Stationary Phases In Gas Chromatography Research Articles

Preparation and characterization of micro-bore wall-coated open-tubular capillaries with low phase ratios for fast-gas chromatography–mass spectrometry: Application to ignitable liquids and fire debris

Fast Gas Chromatography (GC) allows for analysis times that are a fraction of those seen in traditional capillary GC. Key modifications in fast GC include using narrow, highly efficient columns that can resolve mixtures using a shorter column length. Hence, a typical fast GC column has an inner diameter of 100–180 μm. However, to maintain phase ratios that are consistent with typical GC columns, the film thickness of fast GC stationary phases are also low (e.g., 0.1–0.18 μm). Unfortunately, decreased film thickness leads to columns with very low sample capacity and asymmetric peaks for analytes that are not sufficiently dilute. This paper describes micro-bore (50 μm i.d.) capillary columns with thick films (1.25 μm), and low phase ratios (10). These columns have greater sample capacity yet also achieve minimum plate heights as low as 110 μm. Hence, separation efficiency is much higher than would be obtained using standard GC columns. The capillary columns were prepared in-house using a simple static-coating procedure and their plate counts were determined under isothermal conditions. The columns were then evaluated using temperature programming for fast GC–MS analysis of ignitable liquids and their residues on fire debris exemplars. Temperature ramps of up to 75 °C min−1 could be used and separations of ignitable liquids such as gasoline, E85 fuel, and lighter fluid (a medium petroleum distillate) were complete within 3 min. Lastly, simulated fire debris consisting of ignitable liquids burned on carpeting were extracted using passive headspace absorption-elution and the residues successfully classified.

Stationary Phases Based on PIM-1 Polymer of Intrinsic Microporosity for Gas Chromatography

Polyimide PIM-1, which forms a porous polymer layer on the walls of a capillary column, exhibits high thermal stability. It is studied as a stationary phase for gas chromatography. A column with the PIM-1 stationary phase displays a drastic difference in efficiency, depending on the molecular size of the analyte: 2500–3000 theoretical plates per meter for methane and ethane and fewer than 1000 plates for larger molecules. This behavior of the column is attributed to the poor accessibility of sorption sites, as is apparent from the high loss of entropy during the sorption of light hydrocarbons and the low diffusion coefficients for these sorbates. The effect the physical aging of PIM-1 has on the separating properties of a column is studied in the accelerated thermal aging mode using the example of separation of a model C1–C4 hydrocarbon mixture. It is shown that upon heating the stationary phase to 200°C, sorbate retention and column efficiency fall monotonously. When the temperature is raised to 300°C, an unexpected increase in the analyte retention is observed, though the column’s efficiency continues to fall with respect to all sorbates except isobutane, for which this parameter increases. The causes of these unexpected effects have yet to be revealed.

Amphiphilic calix[4]arenes as a highly selective gas chromatographic stationary phase for aromatic amine isomers

Efficient separation of aromatic amine isomers is a challenging issue in chemical industry and environmental analysis. Here we report the use of p-amino-tetradecyloxy-calix[4]arene (C4A-NH2) as a novel stationary phase for gas chromatographic (GC) separations. The statically coated C4A-NH2 capillary column showed a high column efficiency of 4332 plates/m for a 0.25 mm ID column and medium polarity. The C4A-NH2 stationary phase exhibited an excellent separation performance both for aromatic amine isomers and a complex mixture of aliphatic analytes with a wide ranging polarity, showing distinct advantages over the commercial polysiloxane stationary phases via diversified molecular interactions covering H-bonding, π-π, van der Waals interactions and shape-fitting selectivity. The retention mechanisms of aromatic amine isomers on C4A-NH2 column were further investigated by quantum chemistry calculations. In addition, the C4A-NH2 column showed good column repeatability with relative standard deviation (RSD) values of 0.03%-0.07% for run-to-run, 0.10%-0.27% for day-to-day and 2.6%–5.7% for column-to-column, respectively, and thermal stability up to 240℃.

A new type of triptycene-based stationary phases with alkylated benzimidazolium cations for gas chromatographic separations

Favorable physicochemical properties and unique molecular recognition capability endow triptycene-based materials with good potential as stationary phases for gas chromatography (GC). This work reports a new type of triptycene-based materials functionalized by three benzimidazolium cations with different peripheral alkyl lengths (denoted as TP-3Bim-5C and TP-3Bim-12C) and their GC separation performance. As a result, they shared high resolving performance for the naphthalene isomers but differed for the benzene derivatives with varying polarity. Moreover, their capillary columns exhibited good repeatability and thermal stability. This work presents a facile strategy for tailoring the selectivity of the TP-based stationary phases and demonstrates their promising future for chromatographic analysis.

