Phases For Capillary Gas Chromatography Research Articles

Separation performance of polydopamine-based cucurbit[7]uril stationary phase for capillary gas chromatography

Abstract Polydopamine (PDA) coating, a nature-inspired polymer, has attracted great attention in many areas due to its high adhesion strength and stability on almost all types of substrate surfaces. This work presents the first example of using PDA coating as a column pretreatment method in capillary gas chromatography (GC) and its employment in the column fabrication of cucurbit[7]uril (CB7) stationary phase. The fabricated PDA-CB7 column exhibited weakly polar nature and had advantages over CB7 column without PDA for the separations of some critical analytes in GC. This work demonstrates the advantage and potential of using PDA as a facile column pretreatment method in capillary GC column fabrication.

Perhydroxylcucurbit[6]uril as a highly selective gas chromatographic stationary phase for analytes of wide-ranging polarity.

This work describes the separation performance of a perhydroxylcucurbit[6]uril stationary phase for capillary gas chromatography. The perhydroxylcucurbit[6]uril stationary phase exhibits higher resolving capabilities for critical analytes with better peak shapes than cucurbit[6]uril and conventional stationary phases. The advantageous separation feature of the perhydroxylcucurbit[6]uril stationary phase may originate from its unique structure and favorably balanced interactions with the analytes. Also, the perhydroxylcucurbit[6]uril column shows good separation repeatability with relative standard deviations in the range of 0.01-0.13% for intraday, 0.37-0.82% for interday, and 1.0-4.7% for column-to-column repeatability.

Separation performance of cucurbit[7]uril in ionic liquid-based sol-gel coating as stationary phase for capillary gas chromatography

Here we report the separation performance of a new stationary phase of cucurbit[7]uril (CB7) incorporated into an ionic liquid-based sol-gel coating (CB7-SG) for capillary gas chromatography (GC). The CB7-SG stationary phase showed an average polarity of 455, suggesting its polar nature. Abraham system constants revealed that its major interactions with analytes include H-bond basicity (a), dipole–dipole (s) and dispersive (l) interactions. The CB7-SG stationary phase achieved baseline separation for a wide range of analytes with symmetrical peak shapes and showed advantages over the conventional polar stationary phase that failed to resolve some critical analytes. Also, it exhibited different retention behaviors from the conventional stationary phase in terms of retention times and elution order. Most interestingly, in contrast to the conventional polar phase, the CB7-SG stationary phase exhibited longer retentions for analytes of lower polarity but relatively comparable retentions for polar analytes such as alcohols and phenols. The high resolving ability and unique retention behaviors of the CB7-SG stationary phase may stem from the comprehensive interactions of the aforementioned interactions and shape selectivity. Moreover, the CB7-SG column showed good peak shapes for analytes prone to peak tailing, good thermal stability up to 280°C and separation repeatability with RSD values in the range of 0.01–0.11% for intra-day, 0.04–0.41% for inter-day and 2.5–6.0% for column-to-column, respectively. As demonstrated, the proposed coating method can simultaneously address the solubility problem with CBs for the intended purpose and achieve outstanding GC separation performance.

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

Abstract 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.

Novel inorganic mesoporous material with chiral nematic structure derived from nanocrystalline cellulose for high-resolution gas chromatographic separations.

Chiral nematic mesoporous silica (CNMS) has attracted widespread attention due to some unique features, such as its nematic structure, chirality, large pore size, high temperature resistance, low cost, and ease of preparation. We first reported the use of CNMS as a stationary phase for capillary gas chromatography (GC). The CNMS-coated capillary column not only gives good selectivity for the separation of linear alkanes, aromatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and isomers but also offers excellent enantioselectivity for chiral compounds. Compared with enantioseparations on commercial β-DEX 120 and Chirasil-l-Val columns, a CNMS-coated capillary column offers excellent enantioselectivity, chiral recognition complementarity, and the separation of analytes within short elution times. It can also be potentially applied in high-temperature GC at more than 350 °C. This work indicates that CNMS could soon become very attractive for separations.

