New triiodomercurate-modified carbon paste electrode for the potentiometric determination of mercury

A new tetrazolium-triiodomercurate-modified carbon paste electrode has been described for the sensitive and selective determination of mercury. The electrode shows a stable, near-Nernstian response for 1×10⁻³ to 6×10⁻⁶ M [HgI₃]⁻ at 25 °C over the pH range of 4.0-9.0, with an anionic slope of 55.5±0.4 mV. The lower detection limit is 4×10⁻⁶ M with a fast response time of 30-50 s. Selectivity coefficients of a number of interfering anions and iodo complexes of some metal ions have been estimated. The interference from many of the investigated ions is negligible. The determination of 1-200 μg/ml of mercury in aqueous solutions shows an average recovery of 98.5% and a mean relative standard deviation of 1.6% at 50.0 μg/ml. The direct determination of mercury in spiked wastewater, metal amalgams and dental alloy gave results that compare favorably with those obtained by the cold vapor atomic absorption spectrometric method. Potentiometric titration of mercury and phenylmercury acetate with standard potassium iodide has been monitored using the developed triiodomercurate-carbon paste electrode (CPE) as an end point indicator electrode.     

Voltammetric sensor for glutathione determination based on ferrocene-modified carbon paste electrode

The electrocatalytic oxidation of glutathione (GSH) has been studied at the surface of ferrocene-modified carbon paste electrode (FMCPE). Cyclic voltammetry (CV), double potential step chronoamperometry, and differential pulse voltammetry (DPV) techniques were used to investigate the suitability of incorporation of ferrocene into FMCPE as a mediator for the electrocatalytic oxidation of GSH in buffered aqueous solution. Results showed that pH 7.00 is the most suitable for this purpose. In the optimum condition (pH 7.00), the electrocatalytic ability of about 480 mV can be found and the heterogeneous rate constant of catalytic reaction was calculated as . Also, the diffusion coefficient of glutathione, D, was found to be 3.61 × 10^–5 cm² s⁻¹. The electrocatalytic oxidation peak current of glutathione at the surface of this modified electrode was linearly dependent on the GSH concentration and the linear analytical curves were obtained in the ranges of 3.2 × 10^–5 M–1.6 × 10^–3 M and 2.2 × 10^–6 M–3.5 × 10^–3 M with cyclic voltammetry and differential pulse voltammetry methods, respectively. The detection limits (3σ) were determined as 1.8 × 10^–5 M and 2.1 × 10^–6 M using CV and DPV, respectively. Finally, the electrocatalytic oxidation of GSH at the surface of this modified electrode can be employed as a new method for the voltammetric determination of glutathione in real samples such as human plasma.     

Voltammetric sensor for buzepide methiodide determination based on TiO2 nanoparticle-modified carbon paste electrode

In this work, we have prepared nano-material modified carbon paste electrode (CPE) for the sensing of an antidepressant, buzepide methiodide (BZP) by incorporating TiO₂ nanoparticles in carbon paste matrix. Electrochemical studies indicated that the TiO₂ nanoparticles efficiently increased the electron transfer kinetics between drug and the electrode. Compared with the nonmodified CPE, the TiO₂-modified CPE greatly enhances the oxidation signal of BZP with negative shift in peak potential. Based on this, we have proposed a sensitive, rapid and convenient electrochemical method for the determination of BZP. Under the optimized conditions, the oxidation peak current of BZP is found to be proportional to its concentration in the range of 5 × 10⁻⁸ to 5 × 10⁻⁵ M with a detection limit of 8.2 × 10⁻⁹ M. Finally, this sensing method was successfully applied for the determination of BZP in human blood serum and urine samples with good recoveries.     

Highly sensitive determination of cadmium and lead using a low-cost electrochemical flow-through cell based on a carbon paste electrode

A low-cost thin-layer electrochemical flow-through cell based on a carbon paste electrode (CPE), was constructed for the highly sensitive determination of cadmium(II) (Cd(2+)) and lead(II) (Pb(2+)) ions. The sensitivity of the proposed cell for Cd(2+) and Pb(2+) ion detection was improved by using the smallest channel height without the need for any complicated electrode modification. Under the optimum conditions, the detection limits of Cd(2+) and Pb(2+) ions (0.08 and 0.07 μg dm(-3), respectively) were 13.8- and 11.4-fold lower than that of a commercial flow cell (1.1 and 0.8 μg dm(-3), respectively). Moreover, the percentage recoveries of Cd(2+) and Pb(2+) for the in-house designed thin-layer flow cell were higher than those for the commercially available cell in all tested water samples, and within the acceptable range. The proposed flow cell is promising as an inexpensive and alternative one for the highly sensitive monitoring of heavy metal ions.     

