Determination of trace metals in Nile River and ground water by differential pulse stripping voltammetry

The determination of trace metals in river water and ground water by DPSV is seriously disturbed by the presence of organic complexes. The influence of these substances can be eliminated by acidification of the samples with acids. Cd, Pb and Cu were determined at pH 1.1 (HNO₃ medium) and Zn, Cd, Pb and Cu at pH 2 (HCl medium), in both the Nile river and ground water. Zn was determined at pH 3.5 in HCl and pH 4.5 in HNO₃, after neutralizing the samples with NH₃/NH₄Cl buffer. Manganese could then be determined, after further addition of ammoniacal buffer solution up to pH 7.5 and 8.5. Ni and Co were determined in the adsorptive mode after formation of dimethylglyoximates at pH 9.2. The effect of pH on the stripping peaks of manganese was studied. Good agreement was observed between DPSV and AAS results for Zn, Cd, Pb, Cu and Mn, but the concentrations of Ni and Co were below the detection limits for AAS. Good agreement was obtained between DPSV results in HCl and HNO₃ for Ni and Co. The results indicate that decomposition of organic complexes by acidification with HNO₃ is better than in the case with HCl for Zn, Pb, Cu, Ni and Co, but HCl is better than HNO₃ for Cd and Mn.     

Determination of chromium(VI) in dialysis fluids by alternating current and differential pulse voltammetry

Alternating current (ACV) and differential pulse voltammetry (DPV) are employed for the determination of Cr(VI) in dialysis fluids, using 0.1 mol/1 dibasic ammonium citrate as supporting electrolyte (pH 5.9). A three-electrode cell was used: The working electrode was a long-lasting sessile-drop mercury electrode (LLSDME) with a drop time of 240 to 300 s. Precision, expressed as relative standard deviation (s _r%), and accuracy, expressed as relative recovery (R%) are also reported.     

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.      

Determination of dissolved manganese in natural waters by differential pulse cathodic stripping voltammetry

A procedure based on differential pulse cathodic stripping voltammetry on the graphite electrode is described for the determination of dissolved manganese in natural waters buffered at pH about 6.5 with acetate solution. In order to avoid interference of iron(II) the addition of fluoride is used. The limit of detection is 3 g/l for a deposition time of 6 min. Acidification and UV-irradiation are recommended for samples containing dissolved organic matter. Results of manganese determination in table mineral waters are reported and the possibility of manganese speciation is discussed.     

Determination of inorganic antimony species in seawater by differential pulse anodic stripping voltammetry: stability of the trivalent state

A simple method is described for the rapid and reliable determination of ultratrace concentrations of Sb(III) and Sb(V) in seawater by differential pulse anodic stripping voltammetry. It is based on the well-known dependence of Sb(III)/Sb(V) voltammetric response on acidity conditions. Under our optimised conditions (0.5 mol l⁻¹ HCl for Sb(III) and 5 mol l⁻¹ HCl for total Sb, respectively): (i) a detection limit of 11 ng l⁻¹ is obtained for a 10 min deposition time; (ii) no prior elimination of organic matter is needed; and (iii) antimony can be determined in the presence of natural copper levels. Particular care has been taken in order to understand the chemical processes taking place in all the solutions and reactions involved in the sampling and measuring procedures. Our results revealed the need to consider (i) the effect of photooxydation of synthetic and seawater samples on Sb speciation; and (ii) the stability of Sb(III) both in seawater samples and in the analytical solutions.     

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%。     

On-line coupling of sequential injection lab-on-valve to differential pulse anodic stripping voltammetry for determination of Pb in water samples

Sequential injection lab-on-valve (LOV) was first proposed for analyzing ultra-trace amounts of Pb using differential pulse anodic stripping voltammetry (DPASV) with a miniaturized electrochemical flow cell fabricated in the LOV unit. Deposition and stripping processes took place between the renewable mercury film carbon paste electrode and sample solution, the peak current was employed as the basis of quantification. The mercury film displayed a long-term stability and reproducibility for at least 50 cycles before next renewal, the properties of integrated miniature LOV unit not only enhanced the automation of the analysis procedure but also declined sample/reagent consumption. Potential factors that affect the present procedure were investigated in detail, i.e., deposition potential, deposition time, electrode renewable procedure and the volume of sample solution. The practical applicability of the present procedure was demonstrated by determination of Pb in environmental water samples.     

