Cathodic Stripping Square Research Articles

Electrochemical Determination of Paraquat Using Gold Nanoparticle Incorporated Multiwalled Carbon Nanotubes

The present work focuses on electrochemical estimation of the herbicide, paraquat using Au nanoparticle incorporated multi-walled carbon nanotubes (AuNP-MWCNT). The catalyst was synthesized and characterized using physical characterization techniques like HRSEM, HRTEM, Raman spectroscopy, and XRD. The techniques reveal the successful incorporation of Au nanoparticles onto MWCNT and it was utilized for the electrochemical determination of paraquat (PQ). The AuNP-MWCNT modified glassy carbon electrode (AuNP-MWCNT/GCE) was able to detect PQ reversibly using cyclic voltammetric analysis. From the electrochemical tests, it was discovered that the electrode is an efficient catalyst for the effective electrochemical sensing of PQ. Using the cathodic stripping square wave voltammetric technique (CSSWV), the sensitivity and limit of detection of the matrix against PQ were evaluated. They were found to be 0.197 mA μM−1 and 32 nM, respectively. The electrode is able to produce the linear variation in sensitivity in the concentration range of 1.0 μM to 2.0 μM with a regression coefficient value of 0.99. Further, selectivity studies clearly demonstrated that the proposed catalyst was interference-free from other possible foreign molecules. The practical applicability of the electrode was checked in the electrolyte containing real samples and the appreciable recovery was achieved.

Near-electrode pH change for voltammetric detection of insoluble lead carbonate

Lead contamination of drinking water is a concern to all inhabitants of old cities where lead pipes and soldering are still present. Simple on-site electrochemical detection methods are promising technologies that have gained attention recently. However, conventional electrochemical techniques only quantify soluble forms of lead in water without accounting for insoluble particulates. Herein, a simple voltammetric technique for quantification of insoluble lead species is reported. Lead carbonate (PbCO3) was used as a model compound to show the possibility of detecting particulate lead species directly in solution without chemical treatment. Specifically, electrochemical generation of protons was used as an alternative method to dissolve PbCO3 and thus obtain a more realistic assessment of lead contamination. Lead was detected using cathodic stripping square wave voltammetry (CSSWV). After applying a high oxidizing potential to the electrode immersed in a PbCO3 solution with solid PbCO3 particulates, a significant increase in current was observed as compared to that of a saturated PbCO3 solution. The signal was proportional to the amount of added PbCO3, even when the solubility limit was exceeded. Thus, the combination of a local pH change with CSSWV provides a simple, rapid, and reagentless method for an in-situ detection of insoluble lead species.

Signal amplification by electro-oligomerisation for improved isoproturon detection

A novel concept is introduced for signal amplification in electrochemical sensing: the electro-oligomerisation stripping voltammetry, which has been applied here to the improved detection of the isoproturon herbicide in spring waters as a proof-of-principle. It involves a potentiostatic accumulation step onto a glassy carbon electrode (at +1.5 V vs Ag/AgCl reference electrode for 300 s) leading to the formation of an oligomeric film, which is then detected by cathodic stripping square wave voltammetry (SWV). The presence and composition of the film are confirmed by confocal Raman spectroscopy. Its characterisation by cyclic voltammetry demonstrates the reversible nature of the electrodeposited material, confirming its interest for sensitive detection by SWV. Adding a mesoporous silica membrane with vertically oriented nanochannels further enhances the sensitivity of the sensor, exhibiting a linear response in the 10–100 μM concentration range. This effect was even more interesting for real media analysis thanks to the permselective properties of such nanoporous coating in rejecting interferences and/or surface fouling agents. The method should be applicable to other analytes that are usually not detectable by conventional accumulation/stripping voltammetry.

