Stripping Voltammetric Analysis Research Articles

Stripping voltammetric analysis of organophosphate pesticides using Ni/Al layered double hydroxides as solid-phase extraction

A sensitive electrochemical stripping voltammetric biosensor is designed for organophosphate pesticides (OPs) based on solid-phase extraction (SPE) using Ni/Al layered double hydroxides (LDHs) modified glassy carbon electrode (labeled as Ni/Al-LDHs/GCE). The Ni/Al-LDHs as the host are highly efficient to capture OPs, which dramatically facilitates the enrichment of nitroaromatic OPs onto their surface and realizes the stripping voltammetric detection of OPs. The stripping voltammetric performances of methyl parathion (MP) intercalated into LDHs were evaluated by cyclic voltammetric and square-wave voltammetric (SWV) analysis. The combination of the host–guest supramolecular structure, SPE, and stripping voltammetry provides a fast, simple, and sensitive electrochemical method for detecting nitroaromatic OPs by using MP as a model. The stripping analysis is linear over the MP concentration ranges of 0.001–0.1 and 0.2–1.0μgmL−1 with a detection limit of 0.6ngmL−1 (S/N=3). The developed biosensor exhibits good reproducibility and acceptable stability. This study offers a new promising protocol for OPs analysis.

The contents of sesamol and related lignans in sesame, tahina and halva as determined by a newly developed polarographic and stripping voltammetric analysis

The contents of antioxidant lignans (Sesamol) in sesame, commercial formulations of tahina and halva, which are processed tahina foods, were determined by Differential Pulse Polarography (DPP) with a capillary hanging mercury drop electrode (HMDE). A platinum wire was used as the counter electrode and Ag/AgCl was the reference electrode. Samples have been analyzed by standard addition procedures and found to be quantitative (p 2 =0.9999) (p<0.01). The proposed Differential Pulse Polarographic (DPP) method is a rapid, reproducible procedure for the simultaneous determination of phenolic lignans in sesame and food products with sesame. It provides an adequate, sensitive, quantitative detection of these nutraceuticals in the commercial food industry.

Abrasive Stripping Voltammetry in Room Temperature Ionic Liquids

AbstractWe report on the abrasive stripping voltammetry (AbrSV) of six different solid compounds of widely different natures in room temperature ionic liquids (RTILs). Copper as a metal representative, Prussian blue as a typical inorganic complex, indigo as an organic dye model, and anthracene, pyrene, and 9,10‐diphenylanthracene as the typical representatives of aromatic hydrocarbons were chosen in this study. They were immobilized on a gold electrode surface by mechanical abrasion and their subsequent voltammetric measurements were carried out in the ionic liquid [C4mim][NTf2], 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide. The present work demonstrates that RTILs provide an excellent electrochemical solvent environment for abrasive stripping voltammetric analysis; in particular, the much wider potential windows in RTILs as compared to aqueous media greatly enhance the analytical applicability of the AbrSV technique.

An aptamer-based biosensor for sensitive thrombin detection

A sensitive aptamer-based sandwich-type sensor is presented to detect human thrombin using quantum dots as electrochemical label. CdSe quantum dots were labeled to the secondary aptamer, which were determined by the square wave stripping voltammetric analysis after dissolution with nitric acid. The aptasensor has a lower detection limit at 1 pM, while the sample consumption is reduced to 5 μl. The proposed approach shows high selectivity and minimizes the nonspecific adsorption, so that it was used for the detection of target protein in the human serum sample. Such an aptamer-based biosensor provides a promising strategy for screening biomarkers at ultratrace levels in the complex matrices.

Ordered Mesoporous Carbon Paste Electrodes for Electrochemical Sensing and Biosensing

