Electrochemical detection voltammetric methods

Cyclic voltammetry, square-wave voltammetry, and controlled potential electrolysis were used to study the electrochemical oxidation behavior of niclosamide at a glassy carbon electrode. The number of electrons transferred, the wave characteristics, the diffusion coefficient and reversibility of the reactions were investigated. Following optimization of voltammetric parameters, pH, and reproducibility, a linear calibration curve over the range 1 x 10 6 to 1 x 10 4 mol/dm3 niclosamide was achieved. The detection limit was found to be 8 x 10 7 mol/dm3. This voltammetric method was applied for the determination of niclosamide in tablets [33]. 

Another voltammetric method, sinusoidal voltammetry (SV), was also employed. This was a frequency-based electrochemical method, which was found to be more sensitive than the usual constant potential (DC) amperometric detection method. SV has been achieved to detect on-chip separated catecholamines. This method is very similar to fast-scan cyclic voltammetry (CV), except that a... 

Immunoassays, electrochemical — A quantitative or qualitative assay based on the highly selective antibody-antigen binding and electrochemical detection. Poten-tiometric, capacitive, and voltammetric methods are used to detect the immunoreaction, either directly without a label or indirectly with a label compound. The majority of electrochemical immunoassays are based on -> voltammetry (-> amperometry) and detection of redox-active or enzyme labels of one of the immunochemical reaction partners. The assay formats are competitive and noncompetitive (see also -> ELISA). 

Pharmaceutical analysts often have no experience in direct polarographic or voltammetric methods, but almost all will have used high-performance liquid chromatography (HPLC) for the determination of drugs and/or metabolites in biological matrices or drugs and/ or their degradation products in pharmaceutical formulations. Spectroscopy (ultraviolet and fluorescence) is the most common detection method in HPLC, but for molecules that do not possess a suitable chromophore or when increased sensitivity or specificity is required, electrochemical detection offers a suitable alternative. ELCD is applicable to any molecular species capable... 

Figure 3.6 Electrochemical detection of thrombin by interaction between nncleic acid and a redox-active oligothiophene polyelectrolyte (4). (A) Blocking the electrical contact between the polyelectrolyte and the electrode by means of a aptamer-thrombin complex. (B) Separation of the aptamer-thrombin complex by the formation of a PNA-opened aptamer dnplex on the electrode and its analysis by the redox-active polyelectrolyte. (C) Voltammetric response to the analysis of different concentrations of thrombin according to method B (a) OM (b) 125nM (c) 250nM (d) 500nM, 1 p,M (f) 2 p,M. (Reprinted with permission from Floch et al., 2006. Copyright 2006 American Chemical Society.)...

Voltammetric measurements confirm that Hg-modified carbon electrodes are suitable for sensitive electrochemical detection of ODN compared to mercury electrodes. In the presence of the copper ions, these electrodes modified by a mercury layer were used for the detection of a picomolar quantity of ODN. The electrochemical step includes a potential-controlled reduction of the copper ions Cu(II) and accumulation of the Cu(I)-purine base residue complex on the Hg-modified carbon surface. The proposed electrochemical method can be used for the determination of different ODN lengths because the stripping current peak of the electrochemically accumulated Cu(I]-purine complex increased linearly with the length of ODN. The optical microscope images were used for the visualization of the surface morphology of the bare and Hg-modified carbon electrodes [64]. 

In contrast to direct immunosensors, indirect immunosensors, using as a label an enzyme [307-309] or an ionophore [310], have been more developed. This technique is derived from well established and widely utilized enzyme immunoassays evaluated by photometric methods. Enzyme immunoassay with electrochemical detection (EEIA) represents an important innovation of EIA by the replacement of optical detection with voltammetric or potentiometric measurements. It may also be adapted to flow-through systems [311, 312]. 

The combined HPLC with electrochemical detection is a sensitive and selective method for simultaneous determination of different redox-active compounds. The coulometric detection is very similar to the amperometric and voltammetric ones in terms of electrochemical principles and, hence, has wide applications in liquid chromatography (Trojanowicz 2011 Zhang and Wang 2011). 

We have developed a new voltammetric method using a quinone reagent [5]. Based on the voltammetry of quinone and acids, we assembled an electrochemical detector for measuring acid concentration at a given potential. The flow injection analysis with electrochemical detection (FIA-ECD) method we developed is preferable, as it is a simpler, more sensitive, and rapid method for acid determination. This chapter assesses this method for determining the acid content in foods and beverages. 

Akpofure et al. used HPLC and electrochemical detection at an oxidative potential of 0.65 V to quantify daunorubicin and its metabolites in serum and plasma. Using a different method, Chaney and Baldwin determined Adriamycin concentrations in urine. The determination was performed by adsorption of the compound at a carbon paste electrode and then applying pulse voltammetric analysis at the resulting surface. 

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