Anodic stripping voltammetric determination of heavy metals in solutions containing humic acids

Summary Various simultaneous effects of humic acids on the current and potential of differential pulse anodic stripping peaks of copper, lead, cadmium and zinc in weakly alkaline and acidic (pH 2) solutions have been investigated and interpreted with regard to metal complexation and the adsorption of humic acid on the mercury electrode. The applicability of the standard additions method for metal quantitation and the experimental conditions for UV-photolysis with a high-pressure mercury lamp have been examined in model as well as real water samples.     

New methodology for anodic stripping voltammetric determination of methylmercury

A novel procedure for trace methylmercury determinations by anodic stripping voltammetry at a gold film electrode is presented. Measurements were performed in a flow system. For selective determination of methylmercury, the Hg²⁺ ions were masked by complexation with DTPA. Hg-DTPA complex is not reduced at the gold film electrode at the potential of methylmercury reduction to the metallic state. The calibration graph was linear from 5 × 10⁻⁹ to 1 × 10⁻⁷ mol L⁻¹ for an accumulation time 600 s. A detection limit (based on 3σ criterion) for methylmercury was 2.3 × 10⁻⁹ mol L⁻¹. The validation of the proposed procedure was made by analyses of human hair certified reference material.     

Bismuth film electrode for anodic stripping voltammetric determination of tin

The bismuth film electrode (BiFE), in combination with anodic stripping voltammetry, offers convenient measurement of low concentrations of tin. The procedure involves simultaneous in situ formation of the bismuth film electrode on a glassy carbon substrate electrode, together with electrochemical deposition of tin, in a non-deaerated model solution containing bismuth ions, catechol as complexing agent and the metal analyte, followed by an anodic stripping scan. The BiFE is characterized by an attractive electroanalytical performance, with two distinct voltammetric stripping signals corresponding to tin, accompanied with low background contributions. Several experimental parameters were optimized, such as concentration of bismuth ions and catechol, deposition potential, deposition time and pH of the model solution. In addition, a critical comparison is given with bare glassy carbon and mercury film electrodes, revealing the superior characteristics of BiFE for measurement of tin. BiFE exhibited highly linear behavior in the examined concentration range from 1 to 100 μg L⁻¹ of tin (R² = 0.997), an LoD of 0.26 μg L⁻¹ tin, and good reproducibility with a calculated R.S.D. of 7.3% for 10 μg L⁻¹ tin (n = 10). As an example, the practical applicability of BiFE was tested with the measurement of tin in a real sample of seawater.     

Exploiting flow injection and sequential injection anodic stripping voltammetric systems for simultaneous determination of some metals

Flow injection (FI) and sequential injection (SI) systems with anodic stripping voltammetric detection have been exploited for simultaneous determination of some metals. A pre-plated mercury film on a glassy carbon disc electrode was used as a working electrode in both systems. The same film can be repeatedly applied for at least 50 analysis cycles, thus reducing the mercury consumption and waste. A single line FI voltammetric system using an acetate buffer as a carrier and an electrolyte solution was employed. An injected standard/sample zone was mixed with the buffer in a mixing coil before entering a flow cell. Metal ions were deposited on the working electrode by applying a potential of −1.1 V vs Ag/AgCl reference electrode. The stripping was performed by anodically scanning potential of working electrode to +0.25 V, resulting a voltammogram. Effects of acetate buffer concentration, flow rate and sample volume were investigated. Under the selected condition, detection limits of 1 μg l⁻¹ for Cd(II), 18 μg l⁻¹ for Cu(II), 2 μg l⁻¹ for Pb(II) and 17 μg l⁻¹ for Zn(II) with precisions of 2–5% (n=11) were obtained. The SI voltammetric system was similar to the FI system and using an acetate buffer as a carrier solution. The SI system was operated by a PC via in-house written software and employing an autotitrator as a syringe pump. Standard/sample was aspirated and the zone was then sent to a flow cell for measurement. Detection limits for Cd(II), Cu(II), Pb(II) and Zn(II) were 6, 3, 10 and 470 μg l⁻¹, respectively. Applications to water samples were demonstrated. A homemade UV-digester was used for removing organic matters in the wastewater samples prior to analysis by the proposed voltammetric systems.     

