Wall-coated Open-tubular Columns Research Articles

Development of Wall-Coated Open Tubular Columns and Their Application to Nano Liquid Chromatography Coupled to Tandem Mass Spectrometry.

This work presents a study on the application of wall open tubular column (WCOT) in liquid chromatography coupled with tandem mass spectrometry. Each process step reports the column preparation method in detail, subdivided into column pretreatment, silanization, stationary phase coating, and immobilization. Then, an evaluation of the parameters that can affect the efficiency of these columns was made. Atrazine, clomazone, and metolachlor were used as probes during this step. Factors such as stationary phase composition, length, internal diameter, stationary phase mass employed, and injection volume were investigated. In addition, with the help of Knox and Poppe graphs, the columns' performance was evaluated to determine the optimal flow rate and the speed-efficiency relationship, respectively. Based on the results, the best configurations for the WCOT column application to the LC system were defined: length-8 m; inner diameter-25 μm; mass of OV-210-2.5% m/v; and, injection volume-100 nL. Finally, the optimized WCOT column developed in this work was coupled with a commercially-packed trapping column in the nano liquid chromatography system (nanoLC). In this configuration, more significant results were obtained regarding separation resolution, with Rs = 5.9 achieved for the most retained pair of analytes (clomazone and metolachlor).

Valve-based comprehensive two-dimensional gas chromatography with quadrupole mass spectrometry detection using a porous layer open tubular column in the first dimension

A comprehensive two-dimensional gas chromatography instrument with quadrupole mass spectrometry (GC×GC-qMS) is developed and evaluated, by retrofitting a commercial GC-qMS instrument with a high temperature diaphragm valve (HT-DV) modulator. A porous layer open tubular (PLOT) column in the first dimension (1D), and a more polar wall coated open tubular (WCOT) column in the second dimension (2D) were used. The HT-DV can modulate analytes of any volatility and the combination of the PLOT and WCOT columns provides ample separation selectivity for samples containing an extended range of volatility from highly volatile analytes to analytes of more moderate volatility. In addition to instrument development, we describe data visualization considerations when upgrading from GC-qMS to GC×GC-qMS. Unlike time-of-flight mass spectrometry (TOFMS), the mass spectrum cycle time for qMS (defined as the sum of scan time and interscan delay) is a linear function of the range of mass channels (m/z) analyzed. If the cycle time does not divide evenly into the modulation period, PM, visual distortions will appear in the GC×GC chromatogram. We present two approaches to address this GC×GC chromatogram distortion issue. The first method does not require post-run computations; however, care must be taken in selecting an appropriate mass range to minimize the visual distortion issue. A half of the modulation period of total shift in the 2D separations with a PM of 2 s was determined tolerable for a 15 min separation, with 44 mass ranges (and their accompanying scan rate) deemed suitable out of 350 possible mass ranges. Also, a computational “resampling” method, which can be used to correct any qMS scan rate used was implemented. Figures-of-merit for the HT-DV modulated GC×GC-qMS instrument were also examined. Reproducible peak height (average RSDheight = 9.2%, s = 3.5%) and areas (average RSDarea = 9.3%, s = 2.8%) were obtained with low LODs (average LOD = 4.2 mg/L, s = 2.5 mg/L).

Microgeometry-independent equation for measuring infinite dilution activity coefficients using gas-liquid chromatography with static-wall-coated open-tubular columns

Gas-liquid chromatography is an effective method to determine infinite dilution activity coefficients (γ∞). Wall-coated open-tubular (WCOT) column which offers more advantages over packed column should be a preferable column type; however, the small carrier gas flow rate and stationary phase amount in WCOT columns limit its application in the determination of γ∞. Mathematical strategy made some progress to avoid the quantification problem in the determination of γ∞ by static-wall-coated open-tubular (SWCOT) columns. However, the previously reported strategy was based on the assumption that SWCOT column was geometrically an ideal hollow cylinder, which indeed deviates from the reality. In this study, without that assumption, we derived a new microgeometry-independent equation by using the relationship between the hold-up volume (VM) and the volume of stationary phase (VL), and used it to measure the γ∞ of various organic solutes in two ionic liquids (ILs) 1‑butyl‑3-methylimidazolium dicyanamide and 1,3-dibutyronitrile-imidazolium bis((trifluoromethyl)sulfonyl)imide, both of which contain double cyano groups in the anion or cation. Phase loading study was adopted to eliminate the influence of interfacial adsorption to partition. The infinite dilution partial molar excess enthalpy, selectivity and capacity were directly calculated from the experimental γ∞ values, and the linear solvation energy relationship (LSER) model was used to characterize the specific properties of both ILs. This new established equation will promote the application of SWCOT columns in thermodynamic measurement and benefit the fast screening of novel solvents for chemical separation processes.

