Samuel Chigome

A review of opportunities for electrospun nanofibers in analytical chemistry.

Challenges associated with analyte and matrix complexities and the ever increasing pressure from all sectors of industry for alternative analytical devices, have necessitated the development and application of new materials in analytical chemistry. To date, nanomaterials have emerged as having excellent properties for analytical chemistry applications mainly due to their large surface area to volume ratio and the availability of a wide variety of chemical and morphological modification methods. Of the available nanofibrous material fabrication methods, electrospinning has emerged as the most versatile. It is the aim of this contribution to highlight some of the recent developments that harness the great potential shown by electrospun nanofibers for application in analytical chemistry. The review discusses the use of electrospun nanofibers as a platform for low resolution separation or as a chromatographic sorbent bed for high resolution separation. It concludes by discussing the applications of electrospun nanofibers in detection systems with a specific focus on the development of simple electrospun nanofiber based colorimetric probes.

Electrospun carbon nanofibers from polyacrylonitrile blended with activated or graphitized carbonaceous materials for improving anodic bioelectrocatalysis.

The electrospun carbon nanofibers obtained from polyacrylonitrile (PAN) and PAN blends with either activated carbon (PAN-AC) or graphite (PAN-GR) were tested as anodes using Shewanella oneidensis MR-1. Extensive physico-chemical and electrochemical characterization confirmed their formation, their fibrous and porous nature, and their suitability as electrodes. N2 adsorption measurements revealed high specific surface area (229.8, 415.8 and 485.2m(2) g(-1)) and porosity (0.142, 0.202 and 0.239cm(3)g(-1)) for PAN, PAN-AC and PAN-GR, respectively. The chronoamperometric measurements showed a considerable decrease in start-up time and more than a 10-fold increase in the generation of current with these electrodes (115, 139 and 155μAcm(-2) for PAN, PAN-AC and PAN-GR, respectively) compared to the graphite electrode (11.5μAcm(-2)). These results indicate that the bioelectrocatalysis benefits from the blending of PAN with activated or graphitized carbonaceous materials, presumably due to the increased specific surface area, total pore volume and modification of the carbon microstructure.

Semi-micro solid phase extraction with electrospun polystyrene fiber disks

A technique is described for performing solid phase extraction (SPE) at a semi-microscale. 10 mg of electrospun polystyrene fibers (average diameter 2.7 µm) were packed into a SPE barrel to form a disk (5 mm × 1 mm). The device was employed to evaluate the extraction of four steroids: prednisone, hydrocortisone, cortisone acetate and 19-nortestosterone from water and plasma matrices. The analytes were desorbed from the fibers with 100 µl methanol and monitored by high performance liquid chromatography with a diode array detector (HPLC-DAD). The semi-micro SPE method provided extraction recoveries of 51.14–80.13% in plasma and 66.07–93.43% in water. The breakthrough volumes at 500 ng ml−1 ranged from 200–400 µl for all analytes. At optimal conditions, the four analytes followed an excellent linear relationship in the range 12.5–400 ng ml−1 with coefficients of determination (r2) greater than 0.99 and the limits of detection ranged from 0.75 to 1.29 ng ml−1. Due to its simplicity, it is anticipated that the method will greatly simplify disk solid phase extraction.

Synthesis and Characterization of Electrospun Poly(ethylene oxide)/Europium-Doped Yttrium Orthovanadate (PEO/YVO4:Eu3+) Hybrid Nanofibers

Europium-doped yttrium orthovanadate/polyethylene oxide nanofibers were fabricated by firstly, synthesizing crystalline YVO4:Eu3+ nanoparticles using an aqueous precipitation method followed by electrospinning of PEO/YVO4:Eu3+ polymer composites. X-ray diffraction patterns showed that the nanoparticles exhibited well-defined peaks that were indexed as the tetragonal phase of YVO4. No additional peaks of other phases were observed indicating that Eu3+ ions were effectively built into the YVO4 host lattice. The photoluminescence spectra for the nanofibers showed peaks at 593, 615, 650, and 698 nm which was ascribed to the 5D0− 7F1, 5D0− 7F2, 5D0− 7F3 and 5D0− 7F4 transitions of Eu3+. Due to an efficient energy transfer from vanadate groups to Eu3+, the composite nanofibers showed a strong red emission under ultraviolet excitation characteristic of the red luminescence of the europium ion. The results demonstrate that this synthetic approach could prove to be viable for the fabrication of rare earth/polymer composite nanofibers intended for luminescent device applications.