Properties of water as a novel stationary phase in capillary gas chromatography

A novel method of separation that uses water as a stationary phase in capillary gas chromatography (GC) is presented. Through applying a water phase to the interior walls of a stainless steel capillary, good separations were obtained for a large variety of analytes in this format. It was found that carrier gas humidification and backpressure were key factors in promoting stable operation over time at various temperatures. For example, with these measures in place, the retention time of an acetone test analyte was found to reduce by only 44s after 100min of operation at a column temperature of 100°C. In terms of efficiency, under optimum conditions the method produced about 20,000 plates for an acetone test analyte on a 250μm i.d.×30m column. Overall, retention on the stationary phase generally increased with analyte water solubility and polarity, but was relatively little correlated with analyte volatility. Conversely, non-polar analytes were essentially unretained in the system. These features were applied to the direct analysis of different polar analytes in both aqueous and organic samples. Results suggest that this approach could provide an interesting alternative tool in capillary GC separations.

Separation performance of cucurbit[8]uril and its coordination complex with cadmium (II) in capillary gas chromatography

Here we report the investigation of using cucurbit[8]uril (CB8) and its coordination complex with cadmium (II) (CB8-Cd) as stationary phases for capillary gas chromatography (GC). The prepared capillary columns of CB8 and CB8-Cd stationary phases achieved column efficiency of 2200plates/m and 1508plates/m, respectively, and showed weak polarity based on the measured McReynolds constants. Their separation performance was investigated by GC separation of mixtures of different types while a commercial column was used for comparison. The CB8 stationary phase achieved high resolution for a wide range of analytes from nonpolar to polar while the CB8-Cd stationary phase exhibited good separation mainly for nonpolar to weak polar analytes. The CB stationary phases differ from the commercial one in terms of retention behaviors and resolving ability due to their different molecular interactions with analytes. Moreover, energy effect on the retention of analytes on CB8 and CB8-Cd stationary phases was examined, showing that retention on CB8 column was determined mainly by enthalpy change for polar analytes and by both enthalpy change and entropy change for weak polar analytes whereas retention on CB8-Cd column was mainly controlled by entropy change. This work demonstrates the great potential of CB8 and CB8-Cd stationary phases as a new type of GC stationary phases in GC analysis.

Cucurbit[6]uril in combination with guanidinium ionic liquid as a new type of stationary phase for capillary gas chromatography

Cucurbit[n]urils (CBs) possess unique structures and selective interactions with analytes of different variety and high thermal stability and show a great potential as stationary phases for capillary gas chromatography (GC). This work presents the first description of CB6 in combination with a new guanidinium-based ionic liquid (GBIL) as the GC stationary phase by using sol–gel coating method for the preparation of the CB6-GBIL and GBIL columns. Introduction of GBIL greatly improved the solubility of CB6 in the sol solution and successfully made the use of CBs for the intended purpose feasible. The CB6-GBIL and GBIL columns had average polarity of 179 and 280, respectively, suggesting their medium polar nature. The CB6-GBIL column achieves good resolution for a wide range of analytes and exhibits different retention behaviors and resolution for some of the analytes from the GBIL column and the commercial column. Moreover, it also shows good thermal stability up to 250°C. The proposed method integrates the full advantages of CBs, ionic liquids and sol–gel coating method and provides an efficient and feasible way for the wider application of CBs in separation science.