Sono-anodic stripping voltammetric determination of cadmium in the presence of surfactant

The effect of applying ultrasound in anodic stripping voltammetry analysis of Cd²⁺ in pH 4.6 buffer containing the surfactant Triton X-100 has been investigated. Manipulation of the horn intensity and the horn/electrode distance was found to reduce the deleterious influence of the surfactant on the height of the cadmium peak. The system has been optimised to take advantage of the in situ cleaning action offered by ultrasound. As a result facile detection of Cd²⁺ (0.05–4 μM) in solutions containing 10 μg/mL Triton X-100 can be achieved without recourse to sample pretreatments or electrode modifications. Received: 17 April 2000 / Revised: 2 June 2000 / /Accepted: 8 June 2000     

Adsorptive stripping voltammetric determination of netilmicin in the presence of formaldehyde

A linear sweep adsorptive stripping voltammetric method for the determination of netilmicin in the presence of formaldehyde has been proposed for the first time. In the presence of 3.0×10⁻³ g ml⁻¹ formaldehyde, netilmicin exhibits a sensitive cathodic peak at −1.30 V (vs. the saturated calomel electrode, SCE) in a medium of Britton–Robinson buffer (pH 8.7) with a scan rate of 100 mV s⁻¹ after a preconcentration period of 120 s at −1.10 V (vs. SCE). The peak current showed a linear dependence on the netilmicin concentration over the range 4.2×10⁻⁹–1.0×10⁻⁷ g ml⁻¹. The achieved limits of detection and quantitation were 1.0×10⁻¹⁰ and 3.3×10⁻¹⁰ g ml⁻¹ netilmicin, respectively. It was deduced from the experiments that the amine–aldehyde condensation product formed between netilmicin and formaldehyde is mainly responsible for the appearance of the peak. The electrochemical behavior of netilmicin in the presence of formaldehyde has been studied. The method was applied to the direct determination of netilmicin in injectable formulations and spiked human urine and serum samples.      

Sono-anodic stripping voltammetric determination of cadmium in the presence of surfactant

The effect of applying ultrasound in anodic stripping voltammetry analysis of Cd²⁺ in pH 4.6 buffer containing the surfactant Triton X-100 has been investigated. Manipulation of the horn intensity and the horn/electrode distance was found to reduce the deleterious influence of the surfactant on the height of the cadmium peak. The system has been optimised to take advantage of the in situ cleaning action offered by ultrasound. As a result facile detection of Cd²⁺ (0.05–4 μM) in solutions containing 10 μg/mL Triton X-100 can be achieved without recourse to sample pretreatments or electrode modifications. Received: 17 April 2000 / Revised: 2 June 2000 / /Accepted: 8 June 2000     

Application of an autoranging amplifier in the simultaneous determination of trace heavy metals by anodic stripping voltammetry

An autoranging amplifier with a gain of 1–1000 is described, together with its possible application in anodic stripping voltammetry. The performance of the amplifier is demonstrated by differential-pulse anodic stripping voltammetric analysis of stored sea-water, in the subtractive mode with two working electrodes. It is suggested that the autoranging amplifier could save considerable analysis time by eliminating the need for trial runs for gain adjustments and by relieving the operator from the need to change the recorder scale during the analysis.     

Differential pulse stripping voltammetric determination of heavy metals simultaneously using new polymer modified glassy carbon electrodes

Seven novel polymer modified glassy carbon electrodes have been developed for the analysis of metals of zinc, cadmium, lead, arsenic and copper in formulated samples of waters and industrial wastewater samples by differential pulse stripping voltammetry. Very good responses have been observed for all the metals with all the modified electrodes employed. However, the poly(3,4-ethylenedioxythiophene) modified electrode has resulted in very low detection limits. An independent atomic absorption spectroscopic analysis of the industrial wastewater sample was carried out and the results are compared.     

