Catalytic Adsorptive Stripping Research Articles

Application of Aminopolycarboxylic Complexes of V(IV) in Catalytic Adsorptive Stripping Voltammetry of Germanium

In the review, voltammetric analytical procedures that employ vanadium(IV) and aminopolycarboxylic complexes of V(IV) are presented and discussed. The focus of the paper is on the mechanism of vanadium-catalyzed reactions responsible for the amplification of the analytical signal of Ge(IV). The analytical efficacy of different catalytic systems is compared, and the optimal parameters of the respective procedures are reported.

Catalytic Adsorptive Stripping Voltammetric Determination of Germanium Employing the Oxidizing Properties of V(IV)-HEDTA Complex and Bismuth-Modified Carbon-Based Electrodes.

An efficient procedure that may be used to determine germanium traces and combines the advantages of catalytic adsorptive stripping voltammetry (CAdSV) with the convenience of screen-printed electrodes was developed. To induce the CAdSV response of the germanium(IV)-catechol complex, the vanadium(IV)-HEDTA compound was employed in combination with various bismuth-modified homogeneous (glassy carbon, gold coated with a bismuth layer via physical vapor deposition) and heterogeneous (screen-printed carbon, mesoporous carbon, graphene and reduced graphene oxide, polymer-encapsuled carbon fiber) electrodes. This solution had never before been implemented for this purpose. To achieve the most favorable performance of the working electrode, the parameters of bismuth deposition were optimized using a central composite design methodology. SEM imaging and contact angle measurements confirmed the long-term stability and high chemical resistance of the electrodes against the oxidizing action of V(IV)-HEDTA. Under optimized conditions, the method made it possible to detect nanomolar concentrations of germanium with favorable detection limits, high sensitivity, and a wide linear range of 5–90 nM of Ge(IV).

Selection of Optimal Ligand and Vanadium(IV) Complexonate for Sensitive Catalytic Adsorptive Stripping Voltammetric Quantification of Germanium

AbstractThe study describes the properties of catalytic adsorptive stripping voltammetric (CAdSV) systems based on complexes of Ge(IV) with gallic acid, catechol or pyrogallol as well as vanadium complexes with complexones such as NTA, DHPTA, EDTA, and HEDTA, used as catalytic agents. The most pronounced CAdSV response was observed when the Ge(IV)‐pyrogallol complex was coupled with V(IV)‐HEDTA. In 0.05 M of acetate buffer containing 1 mM of pyrogallol, 2 mM of V(IV) and 4 mM of HEDTA, the peak current of germanium exhibited good linearity for Ge(IV) concentrations over the range from 0.25 nM to 25 nM and a low limit of detection (LOD=0.02 nM). The method was verified by measuring Ge(IV) in real water samples.

A novel catalytic adsorptive stripping voltammetric method for the determination of germanium ultratraces in the presence of chloranilic acid and the V(IV)\xb7HEDTA complex

A novel, sensitive catalytic adsorptive stripping voltammetric procedure which can be used to determine trace amounts of germanium is described. The method is based on the interfacial accumulation of the complex formed by Ge(IV) and the product of the reduction of chloranilic acid on the hanging mercury drop electrode or the renewable silver amalgam film electrode, and its subsequent reduction from the adsorbed state followed by the catalytic action of the V(IV)·HEDTA complex. The presence of V(IV)·HEDTA greatly enhances the adsorptive stripping response of Ge. The reduction of the Ge(IV) in the presence of chloranilic acid and V(IV)·HEDTA was investigated in detail and the effects of pH, electrolyte composition, and instrumental parameters were studied. Under optimal conditions, the catalytic peak current of germanium exhibited good linearity for Ge(IV) concentrations in the range of 0.75–60 nM (for 60 s of accumulation at −0.1 V, r2 = 0.995) and a low limit of detection (LOD = 0.085 nM). The procedure was successfully applied to determine Ge in water samples.

Multianalyte voltammetric determination of traffic-linked metals in marine organisms employed as pollution bio-monitors

ABSTRACT A new procedure is proposed for the voltammetric determination of ultra-trace cadmium(II), copper(II), lead(II), platinum(II), palladium(II), rhodium(III) and zinc(II) by a single run of square wave adsorptive catalytic stripping voltammetry. The voltammetric cell was based on a typical three-electrodes set-up: working electrode (stationary hanging mercury drop), reference electrode (Ag|AgCl|KClsat) and auxiliary electrode (platinum). The supporting electrolyte contained the formazone complex together with dimethylglyoxime and the disodium salt of ethylenediaminetetraacetic acid. Validation of the analytical procedure was obtained by the analysis of standard reference materials (Mussel Tissue BCR-CRM 278, Oyster Tissue NIST-SRM 1566a). Comparison with spectroscopic measurements was performed. Good accuracy was achieved. The analytical procedure was finally applied to mussels and clams sampled on the mouth of Po river, employed as bio-monitors.

