The renovated silver ring electrode in determination of lead traces by differential pulse anodic stripping voltammetry

The study of a new type of working electrode - the renovated silver ring electrode (RSRE) - for lead ions detection via differential pulse anodic stripping voltammetry (DP ASV) without removal of oxygen is reported. The only four constituents of the RSRE: a specially constructed silver ring electrode, a silver sheet used as silver counter/quasi-reference electrode and a silicon O-ring, are fastened together in a polypropylene body. The renovation of this electrode is carried out through mechanical removal of solid contaminants and electrochemical activation in the electrolyte which fills the RSRE body. Excellent repeatability and reproducibility - also in organic samples solutions - were reached in a period of a few weeks through the renovation of the electrode surface before each measurement. The reduction and stripping of lead on silver electrode under the DP ASV conditions are underpotential deposition/dissolution phenomena. The RSRE is used for the determination of Pb ions in concentrations ranging from 1 × 10⁻⁹ to 1 × 10⁻⁷ M. The repeatability of DP ASV runs in synthetic solutions covering the entire concentration range is better than 2%. Obtained calibration curves are represented by a correlation coefficient of at least 0.999. The detection limit (LOD) for the time of electrodeposition equal to 60 s is 0.2 × 10⁻⁹ M. LOD for Pb²⁺ detection at the RSRE is similar to this reported for a rotating silver electrode in subtractive anodic stripping voltammetry (E. Kirowa-Eisner, et al., Anal. Chim. Acta, 385 (1999) 325). The analysis of Pb²⁺ in synthetic solutions with and without surfactants, certified reference materials and natural water samples have been performed.     

Simultaneous determination of lead(II) and cadmium(II) at a diacetyldioxime modified carbon paste electrode by differential pulse stripping voltammetry

A simple and effective chemically modified carbon paste electrode (CMCPE) for the simultaneous determination of lead(II) and cadmium(II) was developed in this work. The electrode was prepared by the addition of diacetyldioxime into a carbon paste mixture. Pb²⁺ and Cd²⁺ were preconcentrated on the surface of the modified electrode by complexing with diacetyldioxime and reduced at a negative potential (−1.10 V). Then the reduced products were oxidized by differential pulse stripping. The fact that two stripping peaks appeared on the voltammograms at the potentials of −0.65 V (Cd²⁺) and −0.91 V (Pb²⁺) demonstrates the possibility of simultaneous determination of Pb²⁺ and Cd²⁺. Under the optimized working conditions, calibration graphs were linear in the concentration ranges of 1.0×10⁻⁷-1.5×10⁻⁵ mol l⁻¹ (Pb²⁺) and 2.5×10⁻⁷-2.5×10⁻⁵ mol l⁻¹ (Cd²⁺), respectively. For 5 min preconcentration, detection limits of 1×10⁻⁸ mol l⁻¹ (Pb²⁺) and 4×10⁻⁸ mol l⁻¹ (Cd²⁺) were obtained at the signal noise ratio (SNR) of 3. To evaluate the reproducibility of the newly developed electrode, the measurements of 5×10⁻⁷ mol l⁻¹ Pb²⁺ and Cd²⁺ were parallel carried out for six times at different electrodes and the relative standard deviations were 2.9% (Pb²⁺) and 3.2% (Cd²⁺), respectively. Interferences by some metals were investigated. Only Ni²⁺ and Hg²⁺ apparently affected the peak currents of Pb²⁺ and Cd²⁺. The diacetyldioxime modified carbon paste electrode was applied to the determination of Pb²⁺ and Cd²⁺ in water samples. The results indicate that this electrode is sensitive and effective for the simultaneous determination of Pb²⁺ and Cd²⁺.     