AbstractSurface renewable ordered mesoporous carbon paste electrodes (OMCPE) were prepared by mechanical mixing ordered mesoporous carbon (OMC) and mineral oil. Electrochemical behavior of the composite electrode was evaluated and compared with the conventional graphite paste (GPE) and carbon nanotubes paste (CNTPE) electrodes. The OMCPE provided improved electron transfer kinetics and catalytic capabilities in connection with oxidation and/or reduction of different redox systems, such as ferricyanide and some biological species, e. g. ascorbic acid (AA), uric acid (UA), β‐nicotinamide adenine dinucleotide (NADH), dopamine (DA), epinephrine (EP), acetaminophenol (AP) and hydrogen peroxide. The substantial decrease in the over voltage of the hydrogen peroxide oxidation along with the facile incorporation of glucose oxidase (GOD) into the composite matrix allowed us successfully to fabricate a sensitive and selective glucose biosensor. A linear response up to 15 mM glucose was obtained for the OMCPE modified with 10% GOD (w/w) with a detection limit of 0.072 mM. In addition, we also successfully applied the OMCPE to the anodic stripping voltammetric analysis of heavy metal ions with improved sensitivities in comparison with CNTPE and GPE. The excellent experimental results implicate that the new developed paste electrode holds great promise in the design of electrochemical devices, such as sensors and biosensors.

Stripping voltammetric analysis of organophosphate pesticides based on solid-phase extraction at zirconia nanoparticles modified electrode

A sensitive electrochemical stripping voltammetric method for analyzing organophosphate (OP) compounds was developed based on solid-phase extraction (SPE) at zirconia (ZrO 2) nanoparticles modified electrode. ZrO 2 nanoparticles were proved as a new sorbent for SPE of OP pesticides. Because of the strong affinity of ZrO 2 for the phosphoric group, nitroaromatic OPs can strongly bind to the ZrO 2 nanoparticle surface. The combination of SPE with square-wave voltammetry (SWV) provided a fast, sensitive, and selective electrochemical method for nitroaromatic OP compounds using methyl parathion (MP) as a model. The stripping response was highly linear over the MP range of 0.003–2.0 μg/mL, with a detection limit of 0.001 μg/mL. The fast extraction ability of ZrO 2 nanoparticles makes it promising sorbent for various solid-phase extractions.

Versatile Immunosensor Using CdTe Quantum Dots as Electrochemical and Fluorescent Labels

A versatile immunosensor using CdTe quantum dots as electrochemical and fluorescent labels has been developed for sensitive protein detection. This sandwich-type sensor is fabricated on an indium tin oxide chip covered with a well-ordered gold nanoparticle monolayer. Gel imaging systems were successfully introduced to develop a novel high-efficient optical immunoassay, which could perform simultaneous detection for the samples with a series of different concentrations of a target analyte. The linear range of this assay was between 0.1 and 500 ng/mL, and the assay sensitivity could be further increased to 0.005 ng/mL with the linear range from 0.005 to 100 ng/mL by stripping voltammetric analysis. The immunosensor showed good precision, high sensitivity, acceptable stability, and reproducibility and could be used for the detection of real sample with consistent results in comparison with those obtained by the ELISA method.

Imprinted polymer-modified hanging mercury drop electrode for differential pulse cathodic stripping voltammetric analysis of creatine

The molecularly imprinted polymer [poly(p-aminobenzoicacid-co-1,2-dichloroethane)] film casting was made on the surface of a hanging mercury drop electrode by drop-coating method for the selective and sensitive evaluation of creatine in water, blood serum and pharmaceutical samples. The molecular recognition of creatine by the imprinted polymer was found to be specific via non-covalent (electrostatic) imprinting. The creatine binding could easily be detected by differential pulse, cathodic stripping voltammetric signal at optimised operational conditions: accumulation potential −0.01V (versus Ag/AgCl), polymer deposition time 15s, template accumulation time 60s, pH 7.1 (supporting electrolyte≤5×10−4M NaOH), scan rate 10mVs−1, pulse amplitude 25mV. The modified sensor in the present study was found to be highly reproducible and selective with detection limit 0.11ngmL−1 of creatine. Cross-reactivity studies revealed no response to the addition of urea, creatinine and phenylalanine; however, some insignificant magnitude of current was observed for tryptophan and histidine in the test samples.

