Subtractive Anodic Stripping Voltammetry Research Articles

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 Pb 2+ 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 Pb 2+ in synthetic solutions with and without surfactants, certified reference materials and natural water samples have been performed.

Determination of Thallium at A Silver‐Gold Alloy Electrode by Voltammetric Methods in Plant Material and Bottom Sediment Containing Cd and Pb

AbstractThe applicability of the subtractive anodic stripping voltammetry (SASV) using the square‐wave mode at the silver‐gold alloy electrode has been studied for thallium determination in the presence of large amount of lead and cadmium in natural samples. 10 mmol L−1 perchloric acid was found as the most suitable supporting electrolyte for determination in synthetic solutions. The thallium peak was separated about 200 mV from Cd+Pb peak. Diethylenetriaminepentaacetic acid addition was necessary to determine thallium at the silver‐gold alloy electrode in digested plant and sediment. The determination limit was equal to 1.4 μg L−1. The method was validated by the inter‐method comparison (ICP‐MS).

A CMOS-integrated microinstrument for trace detection of heavy metals

This paper presents a voltammetric microsystem which includes CMOS-integrated sensors, electronic interface, and data conversion circuits for enabling cost-effective, in situ detection of trace metals. The system's electronics were implemented in a 0.5 /spl mu/m, 5 V, CMOS process and occupy 36 mm/sup 2/. Single-chip integration of the system was accomplished using post-CMOS, thin-film fabrication techniques. Due to its reduced ambient noise coupling and an integrated, pseudo-differential potentiostat, this design provides the best figures of merit for detection limit, area, and power published to date for heavy-metal microinstruments. The microsystem dissipates 16 mW and has successfully detected lead at concentrations of 0.3 ppb on 3.2/spl times/10/sup -5/ cm/sup 2/ gold electrodes using subtractive anodic stripping voltammetry.

Determination of Mercury in Hair by Square-Wave Anodic Stripping Voltammetry at a Rotating Gold Disk Electrode After Microwave Digestion

A simple and reliable method for the determination of mercury in hair on a rotating gold disk electrode using subtractive anodic stripping voltammetry without removal of oxygen is reported. Voltammetric and microwave parameters were optimized to obtain the best analytical results. Parameters such as supporting electrolyte concentration, influence of chloride in the Hg peak, deposition potential, scan rate, accumulation time, rotation rate, square-wave amplitude, and electrode conditioning were studied. Pressurized microwave-assisted digestion of hair, suitable for the accurate voltammetric determination of Hg, was evaluated using six acid mixtures and several time-power programs. Under the optimized conditions, no interference by copper, cadmium, lead, nickel, manganese, iron, or zinc was found at concentrations corresponding to their occurrence in normal hair. A calibration plot between 6,67 and 46,69 microg/L was linear, with r(2) better than 0.999. The detection limit for a deposition time of 60 s at 254 g was calculated as 1.92 nM (3omega). Validation of the method was demonstrated with the use of a certified reference sample of hair. Eight real samples of hair (four unexposed children and four exposed persons) were also analyzed.

Determination of Lead and Cadmium at Silver Electrode by Subtractive Anodic Stripping Voltammetry in Plant Materials Containing Tl

Lead and cadmium have been determined by the subtractive anodic stripping voltammetry using the square-wave mode at a silver electrode without removal of oxygen. The samples containing large amount of thallium were collected from a highly contaminated region. The presence of thallium strongly affects the peak shape of Cd. The plant material digestion was performed with HNO3/HClO4 mixture using pressurised microwave decomposition. The proposed method used for the lead determination was validated by the inter-method comparison (ICP-MS). The cadmium determination was validated using certified reference material. The results obtained, supported by statistical tests, demonstrated the usefulness of the method for the lead determination in samples containing large amounts of Cd and Tl. It is important to note that Cd can only be quantified when the thallium concentration is much lower than that of cadmium.

