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The enantiomeric excess of chiral starting materials is one of the important factors determining the enantiopurity of products in asymmetric synthesis. Fifty‐one commercially available chiral reagents used as building blocks, catalysts, and auxiliaries in various enantioselective syntheses were assayed for their enantiomeric purity. The test results were classified within five impurities level (ie, <0.01%, 0.01%‐0.1%, 0.1%‐1%, 1%‐10%, >10%). Previously from 1998 to 2013, several reports have been published on the enantiomeric composition of more than 300 chiral reagents. This series of papers is necessitated by the fact that new reagents are forthcoming and that the enantiomeric purity of the same reagent can vary from batch to batch and/or from supplier to supplier. This report presents chiral liquid chromatography (LC) and gas chromatography (GC) methods to separate enantiomers of chiral compounds and evaluate their enantiomeric purities. The accurate and efficient LC analysis was done using newly introduced superficially porous particle (SPP 2.7 μm) based chiral stationary phases (TeicoShell, VancoShell, LarihcShell‐P, and NicoShell). [ABSTRACT FROM AUTHOR]

Twelve bis- or dicationic ionic liquids (ILs) including eight based on imidazolium, a single one based on phosphonium, and three based on pyrrolidinium cationic units were prepared with the bis(trifluoromethyl sulfonyl) imide anion. The two identical cationic moieties were attached by different alkyl spacers having three or five carbons and differing alkyl substituents attached to the spacer. The SLB-IL111 column, as the most polar commercial stationary phase known, was included in the study for comparison. Isothermal separations of a rapeseed oil fatty acid methyl ester (FAME) sample were used to study and compare the 12 IL-based column performances and selectivities. The retention times of the most retained methyl esters of lignoceric (C24:0) and erucic (C22:1) acids were used to estimate the IL polarity. The phosphonium dicationic IL column was, by far, the least polar. Imidazolium-based dicationic IL columns were the most polar. Polarity and selectivity for the FAME separation were somewhat related. The separation of a 37-FAME standard mixture allowed the investigation of selectivity variations observed on the 12 IL-based columns under temperature gradients up to 230 °C. The remarkable selectivity of the IL-based columns is demonstrated by the detailed analysis of the cis/trans C18:1 isomers of a partially hydrogenated vegetable oil sample on 30-m columns, separations competing with that done following an “official method” performed on a 100-m column.Separation of fatty acid methyl esters on a 30-m 3m2C5(mpy)2. 2NTf2 branched-chain dicationic IL-based column. Branched chain dicationic ILs show great selectivity for separation of cis/trans, ω-3/ω-6, and detailed analysis of cis/trans fats. [ABSTRACT FROM AUTHOR]

Abstract: The analysis of topiramate in the presence of its main degradation products is challenging due to the absence of chromophore moieties and their wide range of polarity. Mixed‐mode chromatography has been used in such cases because it combines two or more modes of separation. Charged aerosol detector is also an alternative since its detection is independent of optical properties and analyte ionization. This study is aimed to develop and validate two new stability‐indicating methods by high‐performance liquid chromatography for the main degradation products of topiramate using mixed‐mode chromatography and a charged aerosol detector. Method 1 employed an Acclaim Trinity P1® column (3.0 mm × 150 mm, 2.7 μm) with a mobile phase comprising of 80% ammonium acetate buffer (20 mM, pH 4.0) and 20% methanol at a flow rate of 0.5 mL/min at 35°C. Method 2 utilized a C18 Acclaim 120® column (4.6 mm × 250 mm; 5 μm) with ACN/water (50:50) at a flow rate of 0.6 mL/min at 50°C. Validation of the two methods demonstrated excellent performance with respect to linearity, precision, accuracy, and selectivity. The limits of detection for topiramate, fructose, sulfate, sulfamate, and compound A were 2.97, 12.08, 4.02, 13.91, and 3.94 μg/mL, respectively. [ABSTRACT FROM AUTHOR]

A headspace gas chromatography (HSGC) method was developed for the determination of water content in honey. This method was shown to work with five different honey varieties which had a range of water from 14–16%. It also utilised two different detectors, the thermal conductivity detector (TCD) and the barrier discharge ionisation detector (BID). This method needs no heating pretreatment step as in the current leading method, (i.e. the measurement of refractive index). The solvent-free procedure negates the possibility of solvent–compound interactions as well as solubility limitations, as is common with Karl Fischer titrations. It was also apparent that the classic loss on drying method consistently and substantially produced results that were lower than the correct values. This approach is shown to be rapid, with an analysis time of 4 min when using the TCD detector and under 3 min when utilising the BID detector. HSGC is feasible for the determination of water due to the new PEG-linked geminal dicationic ionic-liquid-coated GC capillary column. In addition it provides accurate and precise determinations of the water content in honey. When using the sensitive BID detector, other trace volatile compounds are observed as well. [ABSTRACT FROM AUTHOR]