A (-)-norephedrine-based molecularly imprinted polymer for the solid-phase extraction of psychoactive phenylpropylamino alkaloids from Khat (Catha edulis Vahl. Endl.) chewing leaves.

A molecularly imprinted polymer (MIP) was prepared using (-)-norephedrine as the template, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker and chloroform as the porogen. The MIP was used as a selective sorbent in the molecularly imprinted solid-phase extraction (MIP-SPE) of the psychoactive phenylpropylamino alkaloids, norephedrine and its analogs, cathinone and cathine, from Khat (Catha edulis Vahl. Endl.) leaf extracts prior to HPLC-DAD analysis. The MIP was able to selectively extract the alkaloids from the aqueous extracts of Khat. Loading, washing and elution of the alkaloids bound to the MIP were evaluated under different conditions. The clean baseline of the Khat extract obtained after MIP-SPE confirmed that a selective and efficient sample clean-up was achieved. Good recoveries (90.0-107%) and precision (RSDs 2.3-3.2%) were obtained in the validation of the MIP-SPE-HPLC procedure. The content of the three alkaloids in Khat samples determined after treatment with MIP-SPE and a commercial Isolute C18 (EC) SPE cartridge were in good agreement. These findings indicate that MIP-SPE is a reliable method that can be used for sample pre-treatment for the determination of Khat alkaloids in plant extracts or similar matrices and could be applicable in pharmaceutical, forensic and biomedical laboratories. Copyright

Enrichment of Cu(II), Ni(II), and Pb(II) in Aqueous Solutions Using Electrospun Polysulfone Nanofibers Functionalized with 1-[Bis[3-(Dimethylamino)-propyl]amino]-2-propanol

Polysulfone functionalized with 1-[bis[3-(dimethylamino)-propyl]amino]-2-propanol was electrospun into nanofibers and then employed as a novel platform for the enrichment of Cu(II), Ni(II), and Pb(II) metal ions in aqueous solutions. Parameters affecting adsorption such as fiber diameter, contact time, and pH were investigated. The capacity of the functionalized electrospun fibers to enrich metal ions from various aqueous matrices such as tap water, river water, seawater, treated as well as untreated sewage, was evaluated for spiked samples by inductively coupled plasma optical emission spectroscopy. The equilibrating times for maximum enrichment were 20 min for Cu(II) and Pb(II) respectively and 30 min for Ni(II). Recoveries, in 100 mg L−1 metal ion solutions, ranged from 89.58% (in untreated sewage) to 99.86% for Cu(II) in tap water, 69.70% (in untreated sewage) to 98.64% (in river water) for Ni(II), and from 71.46% (in untreated sewage) to 99.01% (for seawater) for Pb(II). The lowest concentration of metal ions that the functionalized nanofibers could detect in real sample matrices was 0.001 mg L−1. The metal adsorption kinetics followed a first order rate while the adsorption isotherms best fitted into the Freundlich model. The nanofibers could be regenerated and reused up to five times without a significant deterioration in adsorption and desorption efficiencies. The functionalized electrospun nanofibers present an excellent platform for trace enrichment of metal ions from aqueous solutions at pH values close to that at which the pollutants occur in the environment.

