Enhanced resolution of Mentha piperita volatile fraction using a novel medium‐polarity ionic liquid gas chromatography stationary phase

The evaluation of a novel medium‐polarity ionic‐liquid‐based gas chromatography column, SLB‐IL60, towards the analysis of a complex essential oil, namely, a peppermint essential oil sample, is reported. The SLB‐IL60 30 m column was subjected to bleeding measurements, by means of conventional gas chromatography with mass spectrometry. The SLB‐IL60 column was then evaluated in the analysis of pure standard compounds, chosen as typical constituents of peppermint essential oil. Resolution and peak symmetry (expressed as tailing factors at 10% of peak height) were measured and the results were compared to those obtained on the most widely used columns in such an application, namely a medium‐polarity [100% poly(ethyleneglycol)] stationary phase, and an apolar 5% diphenyl/95% dimethyl siloxane. The final part of the evaluation was dedicated to the gas chromatography with mass spectrometry analysis of a peppermint essential oil sample and again the data were compared to those obtained on the 100% poly(ethyleneglycol) and the 5% diphenyl/95% dimethyl siloxane phase. Linear retention indices were determined for all the identified components on the ionic liquid capillary.     

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....     

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.     

Analysis of selected ionic liquid cations by ion exchange chromatography and reversed-phase high performance liquid chromatography

The chromatographic behavior of 8 ionic liquids - 7 homologues of 1-alkyl-3-methylimidazolium and 4-methyl-N-butylpyridinium - has been investigated with a strong cation exchange adsorbent. In particular, the dependence of the retention properties of these solutes on mobile phase composition, pH, and buffer concentration was evaluated with the aim of optimizing and improving the selectivity and retention of solute separation. While using the SCX stationary phase, several interactions occurred with varying strengths, depending on the mobile phase composition. Cation exchange, nonspecific hydrophobic interactions, and adsorption chromatography behavior were observed. Reversed phase chromatography occurred at low concentrations of acetonitrile, electrostatic and adsorption interactions at higher organic modifier concentrations. Elevated buffer concentrations lowered the retention factors without affecting the selectivity of ionic liquids. Obtained results were further compared to the chromatographic behaviour of ionic liquids in the reversed phase system. All analyzed ionic liquids follow reversed-phase behavior while being separated. Much lower selectivity in the range of highly hydrophilic compounds is obtained. This suggests preferred use of ion chromatography for separation and analysis of compounds below 4 carbon atoms in the alkyl side chain.     

Conventional and fast gas chromatography analysis of biodiesel blends using an ionic liquid stationary phase

The present research is focused on the GC-FID determination of fatty acid methyl esters (FAMEs) in diesel blends, by means of an ionic liquid stationary phase, characterized by a dicationic 1,9-di(3-vinyl-imidazolium)nonane bis(trifluoromethyl)sulfonylimidate structure (SLB-IL100). The high polarity of the ionic liquid stationary phase allowed the separation of the FAMEs, from the less-retained hydrocarbons, thus avoiding the requirement of a hydrocarbon LC pre-separation. The results derived from the analyses of a soybean FAMEs B20 sample, carried out on an SLB-IL100 conventional column (30 m × 0.25 mm i.d. × 0.20 mm d_f), were compared with those attained on a polyethylene glycol column, of equivalent dimensions. Conventional and fast GC methods, for the analysis of FAMEs in diesel blends, were developed on an SLB-IL100 30 m × 0.25 mm i.d. × 0.20 μm d_f and on an SLB-IL100 12 m × 0.10 mm i.d. × 0.08 μm d_f column, respectively. The optimized IL methods were subjected to validation: retention time and peak area intra-day precision (n = 5) were good, with CV % values lower than 0.08% and 4.9%, respectively. With regards to the quantitation of FAMEs in biodiesel blends, a five points calibration curve was constructed, using C_17:0 as internal standard.     

