Columns For Gas Chromatographic Separation Research Articles

Post-modification of covalent organic framework for gas chromatographic separation of isomers

Separation of isomers is important in diverse areas such as life science, chemical industry, pharmaceutical and environmental science, but still challenging due to their similar physicochemical properties. Development of new stationary phases is an effective way to improve the performance of chromatography for the separation of isomers. Here, we report the post-modification of a new hydroxyl-functionalized covalent organic framework (COF) TzDHNDA with [(1-phenylethyl)amino]acetic acid (PEAA) via esterification reaction to construct PEAA functionalized COF (TzDHNDA-PEAA). The prepared TzDHNDA-PEAA was stable up to 380 °C and used as stationary phase to make TzDHNDA-PEAA coated capillary column for gas chromatographic separation of isomers. The TzDHNDA-PEAA coated capillary column showed a high column efficiency for n-dodecane (12417 plates m−1, 120 °C) and high resolution separation of the isomers of fluoroaniline (Rm-/o-=3.2, Rp-/m-=2.4), chloroaniline (Rm-/o-=5.7, Rp-/m-=1.8), nitrotoluene (Rp-/o-=2.2, Rm-/p-=1.7), pinene (Rβ-/α-=2.4), ionone (Rβ-/α-=4.8) and 1,3-dichloropropene (RE-/Z-=2.0). The fabricated column offered better separation of chloroaniline isomers than commercial capillary columns InertCap WAX, InertCap 1701 and InertCap 5. The introduced benzene ring, secondary amine and carbonyl groups of PEAA into the COF TzDHNDA significantly improved the resolution of isomers due to the enhanced hydrogen-bonding and π-π interactions. This work shows that post-modification strategy is an effective way to prepare novel COFs for chromatographic separation of isomers.

Two Fibers Packed in Capillary Column for Gas Chromatographic Separation

Two Fibers Packed in Capillary Column for Gas Chromatographic Separation

Compact-GC platform: A flexible system integration strategy for a completely microsystems-based gas-chromatograph

The increasing need for portable analysis systems to be used in field sensing applications with the quality and reliability of laboratory analyses, characterized by high sensitivity and specificity, calls for miniaturization and optimization of laboratory analytical techniques, as enabled by the use of micro-electro-mechanical-systems (MEMS) technology. This paper reports on an innovative all-on-MEMS platform for the implementation of miniaturized or portable multi-purpose gas-chromatographic (GC) systems. The use of a directly interconnected MEMS technology for all three main GC components, namely injector, purge&trap pre-concentrator and GC separation column, allows for a very efficient system integration and for a zero dead-volume and chemically inert analytical chain, which can be heated up to 200 °C to avoid sample condensation. In this work, the analytical chain and the integration strategy will be reported, and several applications and analyses will be demonstrated using the compact-GC platform with both photoionization (PID) and thermal conductivity detectors (TCD).

Fabrication of a capillary column coated with the four-fold-interpenetrated MOF Cd(D-Cam)(tmdpy) for gas chromatographic separation

The diverse structures and unique properties of metal organic frameworks (MOFs) are attractive attributes for analytical application. In this work we apply the four-fold-interpenetrated MOF Cd(D-cam)(tmdpy) as the coating material in capillary columns for gas chromatographic separation of aromatic hydrocarbons (ether, acid and alcohol), linear alkane hydrocarbons (aldehyde, acid and ether). The good thermal and chemical stabilities as well as the provision of suitable host-guest interaction sites within the interpenetrating frameworks make it an excellent chromatographic stationary phase for gas separation.

Development of micromachined preconcentrators and gas chromatographic separation columns by an electroless gold plating technology

In this study, a simple process for fabricating a novel micromachined preconcentrator (μPCT) and a gas chromatographic separation column (μSC) for use in a micro gas chromatograph (μGC) using one photomask is described. By electroless gold plating, a high-surface-area gold layer was deposited on the surface of channels inside the μPCT and μSC. For this process, (3-aminopropyl) trimethoxysilane (APTMS) was used as a promoter for attaching gold nanoparticles on a silicon substrate to create a seed layer. For this purpose, a gold sodium sulfite solution was used as reagent for depositing gold to form heating structures. The microchannels of the μPCT and μSC were coated with the adsorbent and stationary phase, Tenax-TA and polydimethylsiloxane (DB-1), respectively. μPCTs were heated at temperatures greater than 280 °C under an applied electrical power of 24 W and a heating rate of 75 °C s−1. Repeatable thermal heating responses for μPCTs were achieved; good linearity (R2 > 0.9997) was attained at three heating rates for the temperature programme for the μSC (0.2, 0.5 and 1 °C s−1). The volatile organic compounds (VOCs) toluene and m-xylene were concentrated over the μPCT by rapid thermal desorption (peak width of half height (PWHH) <1.5 s); preconcentration factors for both VOCs are >7900. The VOCs acetone, benzene, toluene, m-xylene and 1,3,5-trimethylbenzene were also separated on the μSC as evidenced by their different retention times (47–184 s).

