Polymer-Coated Fibrous Materials as the Stationary Phase in Packed Capillary Gas Chromatography

Preconcentration of Aromatic Compounds in Aqueous Samples with a Polymer-coated Fiber-packed Capillary and Subsequent Temperature-programmed Elution with Water for Pseudo-2D LC Separations

A bundle of polymer-coated filaments was successfully introduced as an extraction medium for the preconcentration of an aqueous solution of aromatic compounds. The extraction was simply carried out with pumping the aqueous sample solution to the extraction capillary at ambient temperature. The extracted analytes were sequentially eluted with a flow of pure water using temperature-programmed heating of the extraction capillary in an oven. The results clearly suggest that the polymer-coated fiber-packed capillary could be employed in the sample preparation process for the analysis of various aqueous samples. Introducing the fractions eluted from the fiber-packed capillary to a conventional microcolumn liquid chromatography (micro-LC) system via a home-made valve-based modulator, an on-line coupled extraction/separation system was developed and a possibility to a pseudo-two-dimensional (pseudo-2D) LC separation of aromatic compounds in aqueous matrices has also been demonstrated.

High-temperature separations on a polymer-coated fibrous stationary phase in microcolumn liquid chromatography

Novel polymer-coated fiber-packed microcolumns in liquid chromatography (LC) have been developed. Typical polymeric materials, such as polydimethylsiloxane and polyethyleneglycol, which are conventional stationary phases of capillary columns in gas chromatography (GC), have been employed as coating materials onto the surface of fine filaments. Packed longitudinally with a bundle of polymer-coated filaments into a stainless-steel capillary of 0.8 mm i.d., 150 mm length, several types of polymer-coated fiber-packed columns were prepared, and the retention behavior of aromatic compounds on these columns has been studied. A good linear relationship was obtained for van't Hoff plots over the temperature range between 0 and 200 °C, clearly indicating an excellent heat-resistant property of these polymer-coated fibrous stationary phases. Taking advantage of the heat-resistant feature of the fibrous stationary phases, the separation of several test mixtures with temperature-programmed elution was studied, where a solvent gradient program was additionally introduced if needed. Separation was also carried out with pure water as the mobile phase using an appropriate temperature program.

Rapid temperature-programmed separation and retention prediction on a novel packed-capillary column in gas chromatography

Novel packed-capillary columns for gas chromatography were developed with a thin-wall stainless-steel capillary of 1.0 mm i.d.; and rapid temperature-programmed separations have been carried out after a basic evaluation concerning the compatibility of these columns to the temperature program. With a numerical integration method, the retention of several test analytes during temperature-programmed elution was successfully estimated. In order to confirm the suitability of the packed-capillary columns to relatively fast temperature programming up to 40 degrees C/min, theoretically predicted retention data were compared with that actually measured. The results suggested a good separation performance of the newly developed packed-capillary columns as a particle-packed column conventionally used. Also, the compatibility to a rapid temperature-programmed operation was quite satisfactory for almost all of the separations currently done in typical analytical laboratories.

Retention behavior on aminoethyl-modified poly(p-phenylene terephthalamide) fiber stationary phases in gas chromatography

Surface derivatization of Kevlar, poly(p-phenylene terephthalamide), fiber has been studied along with the evaluation of the surface characteristics of the chemically-modified fiber as the stationary phase in packed-capillary gas chromatography (GC). Several experimental parameters in the derivatization reaction have been optimized, and the retention behavior of the surface-derivatized fibrous stationary phase has been investigated using various standard solutes, such as alkanes, alcohols and alkylbenzenes. By introducing aminoethyl functional groups onto the surface of the fibrous material, a specific selectivity for polar solutes has been observed.

Trends in the adsorption of volatile organic compounds in a large-pore metal-organic framework, IRMOF-1

Metal-organic frameworks have been proposed as useful sorbents for the capture of a variety of compounds. In this work, inverse gas chromatography (IGC) utilizing micropacked capillary columns was used to probe the adsorption of more than 30 volatile organic compounds (VOCs) on IRMOF-1. In an attempt to study the effect of structural degradation upon VOC adsorption, multiple samples of IRMOF-1 with widely ranging properties were investigated. Trends in the differential enthalpies and equilibrium constants for the adsorption of VOCs were determined on the basis of the molecular properties of the adsorbate and the structural properties of the MOF sample. The results indicate that samples of IRMOF-1 that are affected by a moderate amount of structural degradation interact with adsorbed species more strongly than does a sample with fewer defects, resulting in higher heats of adsorption. Samples of IRMOF-1 with specific surface areas of around 1000 m(2)/g show heats of adsorption for alkanes that are higher than those estimated previously via Monte Carlo calculations. Although the data for nonpolar (and weakly polar) species showed many of the anticipated trends for the interactions with IRMOF-1, the equilibrium behavior of polar VOCs did not correlate well with the molecular properties of the adsorbate (i.e., vapor pressure and deformation polarizability), leaving some uncertainty about the nature of the interaction mechanism. The equilibrium data and the heats of adsorption were found to fit well to a small group of molecular descriptors through the application of the Abraham linear free-energy relationship, thus providing insight into the complex interactions between the MOF structure and the VOC compounds. Hydrogen bonding interactions were determined to be the primary contributors to specific interactions between adsorbates and the MOF surface. Size exclusion also seems to play a role in the adsorption of larger species. These results show that the interaction of VOCs with MOFs is more complex than previously assumed and that more work is needed to probe the mechanisms of these processes.

