Evaluation of a sol-gel derived carbon composite electrode as an amperometric detector for capillary electrophoresis

Modulation of inner filter effect of non-conjugated silver nanoparticles on blue emitting ZnS quantum dots for the quantitation of betahistine

A simple, reliable and efficient fluorescent probe has been developed for the detection and quantitation of betahistine using inner filter effect (IFE) of silver nanoparticles (AgNPs) on zinc sulphide (ZnS) quantum dots. The synthesized ZnS exhibited blue emission at 403 nm which was quenched upon mixing with AgNPs due to intensive localized surface plasmon resonance (LSPR) absorption at 401 nm. The presence of IFE was confirmed by UV-Visible and fluorescence spectroscopy, dynamic light scattering and transmission electron microscopy. Addition of betahistine caused aggregation of AgNPs as visualized by the change in colour of nano-suspension. The reduced absorption at LSPR resulted in inhibition of IFE leading to higher fluorescence intensities in the presence of betahistine. Parameters such as pH, incubation time and concentration of AgNPs were suitably optimized. The fluorescence signal (I - I₀/I₀) responded linearly for betahistine in the concentration range from 0.1 to 10 μM under the optimized experimental conditions. Due to the aggregation of AgNPs, a simple colorimetric approach was also studied for quantitation of betahistine in the range 1.0-20 μM. The limit of detection for fluorescence measurement and colorimetric approach was 0.02 μM and 0.23 μM, respectively. Further, the proposed method exhibited excellent selectivity towards betahistine in presence of several cations, biomolecules such as glucose, uric acid, creatinine, amino acids and several anti-vertigo medications. The method was applied to quantify betahistine from pharmaceutical products and results obtained were in good agreement with the claimed values. The proposed sensor can serve a low cost, selective, sensitive and a precise tool for routine quantitation of betahistine.

Spermine-graft-dextran non-covalent copolymer as coating material in separation of basic proteins and neurotransmitters by capillary electrophoresis

Spermine-graft-dextran (Spe-g-Dex) copolymer was synthesized and used as a non-covalent coating for the separation of proteins and neurotransmitters by capillary electrophoresis. The coating was obtained via flushing the capillary with 1.0% Spe-g-Dex copolymer solution for 2min. Electroosmotic flow (EOF) was strongly suppressed, ranging from -1.60x10(-9) to 3.65x10(-9)m(2)V(-1)s(-1). Effect of experimental conditions, such as the copolymer concentration, the concentration and pH of the background electrolyte (BGE), on the Spe-g-Dex coating was investigated. Separation of lysozyme, cytochrome c, ribonuclease A and alpha-chymotrypsinogen yielded high separation efficiencies ranging from 141000 to 303000plates/m and recoveries from 85.4% to 98.3% at pH 4.0 (284.0mM sodium acetate-acetic acid buffer, I=50mM). Run-to-run repeatabilities and day-to-day, and capillary-to-capillary reproducibilities were all below 1.7%. In addition, Spe-g-Dex coating allowed the successful separation of five neurotransmitters, 5-hydroxytryptamine, dopamine, epinephrine, isoprenaline, dobuamine at pH 4.0 with high separation efficiencies of 290000-449000plates/m.

Carbon Fiber/Epoxy Composite Ring-disk Electrode: Fabrication, Characterization and Application to Electrochemical Detection in Capillary High Performance Liquid Chromatography

Carbon fiber/epoxy composite materials, which are manufactured using the pultrusion process, are commercially available in various shapes and sizes at very low cost. Here we demonstrate the application of such a material as an electrochemical detector in a flow system. Cyclic voltammetry shows that the material's electrochemical behavior resembles that of glassy carbon. Using tube and rod composites, we successfully fabricated a ring-disk electrode with a 20 μm gap between the ring and the disk. The narrow gap is favorable for mass transfer in the generator-collector experiment. This composite ring-disk electrode is assembled in a thin-layer radial-flow cell and used as an electrochemical detector. The disk electrode, placed directly opposite to the flow inlet, is operated as a generator electrode with the ring electrode being a collector. The high collection efficiency on the ring electrode (0.8 for a chemically reversible species) enhances the detection selectivity.

A Sensitive Fluorimetric Method for the Determination of Epinephrine

A sensitive fluorimetric method for the determination of epinephrine (E) is described in this paper. The experiments indicate that epinephrine can react with formaldehyde (HCHO) in an acid medium to form a condensation product, which can be oxidized by potassium hexacyanoferrate(III) (K3[Fe(CN)6]) in borax buffer (pH = 9.5). The reaction product can emit strong fluorescence. Ascorbic acid (AA) is used in order to consume excess potassium hexacyanoferrate and stabilize the fluorescent product. Under optimum conditions, a linear relationship has been obtained between the fluorescence intensity and the concentration of epinephrine in the range of 1.4 x 10(-9) - 2.1 x 10(-6) mol/l, and the detection limit is 2.4 x 10(-10) mol/l (4.3 x 10(-11) g/ml, S/N = 3). The method is applied for the determination of E in both actual sample and the synthetic sample with E and norepinephrine (NE) by using the coupling technique of synchronous fluorimetry and H-point standard addition method, and the results obtained are satisfactory.