Pressure‐Tunable Dual‐Column Ensembles for High‐Speed GC and GC/MS

A series‐coupled ensemble of two capillary GC columns of different selectivity with an adjustable pressure at the column junction point is used to obtain tunable selectivity for high‐speed GC and GC/TOFMS. An electronic pressure controller with a 0.1‐psi step size is used to obtain numerous computer‐selected unique selectivities. System configurations for conventional, atmospheric‐pressure outlet operation with flame ionization detection and for vacuum‐outlet operation with photoionization detection are described for GC‐only experiments. Polydimethylsiloxane is used as the non‐polar column and polyethylene glycol (atmospheric outlet) or triflouropropylpolysiloxane (vacuum outlet) is used as the polar column. For GC/TOFMS experiments, 5% phenyl polydimethylsiloxane was used as the non‐polar column, and polyethylene glycol was used as the polar column. The time‐of‐flight mass spectrometer can acquire up to 500 complete mass spectra per second. Since spectral continuity is achieved across the entire chromatographic peak profile, severely overlapping peaks can be spectrally deconvoluted for high‐speed characterization of completely unknown mixtures. For mixture components with significantly different fragmentation patterns, spectral deconvolution can be achieved for chromatographic peak separations of as little as 6.0 ms. This can result is very large peak capacity for time compressed (not completely resolved) chromatograms. The use of columns with tunable selectivity allows for precise peak‐position control, which can result in more efficient utilization of available peak capacity and thus further time compression of chromatograms. The limits of tunability and deconvolution are tested for near co‐elutions of different classes of hydrocarbon compounds as well as for more multi‐functional mixtures.     

In situ fabrication of microporous organic network coated capillary column for high resolution gas chromatographic separation of hydrocarbons

Microporous organic networks (MONs) are a new class of porous materials synthesized via Sonogashira coupling reactions between organic building blocks. Here we report an in situ synthesis approach to fabricate MONs coated capillary column for high resolution GC separation of hydrocarbons. The McReynolds constant evaluation reveals the MONs coated capillary is a non‐polar column. The MONs coated capillary column shows good resolution for GC separation of diverse important industrial hydrocarbons such as linear and branched alkanes, alkylbenzenes, pinene isomers, ethylbenzene and styrene, cyclohexane and benzene. The MONs coated capillary column gave a high column efficiency of 1542 plates per meter for hexane and good precision for replicate separations of the selected hydrocarbons with the RSDs of 0.2–0.3, 1.5–3.1, and 1.9–3.3% for retention time, peak height and peak area, respectively. The MONs coated capillary also offered better resolution than commercial Inert Cap‐1 and Inert Cap‐5 capillary columns for hexane and heptane isomers. These results reveal the potential of MONs as novel stationary phases in GC.     

New benchmark for basic and neutral nitrogen compounds speciation in middle distillates using comprehensive two-dimensional gas chromatography

This paper reports an analytical method for the comprehensive two-dimensional gas chromatography (GC x GC) separation and identification of nitrogen compounds (N-compounds) in middle distillates according to their types (basicity). For the evaluation of the best chromatographic conditions, a non-polar x polar approach was chosen. The impact of the second dimension (stationary phase and column length) on the separation of basic and neutral N-compounds was evaluated by mean of two-dimensional resolution. This study revealed that the implementation of polar secondary column having free electron pairs improves drastically the separation of N-compounds. Indeed, the presence of permanent dipole-permanent dipole interactions between neutral N-compounds and the stationary phase was enlightened. The comparison of two different nitrogen chemiluminescence detectors (NCD) was also evaluated for GC x GC selective monitoring of N-compounds. Owing to higher resolution power and enhanced sensitivity achieved using developed chromatographic and detection conditions, it was possible to identify univocally and to quantitate N-compounds (i) by class of compounds and (ii), within a class, by carbon number. Finally, quantitative comparison of GC x GC-NCD with conventional gas chromatography illustrates the benefits of GC x GC leading to an excellent correlation with results obtained by American Society for Testing Materials (ASTM) methods for the determination of basic/neutral nitrogen ratio in diesel samples.     

