Determination of groundwater mercury (II) content using a disposable gold modified screen printed carbon electrode.

Mercury (II) measurements were performed thanks to a newly developed electrochemical method using a disposable gold modified screen printed carbon electrode. The method has a wide dynamic range (1-100 µg/L), a good accuracy and a limit of detection in compliance with WHO standards. The application of the method to several groundwater samples made it possible to identify, for the first time, mercury content higher than the recommended WHO standard value in a gold mining activity area in the northern part of Burkina Faso. The accuracy of the assay was checked by ICP/MS.

An experimental design approach to optimize an amperometric immunoassay on a screen printed electrode for Clostridium tetani antibody determination.

An immunoassay for the determination of anti-tetani antibodies has been developed using a screen printed electrode (SPE) as solid support for toxoid (antigen) immobilization. The assay was performed in guinea pig serum. The immunoreaction and the subsequent amperometric detection occurred directly onto the SPE surface. The assay consisted of spiking the anti-tetani sample directly onto the toxoid modified SPE, and then a second antibody, i.e. a HRP-labeled anti-immunoglobulin G, was deposited onto the biosensor. Subsequent amperometric detection was realized by spiking 10 µL of a hydroquinone (HQ) solution into 40 µL of buffer solution containing hydrogen peroxide. An experimental design approach was implemented for the optimization of the immunoassay. The variables of interest, such as bovine serum albumin (BSA) concentration, incubation times and labeled antibody dilution, were optimized with the aid of the response surface methodology using a circumscribed central composite design (CCCD). It was observed that two factors exhibited the greatest impact on the response, i.e. the anti-tetani incubation time and the dilution factor of the labeled antibody. It was discovered that in order to maximize the response, the dilution factor should be small, while the anti-tetani antibody incubation time should be long. The BSA concentration and the HRP-anti-IgG incubation had very limited influence. Under the optimized conditions, the immunoassay had a limit of detection of 0.011 IU/mL and a limit of quantification of 0.012 IU/mL. These values were below the protective human antibody limit of 0.06 IU/mL.

Flow-through enzyme immobilized amperometric detector for the rapid screening of acetylcholinesterase inhibitors by flow injection analysis.

A commercially available thin-layer flow-through amperometric detector, with the sensing block customized in an original design, was applied to the screening of drug compounds known as acetylcholinesterase (AChE) inhibitors. AChE from electric eel was covalently immobilized onto a cysteamine modified gold disk adjacent to a silver disk working electrode. On-line studies were performed by flow injection analysis (FIA) in PBS buffer pH 7.4. Seven commercially available AChE inhibitors used in the medical field, namely neostigmine, eserine, tacrine, donepezil, rivastigmine, pyridostigmine and galantamine as well as two natural compounds, quercetin and berberine, were investigated. The same trend of inhibitory potency as described in the literature was observed. Of particular interest and in addition to the determination of the IC50 values, this flow-through system allowed the study of both, the stability of the enzyme-inhibitor complex and the kinetic of the enzyme activity recovery.

Determination of aminothiols by liquid chromatography with amperometric detection at a silver electrode: application to white wines.

Liquid chromatography coupled to a silver electrode based flow-through amperometric detector (LC-EC-Ag) was developed for the determination of aminothiols in white wines. The C18 reversed phase LC system operated in the isocratic mode at 0.7 mL min(-1) and used an acidic mobile phase composed of formic acid, EDTA, sodium nitrate, sodium hydroxide, and methanol 1% (v/v) at pH 4.5. The working electrode operated at 0.08 V vs Ag/AgCl, 3M KCl and its manual cleaning was realized once a month by smoothing on a polishing cloth. The analyzed aminothiols were resolved and eluted within 4 min, and all standard curves were linear in the range 2×10(-7)-2×10(-5) M. The analyzed wine samples needed no preparation other than dilution with the mobile phase. The concentration of cysteine (CYS), homocysteine (HCYS), glutathione (GSH) and N-acetylcysteine (NAC) in bottled white wines, determined by the method of standard addition, was found to be in the low µM range (0.2-2 mg L(-1)) depending on the wine type and its age.