Cathodic stripping voltammetric analysis of arsenic species in environmental water samples

A simple, fast and sensitive arsenic speciation method has been developed for environmental water analysis by using differential pulse cathodic stripping voltammetry (CSV) performed on a hanging mercury drop electrode (HMDE). Electroactive As(III) is determined by direct CSV analysis. As(V) is converted to As(III) species first and is subsequently quantified by the concentration difference between total inorganic arsenic and As(III). A new batch-mode As(V) reduction procedure by l-cysteine was developed in this study. The optimized parameters for quantitative As(V) reduction include treatment with 20 mM l-cysteine and 0.03 M HCl for 6 min at 70 °C. Organic arsenic, including monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), can be decomposed to As(V) through UV photooxidation with peroxydisulfate and quantified through subtracting total inorganic arsenic from the total arsenic. At optimum condition, the detection limits for As(III), As(V), and organic arsenic (MMA and DMA) were all 0.3 μg/L and with the linear range from 2.5 to 190 μg/L. Interference from ions common in natural water (Mn, Fe, Cr, Cd, Ca, Zn, Mg, and phosphate) is minimal. The method was validated by analyzing the NIST 1640 natural water standard reference material and by recovery tests on spiked tap water and groundwater. When applied to on-site analysis of sediment pore water and stream water, the CSV results agree well with those obtained by inductively coupled plasma–mass spectrometry (ICP–MS) and graphite furnace atomic absorption spectrometry (GFAAS) methods.

Electrodeposition of Au Monolayer on Pt(111) Mediated by Self-Assembled Monolayers

In-situ scanning tunneling microscopy (STM), cyclic voltammetry (CV), and infrared reflection-adsorption spectroscopy (IRRAS) have been used to examine the electrodeposition of gold onto Pt(111) electrodes modified with benzenethiol (BT) and benzene-1,2-dithiol (BDT) in 0.1 M HClO4 containing 10 microM HAuCl4. Both BT and BDT were attached to Pt(111) via one sulfur headgroup. STM and IRRAS results indicated that the other SH group of BDT was pendant in the electrolyte. Both BT and BDT formed (2 x 2) structures at the coverage of 0.25, and they were transformed into (square root(3) x square root(3))R30 degrees as the coverage was raised to 0.33. These two organic surface modifiers resulted in 3D and 2D gold islands at BT- and BDT-coated Pt(111) electrodes, respectively. The pendant SH group of BDT could interact specifically with gold adspecies to immobilize gold adatoms on the Pt(111) substrate, which yields a 2D growth of gold deposition. Molecular resolution STM revealed an ordered array of (6 x 2 square root(13)) after a full monolayer of gold was plated on the BDT/Pt(111) electrode. Since BDT was strongly adsorbed on Pt(111), gold adatoms only occupied free sites between BDT admolecules on Pt(111). This is supported by a stripping voltammetric analysis, which reveals no reductive desorption of BDT admolecules at a gold-deposited BDT/Pt(111) electrode. It seems that the BDT adlayer acted as the template for gold deposit on Pt(111). In contrast, a BT adlayer yielded 3D gold deposit on Pt(111). This study demonstrates unambiguously that organic surface modifiers could contribute greatly to the electrodeposition of metal adatoms.

Voltammetric study of Sn(II) reduction on a glassy-carbon electrode from sulfate-tartrate baths

The reduction of Sn(II) from sulfate-tartrate baths on a glassy-carbon electrode is studied. The influence of the tartrate anion and Sn(II) concentrations and the solution pH on the shape of the voltamograms and on the efficiency of the electrodeposition process is examined. A reaction scheme to explain the results is proposed. The voltammetric and anodic stripping analysis of the electrodeposition process shows that the optimal efficiency conditions to obtain Sn deposits are bath solutions without excess of tartrate ligand, not excessively high pH, and low overpotentials.

Enhancing the Efficiency of Anodic Stripping Voltammetry in Systems Permitting a Change of the Solution without Opening the Circuit

A new design for a transducer for voltammetric stripping analysis was proposed. It allows electroaccumulation and electrostripping stages to be carried out in the solutions of different compositions without opening a circuit. The potentialities of the transducer were demonstrated in the analysis of samples containing complex salt and organic matrices without their preliminary mineralization.

Electrochemical detection of ascorbic acid (vitamin C) using a glassy carbon electrode.

A method for the detection of ascorbic acid (AA) was developed using square wave anodic stripping voltammetric (SWASV) analysis with a glassy carbon electrode (GCE). The results indicated a sensitive oxidation peak current of AA on the GCE. A linear curve was obtained within a concentration range of 1-130.0 microg/L with a preconcentration time of 270 s. The relative standard deviation of 30.0 microg/L observed was 0.1016% (n = 12) under optimum conditions. The low detection limit (S/N) was pegged at 0.30 microg/L. Results showed that the method developed can be used to assay biological and pharmaceutical samples, and food samples, as well as other materials requiring AA analyses.

