Stripping Voltammetry Method Research Articles

Environmental concentration of selected elements and relation to physicochemical parameters in honey

The purpose of this study was to evaluate the content of selected elements and physicochemical indicators of the honey of Apis mellifera. Samples of blossom, blend and honeydew honeys were randomly obtained from the Eastern, Western and Central of Slovakia. Contents of elements were measured with the use of flame atomic absorption spectrophotometry (FAAS) method and anodic stripping voltammetry (ASV) method with CGMDE as working electrode. The content of heavy metals (mg/kg dry weight) ranged as follows: Zn 0.25–3.82; Cu 0.12–1.37; Ni 0.06–0.60; Mg 0.10–50.43; Ca 10.32–87.21; Pb and Cd were under detectable limit (0.001 mg/kg). The physical and chemical indicators ranged as follows: moisture (%) 16.00–19.80; HMF (mg/kg) 10.00–40.00; pH 3.58–5.12; conductivity (mS/m) 13.45–99.12 and a w 0.456–0.659. Significant difference (P < 0.05) for elements and physicochemical indicators was analyzed. Significant correlations between Cu – Zn, Cu – Ni, Cu – Mg, Ca – Zn and Ca – Mg were detected. With reference to Codex Alimentarius of Slovakia, maximal levels of heavy metals content and selected physicochemical properties were not exceeded. On average, the content of trace elements decreased in the order: Ca > Mg > Zn > Cu > Ni and physicochemical indicators decreased: conductivity > HMF > moisture > pH > aw.

Analysis of PTH‐Cysteine by Adsorptive Stripping Square‐Wave Voltammetry

AbstractThe aim of this work is the study of cysteine by its derivative form. Cysteine derivation is done by Edman degradation and we obtain the phenylthiohydantoin of cysteine. Edman degradation is one of the most usual procedures for sequentate proteins. From this reaction, the phenylthiohydantoin amino acid derivative (PTH‐amino acid) from the N‐terminal one is obtained, leaving the new amino terminus for the next degradation cycle. To identify the produced PTH‐derivative, a square‐wave cathodic stripping voltammetry method is developed. In this work we show the results obtained for the optimization the instrumental and chemical conditions, and we can conclude that it is an electrochemically irreversible system with adsorptive reduction phemomenon. Under the best conditions we found a new method to analyze proteins with LOD of 2 μg L−1 and LOQ of 5 μg L−1, a RSD less than 10% and a Er minor than 9%. Results of the application of this methodology to a real protein are included.

Kinetic and equilibrium studies for the adsorption process of cadmium(II) and copper(II) onto Pseudomonas aeruginosa using square wave anodic stripping voltammetry method

A novel method for the simultaneous determination of cadmium(II) and copper(II) during the adsorption process onto Pseudomonas aeruginosa was developed. The concentration of the free metal ions was successfully detected by square wave anodic stripping voltammetry (SWASV) on the mercaptoethane sulfonate (MES) modified gold electrode, while the P. aeruginosa was efficiently avoided approaching to the electrode surface by the MES monolayer. And the anodic stripping peaks of Cd 2+ and Cu 2+ appear at −0.13 and 0.34 V respectively, at the concentration range of 5–50 μM, the peak currents of SWASV present linear relationships with the concentrations of cadmium and copper respectively. As the determination of Cd 2+ and Cu 2+ was in real time and without pretreatment, the kinetic characteristics of the adsorption process were studied and all the corresponding regression parameters were obtained by fitting the electrochemical experimental data to the pseudo-second-order kinetic model. Moreover, Langmuir and Freundlich models well described the biosorption isotherms. And there were some differences in the amount of metal ion adsorbed at equilibrium ( q e ) and other kinetics parameters when the two ions coexisted were compared with the unaccompanied condition, which were also discussed in this paper. The proposed electrode system provides excellent platform for the simultaneous determination of trace metals in complex biosorption process.