Construction of a modified carbon paste electrode based on TiO2 nanoparticles for the determination of gallic acid

A modified carbon paste electrode was prepared by incorporating the TiO₂ nanoparticles in the carbon paste matrix. The electrochemical behavior of gallic acid (GA) is investigated on the surface of the electrode using cyclic voltammetry and differential pulse voltammetry. The surface morphology of the prepared electrode was characterized using the scanning electron microscopy. The results indicate that the electrochemical response of GA is improved significantly at the modified electrode compared with the unmodified electrode. Furthermore, the capabilities of electron transfer on these two electrodes were also investigated by electrochemical impedance spectroscopy. Under the optimized condition, a linear dynamic range of 2.5?×?10^?6 to 1.5?×?10^?4?mol?L^?1 with detection limit of 9.4?×?10^?7?mol?L^?1 for GA is obtained in buffered solutions with pH 1.7. Finally, the proposed modified electrode was successfully used in real sample analysis.     

Potentiometric determination of trace silver based on the use of a carbon paste electrode

A carbon paste electrode used as a sensor for silver has been developed and electrode response characteristics have been investigated. The electrode exhibits linear response to the logarithm of the concentration of silver from 5 x 10(-7)M to 1 x 10(-2)M, with a response slope of 63 +/- 2 mV. The detection limit according to IUPAC recommendations is 1 x 10(-7)M. This electrode has been used to determine trace silver in fixing solutions and waste electroplate solutions with good results.     

Voltammetric determination of 2-nitrophenol at a bentonite-modified carbon paste electrode

A bentonite-modified carbon paste electrode has been applied to the determination of 2-nitrophenol by differential pulse voltammmetry. The electrochemical reduction of 2-nitrophenol at –0.8 V is carried out in an artificial sea water-formic acid/sodium formate medium at pH 4. The peak height was found to be dependent on the pH over the range 2–11; the presence of a secondary process was observed in the pH range 8–11. The peak potential showed a dependence on pH, with two linear regions with different slopes. A linear relationship between peak intensity and concentration was obtained in the range 0.07–10 mgl^–1, with a detection limit of 0.03 mg 1^–1 and a coefficient of variation of 1.3% at 5 mg 1^–1. The effects of organic and inorganic species on the 2-nitrophenol determination were studied with a view to testing the resolution of the voltammetric technique. The proposed method has been applied to sea water samples with good results.     

Stripping voltammetric determination of mercury(II) at antimony-coated carbon paste electrode

A new procedure was elaborated to determine mercury(II) using an anodic stripping square-wave voltammetry at the antimony film carbon paste electrode (SbF-CPE). In highly acidic medium of 1 M hydrochloric acid, voltammetric measurements can be realized in a wide potential window. Presence of cadmium(II) allows to separate peaks of Hg(II) and Sb(III) and apparently catalyses reoxidation of electrolytically accumulated mercury, thus allowing its determination at ppb levels. Calibration dependence was linear up to 100 ppb Hg with a detection limit of 1.3 ppb. Applicability of the method was tested on the real river water sample.     

SiO2-modified carbon paste electrode for electrochemical determination of pyrogallol

A silica gel-modified carbon paste electrode (Si-CPE) was fabricated and used for determination of pyrogallol. Cyclic and differential pulse voltammetric studies show that Si-CPE lowers oxidation potential remarkably increases its oxidation peak current and improves electrochemical behavior of pyrogallol, compared to unmodified CPE. The effects of pH value, amount of silica, accumulation potential and time on the oxidation peak current of pyrogallol were examined. As a result, a sensitive, rapid and convenient electroanalytical method was developed for pyrogallol. The linear range is from 2 to 300 μM, and the limit of detection is 0.7 μM after 4.0 min accumulation. Interferences from some inorganic salts and organic compounds were studied. Finally, the method was successfully used to determine pyrogallol in tap water, green tea and artificial urine samples     

Voltammetric determination of trace amounts of mercury with a carbon paste electrode modified with an anion-exchanger