Extremely sensitive germanium stripping voltammetric determination with the use of a new Ge(IV)-catechol-V(IV)-HEDTA catalytic adsorptive system

It was found that the addition of V(IV)-EDTA or V(IV)-HEDTA to a solution containing the Ge(IV)-catechol complex induced certain catalytic processes that significantly enhanced the adsorptive stripping voltammetric (AdSV) response of germanium. The catalytic enhancement achieved with V(IV)-HEDTA was determined to be 7.4 times higher than that in the presence of V(IV)-EDTA; the former oxidant was therefore selected for the development of a new, sensitive catalytic adsorptive stripping voltammetric (CAdSV) procedure of germanium quantification. The optimal CAdSV Ge(IV) response was obtained in a 0.05 M acetate buffer with a pH of 4.4, in the presence of 1.0⋅10−3 M of catechol, 1.0⋅10−3 M of V(IV) and 1.5⋅10−3 M of HEDTA. The sensitivity of the new method was 25.2 nA/nM and the catalytic response was linear within the range of 5·10−11 M to 2·10−8 M Ge(IV) for 80 s of accumulation. The limit of detection was found to be 1.0·10−11 M. The reproducibility was equal to 3.0%. Interferences from inorganic ions and surface-active substances were evaluated. The procedure was applied to determine Ge(IV) in mineral water. It was also shown that both the hanging mercury drop electrode and the non-toxic renewable silver amalgam film electrode can be applied for Ge(IV) quantification by means of the elaborated method, with similar performance.

Theory of square-wave catalytic adsorptive stripping voltammetry. How to obtain mechanistic information from experimental data

The sensitivity of a catalytic adsorptive stripping voltammetric method depends mainly on the strength of adsorption of the electroactive reactant and the efficiency of the catalytic reaction. While the strength of adsorption is associated with the type of reagent and the solution pH, the efficiency of the catalytic step depends on the type and concentration of the oxidant selected for such reaction. Although the probe-and-error approach is commonly used for optimizing a given analytical signal, information about the reaction scheme and some good estimation about the rate constants of involved reactions would help a lot to optimize the analytical system.The possibility for using the quasi-reversible maximum to study the electrode kinetics depends on the values of kcat, Kad, f, Esw, and of course ks. As a result of this, it is rather difficult for experimentalist and also for theoreticians to organize a strategy for detecting and understanding the effect of each variable separately. In this manuscript, it is first shown the effect of different variables on the voltammetric response, and then it is suggested a strategy for studying and estimating the values of those variables. Thus, if the experimental system matches the reaction scheme of an electrochemical reaction complicated by following homogeneous catalytic reaction, then it is advisable to follow a set of simple experimental steps to characterize the kinetic constants of the system.

PVD fabrication of lead film electrodes and their catalytic adsorptive stripping voltammetric performance in the presence of oxidants

For the first time, lead film electrodes resistant to the action of oxidants commonly used to enhance the catalytic electrochemical response were deposited physically from a gaseous phase on thick film gold substrates and applied in catalytic adsorptive stripping voltammetry (CAdSV). The newly developed multilayer electrodes comprising a glass slide, an adhesive layer of titanium, a gold layer and finally, the working layer of lead were characterized by excellent CAdSV performance. Their sensitivity and reproducibility improved further after thermal pretreatment. The proposed sensor was sensitive (LOD = 0.002 μg L−1; tacc = 30 s) and the cobalt response was very reproducible (2.3%) and depended linearly on cobalt concentrations within the range of 0.06–1.05 μg L−1.

Ultrasensitive hexavalent chromium determination at bismuth film electrode prepared with mediator

A bismuth film electrode prepared in situ with a reversibly deposited mediator (Zn) applied for ultrasensitive determination of Cr(VI) using differential pulse catalytic adsorptive stripping voltammetry is presented. The optimization of experimental conditions such as composition of the supporting electrolyte, potential and time of bismuth film formation as well as analyte accumulation, and DP mode parameters is reported. For 180 s accumulation time, very low limits of detection and quantification of Cr(VI) were obtained, with 5.8 × 10–14 and 1.9 × 10–13 mol L−1, respectively. The relative standard deviation for 5.0 × 10–13 mol L−1 of Cr(VI) was 3.9% (n = 5). Finally, the proposed procedure was applied to determine Cr(VI) in the certified reference materials – NASS-6 (seawater), SLEW-3 (estuarine water) and TMRAIN-04 (rainwater) – as well as in river water samples. Furthermore, the obtained results show that the proposed voltammetric procedure employing the bismuth film electrode prepared with mediator appears to form a very promising tool for the speciation of chromium at ultratrace level.

