Stripping Response Research Articles

The Silver Amalgam Film Electrode in Adsorptive Stripping Voltammetric Determination of Palladium(II) as Its Dimethyldioxime Complex

AbstractThe paper features a description of a sensitive adsorptive stripping voltammetric protocol for the palladium(II) determination in the presence of dimethylglyoxime (DMG) at an amalgam film electrode (Hg(Ag)FE) of prolonged analytical applicability. The procedure is based on the adsorptive preconcentration of the Pd(II)‐dimethylglyoxime complex onto the (Hg(Ag)FE) at −0.45 V, followed by a negatively going square‐wave voltammetric scan. Factors affecting the stripping performance, such as the composition of the supporting electrolyte, including different ligands, DMG concentration, pH, potential and time of preconcentration, and SW frequency have been investigated and optimized. The optimized procedure yields favorable and highly stable stripping responses with good precision (RSD=3% for a Pd concentration of 2 μg/L), low detection limit (0.15 μg/L Pd(II)), and good linearity (from 1.0 μg/L up to 50 μg/L, R2=0.998) with a deposition time of 60 s. Possible interferences from coexisting ions and surface active substances were studied.

Cathodic adsorptive stripping voltammetry of drotaverine hydrochloride and its determination in tablets and human urine by differential pulse voltammetry

The stripping voltammetric behaviour of drotaverine hydrochloride (DvCl) was studied using a hanging mercury drop electrode (HMDE). The adsorptive stripping response has been evaluated with respect to pH, accumulation time, accumulation potential, scan rate and other variables. Differential pulse DP mode; over the potential range − 400 to − 1200 mV, is used in the presence of 0.04 M Britton–Robinson buffer pH 2. Cyclic voltammetric study indicates that the reduction process is irreversible and controlled by adsorption. The response of DP technique is linear over the concentration range 21.70–257.34 ng/ml. Limit of detection and limit of quantification were 3.15 and 10.50 ng/ml, respectively. The proposed method was successfully applied for the determination of the drug in commercial tablets and spiked human urine samples.

Sensitive determination of adenine on poly(amidosulfonic acid)-modified glassy carbon electrode

A novel and reliable direct electrochemical method was established for the detection of adenine, based on the differential pulse anodic stripping response at a poly(amidosulfonic acid) (poly-ASA)-modified glassy carbon electrode (GCE) fabricated by electropolymerization. The characterization of electrochemically synthesized poly-ASA film was investigated by atomic force microscopy, electrochemical impedance spectroscopy, and voltammetric methods. This poly-ASA-modified GCE could greatly enhance the detection sensitivity of adenine. At optimum conditions, the anodic peak exhibits a good linear concentration dependence in the range from 3.0 × 10−8 to 1.0 × 10−6 M (r = 0.9994). The detection limit is 8.0 × 10−9 M (S/N = 3). The proposed method could be used to determinate the adenine in tablets of vitamin B4 with satisfactory results.

Anodic stripping voltammetric measurement of trace heavy metals at antimony film carbon paste electrode

The antimony film carbon paste electrode (SbF-CPE) was prepared in situ on the carbon paste substrate electrode as a “mercury-free” electrochemical sensor. Its aptitude for measuring some selected trace heavy metals has been demonstrated in combination with square-wave anodic stripping voltammetry in non-deaerated model solutions of 0.01 M hydrochloric acid with pH 2. Some important operational parameters, such as deposition potential, deposition time, and concentration of antimony ions were optimized, and the electroanalytical performance of the SbF-CPE was critically compared with both bismuth film carbon paste electrode (BiF-CPE) and mercury film carbon paste electrode (MF-CPE) using Cd(II) and Pb(II) as test metal ions. In comparison with BiF-CPE and MF-CPE, the SbF-CPE exhibited superior electroanalytical performance in more acidic medium (pH 2) associated with favorably low hydrogen evolution, improved stripping response for Cd(II), and moreover, stripping signals corresponding to Cd(II) and Pb(II) at the SbF-CPE were slightly narrower than those observed at bismuth and mercury counterparts. In addition, the comparison with antimony film electrode prepared at the glassy carbon substrate electrode displayed higher stripping current response recorded at the SbF-CPE. The newly developed sensor revealed highly linear behavior in the examined concentration range from 5 to 50 μg L −1, with limits of detection (3 σ) of 0.8 μg L −1 for Cd(II), and 0.2 μg L −1 for Pb(II) in connection with 120 s deposition step, offering good reproducibility of ±3.8% for Cd(II), and ±1.2% for Pb(II) (30 μg L −1, n = 10). Preliminary experiments disclosed that SbF-CPE and MF-CPE exhibit comparable performance for measuring trace concentration levels of Zn(II) in acidic medium with pH 2, whereas its detection with BiF-CPE was practically impossible. Finally, the practical applicability of SbF-CPE was demonstrated via measuring Cd(II) and Pb(II) in a real water sample.

An electrochemical sensor based on the reduction of screen-printed bismuth oxide for the determination of trace lead and cadmium

Abstract By combining a screen-printing method with an electrochemical reduction process, an electrochemical sensor to measure trace amounts of lead and cadmium was newly designed, fabricated and characterized. Bismuth oxide was printed on the electrode surface, and it was then electrochemically reduced to bismuth at a potential of −1.2 V in 0.1 M KOH. The stability of the fabricated Bi electrode was evaluated by repetitive measurements, and the interference of copper ions was investigated. The concentrations of lead and cadmium were also measured by square wave anodic stripping voltammetry. Bismuth film, reduced from screen-printed bismuth oxide, showed a well-defined and reproducible stripping response. The electrode exhibited linear behavior in the range of 20–100 μg/L of lead and cadmium (correlation coefficients: 0.999 and 0.998, respectively) with detection limits of 2.3 μg/L for lead and 1.5 μg/L for cadmium. The applicability of the electrode to real samples was evaluated and the results were in good agreement with ICP-MS analysis. These results facilitate the widespread use of screen-printing techniques for the preparation of electrochemical sensors.