Decomposition of vegetables for determination of Zn,Cd, Pb and Cu by stripping voltammetry

A simple and accurate digestion method using nitric acid, perchloric acid and hydrogen peroxide has been developed for use in trace analysis for heavy metals in vegetables by differential pulse anodic stripping voltammetry. The recovery of the metals from the samples is lower if the hydrogen peroxide is omitted from the digestion mixture. Standard reference materials have been analysed satisfactorily by this method.     

微分脉冲阴极溶出伏安法测定呋喃唑酮

研究了呋喃唑酮在玻碳电极上的伏安行为。在 1mol LHCl底液中 ,用微分脉冲阴极溶出伏安法得到一灵敏的呋喃唑酮还原峰 ,峰电位为 0 .0 38V(vs.Ag AgCl)。峰电流与呋喃唑酮浓度在 8× 1 0 -6～ 1× 1 0 -4 mol L范围内呈线性关系 (r=0 .9984) ,检出限为 8× 1 0 -8mol L。该法已用于片剂与合成血清样品中呋喃唑酮含量的测定     

阳极溶出伏安法测定痕量汞的研究

痕量汞的测定方法有很多[1 ] 。原子吸收法虽然具有较高的灵敏性 ,但是仪器设备昂贵 ,分析步骤较繁琐。近年来 ,化学修饰电极阳极溶出伏安法在对汞痕量分析方面的研究报道也不少[2～3] ,测定的检测限一般在 1 0 - 6～ 1 0 - 9ｇ·ｍｌ- 1 ,但它容易产生记忆效应 ,洗脱不良。本文以玻碳电极为工作电极 ,在ＨＣｌ ＮａＣｌ Ｃｄ2 +中 ,示差脉冲阳极溶出伏安法 (ＤＰＳ)测定痕量汞 ,汞的平均回收率达80 %。1　实验部分1 1　主要仪器与试剂ＰＡＲ— 384极谱仪 (美国 ) ;三电极系统 :工作电极为玻碳电极 ,参比电极为Ａｇ/ＡｇＣｌ电极 ,对电极为…     

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.     

Differential pulse anodic stripping voltammetry detection of metallothionein at bismuth film electrodes

As a representation of metalloproteins, metallothionein (MT), which plays important biological and environmental roles such as in the metabolism and detoxification of some metals, was detected at bismuth film electrode (BiFE) by differential pulse anodic stripping voltammetry (DPASV). In pH 2–5.5, two well-defined anodic peaks were produced and attributed to the Zn²⁺ and Cd²⁺ inherent to MT. The calibration plot of DPASV peak currents for Cd²⁺ inherent to MT versus MT concentrations showed a good linearity with a detection limit of 3.86 × 10⁻⁸ mol/L for MT. As a non-toxic excellent electrode material, BiFE shows good performance for detecting MT, and is expected to find further applications in the studies of many other metalloproteins.     

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.     

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.     

Characterization of an electrochemical mercury sensor using alternating current,cyclic, square wave and differential pulse voltammetry

