Separation Properties of a New Polysiloxane-Anchored β-Cyclodextrin Derivative as Gas Chromatography Stationary Phase

A new capillary gas chromatography stationary phase, monokis (2,6 di O benzyl 3 O propyl (3’)) hexakis(2,6 di O benzyl 3 O methyl) β CD bonded polysiloxane, was synthesized. It exhibited separation abilities to disubstituted benzene isomers and some chiral solutes. It was also found that the polarity of CD derivatives can be lowered both by chemically bonding it to polysiloxane and by diluting it in polysiloxane. The separation abilities of the polysiloxane anchored CDs (SP CD) are higher than that of the unbonded CDs (S CD) and the diluted S CD at lower column temperature. Hydrosilylation reaction is one of the best methods to lower the operating temperature of CDs.

Preparation of new hybrid organic/inorganic polymeric chiral stationary phases for ligand-exchange chromatography

Three new hybrid organic/inorganic polymeric ligand-exchange chiral stationary phases were developed by radical chain transfer reaction and surface grafting on silica gel, and successfully used for the enantioseparations of DL-amino acids and DL-hydroxyl adds. The resolutions were achieved by using water containing 2.0 × 10^-4 mol/L of CuAc2 as a mobile phase, column temperature of 40 ℃, flow rate of 1.0 mL/min and detection at UV 254 nm. The elution order of D-isomer before L-isomer was observed for all DL-amino acids resolved except DL-Pro.

Preparation of novel chiral stationary phase based on click chemistry for ligand exchange chromatography

Click chemistry was applied to immobilize L-proline derivative onto azide-modified silica gel to give a novel chiral stationary phase （denoted as click-CSP） for ligand exchange chromatography. The developed protocol combines the benefits of operational simplicity, exceptionally mild conditions and high surface loadings. The enantioselectivity α of some DL-arnino acids on the click- CSP were found to be in the range from 1.13 to 3.46. The chromatographic resolutions of some DL-amino acids and the stability study firmly illustrate the potential of click chemistry for preparation chiral stationary phase for ligand exchange chromatography.

Preparation and Characterization of Titania Microspheres and Their Application in a Liquid Chromatography Stationary Phase

Titania microspheres were synthesized using hydrothermal methods to exploit a new liquid chromatography stationary phase. The prepared titania microspheres were approximately 7 μm in diameter, and the particle size distribution was relatively narrow and uniform. Furthermore, the average specific surface area was 276.0 m2·g·1, the average pore volume was approximately 0.25 mL·g·1, and the pore diameter was approximately 35.9 nm for sintering titania microspheres. These parameters indicate that the titania microspheres prepared for this study have excellent surface properties for chromatography. Additionally, columns filled with the titania microspheres were able to separate basic compounds, including benzene, nitrobenzene and o-nitroanisole. It could be proposed that the titania microspheres prepared for this study would be a promising stationary phase for liquid chromatography.

Separation of Enantiomers of Clopidogrel on Chiral Stationary Phases by Packed Column Supercritical Fluid Chromatography

A packed column supercritical fluid chromatography (SFC) method for the separation of clopidogrel enantiomers on a chiral stationary phase and CO2 with modifier as mobile phase has been developed at an analytical scale. Among 11 different 2 stationary phases the Chiral cel OD-H column showed by far the best separation properties. The influence of different modifiers, injection solvents, temperature, and pressure, and density of the fluid, respectively, on the separation behaviour has been studied. It was found that the separation behaviour strongly depends on the type of modifier and the modifier content. Temperature and pressure are of less influence.

Modification of Chiral Stationary Phases with L-Proline as a Selector for Ligand-exchange Chromatography via Introducing Hydrophobic Groups

Three chiral stationary phases（CSPl, CSP2 and CSP3） for ligand-exchange chromatography were prepared by firstly using dimethylchlorosilane as an endcapping reagent for decreasing residual silanol groups on the surface of silica gel, and then modifying the surface of silica gel with allyl glycidyl ether and alkenes through the hydrosilation reaction, and lastly introducing L-proline as a chiral selector. The enantiomer resolutions of 14 amino acids and 2 hydroxyl acids were completed on the CSPs by using an aqueous solution of Cu（Ac）2 as mobile phase at a flow rate of 1.0 mL/min and column temperature of 40 ℃ with detection at UV 254 nm. In terms of enantioseleetivity a, column efficiency and resolution Rs, the chromatographic behaviors of the analytes on the CSPs were discussed via comparing them to those on the CSP4 prepared via the reference method. The results show that enantioselectivity a, column efficiency and resolution Rs of the analytes on the CSPs could be improved by using the above modifying method.

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 dimethylchlorosilane 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 enantioselectivity α ranging 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.