Characterization and Comparison of Tea Tree and Lavender Oils by Using Comprehensive Gas Chromatography

The essential oils from French lavender (Lavandula angustifolia) and tea tree (Melaleuca alternifolia) were separated by the two‐dimensional GC technique of comprehensive gas chromatography. A coupled column combination of non‐polar (5% phenyl equivalent) and polyethylene glycol phase columns was used to provide the desired resolution performance. By using a range of known standards, some of the peaks in lavender oil can be assigned. Some of these also occur in tea tree oil; however, from our knowledge of the major constituents in this oil and their relative retention behaviour, most of the major peaks may be tentatively assigned within the 2‐dimensional separation space. There appear to be elution patterns within the 2‐D space which should be useful in correlating retention with chemical and structural properties of the components, although this will require further evaluation. A range of coeluting peaks, which may not be so readily separated by using a single column capillary GC analysis, are resolved in the experiment described.     

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

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

Evaluation of ionic liquid stationary phases for one dimensional gas chromatography-mass spectrometry and comprehensive two dimensional gas chromatographic analyses of fatty acids in marine biota

Ionic liquid stationary phases were tested for one dimensional gas chromatography-mass spectrometry (GC-MS) and comprehensive two dimensional gas chromatography (GC×GC) of fatty acid methyl esters from algae. In comparison with polyethylene glycol and cyanopropyl substituted polar stationary phases, ionic liquid stationary phases SLB-IL 82 and SLB-IL 100 showed comparable resolution, but lower column bleeding with MS detection, resulting in better sensitivity. The selectivity and polarity of the ionic liquid phases are similar to a highly polar biscyanopropyl-silicone phase (e.g. HP-88). In GC×GC, using an apolar polydimethyl siloxane×polar ionic liquid column combination, an excellent group-type separation of fatty acids with different carbon numbers and number of unsaturations was obtained, providing information that is complementary to GC-MS identification.     

Proper Tuning of Comprehensive Two‐Dimensional Gas Chromatography (GC×GC) to Optimize the Separation of Complex Oil Fractions

Comprehensive two‐dimensional gas chromatography (GC×GC) is an utterly suitable separation technique for the analysis of complex samples, such as oil fractions. Once the two columns and the operating conditions are properly tuned, the technique is able to provide a detailed characterization of such materials. Some considerations applying to the tuning of a GC×GC system for a specific separation are presented and discussed. The authors present a number of different column sets and conditions which allow the separation of a non‐aromatic hydrocarbon solvent, a kerosene, the light end of a crude oil, and an olefinic fraction, respectively. The highly structured GC×GC chromatograms, together with chemical knowledge about the samples, provide a much more comprehensive characterization of the samples than hitherto possible.     

基于微机电系统的高深宽比气相微色谱柱

色谱柱的微型化是实现气相色谱仪微小型化必须要解决的关键问题之一。该文基于微机电系统技术设计制作了一种具有高深宽比微沟道的气相微色谱柱。通过COMSOL软件进行仿真分析,得出气相微色谱柱具有均匀的流速场分布。测试结果表明,该气相微色谱柱成功分离了烷烃类气体混合物及苯系物,其理论塔板数可达14028 plates/m,C7~C8的分离度最高,为10.82。这种气相微色谱柱由于具有体积小、能耗低、分离性能好等优点,可望在微小型气相色谱仪上获得应用。     

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

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

Comparison of thick film capillaries with packed columns from the point of view of loadability in combination with high resolving power

The present paper compares the potential of high pressure packed column gas chromatography, with a particle size in the range of 30–80 μm and conventional packed column GC. with that of thick film capillaries for obtaining the maximum loadability at a given performance in efficiency and speed of separation. An alternative treatment, discussing the maximum efficiency of the three column types at normalized loadability and speed of separation is given. Known and established relationships describing plate height, loadability, and linear velocity are used to arrive at the said comparisons. The conclusion of the paper indicates a reconsideration of packed column GC for particular types of analyses where large amounts or high concentrations are required in the detection step.     

