Buffer solutions, voltammetry

Alemu et al. [35] developed a very sensitive and selective procedure for the determination of niclosamide based on square-wave voltammetry at a glassy carbon electrode. Cyclic voltammetry was used to investigate the electrochemical reduction of niclosamide at a glassy carbon electrode. Niclosamide was first irreversibly reduced from N02 to NHOH at —0.659 V in aqueous buffer solution of pH 8.5. Following optimization of the voltammetric parameters, pH and reproducibility, a linear calibration curve over the range 5 x 10 x to 1 x 10-6 mol/dm3 was achieved, with a detection limit of 2.05 x 10-8 mol/dm3 niclosamide. The results of the analysis suggested that the proposed method has promise for the routine determination of niclosamide in the products examined [35]. 

Pyrrhotite is one of many sulphides which display collectorless flotation resulting from the formation of sulphur on the mineral surface (Hamilton and Woods, 1981 Heyes and Trahar, 1984 Hodgson and Agar, 1984). The anodic scan section of cyclic voltammetry for pyrrhotite electrode in pH = 2.2, 4.7, 7.0, 8.8, 11, 12.1, 12.7 buffer solutions respectively, is presented in Fig. 2.23. The cyclic voltammograms curve at pH = 8.8 is also presented in Fig. 2.23. It can be seen from Fig. 2.23 that anodic current peak emerges at about -0.1—0 V when pH < 11. As pH increases, the peak moves to the left. This peak may correspond to the following reactions ... 

Figure 4.28 The anodic scan section of cyclic voltammetry for pyrrhotite electrode in different pH buffer solution at potential scan of 10 mV/s (Background solution buffer solution plus 0.1 mol/L KNO3, DDTC 10" mol/L)...

Another transient aminoxyl radical has been generated , and employed in H-abstraction reactivity determinations" . Precursor 1-hydroxybenzotriazole (HBT, Table 2) has been oxidized by cyclic voltammetry (CV) to the corresponding >N—O species, dubbed BTNO (Scheme 9). A redox potential comparable to that of the HPI —PINO oxidation, i.e. E° 1.08 V/NHE, has been obtained in 0.01 M sodium acetate buffered solution at pH 4.7, containing 4% MeCN". Oxidation of HBT by either Pb(OAc)4 in AcOH, or cerium(IV) ammonium nitrate (CAN E° 1.35 V/NHE) in MeCN, has been monitored by spectrophotometry , providing a broad UV-Vis absorption band with A-max at 474 nm and e = 1840 M cm. As in the case of PINO from HPI, the absorption spectrum of aminoxyl radical BTNO is not stable, but decays faster (half-life of 110 s at [HBT] = 0.5 mM) than that of PINO . An EPR spectrum consistent with the structure of BTNO was obtained from equimolar amounts of CAN and HBT in MeCN solution . Finally, laser flash photolysis (LFP) of an Ar-saturated MeCN solution of dicumyl peroxide and HBT at 355 nm gave rise to a species whose absorption spectrum, recorded 1.4 ms after the laser pulse, had the same absorption maximum (ca 474 nm) of the spectrum recorded by conventional spectrophotometry (Scheme 9)59- 54... 

Indicators and Dyes Abdel-Hamid [154] has studied adsorption of phe-nolphthalein at a HMDE in aqueous buffer solutions containing 10% v/v ethanol, applying cychc voltammetry and double potential-step chronocoulometry. At pH =... 

Electroanalytical techniques, such as conductometry [174], potentiometry [22], voltammetry [6], chronoamperometry [25] and EIS [175], have been used extensively for transduction of the detection signal in the MIP-based chemosensors. The chemosensor response may be due to different interfacial phenomena occurring at the electrode-electrolyte interface [16], which will be discussed below in the respective sections. The electrochemical transduction scheme can be devised for accurate measurements tailored to the analytes exhibiting either faradic or non-faradic electrode behaviour. In many instances, the detection medium is an inert buffer solution [24]. In order to enhance the chemosensor response, some of the... 

Radi [41] used an anodic voltammetric assay method for the analysis of omeprazole and lansoprazole on a carbon paste electrode. The electrochemical oxidations of the drugs have been studied at a carbon paste electrode by cyclic and differential-pulse voltammetry in Britton-Robin-son buffer solutions (0.04 M, pH 6-10). The drug produced a single oxidation step. By differential-pulse voltammetry, a linear response was obtained in Britton-Robinson buffer pH 6 in a concentration range from 2 x 10-7to 5 x 10 5 M for lansoprazole or omeprazole. The detection limits were 1 x 10 8 and 2.5 x 10 8 M for lansoprazole and omeprazole, respectively. The method was applied for the analysis of omeprazole in capsules. The results were comparable to those obtained by spectrophotometry. 

