Mercury-free sono-electroanalytical detection of lead in human blood by use of bismuth-film-modified boron-doped diamond electrodes

We report the electroanalytical determination of lead by anodic stripping voltammetry at in-situ-formed, bismuth-film-modified, boron-doped diamond electrodes. Detection limits in 0.1 mol L^–1 nitric acid solution of 9.6x10^–8 mol L^–1 (0.2 ppb) and 1.1x10^–8 mol L^–1 (2.3 ppb) were obtained after 60 and 300 s deposition times, respectively. An acoustically assisted deposition procedure was also investigated and found to result in improved limits of detection of 2.6×10^–8 mol L^–1 (5.4 ppb) and 8.5×10^–10 mol L^–1 (0.18 ppb) for 60 and 300 s accumulation times, respectively. Furthermore, the sensitivity obtained under quiescent and insonated conditions increased from 5.5 (quiescent) to 76.7 A mol^–1 L (insonated) for 60 s accumulation and from 25.8 (quiescent) to 317.6 A mol^–1 L (insonated) for 300 s accumulation. Investigation of the use of ultrasound with diluted blood revealed detection limits of the order of 10^–8 mol L^–1 were achievable with excellent inter- and intra-reproducibility and sensitivity of 411.9 A mol^–1 L . For the first time, electroanalytical detection of lead in diluted blood is shown to be possible by use of insonated in-situ-formed bismuth-film-modified boron-doped diamond electrodes. This method is a rapid, sensitive, and non-toxic means of clinical sensing of lead in whole human blood.     

Sonoelectroanalysis: investigation of bismuth-film-modified glassy carbon electrodes

Bismuth-modified glassy carbon electrodes have been investigated for their suitability in sonoelectroanalysis. The stability of the bismuth film to the application of ultrasound was assessed via voltammetric and atomic force microscopy (AFM) studies which revealed little ablation at powers up to an intensity of 130 W cm^–2 delivered from a 25-kHz sonic horn. Furthermore, bismuth-film-modified glassy carbon electrodes were evaluated for the sonoelectroanalytical quantification of zinc and cadmium. Detection limits of 2×10^–7 M and 6×10^–9 M respectively were found after a 60-s deposition time via an acoustically assisted deposition protocol.     

Manganese detection in marine sediments: anodic vs. cathodic stripping voltammetry

Three different electroanalytical techniques for the detection of manganese in marine sediments are evaluated. The anodic stripping voltammetry of manganese at an in situ bismuth-film-modified boron-doped diamond electrode and cathodic stripping voltammetry at a carbon paste electrode are shown to lack the required sensitivity and reproducibility whereas cathodic stripping voltammetry at a bare boron-doped diamond electrode is shown to be reliable and selective with a limit of detection, from applying a 60 s accumulation period of 7.4 × 10⁻⁷ M and a sensitivity of 0.24 A M⁻¹. The method was used to evaluate the manganese content of marine sediments taken from Šibenik, Croatia.     

Metallic impurity free carbon nanotube paste electrodes

Electrodes modified with carbon nanomaterials find wide ranging applications in electrochemistry such as in energy generation and storage through to applications in electroanalysis. A substantial limitation is the presence of metallic impurities which vary between batches and can produce erroneous results. Consequently we have explored the electrochemical properties of metallic impurity free carbon nanotube paste electrodes using potassium ferrocyanide and hydrogen peroxide as model compounds. In terms of the latter utilising cyclic voltammetry, a linear range from 0.75 to 3 mM with a limit of detection of 0.19 mM is possible using the electrochemical oxidation of hydrogen peroxide while using the electrochemical reduction of the target analyte, a linear range from 0.5 to 249 mM is possible with a detection limit of 0.43 mM.The ultra-small size of the carbon nanotubes and fabrication methodology result in a tightly bound carbon nanotube electrode surface which does not exhibit thin-layer behaviour resulting in highly reproducible electrodes with the %RSD found to be 5.5%. These analytical ranges, detection limits and reproducibility are technologically useful.The carbon nanotubes utilised are completely free from metallic impurities and do not require lengthy processing to remove impurities and consequently have no variation in the purity of the nanomaterial between batches as is commonly the case for other available carbon nanotube material. The impurity free nature of this nanomaterial allows for highly reproducible and intelligent sensors based on carbon nanotubes to be understood and realised for the first time.     