High‐resolution GC/MS studies of a light crude oil fraction

The continuous development in analytical instrumentation has brought the newly developed Orbitrap‐based gas chromatography / mass spectrometry (GC/MS) instrument into the forefront for the analysis of complex mixtures such as crude oil. Traditional instrumentation usually requires a choice to be made between mass resolving power or an efficient chromatographic separation, which ideally enables the distinction of structural isomers that is not possible by mass spectrometry alone. Now, these features can be combined, thus enabling a deeper understanding of the constituents of volatile samples on a molecular level. Although electron ionization is the most popular ionization method employed in GC/MS analysis, the need for softer ionization methods has led to the utilization of atmospheric pressure ionization sources. The last arrival to this family is the atmospheric pressure photoionization (APPI), which was originally developed for liquid chromatography / mass spectrometry (LC/MS). With a newly developed commercial GC‐APPI interface, it is possible to extend the characterization of unknown compounds. Here, first results about the capabilities of the GC/MS instrument under high or low energy EI or APPI are reported on a volatile gas condensate. The use of different ionization energies helps matching the low abundant molecular ions to the structurally important fragment ions. A broad range of compounds from polar to medium polar were successfully detected and complementary information regarding the analyte was obtained.     

Identification of petroleum distillates from fire debris using multidimensional gas chromatography

Summary A method for identifying petroleum distillates (accelerants) in fire debris samples by dynamic headspace analysis and multidimensional gas chromatography is described. The method relies on the separation of target compounds characteristic of different petroleum distillate classes from interfering co-eluting and matrix components. A relatively nonpolar column is used to characterize the volatility distribution of the sample and heartcutting to a second polar column of certain fractions to separate target compounds from interferences unresolved on the first column. The method is demonstrated for the identification of gasoline, kerosene, charcoal lighter fluid, and paint thinners in simulated arson samples.     

Using computer modeling to predict and optimize separations for comprehensive two-dimensional gas chromatography

In order to fully realize the separation power of comprehensive two-dimensional gas chromatography (GC x GC), a means of predicting and optimizing separations based on operating variables was developed. This approach initially calculates the enthalpy (DeltaH) and entropy (DeltaS) for the target compounds from experimental input data, and then uses this information to simultaneously optimize all column and runtime variables, including stationary phase composition, by comparing the performance of large numbers of simulated separations. This use of computer simulation has been shown to be a useful aid in conventional separations. It becomes almost essential for GC x GC optimization because of the large number of variables involved and their very complex interaction. Agreement between experimental and predicted values of standard test samples (Grob mix) using GC x GC separation shows that this approach is accurate. We believe that this success can be extended to more challenging mixtures resulting in optimizations that are simpler and transferable between GC x GC instruments.     

Comprehensive two‐dimensional monolithic liquid chromatography of polar compounds

Two‐dimensional liquid chromatography largely increases the number of separated compounds in a single run, theoretically up to the product of the peaks separated in each dimension on the columns with different selectivities. On‐line coupling of a reversed‐phase column with an aqueous normal‐phase (hydrophilic interaction liquid chromatography) column yields orthogonal systems with high peak capacities. Fast on‐line two‐dimensional liquid chromatography needs a capillary or micro‐bore column providing low‐volume effluent fractions transferred to a short efficient second‐dimension column for separation at a high mobile phase flow rate. We prepared polymethacrylate zwitterionic monolithic micro‐columns in fused silica capillaries with structurally different dimethacrylate cross‐linkers. The columns provide dual retention mechanism (hydrophilic interaction and reversed‐phase). Setting the mobile phase composition allows adjusting the separation selectivity for various polar substance classes. Coupling on‐line an organic polymer monolithic capillary column in the first dimension with a short silica‐based monolithic column in the second dimension provides two‐dimensional liquid chromatography systems with high peak capacities. The silica monolithic C₁₈ columns provide higher separation efficiency than the particle‐packed columns at the flow rates as high as 5 mL/min used in the second dimension. Decreasing the diameter of the silica monolithic columns allows using a higher flow rate at the maximum operation pressure and lower fraction volumes transferred from the first, hydrophilic interaction dimension, into the second, reversed‐phase mode, avoiding the mobile phase compatibility issues, improving the resolution, increasing the peak capacity, and the peak production rate.     