Long-lived sensors with replaceable surface for stripping voltammetric analysis: part II

The tape electrode, consisting of flexible polymer substrate, covered with carbon-containing paste and modified by calomel, has been developed as an alternative to the flexible voltammetric sensor with replaceable surface, which was made of a carbon-containing filament and modified beforehand by insoluble mercury diethyldithiocarbaminate. The tape electrode was fabricated using commercially available materials and the screen-printing technology. Optimal conditions have been chosen for the electrochemical “activation” of the modifying layer of the calomel. These conditions provided a thin mercury layer comprising microscopic droplets 1–4 μm across on the electrode surface. Main experimental data obtained with the use of developed electrode followed the theoretical laws for the discharge-ionization of metals on the surface of solid and mercury thin-film electrodes. As compared to the carbon-containing filament, the tape electrode considerably extends the number of determinable amalgam-forming metals ions and allows decreasing their detection limits by more than one order of magnitude. The detection limit of 0.12 μg l −1 for copper, 0.02 μg l −1 for lead and cadmium and 0.05 μg l −1 for zinc was achieved after a 2 min accumulation. A high reproducibility of analytical response (0.6–2.3% R.S.D.) was achieved for nine repetitive measurements of 1 μg l −1 of these metals. The response values obtained with the tape sensor were directly proportional to the concentration of the metal ions over a broad concentration interval (0.1 μg l −1 to 0.5 mg l −1) at different accumulation times (120–10 s). Therefore, the newly developed low-toxic sensor can be used in automatic systems for environmental monitoring (at the trace level inclusive), processing solutions and waste waters.

Interaction of Pb and Cd during anodic stripping voltammetric analysis at boron-doped diamond electrodes

Highly boron-doped diamond (BDD) films were utilized for simultaneous electrochemical measurement of micromolar-level concentrations of Pb and Cd, and for the examination of their interactions. Differential pulse anodic stripping voltammetry (DPASV) was used for this detection. This approach can help to understand the possible detection of trace metals at BDD electrodes without the aid of mercury. These metals were found to strip at their characteristic potentials, in solutions containing Cd or Pb alone, and in those containing these metals together. The mixed solutions (concentration range: 1–5 μM) yielded well-separated stripping peaks for Pb and Cd and the differential stripping peak currents for the respective metals increased linearly with increasing metal concentration. There were mutual interferences due to Pb–Cd interactions, but these can be taken into account with the aid of three-dimensional calibration plots. A model has been developed to help explain the Pb–Cd interactions.

Long-lived sensors with replaceable surface for stripping voltammetric analysis: part II

The tape electrode, consisting of flexible polymer substrate, covered with carbon-containing paste and modified by calomel, has been developed as an alternative to the flexible voltammetric sensor with replaceable surface, which was made of a carbon-containing filament and modified beforehand by insoluble mercury diethyldithiocarbaminate. The tape electrode was fabricated using commercially available materials and the screen-printing technology. Optimal conditions have been chosen for the electrochemical “activation” of the modifying layer of the calomel. These conditions provided a thin mercury layer comprising microscopic droplets 1–4 μm across on the electrode surface. Main experimental data obtained with the use of developed electrode followed the theoretical laws for the discharge-ionization of metals on the surface of solid and mercury thin-film electrodes. As compared to the carbon-containing filament, the tape electrode considerably extends the number of determinable amalgam-forming metals ions and allows decreasing their detection limits by more than one order of magnitude. The detection limit of 0.12 μg l−1 for copper, 0.02 μg l−1 for lead and cadmium and 0.05 μg l−1 for zinc was achieved after a 2 min accumulation. A high reproducibility of analytical response (0.6–2.3% R.S.D.) was achieved for nine repetitive measurements of 1 μg l−1 of these metals. The response values obtained with the tape sensor were directly proportional to the concentration of the metal ions over a broad concentration interval (0.1 μg l−1 to 0.5 mg l−1) at different accumulation times (120–10 s). Therefore, the newly developed low-toxic sensor can be used in automatic systems for environmental monitoring (at the trace level inclusive), processing solutions and waste waters.