Fast and highly sensitive method for molybdenum(VI) determination by catalytic adsorptive stripping voltammetry

Abstract The determination of Mo(VI) in water samples by electroanalytical techniques has been studied previously. Special attention has been paid to catalytic adsorptive stripping voltammetry (cAdSV) due to the high sensitivity and low detection limits achieved with this technique. In this work, a fast and sensitive method was optimized and developed for Mo(VI) determination by cAdSV. The method is based on the accumulation of the Mo(VI) complex with 5–chloro–7–iodo–8–hydroxyquinoline (Clioquinol, CQ) and its reduction on the electrode surface in the presence of KBrO3. An increase of the intensity of the reduction signal of the complex in the presence of potassium bromate was observed (catalytic effect). The effects of different experimental conditions on the signal response were studied. These were optimized to obtain the highest sensitivity. The optimal conditions were pH: 4.4 (acetate buffer), potassium bromate concentration (CKBrO3): 1.8 × 10−2 mol L−1, CQ concentration (CCQ): 1.5 × 10−5 mol L−1, accumulation potential (Eacc): −0.10 V and accumulation time (tacc): 10 s. Under the optimal conditions, the repeatability was 5.4% (RSD) for 20 successive assays with a 200 ng L−1 solution of Mo(VI). The detection limit (DL) was 3.1 ng L−1, the quantification limit (QL) was 10.3 ng L−1 and linearity was maintained up to 580.0 ng L−1. Studies of the interference were made for 29 foreign metal ions in the presence of 1,2−cyclohexylenedinitrilo tetraacetic acid (CDTA) and fluoride ion as masking agents. The accuracy of the methodology was evaluated using three different water certified reference materials with different Mo(VI) concentrations and matrix compositions. The method was applied to the determination of Mo(VI) in tap water, river water from a mining zone in the north of Chile and purified bottled water with satisfactory results.

Determination and validation method of molybdenum by adsorptive catalytic stripping voltammetry at lead film electrode

Determination and validation method of molybdenum by adsorptive catalytic stripping voltammetry at lead film electrode

Ultrasensitive catalytic-adsorptive stripping voltammetric determination of molybdenum using a Mo(VI)-chloranilic acid-chlorate system

A catalytic adsorptive stripping voltammetric procedure of the determination of ultratrace amounts of molybdenum using a novel catalytic system, Mo(VI)-chloranilic acid-chlorate was elaborated. In a supporting electrolyte containing 0.01M HCl (pH 2), 2.5×10−4M chloranilic acid and 0.4M KClO3, the catalytic adsorptive stripping response observed at −0.23V was proportional to the Mo(VI) concentration within the range of 0.16μgl−1 to 60μgl−1 for 60s of accumulation. The limit of detection was found to be 1.6×10−10M. The reproducibility of the blank signal was equal to 4.8%. The method was validated by quantifying Mo(VI) in certified reference surface water, and it was applied for the determination of Mo(VI) in extracts of fly ashes. The possible scheme of the catalytic reaction was suggested.

Highly sensitive determination of vanadium (V) by catalytic adsorptive stripping voltammetry. Substituent effect on sensitivity III

Catalytic adsorptive stripping voltammetry has been a powerful technique for trace metal determination. We now report one of the most sensitive voltammetric methods developed for vanadium. The determination is based on the complexation of vanadium with quercetin-5-sulfonic acid (QSA), adsorption of V(V)-QSA and reduction to V(III)-QSA onto HMDE; and finally in the scan step electrochemical reduction of V(III)-QSA to V(II) at about −0.78V applying differential pulse catalytic adsorptive stripping voltammetry. With the aim of comparing the effect of the sulfonic group on the sensitivity of the determination, two methods were developed using quercetin (Q) and Quercetin-5-sulfonic acid (QSA) as complexing and adsorbing ligands. The effects of various operational parameters such as pH, ligand, and potassium bromate concentration (CQ, CQSA, CKBrO3), potential, and adsorption time (Eads, tads) were optimized. The best results were obtained with QSA, and the optimal experimental parameters were pH: 7.0; CQSA: 0.6×10−6molL−1, CKBrO3: 3.5×10−2molL−1, Eads: 0.0V, and tads: 30s. Under the best experimental conditions the RSD for a V(V) solution (0.1μgL−1) was 3.4% for ten successive assays. Linearity was maintained up to 0.35μgL−1 and the detection limit was 0.23ngL−1 (tads: 30s; CQSA: 0.6×10−6molL−1). The method was validated using certified reference water (TMDA – 61.2) and finally, the method was applied to the determination of vanadium in tap water, purified drinking water, river water, and commercial water for chromatography.