Ultra-high thermal stability perarylated ionic liquids as gas chromatographic stationary phases for the selective separation of polyaromatic hydrocarbons and polychlorinated biphenyls

Ionic liquids (ILs) are well-known in the field of separation science for their unique selectivity when used as stationary phases in gas chromatography (GC). While a significant amount of knowledge has been attained in correlating structural features of an IL to separation selectivity, developments in producing IL-based stationary phases suitable for high temperature GC studies have lagged behind. Column bleed is a result of the stationary phase undergoing volatilization/decomposition at high temperatures and is undesirable in separations coupled to GC/MS. It has been well-known that traditional classes of ILs with long alkyl side chain substituents are susceptible to Hofmann elimination at elevated temperatures. In this study, a new class of IL stationary phases containing perarylated cations exhibiting improved thermal stability are introduced. These ILs were used to prepare wall-coated open tubular columns with high column efficiency and produced very low bleed at temperatures up to 350 °C. Their unique chemical structures provide stronger π-π interactions compared to many commercially-available stationary phases. To exploit the unique interactions provided by these stationary phases, the separation of two classes of environmentally hazardous aromatic compounds, namely, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), was examined. Both classes of compounds contain structural isomers with high boiling points that are often challenging to separate. The perarylated sulfonium and phosphonium IL-based stationary phases exhibited excellent thermal stability as well as unique selectivity toward isomers of PAHs as well as toxic PCB analyte pairs.

Polymeric ionic liquid open tubular capillary column for on-line in-tube SPME coupled with UHPLC-MS/MS to determine endocannabinoids in plasma samples

This manuscript describes the development of wall-coated open tubular capillary column with polymeric ionic liquids (PILs) for on-line in-tube solid phase microextraction coupled with ultra high-performance liquid chromatography tandem mass spectrometry (in-tube SPME/UHPLC-MS/MS) to determine anandamide (AEA) and 2-arachidonoyl glycerol (2 A G) in plasma samples. Selective PILs were synthetized from the [VC6IM][Cl], [VC16IM][Br], and [(VIM)2C10]2 [Br] - ionic liquids - by in-situ thermal-initiated polymerization in a fused silica capillary column for in-tube SPME. The synthesis procedure was optimized, and the capillary columns were characterized using spectroscopic and chromatography techniques. The chemically bonded and cross-linked PIL-based sorbent phase (thickness coating: 1.7 μm) presented high chemical and mechanical stability. Among the sorbents evaluated, the PIL-based capillary, [VC16IM][Br]/[(VIM)2C10]2 [Br] presented the best performance with a sorption capacity of 37,311 ng cm−3 and 48,307 ng cm−3 for AEA and 2 A G, respectively. This capillary was reused more than ninety times without significant changes in extraction efficiency. The in-tube SPME-UHPLC-MS/MS method presented a linear range from 0.1 ng mL−1 to 100 ng mL−1 for AEA, and from 0.05 ng mL−1 to 100 ng mL−1 for 2 A G, with coefficients of determination higher than 0.99, p-value for Lack-of-fit test higher than 0.05 (α of 0.05), precision with coefficient of variation (CV) values ranging from 1.6 to 14.0% and accuracy with relative standard deviation (RSD) values from −19.6% to 13.2%. This method was successfully applied to determine AEA and 2 A G in plasma patients with Parkinson's disease. The concentrations in these plasma samples ranged from 0.14 to 0.46 ng mL−1 for AEA and from <0.05 ng mL−1 to 0.51 ng mL−1 for 2-AG.