Screening for lead exposure in children in Belize

The objectives of this pilot study were to determine the blood lead levels in children in Belize and to try to relate these findings to demographic variables. With permission from parents, capillary blood was collected from the fingers of 164 children with an age range of 2 to 8 years, living and attending school in the spring of 2002 in four towns: Belize City, San Pedro, Orange Walk, and Benque Viejo. The sample represents 0.4% of all children in Belize in that age range. Lead levels were analyzed by the method of anodic stripping voltammetry using the ESA LeadCare analyzer. The mean blood lead level for the children in the sample was 4.94 micrograms per deciliter (microg/dL) with a standard deviation of 2.46. However, 11 children (7%) had blood lead in the range of 10.1-13.8 microg/dL, which is the level of concern according to guidelines of the Centers for Disease Control and Prevention. Children living in the large urban centers of Belize City and Orange Walk town had higher lead levels (mean 5.80 and 5.74 microg/dL) than children living in the smaller towns of Benque Viejo and San Pedro (mean 4.17 and 4.63 microg/dL). There were no statistically significant differences between male and female children. These data indicate that children in Belize are being exposed to lead and suggest that this pilot study be followed up with a comprehensive study with a larger sample and correlation of the findings to socioeconomic characteristics, to children's behavior, and to the home and school environment.

Simultaneous Quantitative Determination of Cadmium, Lead, and Copper on Carbon‐Ink Screen‐Printed Electrodes by Differential Pulse Anodic Stripping Voltammetry and Partial Least Squares Regression

AbstractWater is a vital commodity for every living entity on the planet. However, water resources are threatened by various sources of contamination from pesticides, hydrocarbons and heavy metals. This has resulted in the development of concepts and technologies to create a basis for provision of safe and high quality drinking water. This paper focuses on the simultaneous quantitative determination of three common contaminants, the heavy metals cadmium, lead and copper. Multivariate calibration was applied to voltammograms acquired on in‐house printed carbon‐ink screen‐printed electrodes by the highly sensitive electrochemical method of differential pulse anodic stripping voltammetry (DPASV). The statistically inspired modification of partial least squares (SIMPLS) algorithm was employed to effect the multivariate calibration. The application of data pretreatment techniques involving range‐scaling, mean‐centering, weighting of variables and the effects of peak realignment are also investigated. It was found that peak realignment in conjunction with weighting and SIMPLS led to the better overall root mean square error of prediction (RMSEP) value. This work represents significant progress in the development of multivariate calibration tools in conjunction with analytical techniques for water quality determination. It is the first time that multivariate calibration has been performed on DPASV voltammograms acquired on carbon‐ink screen‐printed electrodes.

Simultaneous determination of trace aluminum (III), copper (II) and cadmium (II) in water samples by square-wave adsorptive cathodic stripping voltammetry in the presence of oxine

A validated adsorptive cathodic stripping voltammetry method is described for simultaneous determination of Al(III), Cu(II) and Cd(II) in water samples. In acetate buffer (pH 5) containing 10 μM oxine, these metal ions were determined as oxine complexes following adsorptive accumulation onto the HMDE at −0.05 V versus Ag/AgCl/KCls. The best signal to noise ratio was obtained using a square wave of scan increment 10 mV, frequency 120 Hz, and pulse-amplitude 25 mV. Limits of detection as low as 0.020 μg L−1 Al(III), 0.012 μg L−1 Cu(II) and 0.028 μg L−1 Cd(II) were achieved. Interference due to various cations (K(I), Na(I), Mg(II), Ca(II), Mn(II), Fe(III), Bi(III), Sb(III), Se(IV), Pb(II), Zn(II), Ni(II), Co(II)), anions (Cl−, NO3−, SO42−, PO43−) and ascorbic acid was minimal as the measured signals change by 4% at the maximum. The stripping voltammetry method was successfully applied for simultaneous determination of Al(III), Cu(II) and Cd(II) in tap and natural bottled water samples.

Development of a microelectrode array sensing platform for combination electrochemical and spectrochemical aqueous ion testing