Determination of cobalt by adsorptive stripping voltammetry with double accumulation and stripping steps

A double accumulation and stripping steps were proposed to increase the sensitivity of Co(II) determination by catalytic adsorptive stripping voltammetry (AdSV). Electrodes with large and small surface area were used for the first and second accumulation step, respectively. As the accumulation of Co(II) complex at the first electrode was finished, the electrode was placed at a short distance opposite the second one. Then the Co(II) complex desorbed from the first electrode was accumulated at the second electrode. Taking into account the small volume of space between the electrodes, the concentration of the Co(II) complex in solution between the electrodes was drastically higher than that in the bulk solution. The accumulation step at the second electrode was performed from the solution with higher concentration of Co(II) and therefore the detection limit was lowered. The calibration graph of Co(II) determination for accumulation time of 120 s at both electrodes was linear from 1.18 to 58.9 ng L−1. The detection limit for Co(II) was equal to 0.47 ng L−1 and it is so far the lowest detection limit obtained for Co(II) using mercury-free electrodes. The proposed method was applied to Co(II) determination in water certified reference material.

Vanadium and molybdenum concentrations in particulate from Palermo (Italy): analytical methods using voltammetry

The main purpose of this work was to develop a reliable method for the determination of vanadium (V) and molybdenum (Mo) in atmosphere particles or aerosols because they can not be readily measured using conventional techniques. For this research, 30 particulate samples were collected from five different stations located at Palermo, Italy. We used the catalytic adsorptive stripping voltammetry and differential pulsed voltammetry to measure Vand Mo in atmospheric particulate, respectively. The represented method includes advantages of high sensitivity, high selectivity, simplicity, reproducibility, speed and low costs. The quantification limits for V and Mo are, respectively, 0.57 and 0.80 ng·m−3. The precision, expressed as relative standard deviation (RSD %), was about 2% for both metals. The mean recoveries of added V and Mo were about 99.5% and ranged from 97% to 101%. Vanadium concentrations in particulate samples collected in Palermo area ranged from 0.57 to 7.7 ng·m−3, while Mo concentrations were in the range 0.8–51 ng·m−3. In many cases the concentrations of two elements in the particulate samples fall below the detection limits. The mean concentrations for V and Mo in particulate samples, collected in Palermo area, were respectively 3.1 and 5.9 ng·m−3.

Improving the Voltammetric Quantification of Ill-Defined Peaks Using Second Derivative Signal Transformation: Example of the Determination of Platinum in Water and Sediments

The determination of trace elements using stripping voltammetry may be seriously affected by the presence of intensive matrix background or interfering peaks, leading to poorer detection limits and/or inaccurate quantitative results. In this work, we have tested the use of signal transformation (e.g., second derivative) in the analysis of platinum in seawater and sediment digests by means of catalytic adsorptive stripping voltammetry. In natural waters, the limit of detection of Pt is affected by a broad background wave due to the formazone complex used in the sample matrix for its determination, while in sediment digests, the Pt peak may be interfered with due to the presence of elevated concentrations of Zn, affecting the accuracy of the determination. Results applying second derivative signal transformation revealed a significant improvement (2-3-fold) of the detection limit in water due to the minimization of background effects, therefore allowing shorter accumulation times and faster determinations. In the presence of interfering peaks, the inaccuracy resulting from erroneous baseline selection in the original signal is eliminated when the second derivative is used. Signal processing should be considered as a useful tool for other voltammetric methodologies where more accurate or faster determinations are needed.

Catalytic Adsorptive Stripping Chronopotentiometry of Co(II)‐DMG‐Bromate System at an In Situ Plated Lead Film Electrode

AbstractA novel catalytic adsorptive stripping chronopotentiometric (CC‐CAdSCP) procedure for the determination of Co(II) traces was developed using a lead film electrode (PbFE). The PbFE was generated in situ on a glassy carbon support from a 0.1 M ammonia buffer containing 1×10−5 M Pb(II), 6.5×10−5 M DMG and the target metals. An addition of 0.2 M NaBrO3 to the solution yielded an 11‐fold catalytic enhancement of chronopotentiometric response of the Co(II)‐DMG complex. The CC‐CAdSCP curves were well‐developed, sharp and reproducible (RSD 5.0 % for 5×10−9 M Co(II)). The limit of detection for Co(II) for 210 s of accumulation time was 4×10−10 M (0.024 µg L−1). In addition, the elaborated method allowed the simultaneous quantification of Co(II) and Ni(II) simultaneously.