Recent developments on field gas extraction and sample preparation methods for radiokrypton dating of groundwater

Summary Current and foreseen population growths will lead to an increased demand in freshwater, large quantities of which is stored as groundwater. The ventilation age is crucial to the assessment of groundwater resources, complementing the hydrological model approach based on hydrogeological parameters. Ultra-trace radioactive isotopes of Kr ( 81 Kr and 85 Kr) possess the ideal physical and chemical properties for groundwater dating. The recent advent of atom trap trace analyses (ATTA) has enabled determination of ultra-trace noble gas radioisotope abundances using 5–10 μ L of pure Kr. Anticipated developments will enable ATTA to analyze radiokrypton isotope abundances at high sample throughput, which necessitates simple and efficient sample preparation techniques that are adaptable to various sample chemistries. Recent developments of field gas extraction devices and simple and rapid Kr separation method at the University of Chicago are presented herein. Two field gas extraction devices optimized for different sampling conditions were recently designed and constructed, aiming at operational simplicity and portability. A newly developed Kr purification system enriches Kr by flowing a sample gas through a moderately cooled (138 K) activated charcoal column, followed by a gentle fractionating desorption. This simple process uses a single adsorbent and separates 99% of the bulk atmospheric gases from Kr without significant loss. The subsequent two stages of gas chromatographic separation and a hot Ti sponge getter further purify the Kr-enriched gas. Abundant CH4 necessitates multiple passages through one of the gas chromatographic separation columns. The presented Kr separation system has a demonstrated capability of extracting Kr with > 90% yield and 99% purity within 75 min from 1.2 to 26.8 L STP of atmospheric air with various concentrations of CH4. The apparatuses have successfully been deployed for sampling in the field and purification of groundwater samples.

Flow field thermal gradient gas chromatography.

Negative temperature gradients along the gas chromatographic separation column can maximize the separation capabilities for gas chromatography by peak focusing and also lead to lower elution temperatures. Unfortunately, so far a smooth thermal gradient over a several meters long separation column could only be realized by costly and complicated manual setups. Here we describe a simple, yet flexible method for the generation of negative thermal gradients using standard and easily exchangeable separation columns. The measurements made with a first prototype reveal promising new properties of the optimized separation process. The negative thermal gradient and the superposition of temperature programming result in a quasi-parallel separation of components each moving simultaneously near their lowered specific equilibrium temperatures through the column. Therefore, this gradient separation process is better suited for thermally labile molecules such as explosives and natural or aroma components. High-temperature GC methods also benefit from reduced elution temperatures. Even for short columns very high peak capacities can be obtained. In addition, the gradient separation is particularly beneficial for very fast separations below 1 min overall retention time. Very fast measurements of explosives prove the benefits of using negative thermal gradients. The new concept can greatly reduce the cycle time of high-resolution gas chromatography and can be integrated into hyphenated or comprehensive gas chromatography setups.

Exploring reverse shape selectivity and molecular sieving effect of metal-organic framework UIO-66 coated capillary column for gas chromatographic separation

Metal-organic frameworks (MOFs) which offer a variety of topologies, porous networks and high surface areas are promising and have potential for the applications of specific adsorption, isomerization, catalysis and separation. UIO-66 is the first MOF that has been observed to have reverse shape selectivity. However, such reverse shape selectivity of MOFs has never been explored for capillary gas chromatographic separation. Here we report the fabrication of MOF UIO-66 coated capillary column and exploration of the reverse shape selectivity and molecular sieving effect of such column for capillary gas chromatographic separation of alkane isomers and benzene homologues with excellent selectivity and precision. The adsorption enthalpies and entropies on the interaction between hydrocarbons and UIO-66 were measured to illustrate the energy effect on the separation of alkane isomers and benzene homologues on the UIO-66 coated capillary column. UIO-66 coated capillary column gave preferential retention of branched alkane isomers over their linear isomer, showing reverse shape selectivity, making UIO-66 coated capillary column attractive for capillary gas chromatographic separation of alkane isomers. iso-Propylbenzene (branched) eluted after n-propylbenzene on the UIO-66 coated capillary column again shows reverse shape selectivity. However, much bulkier 1,3,5-trimethylbenzene eluted earlier than n-propylbenzene and iso-propylbenzene on the UIO-66 coated capillary column, exhibiting molecular sieving effect. The combination of reverse shape selectivity with molecular sieving effect makes the UIO-66 coated capillary column promising for the separation of structural isomers.