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 20 M (PEG-20 M) as nonpolar and polar stationary phases, respectively. Among the investigated annular and open tubular columns, the PEG-20 M-coated fiber-in-PEG-20 M-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-20 M-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-20 M-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 6m. 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.

Fabrication and performance of fiber electrophoresis microchips

A method based on the in situ polymerization of methyl methacrylate (MMA) has been developed for the rapid fabrication of a novel separation platform, fiber electrophoresis microchip. To demonstrate the concept, prepolymerized MMA molding solution containing a UV initiator was sandwiched between a poly(methyl methacrylate) (PMMA) cover plate and a PMMA base plate bearing glycerol-permeated fiberglass bundles and was exposed to UV light. During the UV-initiated polymerization, the fiberglass bundles were embedded in the PMMA substrate to form fiberglass-packed microchannels. When the glycerol in the fiberglass bundles was flushed away with water, the obtained porous fiberglass-packed channels could be employed to perform electrophoresis separation. Scanning electron micrographs (SEMs) and microscopic images offered insights into the fiber electrophoresis microchip. The analytical performance of the novel microchip has been demonstrated by separating and detecting dopamine and catechol in connection with end-column amperometric detection. The fiber-based microchips can be fabricated by the new approach without the need for complicated and expensive lithography-based microfabrication techniques, indicating great promise for the low-cost production of microchips, and should find a wide range of applications.

Miniaturized sample preparation needle: A versatile design for the rapid analysis of smoking-related compounds in hair and air samples

Miniaturized needle extraction device has been developed as a versatile sample preparation device designed for the rapid and simple analysis of smoking-related compounds in smokers' hair samples and environmental tobacco smoke. Packed with polymeric particle, the resulting particle-packed needle was employed as a miniaturized sample preparation device for the analysis of typical volatile organic compounds in tobacco smoke. Introducing a bundle of polymer-coated filaments as the extraction medium, the needle was further applied as a novel sample preparation device containing simultaneous derivatization/extraction process of volatile aldehydes. Formaldehyde (FA) and acetaldehyde (AA) in smoker's breath during the smoking were successfully derivatized with two derivatization reagents in the polymer-coated fiber-packed needle device followed by the separation and determination in gas chromatography (GC). Smokers' hair samples were also packed into the needle, allowing the direct extraction of nicotine from the hair sample in a conventional GC injector. Optimizing the main experimental parameters for each technique, successful determination of several smoking-related compounds with these needle extraction methods has been demonstrated.

Fiber-packed needle for dynamic extraction of aromatic compounds

A fiber-packed needle was developed as a novel extraction device for gas-chromatographic analysis of trace organic compounds in aqueous samples. In the extraction device, a bundle of the polymer-coated filaments as the sorbent material was longitudinally packed into a specially designed needle. The extraction was made by pumping the aqueous sample solution into the needle extraction device, and the subsequent desorption process was carried out with a flow of desorption solvent through the needle in a heated gas chromatograph injector. The needle device showed an excellent thermal stability for repeated use without any deterioration of extraction performance, and no carryover effect was observed after the optimization of the desorption conditions. Additionally, the extraction efficiency of the fiber-packed needle could be enhanced by optimizing the number of packed filaments. The selectivity for various compounds could be also tuned using an appropriate combination of the fibrous medium and the coating polymer. The relative standard deviation for run to run was from 3.88 to 4.55% (n = 5), and that for needle to needle was 7.21% (n = 3), clearly suggesting a good repeatability of the needle extraction technique developed. Upon successful optimization of the extraction conditions, a rapid extraction of trace organic compounds from an aqueous sample matrix was successfully demonstrated, where each extraction process was completed within 10 min.

