Stripping voltammetric determination of lead using a glassy-carbon electrode system

The effect of the electrochemical pretreatment of the surface of a glassy-carbon indicator electrode on the electrode response and the repeatability of measurements in the stripping voltammetric determination of lead was studied. It was shown that the analytical signal depends on the nature of an electrolyte used for the pretreatment. The electrolytes that gave the most satisfactory results in the pretreatment were proposed     

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.     

依诺沙星在碳糊电极上的阳极吸附伏安法研究

在0.40 mol/L的NaAc-HAc(pH 4.5)缓冲液中,使用JP-303极谱分析仪,依诺沙星在碳糊电极(CPE)上有一灵敏的吸附伏安氧化峰,峰电位为1.17 V(vs.SCE).该氧化峰的二阶导数峰电流与依诺沙星的浓度在4.0×10-9～4.0×10-7 mol/L(富集90 s)范围内呈良好的线性关系,相关系数为0.995,检出限为2.0×10-9 mol/L(S/N=3,富集110 s).探讨了依诺沙星在碳糊电极上的伏安性质和电极反应机理,并且用于诺佳胶囊中依诺沙星的测定.     

Selectivity of voltammetric determination at an ion-exchanger modified electrode

An expression of the selectivity value for the voltammetric determination of an ionic analyte in the presence of interfering component(s) at an electrode chemically modified with an ion-exchanger has been developed and applied to the analysis of a model metal-ion mixture. Using distribution coefficient values, the predicted selectivity value was calculated and compared with that obtained experimentally. The approach allows a choice of the ion-exchange resin and experimental conditions for a given analytical task.     

Sensitive voltammetric determination of rutin at a carbon nanotubes-ionic liquid composite electrode

A new composite electrode of multiwall carbon nanotubes (MWNTs) and 1-dodecyl-3-methylimidazolium hexafluorophosphate (DDMIMPF₆) was fabricated to determine rutin. This electrode showed very attractive electrochemical performances compared to other kinds of ionic liquid modified electrodes and notably improved sensitivity and stability. Electrochemical behavior of rutin at the composite electrode had been investigated in pH 2.09 Britton–Robinson buffer solution by cyclic voltammetry and square wave voltammetry. The experimental results suggested that the composite electrode exhibited an electrocatalytic activity toward the redox of rutin. The electrochemical parameters of rutin were calculated with the results of the charge transfer coefficient (α) and the standard rate constant (k _s) as 0.48 and 2.09 s^?1. Under the selected conditions, the reduction peak current was linearly dependent on the concentration of rutin in the range of 0.03–1.5 μM, with a detection limit of 0.01 μM (S/N?=?3). The relative standard deviation for six times successive determination of 1 μM rutin was 1.6 %. The method was successfully applied to the determination of rutin in tablets and urine samples without the influence of the coexisting substances. In addition, the MWNTs/DDMIMPF₆ composite electrode exhibits a distinct advantage of simple preparation, surface renewal, good reproducibility, and stability.     

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.     

Differential pulse voltammetric determination of trace silicon at a glassy carbon electrode

The heteropoly molybdosilicic acid complex produces five well-developed differential pulse voltammetric peaks at a glassy carbon electrode in citrate buffer solutions containing 20% 2-butanone with peak potentials in the neighborhood of +0.05 V, -0.10 V, -0.25 V, -0.50 V and -0.65 V (vs. Ag/AgCl, 0.1 M KCl). The peak current at each peak potential is clearly developed and is proportional to the silicon concentration; the linear range for the most useful peak at +0.05 V is 10^-5–10^-7 M silicon, the lower limit being fixed by the blank conditions. Nickel-base alloy samples and water samples were analyzed with satisfactory results.     

Electrochemical detection of parathion at a glassy-carbon electrode modified with hexadecane

A modified electrode, based on a hexadecane (C(16))-coated glassy-carbon electrode (GCE) has been developed for the determination of parathion. The electrochemical behavior of parathion was investigated by cyclic voltammetry (CV). The peak potential and peak current were found to depend on the supporting electrolyte and the pH of the buffer solution. The reduction currents for parathion were proportional to parathion concentration over the range 8x10(-8)-2x10(-5) mol L(-1). The detection limit was 2x10(-8) mol L(-1) parathion for an accumulation time of 30 s. The effects of organic and inorganic species on the determination of parathion were also studied. A procedure was developed to extract parathion from spiked soil samples using a mixture of dichloromethane and acetone as the extraction solvent. The complete extraction and analytical procedure are simple, inexpensive and rapid. Parathion was determined in a soil sample by use of linear scan voltammetry (LSV).     

