Adsorptive Cathodic Stripping Voltammetry Research Articles

Determination of Se(iv) by adsorptive cathodic stripping voltammetry at a Bi/Hg film electrode

Method and conditions: determination of trace amounts of Se(IV) by adsorptive cathodic stripping voltammetry at the Bi/Hg film electrode in an open circuit system; limit of detection: 0.07 ng mL−1; limit of quantification: 0.25 ng mL−1; RSD: 2.4% (for five replications of 5 ng mL−1 of Se(iv)); analytical range: 2–50 ng mL−1; interference: selective for Se(iv) – no interference; application: determination of Se(iv) in vegetable, fruits and water samples.

Riboflavin (Vitamin B2) Assay by Adsorptive Cathodic Stripping Voltammetry (Adcsv) at the Hanging Mercury Drop Electrode (HMDE)

In this study the interactions of Riboflavin (Vitamin B2) with a mercury surface are investigated. Firstly, by using Cyclic Voltammetry, it is demonstrated that Riboflavin can be efficiently accumulated, by adsorption from buffered solutions containing an excess of NaClO4, onto the mercury drop of a HMDE. Secondly, it is shown that the adsorbed Riboflavin can be reduced through an electrochemical reaction whose stoichiometry is extricated by confronting simulated with experimental CV voltammograms acquired in a range of pH between about four and nine. Finally, the cathodic current, sustained by the surface reduction of Riboflavin, is exploited for assaying Riboflavin via Differential Pulse Adsorption Cathodic Stripping Voltammetry (DP AdCSV) within the frame of the standard additions calibration procedure. By applying the suggested DP AdCSV procedure with standard voltammetric equipment, typical DP settings and pre-electrolysis time of about 10 s, a linear response is maintained if Riboflavin concentration in the electrolysed solution does not exceed about 2 mg/l. On the other side, a limit of detection (expressed as the concentration of Riboflavin in the electrolysed solution) of 7 μg/l has been achieved with a pre-electrolysis time of 68 s.

Determination of ppt Level Chromium(VI) Using the Gold Nano-Flakes Electrodeposited on Platinum Rotating Disk Electrode and Modified with 4-Thiopyridinium

The nano-gold layer formed on the platinum rotating disk electrode (nano-Au/Pt-RD) inherited the catalytic property for Cr(VI) reduction from platinum surface and owned the good features of nano-gold such as insensitivity with hydrogen ion, high surface area, augmenting diffusion of Cr(VI) and ability for self-assembling with 4-pyridine-ethanethiol (PET) through Au←S linkages, to form PET/nano-Au/Pt-RD electrode capable of accumulating Cr(VI) from sample. The obtained PET/ nano-Au/Pt-RD electrode showed an extreme sensitivity to Cr(VI). By using this electrode, 1.09 ng·L﹣1 was the detection limit of differential pulse adsorptive cathodic stripping voltammetry for Cr(VI) with the accumulation time of only 2 min. Moreover, this electrode was reproducible with 3.5% RSD for 30 times of Cr(VI) accumulating and stripping. In addition, this electrode was also selective for Cr(VI) determination, which was not almost interfered by other inorganic ions.

Macroporous Bismuth Film Screen‐Printed Carbon Electrode for Simultaneous Determination of Ni(II) and Co(II)

AbstractMacroporous bismuth film screen‐printed carbon electrode (mpBiF‐SPCE) was used for simultaneous measurement of Ni(II) and Co(II) at their trace concentration level by means of adsorptive cathodic stripping voltammetry with dimethylglyoxime as a complexing agent. The mpBiF‐SPCE was prepared on a screen printed carbon electrode by colloidal crystal templating using aqueous suspension of polystyrene microspheres which were self‐assembled onto the electrode by slow evaporation of solvent. Following the electrochemical deposition of bismuth film, the microspheres were dissolved with toluene providing the macroporous bismuth film structure. The mpBiF‐SPCE offered good electroanalytical performance with estimated limits of detection of 27 and 94 ng L−1 for Ni(II) and Co(II), respectively, in combination with an accumulation time of 180 s, and relative standard deviations of 3.3 % for Ni(II) and 5.2 % for Co(II). The effect of potentially interfering ions and the surface‐active compounds was also investigated. Both Ni(II) and Co(II) were assayed in the sample of sewer water with satisfactory recovery.

