyclodextrin carbamates depends on the formation of inclusion complexes and also on the hydrogen-bonding interactions between the samples and the CD carbamates.     

A chiral stationary phase with special hydrophobic framework for ligand-exchange chromatography

A novel chiral stationary phase (CSP1) for ligand-exchange chromatography (CLEC) was prepared by firstly using dimethyl- chlorosilane as an endcapping reagent for decreasing residual silanol group on the surface of silica gel,and then introducing L-Pro as a chiral selector and hydrophobic octyl group to the silica gel surface simultaneously.The enantioseparations of 14 DL-amino acids on CSP1 were achieved with the enantioselectivityαranging from 1.09 to 2.44 and the resolution Rs being between 0.8 and 6.3.The chromatographic performances of CSP1 with the bonded phase (CSP2) prepared using reference method were compared.The results showed that the column efficiency and resolution Rs of chiral stationary phase could be improved by using the above modifying method.     

Synthesis of a chiral macrocyclic dibenzodicyclohexanotetraamide-containing stationary phase for liquid chromatography

Allyloxy-substituted macrocyclic dibenzodicyclohexanotetraamide 2 was prepared by the following sequence. MonoBoc-protected chiral 1,2-cyclohexanediamine ( 3 ) was treated with isophthaloyl chloride followed by removal of the Boc group to form bisisophthalamide 5. Compound 5 was then treated with allyloxyphthaloyl chloride to form the macrocyclic tetraamide 2 in a 56% yield. Chiral selector 2 was converted to its ethoxydimethylsilane derivative and heated in a suspension of silica gel and toluene to form the chiral macrocycle-containing silica gel phase 1. This phase separated the enantiomers of (±)-α-methylbenzylamine and (±)-DL-α-aminobutyric acid methyl ester in a liquid chromatograph.     

Enantiomeric separation of alcohols and amines on a proline chiral stationary phase by gas chromatography

A new chiral stationary phase for gas chromatography was prepared by covalently attaching a diproline chiral selector that has proven to be effective in liquid chromatography to a methylhydrosiloxane-dimethylsiloxane copolymer. With this new chiral stationary phase for GC, racemic aromatic alcohols could be resolved without derivatization. Racemic aromatic and aliphatic amines could also be resolved after derivatization of the amino groups with trifluoroacetic anhydride or isopropyl isocyanate. On this stationary phase, the isopropyl isocyanate derivatives of amines showed higher enantioselectivity than the trifluoroacetic anhydride derivatives. In both the enantiomeric separations of alcohols and derivatized amines, the aromatic racemic analytes showed higher enantioselectivities than their aliphatic analogs. Some of the alpha-amino and alpha-hydroxy aromatic acids could also be separated after derivatization to N-trifluoroacetyl methyl esters for amino acids or O-trifluoroacetyl methyl esters for hydroxyl acids.     

Conalbumin-conjugated silica gel, a new chiral stationary phase for high-performance liquid chromatography.

A new chiral stationary phase using conalbumin (from chicken egg white) was developed for high-performance liquid chromatography. Chiral resolution of racemic azelastine, an antiallergic drug, was achieved on a conalbumin-conjugated silica gel column. The effects of the pH, the concentration of organic solvents and salts in the mobile phase, and the temperature on the capacity factor and resolution of racemic azelastine were examined. This column shows good stability and can separate optical isomers with an aqueous mobile phase. It should be very useful in studies on pharmacokinetics and in clinical chemistry.     

Liquid-crystalline polypropyleneimine dendrimer as a stationary phase for gas chromatography

The adsorption properties of a stationary phase for gas chromatography based on a Chromaton N-AW diatomite support modified with a 2K2S16 mesomorphic polypropyleneimine dendrimer are studied. Using the Rohrschneider constants, the studied stationary phase is classified as low polar. It is shown that the new stationary phase is suitable for the separation of both isomers and mixtures of organic substances bearing various functional groups up to a temperature of 150°C.     

Polarizable biphenyl polysiloxane stationary phase for capillary column gas chromatography

A crosslinkable biphenylmethylpolysiloxane stationary phase was synthesized for capillary column gas chromatography and compared with methyl, phenyl, and cyanopropyl polysiloxane stationary phases for the separation of isomeric polycyclic aromatic compounds. While the new phase gave similar separations of nonpolar isomers when compared to the nonpolar phases, separations of polar isomers were greatly improved because of the induced polarity of the biphenyl group of the stationary phase by the solute molecules. This polarizable stationary phase offers a unique selectivity which is not available in other stationary phases.     