Anodic stripping voltammetric determination of vardenafil hydrochloride at pencil graphite electrode

In this paper, we present a very popular and low-cost sensor material as disposable pencil graphite electrode (PGE) system for the trace-level determination of vardenafil hydrochloride (VRL). Electrochemical behavior and determination of VRL was carried out by cyclic and square-wave adsorptive anodic stripping (SW-AdAS) voltammetry. The proposed method was highly sensitive and had a linear calibration range from 3 × 10^?10 to 1 × 10^?7 M with a correlation coefficient of 0.997. The limit of detection and limit of quantitation values were calculated as 1 × 10^?10 and 3 × 10^?10 M, respectively. Developed method with disposable PGE shows high sensitivity, selectivity and stability in a wide concentration range for VRL determination without the necessity of any modification. Additionally, this system was successfully applied in Levitra^® tablets and spiked human serum in trace level of VRL. Some kinetic parameters of VRL’s were represented for the first time. The results showed that the proposed method is highly sensitive, easy and low cost for trace-level determination of VRL.     

Dual-signal anodic stripping voltammetric determination of trace arsenic(III) at a glassy carbon electrode modified with internal-electrolysis deposited gold nanoparticles

A glassy carbon electrode (GCE) modified with internal-electrolysis deposited gold nanoparticles (AuNPs_ied) was applied to sensitively and selectively detect As(III) by anodic stripping linear sweep voltammetry (ASLSV). The AuNPs_ied/GCE was prepared based on the redox replacement reaction between a supporting-electrolyte-free aqueous HAuCl₄ and a copper sheet in saturated KCl separated by a salt bridge. Under optimum conditions (0.5 M aqueous H₂SO₄, 300-s preconcentration at − 0.4 V), the ASLSV peak current for the As(0)–As(III) oxidation responded linearly to As(III) concentration from 0.02 to 3 μM with a limit of detection (LOD) of 0.9 nM (0.07 μg L^− 1) (S/N = 3), while that for the As(III)–As(V) oxidation was linear with As(III) concentration from 0.02 to 1 μM with a LOD of 4 nM (0.3 μg L^− 1) (S/N = 3). An appropriate high-scan-rate for ASLSV can enhance both the sensitivity and signal-to-noise ratio. This method was applied for analyses of As(III) in real water samples.     

Preconcentration and voltammetric determination of trace myoglobin at a 6-mercaptopurine modified silver electrode

6-Mercaptopurine(6-MP) is covalently modified onto a silver electrode to construct a chemically modified electrode (CME). It exhibits the capability of selectively complexing myoglobin and can be applied as a selective biosensor for this compound. Myoglobin is accumulated onto the CME at 0.32 V (vs. SCE); after exchanging the medium it is determined by differential pulse stripping voltammetry. A cathodic stripping peak is obtained at 0.15 V (vs. SCE) by scanning the potential from 0.35 to –0.1 V. The peak currents are linearly proportional to the concentration of myoglobin in the range of 0.2 ∼ 4 μg/mL with a relative standard deviation of 7.8%. The detection limit is about 0.1 μg/mL. The mechanism of the complexation is also discussed. Received: 30 January 1997 / Revised: 7 May 1996 / Accepted: 10 May 1996     

Sensitive voltammetric determination of xanthinol nicotinate at a carbon nanotubes-ionic liquid gel modified electrode

The electrochemistry of xanthinol nicotinate(Xan) was studied by cyclic voltammetry at a glassy carbon electrode modified by a gel containing multi-walled carbon nanotubes(MWNTs) and room-temperature ionic liquid of 1-butyl-3-methylimidazolium hexafluorophosphate(BMTMPF_6).The modified electrode exhibited good promotion to the electrochemical oxidation of Xan and an ultrasensitive electrochemical method was proposed for the determination of Xan.This method was successfully applied to the determination of...     

Preconcentration and voltammetric determination of trace myoglobin at a 6-mercaptopurine modified silver electrode

6-Mercaptopurine(6-MP) is covalently modified onto a silver electrode to construct a chemically modified electrode (CME). It exhibits the capability of selectively complexing myoglobin and can be applied as a selective biosensor for this compound. Myoglobin is accumulated onto the CME at 0.32 V (vs. SCE); after exchanging the medium it is determined by differential pulse stripping voltammetry. A cathodic stripping peak is obtained at 0.15 V (vs. SCE) by scanning the potential from 0.35 to –0.1 V. The peak currents are linearly proportional to the concentration of myoglobin in the range of 0.2 ～ 4 μg/mL with a relative standard deviation of 7.8%. The detection limit is about 0.1 μg/mL. The mechanism of the complexation is also discussed.     

Cathodic stripping voltammetric determination of anti-cancer medicine nitrocaphanum at nafion modified electrode

An electrochemical method for the determination of anti-cancer medicine nitrocaphanum was described. The reaction mechanism of nitrocaphanum at Nafion CME was also discussed. It was found, in pH 2.5 medium, a linear response was observed for nitrocaphanum in the concentration range of 2.2 × 10^–8 M to 1.3 × 10^–6 M. Detection limit of this method is 5 × 10^–9 M, relative standard deviation for 10 measurements is 1.7%. The results of nitrocaphanum determination in real samples were satisfactory.     