A rapid, accurate, and precise headspace gas chromatographic (HSGC) analytical method was developed for the detection and quantification of water in drug products. The analysis is able to be performed in 10 min and automated. The HSGC method used an ionic liquid (IL) based open tubular capillary gas chromatographic column to increase the ruggedness of this method and provide improved peak shapes for water. Due to the ionic liquids low vapor pressure, unique physiochemical properties, and high thermal stability, they also make idea solvents for HSGC. Unlike Karl Fischer titration methods, this HSGC method is not affected by side reactions. The developed method was shown to be broadly applicable. The water content in 12 different samples was found to range from 1%-7% water. The use of HSGC was highly sensitive and only required 10 mg of sample. In addition, it was found to have greater precision and accuracy than Karl Fischer titration and greater precision and speed than loss on drying. [ABSTRACT FROM AUTHOR]

An important step during the development of high-performance liquid chromatography (HPLC) methods for quantitative analysis of drugs is choosing the appropriate detector. High sensitivity, reproducibility, stability, wide linear range, compatibility with gradient elution, non-destructive detection of the analyte and response unaffected by changes in the temperature/floware some of the ideal characteristics of a universal HPLC detector. Topiramate is an anticonvulsant drug mainly used for the treatment of different types of seizures and prophylactic treatment of migraine. Different analytical approaches to quantify topiramate by HPLC have been described because of the lack of chromophoric moieties on its structure, such as derivatization with fluorescent moieties and UV-absorbing moieties, conductivity detection, evaporative light scattering detection, refractive index detection, chemiluminescent nitrogen detection and MS detection. Some methods for the determination of topiramate by capillary electrophoresis and gas chromatography have also been published. This systematic review provides a description of the main analytical methods presented in the literature to analyze topiramate in the drug substance and in pharmaceutical formulations. Each of these methods is briefly discussed, especially considering the detector used with HPLC. In addition, this article presents a review of the data available regarding topiramate stability, degradation products and impurities. [ABSTRACT FROM AUTHOR]

The analysis of Bulgarian and Turkish Rosa damascena Miller essential oils was performed by flow-modulated comprehensive two-dimensional gas chromatography using simultaneous detection of the second column effluent by flame ionization and quadrupole mass spectrometric detection. Enantioselective separations were obtained by running the samples on 2,3-di- O-ethyl-6- O- tert-butyldimethylsilyl-β-cyclodextrin column as the first column and on polyethylene glycol as the second column. The determination of enantiomeric or diastereomeric excess of some terpenoic solutes is a possible route for quality or authenticity control as well as for the elucidation of the country of origin. [ABSTRACT FROM AUTHOR]

• Hyphenation of gas chromatography with multiple spectroscopic techniques is discussed. • The interfaces for different methods are shown. • The advantages and challenges of each combination are mentioned. • Commercialized instruments are introduced. Gas chromatography has always been a simple and widely used technique for the separation of volatile compounds and their quantitation. However, the common detectors used with this technique are mostly universal and do not provide any specific qualitative information. There have been some attempts to combine the separation power of GC with the qualitative capabilities of "high-information" spectroscopic techniques including infrared spectroscopy, nuclear magnetic resonance spectroscopy, molecular rotational resonance spectroscopy, and vacuum ultraviolet spectroscopy. Some of these hyphenations have proven to be quite successful while others were less so. The history of such attempts, up to the most recent studies in this area, are discussed. Most recently, the hyphenation of GC with molecular rotational resonance spectroscopy which provides promising results and is a newly developed technique is reviewed and compared to previous high-information spectroscopic detection approaches. The history, description and features of each method along with their applications and challenges are discussed. [ABSTRACT FROM AUTHOR]

4,6-Di-O-pentyl-3-O-trifluoroacetyl cycloinulohexaose (DP-TA-CF6) and 4,6-di-O-pentyl-3-O-propionyl cycloinulohexaose (DP-PN-CF6) were synthesized and used as chiral stationary phases (CSPs) in gas chromatography (GC). The chiral recognition ability of the two CSPs was investigated. A total of 47 racemic compounds were separated on the two new CSPs, including derivatized amino acids, amino alcohols, amines, alcohols, tartrates and lactones. Interestingly, several analytes were only separated on either the DP-TA-CF6 or the DP-PN-CF6 phase. The chiral recognition mechanism was evaluated through thermodynamic analysis. The result indicated there was no inclusion complex formation involved in the chiral recognition process. [ABSTRACT FROM AUTHOR]

Solid-phase microextraction (SPME) with an ionic liquid (IL) coating was developed for headspace extraction of a group of low molecular weight alcohols (ethanol, n-propanol, butanol, and isopropyl alcohol), acetone, ethyl acetate, and acetonitrile. A first SPME fiber was simply coated with a dedicated IL whose synthesis is described. A second SPME fiber was prepared by gluing silica (Si) particles on which the synthesized IL was chemically bonded. The analytes SPME extraction was optimized for time, temperature, and NaCl salting out content. The headspace extracted analytes were determined by simple temperature desorption into the hot injection port of a gas chromatograph. The coated-IL fiber did not have enough extracting material to be useful. The bonded-IL-Si particle fiber had much more extracting material. Its analytical capabilities were compared to those of two commercially available fibers. The extraction yields of the bonded-IL-Si fiber were inferior to those of the two commercial fibers because they contained a significantly higher amount of extracting material. The linear concentration range could reach up to 120 μg/mL. The recoveries, trueness, and precision (RSD) were in the 97.4-109.5%, 0.1-9.5%, and 0.7-16.5 ranges, respectively. The bonded-IL-Si fiber showed a specific affinity for ethanol giving an ethanol peak height equal or greater than that of the two commercial fibers tested with the same sample. [ABSTRACT FROM AUTHOR]

