Construction and Evaluation of a Gold Tubular Electrode for Flow Analysis: Application to Speciation of Antimony in Water Samples

Potentiometric Stripping Analysis of Cadmium and Lead with Constant Inverse Current in the Analytical Step Using an Open Tubular Mercury-Coated Glassy Carbon Electrode

The most important experimental parameters of the flow potentiometric stripping analysis (PSA) with oxygen as an oxidant were investigated and optimised. A simple, homemade flow system consisting of glassy carbon tubes, which served as a working and auxiliary electrode, was used. By applying a rest period before the stripping step (the flow stop mode) and by imposing a constant reductive current simultaneously with the interruption of potentiostatic control, significant increase of the flow PSA sensitivity was achieved. In the determination of cadmium and lead, quantitation limits of 0.11 and 0.82 μg/L were obtained. The precision of the method was evaluated in terms of repeatability and reproducibility, with values of relative standard deviation lower than 4.0% for cadmium and 4.2% for lead. This modified technique was applied for simultaneous determination of cadmium and lead in milk, after a simple pretreatment of the samples by dilution and acidification. The method accuracy was confirmed by analysing the certified reference material of skimmed milk powder (ERM-BD151).

Biofilm vivacity and destruction on antimicrobial nanosurfaces assayed within a microbial fuel cell

A novel method was developed to assay the antimicrobial capacity of nanostructured surfaces for medical implants in a bicathodic microbial fuel cell. Nano-structured gold surfaces with protruding nanopillars and nanorings were investigated. Escherichia coli K12 were used as a model microbe to record electronic effects caused by the interaction with nanosurfaces. The nanostructured gold surfaces enabled power density maxima up to 1910mW/m(2), indicating fair vivacity, while flat surfaces on the nanoscale provided almost no power 0.35mW/m(2). The biofilm presence on antimicrobial nanosurfaces was confirmed by the addition of ampicillin and its bactericidal effect resulted in oscillating and declining potentiometric signals. Current density experiments showed that biofilms on antimicrobial nanostructured electrodes caused low currents, indicating that E.coli biofilm remained functional before destruction. The bicathodic microbial fuel cell sensor is a novel tool for evaluating antimicrobial effects caused by nanosurfaces and antibiotics.

Unexpectedly high levels of antimony (III) in the pentavalent antimonial drug Glucantime: insights from a new voltammetric approach

Glucantime, a pentavalent antimonial drug, is commonly used for the treatment of leishmaniasis but the presence of residual trivalent antimony, Sb(III), is thought to be responsible for toxic side-effects observed in patients. Numerous analytical studies have focused on determining Sb(III) concentrations in Glucantime but without reaching a consensus: results span over 3 orders of magnitude. In this study, we present a detailed new analytical approach showing that: (1) Sb(III) levels are much higher than previously reported and represent more than 30% of total Sb; (2) determination of Sb(III) concentrations in acidic conditions is hampered by fast oxidation rates. This latter point explains the large variations in previously reported results of Sb(III) concentrations in Glucantime. Measurements were made here at a vibrated gold microwire electrode by stripping voltammetry enabling measurement of Sb(III) in acidic, neutral or alkaline conditions. The developed methods are sensitive (e.g., detection limits of 19 pM for 120 s deposition at pH 4.5), stable (<6%, N = 100), precise (5%, N = 5) and robust (same electrode used for weeks) at all pH values. In diluted solutions of Glucantime, Sb(III) levels were strongly dependent both on pH and ionic strength. At pH < 3, Sb(III) is oxidized with oxidation rates that increase as pH is decreased. At high pH, Sb(III) forms electro-inactive complexes. Highest Sb(III) levels were detected at pH ~3 and at low ionic strength. The presence of several Sb(III) and Sb(V) species was demonstrated by different reduction waves obtained by stripping scanned voltammetry. As an implication of these unexpectedly high Sb(III) concentrations, an alternative model can be proposed for the mode of action of pentavalent antimonials against leishmaniasis, in which antimony complexes may act as molecular carrier of Sb(III) and release it specifically in the acidic intracellular compartment where the Leishmania parasites reside.