Assessing the reliability of wall-coated microfabricated gas chromatographic separation columns

This study addresses several aspects of etched-silicon/glass microfabricated channels that affect their performance as micro-gas chromatographic (μGC) separation columns, including the consistency of stationary phase deposition, deactivation of surface-adsorption sites on the microcolumn walls, and the stability of the stationary phase following repeated thermal cycling. Convolved square-spiral microcolumns 0.5–3-m long with cross sections of 150μm×240μm consisting of deep-reactive-ion-etched (DRIE) Si with anodically bonded Pyrex caps are used. Replicate devices with wall-coated films of the non-polar polydimethylsiloxane (PDMS) or the moderately polar poly(trifluoropropylmethyl)siloxane (PTFPMS) deposited statically to a nominal thickness of 0.15μm provide minimum plate heights that are reproducible to 5% in air or helium carrier gases. Using split-flow injection, 4900theoreticalplates/m can be produced and a 19-vapor mixture can be separated on a 0.5-m PDMS-coated column in air in less than 3.5min. Significant reductions in peak tailing of polar analytes are afforded by surface pre-treatment or post-treatment with the deactivation agent hexamethyldisilazane (HMDS). In addition, retention times remain stable and peak widths remain stable or decrease after prolonged pre-conditioning at 200°C in air. Non-pretreated PTFPMS-coated microcolumns can produce 2300plates/m and also retain high resolution after pre-conditioning at 200°C in air. Marginal improvements in separation efficiency are achieved by pre-treatment with trifluoropropylmethylcyclotrisiloxane. Results demonstrate that efficient μGC columns with polar and non-polar stationary phases can be made reproducibly and operated at elevated temperatures in air.

Single fiber-in-capillary annular column for gas chromatographic separation

A method for preparation of a stationary phase-adjustable column with in-column stationary phase-coated fused-silica fiber annular column was successfully developed. The surface of a 0.12 mm o.d. bare optical fiber was first coated with a stationary phase and then inserted into a fused-silica capillary (non-coated or coated) as an annular column for gas chromatographic study. The optical fiber and capillary were coated with polydimethylsiloxane (SE-30) and polyethylene glycol 20M (PEG-20M) as nonpolar and polar stationary phases, respectively. Among the investigated annular and open tubular columns, the PEG-20M-coated fiber-in-PEG-20M-coated capillary annular column showed the highest column efficiency with a minimum plate height of 0.35 mm and an optimum gas velocity of 25 cm/s. When a SE-30/PEG-20M-coated fiber-in-uncoated capillary annular column was applied to separate a 9-component complex mixture, the total analysis time was 5.3 min and the column length was 12 m. By contrast, when a SE-30-coated fiber-in-PEG-20M-coated capillary annular column was used to separate the same 9-component mixture, the analysis time was reduced to 3.5 min and the column length was shortened by half to 6 m. Our results show that the stationary phase-coated fiber-in-stationary phase-coated capillary annular column is a better choice for gas chromatographic separation as it is more efficient and flexible. In addition, the proposed annular column design provides flexibility in using two or even more types of stationary phases to achieve optimal analytical separation.