TpPa-1/Nafion修饰电极的差分脉冲阳极溶出伏安法同时测定铜离子和汞离子

通过机械化学合成法合成了一种共价有机框架材料TpPa-1,以此作为电极材料制备化学修饰电极,研究了修饰电极的差分脉冲阳极溶出伏安法(DPASV)同时测定铜离子和汞离子。结果表明,TpPa-1/Nafion修饰电极在磷酸盐缓冲溶液中可实现对Cu^2+和Hg^2+的同时检测。Cu^2+的检出限为5.0×10^-8 mol/L线性范围为1.0×10^-7~5.0×10^-5 mol/L,R^2=0.9975。Hg^2+的检出限为1.0×10^-8 mol/L,线性范围为2.0×10^-8~1.0×10^-4 mol/L,R^2=0.9988。采用上述方法对实际样品进行检测,回收率为97.6%~105.5%,RSD均小于4.0%。     

Electrochemical solid phase micro-extraction and determination of salicylic acid from blood samples by cyclic voltammetry and differential pulse voltammetry

The electrochemical solid phase micro-extraction of salicylic acid (SA) at graphite-epoxy-composed solid electrode surface was studied by cyclic voltammetry. SA was oxidized electrochemically in pH 12.0 aqueous solution at 0.70 V (vs. saturated calomel electrode) for 7 s. The oxidized product shows two surface-controlled reversible redox couples with two proton transferred in the pH range of 1.0∼6.0 and one proton transferred in the pH range of 10.0∼13.0 and is extracted on the electrode surface with a kinetic Boltzman function of i _p = 3.473–4.499/[1 + e^{(t − 7.332)/6.123}] (χ ² = 0.00285 μA). The anodic peak current of the extracted specie in differential pulse voltammograms is proportional to the concentration of SA with regression equation of i _p = −5.913 + 0.4843 c (R = 0.995, SD = 1.6 μA) in the range of 5.00∼200 μM. The detection limit is 5.00 μM with RSD of 1.59% at 60 μM. The method is sensitive and convenient and was applied to the detection of SA in mouse blood samples with satisfactory results.     

Evaluation of a new multi-walled carbon nanotube paste electrode modified with Alizarin Red S for the determination of tellurium by differential pulse stripping voltammetry

A new modified carbon paste electrode based on multi-walled carbon nanotube and Alizarin Red S acts as a chelating agent for tellurium(IV) ions, is described. The electrochemical responses were found to be analytically suitable to develop a method for the determination of tellurium at low concentration levels. Under optimised operational conditions, the sensor exhibited linear behaviour in the range of 2.0–300 ng mL^?1 (correlation coefficient: 0.9982) with a detection limit of 0.45 ng mL^?1. The results indicate that the sensor is sensitive and effective for the determination of tellurium in water samples and certified reference materials.     

电活化玻碳电极差分脉冲溶出伏安法测定磺胺嘧啶

采用线性循环溶出伏安法和差分脉冲溶出伏安法对磺胺嘧啶在电活化玻碳电极上的电化学行为进行了研究。玻碳电极在PBS溶液中(pH 7.0),用恒电位法在1.7 V阳极氧化400 s,在B-R缓冲溶液中,磺胺嘧啶在1.02V(vs.Ag/AgCl)处有一良好的氧化峰,在0.02～0.25 V/s范围内,其氧化峰电流与扫描速率呈良好线性关系,表明电极过程为受吸附控制的不可逆过程。差分脉冲溶出伏安法的氧化峰电流(Ipa)与磺胺嘧啶浓度1×10-6～1×10-4mol/L范围内呈良好的线性关系(r=0.9977),检出限为8.7×10-7mol/L(S/N=3)。方法已用于分析磺胺嘧啶片剂的分析。     

二次微分脉冲溶出伏安法同时测定对苯二酚和邻苯二酚

制备了聚牛磺酸修饰玻碳电极,提出了一种灵敏的差分脉冲溶出伏安法(DPSV)同时测定痕量对苯二酚(HQ)和邻苯二酚(CC)的新方法.在HAc-NaAc缓冲溶液(pH4.6)中,于-0.400V(vsSCE)富集后,用DPSV进行分析,HQ和CC分别于0.157V和0.262V处获得灵敏的阳极溶出峰,峰电流与HQ和CC浓度...     