Development of a carbohydrate silylation method in ionic liquids for their gas chromatographic analysis

This paper reports on the feasibility of silylation of low molecular weight carbohydrates dissolved in different ionic liquids (ILs) for their further analysis by gas chromatography (GC). Derivatization reagents (nature and amounts), temperature and time of reaction and stirring conditions were evaluated for different carbohydrates (i.e., glucose, mannose, fructose and lactose) dissolved in 1-ethyl-3-methylimidazolium dicyanamide [EMIM][DCA]. Evaluation of conformational isomerism of glucose dissolved in [EMIM][DCA] revealed the effect of the time of dissolution in the equilibration of α- and β-furanoses (up to 3% and 6%, respectively, after 70 h of incubation) and that 21 h sufficed to obtain results similar to those provided by the reference method involving pyridine. Once optimized, the proposed derivatization procedure provided satisfactory yields (i.e., close to 100%) using 100 μL of trimethylsilylimidazole (TMSI) at mild conditions (25 °C) for a relatively short time (1 h) for most of the investigated carbohydrates. Under these experimental conditions, linear responses (i.e., R² better than 0.974) were obtained in the tested range of 0.25–1 mg of the derivatized target compounds. Other reagents, such as N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) + 1% trimethylchlorosilane (TMCS), were successfully used under ultrasonic conditions for aldose monosaccharides and disaccharides derivatization, while BSTFA was useful for ketose monosaccharides. The possibility of using the proposed method for the derivatization of selected carbohydrates dissolved in different ILs and the efficiency of the method applied to the analysis of carbohydrates present in real samples (fruit juices) have also been investigated.     

Utilization of a benzyl functionalized polymeric ionic liquid for the sensitive determination of polycyclic aromatic hydrocarbons; parabens and alkylphenols in waters using solid-phase microextraction coupled to gas chromatography-flame ionization detection

The functionalized polymeric ionic liquid poly(1-(4-vinylbenzyl)-3-hexadecylimidazolium bis[(trifluoromethyl)sulfonyl]imide (poly(VBHDIm(+)NTf(2)(-))) has been used as successful coating in solid-phase microextraction (SPME) to determine a group of fourteen endocrine disrupting chemicals (ECDs), including polycyclic aromatic hydrocarbons (PAHs), alkylphenols, and parabens, in several water samples. The performance of the PIL fiber in direct immersion mode SPME followed by gas chromatography (GC) with flame-ionization detection (FID) is characterized with average relative recoveries higher than 96.1% from deionized waters and higher than 76.7% from drinking bottled waters, with precision values (RSD) lower than 13% for deionized waters and lower than 14% for drinking bottled waters (spiked level of 1 ng mL(-1)), when using an extraction time of 60 min with 20 mL of aqueous sample. Detection limits varied between 9 ng L(-1) and 7 ng mL(-1). A group of real water samples, including drinking waters, well waters, and swimming pool waters, have been analyzed under the optimized conditions. A comparison has also been carried out with the commercial SPME coatings: polydimethylsyloxane (PDMS) 30 μm, and polyacrylate (PA) 85 μm. The functionalized PIL fiber (～12 μm) demonstrated to be superior to both commercial fibers for the overall group of analytes studied, in spite of its lower coating thickness. A normalized sensitivity parameter is proposed as a qualitative tool to compare among fiber materials, being higher for the poly(VBHDIm(+)NTf(2)(-)) coating. Furthermore, the partition coefficients of the studied analytes to the coating materials have been determined. A quantitative comparison among the partition coefficients also demonstrates the superior extraction capability of the functionalized PIL sorbent coating.     

A new disposable ionic liquid based coating for headspace solid-phase microextraction of methyl tert-butyl ether in a gasoline sample followed by gas chromatography-flame ionization detection

A new ionic liquid (IL) based solid-phase microextraction (SPME) fiber was investigated and used for headspace (HS) extraction of methyl tert-butyl ether (MTBE) in a gasoline sample. Using the new IL coated HS-SPME fiber with the combination of gas chromatography-flame ionization detection (GC-FID); sub-to-low μg L⁻¹ concentrations of MTBE were detected. Four different ILs including 1-butyl-3-methylimidazolium tetraflouroborate ([C₄C₁IM] [BF₄]), 1-octyl-3-methylimidazolium tetraflouroborate ([C₈C₁IM] [BF₄]), 1-octyl-3-methylimidazolium hexaflourophosphate ([C₈C₁IM] [PF₆]) and 1-ethyl-3-methylimidazolium ethylsulphate ([C₂C₁IM] [ETSO₄]) were synthesized and examined for extraction, preconcentration and determination of MTBE. It was observed that [C₈C₁IM] [BF₄] showed the highest extraction efficiency and possessed the best extractability for MTBE. The fiber coating takes up the compounds from the sample by absorption in the case of liquid coatings. The calibration graph was linear in a concentration range of 1-120 μg L⁻¹ (R² > 0.994) with the detection limit of 0.09 μg L⁻¹ level. The new IL-coated fiber was applied successfully for the determination of MTBE in a gasoline sample with good recoveries between 90 and 95%.     

