Suzanne K. Lunsford

THE ELECTROCHEMISTRY OF NEUROTRANSMITTERS AT CONDUCTING ORGANIC POLYMER ELECTRODES : ELECTROCATALYSIS AND ANALYTICAL APPLICATIONS

The electrooxidation of catechols, catecholamines and NADH at conventional electrode materials is generally characterized by high degrees of irreversibility as well as strong adsorption and, hence, fouling by reactants and/or products of the reactions. On the contrary, the rates of the electron transfer are highly catalysed by the use of conducting polymer films, such as poly(3-methylthiophene), polyphenylene, polyanaline and polypyrrole, as described here. Furthermore, the usual fouling problems are eliminated. Even interference from electroinactive large proteins, such as haemoglobin, and other surfactants are substantially reduced. Also, electron spectroscopy for chemical analysis, energy-dispersive analysis of X-rays, theoretical diffusion coefficient calculations, metal ion coordination, solution diffusion analyses of cyclic voltammograms etc. show that the electron transfer occurs at the polymer-solution interface and not at the inert electrode substrate surface after diffusion through the polymer matrix or through pores. The analytical application of these polymer electrodes as amperometric detectors for flow injection analysis and high performance liquid chromatography are given. In addition, selective potentiometric electrodes for catecholamines based on conducting polymer films of crown ethers, such as binaphthyl-20-crown-6, dibenzo-18-crown-6, etc., have been developed and characterized. These potentiometric detectors significantly decrease the usual interferences of ascorbic acid, uric acid and acetaminophen found in amperometric detection.

Voltammetric determination of catechol using a sonogel carbon electrode modified with nanostructured titanium dioxide

In this study, we investigate highly efficient sonogel carbon electrode (SGC/TiO(2)) modified with nanostructured titanium dioxide synthesized via sol-gel method employing surfactant template for tailor-designing the structural properties of TiO(2). The stable SGC/TiO(2) electrode detects catechol, a neurotransmitter, in the presence of ascorbic acid, a common interferent, using cyclic voltammetry. A possible rationale for the stable catechol detection of SGC/TiO(2) electrode is attributed to most likely the adsorption of catechol onto highly porous TiO(2) (surface area of 147m(2)g(-1) and porosity of 46.2%), and the formation of C(6)H(4)(OTi)(2) bond between catechol and TiO(2). The catechol absorbed onto TiO(2) rapidly reaches the SGC surface, then is oxidized, involving two electrons (e(-)) and two protons (H(+)). As a result, the surface of TiO(2) acts as an electron-transfer accelerator between the SGC electrode and catechol. In addition to the quantitative and qualitative detection of catechol, the SGC/TiO(2) electrode developed here meets the profitable features of electrode including mechanical stability, physical rigidity, and enhanced catalytic properties.

Optimization of preparation of poly(3-methylthiophene)-modified Pt microelectrodes for detection of catecholamines

Abstract Prior studies have shown that poly(3-methylthiophene)-modified platinum electrodes (P3MT/Pt) have improved electrochemical reversibility, selectivity, and sensitivity for the detection of catecholamines when compared with conventional electrodes. Difficulties have, however, been encountered, as a P3MT film grows beyond the edges of the Pt electrode substrate during electropolymerization, and, consequently, increases the surface area of the electrode. The width of the film growth beyond the edges of the substrate depends on electropolymerization conditions and the size of the electrode substrate. This makes the catecholamine analysis irreproducible from electrode to electrode, and especially limits the application of the P3MT/Pt system as micro- and ultramicro-electrodes. In order to control the edge effect, optimization of the preparation conditions of P3MT/Pt electrodes, including temperature, monomer concentration, deposition time, voltage, and electrolyte concentration, was studied by fractional factorial design (FFD). Improved P3MT/Pt microelectrodes were achieved by applying the optimal conditions, which simultaneously reduced the edge effect. Also, P3MT/Pt film electrodes polymerized at −20°C exhibited the same electrocatalytic properties, which are essential for detection of catecholamines, as those electrodes made at room temperature.

Electrochemical response of carbon paste electrode modified with mixture of titanium dioxide/zirconium dioxide in the detection of heavy metals: lead and cadmium.

A novel carbon modified electrode was developed by incorporating titanium dioxide/zirconium dioxide into the graphite carbon paste electrode to detect heavy metals-cadmium and lead. In this work, the development of the novel titanium dioxide/zirconium dioxide modified carbon paste electrode was studied to determine the optimum synthesis conditions related to the temperature, heating duration, amount and ratio of titanium dioxide/zirconium dioxide, and amount of surfactant, to create the most reproducible results. Using cyclic voltammetric (CV) analysis, this study has proven that the novel titanium dioxide/zirconium dioxide can be utilized to detect heavy metals-lead and cadmium, at relatively low concentrations (7.6×10(-6) M and 1.1×10(-5) M for Pb and Cd, respectively) at optimum pH value (pH=3). From analyzing CV data the optimal electrodes surface area was estimated to be 0.028 (±0.003) cm(2). Also, under the specific experimental conditions, electron transfer coefficients were estimated to be 0.44 and 0.33 along with the heterogeneous electron transfer rate constants of 5.64×10(-3) and 2.42×10(-3) (cm/s) for Pb and Cd, respectively.