Electrodeposition for obtaining homogeneous or heterogeneous cobalt-copper films

Direct electrodeposition of heterogeneous deposits may be an alternative method for preparing cobalt-copper coatings with magnetoresistive properties. Co-Cu electrodeposition was obtained in sulfate baths containing different citrate concentrations in order to prepare either homogeneous or heterogeneous Co-Cu deposits. X-ray diffraction (XRD) and voltammetric stripping analysis were used to study the kind of deposits formed. Citrate-free baths produced heterogeneous films, although dendritic growth was observed, thus increasing the deposit's thickness. Increasing the Cu(II)/Co(II) ratio in solution enabled the formation of smoother deposits. The presence of citrate at up to twice the total metallic concentration in the bath improved the morphological aspects of the deposits, their structural heterogeneity being maintained. Higher citrate concentrations induced the loss of heterogeneity, and both electrochemical and diffraction peaks tended towards single peaks. Homogeneous Co-Cu deposits, formed by a solid solution structure, were obtained in highly complexed citrate baths.

Heavy metals influence on ascorbic acid level

It is well known that heavy metals (HM) are extremely dangerous pollutants influencing to metabolism in animals' organisms. The vitamin C is one of the most important metabolites taking part in many biochemical processes. We studied the influence of main essential HM - Zn and Cu as well as the based supertoxical elements - Cd and Pd on ascorbic acid level in serum. The studies were carried out in Tulinskoe farm of Novosibirsk region. The objects of investigations were piglets (2 month after weaning) and 6-month pigs of Early Ripe Meat breed. The levels of HM in bristle were found by stripping voltammetric analysis using the TA-2 analyzer. vitamin C content was determined by I.P. Kondrakhin (1985) method using 2,2-dipyridyl. The significant negative correlations between Pb, Cd content and vitamin C (-0.46±0.18, -0.47=0.19) in 6-month pigs were determined. The tendencies of negative correlation between all HM levels in hair and ascorbic acid level in plasma of piglets were revealed. Thus, the obtained correlations let us to suppose that all studied HM influence on 1-gulono-gamma-lactone oxidase and other vitamin C metabolism enzymes activity.

Content of heavy metals in the hair

The aim of our investigation was to determine of HM content in the hair of people and animals. Two of the main essential elements- Zn and Cu and two of the supertoxical heavy metals- Pb and Cd were chosen. The investigations were conducted in Russian Federation and Belarus Republic in 2001- 2002. About 500 hair samples of people, dogs, cats, cattle, horses, yaks, pigs, sheep goats and rabbits were studied by the stripping voltammetric analysis (SVA) method with TA- 2 analyzer to determine Zn, Cu, Pb and Cd concentrations. The hair samples were prepared according to the methods developed in Tomsk University (Russia) and improved by the authors. The essence of the methods is the multiconsecutive burning of hair samples to ashes and boiling them in concentrated acids to dissolve chemical combinations and transform their metals into ion forms. The zinc concentration was the highest in all hair samples (58.65... 195.15 mg/kg). The copper content was several times less (5.49... 22.63 mg/kg). Lead and cadmium were detected in relatively low amounts (0.32... 2.42 mg/kg and 0.04... 0.92 mg/kg respectively). The highest Pb and Cd levels were detected in cats and people hair.

Imprinted Polymer – Modified Hanging Mercury Drop Electrode for Differential Pulse Adsorptive Stripping Voltammetric Analysis of a Diquat Herbicide

AbstractAn imprinted polymer modified hanging mercury drop electrode (HMDE) in Model 303A system in conjunction with a PAR Model 264A Polarographic Analyzer/Stripping Voltammeter has been used for the selective analysis of a diquat herbicide viz., 5,6‐dihydropyrazino[1,2,3,4‐[lmn]‐1,10‐phenanthrolinium dichlorides in differential pulse cathodic stripping voltammetry mode. Complex aqueous samples (drinking water and agricultural soil suspension), spiked with a diquat herbicide, were directly analyzed by the adsorptive accumulation of the analyte over the working electrode (accumulation potential −0.8 V (vs. Ag/AgCl), accumulation time 120 s, pH 7.0, supporting electrolyte 0.1 M KCl, scan rate 10 mV s−1, pulse amplitude 25 mV). The limit of detection for diquat herbicide was found to be 0.34 nmol L−1 (0.1 ppb, RSD 2%, S/N=2).