Analysis of polycyclic aromatic hydrocarbons (PAHs) in environmental samples: a critical review of gas chromatographic (GC) methods

Polycyclic aromatic hydrocarbons (PAHs) are frequently measured in the atmosphere for air quality assessment, in biological tissues for health-effects monitoring, in sediments and mollusks for environmental monitoring, and in foodstuffs for safety reasons. In contemporary analysis of these complex matrices, gas chromatography (GC), rather than liquid chromatography (LC), is often the preferred approach for separation, identification, and quantification of PAHs, largely because GC generally affords greater selectivity, resolution, and sensitivity than LC. This article reviews modern-day GC and state-of-the-art GC techniques used for the determination of PAHs in environmental samples. Standard test methods are discussed. GC separations of PAHs on a variety of capillary columns are examined, and the properties and uses of selected mass spectrometric (MS) techniques are presented. PAH literature on GC with MS techniques, including chemical ionization, ion-trap MS, time-of-flight MS (TOF-MS), and isotope-ratio mass spectrometry (IRMS), is reviewed. Enhancements to GC, for example large-volume injection, thermal desorption, fast GC, and coupling of GC to LC, are also discussed with regard to the determination of PAHs in an effort to demonstrate the vigor and robustness GC continues to achieve in the analytical sciences.

Simultaneous derivatization/preconcentration of volatile aldehydes with a miniaturized fiber-packed sample preparation device designed for gas chromatographic analysis

A novel in-needle sample preparation device has been developed for the determination of volatile aldehydes in gaseous samples. The needle device is designed for the gas chromatographic (GC) analysis of aldehydes and ketones commonly found in typical in-house environments. In order to prepare the extraction device, a bundle of polymer-coated filaments was longitudinally packed into a specially designed needle. Derivatization reactions were prompted by 2,4-dinitrophenylhydrazine (NDPH) included in the needle, and so the aldehydes and ketones were derivatized to the corresponding hydrazones and extracted with the extraction needle. A reproducible extraction needle preparation process was established, along with a repeatable derivatization/extraction process that ensures the successful determination of aldehydes. The storage performance of the extraction needle was also evaluated at room temperature for three days. The results demonstrate the successful application of the fiber-packed extraction device to the preparation of a gaseous sample of aldehydes, and the future possibility of applying the extraction device to the analysis of in-house environments.

In-needle extraction device designed for gas chromatographic analysis of volatile organic compounds

A novel in-needle extraction device has been developed for the preconcentration of gaseous organic compounds prior to the determination in gas chromatography (GC). As the extraction medium, a copolymer of methacrylic acid and ethylene glycol dimethacrylate was synthesized. Based on the results in the preliminary experiments, the desorption conditions such as desorption temperature and time have been optimized along with the evaluation of the extraction efficiency. The storage performance of the needle extraction device was also studied. The results clearly demonstrated the excellent extraction performance for typical organic solvents and also suggested the future possibility such as in the applications for the analysis of working environments.

Surface derivatization of poly(p-phenylene terephthalamide) fiber designed for novel separation and extraction media

The surface derivatization of poly(p-phenylene terephthalamide) fiber was studied. The obtained surface-derivatized filaments were packed into a fused-silica capillary to evaluate its surface characteristics by using GC. As the stationary phase for GC the surface-derivatized fibers showed higher retention for alkanes and alkylbenzenes than that with the untreated Kevlar fiber. The improvements on the retention power and the peak shape were observed on the benzyl-modified fibrous stationary phase. The derivatized fibrous materials were also evaluated as the extraction medium in fiber-in-tube SPE, and the effect of the surface modification on the extraction power was compared to the parent fiber. The results indicated that the modified fiber possessed a higher extraction power than the untreated fiber. Based on the facts, the successful modification of the fiber surface was estimated.

High-temperature separation with polymer-coated fiber in packed capillary gas chromatography

High-temperature gas chromatographic separation of several synthetic polymer mixtures with Dexsil-coated fiber-packed columns was studied. A bundle of heat-resistant filaments, Zylon, was longitudinally packed into a short metal capillary, followed by the conventional coating process with Dexsil 300 material. Prior to the packing process the metal capillary was deactivated by the formation of a silica layer. The typical size of the resulting column was 0.3-mm i.d., 0.5-mm o.d., 1-m length, and packed with about 170 filaments of the Dexsil-coated Zylon. The column temperature could be elevated up to 450 degrees C owing to the good thermal stability of the fiber, Dexsil coating, and metal capillary; furthermore, this allowed the separation of low-volatile compounds to be studied.

Capillary columns in liquid chromatography: between conventional columns and microchips

Liquid chromatography on columns with small internal diameters has been reviewed as the intermediate technique between conventional liquid chromatography and microchip separations. The development of micro column separations in the early years has been described, starting with the papers of Horváth and co-workers and Ishii and co-workers, continuing into the first part of the eighties, then making a leap in time to recent innovations with small-bore columns. Based on internal diameters a classification of the different analytical HPLC columns has been suggested. The advantages of small-bore columns have been discussed, with particular emphasis on the advantage of coupling to concentration sensitive detectors when the sample amount is limited. Open tubular columns are treated as a part of the historic background. The recent developments include a brief look into the current status of monolithic columns, the use of packed nano columns and micro columns with electrospray mass spectrometry, and the potential of two-dimensional comprehensive liquid chromatography. Finally, the coupling of sample preparation to analytical columns and the future applications of the novel technological improvements to the microchip separation methods have been discussed.