Surface-bonded ionic liquid stationary phases in high-performance liquid chromatography—A review

Ionic liquids (ILs) are a class of ionic, nonmolecular solvents which remain in liquid state at temperatures below 100 °C. ILs possess a variety of properties including low to negligible vapor pressure, high thermal stability, miscibility with water or a variety of organic solvents, and variable viscosity. IL-modified silica as novel high-performance liquid chromatography (HPLC) stationary phases have attracted considerable attention for their differential behavior and low free-silanol activity. Indeed, around 21 surface-confined ionic liquids (SCIL) stationary phases have been developed in the last six years. Their chromatographic behavior has been studied, and, despite the presence of a positive charge on the stationary phase, they showed considerable promise for the separation of neutral solutes (not only basic analytes), when operated in reversed phase mode. This aspect points to the potential for truly multimodal stationary phases. This review attempts to summarize the state-of-the-art about SCIL phases including their preparation, chromatographic behavior, and analytical performance.     

High temperature and highly selective stationary phases of ionic liquid bonded polysiloxanes for gas chromatography

Due to the special performance of “dual nature” and synthetic flexibility, ionic liquids (ILs) have been an attractive research subject of stationary phases for gas chromatography (GC). In this work, a novel ionic liquid (IL) bonded polysiloxane ([PSOMIM][NTf₂]) with anion of bis-trifluoromethanesulfonylimide (NTf₂⁻) was synthesized, and another one with chloride anion ([PSOMIM][Cl]) was also prepared for the purpose of comparison. The thermo-stability of the product was evaluated by thermogravimetric (TG) test and the result indicated that [PSOMIM][NTf₂] did not decompose slightly until 380 °C. Then the solvation behaviors of the ILs were characterized using solvation parameter model. Subsequently, [PSOMIM][NTf₂] and [PSOMIM][Cl] were used as stationary phases to prepare capillary columns for GC, respectively. The column efficiency of [PSOMIM][NTf₂] column was 4776 plates/m (k = 3.64 ± 0.08, naphthalene), and that of the other one was 3170 plates/m (k = 2.84 ± 0.11, naphthalene). The selectivity of the novel stationary phases for analytes, including Grob reagent, aromatic positional isomers was further evaluated. Furthermore, the chromatograms of n-alkanes and polycyclic aromatic hydrocarbons (PAHs) on [PSOMIM][NTf₂] column were compared with that on [PSOMIM][Cl] column. [PSOMIM][NTf₂] stationary phase also exerted good selectivity for fatty acid methyl esters (FAMEs), polychlorinated biphenyls (PCBs) and aromatic amines.     

Increasing selectivity in comprehensive three-dimensional gas chromatography via an ionic liquid stationary phase column in one dimension

Recent advances in improving the selectivity and performance for a comprehensive, three-dimensional (3D) gas chromatograph (GC³) instrument are described. With GC³, two six-port diaphragm valves are utilized as the interfaces between three, in-series capillary columns housed in a standard GC instrument fitted with a high data acquisition rate flame ionization detector (FID). Modulation periods for sampling from one column to the next are set so that sufficient slices (i.e., modulations) are acquired by the subsequent dimension resulting in comprehensive data. We present GC³ instrumentation with significantly higher 3D peak capacity than previously reported. An average peak capacity production (i.e., per time) of 180 resolved peaks per minute was experimentally achieved for three representative analytes in a 3D diesel sample separation. This peak capacity production is about 4 times higher than our previous report. We also demonstrate the significant benefit of the added chemical selectivity of the three column GC³ instrument relative to a two column GC × GC instrument, in which one of the three columns is a triflate ionic liquid stationary phase column with a high selectivity for phosphonated compounds (i.e., di-methyl-methyl phosphonate, di-ethyl-methyl phosphonate and di-isopropyl-methyl phosphonate). Using all three separation dimensions, the 2D separation fingerprint of a diesel sample is simultaneously obtained along with selective information regarding the phosphonated compounds in the diesel samples in the additional dimension.     