Dithienyl benzothiadiazole derivatives: A new type of stationary phases for capillary gas chromatography

Dithienyl benzothiadiazole (TBT) derivatives are characteristic of specific molecular structures and excellent thermal stability, offering the great potential for their use as stationary phases for capillary gas chromatography (GC). However, no related publications are available to date. Here we first report the exploration of two TBT derivatives, namely, 4,7-bis(5-dodecylthiophen-2-yl) benzothiadiazole (TBT-C12, a new derivative), and 4,7-di(thiophen-2-yl) benzothiadiazole (TBT), for the purpose. First, TBT-C12 and TBT were synthesized and statically coated onto capillary columns. Both of the as-prepared columns were characterized as nonpolar nature by the determined McReynolds constants. The results showed that both TBT-C12 and TBT columns achieved excellent separations for n-alkanes, esters and polycyclic aromatic hydrocarbons (PAHs), and the TBT-C12 column exhibited better thermal stability (up to 280°C) than the TBT column. Moreover, a comparative study between the TBT-type columns and a commercial column was also made, suggesting the better selectivity of the TBT-type stationary phases toward n-alkanes and PAHs than that of the commercial one. Additionally, thermodynamic parameters suggested that the retention behaviors of n-alkanes and PAHs on the TBT-C12 column was mainly controlled by entropy change (ΔS). In conclusion, this work demonstrates the excellent chromatographic performance of TBT derivatives as a new type of GC stationary phases and their potential in separation science.

Preparation and characterization of alkyl methacrylate-based monolithic columns for capillary gas chromatography applications

Gas chromatography (GC) is considered the least common application of both polymer and silica-based monolithic columns. This study describes the fabrication of alkyl methacrylate monolithic materials for use as stationary phases in capillary gas chromatography. Following the deactivation of the capillary surface with 3-(trimethoxysilyl)propyl methacrylate (TMSM), the monoliths were formed by the co-polymerization of either hexyl methacrylate (HMA) or lauryl methacrylate (LMA) with different percentage of ethylene glycol dimethacrylate (EDMA) in presence of an initiator (azobisisobutyronitrile, AIBN) and a mixture of porogens include 1-propanol, 1,4-butanediol and water. The monoliths were prepared in 500mm length capillaries possessing inner diameters of 250μm. The efficiencies of the monolithic columns for low molecular weight compounds significantly improved as the percentage of crosslinker was increased, because of the greater proportion of pores less than 50nm. The columns containing lower percentages of crosslinker were able to rapidly separate a series of 8 alkane members in 0.7min, but the separation was less efficient for the light alkanes. Columns prepared with the lauryl methacrylate monomer yielded a different morphology for the monolith-interconnected channels. The channels were more branched, which increased the separation time, and unlike the other columns, allowed for temperature programming.

Study of Intermolecular Interactions Involved in Capillary GLC with Liquid Crystal Compounds as Stationary Phases

Abraham's equation was employed in order to investigate nonspecific intermolecular interactions involving liquid crystals. Several aromatic azo derivatives, proved to have liquid crystal behavior, were used as stationary phases in capillary gas chromatography. The polarizability, polarity, hydrophobicity and hydrogen-bond donor or acceptor characters were estimated using the Abraham solvation model. Calculations were based on the isothermal retention times for 25 compounds, in the temperature range between 70˚ and 170˚C, both in the heating and the cooling mode. The descriptors R, � , �� , �� , and logL 16 (Abraham parameters) were converted into orthogonal descriptors following Randi� 's procedure. The above-mentioned properties involve the r, s, a, b and l coefficients, respectively, which were determined by means of multilinear regression applied to the considered set. Following the orthogonalization procedure, the polarizability term (rR*) was found to be statistically insignificant in the case of the studied compounds. Plots of these coefficients vs temperature are discussed, in order to allow estimations regarding the retention mechanism and contributions of polar and Van der Waals interactions. The variation of properties (e.g. polarity, hydrogen-bond donor and hydrogen-bond acceptor character) with temperature was assigned to the changes in the molecular geometry of the compound used as stationary phase.