Voltammetry determination of trace manganese with pretreatment glassy carbon electrode by linear sweep voltammetry

This paper described the determination of trace manganese using linear sweep voltammetry at a pretreatment glassy carbon electrode. The glassy carbon electrode pretreated by electrochemical method in the 0.1 mol l⁻¹ NaOH solution greatly improved the electrode responsibility in the determination of manganese(II). The barrier to the detection of low manganese concentration was overcome by means of autocatalytic effect of manganese oxide deposited on the electrode in advance. Under the optimum experiments condition (0.04 mol l⁻¹ NH₃-NH₄Cl buffer solution, pH 9.0), the linear range was 4×10⁻⁸ to 1×l0⁻⁶ mol l⁻¹ Mn(II) for linear sweep voltammetry and 1×10⁻⁹ to 4×10⁻⁸ mol l⁻¹ Mn(II) for convolution voltammetry. The relative standard deviation for 2×10⁻⁸ mol l⁻¹ Mn(II) is 3.4%. The proposed method is simple, rapid, sensitive and selective. It had been applied to the determination of trace manganese in samples with satisfactory results.     

Simple and rapid determination of clonidine in pharmaceutical samples by voltammetry using a bare glassy carbon electrode

This work presents, for the first time, the voltammetric behavior of clonidine (CLO) drug and its determination, using an unmodified glassy carbon electrode (GCE). CLO exhibited only an irreversible oxidation process on the GCE, with peak potential at +0.85 V in pH 12 (vs Ag/AgCl). CLO oxidation process is pH-dependent and the electrochemical mechanisms on the GCE were proposed in acidic and basic medium. The determination of CLO was optimized in 0.1 mol L⁻¹ phosphate buffer solution at pH 12.0 using differential pulse voltammetry (DPV), which provides a good linear range (0.65 to 106.00 μmol L⁻¹) and low theoretical limit of detection (0.14 μmol L⁻¹) for the quality control of this drug in pharmaceutical samples. In addition, stable responses of CLO at the GCE were obtained in the same day (RSD = 3.4 %; n = 5) and different days (RSD = 2.0 %; n = 3). Moreover, the determination of CLO in a pharmaceutical formulation using the proposed GCE-DPV method presented good accuracy, since the recovery was close to 100 % and the dosing result was in agreement with an official method (HPLC-UV). The proposed method demonstrates a good analytical performance for CLO determination in pharmaceutical samples, providing a faster, simpler and lower-cost alternative for quality control of CLO than other reported methods.     

Determination of bromadiolone in pheasants and foxes by differential pulse voltammetry

Bromadiolone, a commercially used anticoagulant rodenticide, was determined in tissues of various animals by differential pulse voltammetry with a carbon-paste electrode. Under the most suitable experimental conditions (step potential of 25?mV?s^?1 and 0.2?mol?L^?1 acetate buffer, pH 4.2), the limit of detection was 0.5?ng?mL^?1. The electroanalytical method was consequently used to investigate the bromadiolone transport within the food chain. Pheasants were exposed to bromadiolone and then used as feed for a fox. The average levels were 528 and 198?ng of bromadiolone per gram of fresh weight of liver of pheasant and fox, respectively. Due to the surprisingly lower content of bromadiolone in the latter, a basic biochemical analysis, particularly blood coagulation, was performed. Among the parameters studied (thrombin time, prothrombin time, activated partial thromboplastin time, and fibrinogen), there was prolongation of the prothrombin time and activated partial thromboplastin time.     

Application of differential pulse stripping voltammetry and chemometrics for the determination of three antibiotic drugs in food samples

A reliable method for simultaneous determination of three antibiotic drugs(levofloxacin,gatifloxacin and lomefloxacin) by differential pulse stripping voltammetry(DPSV) in Britton-Robinson buffer(pH 7.96) was presented.The method is based on adsorptive accumulation of the antibacterial drugs on a hanging mercury dropping electrode(HMDE),followed by the reduction of the adsorptive species by the technique of DPSV.Optimal conditions,the deposition time of 80 s,the deposition potential of—1250 mV,and the scan rate of 25 mV/s,were obtained.The linear concentration ranges of 0.010-0.080μg/mL were obtained for all these three antibiotic drugs,while the detection limits were 2.38,3.20 and 1.60ng/mL for levofloxacin,gatifloxacin and lomefloxacin,respectively.In this work,chemometrics methods,such as classical least squares(CLS),partial least squares(PLS), principle component regression(PCR) and radial basis function-artificial neural networks(RBF-ANN),were used to quantitatively resolve the overlapping signals.It was found that PCR gave the best results with total relative prediction error(RPE_T) of 7.71%.The proposed method was applied to determine these three drugs in several commercial food samples with spiked method and yielded satisfactory recoveries.     