The development of new GC column stationary phase strategies has been lacking over the past two decades. This situation has changed with the advent of ionic liquids (ILs) in viable GC column formats. Extensive R&D over the last ten years has focused on the properties and uses of ILs in analytical formats. This article discusses the unique properties of ILs and their potential impact as GC stationary phases. Their important role in current and future separations is described. [ABSTRACT FROM AUTHOR]

A high-temperature ionic liquid, trihexyl(tetradecyl)phosphonium bis(trifluoromethane)sulfonamide, was used as the primary column stationary phase for comprehensive two-dimensional gas chromatography (GC × GC). The ionic liquid (IL) column was coupled to a 5% diphenyl/95% dimethyl polysiloxane (HP-5) secondary column. The retention characteristics of the IL column were compared to polyethylene glycol (DB-Wax) and 50% phenyl/50% methyl polysiloxane (HP-50+). A series of homologous compounds that included hydrocarbons, oxygenated organics, and halogenated alkanes were analyzed with each column combination. This comparison showed that the ionic liquid is less polar than DB-Wax but more polar than HP-50+. The most unique feature of the IL × HP-5 column combination is that alkanes, cyclic alkanes, and alkenes eluted in a narrow band in the GC × GC chromatogram; whereas, these compounds occupied a much larger portion of the DB-Wax × HP-5 and the HP-50+ × HP-5 chromatograms. Each column combination was used to analyze diesel fuel. The IL × HP-5 chromatogram displayed narrow bands for three major compound classes in diesel fuel: saturates, monoaromatics, and diaromatics. The IL column was used at temperatures as high as 290 °C for several months without any noticeable changes in column performance. [ABSTRACT FROM AUTHOR]

It is known that room-temperature ionic liquids (RTILs) have wide applicability in many scientific and technological fields. In this work, a series of three new dicationic room-temperature ionic liquids functionalized with poly(ethylene glycol) (PEG) linkages were synthesized and characterized via a linear solvation model. The application of these ILs as new GC stationary phases was studied. The efficient separation of several mixtures containing compounds of different polarities and 24 components of a flavor and fragrance mixture indicated comparable or higher resolving power for the new IL stationary phases compared to the commercial polysiloxane and poly(ethylene glycol)-based stationary phases. In addition, the selectivities of the IL stationary phases could be quite unique. The separation of a homologous alkane and alcohol mixture displayed the “dual nature” of these ionic liquids as GC stationary phases. The thermal stability study showed the column robustness up to 350 °C. The high separation power, unique selectivity, high efficiency and high thermal stability of the new dicationic ionic liquids indicate that they may be applicable as a new type of robust GC stationary phase. [ABSTRACT FROM AUTHOR]

Boromycin is a macrodiolide that exists as a hydrophobic Böeseken complex formed from boric acid and a chiral polyhydroxy macrocyclic ligand. It was covalently bonded to silica gel through a urea linkage to an attached D-valine ester. When evaluated as a chiral stationary phase, it shows pronounced enantioselectivity toward primary amine-containing racemates, separating 98% of those tested. The selectivity is most pronounced in the presence of organic solvents and supercritical CO2 + methanol. The enantioselective binding site and mechanistic factors are examined. Analytes can be complexed as either the free base or their protonated analogues, with the free base being more strongly associated with the chiral selector. [ABSTRACT FROM AUTHOR]