Modular assembly of a preorganised, ditopic receptor for dicarboxylates

Two types of calix[4]arene derived hosts for anions with, respectively, 1,3-alternate and cone conformations have been prepared; the 1,3-alternate system binds dicarboxylate anions in a ditopic manner while the cone compounds are deprotonated by carboxylates.     

The Heterogeneity of Multiwalled and Single‐Walled Carbon Nanotubes: Iron Oxide Impurities Can Catalyze the Electrochemical Oxidation of Glucose

It is well established that the heterogeneity of carbon nanotubes must be determined before the origin of the electrochemical performance can be attributed. Recently it has been diligently reported that for the case of multiwalled carbon nanotube modified electrodes, copper oxide impurities are responsible for the electrochemical activity facilitating a nonenzymatic sensing strategy towards glucose. We have explored both commercially available multiwalled and single‐walled carbon nanotubes for the sensing of glucose and find that iron oxide impurities remaining from the fabrication process are the electroactive sites facilitating the nonenzymatic detection of glucose. Given that the multiwalled carbon nanotubes in this work are purchased from the same leading supplier as that used recently, discrepancies in the fabrication process exist which clearly has implications in the commercialization of electrochemical sensors based on multiwalled carbon nanotubes.     

The Effect of a Hydrogen Bonding Environment (Dimethyl Sulfoxide) on the Ionisation and Redox Properties of the Thiol Group in Cysteine and a Protein Disulfide Isomerase Mimic (Vectrase)

Increasing enrichment of dimethyl sulfoxide, DMSO, in DMSO-water mixtures causes a reversal in the thermodynamic dissociation constants, pK _as, and has a marked effect on the redox potentails of the thiolic and amino groups in cysteine and the protein disulfide isomerase (PDI) mimic BMC, Vectrase. This paper illustrates the effect of a hydrogen-bonding environment on the ionisation and redox properties of thiol groups in amino acids. A combination of potentiometry and Raman spectroscopy was applied to rationalise the observations. Intracellular environments are full of hydrophobic, hydrogen-bonding environments. The results illustrate the profound effects of the local environment on the thiol group.     

Electroanalytical detection of zinc in whole blood

Three different electroanalytical techniques for the determination of zinc in blood are investigated. The direct determination in diluted blood via anodic stripping voltammetry at glassy carbon and the use of Nafion-coated glassy carbon mercury electrodes are shown to lack the necessary sensitivity whereas an acoustically assisted double extraction followed by sono-ASV using a glassy carbon electrode is found to be rapid, reliable and sensitive.     

Calculation of core-level electron spectra of ionic liquids

On the example of 40 ion pairs (5 cations times 8 anions), this study demonstrates how the core-level binding energy values can be calculated and used to plot theoretical spectra at low computational cost using density functional theory methods. Three approaches for obtaining the binding energy values are based on delta Kohn–Sham (ΔKS) calculations, 1s KS orbital energies, and atomic charges. The ΔKS results show reasonable agreement with the available experimental X-ray photoelectron data. The 1s KS orbital energies correlate well with the ΔKS results. Atomic charge correlation with ΔKS is improved by accounting for the charges of neighboring atoms. Assignment of binding energies to atoms and the applicability of the mentioned methods to model systems of ionic liquids are discussed.     

The electrochemical behaviour of butyltrimethylammonium bis(trifluoromethylsulfonyl)imide at negatively polarised aluminium electrode studied by in situ soft X-ray photoelectron spectroscopy,electrochemical impedance spectroscopy and cyclic voltammetry techniques

The in situ X-ray photoelectron spectroscopy data indicate that butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (N4111(TFSI)) adsorbs strongly within the potential range −3.25 V < E < −2.25 V and specifically at E < −3.25 V (vs. Ag-QRE) at the Al electrode. Strong adsorption of the intermediates of N4111(TFSI) electrochemical decomposition was observed in electrochemical impedance spectroscopy and cyclic voltammetry measurements. At E < −4.25 V (vs. Ag-QRE), very intensive electrochemical reduction of N4111(TFSI) took place at the Al electrode giving gaseous products. In the potential range from − 2.25 to 0.00 V (vs. Ag-QRE), non-specific adsorption of N4111(TFSI) exists et al. surface.