Selectivity of guanidinium ionic liquid for capillary gas chromatography

<正>A guanidinium ionic liquid,N,N,N',N'-tetrahexyl-N",N"-dimethylguanidinium bis(trifluoromethane)sulfonylimide(THDMGNTf_2), was synthesized and used as stationary phase for capillary gas chromatography.In comparison with imidazolium ionic liquid stationary phase,the present new stationary phase exhibits quite different selectivity and behaves more like a low polar stationary phase.The guanidinium ionic liquid of THDMG-NTf_2 exhibited better separation of Grab test mixture than imidazolium ionic liquid of 1-octyl-3-butylimidazolium bis(trifluoromethane)sulfonylimide(OBIM-NTf_2).Solvation parameter model was also used to evaluate the selectivity of THDMG-NTf_2.Additionally,essential oil of Magnolia biondii Pamp was analyzed to further evaluate the selectivity of THDMG-NTf_2 for a sample of complicated components.Satisfactory separation of the essential oil was achieved on a THDMG-NTf_2 column(10 m) while using a commercial column(30 m) as reference.The present study shows that the guanidinium ionic liquid possesses novel chromatographic selectivity and has great potential for wide applications.     

Characterization of hexacationic imidazolium ionic liquids as effective and highly stable gas chromatography stationary phases

Polycationic ionic liquids (ILs) are an attractive class of ILs with great potential applicability as gas chromatography stationary phases. A family of hexacationic imidazolium ILs derived from the cycloalkanol family was chemically first prepared in a straightforward manner and then applied for analytical separation purposes. Four tuneable engineering vectors, namely cation ring size structure, anion nature, spatial disposition of cycloalkanol substituents and O‐substitution, were considered as experimental parameters for the design of the desired ionic liquids. A total number of five new phases based on a common benzene core respectively exhibited column efficiencies around to 2500 plates/m, broad operating temperature ranges and also, even more importantly, good thermal stabilities (bleeding temperature between 260 and 365°C), finding variations in the selectivity and analytes elution orders depending on the IL structures. Their solvation characteristics were evaluated using the Abraham solvation parameter model, establishing clear correlations between their cation structure and retention capability with respect to certain analytes. The study of relationships between the ILs structure and solvation parameters gives us an idea of the IL stationary phase to be used for specific separations.     

两种高热稳定性端羟基单阳离子型咪唑离子液体毛细管气相色谱固定相的性能评价

采用静态法将合成的端羟基单阳离子咪唑离子液体1-(6-羟己基)-3-丁基咪唑二(三氟甲基)磺酰亚胺盐(HHBIM-NTf₂)和1-(8-羟辛基)-3-丁基咪唑二(三氟甲基)磺酰亚胺盐(HOBIM-NTf₂)作为固定相制备离子液体毛细管气相色谱柱。采用Grob试剂、混合醇样品和芳香族异构体混合物对固定相色谱选择性进行了考察,Grob试剂和混合醇组分产生的尖锐、对称的色谱峰形及异构体混合物组分达到基线分离的结果均表明端羟基离子液体固定相具有良好的色谱选择性。HHBIM-NTf₂柱和HOBIM-NTf₂柱经250 ℃老化8 h后对异构体混合物的分离能力没有明显下降,而HHBIM-NTf₂柱经300 ℃老化后仍有理想的异构体选择性,表明端羟基离子液体固定相具有理想的热稳定性。本结果为进一步改善单阳离子型咪唑离子液体固定相的色谱性能提供了有效途径。     

A novel ionic liquids grafted polysiloxane for capillary gas chromatography

A new ionic liquids grafted polysiloxane used as stationary phase for capillary gas chromatography(CGC) is described.The stationary phase of 1-vinyl-3-hexylimidazolium hexafluorophosphate anchored to polysiloxane(PMHS-[VHIm][PF_6]) was synthesized, characterized and coated onto capillary columns by static coating.The results show that the present stationary phase exhibits a very good chromatographic resolution and selectivity for Grob test mixture and alcohols with baseline resolution and symmetry peaks....     

Nonextractable cyanopropyl polysiloxane stationary phases for capillary chromatography

Summary Crosslinkable cyanopropylpolysiloxane stationary phases have been difficult to produce because of steric effects of the large cyanopropyl groups or because of the interaction between the polar cyanopropyl groups and the groups added for crosslinking. Various polymers containing 50% to 90% cyanopropyl were synthesized which contained vinyl,p-tolyl, or 4-vinylphenyl groups for crosslinking. Thep-tolyl group was found to give satisfactory crosslinking if there were two such groups attached to one silicon atom.     