Characteristics of Subtractive Anodic Stripping Voltammetry of Lead, Cadmium and Thallium at Silver‐Gold Alloy Electrodes

AbstractSilver‐gold alloy electrodes have been studied for the purpose of the quantitative determination of heavy metals by subtractive anodic stripping voltammetry, (SASV). The results have been compared with those obtained with the silver and gold electrodes. The 50/50 a/o Ag/Au alloy electrode is the most suitable for quantifying thallium in the presence of lead and cadmium. The separation of its peak from those of lead and cadmium is 200 mV, which is about twice the separation obtained on the pure metal electrodes and is also better than on mercury. The silver electrode is suitable for the simultaneous determination of thallium, lead and cadmium. The peaks of lead and cadmium overlap on the 50/50 alloy. Pure silver or pure gold can be used for simultaneous quantification of these two metals. The use of gold for quantifying lead and cadmium is more limited because the peak potential of cadmium is shifted in the negative direction as its concentration increases and at [Cd2+]>200 nM, the two peaks merge. SASV enables correction for background currents and is of utmost importance for obtaining well‐defined peaks. The peaks of lead, cadmium and thallium appear over a relatively narrow potential range (ca. 200 mV) on all the electrodes presented in this work. For this reason, the quantifying of a peak is based on the derivative at the inflection point of only one of its branches (ascending or descending). All SASV measurements were carried out without removal of oxygen.

Characteristics of subtractive anodic stripping voltammetry of Pb and Cd at silver and gold electrodes

Silver and gold electrodes are useful for the quantitative determination of lead and cadmium with subtractive anodic stripping voltammetry (SASV). The use of SASV is essential for achieving good separation between the two peaks, to eliminate the interference of nitrates when cadmium is present and to allow analysis at very low concentrations without the removal of oxygen. The deposition and dissolution of Pb 2+ and Cd 2+ proceed at underpotential (UPD) on both electrodes. The UPD properties of the deposits are the main factor determining the analytical characteristics of the ASV method and are strongly affected by the type and concentration of the electrolyte. The effects of anions (Cl −, Br −, SO 4 2−, NO 3 −) and acids (HNO 3, HClO 4, H 2SO 4, HCl) are shown. The two electrodes complement each other and, in addition, enable the qualitative identification of Pb 2+ and Cd 2+, since the peaks appear in opposite order on the two electrodes. Analysis of mixtures of the two analytes is restricted on gold but not on silver. At gold the two peaks overlap: (i) at concentrations of cadmium higher than 250 nM at deposition times greater than 30 s, (ii) in the presence of copper at concentrations higher than 1 μM, and (iii) in the presence of Triton X-100 at concentrations above 10 mg/l. The repeatability at 10 nM analyte is better than 2.5%. The detection limits for Pb 2+ and Cd 2+ at 120 s deposition time and 3500 rpm rotation rate are: dl Pb/Ag=0.04 nM; dl Cd/Ag=0.7 nM; dl Pb/Au=0.1 nM; dl Cd/Au=0.3 nM. The analysis of lead and cadmium in natural waters has been performed.

Determination of nanomolar concentrations of lead and cadmium by anodic-stripping voltammetry at the silver electrode

Lead and cadmium have been determined by subtractive anodic-stripping voltammetry (SASV) in the square-wave mode at a silver electrode without removal of oxygen. The sensitivities and detection limits for the two metals differ considerably. Detection limits of 0.05 nM for lead and 1 nM for cadmium have been achieved following 90 s electrodeposition. The repeatability of consecutive SASV runs is good (for lead 0.5% at 20 nM for 30 s electrolysis, 5% at 0.3 nM for 60 s electrolysis; for cadmium 2.5% at 20 nM for 30 s electrolysis, 5% at 5 nM for 60 s). Hundreds of runs can be carried out without any pretreatment of the electrode. The high stability is attributed to renewal of the electrode surface that takes place during the electrodeposition step in a two-electrode cell: the silver counter/quasi-reference electrode generates silver ions that codeposit with lead and cadmium at the Ag-RDE, thus ensuring a continuity of the latter. Underpotential deposition (UPD) plays a central role in anodic-stripping voltammetry (ASV). During the deposition step, the adatom coverage of trace elements is in the range of 0.01–1% and no bulk deposition is invoked for metals that exhibit UPD. The UPD properties and, as a result, the ASV signals are strongly affected by the type and concentration of the supporting electrolyte. The effects of Cl −, Br −, SO 4 2− and NO 3 − are shown. The analysis of lead and cadmium in natural waters has been performed. Surfactants distort the SASV signal. In order to ensure surfactant-free solutions, the samples were pretreated by wet ashing.