A method for the airborne measurement of PAN, PPN, and MPAN

An aircraft‐based instrument for the measurement of peroxyacetic nitric anhydride (PAN) and related compounds peroxypropionic nitric anhydride (PPN), and peroxymethacrylic nitric anhydride (MPAN) is described. The instrument functions by direct injection of a small sample (2 ambient cm2) into a wide bore fused silica capillary gas chromatographic separation column with subsequent detection by electron capture. The efficiency of separation and early elution of water made possible a sampling frequency of once every 5 min. The selective destruction of PAN type compounds at 125°C in actual ambient samples showed that no interfering species were present. Calibration of the instrument was accomplished by the total odd‐nitrogen (NOy) measurement of air mixtures of high‐purity PANs. Inflight calibrations of PAN in either thermally decomposed ambient air or dry zero air showed that the sensitivity of the instrument to PAN was not affected by other matrix species such as carbon dioxide or water. The instrument response to PPN and MPAN relative to that of PAN was consistent (within 5%) over the span of several months. The instrument response to PAN was linear up to 3.5 ppbv and the slope of the response versus [PAN] indicated a relative standard deviation of 2% over the course of a 30‐day field study. The detection limits of the method for PAN and PPN were estimated to be 5 pptv (3s) based on the uncertainty of peak detection. The overall accuracy of the PAN measurement was estimated to be ±(5 pptv+15%) in one campaign and ±(5 pptv+20%) in others.

Features of metal capillary columns

Because of the inertness of their inner wall surface and their excellent bending strength and flexibility, fused silica (FS) columns have made a great contribution to the progress of gas chromatographic (GC) analysis. While maintaining such satisfactory basic properties, it is important that GC capillary columns have durability to withstand elevated temperature, an inner wall surface structure resistant to buildup, and a large sample loading capacity. Highly inert metal capillary columns that fulfill all of these requirements have been developed. This article discusses the features of these columns, which appear to be useful GC separation columns in the future. © 2000 John Wiley & Sons, Inc. J Micro Sep 12: 345–350, 2000

Optimization of the composition of mixed-phase columns for gas chromatographic separation of C 1C 2 halocarbons

Mixed-phase polar and non-polar columns were used for the separation of many chloro-, bromo- and iodomethanes, ethanes and ethenes, having one or more of the same or different halogen atoms in the molecule. The optimum phase composition was determined by using the window-diagram method. A column comprising 60% of OV-1 and 40% of SP-1000 [both 10% (w/w) on Chromosorb W DMCS (80–100 mesh)] was found useful for the separation of 33 different halogenated compounds. The effect of the analysis temperature on the resolution of closely eluted groups of peaks was investigated.

Determination of reduced sulfur gases in antarctic lakes and seawater by gas chromatography after solid adsorbent preconcentration

A preconcentration method for low levels of reduced sulfur compounds ( RSCs), such as dimethyl sulfide ( DMS), in aqueous samples was developed and tested in Antarctica. The gases were trapped in a solid adsorbent, Molecular Sieve 5 Å (80–100 mesh). RSCs were backflushed onto a gas chromatographic separation column after thermal desorption from the trap. The RSCs were detected with a sulfur specific dual flame photometric detector. RSCs in fresh samples from two meromictic lakes in the Vesthold Hills (Antarctica) were quantified with this method. A profile of DMS in Antarctic seawater was obtained during a period of phytoplankton bloom in the Antarctic summer. DMS, carbonyl sulfide and hydrogen sulfide were the major RSCs found. A study of recoveries from samples preserved for eight months with mercuric chloride showed that substancial losses of RSCs occurred. Carbon disulfide was detected in preserved samples from the lakes studied. Detection limits of DMS and carbonyl sulfide were 10 ng 1 −1 and 5 ng 1 −1 respectively.

The measurement of airflows using a rapid response tracer gas technique

The multiple tracer gas technique of I'Anson et al.1 has been improved, in order to increase the rate at which samples can be taken. Using parallel gas chromatographic separation columns, in conjunction with an electron capture detector, it is now possible to take an air/tracer gas sample every 30 seconds in the case of a 2-zone ventilation and air movement test. Rapid sampling enables a new, simplified analysis of the air movement between two connected zones to be employed. This analysis derives ventilation rates and intercell airflows simultaneously. A specimen set of results for 2 cell ventilation/air movement is given.

Determination of hydrocarbons in the parts per 10 9 range using glass capillary columns coated with aluminium oxide

The properties and limitations of a highly efficient gas chromatographic separation column are described. The column is of importance in the analysis of hydrocarbon emissions as it has the following advantages: high separation efficiency; good detection performance owing to a high signal-to-noise ratio; simultaneous determination of aromatics in the presence of other hydrocarbons in the C 1–C 9 range in a short time and without the need for a multi-column techniqe; simple on-line computer connection even in the parts per 10 9 range. The preparation of the column and its applications and use with suitable measuring equipment are described in detail.

A New Gas Chromatographic Separation Column for Pesticide Analysis

A New Gas Chromatographic Separation Column for Pesticide Analysis