The seeming “dual nature” of ionic liquids (ILs) for separating both apolar and polar compounds suggests that ILs may have a great potential for complex samples like essential oils from herbal plants that contain a great variety of compounds. In the present work, a geminal dicationic IL, 1,9-di(3-vinylimidazolium)nonane bis[(trifluoromethyl)sulfonyl]imidate, was investigated for this purpose. To find the best way to achieve satisfactory separations simultaneously for the compounds in essential oils, the dicationic IL was used as the stationary phase for capillary gas chromatography (GC) in two ways, either in its pure state or as a mixed stationary phase with monocationic ILs and a polysiloxane diluent. Interestingly, it was found that the mixed stationary phase exhibited a much better selectivity for polar and nonpolar compounds than either the dicationic IL or the polysiloxane, suggesting that a kind of synergistic effect occurred when these stationary phases were combined in the way described. A comparison with two commercial stationary phases (polar and nonpolar) indicated that this novel mixed stationary phase behaved in a way closer to a polar stationary phase in terms of selectivity and elution order. The present work demonstrates that the mixed stationary phase is efficient and selective and can be an alternative choice for the GC analysis of samples of complex composition. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) are a class of nonmolecular solvents in which the cation/anion combination can be easily tuned to provide desired chemical and physical properties. When used as stationary phases in gas-liquid chromatography, ionic liquids exhibit dual nature retention selectivity. That is, they are able to separate polar molecules such as a polar stationary phase and nonpolar molecules such as a nonpolar stationary phase. However, issues such as optimization of the wetting ability of the ionic liquid on fused-silica capillaries, the maximum operating temperatures of the stationary phases, and nonuniform film thickness on the wail of the capillary at high temperatures have limited theft use in gas chromatography. As described in this paper, these limitations are overcome by cross-linking a new class of ionic liquid monomers by free radical reactions to provide a more durable and robust stationary phase. By lightly cross-linking the ionic liquid stationary phase using a small amount of free radical initiator, high-efficiency capillary columns were produced that are able to endure high temperatures with little column bleed. Two types of cross-linked IL stationary phases are developed. A partially cross-linked stationary phase allows for high-efficiency separations up to temperatures of ∼280 °C. However, by creating a more highly cross-linked stationary phase of geminal dicationic ILs, exclusively, an increase in efficiency is observed at high temperatures allowing for its use over 350 °C. In addition, through the use of solvation thermodynamics and interaction parameters, it was shown that the cross-linking/immobilization of the ionic liquid does not affect the selectivity of the stationary phase thereby preserving its dual nature retention behavior. [ABSTRACT FROM AUTHOR]

A versatile method for measuring the partition coefficients of volatile analytes with an aqueous pseudophase using headspace gas chromatography is reported. A “three-phase” model accounts for all equilibria present in the system, including the partitioning of the analyte in the gas and aqueous phases to the pseudophase. This method is applicable to a wide variety of volatile analytes and aqueous pseudophases, providing that sufficient pseudophase may be used to reduce the analyte partial pressure. Generally, the method offers good reproducibility and high sensitivity. The associations of five volatile analytes (hydrogen sulfide, methanethiol, dimethyl sulfide, dichloromethane, and ethyl ether) with various cyclodextrins were examined. All analytes were found to partition preferentially to the cyclodextrin pseudophase compared to the aqueous phase. In addition, several analyte–cyclodextrin combinations formed insoluble complexes in solution that enhanced the extraction of the analyte from the gas and aqueous phases. Derivatization of the cyclodextrins generally decreased the extent of analyte–cyclodextrin interaction. [ABSTRACT FROM AUTHOR]

Room-temperature ionic liquids are a class of nonmolecular ionic solvents with low melting points. Their properties have the potential to be especially useful as stationary phases in gas-liquid chromatography (GLC). A series of common ionic liquids were evaluated as GLC stationary phases. It was found that many of these ionic liquids suffer from low thermal stability and possess unfavorable retention behavior for some classes of molecules. Two new ionic liquids were engineered and synthesized to overcome these drawbacks. The two new ionic liquids (l-benzyl-3-methylimidazolium trifluoromethanesuffonate and 1-(4-methoxyphenyl)-3-methylimidazolium trifiuoromethanesulfonate) are based on "bulky" imidazolium cations with trifluoromethanesuffonate anions. Their solvation characteristics were evaluated using the Abraham solvation parameter model and correlations made between the structure of the cation and the degree to which the ionic liquids retain certain analytes. The new ionic liquids have good thermal stability up to 260 °C, provide symmetrical peak shapes, and because of their broad range of solvation-type interactions, exhibit dualnature selectivity behavior. In addition, the ionic liquid stationary phases provided different retention behavior for many analytes compared to a commercial methylphenyl polysiloxane GLC stationary phase. This difference in selectivity is due to the unique solvation characteristics of the ionic liquids and makes them very useful as dualnature GLC stationary phases. [ABSTRACT FROM AUTHOR]

The authors would like to call the reader’s attention to the fact that the original publication included some corrections needed to be addressed. [ABSTRACT FROM AUTHOR]

The article focuses on the multidimensional separations. Topics discussed include several techniques used to separate complex samples, such as planar chromatographic and slab gel electrophoresis, comprehensive 2D chromatography, and development and use of multidimensional gas chromatography and liquid chromatography. Also mentioned are proteomics, petroleomics, and lipidomics.