Monitoring of 2-butanone using a Ag–Cu bimetallic alloy nanoscale electrochemical sensor

Spherical shaped silver–copper alloy nanoparticles of 10–15 nm size were synthesized by an aqueous polymer solution method. The synthesized nanoscale Ag–Cu alloy was characterized by UV-Visible spectroscopy, X-ray diffraction spectroscopy, transmission electron microscopy (TEM), high resolution TEM, and energy dispersive spectroscopy. The XRD pattern showed high crystallinity and phase formation of the nanoparticles. The bimetallic alloy nanoparticles were coated over a well-polished glassy carbon electrode and the designed sensor was applied for the detection of a highly carcinogenic carbonyl compound, 2-butanone. Electrochemical studies revealed that PEI used as a capping agent also enhances the sensing of the modified electrode for the recognition of 2-butanone. The sensor developed from Ag–Cu (1 : 1) alloy nanoparticles showed the best sensing properties for the detection of 2-butanone as evidenced by electrochemical impedance spectroscopy and a 0.1 μM detection limit.

Spectroscopic Analysis of Au-Cu Alloy Nanoparticles of Various Compositions Synthesized by a Chemical Reduction Method

Au-Cu alloy nanoparticles were synthesized by a chemical reduction method. Five samples having different compositions of Au and Cu (Au-Cu 3 : 1, Au-Cu 2 : 1, Au-Cu 1 : 1, Au-Cu 1 : 2, and Au-Cu 1 : 3) were prepared. The newly synthesized nanoparticles were characterized by electronic absorption, fluorescence, and X-ray diffraction spectroscopy (XRD). These alloy nanoparticles were also analyzed by SEM and TEM. The particle size was determined by SEM and TEM and calculated by Debye Scherrer’s equation as well. The results revealed that the average diameter of nanoparticles gets lowered from 80 to 65 nm as the amount of Cu is increased in alloy nanoparticles. Some physical properties were found to change with change in molar composition of Au and Cu. Most of the properties showed optimum values for Au-Cu alloy nanoparticles of 1 : 3. Cu in Au-Cu alloy caused decrease in the intensity of the emission peak and acted as a quencher. The fluorescence data was utilized for the evaluation of number of binding sites, total number of atoms in alloy nanoparticle, binding constant, and free energy of binding while morphology was deduced from SEM and TEM.

The Determination of Catechols in the Presence of Ascorbic Acid and Uric Acid by Flow Injection Analysis Employing a Potentiometric Dibenzo-18-crown-6 Electrode Detector

Abstract A polished platinum disc was modified by electropolymerization of dibenzo-18-crown-6 (DB-18-C-6) onto the surface. This DB-18-C-6 electrode has been used as a detector for catechol and catecholamines in a potentiometric-flow injection mode. The potentiometric-flow injection response of the DB-18-C-6 modified electrode exhibited a linear response for catechol and catecholamine concentrations from 10-2—10-6 M achieving detection limits as low as 0.5 × 10-6M. An interference study was carried out with ascorbic acid and uric acid which are serious interferents using amperometric detectors. No significant interference was observed for the presence of either of these two or mixture of these two common interferents until they were in greater than a 10-fold excess. 1 Present address: Department of Chemistry, College of Sciences, University of Cairo, Giza, Egypt 2 Present address: Teledyne, 16830 Chestnut Street, City of Industry, CA 91749—1580 3 Present address: College of Medicine, Univ. of Florida, Gai...

NMR Studies of the Interaction of Catechol and Ascorbic Acid with the Crown Ether

Abstract Various crown ethers have been electropolymerized onto a platinum electrode for the determination of catechol and catecholamines by static potentiometry and potentiometric-flow injection analysis(FIA). The response mechanism of this modified electrode was investigated by scanning electron microscopy (SEM), electron dispersive X-ray analysis (EDAX), and electron spectroscopy for chemical analysis(ESCA). However, these studies were not conclusive with respect to possible mechanisms, and, therefore, nuclear magnetic resonance (NMR) studies were carried out on similar soluble crown ethers to determine the mode of interaction. As the crown ether resonances were shifted to higher fields by the added catechol in D2O but not d6-DMSO, it is postulated that the crown ether and catechol associate via interactions between hydrophobic surfaces. Hydrophilic ascorbic acid showed no NMR shifts which is consistent with its lack of potentiometric response. The EDAX and ESCA results indicated that there was also an...

Conducting Polymer Matrix Poly(2,2′-bithiophene) Mercury Metal Incorporation

This article has been retracted.

Poly-binaphthyl-20 crown-6 as Receptor Based Molecule Selective Potentiometric Electrodes for Molecules Containing 1,2-Dihydroxybenzene Moieties

This chapter discusses a study examining poly-binaphthyl-20-crown-6 as receptor based molecule selective potentiometric electrodes for molecules containing 1,2-dihydroxybenzene moieties. A new potentiometric electrode for the determination of 1,2-dihydroxybenzene moieties such as catecholamines, known as important neurotransmitter, was constructed by means of simple electrochemical polymerization. The synthesized poly-binaphthyl-20-crown-6 was employed as the sensing material of the electrode and Pt electrode served as substrate. The response of the new electrode is based on molecular recognition. The potentiometric response is dependent of the pH of the solution and nature of the buffer medium. The linearity of LogC vs E curve ranges from 10 −7 –2 × 10 −6 M with supper Nernstian slope of 110 to 130 mV/decade, and detection limit of 6 × 10 −8 M in phosphate buffer (0.1 M, pH 9.4). The potentiometric electrode showed virtually no interfering inorganic ions and circumvented the interference from ascorbic acid, which is often met using amperometric methods. The response mechanism of the present electrode is discussed, supported by results from SEM and X-ray analysis.