Catalytic Adsorptive Stripping Voltammetry 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).

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.

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

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 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 Cr(III), Cr(VI) and total chromium in atmospheric aerosol samples

This study addresses the optimization and validation of an analytical method based on the ultrasound-assisted extraction of soluble Cr from atmospheric particulate matter (PM) and subsequent determination of Cr(III) and Cr(VI) by catalytic adsorptive stripping voltammetry (CAdSV) by using diethylenetriammino pentaacetic acid (DTPA) as complexing agent in the presence of nitrate. We evaluated the influence of various filter materials and of extracting conditions and validated the method on both reference material and real PM10 samples. The accuracy of total extractable Cr determination was checked by parallel ICP-OES measurements. The determination of total chromium was performed by ED-XRF. Results of field campaigns carried out in two industrial areas (North Italy and Tunis) and at a peri-urban site near Rome are reported. At the peri-urban site, the total Cr concentration in PM10 ranged from 2 to 5 ng/m 3 , with a soluble fraction of 5-13%, and Cr(VI) concentration was always below the detection limits (50 pg/m 3 ). In the industrial area of Northern Italy, total Cr concentration ranged between 6 and 11 ng/m 3 , the soluble fraction was about 11-28% and detectable amounts of Cr(VI) were found, with a Cr(VI)/Cr(III) ratio ranging from 0.5 to 2.5. A further increase of Cr(VI) concentration was evidenced at the industrial site of Tunis, where the total Cr concentration ranged from 6 to 26 ng/m 3 , with a soluble fraction accounting for about 8-44% and a Cr(VI)/Cr(III) ranging from 1.6 to 3.6. The results of size-segregated samples, collected in Northen Italy by a 10-stage cascade impactor, indicate a relevant fine fraction of Cr(VI), with Cr(VI)/Cr(III) ratios increasing with the decrease of particle size.

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.

Determination of trace titanium(iv) by differential pulse catalytic adsorptive stripping voltammetry at a bismuth film electrode

The differential pulse catalytic adsorptive stripping voltammetry behavior of titanium(IV)–cupferron system at bismuth coated glassy carbon electrode (BiFE) has been investigated. In the piperazine-N,N′-bis(2-ethanesulfonic acid) (PIPES)–KCl solution (pH 6.4), the deposition potential at −0.70 V for 120 s, a well-defined and sensitive stripping peak of Ti(IV)–cupferron complex at −0.97 V (vs. SCE) was observed. Under optimized conditions, the peak current was linear to the concentration of Ti(IV) in the range from 10 to 60 μg L−1 with the detection limit of 0.5 μg L−1. To further demonstrate its possible application, the method was successfully applied to detect trace Ti(IV) in hair and water samples with satisfactory results.

Catalytic Adsorptive Stripping Voltammetric Determination of Chromium(VI) in Overlying and Interstitial Waters Isolated from Sediments Contaminated by Tannery Waste

In the present paper, catalytic adsorptive stripping voltammetry (CAdSV) has been applied for the first time in a chromium speciation study conducted in pore sediments and overlying waters containing Cr(VI) in the presence of a great excess of Cr(III) and organic matter. The method is based on the adsorptive accumulation of the active Cr(III)-DTPA (diethylenetriammine-N,N,N′,N″,N″-pentaacetic acid) complex, which is formed instantaneously on the electrode surface as a result of Cr(VI) reduction to Cr(III), its complexation with DTPA, reduction to Cr(II)-DTPA, and its catalytic oxidation to Cr(III)-DTPA with nitrate. The main efforts were focused on the elimination of the influence of dissolved organic matter including organic surface-active substances (SAS) that adsorb at the electrode surface, and disturb the Cr(VI) determination or, in extreme cases, make it impossible. Of the three procedures applied for the elimination of this negative effect caused, namely, the matrix-exchange method, the removal of SAS by means of fumed silica, and their adsorption on the XAD-7 Amberlite resin present directly in voltammetric vessel, the last one proved to be the most useful. The matrix-exchange procedure also provides accurate and precise results but requires more reagents and time. The CAdSV method combined with the adsorption of surface-active substances on the XAD-7 Amberlite resin was successfully applied for the determination of the Cr(VI) in vertical profile in sediments from Dunajec River, which are severely polluted with chromium from tannery wastes.

Ultra trace quantification of chromium(VI) in food and water samples by highly sensitive catalytic adsorptive stripping voltammetry with rubeanic acid

Abstract A simple and highly selective and sensitive catalytic adsorptive stripping voltammetric procedure for determination of ultra trace levels of chromium(VI) on hanging mercury drop electrode is reported. The method is based on the adsorptive preconcentration of the Cr(III)–dithiooxamide (rubeanic acid) complex and the utilization of the catalytic reaction in the presence of nitrate. At optimized conditions the calibration graph is linear from 0.01 to 6 ng/ml and detection limit is 0.002 ng/ml for accumulation time of 50 s. The interference of some common ions was studied and this method has been applied to the determination of chromium in food and waste water samples with satisfactory results.

Cr(VI)/Cr(III) and As(V)/As(III) Ratio Assessments in Jordanian Spent Oil Shale Produced by Aerobic Combustion and Anaerobic Pyrolysis

With the increase in the awareness of the public in the environmental impact of oil shale utilization, it is of interest to reveal the mobility of potentially toxic trace elements in spent oil shale. Therefore, the Cr and As oxidation state in a representative Jordanian oil shale sample from the El-Lajjoun area were investigated upon different lab-scale furnace treatments. The anaerobic pyrolysis was performed in a retort flushed by nitrogen gas at temperatures in between 600 and 800 °C (pyrolytic oil shale, POS). The aerobic combustion was simply performed in porcelain cups heated in a muffle furnace for 4 h at temperatures in between 700 and 1000 °C (burned oil shale, BOS). The high loss-on-ignition in the BOS samples of up to 370 g kg(-1) results from both calcium carbonate and organic carbon degradation. The LOI leads to enrichment in the Cr concentrations from 480 mg kg(-1) in the original oil shale up to 675 mg kg(-1) in the ≥ 850 °C BOS samples. Arsenic concentrations were not much elevated beyond that in the average shale standard (13 mg kg(-1)). Synchrotron-based X-ray absorption near-edge structure (XANES) analysis revealed that within the original oil shale the oxidation states of Cr and As were lower than after its aerobic combustion. Cr(VI) increased from 0% in the untreated or pyrolyzed oil shale up to 60% in the BOS ash combusted at 850 °C, while As(V) increased from 64% in the original oil shale up to 100% in the BOS ash at 700 °C. No Cr was released from original oil shale and POS products by the European compliance leaching test CEN/TC 292 EN 12457-1 (1:2 solid/water ratio, 24 h shaking), whereas leachates from BOS samples showed Cr release in the order of one mmol L(-1). The leachable Cr content is dominated by chromate as revealed by catalytic adsorptive stripping voltammetry (CAdSV) which could cause harmful contamination of surface and groundwater in the semiarid environment of Jordan.