Most peak shapes obtained in separation science depart from linearity for various reasons such as thermodynamic, kinetic, or flow based effects. An indication of the nature of asymmetry often helps in problem solving e.g. in column overloading, slurry packing, buffer mismatch, and extra-column band broadening. However, existing tests for symmetry/asymmetry only indicate the skewness in excess (tail or front) and not the presence of both. Two simple graphical approaches are presented to analyze peak shapes typically observed in gas, liquid, and supercritical fluid chromatography as well as capillary electrophoresis. The derivative test relies on the symmetry of the inflection points and the maximum and minimum values of the derivative. The Gaussian test is a constrained curve fitting approach and determines the residuals. The residual pattern graphically allows the user to assess the problematic regions in a given peak, e.g., concurrent tailing or fronting, something which cannot be easily done with other current methods. The template provided in MS Excel automates this process. The total peak shape analysis extracts the peak parameters from the upper sections (> 80% height) of the peak rather than the half height as is done conventionally. A number of situations are presented and the utility of this approach in solving practical problems is demonstrated. [ABSTRACT FROM AUTHOR]

Highlights: [•] Headspace GC with ionic liquids diluent could evaluate water content in 4mg samples. [•] Water content was determined for 22 active pharmaceutical ingredients. [•] 2 different highly efficient GC detectors, thermal conductivity detection and the new barrier ionization detector were utilized. [Copyright &y& Elsevier]

Abstract: Ionic liquids (ILs) are used to dissolve ionic cyclodextrin (CD) derivatives to produce a new type of gas chromatographic chiral stationary phase. Compared to a previous study with neutral cyclodextrin chiral selectors, the new ionic liquid-based stationary phase exhibits broader enantioselectivities, up to seven times higher efficiencies, and greater thermal stabilities. When compared to the analogous commercial column with polysiloxane matrix, it exhibits different enantioselectivities, more symmetric peak shapes and some complementary enantioseparations. The most profound separation enhancements are usually found for more polar analytes. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Recently, it has been found that room-temperature ionic liquids can be used as stable, unusual selectivity stationary phases. They show "dual nature" properties, in that they separate nonpolar compounds as if they are nonpolar stationary phases and separate polar compounds as if they are polar stationary phases. Extending ionic liquids to the realm of chin! separations can be done in two ways: (1) a chiral selector can be dissolved in an achiral ionic liquid, or (2) the ionic liquid itself can be chiral. There is a single precedent for the first approach, but nothing has been reported for the second approach. In this work, we present the first enantiomeric separations using chiral ionic liquid stationary phases in gas chromatography. Compounds that have been separated using these ionic liquid chiral selectors include alcohols, diols, sulfoxides, epoxides, and acetylated amines. Because of the synthetic nature of these chiral selectors, the configuration of the stereogenic center can be controlled and altered for mechanistic studies and reversing enantiomeric retention. [ABSTRACT FROM AUTHOR]

The separation of deuterated compounds from their protiated counterparts is essential in areas of drug discovery and development, investigating kinetic isotope effects and quantitative methods of non-mass spectrometry-based stable isotope dilution assay (non-MS SIDA). The separations of 47 isotopologue pairs of common compounds and drugs were achieved by gas-liquid chromatography, employing twelve different stationary phases. Polydimethylsiloxane phase, phenyl substituted polydimethylsiloxane phases, wax phases, ionic liquid phases, and chiral stationary phases were selected to encompass a wide polarity range and diverse chemical interactions. The best-performing stationary phases are presented for separation of protic-polar, aprotic-dipolar, nonpolar analytes. Overall, the IL111i, SPB-20, and PAG stationary phases were remarkable in their ability to separate the isotopologues. The isotope effect was also evaluated. It was observed that nonpolar stationary phases often exhibit an inverse isotope effect in which heavier isotopic compounds elute earlier than their lighter counterparts. Conversely, polar stationary phases often show a normal isotope effect, while those of intermediate polarities can show both effects depending on the isotopologues. The location of deuterium atoms, however, affects isotopologue retention times. Deuterium substituted aliphatic groups appear to have a greater inverse isotope effect on retention than aromatic substituents. [Display omitted] • Polarity of the stationary phase plays an important role in separation of isotopologues. • IL111i, SPB-20 and PAG were the best performing columns in this study. • IL111i columns showed normal isotope effect for all separations. • The position of deuterium atoms plays an important role in the separations. [ABSTRACT FROM AUTHOR]

Abstract Dicationic ionic liquids (DILs) are more and more accepted as a new class of high temperature and polar stationary phases for gas chromatography (GC). This study deals with the effect of seven different fluorosulfonyl derivatized anions associated with two dications: 1,3-di(3-methylimidazolium)-2-methylpropane [2mC 3 (mim) 2 ], and 1,3-di(3-methylimidazolium)-isobutene [i-eneC 4 (mim) 2 ]. Thermophysical properties of the 14 synthesized DILs were evaluated in terms of melting point, viscosity, and thermal stability. The optimal physicochemical properties of 13 DILs allowed preparing 13 GC capillary columns. Accordingly, the polarity and selectivity of the DILs were evaluated by determining the Rohrschneider-McReynolds constants and the equivalent chain lengths of C18 fatty acid methyl esters (FAMEs). The symmetrical fluoroalkylsulfonyl and the trifluorosulfonate anions seem to produce the most polar DILs. Compared to classical polyethyleneglycol phases, the DILs showed substantially decreased retention of apolar compounds and a much stronger retention of the polar ones. Unique selectivities were observed with unsaturated FAMEs, polyaromatic hydrocarbons, and bacterial specific FAMEs. The two applications presented included a biodiesel and bacterial FAME analyses. Graphical abstract Image 1 Highlights • 14 newly synthesized dicationic ionic liquids varying by the anion. • A McReynolds polarity passing 6000 or polarity number of 143. • Strong selectivity differences between polar and apolar solutes. • Anthracene eluting BEFORE phenanthrene showing unique shape selectivity. [ABSTRACT FROM AUTHOR]