Catalytic adsorptive stripping voltammetry of Co(II)-dioxime-bromate systems at renewable amalgam film electrode

The properties, sensitivity and selectivity of several catalytic adsorptive systems consisting of Co(II)-dioximate complexes (dimethylglyoxime (DMG), nioxime) and the oxidation agents (bromate or nitrite) were compared in conditions of adsorptive stripping voltammetry at the hanging mercury drop or amalgam film (Hg(Ag)FE) electrodes. For this purpose the catalytic behaviour of the catalytic systems Co(II)-nitrite and Co(II)-bromate in the absence of dioximes was also investigated. It was demonstrated that the Co(II)-(NH3)x complex induces the catalytic reduction of BrO3− ions in the ammonia buffer solution. The electrode mechanism of the reduction of the most sensitive system, i.e. Co(II)-DMG-BrO3−, was elucidated by means of cyclic voltammetry and using criteria established for square wave voltammetry. It was assumed that in the Co(II)-DMG-BrO3− system the intermediate product–the composite complex of Co(II) with DMG and BrO3− – takes part in the cyclic catalytic reduction of BrO3− ions. Combining adsorptive stripping accumulation with the catalytic enhancement of the analytical signal of Co(II)-DMG by BrO3− ensures extremely high sensitivity of Co determination.After 60s of accumulation at −0.7V in the supporting electrolyte containing 6.5×10−5M DMG, 0.2M BrO3− and 0.1M ammonia buffer, cobalt may be determined in the concentration range of 5×10−10–1×10−7M Co(II) by means of SW-CAdSV at the Hg(Ag)FE. The limit of detection was 1×10−10M Co. The proposed method of cobalt determination was successfully applied and validated by studying the certified reference material TMRAIN-95 (water sample). The elaborated method ensures very sensitive determination of Co(II) as well as simultaneous estimation of Co(II) and Ni(II) in the presence of a 4000-fold excess of Zn(II).

Behavior of platinum during estuarine mixing (Pontevedra Ria, NW Iberian Peninsula)

The concentrations of Pt in sediments, water and suspended particulate matter (SPM) were determined in the Lérez River estuary (Pontevedra Ria, NW Iberian Peninsula) on two sampling dates in 2008 and 2011, by means of catalytic adsorptive stripping voltammetry. Average concentrations in sediments (1.2±0.5ngg−1; n=13) corresponded to an enrichment factor of 2–4 compared to background values, and were in the range of those found in the SPM during the 2011 sampling (2.1±2.4ngg−1; n=15), but significantly lower than those in 2008 SPM (8.0±4.4ngg−1; n=15). Higher dissolved Pt concentrations were also found in 2008 (0.21 and 0.62pM in the freshwater and seawater end-member) compared to the 2011 campaign (0.03 — freshwater and 0.40pM — seawater end-member). Concentrations in the seawater end-members exceed those of typical North Atlantic waters, suggesting inputs of this element within the estuary. The extremely low value for the freshwater end-member in 2011 appears to be among the lowest Pt concentrations ever reported in the literature. Non-conservative behavior of Pt during estuarine mixing was observed on both sampling dates. Particle–water distribution coefficients (KD) show a decrease with salinity, in agreement with speciation calculations, which predict a transfer from neutral Pt(II) (as Pt(OH)2) in freshwater to negatively charged Pt(IV) (as PtCl5(OH)2−) species in seawater. Such behavior during estuarine mixing can play an important role in Pt mobilization from contaminated particles discharged into estuaries and coasts.

Determination of zineb in tap water and tomato samples by adsorptive catalytic stripping voltammetry

This paper describes a sensitive and accurate adsorptive catalytic stripping voltammetric method for the determination of zineb (zinc ethylene-bis- dithiocarbamate) in tap water and tomato samples. The method is based on the reduction of adsorbed zineb at a hanging mercury drop electrode following its catalytic oxidation using peroxydisulfate as an oxidizing reagent. Chemical and instrumental parameters of the process were optimized. The catalytic mechanism of the reduction of zineb is discussed as well. The limits of detection (3 s) and quantification (10 s) and linear range of the method for accumulation time of 60 s were calculated as 8.1 nM, 28 nM, and 0.028--7.00 \mu M, respectively. The relative standard deviation of the method was 3.68% for 2.5 \mu M zineb (N = 5). The proposed method was applied successfully for the determination of zineb in tap water and tomato samples.