Palladium(II) chelate of tetradentate Schiff base as mixed stationary phase for gas chromatography

Bis(acetylacetone)ethylenediiminepalladium(II) (PdAA2en) was examined as a mixed stationary phase with OV-1 on Chromosorb G/NAW 60-80 mesh size for the GC separation of aromatic hydrocarbons, heteroaromatics, alcohols, aldehydes, ketones, esters, and nitro compounds. Forty-two compounds were examined and the GC results were compared with those obtained with 3% OV-1 on Chromosorb G/NAW 60-80 mesh size under similar operating conditions. Improved resolution, peak asymmetry, theoretical plate numbers, and Kovats indices were obtained on the mixed stationary phase of 3% OV-1 + 5% PdAA2en compared to 3% OV-1 column. The stability constant (Km), enthalpies (deltaH), entropies (deltaS), and Gibbs free energies (deltaG) of the GC elution on the column (2 m x 3 mm id) packed with 3% OV-1 + 5% PdAA2en on Chromosorb G/NAW 60-80 mesh size have been calculated. Donor-acceptor complexation in the gas phase is indicated by negative values of enthalpy (-deltaH) within 5.81 to 10.89 kcal/mol and Gibbs free energy (-deltaG) from 1.34 to 4.08 kcal/mol. The retention time transformations on both the phases were calculated and the ratios obtained from the stationary phases 3% OV-1 and 3% OV-1 + 5% PdAA2en were plotted on the x-axis and the y-axis, respectively, and the coefficients of determination for alkanes, aromatic and heteroaromatics, ketones, and alcohols were observed to lie within 0.5253 to 0.9742, indicative of some different kinds of interaction of the two stationary phases with the solutes.     

Selectivity of the stationary phase in gas chromatography

The reaction of some simple molecules with polar and nonpolar stationary phases in gas-liquid chromatography has been examined. The important part played by the structure of the stationary phase in determining the form of the thermodynamic functions has been demonstrated. The individual elementary characteristics of the thermodynamic functions for dissolution in gas-liquid chromatography have been determined.     

Enantiomer separation by gas chromatography on cyclodextrin chiral stationary phases

Fused silica capillary columns coated with several alkyl or acyl cyclodextrin derivatives, especially those of α- and β-cyclodextrins, are suitable for the enantiomer separation of a wide variety of volatile compounds of different molecular size and functionality. Positional isomers and more than 250 pairs of optical isomers have been resolved, including chiral hydrocarbons, acetals, ethers, epoxides, carbonates, lactones, esters, acids, ketones, aldehydes, alcohols, halocarbons, and also nitrogen-and sulfur-containing compounds. The physical properties of the cyclodextrin derivatives, even those obtained as viscous fluids, could be improved by dissolving them in polysiloxane liquid phases commonly used for GLC.     

High performance liquid chromatography on the chiral stationary phase (R,R)-DACH-DNB using carbon dioxide-based eluents

Fast and efficient separations of chiral stereolabile compounds were obtained at very low temperature on a π-acid chiral stationary phase (R,R-DACH-DNB) using carbon dioxide-based mobile phases containing alcoholic polar modifiers. Furthermore, efficient separations of the newly discovered spherical carbon cluster buckminsterfullerene (C₆₀) and the related higher fullerenes (C₇₀, etc.) have been performed on the same stationary phase using eluents based on either n-hexane or carbon dioxide.     

一种新型主链杯芳冠醚聚硅氧烷毛细管气相色谱固定相(英文):

选用特殊的硅氢加成试剂（ＣＨ３）２ＳｉＨＣｌ,首次合成了一种杯芳冠醚单元位于聚硅氧烷主链的新型毛细管气相色谱固定相（Ｍ－Ｃ［４］Ｃ－５ＰＳＯ）。新型固定相具有很好的热稳定性,并对酚类、硝基及氯取代类芳香族位置异构体有良好的分离。其进一步的应用及分离机理有待于深入研究。     

Cyclodextrin dimer derivatives used as stationary phase for capillary gas chromatography

Summary Four cyclodetrin dimer derivatives were synthesized by linking two single cyclodextrin derivatives with difunctional spacer at the primary side of cyclodetrin. The separation properties of these cylodextrin dimer derivatives as CGC stationary phases were investigated and compared with those of the unbridged native cyclodextrin derivative. The results show that two recognition sites and one link spacer of these cyclodextrin dimer derivatives cooperate in separation and affect the separation of disubstituted benzene positional isomers.     

Sorption,thermodynamic, and selective properties of camphor-substituted copper(II) tetrapyrazinoporphyrazine as a stationary phase for gas chromatography

The surface of a Chromaton N-AW diatomite adsorbent was modified with copper(II) tetra(1',7',7'-trimethylbicyclo[2.2.1]heptano-[2',3'-b]-pyrazino)porphyrazine. Adsorption of vapors of 20 organic compounds on the surface of the modified adsorbent was studied by inverse gas chromatography. Electron-donor isomers of methylpyridine and dimethylpyridine, isomers of weakly polar xylenes and cresols, aliphatic alcohols, and other hydrocarbons capable of showing various types of intermolecular interactions with the complex of camphor-substituted tetrapyrazinoporphyrazine with copper(II) were chosen as adsorbates. Specific retention volumes of adsorbates, heat and adsorption entropy, and Gibbs adsorption energy were calculated. The effects of temperature and chemical nature of the adsorbates on the thermodynamic characteristics of sorption are discussed. Factors of separation of closely-boiling hydrocarbons are calculated. It has been found experimentally that the macroheterocycle-based adsorbent shows high selectivity to closely-boiling compounds of various types, unattainable for the unmodified adsorbent.