Lithium ions determination by selective pre-concentration and differential pulse anodic stripping voltammetry using a carbon paste electrode modified with a spinel-type manganese oxide

The use of selective pre-concentration and differential pulse anodic stripping voltammetry (DPASV) using a carbon paste electrode modified (CPEM) with spinel-type manganese oxide has been proposed for the determination of lithium ions content in natural waters. The new procedure is based on the effective pre-concentration of lithium ions on the electrode surface containing spinel-type Mn(IV) oxide with the reduction of Mn(IV) to Mn(III) and consequently the lithium ions intercalation (insertion) into the spinel structure. The best DPASV response was reached for an electrode composition of 25% (m/m) spinel-type MnO₂ in the paste, 0.1 mol l⁻¹ tris(hydroxymethyl)aminomethane (TRIS) buffer solution of pH 8.3, scan rate of 5 mV s⁻¹, accumulation potential of 0.3 V versus saturated calomel reference electrode (SCE), pre-concentration time of 30 s and potential pulse amplitude of 50 mV. In these experimental conditions, the proposed methodology responds to lithium ions in the concentration range of 2.8×10⁻⁶ to 2.0×10⁻³ mol l⁻¹ with a detection limit of 5.6×10⁻⁷ mol l⁻¹. The determination of the lithium ions content in different samples of natural waters samples using the proposed methodology and atomic absorption spectrophotometry are in agreement at the 95% confidence level and within an acceptable range of error.     

Solid-contact ionophore-based electrode for determination of pH in acidic media

Solid-contact electrode for pH measurements in acidic media is described. The sensor membrane is made of polyvinyl chloride plasticized with bis(2-ethylhexyl)phthalate and contains neutral pH-selective ionophore hexabutyltriamidophosphate and potassium tetrakis-p-Cl-phenylborate cation exchanger. The transducer layer of the solid-contact electrode contains the same membrane composition and also carbon black and electron–ion-exchanger resin EI-21(a cation exchange resin containing fine dispersion of metal copper) for stabilization of the electrode potential. The electrode is suitable for measurements of pH in the range 0–6 and works also in hydrofluoric acid (HF) solutions up to 0.1 M HF. Chronopotentiometric measurements show diffusion-limited polarization at the interface between sensor membrane and transducer layer. The slope of the linearized polarization curve correlates with the long-term stability of the electrode potentials providing a tool for prediction of the long-term stability of solid-contact potentiometric sensors.     

碳纳米管／纳米二氧化钛-聚苯胺载铂复合电极微分脉冲法测定葡萄糖

研究了多壁碳纳米管/纳米二氧化钛-聚苯胺载铂(CNT/nanoTiO2-PAn-Pt)复合电极对葡萄糖的电催化氧化作用。以0.5 mol/LKOH水溶液为底液,采用微分脉冲法在-0.5-0.2V电位区间扫描,在-0.33V(vs,SCE)附近产生的氧化电流峰灵敏度高且峰型好,故以此峰为定量峰。葡萄糖浓度在1.25×10-2~1.0×10-5mol/L与峰电流呈良好的线性关系,线性相关系数为0.99881,检出限为5.0×10-6mol/L。加入0.06m mol/L的抗坏血酸或0.3m mol/L的尿酸(模拟人血成份)均不干扰葡萄糖的测定。该电极对模拟血液中葡萄糖的测定,结果令人满意。     

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.      

纳米银修饰电极差分脉冲伏安法测定盐酸金霉素

建立了快速测定盐酸金霉素(CTC)的方法。通过NaBH4还原法制备纳米银(AgNPs)溶胶,并利用X射线衍射和紫外-可见光谱进行表征。将制备好的AgNPs滴涂到玻碳电极表面制备修饰电极(AgNPs/GCE),研究了CTC在AgNPs/GCE上的电化学行为及伏安法测定,优化了缓冲溶液和pH等检测条件。结果表明,CTC在pH 3.3的柠檬酸-NaOH-HCl缓冲溶液中检测效果最佳。CTC在AgNPs/GCE上发生2个电子和2个质子的不可逆电化学氧化反应,且反应受吸附控制。最佳条件下,CTC的氧化峰电流与其浓度呈现良好的线性关系,线性范围为0.5~100μmol/L,检出限为0.14μmol/L。该修饰电极可用于河水样品检测。     