Accurate Measurements of Infinite Dilution Activity Coefficients Using Gas Chromatography with Static-Wall-Coated Open-Tubular Columns

Wall-coated open-tubular (WCOT) columns provide higher column efficiency and lower solute interfacial adsorption effect than packed columns. However, previous efforts used to measure the infinite dilution activity coefficient (γ(∞)) via a chromatographic technique have used packed columns, because the low carrier gas flow rate (U) and the small stationary phase amount (n(2)) in WCOT columns raise large errors. By rationally revising the γ(∞)-calculation equation for static-wall-coated open-tubular column, we observed that U and n(2) are not necessarily needed and the resulting error could be reduced, and WCOT column gas chromatography subsequently became a superior method for the accurate γ(∞) determination. In this study, we validate our revised γ(∞)-calculation equation by measuring γ(∞) in an ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate system, in which 55 organic compounds covering a wide range of functional groups were used as probe solutes and their γ(∞) values in the ionic liquid were determined at 40.0, 50.0, and 60.0 °C. Experimental error analysis shows that our revised equation remarkably reduces the error compared to the common γ(∞)-calculation equation. Our data is consistent with previously reported values obtained via other techniques, which further proves the credibility of our revised equation. The accurately determined γ(∞) values can be directly used to calculate the partial molar excess enthalpy, selectivity, and capacity, which will benefit for the rapid screening of solvents (especially ionic liquids) in separation approaches.

Multi-dimensional gas chromatography with a planar microfluidic device for the characterization of volatile oxygenated organic compounds

Oxygenated compounds like methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, acetaldehyde, crotonaldehyde, ethylene oxide, tetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, and 2-chloromethyl-1,3-dioxolane are commonly encountered in industrial manufacturing processes. Despite the availability of a variety of column stationary phases for chromatographic separation, it is difficult to separate these solutes from their respective matrices using single dimension gas chromatography. Implemented with a planar microfluidic device, conventional two-dimensional gas chromatography and the employment of chromatographic columns using dissimilar separation mechanisms like that of a selective wall-coated open tubular column and an ionic sorbent column have been successfully applied to resolve twelve industrially significant volatile oxygenated compounds in both gas and aqueous matrices. A Large Volume Gas Injection System (LVGIS) was also employed for sample introduction to enhance system automation and precision. By successfully integrating these concepts, in addition to having the capability to separate all twelve components in one single analysis, features associated with multi-dimensional gas chromatography like dual retention time capability, and the ability to quarantine undesired chromatographic contaminants or matrix components in the first dimension column to enhance overall system cleanliness were realized. With this technique, a complete separation for all the compounds mentioned can be carried out in less than 15min. The compounds cited can be analyzed over a range of 250ppm (v/v) to 100ppm (v/v) with a relative standard deviation of less than 5% (n=20) with high degree of reliability.

Dual column capillary gas chromatographic system for the in situ analysis of volatile organic compounds on a cometary nucleus.

Two Wall Coated Open Tubular capillary columns, coated with poly(cyanopropylphenyl-dimethyl)siloxane and poly(diphenyl-dimethyl)siloxane stationary phases, have been selected for use in the COmetary SAmpling and Composition space experiment for the separation and identification of the wide range of volatile organic compounds which could be present in cometary nuclei. This article presents the main characteristics of the tandem column system for the analysis of solutes of cometary interest within the constraints of space instrumental operating conditions. The high efficiency of the columns is demonstrated and the influence of the operating conditions on their separation properties are investigated. The studied columns exhibit complementary retention pattern: their use in a dual column system makes it possible to achieve the separation and the identification of the compounds of interest. Finally, the good analytical behavior of the columns when analyzing samples which include large amounts of water, the main presumed volatile in comets, is demonstrated. The presented results thus show the suitability of the selected tandem columns system for the desired analyses, and their performance on adaptation to in-situ cometary chemical investigation.

Enthalpy of fuel gas odorants on surrogate soil surfaces by gas chromatography

Heats of adsorption and heats of interaction for natural gas odorants on clay and organo-clay, respectively, were determined by means of wall-coated open-tubular (WCOT) column gas chromatography. The odorants studied are organic thiol and sulfide compounds. Clay stationary phases were created from the synthetic clay Laponite-RD. Subsequent coatings with octadecane created an organo-clay stationary phase. Experimental results show that, as a class, sulfide odorants have larger enthalpies on clay and organo-clay surfaces than thiol odorants. Therefore, we conclude that thiols are less likely to be sequestered on soil surfaces. The effect of hydrated clay surfaces on odorant enthalpies is also presented. Further, we demonstrate that Lewis acid–base chemistry on clay surfaces explains the significant difference in enthalpy magnitudes between the sulfide and thiol classes.