Summary A carbon paste electrode modified with a liquid anion exchanger (Amberlite LA2) was used for the voltammetric determination of mercury(II). Mercury is preconcentrated, as tetrachloromercurate(II), onto the surface of the modified electrode only by the ion-exchange effect of the modifier without application of potential. After exchange of the medium the accumulated amount of mercury(II) is determined by differential pulse anodic stripping voltammetry in a blank electrolyte solution. The response depends on the concentration of mercury in the bulk solution, preconcentration time, and other parameters. The detection limit was 1 g Hg(II)/l when a suitable time for preconcentration was chosen. Preconcentration for 5 min yields a linear calibration graph for concentrations up to 1000 g Hg(II)/l. The effect of other ions on the determination of mercury and the applicability of the method to the analysis of phenylmercury compounds in pharmaceutical preparations were investigated.     

A novel chemically modified carbon paste electrode based on a new mercury(II) complex for selective potentiometric determination of bromide ion

A new modified carbon paste electrode based on a recently synthesized mercury (II) complex of a pyridine containing proton transfer compound as a suitable carrier for Br⁻ ion is described. The electrode has a linear dynamic range between 3.00×10⁻² and 1.0×10⁻⁵ M with a near-Nernastian slope of 61.0±0.9 mV per decade and a detection limit of 4.0×10⁻⁶ M (0.32 ppm). The potentiometric response is independent of the pH of the solution in the pH range 4.0–8.3. The electrode possesses the advantages of low resistance, fast response and good over a variety of other anions. It was applied as an indicator electrode in potentiometric titration of bromide ions and for the recovery of Br⁻ from tap water.     

Silver particle-decorated carbon paste electrode based on ionic liquid for improved determination of nitrite

A simple silver particle-modified carbon paste electrode is proposed for the determination of low concentration levels of nitrite ions. The electrode consists of a carbon powder decorated with silver sub-micrometre particles (AgPs) and a hydrophobic ionic liquid trihexyltetradecylphosphonium chloride as a binder. It has been shown that AgPs exhibit a strong electrocatalytic effect on the nitrite oxidation. For optimal electroanalytical performance the electrode was conditioned via silver oxidation/reduction cycle. The electrode revealed a linear square-wave voltammetric response in a wide examined concentration range of 0.05 to 1.0 mmol L^− 1, limit of detection (LOD) of 3 μmol L^− 1 and excellent repeatability with RSD of 0.3%.     

Preparation and characterization of a new carbon paste electrode based on ketotifen–hexacyanoferrate

A new type of carbon paste electrode (CPE) was made using ketotifen fumarate (C₂₃H₂₃NO₅S; an antiasthmatic/antianaphylactic drug) and hexacyanoferrate. This electrode was constructed using an acidic solution of ketotifen fumarate and potassium hexacyanoferrate. For this purpose, ketotifen fumarate was dissolved in acidic solution (pH 1) and hexacyanoferrate was added by agitation, resulting in ketotifen–hexacyanoferrate (Ket–HCF) precipitate. The obtained precipitate was separated and introduced into carbon paste. The electrochemical behavior of Ket–HCF CPE was studied by cyclic voltammetry. A modified electrode shows one pair of peaks with surface-confined characteristics, with a 0.1-M phosphate buffer as supporting electrolyte. The effects of pH, alkali metal cations, and anions of supporting electrolytes on the electrochemical characteristics of modified electrodes were studied. The diffusion coefficients of hydrated K⁺ in film (D), the transfer coefficient (α), and the transfer rate constant for electrons (k _s) were determined.     

Poly-glutamic acid modified carbon nanotube-doped carbon paste electrode for sensitive detection of L-tryptophan

A novel poly-glutamic acid (PGA) film modified carbon paste electrode (CPE) incorporating carbon nanotubes (CNTs) was first prepared for the determination of l-tryptophan (l-Trp). Scanning electron microscopy and Fourier transform infrared spectroscopy were applied for characterization of the surface morphology of the modified electrodes and cyclic voltammetry was used to investigate the electrochemical properties of the proposed electrode towards the oxidation of l-Trp. Optimization of the experimental parameters was performed with regard to pH, ratio of CNTs, concentration of glutamic acid, electro-polymerization cycles, accumulation time and concentration of sodium dodecylbenzene sulfonate. The linearity between the oxidation peak current and the l-Trp concentration was obtained in the range of 5.0×10(-8) to 1.0×10(-4)M with a detection limit of 1.0×10(-8)M (S/N=3) and the sensitivity was calculated to be 1143.79μA?mM(-1)?cm(-2). In addition, the PGA modified CPE incorporating CNTs displayed high selectivity, good stability and reproducibility, making it suitable for the routine analysis of l-Trp in clinical use.     