Simultaneous determination of chromium(III) and cadmium(II) by differential pulse anodic stripping voltammetry on a stannum film electrode

A stannum film electrode has been developed for the simultaneous determination of trace levels of chromium(III) and cadmium(II) by differential pulse anodic stripping voltammetry (DPASV). The stannum film electrode was generated in situ by depositing simultaneously the stannum film and the metals obtained by reduction of Cd(II) and Cr(III) at −1.4 V on a glassy carbon electrode. Then, the reduced products were oxidized by scanning the potential of the electrode from −1.4 to −0.4 V using DPASV. The electrode exhibited well-defined and separated stripping signals for both metals accompanied with a low background contribution. The possible mechanism of this design was proposed. Under the optimized working conditions, the detection limit was 2.0 and 1.1 μg l⁻¹ for Cr(III) and Cd(II) at a deposition time of 3 min. Finally, the stannum film electrode was successfully applied to the determination of Cd(II) in tap water with satisfactory results.     

Determination of nitrobenzene by differential pulse voltammetry and its application in wastewater analysis

A new method for the determination of nitrobenzene (NB) by differential pulse voltammetry (DPV) based on an adsorptive stripping technique was developed. Cyclic voltammetry (CV) was used in a comparative investigation into the electrochemical reduction of NB at a glassy carbon electrode (GCE). With this electrode, the sharp peak of NB appeared at −0.71 V (vs. Ag/AgCl). The experimental parameters were optimized. Studies on the effect of pH on the peak height and peak potential were carried out over the pH range ca. 9.0–11.5 with sodium carbonate/sodium hydrogen carbonate buffer solution. A solution of pH 9.9 was chosen as analytical medium. Cathodic peak currents were found to be linearly related to the concentration of NB over the range ca. 12.3–1.23 × 10⁴ μg L⁻¹ with relative standard deviations of ca. 3.26–6.75%. The detection limit of NB in water was 5.42 μg L⁻¹. The interference of organic and inorganic species on the voltammetric response was also studied. The proposed method was applied to the determination of NB in wastewater samples with an average recovery of ca. 95.9–102.4%.     

Determination of linuron in water and vegetable samples using stripping voltammetry with a carbon paste electrode

A carbon paste electrode was used for the electrochemical determination of linuron concentrations in water and vegetable extracts. Optimal conditions were established with respect to electrode activation (electrochemical pretreatment), time accumulation, potential accumulation, scan rate, and pH. The limit of detection achieved with a pre-concentration step was 23.0 μg L⁻¹. Recovery measurements in vegetable extract and natural water samples were in the range of 98-103%, indicating that the proposed electrochemical method can be employed to analyze linuron in these matrices. The determination results were in good agreement with HPLC results.     

Electrochemical determination of lead(II) using a montmorillonite calcium-modified carbon paste electrode

Utilizing the fascinating properties of montmorillonite calcium (MMT-Ca), such as huge cationic exchange capacity, strong adsorptive ability, high chemical and mechanical stability, an MMT-Ca modified carbon paste electrode (CPE) was constructed for the sensitive determination of Pb²⁺. In 0.01 mol·L⁻¹ HCl, Pb²⁺ was firstly exchanged and accumulated on an MMT-Ca modified CPE surface and secondly reduced to Pb at −0.90 V. In the following potential sweep from −0.90 to −0.50 V, reduced Pb was oxidized, resulting in an obvious stripping peak at −0.58 V. After optimizing the parameters, such as determining medium, content of MMT-Ca, accumulation potential and time, an electrochemical method was developed for the analysis of Pb²⁺. Compared with bare CPE, the MMT-Ca modified CPE significantly enhances the sensitivity of Pb²⁺ analysis. The limit of detection is evaluated to be 6.0 × 10⁻⁹ mol L⁻¹ Pb²⁺. Finally, this method was successfully employed to determine trace levels of Pb²⁺ in water samples. The first two authors contribute equally do this work