Iron-binding ligands and humic substances in the San Francisco Bay estuary and estuarine-influenced shelf regions of coastal California

Dissolved iron (dFe) and organic dFe-binding ligands were determined in San Francisco Bay, California by competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-ACSV) along a salinity gradient from the freshwater endmember of the Sacramento River (salinity <2) to the mouth of the estuary (salinity >26). A range of dFe-binding ligand classes was simultaneously determined using multiple analytical window analysis, involving titrations with multiple concentrations of the added ligand, salicylaldoxime. The highest dFe and ligand concentrations were determined in the low salinity end of the estuary, with dFe equal to 131.5nmolL−1 and strong ligand (log KFeL,Fe′cond≥12.0) concentrations equal to 139.5nmolL−1. The weakest ligands (log KFeL,Fe′cond<10.0) were always in excess of dFe in low salinity waters, but were rapidly flocculated within the estuary and were not detected at salinities greater than 7. The strongest ligands (log KFeL,Fe′cond>11.0) were tightly coupled to dFe throughout the estuary, with average excess ligand concentrations ([L]–[dFe]) equal to 0.5nmolL−1. Humic-like substances analyzed via both CLE-ACSV and proton nuclear magnetic resonance in several samples were found to be a significant portion of the dFe-binding ligand pool in San Francisco Bay, with concentrations ranging from 559.5μgL−1 to 67.5μgL−1 in the lowest and highest salinity samples, respectively. DFe-binding ligands and humic-like substances were also found in benthic boundary layer samples taken from the shelf near the mouths of San Francisco Bay and Eel River, suggesting estuaries are an important source of dFe-binding ligands to California coastal shelf waters.

A new biomimetic sensor based on molecularly imprinted polymers for highly sensitive and selective determination of hexazinone herbicide

A new selective sensor based on molecularly imprinted polymers (MIPs) was developed for the determination of hexazinone (HXZ) in environmental samples. MIPs were synthesized using a non-covalent approach, and selection of the monomers employed in the polymerization reaction was carried out by molecular modeling. Three functional monomers with high (2-vinylpyridine (MP17)) and intermediate (methacrylic acid (MP12) and acrylamide (MP5)) energies of binding to the template (HXZ) were selected for preparation of the MIPs, in order to conduct comparative studies and validate the theoretical data. For sensor construction, carbon pastes were modified with each MIP or NIP (non-imprinted polymer), and HXZ determination was performed using differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV). All parameters affecting the sensor response were optimized. In HCl at pH 2.5, the sensor prepared with MP17 (5% w/w in the paste) showed a dynamic linear range between 1.9×10−11 and 1.1×10−10molL−1, and a detection limit of 2.6×10−12molL−1, under the following conditions: accumulation time of 200s at a potential of −0.5V, scan rate of 50mVs−1, pulse amplitude of 60mV, and pulse width of 50ms. The sensor was selective in the presence of other similar compounds, and was successfully applied to the analysis of HXZ in river water samples.

ProMCC: An all-in-one tool for trace metal complexation studies

A new windows-based, user friendly program (ProMCC) for (i) the determination of metal complexation parameters (ligand concentration (L) and conditional stability constants (K′)) and for (ii) theoretical simulation of metal complexometric titration, assuming discrete ligand model, is developed. Although primarily intended for treatment of experimental data obtained either by anodic stripping voltammetry (ASV) or competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-AdCSV), it could manage titration-type data of other techniques (e.g. ISE, sorption isotherm). Currently, the program is capable to process (fit and/or simulate) titration data up to three discrete ligand classes. Procedure for adjustment of “true” analytical sensitivity incorporated in ProMCC was found to provide reasonably good estimates of sensitivity either for one-ligand or two-ligand system. The particular feature of ProMCC is that it incorporates two complementary fitting methodologies: (1) a non-linear fitting of conventional linearized transformations (e.g. Ružić/Van Den Berg, Langmuir/Gerringa) and (2) a “complete complexation model” — a matrix based optimization of mass balance equations. Comparison test of different non-linear fitting modes and titration types revealed that a slight underestimation of ligand concentration and overestimation of conditional stability constant may occur if titration is performed in logarithmic mode, mainly due to unfavorable noise distribution. An advantage of implemented “complete complexation model” fitting mode is that it allows simultaneous analysis of titrations obtained at multiple detection windows as unified dataset (multi-detection window approach), providing complexation parameters for up to three ligand classes. A new alternative “RAL-approach” in analyzing complexometric titrations obtained at multiple detection windows for copper–salicylaldoxime (Cu–SA) system is suggested. It assumes that the analytical sensitivity is changing along the titration curve respecting the true speciation of Cu–SA in sample. An adapted empirical equation for calculation of relative intensity (RAL) is proposed. Flexibility in adjusting parameters, immediate graphical feedback and visualizations make ProMCC handy for treatment of large set of experimental data, and a tool for research in refinement of the methods of metal complexing capacity determination which is continuously improving.