Highlights: [•] Informal entropy is used to assess distribution of sample components in GC×GC. [•] Individual column flows and a temperature rate are optimized for GC×GC separations. [•] Maximum informal entropy corresponds to maximum distribution of solutes in GC×GC. [ABSTRACT FROM AUTHOR]

Highlights: [•] Study of the data acquisition frequency (DAF) of qMSD on the GC×GC analysis. [•] Quality of the mass spectra drops with an increase of DAF. [•] The sensitivity of the method decreases with an increase of DAF. [•] LOD and LOQ increase with an increase of DAF. [ABSTRACT FROM AUTHOR]

Highlights: [•] The use of ionic liquid capillary columns, SLB-IL100 and SLB-IL111 for GC×GC. [•] GC×GC analysis by simultaneous monitoring of 2D effluent by FID and qMSD. [•] GC-FID, GC-qMSD, GC×GC-FID and GC×GC-qMSD analysis of BTEX. [ABSTRACT FROM AUTHOR]

Abstract: Flow-modulated comprehensive two-dimensional gas chromatography with simultaneous monitoring of the separation by flame ionization (GC×GC-FID) and quadrupole mass spectrometric (GC×GC-qMSD) detection was studied for the analysis of gasoline and kerosene samples. The acquisition frequency of the FID was 100Hz and of the qMSD 18Hz for the mass range m/z 40–300. The instrumental set-up is such that both one-dimensional (GC-FID and GC-qMSD) and two-dimensional separations using the same working conditions can be performed. Gasoline and kerosene samples were analyzed on the column combination HP-5MS (1D)+HP INNOWax (2D). Three modulated peaks were obtained for each hydrocarbon present above 0.1% with ca. 300ms peak width at the base using 6 s modulation times. Modulated peaks in GC×GC-FID were thus characterized by ca. 30 points while those in GC×GC-qMSD method by 6–8 points only. The FID speed is sufficient for reliable quantitative analysis, while the qMSD scan speed is perfectly appropriate for identification purposes. Moreover, in the GC×GC-qMSD method considerably improved quality of uncorrected spectra was obtained, arising from the enhanced separation over one-dimensional GC-MSD analysis. Spectral match qualities of up to 98% were found. [Copyright &y& Elsevier]

Abstract: Retentivity tuning in comprehensive two dimensional GC separations of aliphatics (linear and cyclic hydrocarbons) and aromatics in gasoline by changing the carrier gas flows in the column series at constant working temperature parameters of both columns is discussed. Comprehensive 2D techniques studied include GC×GC with cryogenic and differential flow modulation and non-modulated transfer (NMT). In all configurations, the first dimension was a non-polar column and the second dimension a polar column. Using three different flows (0.6, 1.0 and 1.4mL/min) of helium carrier gas in cryogenic modulated GC×GC illustrated that, as expected, retention of the solutes on the 1D and 2D columns increased but the separation quality was nearly constant. A change of carrier gas pressure (p m =175–125kPa) on the 1D and 2D columns joint point at constant inlet pressure (p i =525kPa) in NMT, induces an increase of the carrier gas flow rate on the 1D and a decrease on the 2D column, respectively. The higher retentivity of the 2D column improved the group type separation of aliphatic/cyclic hydrocarbons and aromatics and a higher distribution of aromatics on the 2D retention plane was noted. Retentivity tuning was also performed in flow modulated GC×GC by operating the 1D column at 0.8mL/min and the 2D column at 20 and 26mL/min. The higher retentivity at 20mL/min improved the group type separation of aliphatic/cyclic hydrocarbons and aromatics in the 2D retention plane. [Copyright &y& Elsevier]

Abstract: A total of 196 out of 209 polychlorobiphenyl (PCB) congeners were resolved using GC×GC–TOFMS with a non-polar/ionic liquid column series consisting of poly(50%-n-octyl-50%-methyl)siloxane and (1,12-di(tripropylphosphonium)dodecane bis(trifluoromethansulfonyl)amide) in the first and second dimension, respectively. It has been found that 13 PCB congeners overlap in five doublets (CB12+CB13, CB62+CB75, CB70+CB76, CB97+CB125 and CB153+CB168) and one triplet (CB90+CB101+CB113). All toxic, “dioxin like” congeners were separated with no interferences from any PCB congener. The 109 PCBs present in Aroclor 1242 and the 82 PCBs present in Aroclor 1260 were resolved GC×GC–TOFMS analysis on this column set. [ABSTRACT FROM AUTHOR]