Stationary Phase for Gas Chromatography on the Basis of a Precursor of Macroheterocycles and a Nematic Liquid Crystal

The stationary phase for gas chromatography on the basis of the chiral R(+)-1′,7′,7′-trimethylbicyclo-[2.2.1]heptano[2′,3′-b]-2,3-dicyanopyrazine (10.4 wt %) and a liquid crystalline 4,4′-dihexyloxyazoxybenzene was studied. The phase transition temperatures of the binary mixture were measured by polarizing microscopy. It was shown that the chiral camphor-substituted 2,3-dicyanopyrazine induces formation of an enantiotropic chiral helically coiled nematic phase in the achiral liquid crystal over a wide temperature range. The gas chromatographic retention times of organic compounds on this sorbents were measured. The structural and chiral selectivity of the stationary phase on the basis of a liquid crystal and camphor-substituted 2,3-dicyanopyrazine was determined. The retention volumes, activity coefficients, and sorption enthalpies and entropies were calculated and analyzed.

Ethyl Carbazole-Grafted Polysiloxane as Stationary Phase for Gas Chromatography

In this work, we synthesized ethyl carbazole-grafted polysiloxanes, namely, ECP-9 and ECP-18, which possessed ethyl carbazole contents of 9% and 18%, respectively. The results of thermogravimetric analysis showed that ECP-9 and ECP-18 polymers lost 2% of weight at 365 °C and 380 °C. The minimum allowable operating temperature for the ECP-9 and ECP-18 was 40 °C. In addition, the ECP-9 and ECP-18 columns were thermally stable at 340 °C and 360 °C. The column average efficiencies of ECP-9 were 2306–3090 plates m−1 for a 10 m column and 2594–3438 plates m−1 for a 30 m column. The column efficiencies of ECP-18 were 2497–3428 plates m−1 for a 10 m column and 2829–3700 plates m−1 for a 30 m column. ECP-9 and ECP-18 as stationary phases exhibited moderate polarity based on the McReynolds constants. Given its specific dipole–dipole, dipole-induced dipole, π–π stacking interactions, and hydrogen bond force with solutes, the ECP stationary phases achieved excellent separation for aromatic isomers, substituted benzenes, polycyclic aromatic mixtures, polycyclic aromatic hydrocarbons, and fatty acid esters with satisfactory peak shapes.

Thermodynamic Studies on a Hydrogen Bonded Acidic 3,5-Bis(trifluoromethyl)phenol-functionalized Polymer as a Gas Chromatography Stationary Phase for Selectively Speciating Chemical Warfare Agents.

We describe for the first time hydrogen bonded acid (HBA) polymer, poly{methyl[3-(2-hydroxyl, 4,6-bistrifluoromethyl)phenyl]propylsiloxane}, (DKAP), as stationary phase for gas chromatography (μGC) of organophosphate (OP), chemical warfare agent (CWA) surrogates, dimethylmethylphosphonate (DMMP), diisopropylmethylphosphonate (DIMP), diethylmethylphosphonate (DEMP), and trimethylphosphate (TMP), with high selectivity. Absorption of OPs to DKAP was one-to-several orders of magnitude higher relative to commercial polar, mid-polar, and nonpolar stationary phases. We also present for the first-time thermodynamic studies on the absorption of OP vapors and quantitative binding energy data for interactions with various stationary phases. These data help to identify the best pair of hetero-polar columns for a two-dimensional GC system, employing a nonpolar stationary phase as GC1 and DKAP as the GC2 stationary phase, for selective and rapid field detection of CWAs.

Retention Behaviour of Alkylated and Non-Alkylated Polycyclic Aromatic Hydrocarbons on Different Types of Stationary Phases in Gas Chromatography

The gas chromatographic retention behaviour of 16 polycyclic aromatic hydrocarbons (PAHs) and alkylated PAHs on a new ionic liquid stationary phase, 1,12-di(tripropylphosphonium) dodecane bis(trifluoromethanesulfonyl)imide (SLB®-ILPAH) intended for the separation of PAH mixtures, was compared with the elution pattern on more traditional stationary phases: a non-polar phenyl arylene (DB-5ms) and a semi-polar 50% phenyl dimethyl siloxane (SLB PAHms) column. All columns were tested by injections of working solutions containing 20 parental PAHs from molecular weight of 128 to 278 g/mol and 48 alkylated PAHs from molecular weight of 142 to 280 g/mol on a one dimensional gas chromatography-mass spectrometry (GC-MS) system. The SLB PAHms column allowed separation of most isomers. The SLB®-ILPAH column showed a rather different retention pattern compared to the other two columns and, therefore, provided a potential for use in comprehensive two-dimensional GC (GC×GC). The ionic liquid column and the 50% phenyl column showed good thermal stability with a low bleed profile, even lower than that of the phenyl arylene “low bleed” column.