A microelectrode array sensor platform was designed and fabricated to increase diversity, flexibility, and versatility of testing capabilities over that of traditionally reported sensor platforms. These new sensor platforms consist of 18 individual addressable microelectrodes, photolithography fabricated, that employ a glass base substrate and a resist polymer layer that acts as an insulating agent to protect the circuitry and wiring of the sensor from undesired solution interactions. Individually addressable microelectrodes increase diversity by allowing isolated electrochemical testing between electrodes, global array testing, or some combination of electrodes to perform electrochemical methods. Furthermore, because of the optical transparency of the glass base substrate and the resist mask layer, along with the small size of the electrode array, spectrochemical analysis is possible within the sample area that acts as electrochemical cell and cuvette, while the microelectrode array passively resides within the optical path length during spectrochemical testing. This unique arrangement offers improved testing possibilities for various applications, including simultaneous electrochemical and spectrochemical analysis in environmental testing, identification or quantification of possible species for bioavailability in the biotechnology field, and process control in industrial applications. Electrochemical characteristics and spectrochemcial use of the sensor platform are proven with potassium ferricyanide, an electrochemical standard analyte, and electrochemical measurements are compared against a commercially available working electrode of similar size. Additionally, the electrochemical method of differential pulse anodic stripping voltammetry is performed with the sensor platform to detect copper and lead heavy metal ions in aqueous solution, demonstrating the potential for use with environmental samples.

Ultra-sensitive detection of mutated papillary thyroid carcinoma DNA using square wave stripping voltammetry method and amplified gold nanoparticle biomarkers

This study presents an ultra-sensitive technique for the electrochemical detection of the mutated BRAF gene associated with papillary thyroid carcinomas (PTC). In the proposed approach, a biotinylated 30-nucleotides probe DNA was immobilized in a streptavidin-modified 96-well microtiter plate and the free active sites of the streptavidin were blocked using biotinylated bovine serum albumin (BSA). The biotinylated target DNA was then added and allowed to hybridize with the immobilized probe DNA for 30min. Subsequently, streptavidin-labeled gold nanoparticles were added, and a nanoparticle enlargement process was performed using gold ion solution and formaldehyde reductant. The gold particles were then dissolved in bromide and DNA hybridization detection process was performed using a square wave stripping voltammetry (SWSV) technique. The results indicated a stable SWSV response in differential detection between blank solution and target DNA solution with a concentration of 130aM. Moreover, the coefficient of determination (R2) of the semi-log plot of the SWSV response current against the target DNA concentration (0.52–1300aM) was found to be 0.9982. The detection limit was estimated to be 0.35aM (based on a signal-to-noise ratio of 3:1). This value was approximately three orders of magnitude lower than that obtained using the same method but without gold amplification process. Finally, the proposed approach is successful in differentiating between the mutant and wildtype BRAF sequences that are present in genuine 224-nucleotides DNA.

Effects of Zn-complexes on zinc uptake by wheat (Triticum aestivum) roots: a comprehensive consideration of physical, chemical and biological processes on biouptake

Commonly used equilibrium models for metal biouptake, such as the Free Ion Activity Model (FIAM) and the Biotic Ligand Model (BLM), are limited to the cases in which mass diffusive transport is not the flux-determining step. In analyses of metal biouptake from a complexing medium, all the physical (diffusion), chemical (dissociation kinetics of metal complexes), and biological (transport and internalization) processes have to be taken into account. A short-term zinc uptake by wheat (Triticum aestivum) roots from culture solutions in the absence or presence of synthetic ligands (NTA, nitrilotriacetic acid, and EDTA, ethylenediaminetetraacetate) was studied. At the same free Zn2+ concentration \(\left( {\left\{ {{\text{Zn}}^{{\text{2 + }}} } \right\} = 1.5 \times 10^{ - 8} {\text{M}}} \right)\) , the uptake of Zn was significantly enhanced in the presence of ligands and was larger when Zn complexes have a quicker dissociation rate. The diffusional fluxes in the same culture solution were determined with the differential pulse anodic stripping voltammetry (DPASV) method, and the diffusive gels in thin film (DGT) technique. The contribution from Zn complexes to root Zn uptake was in better agreement with the degree of Zn complex labilities measured with DPASV than with DGT. The diffusion of free Zn2+ ion to the root surface is a rate-controlling step for Zinc biouptake when the free Zn2+ concentration is low. Based on the comprehensive consideration of the diffusion and dissociation processes of Zn2+ ion and Zn complexes and the existence of high- and low-affinity uptake systems in the root surface, a two-pathway Zn uptake model was developed to predict the resulting Zn uptake fluxes into roots in the overall range of exposure.

