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Electrospun polymer nanofiber stationary phases were examined for their application to planar electrochromatography (PEC). Separations were performed on polyacrylonitrile nanofiber ultra-thin-layer chromatography (UTLC) plates in 1-2 min using a ternary mobile phase. The influences of buffer concentration and pH, ratio of organic modifier, and development time on analyte migration distances were studied. Band broadening in this system was studied as a function of distance. The plate height initially decreased and then plateaued with a minimum plate height value as low as 11 μm. Nanofiber alignment considerably increased analyte migration rate, but larger spot sizes were noted when nearly complete fiber alignment was used. The easily tunable stationary phase thickness can be tailored to a given separation, where thinner layers promote faster separations and thicker layers are ideal for more complex mixtures. Compared to UTLC, PEC offers unique selectivity and decreased analysis time (4 times faster over 15 mm). Results for a two-dimensional separation using UTLC and PEC are also reported. These rapid separations required 11 min using a 40 × 40 mm plate and exhibited a significant increase in separation number (70-77).

Small diameter nanofibers of silica and silica/polymer are produced by electrospinning silica/polyvinylpyrrolidone (SiO2/PVP) mixtures composed of silica nanoparticles dispersed in polyvinylpyrrolidone solutions. By controlling various parameters, 380 ± 100 nm diameter composite nanofibers were obtained with a high silica concentration (57.14%). When the polymer concentration was low, “beads-on-a-string” morphology resulted. Nanofiber morphology was affected by applied voltage and relative humidity. Tip-to-collector distance did not affect the nanofiber diameter or morphology, but it did affect the area and thickness of the mat. Heat treatment of the composite nanofibers at 200°C crosslinked the polymer yielding solvent-resistant composite nanofibers, while heating at 465°C calcined and selectively removed the polymer from the composite. Crosslinking did not change the nanofiber diameter, while calcined nanofibers decreased in diameter (300 ± 90 nm) and increased in surface area to volume ratio. Nanofibers were characterized by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40966.

Nanofibrous silica-based stationary phases for electrospun ultra-thin layer chromatography (E-UTLC) are described. Nanofibers were produced by electrospinning a solution of silica nanoparticles dispersed in polyvinylpyrrolidone solutions to create composite silica/polymer nanofibers. Stationary phases were created from as-spun nanofibers, or the nanofibers were heated either to crosslink the polyvinylpyrrolidone or to calcine and selectively remove the polymer. As-spun, crosslinked, and calcined nanofibers with similar mat thicknesses (23–25 μm) were evaluated as stationary phases for E-UTLC separations of laser dyes and amino acids and compared to commercial silica TLC plates. As-spun nanofiber plates offered fast mobile phase velocities, but like other polymer-based nanofibers, separations were only compatible with techniques using nonsolvents of the polymer. Crosslinked nanofibers were not as limited in terms of chemical stability, but separations produced tailed spot shapes. No limitations in terms of mobile phases, analyte solvents, and visualization techniques were observed for calcined nanofibers. Highly efficient separations of amino acids were performed in 15 mm on calcined nanofiber plates, with observed plate heights as low as 8.6 μm, and plate numbers as large as 1400. Additional alignment of the nanofibers provided shorter analysis times but also larger spot widths. The extension of stationary phases to silica-based nanofibers vastly expands the range of mobile phases, analyte solvents, and visualization techniques which can be used for E-UTLC separations.

Electrospun epoxide polymer and carbon nanofiber-based SPME phases were examined for their application to the direct extraction of nonvolatile analytes coupled to liquid chromatography (LC). All of the electrospun nanofiber-coated SPME fibers demonstrated superior extraction efficiencies which were 2-32 times higher than a commercially available SPME fiber, with the electrospun coating processed at 800°C demonstrating the highest extraction efficiency. The carbonized electrospun nanofiber-coated SPME fibers showed no swelling when immersed in a variety of liquids, demonstrating the improved chemical stability these coatings have over traditional polymer-coated SPME fibers, which typically swell during direct extraction. Additionally, these robust coatings exhibit prolonged fiber lifetimes, withstanding up to 100 direct extractions without significant damage or change in nanofiber morphology. The detection limits of the method were found to be 2-3 orders of magnitude lower than those reported when using commercially available polyacrylate (PA) SPME fiber under similar conditions.

The development and application of a novel extractive phase for solid-phase microextraction (SPME) is described herein. The extractive phase is comprised of polymeric nanofibers, deposited on a small stainless steel support via electrospinning; these polymeric nanofibers can then be pyrolyzed to give carbon nanofibers. The electrospun nanofibrous SPME coatings provide a high surface area sorbent, giving low detection limits and high extraction efficiencies for both nonpolar and polar compounds. The electrospun SPME fibers consistently outperform commercially available SPME devices. The carbon nanofiber-based SPME phases also demonstrate high chemical and thermal stability, allowing for application to a diverse array of matrices. Here, the electrospun nanofibrous SPME devices are applied to the headspace extraction of benzene, toluene, ethylbenzene, and o-xylene (BTEX) and a mixture of phenolic compounds, followed by separation and quantitation utilizing gas chromatography (GC). Additionally, these same fibers were applied to the direct extraction of a variety of pharmaceutical pollutants, specifically an aqueous mixture of β-blockers and steroidal compounds. The fibers were subsequently analyzed utilizing on-line desorption and liquid chromatography (LC).