Field-effect transistor array modified by a stationary phase to generate informative signal patterns for machine learning-assisted recognition of gas-phase chemicals

We propose an artificial intelligence-based chemical-sensing system integrating a porous gate field-effect transistor (PGFET) array modified by gas chromatography stationary phase materials and machine-learning techniques.

A flexible and convenient strategy for synthesis of ionic liquid bonded polysiloxane stationary phases

Ionic liquid bonded polysiloxanes (PILs) are a class of polysiloxanes whose side chains contain ionic liquid (IL) moieties. Considering their excellent selectivity and thermo-stability, PILs have great potentials in the development of polar stationary phases for gas chromatography. In this paper, a novel synthesis strategy for PILs is proposed to diversify PIL stationary phases and also facilitate the study on relationships between stationary phase structure and separation performances. The polysiloxane with imidazole groups at the side chains was synthesized firstly, and then these imidazole groups further reacted with halogenated compounds to produce various IL groups. Upon this, fifteen PIL stationary phases differing in IL content, IL group or combination of different IL groups have been synthesized and used to prepare capillary columns through static coating method. These columns have quite different general polarity indexes (the average value of all Rohrschneider-McReynolds constants in this paper) falling in a broad range from 218 to 717, and most columns have column efficiency values over 3000 plates/m. In addition, IL content, structure of the IL and combination of different IL groups have noticeable influences on interaction features of the stationary phases. After that, the separation performances of these PIL stationary phases were demonstrated by separating various mixed samples of aliphatic esters, dichloro-anilines, alcohols, aromatic amines, substituted alkanes, and so on. In order to reveal the relationship of interaction characteristics and separation performances, a set of indexes of contribution rates (CRs) is proposed. Based on CRs, the separation selectivity of the PIL stationary phases has been discussed in detail. The results indicate that there are significant differences in the separation selectivity not only between PILs and conventional polar stationary phases, but also among different PILs. All of these imply a family of practical PILs with special selectivity could be constructed upon this synthesis strategy.

Thermodynamic Parameters of a New Synthesized Tricationic Ionic Liquid Stationary Phase by Inverse Gas Chromatography

A new tricationic ionic liquid [benz(2NPTim)3](NTf2)3 with three N-naphthyl imidazolium cations has been synthesized and used as a stationary phase in gas chromatography. The stationary phase was characterized using the inverse gas chromatography technique. The McReynolds constants, Abraham solvation parameters, the activity coeficients (γ∞), selectivities (Sij∞), and capacities (kj∞) at infinite dilution were determined accordingly. The TGA analysis showed that the stationary phase had high thermal stability up to 673 K. On the basis of the obtained data from the McReynolds constants, the stationary phase had an average polarity of 1153 and polarity number equal to 130, which indicates its highly polar nature. The Abraham solvation parameters were compared to that of other stationary phases and revealed stronger H-bond basicity, dipole–dipole, and dispersive interactions with the solutes. The Kovats retention indexes obtained for polyaromatic compounds suggest that the stationary phase has strong interac...

Selective removal of nicotine from the main stream smoke by using a surface-imprinted polymer monolith as adsorbent.

Using molecularly imprinted polymer as a selective adsorbent for gaseous toxicants is a novel attempt. In present work, a nicotine surface-imprinted monolith (MIM) was used for the selective removal of nicotine from smoke. First, the retention capacity and selectivity for this MIM was tested by using it as the stationary phase in gas chromatography and chromatographic conditions optimized. Then, the gas phase adsorption isotherms of MIM were constructed and the adsorption thermodynamics explored. At last, the applicability for MIM in the removal of nicotine in smoke was explored. Results indicated a stronger retention capacity and a higher selectivity of MIM toward the template vapor, with a capacity factor (87.88) and a selectivity factor (10.15) under the optimized conditions. A higher standard adsorption enthalpy change for this MIM toward the template (ΔHa0 = 65.53 kJ mol-1) than that for the non-imprinted monolith (NIM) column (ΔHa0 = 47.46 kJ mol-1) was observed. The adsorption isotherm for MIM appears the BET type II shape, while that for the NIM was approximately linear. When this MIM was used as the adsorbent, it exhibited a high performance in the selective removal of nicotine from the main stream smoke, with an adsorption percentage of 99.43%.