Crosslinked methylphenylsilicones as stationary phases for capillary gas chromatography

Summary Methyl(phenyl)silicones offer useful selectivities when used as stationary phases in gas chromatography (GC). Such phases have, however, hitherto been of restricted importance in capillary GC due to the lack of phases having a viscosity high enough to ensure stationary phase film stability. Further, to utilize fully the possibilities of a methyl(phenyl)silicone capillary column, it must also possess high efficiency and a high degree of deactivation.In this work, the preparation of soda-glass capillary columns coated within situ cured methyl(phenyl) and methyl(tolyl)-silicones is presented. Vulcanization was made possible by the introduction of some vinyl substitution in the gum to be cured: tolyl-containing gums could be cured without the presence of vinyl groups. In addition, fused silica capillary columns coated with OV-1701 were prepared.The columns show a coating efficiency of above 80%, a thermal stability up to 320 °C and a high degree of deactivation. Their utility is demonstrated by the separation of samples containing polynuclear aromatics, antidepressants and some potent mutagens.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Polymeric imidazolium ionic liquids as valuable stationary phases in gas chromatography: Chemical synthesis and full characterization

Seven new functionalized polymerizable ionic liquids were chemically prepared, and later applied for the preparation of polymeric stationary phases in gas chromatography. These coated GC columns, which exhibited good thermal stabilities (240–300 °C) and very high efficiencies (3120–4200 plates/m), have been characterized using the Abraham solvation parameter model. The chromatographic behavior of these polymeric IL columns has been deeply studied observing excellent selectivities in the separation of many organic substances such as alkanes, ketones, alcohols, amines or esters in mixtures of polar and non polar solvents or fragrances. Remarkably, the challenging separation of xylene isomers has been possible using a bis(trifluoromethylsulfonyl)amide based imidazolium IL coated column as a gas chromatography stationary phase.     

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

<正>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.     

聚合离子液体毛细管气相色谱固定相的性能评价

离子液体作为毛细管气相色谱固定相的选择性和热稳定性是近年人们关注的课题。本文合成了1-烯基-3-苄基咪唑-二(三氟甲基磺酰)亚胺盐(VBIm-NTf2)离子液体并经毛细管柱内聚合制得了聚合离子液体PVBIm-NTf2色谱柱。与VBIm-NTf2色谱柱相比,PVBIm-NTf2色谱柱具有良好的色谱选择性和热稳定性。PVBIm-NTf2色谱柱对Grob试剂、醇混合物、酯混合物和苯系物等都表现了很好的分离能力,并且色谱峰峰形窄且对称。该聚合色谱柱在250 ℃下老化6 h后仍具有良好的分离能力和选择性。本文还测定了PVBIm-NTf2的Abraham溶剂化参数,解析了该固定相与溶质间的相互作用,相关研究国内尚未见报道。研究表明,对常规离子液体进行柱内聚合是改善常规离子液体气相色谱固定相的热稳定性和选择性的有效途径。     

Effect of viscosity on stationary phase stability in capillary column gas chromatography

With recent advances in column technology it is now possible to prepare highly efficient, very inert, and thermally stable capillary columns coated with nonpolar polysiloxane stationary phases. Unfortunately, the same degree of success has not been achieved for some of the more polar polysiloxane phases. A parameter that has been studied little in the past in relation to stationary phase film stability is the viscosity of the stationary phase. In this paper the efficiency and stability of coated columns are correlated to the viscosity of the phase. Due to their structure, the viscosity of the phenyl-containing polysiloxanes change rapidly with temperature and hence, thin-film coatings are not stable at elevated temperatures. By using high viscosity phenyl-containing methylphenylpolysiloxanes which were recently synthesized, efficient and stable columns have been prepared.     

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.     

Retention characteristics of organic compounds on molten salt and ionic liquid-based gas chromatography stationary phases

The interest of using ionic liquids (ILs) as stationary phases in gas chromatography (GC) has increased in recent years. This is largely due to the fact that new classes of ILs are being developed that are capable of satisfying many of the requirements of GC stationary phases. This review highlights the major requirements of GC stationary phases and describes how molten salts/ILs can be designed to largely meet these needs. The retention characteristics of organic solutes will be discussed for ammonium, pyridinium, and phosphonium-based molten salts followed by imidazolium, pyridinium, pyrollidinium, and phosphonium-based IL stationary phases. The versatility of ILs allows for the development of stationary phases based on dicationic ILs, polymeric ILs, and IL mixtures. To aid in choosing the appropriate IL stationary phase for a particular separation, the reader is guided through the different types of stationary phases available to identify those capable of providing the desired separation selectivity of organic solutes while allowing for flexibility in ranges of temperature used throughout the separation.     

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.     