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.     

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.     

Reduction of silanophilic interactions in liquid chromatography with the use of ionic liquids

A suppression of silanophilic interactions by the selected ionic liquids added to the mobile phase in thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) is reported. Acetonitrile was used as the eluent, alone or with various concentrations of water and phosphoric buffer pH 3. Selectivity of the normal (NP) and the reversed (RP) stationary phase material was examined using a series of proton-acceptor basic drugs analytes. The ionic liquids studied appeared to significantly affect analyte retention in NP-TLC, RP-TLC and RP-HPLC systems tested. Consequently, the increased separation selectivity was attained. Due to ionic liquid additives to eluent even analytes could be chromatographed, which were not eluted from the silica-based stationary phase materials with 100% of acetonitrile in the mobile phase. Addition of ionic liquid already in very small concentration (0.5%, v/v) could reduce the amount of acetonitrile used during the optimization of basic analytes separations in TLC and HPLC systems. Moreover, the influence of temperature on the separation of basic analytes was demonstrated and considered in practical HPLC method development.     

Selective extraction of CO2 from simulated flue gas using polymeric ionic liquid sorbent coatings in solid-phase microextraction gas chromatography

The CO₂ selectivity of two polymeric task-specific ionic liquid sorbent coatings, poly(1-vinyl-3-hexylimidazolium) bis[(trifluoromethyl)sulfonyl]imide [poly(VHIM-NTf₂)] and poly(1-vinyl-3-hexylimidazolium) taurate [poly(VHIM-taurate)], was examined using solid-phase microextraction (SPME) for the determination of CO₂ in simulated flue gas. For comparison purposes, a commercial SPME fiber, Carboxen™-PDMS, was also studied. A study into the effect of humidity revealed that the poly(VHIM-taurate) fiber exhibited enhanced resistance to water, presumably due to the unique mechanism of CO₂ capture. The effect of temperature on the performance of the PIL-based and Carboxen fibers was examined by generating calibration curves under various temperatures. The sensitivity, linearity, and linear range of the three fibers were evaluated. The extraction of CH₄ and N₂ was performed and the selectivities of the PIL-based and Carboxen fibers were compared. The poly(VHIM-NTf₂) fiber was found to possess superior CO₂/CH₄ and CO₂/N₂ selectivities compared to the Carboxen fiber, despite the smaller film thicknesses of the PIL-based fibers. A scanning electron microscopy study suggests that the amine group of the poly(VHIM-taurate) is capable of selectively reacting with CO₂ but not CH₄ or N₂, resulting in a significant surface morphology change of the sorbent coating.     

Determination of water pollutants by direct-immersion solid-phase microextraction using polymeric ionic liquid coatings

The determination of a group of eighteen pollutants in waters, including polycyclic aromatic hydrocarbons and substituted phenols, is conducted in direct-immersion solid-phase microextraction (SPME) using the polymeric ionic liquid (PIL) poly(1-vinyl-3-hexadecylimidazolium) bis[(trifluoromethyl)sulfonyl]imide as a novel coating material. The performance of the PIL fiber coating in the developed IL-SPME-gas chromatography (GC)–mass spectrometry (MS) method is characterized by average relative recoveries of 92.5% for deionized waters and 90.8% for well waters, average precision values (as relative standard deviations, RSD%) of 11% for deionized waters and 12% for well waters, using a spiked level of 5 ng mL⁻¹. The detection limits oscillate from 0.005 ng mL⁻¹ for fluoranthene to 4.4 ng mL⁻¹ for 4-chloro-3-methylphenol, when using an extraction time of 60 min with 20 mL of aqueous sample. The extraction capabilities of the PIL fiber have been compared with the commercial SPME coatings: polydimethylsyloxane (PDMS) 30 μm, PDMS 100 μm and polyacrylate (PA) 85 μm. The PIL fiber is superior to the PDMS 30 μm for all analytes studied. A qualitative study was also carried out to compare among the nature of the coating materials by normalizing the coating thickness. The PIL material was shown to be more efficient than the PDMS material for all analytes studied. The PIL coating was also adequate for nonpolar analytes whereas the PA material was more sensitive for polar compounds.     