Evaluation of electrospun fibers as solid phase extraction sorbents for sample preparation in HPLC-MS/MS confirmatory doping control analysis of dexamethasone and betamethasone

The aim of the present work was to evaluate the possibility of a fast, simple, and greener sample preparation method using electrospun fibers as SPE sorbents and its application for doping control analysis. Electrospun polymer fibers of polystyrene with smooth morphology (1.3 μm average diameter) were used as sorbent materials for the fabrication of miniaturized solid phase extraction devices. A microcolumn SPE device (10 mg of electrospun fibers packed in a 200 μL pipette tip) and a SPE disk device (10 mg of electrospun fibers packed in a 500 μL polypropylene barrel) were used. Their performance was evaluated using dexamethasone and betamethasone as model analytes for the analysis of drug residues in biological samples. A qualitative confirmatory method for the detection of these glucocorticosteroids by HPLC-MS/MS in human urine was developed using electrospun microfibers for sample clean-up and pre-concentration. The limit of detection for both analytes was 10 ng mL−1 in urine matrix, and the resulting analytical method is at the same time fit for purpose (complying with strict requirements of doping control international organizations), simple (using tip-based microcolumns) and has a greener footprint (using very small amounts of organic solvents).

Electrospun nanofiber sorbents for the pre-concentration of urinary 1-hydroxypyrene

BackgroundSynthetic polymers have some qualities that make them good candidates for pre concentration of trace analytes biological fluids because of their great potentials to be functionalized and electrospun into nanofibres.MethodsIn this study, Electrospun nanofiber sorbents fabricated from 11 polymers {poly(styrene-co-methacrylic acid), poly(styrene-co-divinylbenzene) (SDVB), poly(styrene-co-acrylamide), poly(styrene-co-p-sodium styrene sulfonate), polystyrene, poly(vinyl benzyl chloride), cellulose acetate, polyethylene terephthalate (PET), polysulfone, nylon 6} were evaluated for the extraction and pre-concentration of 1-hydroxypyrene from a water sample.ResultsScanning electron microscopy (SEM) studies revealed the formation of continuous fine bead-free and randomly arrayed fibers with their average diameters ranging from 110 to 650 nm. The percentage recoveries were highest for nylon 6 with 72%, SDVB with 70%, whereas PET achieved the lowest recovery at 34%. Under optimized conditions, the analyte followed a linear relationship for all sorbents in the concentration range of 1 to 1,000 μg/L. The coefficient of determination (r2) was between 0.9990 to 0.9999, with precision (%relative standard deviation (RSD)) ≤ 9.51% (n = 6) for all the analysis. The %RSD for intra- and inter-day precision at three different concentrations, 10, 25, and 50 μg/L, was ≤7.88% for intraday and ≤8.04% inter-day (3 days), respectively, for all evaluated sorbents. The LOD and LOQ were found to be between 0.054 and 0.16 μg/L and 0.18 and 0.53 μg/L, respectively, using a fluorescent detector.ConclusionsThe study suggested that if packed into cartridges, nylon 6 and SDVB nanofiber sorbents could serve as alternatives to the conventional C-18 sorbents in the pre-concentration and clean-up of the tumorigenic biomarker, 1-hydroxypyrene in human urine. The fabrication of selective nanofibers could also extend and simplify sample preparation for organic and biological analytes.

Development of a Styrene Based Molecularly Imprinted Polymer and Its Molecular Recognition Properties of Vanadyl Tetraphenylporphyrin in Organic Media

A highly selective molecularly imprinted polymer (MIP) was synthesized and employed as an adsorbent material for the removal of vanadyl tetraphenylporphyrin (VTPP) from organic media. The maximum adsorption capacity of MIP (0.600 mg/g) toward VTPP was higher than that of the nonimprinted polymer (NIP; 0.281 mg/g). The accuracy of the method was validated by analyzing the certified reference material (CRM) NIST SRM 1634c, Trace Metals in Residual Fuel Oil, and the concentration of VTPP in the CRM was found to be 28.49 mg/kg, which was significantly comparable with the certified value of 28.19 mg/kg.

A thirst for advancement

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