Electrochemical analysis of the alanine phenylthiohydantoin derivative by cathodic stripping voltammetry

A square-wave cathodic stripping voltammetry method for alanine determination as its phenylthiohydantoin (PTH-alanine) derivative is developed. To this end, all the chemical and instrumental variables affecting the determination of PTH-alanine are optimized. From studies of the mechanisms governing the electrochemical response of PTH-alanine, it was concluded that it is an electrochemically irreversible system with a diffusive-adsorptive reduction phenomenon . Under optimal conditions, the variation of analytical signal ( I p) with PTH-alanine concentration is linear in the 2.4 × 10 −8 − 4.8 × 10 −7 M range, with a LOD of 1.2 × 10 −8 M and a LOQ of 4.2 × 10 −8 M, a RSD (%) less than 11%, and a E r (%) less than 10%. The optimized method was applied to the determination of PTH-alanine obtained from a synthetic protein after Edman reaction and the results were corroborated by high-performance liquid chromatography with UV detection.

Determination of trace amounts of morphine in human plasma by anodic adsorptive stripping differential pulse voltammetry

New adsorptive anodic differential pulse stripping voltammetry method for the direct determination of morphine at trace levels in human plasma of addicts is proposed. The procedure involves an adsorptive accumulation of morphine on a HMDE, followed by oxidation of adsorbed morphine by voltammetry scan using differential pulse modulation. The optimum conditions for the analysis of morphine are pH 10.5, E acc of −100 mV (vs. Ag/AgCl), and t acc of 120 s. The peak current is proportional to the concentration of morphine, and a linear calibration graph is obtained at 0.01–3.10 μg mL −1. A relative standard deviation of 1.06% ( n = 5) was obtained, and the limit of detection was 3 ng mL −1. The capability of the method for the analysis of real samples was evaluated by the determination of morphine in spiked human plasma and addicts human plasma with satisfactory results.

Use of a modified, high-sensitivity, anodic stripping voltammetry method for determination of zinc speciation in the North Atlantic Ocean

Zinc speciation is considered to be an important determinant of the biological availability of zinc. Yet in oceanic surface waters, characterization of zinc speciation is difficult due to the low concentrations of this essential micronutrient. In this study, an anodic stripping voltammetry method previously developed for the total determination of cadmium and lead was successfully adapted to the measurement of zinc speciation. The method differs from previous zinc speciation anodic stripping voltammetry methods in that a fresh mercury film is plated with each sample aliquot. The fresh film anodic stripping voltammetry method was compared to competitive ligand exchange cathodic stripping voltammetry in a profile from the North Atlantic Ocean. Results using the fresh film anodic stripping voltammetry method were similar to those determined using the cathodic stripping voltammetry method, though ligand concentrations determined by fresh film anodic stripping voltammetry were generally slightly higher than those determined by cathodic stripping voltammetry. There did not seem to be a systematic difference between methods for the estimates of conditional stability constants. The ligand concentration in the North Atlantic profile ranged from 0.9 to 1.5 nmol L −1 as determined by fresh film anodic stripping voltammetry and 0.6 to 1.3 nmol L −1 as determined by cathodic stripping voltammetry. The conditional stability constants determined by fresh film anodic stripping voltammetry were 10 9.8–10 10.5 and by cathodic stripping voltammetry were 10 9.8–10 11.3.

Determination of iron in water samples by adsorptive stripping voltammetry with a bismuth film electrode in the presence of 1-(2-piridylazo)-2-naphthol

An adsorptive stripping voltammetry method for the determination of iron has been developed. The procedure is based on the adsorptive collection of a complex of iron with 1-(2-piridylazo)-2-naphthol (PAN) on a bismuth-coated glassy carbon electrode (BiFE). Factors affecting the stripping performance, such as pH, PAN concentration ( C PAN), potential, accumulation time ( E ads, t ads), and interference by other ions were also studied. The optimum conditions were obtained in a 0.1 mol L −1 acetate buffer at pH 4.0, C PAN 5.0 μmol L −1, t ads 60 s, E ads −400 mV, pulse height 4.0 mV, pulse amplitude 25 mV, and frequency 15 Hz. The detection limit was found to be 0.1 μg L −1 when a t ads of 60 s was used, and the linear range was from 0.4 to 60.0 μg L −1. The proposed procedure was validated by determining of Fe(III) in CRM-MFD, QCS-19 and CRM-SW certified reference materials and applied in seawater samples with satisfactory results.