Abstract: The orthogonality of three columns coupled in two series was studied for the congener specific comprehensive two-dimensional GC separation of polychlorinated biphenyls (PCBs). A non-polar capillary column coated with poly(5%-phenyl–95%-methyl)siloxane was used as the first (1D) column in both series. A polar capillary column coated with 70% cyanopropyl-polysilphenylene-siloxane or a capillary column coated with the ionic liquid 1,12-di(tripropylphosphonium)dodecane bis(trifluoromethane-sulfonyl)imide were used as the second (2D) columns. Nine multi-congener standard PCB solutions containing subsets of all native 209 PCBs, a mixture of 209 PCBs as well as Aroclor 1242 and 1260 formulations were used to study the orthogonality of both column series. Retention times of the corresponding PCB congeners on 1D and 2D columns were used to construct retention time dependences (apex plots) for assessing orthogonality of both columns coupled in series. For a visual assessment of the peak density of PCBs congeners on a retention plane, 2D images were compared. The degree of orthogonality of both column series was, along the visual assessment of distribution of PCBs on the retention plane, evaluated also by Pearson''s correlation coefficient, which was found by correlation of retention times t R,i,2D and t R,i,1D of corresponding PCB congeners on both column series. It was demonstrated that the apolar+ionic liquid column series is almost orthogonal both for the 2D separation of PCBs present in Aroclor 1242 and 1260 formulations as well as for the separation of all of 209 PCBs. All toxic, dioxin-like PCBs, with the exception of PCB 118 that overlaps with PCB 106, were resolved by the apolar/ionic liquid series while on the apolar/polar column series three toxic PCBs overlapped (105+127, 81+148 and 118+106). [Copyright &y& Elsevier]

Trigonal tricationic ionic liquids (ILs) are a new class of ILs that appear to be unique when used as gas chromatographic stationary phases. They consist of four core structures; (1) A = mesitylene core, (2) B = benzene core, (3) C = triethylamine core, and (4) D = tri(2-hexanamido)ethylamine core; to which three identical imidazolium or phosphonium cationic moieties were attached. These were coated on fused silica capillaries, and their gas chromatographic properties were evaluated. They were characterized using a linear solvation parameter model and a number of test mixtures. On the basis of the literature, it is known that both monocationic and dicationic ILs possess almost identical polarities, solvation characteristics, and chromatographic selectivities. However, some of the trigonal tricationic ILs were quite different. The different solvation parameters and higher apparent polarities appear to generate from the more rigid trigonal geometry of these Its, as well as their ability to retain the positive charges in relatively close proximity to one another in some cases. Their unique selectivities, retention behaviors, and separation efficiencies were demonstrated using the Grob mixture, a flavor and fragrance test mixture, alcohols/alkanes test, and FAME isomer separations. Two ILs C1 (methylimidazolium substitution) and C4 (2-hydroxyethylimidazolium substitution) had higher apparent polarities than any know IL (mono, di, and tricationic ILs) or commercial stationary phases. The tri(2-hexanamido)ethylamine core IL series proved to be very interesting in that it not only showed the highest separation efficiency for all test mixtures, but it also is the first IL stationary phase (containing NTf2- anions) that eliminates peak tailing for alcohols and other H-bonding analytes. The thermal stabilities were investigated using three methods: thermogravimetric analysis (TGA) method, temperature programmed gas chromatographic method (LPGC), and isothermal gas chromatographic method. The D core series had a high working temperature range, exceptional selectivities, and higher separation efficiencies than comparable polarity commercial columns. It appears that this specific type of multifunctional ILs may have the most promising future as a new generation of gas chromatographic stationary phases. [ABSTRACT FROM AUTHOR]

Trigonal tricationic ionic liquids (ILs) are a new class of ILs that appear to be unique when used as gas chromatographic stationary phases. They consist of four core structures; (1) A = mesitylene core, (2) B = benzene core, (3) C = triethylamine core, and (4) D = tri(2-hexanamido)ethylamine core; to which three identical imidazolium or phosphonium calionic moieties were attached. These were coated on fused silica capillaries, and their gas chromatographic properties were evaluated. They were characterized using a linear solvation parameter model and a number of test mixtures. On the basis of the literature, it is known that both monocationic and dicationic ILs possess almost identical polarities, solvation characteristics, and chromatographic selectivilies. However, some of the Irigonal tricalionic ILs were quite different. The different solvation parameters and higher apparent polarities appear to generate from the more rigid trigonal geometry of these ILs, as well as their ability to retain the positive charges in relatively close proximity to one another in some cases. Their unique selectivities, retention behaviors, and separation efficiencies were demonstrated using the Grob mixture, a flavor and fragrance test mixture, alcohols/alkanes test, and FAME isomer separations. Two ILs Cl (methylimidazolium substitution) and C4 (2-hydroxyethylimidazolium substitution) had higher apparent polarities than any know IL (mono, di, and tricationic ILs) or commercial stationary phases. The tri(2-hexanamido)ethylamine core IL series proved to be very interesting in that it not only showed the highest separation efficiency for all test mixtures, but it also is the first IL stationary phase (containing NTf2 anions) that eliminates peak tailing for alcohols and other H-bonding analytes. The thermal stabilities were investigated using three methods: thermogravimetric analysis (TGA) method, temperature programmed gas chromatographic method (TPGC), and isothermal gas chromatographic method. The D core series had a high working temperature range, exceptional selectivities, and higher separation efficiencies than comparable polarity commercial columns. It appears that this specific type of multifunctional ILs may have the most promising future as a new generation of gas chromatographic stationary phases. [ABSTRACT FROM AUTHOR]