Highly selective GC stationary phases consisting of binary mixtures of polymeric ionic liquids

GC stationary phases composed of binary mixtures of two polymeric ionic liquids (PILs), namely, poly(1‐vinyl‐3‐hexylimidazolium) bis[(trifluoromethyl)sulfonyl]imide (poly(ViHIm‐NTf₂))/poly(1‐vinyl‐3‐hexylimidazolium) chloride (poly(ViHIm‐Cl)) and poly(1‐vinyl‐3‐hexadecylimidazolium) bis[(trifluoromethyl)sulfonyl]imide (poly(ViHDIm‐NTf₂))/poly(1‐vinyl‐3‐hexadecylimidazolium) chloride (poly(ViHDIm‐Cl)), were evaluated in terms of their on‐set bleed temperature and separation selectivity. A total of six neat or binary PIL stationary phases were characterized using the solvation parameter model to investigate the effects of the polymeric cation and anion and PIL composition on the system constants of the resulting stationary phases. The hydrogen bond basicity of the mixed poly(ViHIm‐NTf₂)/poly(ViHIm‐Cl) stationary phases was enriched linearly with the increase in the poly(ViHIm‐Cl) content. Results revealed that tuning the composition of the stationary phase allowed for fine control of the retention factors and separation selectivity for alcohols and carboxylic acids as well as selected ketones, aldehydes, and aromatic compounds. A reversal of elution order was observed for particular classes of analytes when the weight percentage of the chloride‐based PIL was increased.     

Ionic liquid stationary phases for gas chromatography

This article provides a summary of the development of ionic liquids as stationary phases for gas chromatography beginning with early work on packed columns that established details of the retention mechanism and established working methods to characterize selectivity differences compared with molecular stationary phases through the modern development of multi-centered cation and cross-linked ionic liquids for high-temperature applications in capillary gas chromatography. Since there are many reviews on ionic liquids dealing with all aspects of their chemical and physical properties, the emphasis in this article is placed on the role of gas chromatography played in the design of ionic liquids of low melting point, high thermal stability, high viscosity, and variable selectivity for separations. Ionic liquids provide unprecedented opportunities for extending the selectivity range and temperature-operating range of columns for gas chromatography, an area of separation science that has otherwise been almost stagnant for over a decade.     

Dicyanobiphenyl polysioloxane stationary phases for capillary column gas chromatography

Summary The chromatographic performance of newly developed dicyanobiphenyl polysiloxane stationary phases were evaluated and compared with the performance of other polar stationary phases, including the previously reported monocyanobiphenyl polysiloxanes. Due to the unique combination of polarizable biphenyl and polar cyano functionalities in the side chains of the flexible polysiloxane backbone, and by virtue of their mild liquid crystalline properties, the new stationary phases provide excellent resolution of a wide variety of analytes, both polar and nonpolar, in both GC and SFC. They can be easily coated and cross-linked in open tubular columns, and the resultant columns demonstrate excellent efficiency and performance at temperatures up to 280–300°C. The new stationary phases exhibit enhanced selectivities for various types of isomeric compounds.     

Autocrosslinkable methyl-2-phenylethylpolysiloxane stationary phase for capillary column gas chromatography

Methyl-2-phenylethylpolysiloxane polymers have been synthesized for comparison with methylphenylpolysiloxane stationary phases for gas chromatography. The 50% 2-phenylethyl polysiloxane was found to be autocrosslinkable at 260°C without addition of free redical initiator. Although the selectivity of this phase appears to be similar to the 50% phenyl polysiloxane, its thermal stability is not as high.     

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.     

Evaluation of smectic biphenylcarboxylate ester liquid-crystalline polysiloxane stationary phases for capillary column gas chromatography

Mesomorphic biphenylcarboxylate esters were coupled via flexible aliphatic hydrocarbon spacers to a polysiloxane backbone. The influence of spacer length, percent mesomorphic substitution, and crosslinking of the stationary phase on liquid-crystalline transition temperatures and on chromatographic performance was investigated. Unique selectivity and good efficiency over a wide temperature range for gum and cross-linked liquid-crystalline phases were demonstrated by the separation of various isomeric polycyclic aromatic compounds.     

Chromatographic determination of hydrophobicity of dialkylimidazolium ionic liquids using selected stationary phase

The determination of hydrophobicity of ionic liquids (ILs) is essential for the reason that some of these salts' classes are of toxic character. The conventional shake flask method of logP estimation fails in case of ILs. This is connected with their ionic character. Therefore other methods need to be developed and optimized. Chromatographic methods seem to be the proper ones. For that reason, several specific stationary phases (octadecyl, octyl, aminopropyl, alkylamide, cholesterolic, immobilized artificial membrane, phenyl) have been used for the determination of logk(w) of alkylimidazolium ILs. Then, logk(w) were used for the correlation with calculated logP for ILs. Depending on applied calculation procedure, high values of determination coefficient were obtained for alkyl-based silica stationary phases or for more specific column packing. This result is very promising as it has already been proven that several, different in nature, stationary phases can be successfully used for estimation of logP of IL cations.