Multivariate cathodic square wave stripping voltammetry optimization for nitro group compounds determination using antimony film electrodes

The main goal of this paper is the optimization of the square wave voltammetric response of antimony film electrode (SbFE) to determine reducible nitro groups using response surface methodology (RSM). The SbFE was prepared on a glassy carbon electrode (GCE) while cathodic stripping square wave voltammetry (CSSWV) was used as detection technique. In this study, the optimization process of solution pH and 4,6-dinitro-o-cresol (DNOC) accumulation time was carried out using a Central Composite Design (CCD) while a Box–Behnken Design for SWV instrumental variables optimization. The two reduction current peaks were used as dependent variable to evaluate the performance of the system. For solution pH and DNOC accumulation time the optimization process considered only reduction current peak, while for SWV instrumental parameters (step, amplitude and frequency) both the relationship between current peak and standard deviation with the different factors were analysed, finally both designs were quantitatively described by a multivariate regression model through the RSM. Furthermore, the optimal parameter combinations were obtained by maximizing the reduction current peak and minimizing standard deviation within the studied experimental range. Under the optimal parameter combination, a linear calibration curve ranged from (1.0 to 15)×10−6molL−1 with a detection limit of 1.12×10−6molL−1 was obtained. The proposed analytical procedure was further applied to detect DNOC in natural water samples with satisfactory results.

Electrochemical behavior and assay of anti-Parkinson drug selegiline using cathodic adsorptive stripping square wave voltammetry in bulk form

Electrochemical behavior and assay of anti-Parkinson drug selegiline using cathodic adsorptive stripping square wave voltammetry in bulk form Priyanka Sinha, Anjuman Shekhawat, Digish K Sharma Electrochemical Research Laboratory, Department of Chemistry, University of Rajasthan, Jaipur, India Abstract: The electrochemical reduction behavior of selegiline was investigated by cyclic voltammetry using glassy carbon electrode and validated by square wave cathodic adsorptive stripping voltammetry. Selegiline gave one well-defined reduction peak in the potential range −0.4 to −0.5 V versus Ag/AgCl electrode. The reduction process is irreversible and partial diffusion controlled. Various chemical and instrumental parameters affecting the electroanalytical response for the determination of selegiline were investigated and optimized. Under optimized conditions, the adsorptive stripping peak current is found to be linear over the concentration range of 3.0×10–7–2.5×10–5 M with a detection limit of 3.04×10–8 M and a lower limit of quantification of 1.01×10–7 M. Keywords: selegiline, anti-Parkinson drug, glassy carbon electrode, square wave cathodic adsorptive stripping voltammetry, diffusion controlled

Pyrolyzed Photoresist Carbon Electrodes for Trace Electroanalysis of Nickel(II)

Novel pyrolyzed photoresist carbon electrodes for electroanalytical applications have been produced by photolithographic technology followed by pyrolysis of the photoresist. A study of the determination of Ni(II) dimethylglyoximate (Ni-DMG) through adsorptive cathodic stripping voltammetry at an in situ bismuth-modified pyrolyzed photoresist electrode (Bi-PPCE) is reported. The experimental conditions for the deposition of a bismuth film on the PPCE were optimized. The Bi-PPCE allowed the analysis of trace concentrations of Ni(II), even in the presence of Co(II), which is the main interference in this analysis, with cathodic stripping square wave voltammograms characterized by well-separated stripping peaks. The calculated limits of detection (LOD) were 20 ng∙L−1 for Ni(II) alone and 500 ng∙L−1 in the presence of Co(II). The optimized method was finally applied to the analysis of certified spring water (NIST1640a).

The Summer Distribution of Dissolved Inorganic Iodine along 18N in the South China Sea

Dissolved inorganic iodine (iodate and iodide) in seawater samples collected in the northern South China Sea (SCS) were investigated using differential pulse polarography and cathodic stripping square wave voltammetry, respectively. High concentration of iodide was observed in the surface layer in agreement with those previously reported for tropical waters. Iodine speciation and macro-nutrients were strongly coupled as observed in other tropical oceans. The vertical distributions of iodine and macro-nutrients can be classified into three biogeochemical regimes: (1) in the upper 50 m of the water column, low iodate was observed as nutrients were depleted and photosynthesis was low in summer. In contrast, substantial amount of iodide produced by high phytoplankton productivity and intense bacterial action in winter and spring was saved till summer; (2) in the water column between 50 m and the Tropical Water at around 150 m, the amount of iodide oxidation varied proportionally with nitrification, leading to rapid increase of nitrate and iodate with depth; (3) below the Tropical Water, iodate and nitrate are regenerated mainly due to re-mineralization of organic matter sinking from the euphotic zone. The distribution of dissolved inorganic iodine and hydrographic parameters (salinity, temperature, dissolved oxygen, and macro-nutrients) were influenced by the downwelling of the mesoscale warm eddy.

