Open Tubular Silica Research Articles

Adjustable Methacrylate Porous Monolith Polymer Layer Open Tubular Silica Capillary Microextraction for the Determination of Polycyclic Aromatic Hydrocarbons

ABSTRACTA novel adjustable porous polymer monolith layer open tubular silica capillary microextraction (PLOT-ME) device was fabricated by thermal polymerization of a poly(glycidylmethacrylate-co-ethylene glycol dimethacrylate) (GMA-co-EDMA) polymer film (∼20 µm) within a 250 µm internal diameter silica capillary initiated with 4,4′-azobis(4-cyanopentanoyl chloride). The polymer film thickness and morphology were controlled by the polymerization time and temperature. The length of the microextraction platform immersed in the sample was adjusted by the sample concentration and sample matrix. Furthermore, since the microextraction platform performance typically degraded with use, the PLOT-ME device affords a new microextraction zone that may be exposed by cleaving off the end. This ability significantly reduces the cost of microextraction for academic and research environments. The performance of the PLOT-ME device was tested for microextraction of polycyclic aromatic hydrocarbons (PAHs): naphthalene, 2,6-dimethylnaphthalene, anthracene, 9-methylanthracene, and phenanthrene in aqueous media. Linear calibration curves for the PAHs were obtained with correlation coefficients near unity and relative standard deviations from 2 to 20% for PAH standards from 100 to 0.1 µg/L. The limits of detection for the PAHs were between 0.02 and 0.06 µg/L, while the recoveries were from 97 to 104% in lake water. The precision between different PLOT-ME devices was 11%.

Preparation and kinetic performance assessment of thick film 10–20 μm open tubular silica capillaries in normal phase high pressure liquid chromatography

It is well-known that the open tubular column design basically can offer very high plate numbers. Experimental realization has however not kept pace with theoretical considerations, lacking efficient methods for the deposition of a thick film porous layer within a microbore capillary. A previously published sol–gel synthesis method was extended from 20μm to 10μm inner diameter fused silica capillaries and the resulting columns were compared to a monolithic reference capillary in terms of kinetic performance at pressure maximum. Column permeability was investigated and pressure/flow-diagrams were obtained with a 400-fold permeability gain for the open tubes. Structural characterizations regarding layer thickness and surface porosity were carried out and displayed via scanning electron microscopy and nitrogen sorption analysis. Chromatographic results in normal phase mode at elevated mobile phase flow rate reveal the intrinsic performance potential of this column format when it comes to kinetic performance limitation plots, which were constructed for all columns prepared and compared to the monolithic silica reference capillary.

Performance evaluation of thick film open tubular silica capillary by reversed phase liquid chromatography

The unquestioned potential of open tubular column design for miniaturized liquid chromatography systems has been assessed recently. Instrument limitation and insufficient mass loadability of the columns, however, have prevented experimental breakthrough in this field, the latter requiring new methods for the deposition of thick films as the stationary phase. In this work, a previously proposed synthesis strategy has been applied for the preparation of a C8 modified 15μm inner diameter variant of 3m length, providing a silica porous layer with a thickness of approximately 500nm. The capillary column has been evaluated in terms of usability, permeability and chromatographic efficiency in reversed phase mode. Data was compared to both a monolithic and a particulate, commercially available C18 capillary column. High theoretical plate numbers have been generated in a test mixture separation composed of small molecules and the applicability of this new type of column was demonstrated by two reversed phase applications.

Synthesis and characterization of new generation open tubular silica capillaries for liquid chromatography

The chromatographic performance gain of open tubular (OT) silica capillaries over packed beds has been demonstrated theoretically. However, experimental progress in the preparative realization of these columns is still lacking behind as thick films are required for a sufficient mass loadability. Here, silica sol–gel chemistry in confined spaces was applied to the preparation of thick-film OT capillaries comprising a mesoporous layer with a thickness of approximately 500nm covalently attached to the capillary wall. Samples were synthesized varying both in length and inner diameter (ID) and the resulting layer morphology was investigated using scanning electron microscopy. The chromatographic performance of these first generation columns was evaluated by normal phase chromatography utilizing standard capillary-LC equipment. Separations of small molecules in a 15μm ID column provided high theoretical plate numbers (up to 170,000) and a good retention capacity within reasonable retention times (<1h), bearing the unavoidable trade-off between column efficiency and analysis time.

Comparative study for differentiation of aquatic humic-type organic constituents by capillary zone electrophoresis using polyvinyl alcohol-coated capillary

Capillary zone electrophoresis (CZE) with UV detection (254 nm) was applied to characterize aquatic dissolved humic matter (DHM) from different environmental sources (lake, river and sea waters, in all 15 different samples). A series of separation examples of DHMs using a polyvinyl alcohol (PVA)-coated silica open tubular capillary were carried out in a phosphate buffer (40 mM) as a background electrolyte at neutral acidity (pH 6.8). The separative power of electropherograms was reasonable and the reproducibility was above the mark. Each electropherogram was characteristic of the corresponding humic sample. Special functional fulvic and humic acids or their overall mixtures separated with XAD, DAX and DEAE sorbing solids as well as the original dissolved organic matter (DOM) were nicely differentiated according to their environmental sources. The PVA coating of open tubular silica capillaries seems to be very potential in electrophoretic characterization and separation of different humic solutes at neutral acidities with low sample concentrations thus permitting a workable technique, in a growing series of CZE studies, for better compared results from different studies.

Capillary gas-liquid chromatography of faecal free and esterified neutral sterols

A method is described for the analysis of faecal free and esterified neutral sterols by high-resolution capillary gas-liquid chromatography (GC). After homogenization and filtration of the sample, free and esterified sterols are separated by reversed-phase Lipidex-5000 chromatography. The esterified sterols are saponified and analysed by GC. The free sterols are further fractionated on a Lipidex-5000 straight-phase column into oxo- and hydroxysterols, respectively. The GC separation of the compounds is achieved with an SE-30 open-tubular silica capillary column. The mean recoveries of the authentic sterols are 90.0% +/- 5.8% (SD) and the mean within-assay coefficients of variations are 3.7% +/- 2.9% (SD). The method permits determination of (A) the main animal sterols (cholesterol, coprostanol, epicoprostanol, cholestanol, coprostanone and cholestanone), (B) the amount of total plant sterols (beta-sitosterol, campesterol, stigmasterol and their metabolic conversion products) and (C) the degree of esterification of neutral sterols. In addition results obtained in faecal samples from eight healthy young men eating normal Finnish food are presented.