The relevance of ligand exchange kinetics in the measurement of iron speciation by CLE–AdCSV in seawater

CLE–AdCSV (competitive ligand exchange–adsorptive cathodic stripping voltammetry) has proved to be a decisive technique in recognising the key role that organic matter plays in modulating the biogeochemical cycle of iron in aquatic ecosystems. As the method requires equilibrium among all the constituents of the solution before measurements are taken, accurate knowledge of the kinetics of the undergoing ligand exchange is essential. The kinetics of the process has been most frequently described in terms of a dissociative (or Eigen–Wilkins) mechanism, with some authors even claiming that, under such approach, iron complexes would dissociate during CLE so slowly that the method would be invalidated. The complexity of the processes—largely exceeding the simple mechanistic description of the Eigen–Wilkins mechanism—is discussed on the basis of a broad overview of possible reaction routes. Evidence of the role of matrix components of natural waters is presented and the impossibility of exporting kinetic constants to systems characterised by different molecular mechanics, mostly ignored in previous studies, is highlighted. Experimental evidence obtained from various methodological approaches allows inferring the range of CLE equilibration times to be applied in CLE–AdCSV measurements and further proves that the Eigen–Wilkins mechanism is just one of the many reaction routes applicable in natural waters. Studying iron CLE mechanisms for proposed competing ligands before designing any experiment using CLE–AdCSV is recommended.

Application of Nitrilotriacetic Acid Modified Gold Electrode for Determination of Lead in Natural Waters with Differential Pulse Adsorptive Cathodic Stripping Voltammetry

Application of Nitrilotriacetic Acid Modified Gold Electrode for Determination of Lead in Natural Waters with Differential Pulse Adsorptive Cathodic Stripping Voltammetry

Dissolved copper speciation in the Tasman Sea, SW Pacific Ocean

The speciation of copper (Cu) in seawater is dominated by organic complexation but the sources, distribution and nature of these natural organic ligands remain unclear. The spatial distribution and character of organic copper binding ligands at two sites in the Tasman Sea were investigated using competitive ligand exchange adsorptive cathodic stripping voltammetry, utilising salicylaldoxime as the competing ligand. The first station was located in the oligotrophic north Tasman Sea and was contrasted with a second, mesotrophic, station in the south of the region where sampling coincided with a coccolithophore bloom. The northern P1 site (0–3000m) was characterised by detection of a single, strong, class of ligand with a uniformly distributed conditional stability constant (log K′CuL=12.97±0.26). At the two shallowest depths of the southern P3 site (13 and 28m), two ligands were detected. A single, stronger, ligand was detected at all other depths for this site. Below 120m, conditional stability constants at the southern P3 site (0–3500m) were uniformly distributed (log K′CuL=13.32±0.21). At both stations, ligand concentrations usually exceeded the total dissolved Cu concentration and mirrored the bio-intermediate Cu profile at depth. Dissolved Cu was more than 99% complexed by organic ligands at all depths except one, when dissolved Cu concentration exceeds the dissolve ligand concentration. The variability in ligand concentrations was greatest in the top 0–50m at the northern P1 site and 0–80m at the southern site. Based on a combination of phototrophic cell counts and biomarker pigment concentrations, the source of organic Cu-binding ligands in the north Tasman Sea is thought to be from cyanobacterial production, namely Synechococcus spp which dominates in the region. The detection of two organic Cu binding ligand classes at the southern P3 station indicates a more complex Cu-binding ligand pool in the surface waters. At this site, the ligands are likely sourced from cyanobacteria and eukaryotes, namely coccolithophores. At the northern P1 station only, a relationship between the proportion of unbound ligand available and the dissolved oxygen concentration was obtained. Given the simpler ligand pool dynamics of the northern station relative to the south, this relationship may reveal that complexation of organic Cu-binding ligands is important to prevent or slow ligand degradation in the deep sea.

Adsorptive Cathodic Stripping Voltammetric Determination of Uranium(VI) in Presence of N‐Phenylanthranilic Acid

AbstractN‐Phenylanthranilic acid was used as a complexing agent for determination of uranium(VI) by adsorptive cathodic stripping voltammetry. Under the optimal experimental conditions of the experimental parameters, the peak current was proportional to the concentration of U(VI) in the range 0.75–30 ng mL−1 and the detection limit was 0.036 ng mL−1. The influence of possible interferences was investigated. The method was applied for determination of uranium in waste water from uranium conversion facility and natural water samples. Application of the method for simultaneous determination of U(VI) and Cu(II) showed that these ions could be simultaneously determined in a single scan at relatively wide concentration range.