Cathodic stripping voltammetry of clothianidin: Application to environmental studies

A new, rapid and very sensitive electrochemical method for the determination of a new pesticide clothianidin in tap and river water was developed. The electrochemical reduction and determination of clothianidin have been carried out at a hanging mercury drop electrode (HMDE) in various aqueous solutions in the pH range of 2–10 by cyclic voltammetry (CV) and cathodic stripping square wave voltammetry (SW CSV). The best results were obtained for the clothianidin determination by SW CSV method in 0.04 mol l–1 Britton Robinson buffer at pH 8.1. Various conditions of the procedure were checked. Elaborated electroanalytical procedure enable clothianidin determination in the concentration range of 2.0 × 10–8–9.9 × 10–7 mol l–1. The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 2.00 × 10–9 and 2.36 × 10–8 mol l–1, respectively. Precision and accuracy of the developed method were checked by recovery studies in spiked tap and river water. The voltammetric determination has been validated using HPLC with UV detection.

Intensive sampling of iodine and nutrient speciation in naturally eutrophicated anchialine pond (Rogoznica Lake) during spring and summer seasons

A study of inorganic iodine speciation in the water column of a naturally eutrophicated anchialine pond (Rogoznica Lake, East Adriatic Coast) was conducted in a period between April and July 2004 to obtain information how close the inorganic iodine system is to that of inorganic nutrients during spring, when phytoplankton activity is at maximum, and how the system changes up to summer, when highly reducible redox-conditions prevail in deep water. Iodate and iodide concentrations were determined by differential pulse voltammetry and cathodic stripping square wave voltammetry, respectively. In addition, total iodine concentrations were determined by ICP-MS in May. The hydrographic and nutrient profiles indicate that the system was greatly affected by photosynthesis and demonstrate strong seasonal change in predominant phytoplankton assemblages. The hypolimnion depths were dominated by regeneration processes and benthic influence, with anoxic and sulphidic conditions at maximum sampling depth in July. The iodine profiles show no clear direct relationship between the iodine and nutrient system regarding to the phytoplankton production. Meanwhile, the results demonstrate temporal matching between high iodate and high regenerated nitrate concentrations in the surface layers, and close spatial matching of iodate production and nitrification at mid-depths of hypolimnion. The key role of nitrifers is discussed and the implication of these findings is explored.

Avaliação da influência de sulfetos solúveis na complexação do cobre em águas superficiais empregando métodos voltamétricos

In this work a sulfide quantification protocol using voltammetric methods was developed to evaluate the effect of dissolved sulfides on copper complexation. On the basis of pH, sulfide release from the dissociation of specific metal sulfide complexes can be electrochemically measured and then removed (as H2S) by a N2 purge. Cathodic stripping square wave voltammetry (CSSWV) was conducted to quantify Cu sulfides complexes which dissociate at pH < 5.0 during the process of acid titration.

The distribution of iodide and iodate in anchialine cave waters — Evidence for sustained localised oxidation of iodide to iodate in marine water

A study of inorganic iodine speciation in the waters of seven Croatian coastal caves is described. These are anchialine caves as they are connected hydraulically with Adriatic Sea surface water, with the tide inside the cave rising and falling with that outside, but replenishment of the water is restricted by the karst rock. In effect, the water in the cave probably acts more like a piston, and although moving slightly vertically, has a long residence time compared to a fully-flushing cave. Anchialine environments display a number of unusual features, e.g., a well-developed pycnocline, hypoxia and endemic fauna. Iodate and iodide were determined by differential pulse voltammetry and cathodic stripping square wave voltammetry, respectively. Low iodide concentrations (< 10 nM) have been consistently identified in the bottom water of the caves where concentrations of 90–100 nM would ordinarily be expected from intrusion of Eastern Adriatic surface seawater. Where total inorganic iodine concentrations behave conservatively with salinity the loss of the iodide implies oxidation to iodate. As iodide oxidation remains one of the enduring academic problems of the marine iodine system the study of iodine in anchialine caves may help unravel it. Iodate reduction was observed in mid-water, at the halocline, and mechanisms for the reduction involving either respiration or chemolitho-autotrophic bacteria are considered. The respiration mechanism is favoured because of enhanced alkalinity found in the near surface waters of the caves.