Thermal stability of poly[1-(trimethylsilyl)-1-propyne] and the gas chromatographic stationary phase based on it.

The thermal stability of poly[1-(trimethylsilyl)-1-propyne] is investigated by heating the capillary column with this polymer as the stationary phase with the subsequent separation of the test mixture of light hydrocarbons. It is shown that heating of the column up to 130°C does not cause a decrease in efficiency or in the retention time of solutes. A further increase in temperature results in both decrease in column efficiency and sorbate retention. However, a decrease in column retentivity goes in one way for all the tested hydrocarbons. At the same time, the efficiency of the column is changed to a lesser degree for methane and ethane up to the temperature of polymer degradation, while for propane, butane, and iso-butane the difference is rather sharp. The most expressed decrease in efficiency was found for iso-butane: the column efficiency for this sorbate versus temperature of heating had two stages. The diffusion coefficients for sorbates in the polymeric phase were also evaluated and the sharp decrease in their values was found after the column heating.

Variation of anionic moieties of dicationic ionic liquid GC stationary phases: Effect on stability and selectivity

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 [2mC3(mim)2], and 1,3-di(3-methylimidazolium)-isobutene [i-eneC4(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.

Poly(3-hexylthiophene) stationary phase for gas chromatographic separations of aliphatic and aromatic isomers

This work describes the investigation of utilizing a chain-typed thiophene-based π-conjugated polymer, i.e., poly(3-hexylthiophene) (P3HT), as the stationary phase for gas chromatography (GC). The P3HT column was statically prepared and investigated for its column efficiency, polarity, separation performance, repeatability and thermal stability. As a result, it showed moderate polarity and column efficiencies of 3260, 3310 and 3790 plates/m for 1-octanol, naphthalene and n-dodecane, respectively. As evidenced, it exhibited high-resolution performance for aliphatic and aromatic isomers, including those critical pairs such as phenanthrene/anthracene and p-/m-benzenediol isomers. Moreover, it displayed stronger retention for alkanes, alcohols and phenols in comparison to the polysiloxane stationary phase with close polarity. Also, the P3HT column had good repeatability and reproducibility with the RSD values less than 0.05% for run-to-run, 0.17–0.54% for day-to-day and 2.7–5.2% for column-to-column, and good thermal stability up to 260 °C. This work demonstrates the promising future of the thiophene-based polymer and its derivatives in separation science.

Hexagonal boron nitride stationary phase for gas chromatography

This work describes the separation performance of utilizing hexagonal boron nitride (h-BN) as the stationary phase for capillary gas chromatography (GC). The statically coated h-BN column showed moderate polarity and achieved column efficiencies of 3455 plates/m and 3800 plates/m for naphthalene and n-dodecane, respectively. With temperature-dependent structure properties, the h-BN stationary phase exhibited stronger retention for polycyclic aromatic hydrocarbons (PAHs) over phthalic acid esters (PAEs) and showed advantageous separation performance over the g-C3N4 and commercial polysiloxane stationary phases. Moreover, it displayed preferential retention for halogenated analytes and high resolution performance for structural and positional isomers. In addition, the h-BN column showed good column repeatability with relative standard deviation (RSD) values of 0.03%–0.07% for run-to-run, 0.31%–0.71% for day-to-day and 2.6%–5.3% for column-to-column, respectively, and thermal stability up to 260 °C.

Molecular-sieve porous graphene as a steady phase of gas chromatography column for dissociation and measurement of nitrous oxide, carbon dioxide and gaseous hydrocarbons

