Voltammetric determination of mesotrione at hanging mercury drop electrode

A study of the electrochemical reduction of the mesotrione pesticide on a hanging mercury drop electrode (HMDE) was performed as a basis for the development of a sensitive analytical method for natural samples. The electrochemical characteristics of herbicide mesotrione dissolved in a phosphate buffer (pH 7.0) have been determined by means of electrochemical techniques such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV) over a wide range of pH from 2.0 to 10.0. The experimental parameters, such as electrolyte type and its pH, pulse amplitude, and scan rate were optimized. The method was applied to the determination of the pesticide in a spiked soil samples. Using this method, a linear calibration curve for mesotrione was obtained up to the 0.1 μM range in pH 7 phosphate buffer solution with a detection limit (S/N = 3) of 50 nM. The method can be applied successfully to the determination of mesotrione in soils. The text was submitted by the authors in English.     

Adsorptive stripping voltammetric determination of dimenhydrinate at a hanging mercury drop electrode

Dimenhydrinate exhibits a single adsorptive stripping peak at a hanging mercury drop electrode after accumulation at 0.0V vs Ag/AgCl electrode at pH 3.8 (acetate buffer). The addition of trace amounts of copper ions enhanced the dimenhydrinate peak and its height depends on the concentration of each dimenhydrinate and Cu²⁺. The adsorptive stripping response was evaluated with respect to accumulation time and potential, concentration dependence, electrolyte, the presence of other purines, surfactants and other metal ions, and some variables. The calibration graph for dimenhydrinate determination is linear over the range 2.0×10^–8–2.0×10^–7 M (pre-concentration for 60s). The correlation factor is found to be 0.985 and RSD is 3.2% at 1.0×10^–7 M. Detection limit is 1.0×10^–8 M after 5 min accumulation. The determination of dimenhydrinate in pharmaceutical formulations by the proposed method is also reported.     

The cathodic stripping voltammetric determination of traces of iodide with a hanging copper amalgam drop electrode

A hanging copper amalgam drop electrode (HCADE) is used for the determination of traces of iodide by cathodic stripping voltammetry. The cathodic stripping peak of copper(I) iodide from the HCADE is better defined than that of mercury(I) iodide from a hanging mercury drop electrode. Optimum conditions and interferences are reported. With a 3-min deposition time at ?0.1 V vs. SCE, the calibration plot is linear up to 2 × 10^?6 mol dm^?3 iodide. The detection limit for iodide with the HCADE under voltammetric conditions is 4 × 10^?8 mol dm^?3; this is lowered to 8 × 10^?9 mol dm^?3 by using the differential pulse stripping technique.     

Electrolysis at the interface between two immiscible electrolyte solutions by means of a hanging electrolyte drop electrode

A three-electrode system with a hanging electrolyte drop electrode is described. The system facilitates analytical exploitation of electrolysis at the interface between two immiscible electrolyte solutions. Its use is demonstrated for the determination of micromolar concentrations of tetraethylammonium cation by differential pulse stripping voltammetry, based on transfer of the cation from water to nitrobenzene.     

Convolutive forecasting at a hanging mercury drop electrode

Convolutive forecasting is a procedure which converts a non-steady-state voltammogram into a steady-state voltammogram. The procedure was found to be successful on a range of sphericities generated by varying the size of a hanging mercury drop and the potential sweep rate in a series of cyclic voltammetric experiments. Both theoretical and experimental analyses on a reversible electrochemical system were considered. An expression establishing the relationship between the radius of a spherical electrode and the potential sweep rate was developed to define the limits of the convolutive forecasting algorithm which was used.     

甘草苷在悬汞电极上的电化学行为及方法研究

运用循环伏安法(CV)考察了甘草苷在悬汞电极(HMDE)上的电化学还原行为,在-0.7~-1.7 V(vs.SCE)电位窗口及0.10 mol/L(NH4)2SO4溶液中甘草苷在HMDE上的循环伏安行为是一在低扫描速度(<100 mV/s)下受吸附控制,在高扫描速度下受扩散控制的不可逆还原过程,还原峰电位(Epc)为-1.491 V。运用计时库仑法(CC)、计时电流法(CA)测定并计算了甘草苷的电荷传递系数α、扩散系数D以及表观速率常数Kf等电极过程动力学参数。初步探讨了甘草苷在HMDE上的反应机理,同时运用方波伏安法(SWV)研究了甘草苷在HMDE上的方波伏安行为,还原峰电流与其浓度在1.2×10-6~1.2×10-5mol/L及1.2×10-5~1.2×10-3mol/L范围内呈良好的线性关系,相关系数R=0.9936及0.9966,检出限8.0×10-7mol/L,据此可建立直接电化学测定甘草苷含量的方法。     