Electrochemical study of taxol (paclitaxel) by cathodic stripping voltammetry: determination in human urine

An analytical method for the determination of taxol (paclitaxel) via cathodic stripping square wave voltammetry has been developed. The method allows to achieve a detection limit of 5.2 ng ml −1 and a determination limit of 11.0 ng ml −1 working with a mercury drop electrode in 0.05 M boric acid/borate buffer pH 9.0, previously accumulated at −0.1 V (v.s. Ag/AgCl/KCl 3 M) for 360 s. Moreover, information about the mechanisms governing the reduction of taxol has been obtained from the studies of the instrumental parameters of square wave voltammetry technique. After addition of an internal standard, taxol was extracted from spiked human urine and the proposed method was successfully applied to the quantification of the analyte.

Geochemical factors controlling free Cu ion concentrations in river water

Copper speciation was determined monthly at seven sites on four rivers in southern New England to understand which geochemical factors control free metal ion concentrations in river water. Samples were conventionally filtered (<0.45 μm) and then ultrafiltered (3.000 molecular weight cut-off) to determine Cu speciation in the truly dissolved size fraction. Differential pulse anodic stripping voltammetry (DPASV) was used to quantify natural organic complexation and cathodic stripping square wave voltammetry (CSSWV) to measure directly both Cu sulfide complexes and total EDTA concentrations. The results showed both dissolved organic matter (DOM) and sulfide complexation dominate Cu speciation and control the concentrations of free ion. Free Cu2+ was calculated to be in the subnanomolar range for the majority of the year. Only in the winter months, when concentrations of DOM and metal sulfides complexes were at a minimum were free metal ions directly measurable by DPASV at low nanomolar concentrations. The extent of sulfide complexation appears to be dominated by the size of headwater marshes (upstream sampling sites) and by the amount of sewage treatment plant effluent (downstream sites). DOM complexation was related to the organic matter composition and followed model organic ligands. Indirect evidence suggests variations in river water pH and Ca2+ (metal competition) has only a minor role in Cu complexation. Measured concentrations of total EDTA suggest this synthetic ligand can control Cu speciation in some highly developed watersheds; however, competition from Ni (and possibly Fe) limits the extent of this complexation.

Determination of abscisic acid by cathodic stripping square wave voltammetry

In this paper a study is accomplished on behavior in a mercury electrode, of the phytohormone abscisic acid and of the conditions of accumulation in a HMDE. A mechanism is proposed of reduction based on its electrochemical behavior and proving the product of the reduction through mass spectrometry of bulks. A method is proposed for the determination of Abscisic acid (ABA) with a quantification limit of 58 ng ml −1. The procedure is applied wing determination of ABA in pears through the combination of high performance liquid chromatography (HPLC) with electrochemical quantification.

Nickel quantification in mice organs by adsorptive cathodic stripping voltammetry using mercury microelectrodes

AbstractMercury film microelectrodes (MFMs) were used to quantify trace levels of nickel accumulated in mice organs samples after dosing the mice with a physiological solution containing 150 ppm of Ni ions over a period of time, by performing adsorptive cathodic stripping square wave voltammetry (AdSWV). The residues obtained after digestion of the biological organs with nitric acid which affects the electrochemical response of Ni were investigated by XRD and IR spectrometry and found to be mainly composed by p‐nitrobenzoic acid. Electrochemical conditions for the quantification of Niwith MFMs in the biological solutions were optimized. The electrochemical data compared favorably with that obtained by atomic absorption spectrometry.

On the existence of free and metal complexed sulfide in the Arabian Sea and its oxygen minimum zone

Free hydrogen sulfide was not detected in the oxygen minimum zone (OMZ) of the Arabian Sea during legs D1 (September 1992) and D3 (October–November 1992) of the Netherlands Indian Ocean Programme (NIOP). However, sulfide complexed to metals was detected by cathodic stripping square wave voltammetry at 2 nM or less throughout the water column. A slight increase in sulfide was measured in the OMZ relative to the surface waters and may be related to sulfur release from organic matter during decomposition. Sulfide complexes are of two general types at low concentrations of metal and sulfide. First, metals such as Mn, Fe, Co and Ni form complexes with bisulfide ion (HS −) that are kinetically labile to dissociation and are reactive. Second, metals such as Cu and Zn form multinuclear complexes with sulfide (S 2−) that are kinetically inert to dissociation; thus, they are less reactive than free (bi)sulfide and the labile metal bisulfide complexes. Zinc and copper sulfide complexes are important in allowing hydrogen sulfide to persist in seawater which contains measurable oxygen.