A novel tin-bismuth alloy electrode for anodic stripping voltammetric determination of zinc

We report on a novel tin-bismuth alloy electrode (SnBiE) for the determination of trace concentrations of zinc ions by square-wave anodic stripping voltammetry without deoxygenation. The SnBiE has the advantages of easy fabrication and low cost, and does not require a pre-treatment (in terms of modification) prior to measurements. A study on the potential window of the electrode revealed a high hydrogen overvoltage though a limited anodic range due to the oxidation of tin. The effects of pH value, accumulation potential, and accumulation time were optimized with respect to the determination of trace zinc(II) at pH 5.0. The response of the SnBiE to zinc(II) ion is linear in the 0.5–25?μM concentration range. The detection limit is 50?nM (after 60?s of accumulation). The SnBiE was applied to the determination of zinc(II) in wines and honeys, and the results were consistent with those of AAS.

Selenium-coated carbon electrode for anodic stripping voltammetric determination of copper(II)

We describe a new and promising type of selenium film electrode for anodic stripping voltammetry. This method is based on formation of copper selenide onto an in-situ formed selenium-film carbon electrode, this followed by Osteryoung square-wave anodic stripping voltammetry. Copper(II) is also in-situ electroplated in a test solution containing 0.01 mol L^-1 hydrochloric acid, 0.05 mol L^?1 potassium chloride and 500 µg L^?1 Se(IV) at a deposition potential of ?300 mV. The well-defined anodic peak current observed at about 200 mV is directly proportional to the Cu(II) concentration over the range from 1.0 to 100 µg L^?1 under the optimized conditions. The detection limit (three sigma level) is 0.2 µg L^?1 Cu(II) at 180 s deposition time. Relatively less interferences are shown from most of metal ions except for antimony(III). The method can be applied to analyses of river water and oyster tissue with good accuracy.     

Adsorptive stripping voltammetric determination of pipemidic acid in human urine

The electrochemical behaviour of pipemidic acid (8-ethyl-5,8-dihydro-5-oxo-2-(1-piperazinyl)-pyrido[2,3-d]pyrimidine-6- carboxylic acid), a well known antimicrobial agent used for urinary infections, was investigated by linear-sweep, differential-pulse and square-wave voltammetry at a hanging mercury drop electrode. Two reduction processes were observed in Britton-Robinson buffers at acid pH, whereas only one or two processes were observed in alkaline solutions, dependent on the pH of the buffer employed. Adsorptive effects were used to accumulate the drug on to the electrode. The adsorbed species were measured voltammetrically by using a cathodic process appearing at -0.76 V in 0.1 M HCIO4. Linear calibration graphs were obtained in the range 2.5 x 10(-9)-2.0 x 10(-7) M. A simple procedure of extraction was employed for the determination of the drug in urine samples.     

Differential pulse anodic stripping voltammetric determination of ziram (a dithiocarbamate fungicide)

A d.c. polarographic technique has been used previously for the determination of the pesticide, ziram, in aqueous samples, this paper reports differential pulse anodic stripping voltammetric determination of ziram zinc in rice samples using a static mercury drop electrode. The procedure developed distinguishes inorganic zinc and ziram zinc in sodium acetate-sodium chloride media. The procedure developed is suitable for the determination of concentrations as low as 10 ppb of ziram with a precision of 2.1% for five successive determinations of 150 ppb of ziram.     

Copper film electrode for anodic stripping voltammetric determination of trace mercury and lead

A novel in-situ prepared copper film electrode (CuFE) for anodic stripping voltammetric measurement of trace levels of Hg(II) and Pb(II) is presented. The optimal electroanalytical performance of the CuFE was achieved in electrolyte solution comprising 0.1 M HCl and 0.4 M NaCl. The CuFE exhibited excellent operation in the presence of dissolved oxygen with calculated LoD of 0.1 μg L^− 1 Hg(II) and 0.06 μg L^− 1 Pb(II) in combination with 300 s accumulation time, repeatability with RSD of 4.5% for Hg(II) and 0.9% for Pb(II) (n = 12), and favourable linear response in the examined concentration range of 10–100 μg L^− 1 (R² = 0.997) for Hg and 5–70 μg L^− 1 (R² = 0.999) for Pb after 120 s accumulation. The electrode enabled also simultaneous detection of both investigated metal ions and revealed promising electroanalytical characteristics similar to or in certain cases surpassing those of commonly used gold electrodes.     