Anodic stripping voltammetric determination of arsenic(III) using a glassy carbon electrode modified with gold-palladium bimetallic nanoparticles

We have developed a method for the determination of the three catecholamines (CAs) epinephrine (EP), norepinephrine (NE), and dopamine (DA) at sub-nanomolar levels. It is found that the luminescence of the complexes formed between the CAs and Tb³⁺ ion is strongly enhanced in the presence of colloidal silver nanoparticles (Ag-NPs). The Ag-NPs cause a transfer of the resonance energy to the fluorophores through the interaction of the excited-state fluorophores and surface plasmon electrons in the Ag-NPs. Under the optimized condition, the luminescence intensity of the system is linearly related to the concentration of the CAs. Linearity is observed in the concentration ranges of 2.5–110?nM for EP, 2.8–240?nM for NE, and 2.4–140?nM for DA, with limits of detection as low as 0.25?nM, 0.64?nM and 0.42?nM, respectively. Relative standard deviations were determined at 10?nM concentrations (for n?=?10) and gave values of 0.98%, 1.05% and 0.96% for EP, NE and DA, respectively. Catecholamines were successfully determined in pharmaceutical preparations, and successful recovery experiments are demonstrated for urine and serum samples.

Direct electrochemistry and voltammetric determination of midecamycin at a multi-walled carbon nanotube coated gold electrode

Magnesium l-ascorbic acid 2-phosphate (MAAP) and α-tocopherol acetate (α-TAc), as the stable vitamin C and vitamin E derivative, respectively, are often applied to skin care products for reducing UV damage. The encapsulation of MAAP (0.5%, g/mL) and α-TAc (5%, g/mL) together within the polyacrylonitrile (PAN) nanofibers was demonstrated using a coaxial electrospinning technique. The structure and morphology characterizations of the core-shell fibers MAAP/α-TAc-PAN were investigated by SEM, FTIR and XRD. As a negative control, the blend nanofibers MAAP/α-TAc/PAN were prepared from a normal electrospinning method. The results from SEM indicated that the morphology and diameter of the nanofibers were influenced by concentration of spinning solution, the polymer component of the shell, the carrying agent of the core and the fabricating methods, and the core-shell nanofibers obtained at the concentration of 8% had finer and uniform structure with the average diameters of 200 ± 15 nm. From in vitro release studies it could be seen that both different fiber specimens showed a gradual increase in the amount of α-TAc or MAAP released from the nanofibers. Furthermore, α-TAc and MAAP released from the blend nanofibers showed the burst release at the maximum release of ～15% and ～40% during the first 6 h, respectively, but their release amount from the core-shell nanofibers was only 10–12% during the initial part of the process. These results showed that core-shell nanofibers alleviated the initial burst release and gave better sustainability compared to that of the blend nanofibers. The present study would provide a basis for further optimization of processing conditions to obtain desired structured core-shell nanofibers and release kinetics for practical applications in dermal tissue.     

Adsorptive stripping voltammetric determination of 4-aminophenol at a single-wall carbon nanotubes film coated electrode

A single-wall carbon nanotubes (SWNT)-Nafion film coated glassy carbon electrode (GCE) was described for the determination of 4-aminophenol. In pH 3.0 sodium citrate-HCl buffer, the oxidation peak current of 4-aminophenol increases greatly at the SWNT-Nafion film coated GCE in contrast to that at both bare GCE and Nafion-film coated GCE. Moreover, the oxidation peak potential shifts to more negative potential. All the experimental parameters were optimized for the determination of 4-aminophenol. The oxidation peak current is proportional to the concentration of 4-aminophenol over the range from 5×10⁻⁹ to 2×10⁻⁶ mol l⁻¹. The detection limit is 8×10⁻¹⁰ mol l⁻¹ at 4 min of accumulation. Using the proposed method, 4-aminophenol in water samples was determined.     

Stripping voltammetric determination of platinum metals at a carbon paste electrode modified with cationic surfactants

In this contribution, a novel method is described for the determination of platinum metals. The procedure developed employs a carbon paste electrode modified in situ with cationic surfactants of the quaternary ammonium salt type. The pre-concentration step is based on a specific accumulation mechanism involving ion-pair formation; the detection being performed by cathodic scanning in the differential pulse voltammetric mode. Regarding the individual forms of platinum metals, the method has been found convenient for the determination of three heavy platinum metals in the form of Pt(IV), Ir(III) and Os(IV), whereas for the remaining elements (Ru, Rh, and Pd) was almost inapplicable. Platinum metals of the former group can be pre-concentrated in chloride-containing supporting media via PtCl₆²⁻, IrCl₆³⁻ and OsCl₆²⁻ complex anions, the central atom of each species being fairly reducible during the voltammetric scan. Stripping signals for both platinum and iridium were proportional to the concentration in a range of 1-10 × 10⁻⁶ M Pt(IV) and Ir(III); the response for osmium being linear within 0.1-6 × 10⁻⁷ M Os(IV) with a detection limit of about 5 × 10⁻⁹ mol l⁻¹. During optimisation, special attention was paid to the accumulation mechanism, choice of key experimental conditions, and to interference effects from foreign ions with potentially ion-pairing capabilities (AuCl₄⁻, TlCl₄⁻, CrO₄²⁻, MnO₄⁻, SCN⁻, and I⁻). The method elaborated has been tested on both model solutions and real samples of industrial waste water, showing in both cases satisfactory analytical performance.