气相色谱／质谱法鉴定甲基异丁基酮产品中的杂质组分

采用ＧＣ／ＭＳ联用技术分离出甲基异丁基酮产品中６个杂质峰。将标准图谱库，质量色谱图等手段结合起来鉴定出７种杂质，并用标样，双柱对部分ＧＣ／ＭＳ的结果进行了证实，为产品质量控制提供依据。     

Preparation and evaluation of a novel bonded imidazolium ionic liquid as stationary phase for gas chromatography

1‐Butyl‐3‐[(3‐trimethoxysilyl)propyl]imidazolium chloride ionic liquid was synthesized and chemically modified onto the inner wall of a fused capillary column as a stationary phase for gas chromatography. The 1‐butyl‐3‐[(3‐trimethoxysilyl)propyl]imidazolium chloride ionic liquid bonded capillary column was evaluated in detail. The results revealed that the ionic liquid bonded capillary column exhibited high column efficiency of 1.08 × 10⁴ plates/m, and good chromatographic separation selectivity (α ) for polar and non‐polar substances, and a good thermal stability between room temperature and 400°C. Moreover, the determination of thermodynamic parameters and the linear solvation energy relationship were further carried out. The results indicated that the chromatographic retention of each probe molecule on the ionic liquid bonded stationary phase was an enthalpy‐driven process, and the system constants of the linear solvation energy relationship signified that the dispersion interaction, the hydrogen bonding acidity and hydrogen bonding basicity were dominant interactions between probes and stationary phase among five interactions during the chromatographic separation. However, the contribution of each specific interaction for the stationary phase is ranked as the dispersion interaction > the hydrogen bonding basicity > the hydrogen bonding acidity.     

Separation of phenol‐containing pyrolysis products using comprehensive two‐dimensional chromatography with columns based on pyridinium ionic liquids

We describe the application of columns with highly polar stationary liquid phases based on pyridinium ionic liquids for the two‐dimensional chromatography separation of bio‐oil and product of coal pyrolysis. By using inverse combination columns—a first ionic liquid column and a second nonpolar column—good separation results have been obtained. In the analysis of coal pyrolysis products, the suggested approach provides a much better resolution between components in comparison with a less polar first‐dimension column (based on polyethylene glycol). A good selectivity for the peaks of phenols is observed, and the group of phenols is well detached and separated from the group of diaromatics. A good separation picture was obtained also for bio‐oil, the groups of phenols and guaiacol derivatives are distinguished with good resolution of substances within each group.     

原油非烃化合物结构与含量的馏分分离及联用色谱信息获取通用方法

用正己烷将沥青质从油样中分离,再根据类组分之间极性差别,用中性氧化铝-硅胶双层析柱将原油样其余部分分成脂肪烃、芳香烃和7个非烃馏分。各馏分回收完全。用色-质联用技术,将非烃馏分再分离并获取实验数据,为原油非烃结构和含量测定奠定有关的信息基础。不同油井样品研究和重复实验表明,方法对各种原油非烃化合物分离和信息测定有很好的重现性。     

On-line high performance liquid chromatography — multidimensional gas chromatography and its application to the determination of stilbene hormones in corned beef

The combination of high performance liquid chromatography interfaced on-line with multidimensional gas chromatography (HPLC–GC–GC) is described. The HPLC column was interfaced to the GC via an on column interface, with automated pneumatic control of solvent evaporation and GC column switching. Cryogenic cold trapping was used for analyte focusing at the head of the first, non-polar GC capillary column and optionally at the head of the second, polar column. The determination of stilbene hormones in corned beef as their methylated derivatives by flame ionization detection is described.