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.     

Direct determination of traces of silver in mercury by voltammetry at the hanging mercury drop electrode in acetonitrile medium

A direct method for the determination of silver in mercury is described. The sample of mercury is introduced into the container of the hanging mercury drop electrode and the anodic voltammograms are recorded in a 0.1 M lithium perchlorate solution in acetonitrile. The anodic peak of silver obtained under these conditions is well separated from the mercury dissolution current. The peak height is proportional to silver concentration over the wide range 2 × 10^?6 mol dm^?3 (1.6 × 10^?6%) to at least 2.0 × 10^?2 mol dm^?3. No prior separation is needed; the procedure requires less than 20 min. The diffusion coefficient of silver in mercury was determined at several temperatures. It was found that silver in mercury does not form intermetallic compounds with copper, lead, thallium, cadmium, tin and bismuth.     

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.     

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.     

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.     

Square-wave voltammetry of the o-catechol-Ge(IV) catalytic system after adsorptive preconcentration at a hanging mercury drop electrode

Square-wave (SW) voltammetry in connection with a hanging mercury drop electrode has been applied for studying the reduction of Ge(IV) catalyzed by o-catechol after adsorptive preconcentration. Acetate buffer solutions with low and high analytical concentrations of o-catechol [with respect to that of Ge(IV)] have been used. Dependences of SW catalytic peaks on accumulation conditions have been attributed to the formation of the catalytic complexes via a direct-adsorption mechanism. The nature of the electrocatalytic process (involving an apparently quasi-reversible electrode reaction with an adsorbed reactant and a diffusing product) allows us to explain complex dependences of catalytic peaks on SW-parameters. Adequate conditions for determination of o-catechol and Ge(IV) by means of SW catalytic adsorptive voltammetry have been established.     

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。     

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.     

Electrochemical behaviour of tilmicosin at the hanging mercury drop electrode

The electrochemical behaviour of tilmicosin (TIM) was investigated using cyclic voltammetry and square-wave voltammetry in Britton-Robinson buffers (pH 2–12). The voltammograms of TIM showed one-irreversible peak which attributed to reduction of the >C=C< group in the entire pH values. However, an additional peak was shown over the pH range 2.00 to 4.00. Its peak potential is more positive potential from that of >C=C< group, and its potential was not practically dependent on the pH. On the other hand, the peak potential of >C=C< group was shifted to the more negative values with increasing pH. According to the obtained voltammetric data, the probable reaction mechanism for the reduction of TIM was proposed. Moreover, the adsorption of TIM on the mercury electrode surface by means of square-wave adsorptive stripping voltammetry measurements is studied at different pH values. The peak current variations with the deposition time and TIM concentration were observed.     

Determination of traces of selenium(IV) by cathodic stripping voltammetry at the hanging mercury drop electrode

Conditions convenient for the determination of traces of seIenium(IV) by cathodic stripping technique are described. Several electrolytes were tested. Three procedures are given in which the troublesome splitting of the stripping peak is eliminated. Suitable conditions include perchloric acid solution at elevated temperature, hydrochloric acid solution after preconcentration at zero current, and perchloric acid solution containing a small amount of iodide. The detection limits are 5 × 10^-9, 2 × 10^-9 and 5 × 10^-10 mol dm^-3, respectively. The time required for the entire procedure is about 30 min starting with a soluble seIenium(IV) sample.     

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。     

Adsorptive stripping voltammetry of chlordiazepoxide at the hanging mercury drop electrode

Controlled adsorptive accumulation at the hanging mercury drop electrode enables 0.8–11 × 10^?5 M chlordiazepoxide to be quantified by differential-pulse stripping voltammetry with accumulation times of 1–3 min. With 3-min accumulation, the peak current is enhanced 12-fold for 1.0 × 10^?7 M chlordiazepoxide compared to the current from differential pulse polarography. The detection limit is 0.9 × 10^?9 M for 4-min accumulation. The procedure is applied to spiked human serum after preseparation of the drug on a Sep-Pak C₁₈ cartridge.     

Parameter evaluation for the determination of selenium by cathodic stripping voltammetry at the hanging mercury drop electrode

The behaviour of selenium(IV) in cathodic stripping voltammetry is evaluated systematically. The effects of copper concentration, pH, deposition potential and complexing agents on the stripping peak are examined and criteria are given for the choice of suitable quantitative parameters. The detection limit was found to be 20 ng l^?1 and the background contamination level was 35 ng l^?1. Zinc and lead do not affect the determination of selenium if EDTA is added to the solution whereas cadmium interferes badly; the corresponding mechanisms are discussed.     

Anodic stripping voltammetry of germanium at the hanging mercury drop electrode

The Ge(IV)—Ge(0) system was investigated by cyclic and stripping voltammetry at HMDE in acidic pyrogallol medium and in phosphate, borate and carbonate buffers. It was found that germanium electrodeposited from dilute Ge(IV) solutions dissolved anodically forming two peaks corresponding to the oxidation of the unstable homogeneous and stable heterogeneous amalgams. Both peaks can be exploited analytically for the determination of traces of germanium but due to the complex nature of the germanium amalgam the sensitivity and reproducibility of the determinations are lower compared to the results obtained for metals well-soluble in mercury.     

Adsorption of cationic surfactants on covered hanging mercury drop electrode surface of variable area

Cetyldimethylbenzylammonium chloride (CDBACl) or cetyltrimethylammonium bromide (CTAB) is preadsorbed on mercury and used as substrate. The adsorptive stripping voltammetry with the two-step procedure is used. The mercury droplet with the preadsorbed surfactant is expanded in aqueous solutions of KCl, KBr, CTAB, CDBACl, or cetylethyldimethylammonium bromide (CEDAB). The surface area was increased from 0.0022cm(2) up to 0.0571cm(2). The surfactant molecules are maintained close to each other and in the vicinity of the electrode by the applied electric field. The expanding of the droplets resulted in a reorientation of the adsorbed molecules depending on the surfactant surface concentration. In some cases, condensed films were observed. Differences were noticed in the adsorption and desorption potential region. A linear increase in the capacitance current with the surface area was found in all cases up to a maximum increase in the surface area. Partly disorganized films were also observed. In some cases, defects were noticed during expansion. In one case, fractal structure was observed.     

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.     

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     

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.     

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.