Novel guanidinium-based ionic liquids as stationary phases for capillary gas chromatography

The present study describes guanidinium-based ionic liquids（GBILs） as stationary phases for capillary gas chromatography （CGC） and to the best of our knowledge,no related reports are available up to now.In this study,a hexaalkylguanidinium ionic liquid（DOTMG-NTf;） was synthesized and coated statically onto capillary columns.Selectivity of the stationary phase was evaluated by separating Grob test mixture,test mixture,alcohols mixture,and fatty acid methyl esters mixture,and thermal stability was investigated as well.The present study demonstrates that GBILs as CGC stationary phases exhibit satisfactory selectivity and thermal stability and have a great potential as new candidates for CGC stationary phases.

Retention behaviors of novel ionic liquid stationary phases and their selectivity for capillary gas chromatography

One chloride-terminated ionic liquid（CTIL） and two hydroxyl-terminated ionic liquids（HTILs） were synthesized and used as stationary phases for capillary gas chromatography（CGC）.Molecular interactions of these stationary phases were evaluated by Abraham solvation parameter model,indicating that the CTIL exhibits remarkably strong H-bond basicity and the HTILs possess both H-bond basicity and acidity.The molecular interactions were further confirmed by separation of a complex mixture consisting of ketones,aldehydes,esters,alcohols and aromatic compounds.It was found that the obtained solvation parameters correlate well with the chromatographic performances of the analytes in terms of elution order and resolution.The well correlated relationship between the solvation parameters and the selectivity of the CTIL and HTILs stationary phases is quite helpful in predicting and understanding the retention behaviors of different types of analytes on these stationary phases.

Polysiloxane with Pendant [60]Fulleropyrrolidines as Stationary Phase for Capillary Gas Chromatography

Polysiloxane with pendant [60] fulleropyrrolidines was synthesized and used as the stationary phase for capillary gas chromatography for the first time. A preliminary investigation of its property shows that it has an excellent thermostability and a wide range of allowable operating temperature from 80 degrees C to 360 degrees C.

Porous Monoliths: Stationary Phases of Choice for High Performance Liquid Chromatography in Various Formats

Modern porous monoliths have been conceived as a new class of stationary phases for high performance liquid chromatography(HPLC) in classical columns in the early 1990s and later extended to the capillary format.These monolithic materials are prepared using simple processes carried out in an external mold(inorganic monoliths) or within the confines of the column(organic monoliths and all capillary columns).These methods afford macroporous materials with large through-pores that enable applications in a rapid flow-through mode.Since all the mobile phase must flow through the monolith,the convection considerably accelerates mass transport within the monolithic separation medium and improves the separations.As a result,the monolithic columns perform well even at very high flow rates.The applications of monolithic capillary columns are demonstrated on numerous separations in the HPLC mode.

Separation of substituted phenylpiperazine derivatives with immobilized polysaccharide-based chiral stationary phases by supercritical and subcritical fluid chromatography

Six newly synthesized racemic 1-（substituted phenyl）-4-[3-（indole-4-yl-oxy）-2-hydroxypropyl]-piperazine 1-6 were successfully resolved by carbon dioxide supercritical fluid chromatography （SFC） on an analytical scale column packed with immobilized polysaccharide-based chiral stationary phases （CSPs）. We found that separation on the Chiralpak IA CSP was superior to the other two immobilized CSPs （Chiralpak IB and Chiralpak IC）, and isopropanol （IPA） was a superior modifier compared to the other five solvents including ethanol, methanol, tetrahydrofuran, acetonitrile and dichloromethane. The effects of organic modifier composition, back pressure, and column temperature for enantioseparation of all six compounds were studied. Of the physical parameters studied, modifier composition had the greatest impact on retention. Changing temperature generally had less impact on retention but produced the greatest selectivity changes. The optimum condition was found as follows： Chiralpak IA column, column temperature 35 ~C, back pressure 120 bar, 35% IPA containing 0.1% diethylamine （v/v） in mobile phase, flow rate of mobile phase 3.0 mL/min, UV detection 283 nm. Separation of all six racemic compounds was completed within 10 rain and excellent resolution was obtained. Thus, SFC was found to be the methodology of choice for resolving the enantiomers of this class of compounds.

The Synthesis of A New Cyclodextrin-Crown Ether Chiral Stationary Phase and Application in Gas Chromatography

A new compound of mono 6 (1' benzo aza 15 crown 5) 2,3,6 permethyl β cyclodextrin (BA 15C5 PM CD) was synthesized. The structure was determined to be coincide with our anticipation by spectroscopy. As a stationary phase for capillary gas chromatography, excellent separation for enantiomers and positional isomers was achieved.

Comparative Optical Separation of Racemic Ibuprofen by Using Chiral Stationary Phase

Ibuprofen is widely used as a non-steroidal anti-inflammatory drug and produced as racemic mixture. Its pharmacological activity resides only in S-(+)-enantiomer, and R-()-enantiomer is not only inactive but also has many side effects. Thus it is necessary to separate R-enantiomer from racemic ibuprofen. We studied optical separation of racemic Ibuprofen with chiral high performance liquid chromatography (HPLC). Out of three different chiral stationary phases, which were selected on the basis of structure and availability, two were found to be ef-fective. There was optimum eluent composition for each stationary phase for good resolution in optical separation. Resolution decreased with increase of eluent flow rate, but effect of injection volume on resolution was insignificant at high eluent flow rate.