Role of counteranions in polymeric ionic liquid-based solid-phase microextraction coatings for the selective extraction of polar compounds

A polymeric ionic liquid (PIL) poly(1-vinyl-3-hexylimidazolium chloride) (poly(ViHIm⁺Cl⁻)) was designed as a coating material for solid phase microextraction (SPME) to extract polar compounds including volatile fatty acids (VFAs) and alcohols. The extracted analytes were analyzed by using gas chromatography (GC) coupled with flame ionization detection (FID). Extraction parameters of the HS–SPME–GC–FID method, such as ionic strength, extraction temperature, pH and extraction time were optimized. Calibration studies were carried out under the optimized conditions to further evaluate the performance of the PIL-based SPME coating. For comparison purposes, the PIL poly(1-vinyl-3-hexylimidazolium bis[(trifluoromethyl)sulfonyl]imide) (poly(ViHIm⁺NTf₂⁻)) was also used as the SPME coating to extract the same analytes. The results showed that the poly(ViHIm⁺Cl⁻) PIL coating had higher selectivity towards more polar analytes due to the presence of the Cl⁻ anion which provides higher hydrogen bond basicity than the NTf₂⁻ anion. The limits of detection (LODs) determined by the designed poly(ViHIm⁺Cl⁻) PIL coating ranged from 0.02 μg L⁻¹ for octanoic acid and decanoic acid and 7.5 μg L⁻¹ for 2-nitrophenol, with precision values (as relative standard deviation) lower than 14%. The observed performance of the poly(ViHIm⁺Cl⁻) PIL coating was comparable to previously reported work in which commercial or novel materials were used as SPME coatings. The selectivity of the developed PIL coatings was also evaluated using heptane as the matrix solvent. This work demonstrates that the selectivity of PIL-based SPME coatings can be simply tuned by incorporating different counteranions to the sorbent coating.     

Determination of chlorophenols in red wine using ionic liquid countercurrent chromatography as a new pretreatment method followed by high‐performance liquid chromatography

A countercurrent chromatography method for the enrichment and cleanup of chlorophenols from food samples was successfully established by using an ionic‐liquid‐modified two‐phase solvent system composed of dichloromethane containing 2% 1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide and water. The column was firstly filled with the organic stationary phase, and then a large volume of sample was pumped into the column after it was equilibrated with pure water at the rotation speed. Finally, the trace amounts of chlorophenols extracted and enriched in the stationary phase were eluted out by an alkaline mobile phase and determined by high‐performance liquid chromatography. Under optimized conditions, the enrichment and cleanup of the chlorophenols can be fulfilled online with enrichment factors (34–65) and high recoveries (84.69–95.23%). The method has been applied to the determination of chlorophenols in real red wine samples with the limits of detection in the range of 1.89–4.21 μg/L. The present method is highly suitable for the pretreatment of large volume of aqueous sample for the determination of trace amounts of contaminants in food and environmental samples.     

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.     

Solubility of carbon dioxide in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

In this work, the phase behaviour of the binary system of carbon dioxide and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf₂N]) has been studied experimentally. The equipment used for the experiments is the Cailletet set-up, based on visual observations of phase transitions of systems with constant overall composition. Results are reported for carbon dioxide concentrations ranging from 12.3 to 59.3 mol%, and within temperature and pressure ranges of 310–450 K and 0–15 MPa, respectively. The data reveal an extremely high capacity of the selected ionic liquid for dissolving CO₂ gas, for example, reaching up to about 60 mol% within the above-mentioned pressure and temperature range. Also, the solubility of CO₂ in the ionic liquid [emim][Tf₂N] is compared to the solubility of CO₂ in the ionic liquid [emim][PF₆], an ionic liquid that shares the same cation.