Here we report the characterization of an electrochemical mercury (Hg²⁺) sensor constructed with a methylene blue (MB)-modified and thymine-containing linear DNA probe. Similar to the linear probe electrochemical DNA sensor, the resultant sensor behaved as a “signal-off” sensor in alternating current voltammetry and cyclic voltammetry. However, depending on the applied frequency or pulse width, the sensor can behave as either a “signal-off” or “signal-on” sensor in square wave voltammetry (SWV) and differential pulse voltammetry (DPV). In SWV, the sensor showed “signal-on” behavior at low frequencies and “signal-off” behavior at high frequencies. In DPV, the sensor showed “signal-off” behavior at short pulse widths and “signal-on” behavior at long pulse widths. Independent of the sensor interrogation technique, the limit of detection was found to be 10 nM, with a linear dynamic range between 10 nM and 500 nM. In addition, the sensor responded to Hg²⁺ rather rapidly; majority of the signal change occurred in <20 min. Overall, the sensor retains all the characteristics of this class of sensors; it is reagentless, reusable, sensitive, specific and selective. This study also highlights the feasibility of using a MB-modified probe for real-time sensing of Hg²⁺, which has not been previously reported. More importantly, the observed “switching” behavior in SWV and DPV is potentially generalizable and should be applicable to most sensors in this class of dynamics-based electrochemical biosensors.     

Determination of arsenic in gold samples using matrix exchange differential pulse stripping voltammetry

A method comprising matrix exchange differential pulse stripping voltammetry (DPSV) at a gold film electrode has been proposed for the determination of small quantities of arsenic in pure gold. A wall-jet cell (WJC) and an on-line deoxygenation system were used to facilitate matrix exchange. The gold(I) cyanide complex was formed to avoid gold deposition on the electrode together with the arsenic. The pH of the sample solutions were adjusted to 3, as alkaline solutions gold(I) cyanide produced interference and the uncomplexed cyanide led to passivation of the gold film electrode. Matrix exchange electrolytes consisting of 4 mol l⁻¹ hydrochloric acid or a combination of 2 mol l⁻¹ sulphuric acid and 0.2 mol l⁻¹ hydrochloric acid could be utilised. Arsenic concentrations as low as 0.1 mg l⁻¹, could readily be detected in a gold matrix with a 60 s deposition time. While, cobalt and silver did not interfere with the arsenic determination, copper interfered even when present at similar concentrations to that of arsenic.     

Faradaic alternating current response of the adsorbed redox couple

A simple theoretical model to explain the a.c. voltammetry of the adsorbed reactant and product is developed. The theory indicates that maximum a.c. responses of the reversible redox reactions appear out of phase, whilst for the totally irreversible reaction, response appears in phase with the excitation signal. Theoretical predictions are compared with a.c. voltammograms of berberine.     

An optimization procedure for determination of indomethacin and acemethacin by differential pulse adsorptive stripping voltammetry. Application on urine samples

Procedures for the determination of indomethacin and acemethacin by differential pulse adsorptive stripping voltammetry with a mercury electrode have been described and optimised. The selection and optimization of the experimental parameters was done using factorial and central composite designs. Indomethacin and acemethacin in urine were determined by this method with good results and without the need for tedious prior separation. For routine calibration and calculation of the ‘capacity to detect’, the robust regression method least median squares (LMS) has been proposed.     

A study of bismuth-film electrodes for the detection of trace metals by anodic stripping voltammetry and their application to the determination of Pb and Zn in tapwater and human hair

This work reports the simultaneous determination of Cd(II), Pb(II) and Zn(II) at the low μg l⁻¹ concentration levels by square wave anodic stripping voltammetry (SWASV) on a bismuth-film electrode (BFE) plated in situ. The metal ions and bismuth were simultaneously deposited by reduction at −1.4 V on a rotating glassy carbon disk electrode. Then, the preconcentrated metals were oxidised by scanning the potential of the electrode from −1.4 to 0 V using a square-wave waveform. The stripping current arising from the oxidation of each metal was related to the concentration of each metal in the sample. The parameters for the simultaneous determination of the three metals were investigated with the view to apply this type of voltammetric sensor to real samples containing low concentrations of metals. Using the selected conditions, the limits of detection were 0.2 μg l⁻¹ for Cd and for Pb and 0.7 μg l⁻¹ for Zn at a preconcentration time of 10 min. Finally, BFE's were successfully applied to the determination of Pb and Zn in tapwater and human hair and the results were in satisfactory statistical agreement with atomic absorption spectroscopy (AAS).     

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。