Wall-coated open-tubular column chromatography on an organo–clay stationary phase

Wall-coated open-tubular (WCOT) column chromatography is shown to be a viable tool to measure hydrocarbon interactions with an organo–clay as the stationary phase. In this paper, we report the heats of interaction for a series of hydrocarbons ( n-alkanes of C 6–C 12, and cyclohexane) on a cetyltrimethylammonium bromide (CTAB)-modified Laponite-RD clay. The measurements were performed with a new WCOT method that we have developed, and also a conventional packed-column approach. Although the measurements from both techniques yield the same values of enthalpy (on the basis of our statistical analysis), we argue that WCOT column chromatography gave the more reliable results, with lower uncertainties and better chromatographic behavior.

Contribution to the time balance in gas–liquid chromatography: New definition equations of the retention times and retention volumes

The numerous research groups and researchers, as well as IUPAC, that during the last half century have dealt with different theoretical and practical problems in gas–liquid chromatography (GLC), including its nomenclature, have failed in giving an exact definition equation of the net retention time. Using our earlier results and starting from a time balance of GLC we have solved this problem by introducing the so-called acceleration time, t ac, in the absence of which, the theoretical plate number concept, including the stationary phase transfer, is misinterpreted. The measurements were carried out both on support coated and on wall-coated open tubular columns with apolar and polar stationary phases. Different relationships of t ac with some solute properties and the column temperature for a series of n-alkanes on an apolar stationary phase under isothermal conditions were tested. The results obtained are presented in different tables and mathematical relationships.

Gas chromatography for in situ analysis of a cometary nucleus: III. Multi-capillary column system for the cometary sampling and composition experiment of the Rosetta lander probe

The cometary sampling and composition (COSAC) experiment is one of the principal experiments of the surface lander probe of the European Space Agency Rosetta mission to be launched in January 2003. The instrument is designed for the in situ chemical analysis of a cometary nucleus as the details of the nucleus composition are of primary importance for understanding both the formation of the solar system, and the origin of life on Earth. The COSAC experiment consists of an evaporation/pyrolysis device and two analytical systems: a multi-column gas chromatograph and a high-resolution time-of-flight mass spectrometer which may either be operated alone or in a coupled mode. The gas chromatograph includes five general purpose chromatographic columns and three chiral ones, all mounted in parallel. Taking into account the chemical species potentially present in the cometary nucleus as well as the space constraints, a set of five complementary columns was selected to perform the separation and identification of the compounds present in the cometary nucleus. This set of columns includes a carbon molecular sieve porous-layer open tubular (PLOT) column used for the separation of both the noble and other permanent gases, and the C 1–C 2 hydrocarbons. A second PLOT column uses a divinylbenzene–ethylene glycol–dimethylacrylate porous polymer as stationary phase for the analysis of a wide range of C 1–C 2 organic molecules. Two complementary wall-coated open tubular (WCOT) columns with polydimethylsiloxane (PDMS) liquid stationary phases, one containing cyanopropyl–phenylsiloxane and the other diphenylsiloxane groups, are designed to target the same range of organic compounds (C 3–C 7) which could be representative of the widest range of cometary compounds. A third WCOT column with an apolar stationary phase made of non-substituted PDMS is used for the separation and identification of higher-molecular-mass compounds (up to C 10) and aromatic species (monoaromatic and polyaromatic). This paper describes these five general-purpose capillary PLOT and WCOT columns, selected to be used in the COSAC GC system. The analytical capabilities are examined with a special emphasis on the exobiological and planetological implications.

Chromatographic enantioseparation on a wall-coated open tubular capillary column containing covalently bound cellulose (3,5-dichlorophenyl carbamate) as chiral selector

Chromatographic enantioseparation on a wall-coated open tubular capillary column containing covalently bound cellulose (3,5-dichlorophenyl carbamate) as chiral selector

Determination of heats of adsorption of hydrocarbons on a synthetic clay by gas–solid chromatography using a wall coated open tubular column approach

Heats of adsorption for a series of hydrocarbons on Laponite-RD clay were determined by two gas chromatographic methods. The first method was an extension of packed-column gas–solid chromatography. The second method employed a novel wall coated open tubular (WCOT) column that was prepared from clay aqueous suspensions. The two different methods of preparing chromatographic columns are discussed in this paper, and a comparison between the results obtained on the two systems is made. We conclude that the WCOT column method provides the same thermodynamic results as does the conventional packed-column method, while offering some definite improvements in the measurement process and data behavior.