Use of 4-chloro-7-nitrobenzofurazane as a derivative reagent for the determination of amino acids by cathodic stripping square wave voltammetry in biological fluids

The rapid and simple reaction of 4-chloro-7-nitrobenzofurazane with amino acids allows the determination of amino acids in urine using cathodic stripping square wave voltammetry. The obtained compounds are adsorbed on a hanging mercury drop electrode for determination by voltammetric methods using phosphate buffer at pH 2.0 as supporting electrolyte. The proposed method allows determination with an error of ⩽ 5.68%. A limit of detection (3 σ) of 3.64 nM (0.766 ng ml −1) and a limit of determination (10 σ) of 12.12 nM (2.55 ng ml −1) are obtained for arginine determination. The proposed method has been applied to the determination of amino acids in urine.

Iodine speciation: a potential indicator to evaluate new production versus regenerated production

Vertical profiles of iodide, iodate and total free iodine were determined monthly for one year (from July 1993 to June 1994) at the DYFAMED permanent station located in the northwestern Mediterranean Sea. Dissolved iodate and iodide were directly determined by differential pulse polarography and cathodic stripping square wave voltammetry, respectively. Iodate is the predominant species, ranging from 390 nM in surface waters to 485 nM in deep waters. Iodide is present in significant concentrations up to 80 nM in surface waters and from undetectable levels to several nanomolar (< 10 nM) in deep waters. Concentrations of total free iodine are slightly lower in surface waters (467–478 nM with an average of 472 nM) than in deep waters (475–486 nM with an average of 481 nM). Considerable variations in iodine speciation were observed. Iodide concentrations in surface waters were relatively low and stable from February to April (about 20 nM), increased up to 80 nM from May until November, and then decreased from December to February. Comparison between iodide abundance and primary production demonstrates that the transformation from iodate to iodide in surface waters is linked to the regenerated production. The stability of regenerated iodide in surface seawater makes iodide a potential indicator to evaluate new production vs regenerated production.

Iodine speciation in the water column of the Rogoznica Lake (Eastern Adriatic Coast)

Specific concentration profiles of iodate, iodide and organo-iodine in the water column of the Rogoznica Lake, where both oxic and anoxic conditions occur, were observed. Iodate and iodide concentrations were determined directly in water samples by differential pulse voltammetry (DPV) and cathodic stripping square wave voltammetry (CSSWV), respectively. Concentrations of ‘labile’ and ‘stabile’ organo-iodine were determined by DPV in the samples pretreated with chlorine water and UV-irradiation (combined with hydrogen peroxide and followed by chlorine water addition), respectively. In this stratified water column (salinity and dissolved oxygen gradients) with pronounced biological productivity, high concentrations of iodide (up to 0.87 μM) and significant percentages of ‘labile’ and ‘stabile’ organo-iodine, up to 37% and 30% respectively, were found. The formation of ‘labile’ organo-iodine is primarily governed by chemical reactions with dissolved sulphur forms and organic compounds, as well as remineralization processes of ‘stabile’ organo-iodine.

Iodine speciation in the northwestern Mediterranean Sea, method and vertical profile

Abstract Iodine speciation analysis was carried out upon seawater samples collected in July 1993 at the Dyfamed station (43 °25′N, 7 °52′E) located in the northwestern Mediterranean Sea. Dissolved iodate and iodide were directly determined by differential pulse polarography and cathodic stripping square wave voltammetry, respectively, and organically bound iodine was estimated by wet-chemical oxidation with sodium hypochlorite. Iodate is the predominant species ranging from 416 nM in surface waters to 480 nM in bottom waters. Iodide is present in significant concentrations up to 60 nM in surface waters, undetectable between 500 and 1000 m depth and present in very low but measurable concentrations (about 6 nM) in deep waters. The vertical profile of total free iodine demonstrates observable removal from surface waters, slight enrichment at about 200 m depth and constant there below. Up to 40 nM of organically bound iodine has been estimated between 20 to 30 m. Factorial analysis of different iodine species with biologically relevant parameters provided strong evidence for iodine biophilic features.