Development and Validation of an Adsorptive Stripping Voltammetric Method for the Quantification of Vincamine in Its Formulations and Human Serum Using a Nujol-Based Carbon Paste Electrode

An easy, rapid and selective adsorptive stripping voltammetry (AdSV) method for the determination of vincamine in its formulation and human serum was developed and validated. It was based on the oxidation of the drug onto a Nujol-based carbon paste electrode. The stripping step was carried out by using a square-wave (SW) potential-time voltammetric excitation signal. The optimal experimental variables as well as accumulation parameters were investigated as; frequency f=120 Hz, scan increment DeltaE(i)=10 mV, pulse-amplitude DeltaE(a)=25 mV and an accumulation potential E(acc) of 0.0 V using a Britton-Robinson (B-R) universal buffer of pH 5 as a supporting electrolyte. After validation of the described method, it was applied for determination of vincamine in its formulation and human serum. Mean recovery of 100.41+/-0.74 (n=5) was achieved for assay of vincamine in Oxybral capsules. Limits of detection and quantitation of 6.0 x 10(-9) M (2.20 ng ml(-1)) and 2 x 10(-8) M (7.33 ng ml(-1)) vincamine were achieved in human serum with a mean recovery of 99.5+/-1.79%, without prior extraction of the drug. No interferences were observed in formulation and/or human serum. Due to high sensitivity and specificity of the developed method, it was successfully applied for evaluating some pharmacokinetic parameters of two healthy volunteers after administration of a single oral Oxybral capsule.

Anodic stripping voltammetry of inorganic species of As 3+ and As 5+ at gold-modified boron doped diamond electrodes

Electrochemical detection of mixture solutions of As 3+ and As 5+ has been investigated by stripping voltammetry at gold-modified diamond electrodes. The method was performed based on stripping oxidation of As 0 deposited at the electrode surface. Whereas As 3+ can be deposited by simple electrochemical reduction of As 3+ to As 0 at −0.4 V (vs. Ag/AgCl), much higher potential is required to overcome the activation energy of As 5+ reduction. However, in such a high potential, hydrogen evolution also occurs. Consequently, one more step should be added to release the hydrogen gas adsorbed at the electrode surface during the reduction step. During the deposition of As 5+, As 3+ species was also simultaneously deposited. Therefore, to differentiate As 3+ and As 5+ quantification in a mixture solution, both stripping voltammetry methods should be performed and calculated mathematically. Comparison of stripping voltammograms of both methods for As 3+ solution in the absence of As 5+ demonstrated similar peak shapes and current intensities, confirming that error calculation of As 5+ concentration in the mixture solution with As 3+ can be avoided. Good linear responses were observed for each standard solution of As 3+ and As 5+. Linear calibration curve could also be achieved for a series concentrations of 100–1000 ppb As 5+ in a mixture solution with 100 ppb As 3+ ( r 2 = 0.99) and for a series concentrations of 5–30 ppb As 3+ in a mixture solution with 100 ppb As 5+. Detection limits of 5 and 100 ppb can be achieved for As 3+ and As 5+ in a mixture solution, respectively. The reproducibility was shown for stripping voltammetry of As 3+ and As 5+ with an RSD ( n = 8) of 7.5% and 8.4%, respectively. Good stability of gold-modified diamond electrodes before and after arsenic detection was also evaluated by SEM image. Application of the method for real sample analysis was performed for arsenic detection in Yokohama tap water.

Adsorptive Stripping Differential Pulse Voltammetry for Determination of Trace Amounts of Noscapine in Human Plasma

AbstractA new adsorptive anodic differential pulse stripping voltammetry method for the direct determination of noscapine at trace levels in human plasma of addicts is proposed. The procedure involves an adsorptive accumulation of noscapine on a hanging mercury drop electrode (HMDE), followed by oxidation of adsorbed noscapine by voltammetry scan using differential pulse modulation. The optimum conditions for the analysis of noscapine are pH = 8.5 using Britton‐Robinson (B‐R) buffer, accumulation potential of −100 mV (vs. Ag/AgCl), and accumulation time of 150 s. The peak current is proportional to the concentration of noscapine, and a linear calibration graph is obtained at 0.015–2.75 μg mL−1. A relative standard deviation of 1.28% (n = 5) was obtained, and the limit of detection was 7 ng mL−1. The capability of the method for the analysis of real samples was evaluated by determination of noscapine in spiked human plasma and addicts, human plasma with satisfactory results.