A novel gas chromatography stationary phase is introduced for efficient separation of air, nitrous oxide, methane, carbon dioxide, ethane, propane, butane and pentane. Porous graphene was synthesized through a cost-effective approach. The structure and porous texture of the prepared graphene were evaluated by field-emission scanning electron microscopy and nitrogen adsorption/desorption isotherms. The results confirmed the high porosity and surface area of the synthesized porous graphene. Also, the nitrogen adsorption/desorption isotherms showed highly microporous structures with the average pore size being < 2 nm, which has high contribution in gas molecules separation. The prepared structure exhibited an excellent chromatography performance and separation efficiency compared with multi-wall, single-wall carbon nanotube and activated carbon. In addition, common problems in GC packed column by nanomaterials, such as avoiding the use of long column, flow rate reduction, agglomeration, packing compression and high back-pressure, were completely addressed; therefore, in order to overcome these problems and fabricate chromatography column 1.8″, stainless steel tubes were used in three lengths of 10, 20, 30 cm. After testing, the 30 cm column was used for determination and separation of the entered gases in continued work. In this experiment, two types of samples were used. The first sample contains air, methane, carbon dioxide and nitrous oxide gases at 40 °C, and the second sample was compared of methane, ethane, propane, butane and pentane containing hydrocarbons with temperature action of 40–200 °C. The analytical results demonstrated the superior separation efficiency of porous graphene steady phase for some gas dissociation at 40 °C and good preservative for hydrocarbons C1–C5 (while using ramp up rate of 6 °C/min) in temperature range of 40–200 °C. The packed prepared column also showed high resolution, wide linear range and acceptable repeatability in separation of studying gas mixture. The obtained detection limits obtained were lower than 4.2 ppm.

Synthesis of four liquid crystals and study of alkyl chain effect on the nematic range for application in GC

Four liquid crystals (LCs) compounds which contain the 1,3,4-oxadiazole group were synthesized and characterized with spectroscopic techniques (IR, 1H- and 13C NMR), their thermal properties were analyzed by the Differential Scanning Calorimetry (DSC) and the polarizing microscope (POM). A comparative study of the mesomorphic properties of these LCs and three other compounds which have already been used as a stationary phase in gas chromatography (GC) was carried out. These compounds have the same main nucleus. LCs V1, LC1, LC2 and LC3 gave a nematic (N) phase to the heating, LCs V2 and V3 recorded smectic A (SmA) and N phases. However, the range (N) has disappeared in V4.

Azulene-Modified Polysiloxanes as Gas Chromatographic Stationary Phases: Comparison of the Separatory Properties of Azulene and Naphthalene

ABSTRACTAzulene is an aromatic molecule with interesting properties, most notably a permanent dipole moment of 1.08D. This degree of polarity in the absence of heteroatoms is quite rare and offers potential for use in unique gas chromatographic stationary phases. Here, we report the first examples of azulene-derivatized stationary phases for gas chromatographic separations. Poly(dimethyl/azulenylmethyl) siloxane polymers containing 15 and 35% of an azulene derivative were synthesized, coated on capillary columns, and evaluated. To compare the effects of increased polarity vs. the effects of polarizability, isomeric naphthalene analogues were also prepared, coated, and evaluated. The coated phases displayed efficiencies up to 2700 plates/m. For both azulene and naphthalene columns, retention increased as substitution level increased. The more polarizable naphthalene columns tended to retain analytes more strongly. Columns were also evaluated for the separation of several different mixtures of isomers against a commercial HP-5 column. All azulene and naphthalene columns exhibited separations comparable to the commercial column. The solvation thermodynamic parameters phases were measured, showing an excellent linear relationship and no change in the mechanism of interaction over the temperature range measured.

Ionic liquids as water-compatible GC stationary phases for the analysis of fragrances and essential oils

Fragrances and products deriving from essential oils are often formulated or diluted in aqueous media, usually ethanol/water. Gas chromatography (GC) is the technique of choice to analyze volatiles. However, when using columns coated with conventional stationary phases, its application to aqueous samples often requires time-consuming and/or discriminative sample preparation techniques to extract the target analytes from the aqueous medium, so as to avoid its direct injection. In GC with conventional columns, water produces peak asymmetry, poor sensitivity and efficiency, strong adsorption, stationary phase degradation, and, last but not least, it is not easy to detect reliably when present in high amounts. In 2012, Armstrong's group introduced new fully water-compatible ionic-liquid (IL)-based GC capillary columns based on phosphonium and imidazolium derivative cations combined with trifluoromethanesulphonate. These columns were recently made available commercially by Supelco, under the trade name Watercol™. These derivatives maintain IL's unique selectivity and chromatographic properties, and enable water to be used as injection solvent, thus avoiding the sample preparation procedures required by conventional columns. This study reports and critically discusses the results of commercially available water-compatible IL columns for direct analysis of aqueous samples in the fragrance and essential oil fields by GC with thermal conductivity (TCD) and/or flame ionization detectors (FID). The results showed that water-compatible IL-based stationary phases can successfully be adopted for qualitative and quantitative analysis of fragrances and essential oils directly diluted in aqueous solvents. On the other hand, the study also shows that their inertness needs to be further increased and (possibly) the range of operative temperature extended when water is the main solvent of the sample.