Characterization of Calixarene/Ionic Liquid Mixture as Gas Chromatographic Stationary Phase through Thermodynamic Parameters and LSER

A mixture of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetraethoxycarbonylmethyloxy calix[4]arene (C[4]TECM) and 1-octyl-3-methylimidazolium tetrafluoroborate ionic liquid (OmI m + BF4 −) has been employed as stationary phases in capillary gas chromatography. Its properties have been characterized through thermodynamic parameters and linear solvation energy relationship. The experimental results showed that C[4]TECM–OmI m + BF4 − mixture as gas chromatographic stationary phase has high column efficiency and peak symmetry, which were evaluated using naphthalene and n-octanol, respectively. It was demonstrated that the interaction forces between the probe molecules and the stationary phase did not change over the entire temperature range studied due to an excellent linear relationship between lnk and 1/T, the retentions of the probe molecules on the C[4]TECM–OmI m + BF4 − stationary phase are enthalpy-driven processes, and the interactions of the probe molecules with C[4]TECM–OmI m + BF4 − stationary phase mainly include hydrogen bonding interaction, dipole–dipole interaction and dispersive interaction. However, the contribution of each interaction is in the order of A > L > S for the C[4]TECM–OmI m + BF4 − stationary phase.

Novel Geminal Dicationic Ionic Liquid as Stationary Phase for Capillary Gas Chromatography

One geminal dicationic ionic liquid (IL) was synthesized and coated in column as stationary phase for capillary gas chromatography (CGC). In this study, two times imidazolium cations were reacted with 1,4-bis(chloromethyl)-benzene and then the anions exchanged to bis(trifluoromethylsulfonyl)-imide (NTf2-). The new ILs was coated statically in capillary column. The outcome of the stationary phase was evaluated by separating Grobs mixture, n-alkanes mixture, alcohols mixture and aromatic position isomers mixture such as xylene, nitrotoluene, dichlorobenzene and cresol. The results indicated that new IL possessed good column coating properties and chromatographic separation abilities.

Application of Quaternary Aminated β-Cyclodextrin Ionic Liquid Stationary Phase in Capillary Gas Chromatography

Two kinds of quaternary aminated β-cyclodextrin ionic liquids were synthesized and used as stationary phases in capillary gas chromatography. The influences of different counter ions (tetra- borofluoride, bis-trifluoromethanesulfonylimide) were studied. The results indicated that quaternary aminated β-cyclodextrin ionic liquids possessed good column coating properties and a chromatographic separation abilities. The Grobs mixture, alkanes, alcohols and aromatic position isomers, such as xylene, nitrotoluene, dichlorobenzene and cresol were separated well. These quaternary aminated β-cyclodextrin ionic liquids have potential to separate some complex compounds including alcohol, amine, ester etc.

Synthesis and Application of Poly-Allyl-Imidazolium Ionic Liquid Stationary Phase in Capillary Gas Chromatography

Two 1-allyl-3-butylimidazolium ionic liquids were synthesized and polymerized in- column as stationary phases in capillary gas chromatography. The influences of different counter ions (hexafluorophosphate, tetrafluoroborate) were studied. The results indicated that 1-allyl-3-butyl- imidazolium ionic liquids possessed good column coating properties and chromatographic separation abilities after polymerized in-column. The Grobs mixture, alcohols and alkanes and aromatic position isomers, such as xylene, nitrotoluene, dichlorobenzene and cresol were separated well. These polymeric ionic liquids gave potential to separate some complex compounds including alcohol, amine, ester etc.

