Timothy Gareth John Jones

The electrochemical analog of the methylene blue reaction: A novel amperometric approach to the detection of hydrogen sulfide

The electrochemical oxidation of N,N-dimethylphenylenediamine at glassy carbon electrodes in aqueous solution in the pH range 3-6 is shown to lead to currents which are considerably amplified in the presence of dissolved hydrogen sulfide. The mechanism of the electrode process is investigated and the reaction is shown to provide an attractive basis for the amperometric sensing of sulfide with an accessible range of ca. 3 to 150 muM (0.1 to 4.8 ppm).

Electrochemical determination of sulphide at nickel electrodes in alkaline media: a new electrochemical sensor

The electrochemistry of a nickel hydroxide electrode has been studied both in the presence and absence of sulphide at microdisc and macroelectrodes. With sulphide present a new oxidative wave is observed. At a macroelectrode, this response produced a linear range from 20 to 200 μM with a corresponding limit of detection of 19 μM. Under the microelectrode regime, the response was found to be linear from 20 to 200 μM with a detection limit of 10 μM. The protocol has been developed into the design of a simple and cheap electrochemical sensing cell for the detection of sulphide in aqueous media.

Anthraquinone-derivatised carbon powder: reagentless voltammetric pH electrodes

A simple pH probe is developed based upon the covalent chemical derivatisation of carbon particles with anthraquinone. The amperometric response of electrodes constructed from this material is examined and shown to produce a Nernstian linear response to pH from 1 to 9, over a range of temperatures from 20 to 70 degrees C, consistent with a two-electron, two-proton electrochemical process.

Determining cement composition by Fourier transform infrared spectroscopy

Abstract A diffuse reflectance mid-infrared Fourier transform spectroscopy (DRIFTS) method is described for obtaining high quality Fourier transform infrared (FTIR) spectra of cements. DRIFT spectra of synthetic C3S, C2S, C3A, and C4AF and of pure gypsum, bassanite, anhydrite, syngenite, and calcite are shown. Typical spectra of American Petroleum Institute class G and class A cements display characteristic features which can be related qualitatively to variations in the constituent minerals. For quantitative analysis, the FTIR spectra of 156 cements of varied origin and known elemental composition have been used to construct multivariate calibration models. These relate the spectrum to composition (expressed in terms of nine mineral components and five minor oxides) and allow the composition of unknown cements to be determined rapidly from the FTIR spectrum alone. Error estimates are given.

Derivatised carbon powder electrodes: reagentless pH sensors

In this report, we derivatise carbon powder with anthracene, azobenzene, diphenylamine, 9,10-diphenylanthracene, methylene blue, 3-nitrofluoranthene, 6-nitrochrysene, 9-nitroanthracene, 9,10-phenanthraquinone (PAQ), thionin, and fast black K (2,5-dimethoxy-4-[(4-nitrophenyl)azo]benzenediazonium chloride) and separately immobilise the resulting material onto a bppg electrode. We use cyclic voltammetry (CV) to demonstrate that the observed voltammetric response for each derivatised carbon is consistent with that of an immobilised species. Further, we use CV and square wave voltammetry (SWV) to investigate the effect of pH on the peak potentials of each compound studied over the range pH 1-12 and at elevated temperatures up to 70 degrees C in order to demonstrate the versatility of derivatised carbon electrodes as reagentless pH sensors.

Electroanalytical applications of boron-doped diamond microelectrode arrays.

The electrochemical characteristics of a novel all diamond fabricated boron-doped diamond microelectrode array (BDD-MEA) are critically appraised. The voltammetric response of simple electron transfer processes has been investigated and found to generate sigmoidal voltammetric curves. Furthermore, the device has been utilized for various analytical applications including, the direct detection of 4-nitrophenol over the concentration range 1.8-9.2muM, manganese over the range 0.1-4.8muM and the indirect determination of sulfide producing a limit of detection of 23muM.

Boron-doped diamond microdisc arrays: electrochemical characterisation and their use as a substrate for the production of microelectrode arrays of diverse metals (Ag, Au, Cu)via electrodeposition

A novel boron-doped diamond (BDD) microelectrode array is characterised with electrochemical and atomic force microscopic techniques. The array consists of 40 micron-diameter sized BDD discs which are separated by 250 microns from their nearest neighbour in a hexagonal arrangement. The conducting discs can be electroplated to produce arrays of copper, silver or gold for analytical purposes in addition to operating as an array of BDD-microelectrodes. Proof-of-concept is shown for four separate examples; a gold plated array for arsenic detection, a copper plated array for nitrate analysis, a silver plated array for hydrogen peroxide monitoring and last, cathodic stripping voltammetry for lead at the bare BDD-array.

Amperometric Detection of Sulfide at a Boron Doped Diamond Electrode: The Electrocatalytic Reaction of Sulfide with Ferricyanide in Aqueous Solution.

The oxidation of sulfide at a boron doped diamond (BDD) electrode has been examined and its analytical utility appraised and compared with other common electrode substrates (Pt, Au, glassy carbon). The suitability of using BDD as a sulfide sensing substrate has been assessed through examining the electrocatalytic oxidation of ferrocyanide to ferricyanide in the presence of sulfide using both cyclic voltammetry and chronoamperometry. The high oxidation potential for the direct oxidation of sulfide at a BDD electrode allows clear resolution of both the ferrocyanide wave and sulfide oxidation wave producing a distinct analytical signal at the oxidation peak potential of ferrocyanide. The procedure was applied to the recovery of a sulfide spike in sewage effluents with a recovery of 102±4.5%.

Anodic stripping voltammetry of sulphide at a nickel film: towards the development of a reagentless sensor

The determination of sulphide at an electrochemically generated nickel oxide layer at glassy carbon and screen-printed electrodes in acidic media has been examined and appraised. The NiO layer was found to produce a stripping-like signal to sulphide and gave a linear peak current response from 20 to 90 muM. The response was further enhanced by repetitive cycling allowing accumulation of nickel sulphide at the electrode surface such that lower micromolar levels of sulphide (i.e. 5 muM) can be determined. The response at the NiO layer to sulphide is shown to be reproducible over a period of 24 h, thereby offering the development of a disposable amperometric sensor for sulphide.

Graphite powder derivatised with poly-L-cysteine using “building-block” chemistry—a novel material for the extraction of heavy metal ions

Graphite powder derivatised with 4-nitrophenyl moieties (NPcarbon) can be used to successively attach other chemical species to the graphite surface in a controlled and selective manner. Characterisation of these novel materials was undertaken using electrochemical and X-ray photoelectron spectroscopic (XPS) techniques. We demonstrate the proof of concept of this “building-block” chemistry by first reducing the nitro groups on the NPcarbon using a Sn–HCl reduction to the corresponding aniline-like moieties, and then coupling p-nitrobenzoic acid to these via an amide-linkage. Next we demonstrate the utility of this novel derivatisation method by coupling poly-S-benzyl-L-cysteine to the reduced NPcarbon in an analogous manner. After deprotection of the thiol groups using Na in liquid ammonia, the poly-L-cysteine derivatised carbon (PCcarbon) was found to complex cadmium(II) ions. Quantitative analysis of the uptake of Cd2+ from aqueous solutions at pH 5.0 by PCcarbon was carried out using stripping-voltammetry at a boron doped diamond (BDD) electrode and revealed that PCcarbon complexed 137 ± 20 mg of Cd2+ per gram of modified PCcarbon.