Comparison of the performance of chiral stationary phase for separation of fluoxetine enantiomers

Separation of fluoxetine enantiomers on five chiral stationary phases （chiralcel OD-H, chiralcel OJ-H, chiralpak AD-H, cyclobond 1 2000 DM and kromasil CHI-TBB） was investigated. The optimal mobile phase compositions of fluoxetine separation on each column were hexane/isopropanol/diethyl amine （98/2/0.2, v/v/v）, hexane/isopropanol/diethyl amine （99/1/0. l, v/v/v）, hexane/isopropanol/diethyl amine （98/2/0.2, v/v/v）, methanol/0.2% triethylamine acetic acid （TEAA） （25/75, v/v; pH 3.8） and hexane/isopropanol/diethyl amine （98/2/0.2, v/v/v）, respectively. Experimental results demonstrated that baseline separation （Rs〉1.5） of fluoxetine enantiomers was obtained on chiralcel OD-H, chiralpak AD-H, and cyclobond I 2000 DM while the best separation was obtained on the last one. The eluate orders of fluoxetine enantiomers on the columns were determined. The first eluate by chiralcel OJ-H and kromasil CHI-TBB is the S-enantiomer, while by chiralpak AD-H and cyclobond 12000 DM is the R-enantiomer.

Synergistic Effect in Special Selectivity Mixed Gas Chromatographic Stationary Phase in the Separation of Aromatic Compounds

The gas chromatographic separations of aromatic compounds using special mixed stationary phases consisting of pp-beta-CD+AgNO3, pp-beta-CD+TINO3, pp-beta-CD+di-n-butly phthalate, pp-beta-CD+BPBHpB liquid crystalline, and bentone-34+AgNO3 were investigated. Besides pp-beta-CD+di-n-butyl phthalate, most of the separations deviated from the additivity and a synergistic effect was observed. The separation effects depend on the temperature and how mixing is accomplished.

Preparation and Characterization of a New Quercetin-bonded Stationary Phase for High Performance Liquid Chromatography

A quercetin-bonded silica gel stationary phase （QUSP） containing natural flavonoid ligand was first prepared via γ-glycidoxypropyltrimethoxysilane （KH-560） as a coupling reagent for high-performance liquid chromatography. Its chemical structure was characterized by Fourier infrared spectroscopy, elemental analysis, thermal thermogravimetry and 13C cross polarization/magic angle spinning nuclear magnetic resonance （CP/MAS NMR）. The chromatographic property of QUSP was systematically evaluated by using neutral, basic and acidic aromatic com- pounds as probes. In order to clarify its retention mechanism, a comparative study of QUSP with conventional oc- tadecylsilyl-bonded stationary phase （ODS） was also carried out under the same conditions. The results showed that the new quercetin-bonded phase exhibited an excellent reversed-phase chromatographic property with relatively weak hydrophobicity. However, it has an advantage over ODS in the fast separation of polar aromatic compounds because the quercetin ligand could provide various sites besides hydrophobicity, such as hydrogen bonding, dipole-dipole, n-n staking and charge transfer interactions. QUSP was performed in the baseline separations of ion- ized polar basic or acidic compounds, including pyridines, anilines, pyrimidines, purines and phenols with symmet- ric peak shape in common mobile phases without buffer salt within relatively short time. The natural ligands from herbs are readily available and contain a variety of active sites, which facilitate the exploration of industrial chromatographic separation materials for green products.

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 column had excellent selectivity, not only for the separation of linear alkanes, linear alcohols, fatty acid methyl esters mixture, the Grob mixture and positional isomers, but also for the resolution of chiral compounds, including chiral alcohols, aldehydes, ethers, and amino acid derivatives. In addition, the β-CD-COF-coated capillary column presented good repeatability and reproducibility. This work indicated the great potential of the CCOFs coated capillary column for the chromatographic separation of enantiomers.

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 selec- tivity of enantiomers D and L in normal-phase chiral stationary phase liquid chromatography cam be described by the equation lnα=⊿a+⊿blnC_b,but in reversed-phase chiral stationary phase liquid chromatography the selectivity is almost independant of the mobile phase composition.

Separation performance of graphene oxide as stationary phase for capillary gas chromatography

Graphene oxide（GO） has attracted extensive attention due to its unique properties and potential applications.Here,we report the investigation of GO nanosheets as a stationary phase for capillary gas chromatographic（GC） separations.The GO column,fabricated by a new one-step coating approach,showed average McReynolds constants of 308,suggesting the medium polar nature of the GC stationary phase.The GO stationary phase achieves good separation for analytes of different types with good peak shapes,especially for H-bonding analytes,such as alcohols and amines.The different retention behaviors of GO stationary phase from the conventional stationary phase may originate from its multiple interactions with analytes,involving H-bonding,dipole-dipole,π-π stacking and dispersive interactions.Moreover,GO column showed good separation reproducibility with relative standard deviation（RSD%） less than 0.24%（n = 5） on retention times of analytes.