A simple pretreatment of unrine for the direct differential-pulse anodic stripping voltammetric determination of lead

Lead can be determined directly in urine at the μg l^?1 level after a simple clean-up procedure consisting of an adsorptive removal of parts of the organic matrix on an apolar chromatographic medium followed by a filtration step.     

Adsorptive stripping voltammetric determination of cobalt in the presence of dimethylglyoxime and cetyltrimethylammonium bromide

A sensitive procedure for determination of micro-traces of Co(II) by adsorptive stripping voltammetry is proposed. The procedure exploits the enhancement of the cobalt peak obtained by use of the system Co(II)–dimethylglyoxime–piperazine-1,4-bis(2-ethanesulfonic acid)–cetyltrimethylammonium bromide. Using the optimized conditions, a detection limit (based on the 3 criterion) for Co(II) of 1.2×10^–11 mol L^–1 (0.7 ng L^–1) was achieved. The calibration plot for an accumulation time of 30 s was linear from 5×10^–11 to 4×10^–9 mol L^–1. The procedure was validated by analysis of certified reference materials and natural water samples.     

A direct differential pulse anodic stripping voltammetric method for the determination of thallium in natural waters

A dual direct method for the ultratrace determination of thallium in natural waters by differential pulse anodic stripping voltamrnetry (d.p.a.s.v.) is presented. D.p.a.s.v. at the hanging mercury drop electrode and at the mercury film electrode is used in the concentration ranges 0.5–100 μg Tl l^-1, and 0.01–10 μg Tl l^-1, respectively. Quantification is aided by the technique of standard additions. The response of the method is optimized for typical natural surface water matrices. An intercomparison of thalium determinations performed by the two anodic stripping methods and electrothermal-atomization atomic absorption spectrometry on normal and thallium-spiked surface water samples demonstrates equivalent accuracy within the range where atomic absorption is applicable. The method appears free from serious interferences.     

Differential pulse voltammetric determination of tin in the presence of noble metals

A voltammetric method for the determination of tin is proposed to minimise interferences from noble metals that are commonly encountered with other analytical techniques. Strong distortions of voltammetric peaks are observed in the presence of platinum. On the basis of a full investigation, the formation of an intermediate Sn(II)–Pt mixed chloro-complex at the electrode surface is identified as being responsible for the platinum interference, as it competes with the normal Sn(IV)→Sn(0)_Hg reduction. The use of a higher scan rate prevents the relatively low reaction kinetics and thus gets rid of this interference. No problems are encountered with other noble metals such as Pd, Ir, Re, Rh and Ru when using the modified method, although a baseline subtraction is necessary for the latter one. The proposed method is validated with real Pt–Sn catalysts.     

Analytical procedures for the simultaneous voltammetric determination of heavy metals in meals

An analytical procedure regarding the determination of copper(II), lead(II), cadmium(II), zinc(II) and antimony(III) in matrices involved in foods and food chain as wholemeal, wheat and maize meal is proposed. The digestion of each matrix was carried out using concentrated HCl suprapure at 130 °C for 3 h. Differential pulse anodic stripping voltammetry (DPASV) was employed for simultaneously determining all the elements, using a conventional three-electrode cell and 0.5 M HCl as supporting electrolyte. The analytical procedure has been verified on the reference standard materials Wholemeal BCR-CRM 189, Wheat Flour NIST-SRM 1567a and Rice Flour NIST-SRM 1568a. For all the elements in the certified matrix, the precision as repeatability, expressed as relative standard deviation (s_r), and the accuracy, expressed as relative error (e), were of the order of 3 to 6%. The limits of detection were in the range 0.009–0.096 μg/g.