When a ferrocene derivative loaded Pt/Nafion-GOD electrode is transferred to a phosphate buffer solution containing no ferrocene derivatives, the observed redox waves reflect their electrochemical behavior in the film. The scan rate dependence of the cyclic voltammetry for the Pt/Nafion-GOD incorporated with different ferrocene derivatives was studied. A linear plot of the anodic peak current against the square root of the scan rate was obtained in all cases, which is indicative of diffusion controlled redox process. Typical chronoamperometric... 

These interfacial pH effects have been investigated by probing the voltammetry in buffered solutions. Figure 5.16 shows that for 1.0 < pFl < 10.6, E0 depends linearly on pH, with a slope of 63 3 mV. This value is indistinguishable from the slope of 59 mV pH-1 expected for a coupled proton/electron transfer and indicates that the H2Q species is produced when the monolayer is reduced. Between pH 10.6 and 12.0, the slope decreases to 25 4 mV pH-1, which compares favorably with the slope expected (29.5 mV pH-1) for a two-electron, one-proton transfer reaction. Therefore, over this pH range Q is reduced to HQ- and the p/12.0, E0 is independent of pH, thus indicating that the pKa of the HQ-/Q2- couple is 12.0 0.2. 

Fig. 2.19. (A) The effect of potential on the observed electrocatalytic response obtained at poly(aniline)/poly(vjnylsu fonate) electrode (geometric area 0.38 cm2, Q, 150 mC) rotated at 9 Hz in 0.1 mol dm-2 citrate/phosphate pH 7 buffer solution. Responses have been recorded at four different concentrations of NADH ( ) 0.12 mmol dm- ( ) 0.3 mmol dm"3 ( ) 0.6 mmol dm-3 and (O) 0.8 mmol dm"3. (B) Cyclic voltammetry of an identical poly(aniline)/poly(vinylsulfonate) electrode in 0.1 mol dm" 3 citrate/phosphate pH 7 buffer scanned at 5mVs , superimposed on this trace is the measured resistance for the same...

Different sehemes of eleetroehemieal pretreatments have been proposed. In general, they depend on the system under investigation. For instance, for the oxidation of dopamine, 18 cyeles between -1.00 V and 1.50 V at 1.0 V/s in a 0.050 M phosphate buffer pH 7.40 demonstrated to be the optimum pretreatment for obtaining the best voltammetrie behavior of dopamine [46]. However, for the oxidation of amitrole, 75 cyeles between -1.0 and 1.5 V at 1.0 V/s in 0.050 M phosphate buffer solution pH 7.4 were necessary to obtain the best analytical signal [47]. 

Figure 35. UV-visible spectra of catalase in PBS (pH 7) phosphate buffer solution (curve A) and Hb-CoOx film on ITO electrode (curveB).(B) CVs of glassy carbon electrode modified with cobalt oxide nanoparticles (a) and Glassy carbon electrode modified with cobalt oxide nanoparticles and Hb (b), electrolyte is PBS (pH7), scan rate is 100 mVs Reprinted from Biophysical Chemistry, 62, A.Salimi, R. Hallaj, S. Soltanian, Immobilization of hemoglobin on electrodeposited cobalt-oxide nanoparticles Direct voltammetry and electrocatalytic activity,124,125, Copyrights(2007) with permission from Elsevier.

Due to high biocompability and large surface are of cobalt oxide nanoparticles it can be used for immobilization of other biomolecules. Flavin adenine FAD is a flavoprotein coenzyme that plays an important biological role in many oxidoreductase processes and biochemical reactions. The immobilized FAD onto different electrode surfaces provides a basis for fabrication of sensors, biosensors, enzymatic reactors and biomedical devices. The electrocatalytic oxidation of NADH on the surface of graphite electrode modified with immobilization of FAD was investigated [276], Recently we used cyclic voltammetry as simple technique for cobalt-oxide nanoparticles formation and immobilization flavin adenine dinucleotide (FAD) [277], Repeated cyclic voltammograms of GC/ CoOx nanoparticles modified electrode in buffer solution containing FAD is shown in Fig.37A. 

Lead azide, Pb(N3)2, can be analysed by voltammetry, oxidizing azide ions at a carbon paste electrode and reducing lead ions at a dropping mercury electrode at pH 4.6 in an acetate buffer solution. Lead azide is poorly soluble in a pure aqueous solution, but can be dissolved when acetate ions are present. In Fig.l7 a differential pulse voltammogram for the determination of azide at a carbon paste electrode is shown. Some results from the analysis of lead azide are given in Table 7. 

Aminodiphenylamine (PAD) Allendoerfer and coworker [114] studied the oxidation of PAD at platinum electrodes in aqueous solution, in the pH range 1.2-4.8. Cyclic voltammetry in buffered solution produces a single peak, with (=0-5( p +... 

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