Complexation of copper ions in atmospheric precipitation in Croatia

Organic complexation in atmospheric precipitation is an important control mechanism of the biogeochemistry of metal ions. We have measured complexation of copper ions in bulk precipitation by the method of differential pulse anodic stripping voltammetry (DPASV), which introduces least perturbation in the samples. The precipitation samples were collected periodically during one year in the mainland area of Croatia (Zagreb) and at the Adriatic coast (Šibenik). The results have shown the complexation of copper ions in all the samples. The method of determination presumes the existence of 1:1 copper ion–ligand complexes. The complexing capacity of rainwater samples for copper ions ranged between 0.010 and 1.4 μM. The highest capacity was measured in April 2003 in rainwater sample from the Šibenik area, which could be associated to the contribution of biogenically driven organics to marine aerosol. Apparent stability constants determined were in the range of 6.1–10. The sources of organic ligands in the samples could be multiple. The concentrations of dissolved organic carbon (DOC) as well as of surface active substances (SAS) were measured. The proportion of complexing ligands in these two organic matter fractions has also been discussed.

Blood Lead Misclassification Due to Defective LeadCare® Blood Lead Testing Equipment

In May, 2005, a partial recall of LeadCare® portable blood lead testing kits was initiated after proficiency testing revealed a negative error (mean, −25%; 95% CI, −15% to −35%) in blood lead concentrations (often called blood lead level in the US) analyzed with this device (1)(2). This bias exceeded previously recommended 95% error thresholds established with graphite furnace atomic absorption spectroscopy (3). The recall included 8 lots of defective sensors containing enough material for an estimated 500 000 patient tests distributed between September 2003 and May 2005. The LeadCare device uses an anodic stripping voltammetry method to measure lead. Capillary sampling by fingerstick is the most common method of specimen collection. Assessments of the portable units by testing of venous samples from occupationally exposed workers have demonstrated that measurements obtained with these units show an insignificant positive error that decreases as blood lead concentrations increase (4). A blood lead concentration ≥10 μg/dL (100 μg/L) has been established as the …

Square wave adsorptive stripping voltametric determination of the mixture of nalidixic acid and its main metabolite (7-hydroxymethylnalidixic acid) by multivariate methods and artificial neural network

Nalidixic acid (NA) and its main metabolite, 7-hydroximethylnalidixic acid (OHNA), are quinolones antibacterial used as agents used for the treatment of urinary tract infection. For both compounds an adsorption process on a hanging mercury electrode (HMDE). On this basis, a square wave adsorptive stripping voltammetry (SWadSV) method has been developed for the individual and simultaneous determination of NA and OHNA. The variables that affect to accumulation process, such as concentration of perchloric acid, accumulation potential and accumulation time have been optimised by using an experimental design (concretely a Box–Behnken design with three levels) together with the response surface methodology (RSM). Calibration curves were linear in the range (0–1.38) × 10 −7 mol L −1 for NA and (0–3.23) × 10 −8 mol L −1 for OHNA, in the optimized conditions, with detection limits of 9.48 × 10 −9 mol L −1 and 8.06 × 10 −10 mol L −1 for NA and OHNA, respectively. The method was applied to urine samples containing only one of the analytes with satisfactory recoveries. As the voltammetric signals of these compounds show a high overlapping, different chemometric methods, such as classical least squares (CLS), partial least squares (PLS), principal component regression (PCR) and artificial neural network (ANN) have been used for the resolution of the mixture. The analysis of these compounds in urine samples were carried out using the different chemometric tools and the best recoveries were obtained by using ANN. No pre-treatment of the sample was necessary.

Monitoring of the concentration of lithium and heavy metals in drinking water by the method of stripping voltammetry

A method for monitoring of the concentration of lithium, zinc, cadmium, lead, and copper in drinking water is suggested. Monitoring can be performed within the range of 1.5(10(-8) - 2.0(10(-6) mg/dm3. A new design of the electrochemical cell is suggested. Analysis is performed against the background of 0.02 M dimethylformamide solution of (C4H9)4NCIO4. The time and potential of electrolysis are determined experimentally. The method can be used in medical research.