Surface Properties of Silica-Based Adsorbents Measured by Inverse Gas−Solid Chromatography at Finite Concentration

The adsorption energy distributions (AEDs) of methanol and dichloromethane on samples of the same silica unmodified and modified with octadecyldimethylsilyl (C18) were estimated from isotherm data obtained by inverse gas chromatography at finite concentration. Wall-coated open tubular columns were used as they provide a high efficiency and a low pressure drop, allowing the acquisition of accurate isotherm data. The adsorption isotherms were obtained from nonlinear elution profiles using the characteristic points method of chromatography. The numerical estimation of AEDs was made by applying the expectation-maximization method to the experimental, unfitted adsorption isotherm data. The adsorption energy distributions obtained exhibit two peaks of adsorption energy. The height of the higher energy peak is reduced after chemical modification of the silica surface.

Gas chromatography of Titan's atmosphere VI. Analysis of low-molecular-mass hydrocarbons and nitriles with BPX5 capillary columns

Wall-coated open-tubular capillary columns (0.15 mm I.D., 12 and 25 m long with a 0.25-μm film thickness and 12 m long with a 2-μm film thickness with a chemically bonded stationary phase (5% phenyl-95% dimethylpolysiloxane) were used for the gas chromatographic analysis of various mixtures of low-molecular-mass saturated and unsaturated hydrocarbons and nitriles. Retention indices are given for these solutes at 30°C. Van Deemter curves were also plotted for propionitrile, n-hexane and benzene at 30°C for both film thicknesses. Both columns proved efficient and yielded good resolution. The analysis of the experimental band broadening on the basis of Golay's equation indicates the important role of the instrumental contribution to band broadening for columns with thin films of stationary phase.

New equation for specific retention volumes in capillary column gas chromatography

The evaluation of specific retention volumes in gas chromatography is subject to several sources of error. The use of wall-coated open-tubular columns should yield better values for specific retention volumes. However, on scaling down the flow-rate of the carrier gas, mass of stationary phase and column head pressure, new sources of error are introduced. A careful consideration of the possible sources of error is presented. It was found that, for the use of capillary columns, the classical equation describing the specific retention volume may be modified so that no flow-rates, column head and outlet pressures or mass of stationary phase in the column are necessary in order to obtain correct specific retention volumes.

Determination of toxaphene in soil by electron-capture negative-ion mass spectrometry and capillary column gas chromatography

Although toxaphene is now limited in use, interest in its analysis continues because of its persistence and widespread atmospheric transport in the environment and its presence in many dump-sites all over the world. Top soil samples collected from a dump site were analyzed for toxaphene residues. Analyses were performed by wall-coated open tubular column gas chromatography in tandem with electron-capture negative-ion mass spectrometry. Since the concentrations of toxaphene residues were at mg/kg levels, the application of a mass spectrometer as a substance-selective detector has been applied. Advantages of this mode of real-time acquisition in continuous repetitive scanning of mass spectra has significant advantages in comparison to the selected-ion monitoring technique. An average R.S.D. of 10% and recoveries of 90 to 109% were obtained. Levels down to 50 μg/kg are obtainable.

Analysis of chlorofluorocarbon replacement compounds by capillary gas chromatography

Several thick film wall-coated open tubular and porous-layer open tubular (PLOT) type capillary columns have been investigated for the separation of wi

Stainless steel capillary columns for high temperature gas chromatography

AbstractA layer of elemental silicon has been deposited on the surface of stainless steel tubing by means of chemical vapor deposition (CVD). Two kinds of capillary column were prepared from the deactivated tubing: cross‐linked, silanol‐terminated polydime‐thylsiloxane wall coated open tubular (WCOT) columns and molecular sieve 13X porous layer open tubular (PLOT) columns. Unlike fused silica capillary columns, stainless steel WCOT and PLOT columns can be operated at temperatures in excess of 400°C. High temperature simulated distillation has been performed successfully with a macro bore WCOT column and rapid PNA (paraffin, naphthene, and aromatic) analysis with a multidimensional gas solid chromatographic (GSC) system using PLOT columns.