Determination of sub-μg l −1 concentrations of copper by anodic stripping voltammetry at the gold electrode

A rotating disc gold electrode is used for the determination of copper in μg l −1 and sub-μg l −1 concentrations without removal of oxygen by the method of subtractive anodic stripping voltammetry (SASV). The detection limit for a 90 s electrodeposition is 0.2 nM. The reduction and stripping of copper on gold under the SASV conditions are underpotential deposition/dissolution phenomena. A uniformly distributed submonolayer of copper, occupying 0.01–5% of the real surface of the electrode, is formed. Linearity in calibration plot is obtained up to 5% electrode coverage; in terms of the experimental parameters of the deposition step (rate of rotation and time of electrolysis), this condition for linearity is C Cu 2+ N 1/2t d ≤7×10 5 nM rpm 1/2 s . The bulk and underpotential deposition of Cu 2+ have been characterized in the supporting electrolyte used (10 mM HNO 3 and 10 mM NaCl). The analysis of copper in drinking and in sea waters has been performed.

Subtractive anodic stripping voltammetry with flow injection analysis

Le systeme decrit permet le dosage simultane de divers metaux en traces au niveau de la ppb en utilisant un volume d'echantillon de 200 μl et une vitesse d'injection de 24 echantillons a l'heure

Reliability of background current subtraction in anodic stripping voltammetry at mercury film electrodes

The effectiveness and accuracy of the correction for background current in subtractive anodic stripping voltammetry at rotating mercury film electrodes are discussed. The effects of different experimental parameters on the subtracted baseline are examined. Long deposition periods, at extreme potentials, result in large errors in the background correction. The incomplete background correction is attributed mainly to changes in the morphology of the working electrode. Different approaches for obtaining the subtractive stripping response are compared. Errors are reduced when subtractive differential pulse stripping is used at different convection rates, resulting in a detection limit of 2 × 10 -9 M cadmium with 1-min deposition. Cadmium, lead, and zinc ions at nano molar concentrations were used as test ions.

Subtractive anodic stripping voltammetry at a blocked set of electrodes

The construction of a blocked set of electrodes (BSE) for subtractive anodic stripping voltammetry (SASV) is described. The set consists of the following elements: two working epoxy-resin-impregnated graphite electrodes, mercury coated in situ; an auxiliary platinum electrode; a salt-bridge; channels for gas and for metering the standards. The influence of the gas outflow speed on the deposition process was examined and the working conditions of the electrode set were optimized. The work of the BSE is illustrated by determining the Cu, Pb and Cd contents in the ppb range at a deposition time of 60 s.

Subtractive anodic stripping voltammetry at a blocked set of electrodes

The construction of a blocked set of electrodes (BSE) for subtractive anodic stripping voltammetry (SASV) is described. The set consists of the following elements: two working epoxy-resin-impregnated graphite electrodes, mercury coated in situ; an auxiliary platinum electrode; a salt-bridge; channels for gas and for metering the standards. The influence of the gas outflow speed on the deposition process was examined and the working conditions of the electrode set were optimized. The work of the BSE is illustrated by determining the Cu, Pb and Cd contents in the ppb range at a deposition time of 60 s.

Subtractive anodic stripping voltammetry with twin identical mercury-film electrodes differing in their convection transport during deposition

Subtractive anodic stripping voltammetry based on the use of different convection rates at the surface of two identical working electrodes during the deposition step is described. Twin mercury-film glassy-carbon disc electrodes, one rotated and one stationary, are used to demonstrate this technique. All background currents arising from nonconvective-dependent sources are effectively compensated. Deposition times of 3–5 min suffice for measuring heavy metal ions at sub-μg ml -1 concentration levels.

Subtractive anodic stripping voltammetry with rotating mercury coated glassy carbon electrode

The application of subtractive anodic stripping voltammetry (SASV) with a rotating mercury coated glassy carbon split-disk electrode to determine trace metals is described. Design of the electrode used, calibration curves, and relative standard deviations are reported. The results obtained show that this method has higher sensitivity than the simple ASV. Deposition time of 2–3 min is enough for simultaneous determinations of Cd, Pb and Cu in high purity NaCl solutions and natural sea water samples.

Subtractive anodic stripping voltammetry with rotating mercury coated glassy carbon electrode

The application of subtractive anodic stripping voltammetry (SASV) with a rotating mercury coated glassy carbon split-disk electrode to determine trace metals is described. Design of the electrode used, calibration curves, and relative standard deviations are reported. The results obtained show that this method has higher sensitivity than the simple ASV. Deposition time of 2–3 min is enough for simultaneous determinations of Cd, Pb and Cu in high purity NaCl solutions and natural sea water samples.