Evaluation of new ionic liquids as high stability selective stationary phases in gas chromatography

Two ionic liquids (ILs), namely (S,S)-1-butyl-3-(2'-hydroxy-cyclohexyl)-3H-imidazol-1-ium tetrafluoroborate and (S,S)-1-butyl-3-(2'-acetyl-cyclohexyl)-3H-imidazol-1-ium tetrafluoroborate have been employed as stationary phases in capillary gas chromatography. These new phases exhibit a column efficiency of 1,600 and 2,100 plates m(-1) for IL 1 and IL 2, respectively, a wide operating temperature range and good thermal stability (bleeding temperature of 250 °C for IL 1 and 160 °C for IL 2). Inverse gas chromatography (GC) analyses were used to study the solvation properties of these ILs through a linear solvation energy model. The application of these ILs as new GC stationary phases was studied. These stationary phases exhibited unique selectivity for many organic substances, such as alkanes, ketones, esters, and aromatic compounds. The efficient separation of several mixtures containing compounds of different polarities and the good separation of fatty acid methyl esters (FAMEs) and cis/trans isomers indicate that these ILs may be applicable as a new type of GC 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.

Evaluation of two hydroxyl-terminated monocationic ionic liquid stationary phases with high thermal stability for capillary gas chromatography

Novel hydroxyl-terminated ionic liquids of 1-(6-hydroxyhexyl)-3-butyl imidazolium bis(trifluoromethyl) sulfonylimide (HHBIM-NTf2) and 1-(8-hydroxyoctyl) -3-butyl imidazolium bis(trifluoromethyl) sulfonylimide (HOBIM-NTf2) were synthesized as stationary phases for capillary gas chromatography (GC). Besides, 1-octyl-3-butyl imidazolium bis(trifluoromethyl) sulfonylimide (OBIM-NTf2) was used as the reference. Selectivities and thermal stabilities of HHBIM-NTf2, HOBIM-NTf2 and OBIM-NTf2 were evaluated by means of the separation of Grob test mixture and positional isomers after the columns were conditioned up to 160 degrees C, 250 degrees C and 300 degrees C, respectively. As a result, baseline separations of Grob test mixture and alcohol mixture and better peak shapes were observed with HHBIM-NTf2 and HOBIM-NTf2. Importantly, baseline separation of dimethoxybenzene isomers was also achieved with HHBIM-NTf2 and HOBIM-NTf2. Satisfactory selectivity of HHBIM-NTf2 still remained even after conditioned at 300 degrees C for 8 h. The results for thermal stability showed that as GC stationary phases, HHBIM-NTf2 and HOBIM-NTf2 were stable at least up to 300 degrees C and 250 degrees C, respectively. The hydroxyl-terminated monocationic ionic liquids possess excellent selectivity and thermal stability and are alternative candidates for GC stationary phases.

Ionic liquid‐bonded polysiloxane as stationary phase for capillary gas chromatography

Ionic liquid (IL) stationary phase is especially suitable for separation of complex samples, owing to the "dual nature" of IL. In this study, a synthetic method of ionic liquid-bonded polysiloxane (PSOIL) as stationary phase of GC was proposed. Then, the PSOIL was used to prepare an 8 m capillary column by static method. The column efficiency was measured to be about 4000 plates/m (k=3.55, naphthalene) after the column had been conditioned at 210°C. The durability of PSOIL column was better than that of the mixed stationary phase of IL and OV-1. Moreover, the Abraham solvation parameter model was employed to characterize the PSOIL. The result revealed that the PSOIL had stronger dispersion force (l) than neat IL and stronger hydrogen bond basicity (a) than DB-1. That meant the PSOIL might offer good selectivity for both polar and non-polar analytes. The column exhibited unique selectivity for various organic substances, such as the homologous compounds of alkanes, esters, alcohols and aromatic compounds. It was also found that some aromatic positional isomers could be separated better on the PSOIL column than on the DB-1 column. Furthermore, the stationary phase was suitable for separation of high-boiling point compounds such as polycyclic aromatic hydrocarbons, phthalic esters, etc. All of these demonstrated that the PSOIL offered good selectivity and high separation efficiency for a wide range of analytes.

Selectivity of guanidinium ionic liquid for capillary gas chromatography

A guanidinium ionic liquid, N, N, N′, N′-tetrahexyl- N″, N″-dimethylguanidinium bis(trifluoromethane)sulfonylimide (THDMG-NTf 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 Grob 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.