Abstract: Fast GC separations of a broad range of analytes are demonstrated using a capillary column coated with a novel immobilized ionic liquid (IIL) stationary phase. Both completely cross-linked and partially cross-linked columns were evaluated, yielding ∼1600 and ∼2000 theoretical plates per meter, respectively. Enhanced separation is demonstrated using a dual-column ensemble comprised of an IIL column, a commercially coated Rtx-1 column, and a pneumatic valve connecting the inlet to the junction point between the two columns. Enhanced separation of 20 components, with two sets of co-eluting peaks is shown in ∼150s, while sacrificing only a length of time equivalent to the sum of the stop flow pulses, or about 15.5s. A novel application of a band trajectory model that shows band position as a function of analysis time as analytes move through the column ensemble is employed to determine pulse application times. The model predicts component retention times within a few seconds. Another method of selectivity enhancement of the IIL stationary phase-coated columns is demonstrated using a differential mobility spectrometer (DMS) that provides a second dimension separation based on ion mobility in a high-frequency electrical field. The DMS is able to separate all but one set of co-eluting components from the IIL column. The separation of 13 components found in the headspace above U.S. currency is demonstrated using the IIL column in a dual-column ensemble as well as with the DMS. [Copyright &y& Elsevier]

Abstract: The use of micelles in ionic liquid based gas-chromatography stationary phases was evaluated using equations derived for a “three-phase” model. This model allows the determination of all three partition coefficients involved in the system, and elucidates the micellar contribution to retention and selectivity. Four types of micellar-ionic liquid columns were examined in this study: 1-butyl-3-methylimidazolium chloride with sodium dodecylsulfate or dioctyl sulfosuccinate, and 1-butyl-3-methylimidazolium hexafluorophosphate with polyoxyethylene-100-stearyl ether or polyoxyethylene-23-lauryl ether. The partition coefficients were measured for a wide range of probe molecules capable of a variety of types and magnitudes of interactions. In general, most probe molecules preferentially partitioned to the micellar pseudophase over the bulk ionic liquid component of the stationary phase. Therefore, addition of surfactant to the stationary phase usually resulted in greater solute retention. It is also shown that the selectivity of the stationary phase is significantly altered by the presence of micelles, either by enhancing or lessening the separation. The effects of surfactant on the interaction parameters of the stationary phase are determined using the Abraham solvation parameter model. The addition of sodium dodecylsulfate and dioctyl sulfosuccinate to 1-butyl-3-methylimidazolium chloride stationary phases generally increased the phase''s hydrogen bond basicity and increased the level of dispersion interaction. Polyoxyethylene-100-stearyl ether and polyoxyethylene-23-lauryl ether surfactants, however, enhanced the π–π/n–π, polarizability/dipolarity, and hydrogen bond basicity interactions of 1-butyl-3-methylimidazolium hexafluorophosphate to a greater degree than the ionic surfactants with 1-butyl-3-methylimidazolium chloride. However, these nonionic surfactants appeared to hinder the ability of the stationary phase to interact with solutes via dispersion forces. Therefore, it is possible to effectively predict which analytes will be most highly retained by these micellar-ionic liquid stationary phases. [Copyright &y& Elsevier]

The theory and use of the "three-phase" model in enantioselective gas-liquid chromatography utilizing a methylated cyclodextrin/polysiloxane stationary phase is presented for the first time. Equations are derived that account for all three partition equilibria in the system, including partitioning between the gas mobile phase and both stationary-phase components and the analyte equilibrium between the polysioxane and cyclodextrin pseudophase. The separation of the retention contributions from the achiral and chiral parts of the stationary phase can be easily accomplished. Also, it allows the direct examination of the two contributions to enantioselctivity, i.e., that which occurs completely in the liquid stationary phase versus the direct transfer of the chiral analyte in the gas phase to the dissolved chiral selector. Six compounds were studied to verify the model: 1-phenylethanol, α-ion- one, 3-methyl-1-indanone, o-(chloromethyl)phenyl sulfoxide, o-(bromomethyl)phenyl sulfoxide, and ethyl p-tolylsulfonate. Generally, the cyclodextrin component of the stationary phase contributes to retention more than the bulk liquid polysiloxane. This may be an important requirement for effective GC chiral stationary phases. In addition, the roles of enthalpy and entropy toward enantiorecognition by this stationary phase were examined. While enantiomeric differences in both enthalpy and entropy provide chiral discrimination, the contribution of entropy appears to be more significant in this regard. The three-phase model may be applied to any gas-liquid chromatography stationary phase involving a pseudophase. [ABSTRACT FROM AUTHOR]