Distinct pools of dissolved iron‐binding ligands in the surface and benthic boundary layer of the California Current

Organic dissolved iron (dFe)—binding ligands were measured by competitive ligand exchange—adsorptive cathodic stripping voltammetry (CLE‐ACSV) at multiple analytical windows (side reaction coefficient of salicylaldoxime, αFe(SA)2 = 30, 60 and 100) in surface and benthic boundary layer (BBL) samples along the central California coast during spring and summer. The weakest ligands were detected in the BBL at the lowest analytical window with average log KcondFeL,Fe' = 10.2 ± 0.4 in the summer and 10.8 ± 0.2 in the spring. Between 3% and 18% of the dFe complexation in the BBL was accounted for by HS, which were measured separately in samples by ACSV and may indicate a source of dFe‐binding ligands from San Francisco Bay. The strongest ligands were found in nearshore spring surface waters at the highest analytical window with average log KcondFeL,Fe' = 11.9 ± 0.3, and the concentrations of these ligands declined rapidly offshore. The ligand pools in the surface and BBL waters were distinct from each other based on principal components analysis, with variances in the BBL ligand pool explained by sample location, and variance in surface waters explained by water mass. The use of multiple analytical window analysis elucidated several distinct iron‐binding ligand pools, each with unique distributions in the central California Current system.

EVALUATION OF ALUMINUM LABILITY IN YERBA MATE INFUSIONS BY ADSORPTIVE CATHODIC STRIPPING VOLTAMMETRY

Infusions of yerba mate obtained at different stages of industrialization were evaluated to determine the bioavailable fraction of Al. Adsorptive Cathodic Stripping Voltammetry using DASA (complexing agent) was applied to determine the labile fraction of Al at pH 5.0 and pH 8.0 for the total fraction of dissolved Al. The results indicate that on average 60% of Al is complexed with organic compounds, minimizing their bioavailability; however, the labile fraction exceeds by up to 4 times the maximum weekly intake recommended by the World Health Organization.

Determination of Losartan in tablet dosage form and some biological body fluids via copmlexation with Cu (II) using Cathodic Adsorptive Stripping Voltammetry

Determination of Losartan in tablet dosage form and some biological body fluids via copmlexation with Cu (II) using Cathodic Adsorptive Stripping Voltammetry

Electrochemical Reduction and Stripping Voltammetric Determination of the Anti-Glaucoma Drug Levobunolol HCl in Formulation and Human Serum at the Mercury Electrode

Levobunolol HCl is a potent non-selective s-adrenoceptor blocking agent used for the topical treatment of increased intraocular pressure in patients with chronic open angle glaucoma or ocular hypertension. Precise, rapid and extraction-free square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV) method has been described for trace quantitation of levobunolol HCl in bulk form, commercial formulation (ophthalmologic drops) and human serum. Limits of quantification (LOQ) of 1.0 × 10-10 mol L-1 (in bulk form) and 2.5 × 10-10 mol L-1 levobunolol HCl (in spiked human serum) were achieved by the described method. Insignificant interferences from excipients associated with formulation of levobunolol HCl and from some common metal ions, co-administrated drugs, some other s-blocker agents and its metabolite dihydrolevobunolol that are likely to be present in the biological fluids were obtained. The described SW-AdCSV method is sensitive enough to assay the drug in human serum compared to most of the reported methods.

Lead determination in canned food by square-wave adsorptive cathodic stripping voltammetry

A sensitive and rapid method to analyse Pb(II) in canned fish samples was developed using square-wave adsorptive cathodic stripping voltammetry based on the adsorptive accumulation of 8-hydroxyquinoline complexes of Pb(II) onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan with square wave pulse modulation. The optimum conditions were found to be 0.1 M CH3COONH4 as a supporting electrolyte, pH 7.5, 8-hydroxyquinoline concentration of 15 µM, accumulation potential 0.70 V (versus Ag/AgCl), accumulation time 120 s, scan rate 0.3 V/s, and pulse amplitude 20 mV. Under the optimum conditions a linear calibration graph was obtained in the concentration range of 0.5-90.0 µg/l with correlation coefficient 0.9973, a limit of detection of 0.108 µg/l, and a limit of quantification of 0.360 µg/l. The recovery values were obtained in the range 93.7-95.1%. The relative standard deviations (n = 10) at lead concentration 5.0 µg/l was 2%. The method was successfully applied to the determination of lead content in canned fish samples. The concentration of Pb(II) in canned fish samples (wet weight) was found to be in the range of 0.121-0.285 µg/g, which is lower than the limit (1.00 µg/g) issued by the Ministry of Public Health of Thailand.