槲皮素在悬汞电极上的伏安行为研究

应用循环扫描伏安法考察槲皮素在悬汞电极上的电化学行为,并用线性扫描伏安法测定其含量。在0.1mol/LNa2CO3-NaHCO3(pH9.51)缓冲溶液中,槲皮素在-1.33V(vs.Ag/AgCl)处出现灵敏的还原峰,峰电流与其浓度在2.0×10-6～2.0×10-5mol/L(r=0.9989)范围内呈良好的线性关系。该方法可直接用于罗布麻叶中槲皮素的含量测定。     

Electrochemical behaviour of sertraline at a hanging mercury drop electrode and its determination in pharmaceutical products

The electrochemical behaviour of sertraline at a hanging mercury drop electrode (HMDE) was described. Different voltammetric techniques, such as cyclic, linear sweep, differential pulse and square wave voltammetry, were used. Voltammograms were obtained at different pH values with a Britton-Robinson buffer solution used as supporting electrolyte. The best results were found by square wave voltammetry with electrodeposition at alkaline pH using a borate buffer with a pH = 8.2 for the samples, containing 12% (v/v) methanol. Under optimised conditions, a linear relationship between 2.33 x 10(-7) and 3.15 x 10(-6) M of sertraline with a limit of detection of 1.98 x 10(-7) M was obtained. The electrochemical method developed was applied to the determination of sertraline in pharmaceutical formulations. Recoveries were close to 100%, thus proving efficacy of the proposed method for the quantification of sertraline in commercial samples.     

Electrochemical behaviour of sertraline at a hanging mercury drop electrode and its determination in pharmaceutical products

The electrochemical behaviour of sertraline at a hanging mercury drop electrode (HMDE) was described. Different voltammetric techniques, such as cyclic, linear sweep, differential pulse and square wave voltammetry, were used. Voltammograms were obtained at different pH values with a Britton-Robinson buffer solution used as supporting electrolyte. The best results were found by square wave voltammetry with electrodeposition at alkaline pH using a borate buffer with a pH = 8.2 for the samples, containing 12% (v/v) methanol. Under optimised conditions, a linear relationship between 2.33 × 10^–7 and 3.15 × 10^–6 M of sertraline with a limit of detection of 1.98 × 10^–7 M was obtained. The electrochemical method developed was applied to the determination of sertraline in pharmaceutical formulations. Recoveries were close to 100%, thus proving efficacy of the proposed method for the quantification of sertraline in commercial samples. Received: 26 September 2000 / Revised: 1 December 2000 / Accepted: 5 December 2000     

Indirect determination of lutetium by differential pulse anodic stripping voltammetry at a hanging mercury drop electrode

Lutetium has been determined by differential pulse anodic stripping voltammetry in an acidic solution containing Zn-EDTA. Lutetium (III) ions liberated zinc (II), which was preconcentrated on a hanging mercury drop electrode and stripped anodically, resulting in peak current linearly dependent on lutetium (III) concentration. Less than 0.4 ng mL⁻¹ lutetium could be detected after a 2 min deposition.      

Electroreduction of diphenyldiazomethane in acetonitrile at a hanging mercury drop electrode

Cyclic voltammetric studies of the reduction of diphenyldiazomethane (Ph₂CN₂) in CH₃CN-Me₄NPF₆ at a hanging mercury drop electrode have established that the halflife of Ph₂CN₂^? is less than l ms at either 8°C or ?37°C.     

Study of the voltammetric behaviour of maleic hydrazide and its determination at a hanging mercury drop electrode

Voltammetric behaviour of maleic hydrazide pesticide dissolved in a Britton-Robertson buffer was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that the process at the Hg electrode was diffusion controlled; the reaction was irreversible and involved a change of one proton and a transfer of one electron. A quantitative differential pulse voltammetric method for determination of maleic hydrazide was developed on the basis of these studies involving the reduction of the compound at a hanging mercury drop electrode. A linear calibration was obtained in the range of 0.5-5.5 mg l⁻¹, and the developed DPV methodology was then applied for the determination of maleic hydrazide in spiked vegetable samples by the standard addition method. Satisfactory percentage R.S.D. (∼2%), percentage recovery values (∼85%) and LOD (0.215 mg l⁻¹) were obtained. These compared well with the results from the alternative spectrophotometric method.     

The determination of zinc,cadmium, lead and copper in human hair by differential pulse anodic stripping voltammetry at a hanging mercury drop electrode after nitrate fusion

Samples of hair are digested with nitric acid and fused with alkali metal nitrates, prior to the determination of Zn, Cd, Pb and Cu by differential pulse anodic stripping voltammetry at a hanging mercury drop electrode. Recoveries from spiked samples range from 91 to 101%. Relative standard deviations vary from 2.6 to 13%, depending on the metal and sample source. Some causes of poor reproducibility are discussed.     

Voltammetric determination of benzidine and its derivatives, at a glassy-carbon electrode

Conditions have been found for the determination of benzidine, o-tolidine, o-dianisidine, 3,3'-diaminobenzidine and 3,3'-dichlorobenzidine by classical and differential pulse voltammetry at a glassy-carbon stationary or rotating electrode, in the concentration range 10(-5)-10(-3)M. The mechanism of the oxidation is discussed and applications are presented for the determination of these chemical carcinogens and their mixtures either directly, or after preliminary separation by extraction or thin-layer chromatography.     