A sensitive determination of dopamine in the presence of ascorbic acid using a nafion-coated clinoptilolite-modified carbon paste electrode

A selective dopamine determination using a nafion-coated clinoptilolite-modified carbon paste electrode in the presence of ascorbic acid was studied. Both cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV) were used for measurements of dopamine. To improve the selectivity of the clinoptilolite-modified carbon paste electrode in presence of a high concentration of ascorbic acid, the electrode surface was coated with nafion membrane. Experimental parameters affecting the determination of dopamine, including the clinoptilolite ratio, nafion membrane thickness, preconcentration time, preconcentration solution pH, stripping solution pH and interferences are discussed. The developed sensor has a wide linear range, a low detection limit, and good stability and reproducibility. The sensor offers a good alternative to existing analytical methods for dopamine, permits a relatively short analysis time, and is simple, selective and inexpensive.     

Voltamperometric determination of kinetin with a carbon paste modified electrode

The electrochemical behaviour of kinetin (6-furfurylaminopurine) on a carbon paste modified with OV-17 silicone electrode, is studied. The determination of kinetin is possible working in square wave voltammetric techniques, reaching limits of determination of 38.7 ng ml⁻¹. The proposed method was successfully applied to determine the cytokinin in extracts of apples (previously spiked with kinetin) and the obtained results were in accordance with the results obtained with HPLC-UV.     

Voltammetric determination of mifepristone at a DNA-modified carbon paste electrode

A new strategy for the preparation of a DNA-modified carbon paste electrode is developed. It is found that the anodic response of mifepristone is greatly enhanced at the dsDNA-modified carbon paste electrode comparing with that obtained at the bare electrode, while the response at a ssDNA-modified electrode is similar to bare electrode. So the dsDNA-modified electrode is employed as a sensitive biosensor for the detection of mifepristone. A linear dependence of the peak currents on the concentration is observed in the range 2.0 x 10(-7) approximately 2.0 x 10(6) mol/L, with a detection limit of 1.0 x 10(-7) mol/L. The relative standard deviation is 4.3% for six successive determinations of 1.0 x 10(6) mol/L mifepristone. The determination of mifepristone tablets is carried out and satisfactory results are obtained.     

Electrochemical determination of tryptophan based on silicon dioxide nanopartilces modified carbon paste electrode

Silicon dioxide nanoparticles modified carbon paste electrode was fabricated and used for electrochemical investigation of tryptophan. Compared with the unmodified electrode, the peak current significantly increased. Experimental conditions for tryptophan determination were optimized. Linear relationship between the peak current and tryptophan concentration was obtained in the range of 1.0 × 10^?7?5.0 × 10^?6 mol L^?1 and 5.0 × 10^?6?5.0 × 10^?5 mol L^?1 with an estimated detection limit of 3.6 × 10^?8 mol L^?1 (S/N = 3). Tryptophan in pharmaceutical and human serum samples were successfully determined by the proposed method.     

Voltammetric determination of azithromycin at the carbon paste electrode

Azithromycin (AZ) is the first member of a class of macrolide azalides antibiotics called azolides. A simple and selective square-wave voltammetric (SWV) method has been developed for the determination of azithromycin in pure form, in pharmaceutical preparation and in biological samples. Determination of azithromycin was accomplished with hand-make carbon paste electrode (CPE) in oxidative screen mode. The counter and reference electrodes were a Pt wire and a Ag/AgCl, respectively. Various parameters that can influence the peak signal (effect of buffer, ionic strength, accumulation time, pH and the composition of the paste) have been scrutinized. The best results were obtained in acetonitrile—aqueous 1 M sodium acetate-acetic acid buffer (pH 4.6) containing 0.1 M KCl (1:9; v/v) using a 15% paraffin oil CPE. The limits of detection and quantification of the pure drug are 0.463 and 1.544 ppb (with the correlation coefficient, r=0.9785and the standard deviation, S.D.=0.1 (n=5), for the accumulation time of 60 s), respectively. The method was successfully applied to the determination of the drug in urine and two forms of pharmaceutical formulations. Recoveries were 99.2—100.5% with S.D.=0.1—and 0.8% (n=5).