Evidence of Increased Anthropogenic Emissions of Platinum in Coastal Systems from Time-Series Analysis of Mussels Samples (1991-2011)

Evidence of Increased Anthropogenic Emissions of Platinum in Coastal Systems from Time-Series Analysis of Mussels Samples (1991-2011)

Determination of Trace Antimony by Square-Wave Adsorptive Cathodic Stripping Voltammetry at an Ex Situ Prepared Bismuth Film Electrode

A square-wave adsorptive cathodic stripping voltammetric protocol to determine trace antimony(III) in the presence of gallic acid (GA) at an ex situ prepared bismuth film electrode (BiFE) has been investigated. A well-defined and sensitive stripping peak of the Sb(III)-gallic acid complex was observed at −0.53 V (vs. SCE) in a 0.1M acetate buffer solution (pH 4.8) at a deposition potential of −0.38 V (120 s). The experimental variables as well as potential interferences were studied. Compared with the ex situ mercury film electrode (MFE), the ex situ prepared BiFE displayed a better electroanalytical performance for the determination of antimony(III). Under the optimized conditions, the linear range was obtained between 2–25 μg/L, the limit of detection for antimony(III) was 60 ng/L and the relative standard deviation was 3.37% at the 10 μg/L level (n = 10). This method was applied to determine trace amounts of antimony in several environmental samples with the satisfactory results.

Adsorptive Cathodic Stripping Voltammetric Determination of Ciprofloxacin in Bulk Powder, Pharmaceutical Dosage Forms and Urine

Purpose: To investigate the electro-reduction behaviour and determination of ciprofloxacin using a hanging mercury drop electrode.Methods: Cyclic voltammograms of ciprofloxacin recorded in Britton – Robinson buffers pH 2 – 5 exhibit a single irreversible cathodic peak. The dependence of the peak current and peak potential values on buffer (nature, pH and concentration) and accumulation conditions (time and potential) were examined and used for the quantitative analysis of ciprofloxacin in dosage forms and urine. Acetate buffer (0.08 M, pH 3.6) was selected as a supporting electrolyte for quantitative purposes by differential pulse and square wave adsorptive cathodic stripping voltammetry.Results: A reduction wave was seen in the range of – 1.3 to – 1.5 V. These techniques were successfully validated as per ICH guidelines and comparable to US Pharmacopoeia HPLC method. The techniques was applied to the determination of ciprofloxacin in pharmaceutical formulations (i.e. precision (RSD &lt; 1%) and accuracy (99 – 101%)), and was further extended to determine ciprofloxacin in spiked human urine with no matrix effect (i.e. LLOQ 0.01 μg/ml, precision (RSD &lt; 15%) and accuracy (85 – 115%)).Conclusion: Validated adsorptive cathodic stripping voltammetric technique can be recommended for use in quality control and pharmacokinetics studies.Keywords: Ciprofloxacin, Mercury electrode, Adsorptive cathodic stripping voltammetry, Pharmaceutical formulation, Urine.

Improved Bi Film Wrapped Single Walled Carbon Nanotubes for Ultrasensitive Electrochemical Detection of Trace Cr(VI).

We report here the successful fabrication of an improved Bi film wrapped single walled carbon nanotubes modified glassy carbon electrode (Bi/SWNTs/GCE) as a highly sensitive platform for ultratrace Cr(VI) detection through catalytic adsorptive cathodic stripping voltammetry (AdCSV). The introduction of negatively charged SWNTs extraordinarily decreased the size of Bi particles to nanoscale due to electrostatic interaction which made Bi(III) cations easily attracted onto the surface of SWNTs in good order, leading to higher quality of Bi film deposition. The obtained Bi/SWNTs composite was well characterized with electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), the static water contact angle and the voltammetric measurements. The results demonstrates the improvements in the quality of Bi film deposited on the surface of SWNTs such as faster speed of electron transfer, more uniform and smoother morphology, better hydrophilicity and higher stripping signal. Using diethylene triaminepentaacetic acid (DTPA) as complexing ligand, the fabricated electrode displays a well-defined and highly sensitive peak for the reduction of Cr(III)-DTPA complex at -1.06 V (vs. Ag/AgCl) with a linear concentration range of 0-25 nM and a fairly low detection limit of 0.036 nM. No interference was found in the presence of coexisting ions, and good recoveries were achieved for the analysis of a river sample. In comparison to previous approaches using Bi film modified GCE, the newly designed electrode exhibits better reproducibility and repeatability towards aqueous detection of trace Cr(VI) and appears to be very promising as the basis of a highly sensitive and selective voltammetric procedure for Cr(VI) detection at trace level in real samples.