Voltammetric determination of selenosulfate ions at a mercury-film electrode

A procedure is proposed for the voltammetric determination of selenium as selenosulfate (SO₃Se^2?) ions at a mercury-film electrode (MFE). Selenosulfate ions are determined in the range from 2 × 10^?4 to 1.0 × 10^?3 M without analyte accumulation, using peak current at ?0.92 ± 0.02 V and in the range from 1 × 10^?7 to 2 × 10^?4 M after analyte accumulation with the open circuit, using peak current at ?1.18 ± 0.03 V as the analytical signal. The mechanisms of SO₃Se^2? reduction at an MFE under the conditions of direct voltammetry and stripping voltammetry with accumulation are proposed and discussed.     

Voltammetric determination of niclosamide at a glassy carbon electrode

A very sensitive and selective procedure was developed 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 NO2 to NHOH at -0.659 V in aqueous buffer solution of pH 8.5. Reversible and well defined peaks at -0.164 V and -0.195 V (vs. Ag/AgCl) were obtained that are responsible for two electron peaks between NHOH and NO. Following optimisation of the voltammetric parameters, pH and reproducibility, a linear calibration curve over the range 5 x 10(-8)-1 x 10(-6) mol dm(-3) was achieved. The detection limit was found to be 2.05 x 10(-8) mol dm(-3) niclosamide. For eight successive determinations of 5 x 10(-7) mol dm(-3) niclosamide, a relative standard deviation of 2.4% was obtained. This voltammetric method was applied to the direct determination of niclosamide in tablets. The results of the analysis suggest that the proposed method has promise for the routine determination of niclosamide in the products examined.     

Reversible and irreversible adsorption of surfactants at a hanging mercury drop electrode.

The adsorption-desorption phenomena of surfactants were studied by measuring differential capacity-potential curves in a static solution and differential capacity-time curves in a flowing solution. The surfactants investigated were Aerosol OT, cetylpyridinium chloride, Hyamin 1622, tetrabutylammonium bromide, Triton X-100 and trioctylphosphineoxide. The differential capacity-potential and differential capacity-time curves for these surfactants showed different shapes, with and without peaks. The differential capacity-time curves were used to study the adsorption reversibility of the surfactants at a mercury electrode. The adsorptions of Hyamin 1622 and Triton X-100 were irreversible at all the potentials investigated. The adsorptions of Aerosol OT and trioctylphosphineoxide were irreversible except at the potential more positive than -0.2 V. The adsorption of tetrabutylammonium bromide was almost reversible at any potential investigated. The adsorption of cetylpyridinium chloride was complicated, indicating different orientations of adsorption.     

Catalytic currents of albumin at the hanging mercury drop electrode

Bovine serum albumin (BSA), as well as completely reduced BSA denoted by P (SH)₃₅, are adsorbed on the hanging mercury drop electrode (HMDE) from alkaline buffer solutions. When time is allowed, a monolayer is adsorbed from very dilute (10^?9M) BSA solutions in ammoniacal and borate buffers. With a monolayer of adsorbed protein the voltammograms at the HMDE are then identical in a given ammoniacal or borax buffer containing cobalt(III) or (II) and different BSA concentrations. Voltammograms of P (SH)₃₅ are virtually identical with those of native BSA. At the HMDE the second Brdi?ka current is proportional to concentration of cobalt(III) or (II) and the first current nearly so. Incompletely or completely adsorbed BSA or P (SH)₃₅ is not desorbed on keeping the HMDE for one hour in ammonia buffers. An incomplete layer of adsorbed BSA or P (SH)₃₅ is relatively rapidly desorbed at ?1.6 V (vs. SCE) and a complete film at ?1.65 V, some desorption occurring at ?1.6 V. Upon desorption, the second Brdi?ka current decreases faster than the first one; this is particularly striking in 1 M ammonia buffer. The rate of desorption is increased by calcium chloride, but the rate of adsorption is not, or only slightly, increased in the presence of calcium. Incomplete adsorption occurs at ?1.60 V (vs. SCE) and no adsorption at ?1.65 V. Indications are obtained that “presodium currents” yield a slight plateau at ?1.67 to ?1.70 V, the plateau currents being attributed to adsorbed BSA, while unadsorbed BSA yields catalytic currents without a plateau, the currents merging with the residual one of the buffer. Calcium chloride greatly increases the presodium currents. From many kinetic data obtained at the dropping mercury electrode (DME) and from results at the HMDE it is concluded that, depending on the BSA concentration, Brdi?ka currents at the DME are partly of a kinetic and partly of a surface adsorption nature and partly diffusion-controlled. Adsorption equilibrium is not attained at the DME at 25° at concentrations of BSA smaller than 10^?6M.