Sensitive and stable monitoring of lead and cadmium in seawater using screen-printed electrode and electrochemical stripping analysis

Sensitive and stable monitoring of heavy metals in seawater using screen-printed electrodes (SPE) is presented. The analytical performance of SPE coupled with square wave anodic stripping voltammetry (SWASV) for the simultaneous determination of Pb and Cd in seawater samples, in the low μg L −1 range, is evaluated. The stripping response for the heavy metals following 2 min deposition was linear over the concentration range examined (10–2000 μg L −1) with detection limits of 1.8 and 2.9 μg L −1 for Pb and Cd, respectively. The accuracy of the method was validated by analyzing metal contents in different spiked seawater samples and comparing these results to those obtained with the well-established anodic stripping voltammetry using the hanging mercury drop electrode. Moreover, a certified reference material was also used and the results obtained were satisfactory.

Determination of azinphos-ethyl insecticide by adsorptive stripping voltammetry on the hanging mercury-drop electrode

The electrochemical characteristics of azinphos-ethyl (APE) have been determined by means of electrochemical techniques such as cyclic voltammetry (CV) and adsorptive stripping voltammetry (ASV) at a hanging mercury drop electrode (HMDE) over a wide range of pH from 2.0 to 8.0. The cyclic voltammograms demonstrate the adsorption of this compound at the mercury electrode. A systematic study of the various operational parameters that affect the stripping response was carried out by differential pulse voltammetry (DPV). With a preconcentration potential of −0.6 V and a 60 s preconcentration time, the limit of detection was 5.42 × 10−9 M, and the relative standard deviation (n = 5) was 2.7 % at concentration level of 6.45 × 10−7 M APE. The degree of interference from diverse ions and some other pesticides on the differential pulse stripping signal for APE was evaluated. Finally, the method was applied to the determination of APM in spiked soil, tap water, and treated wastewater.

Adsorptive Stripping Voltammetric Determination of Irbesartan in Bulk and Pharmaceutical Products

Adsorptive stripping Voltammetric determination of irbesartan using a hanging mercury drop electrode (HMDE) is described. The method is based on adsorptive accumulation of the species at the HMDE, followed by a first-harmonic alternating current (AC) stripping sweep at pH 6. The behavior of the adsorptive stripping response was studied under various experimental conditions, e.g., type of supporting electrolyte, pH, accumulation time, scan rate, and mode of sweep. In Britton-Robinson buffer solution, a quasi-reversible reduction process involving transfer of two electrons and two protons takes place. The response was linear over the concentration range of 0.16–1.60 µg/ml with regression coefficient 0.997 and detection limit 0.11 µg/ml. The average of determinations of the cited compound in oral dosages with its standard deviation was 99.39 ± 4.33 %.The result obtained by the proposed method was compared with that obtained by the uv-spectrophotometric technique. Furthermore, the proposed method was also successfully applied as a stability-indicating method.

Nafion ®/2,2′-bipyridyl-modified bismuth film electrode for anodic stripping voltammetry

This paper describes the fabrication, characterisation and the application of a Nafion/2,2′-bipyridyl/bismuth composite film-coated glassy carbon electrode (NC(Bpy)BiFE) for the anodic stripping voltammetric determination of trace metal ions (Zn 2+, Cd 2+ and Pb 2+). The NC(Bpy)BiFE electrode is prepared by first applying a 2.5 mm 3 drop of a coating solution containing 0.5 wt% Nafion and 0.1% (w/v) 2,2′-bipyridil (Bpy) onto the surface of a glassy carbon electrode, while the Bi film was plated in situ simultaneously with the target metal ions at −1.4 V. The main advantage of the polymer coated bismuth film electrode is that the sensitivity of the stripping responses is increased considerably due to the incorporation of the neutral chelating agent of 2,2′-bipyridyl (Bpy) in the Nafion film, while the Nafion coating improved the mechanical stability of the bismuth film and its resistance to the interference of surfactants. The key experimental parameters relevant to both the electrode fabrication and the voltammetric measurement were optimized on the basis of the stripping signals. With a 2 min deposition time in the presence of oxygen, linear calibration curves were obtained in a wide concentration range (about 2–0.001 μM) with detection limits of 8.6 nM (0.56 μg dm −3) for Zn 2+, 1.1 nM (0.12 μg dm −3) for Cd 2+ and 0.37 nM (0.077 μg dm −3) for Pb 2+. For nine successive preconcentration/determination/electrode renewal experiments the standard deviations were between 3 and 5% at 1.2 μM for zinc and 0.3–0.3 μM concentration level for lead and cadmium, respectively, and the method exhibited excellent selectivity in the presence of the excess of several potential interfering metal ions. The analytical utility of the stripping voltammetric method elaborated was tested in the assay of heavy metals in some real samples and the method was validated by ICP-MS technique.

Nanomolar detection of rutin based on adsorptive stripping analysis at single-sided heated graphite cylindrical electrodes with direct current heating

Abstract A single-sided heated graphite cylindrical electrode (ss-HGCE) was designed. Compared to previous alternative current (AC) heating, much simpler and cheaper direct current (DC) heating supplier was adopted for the first time to perform adsorptive accumulation of rutin at ss-HGCE at elevated electrode temperature. This offers great promise for low cost, miniaturization and high compatibility with portability. The square wave voltammetry (SWV) stripping peak current was enhanced with increasing the electrode temperature only during preconcentration step. This enhancement was contributed to the forced thermal convection induced by heating the electrode rather than the bulk solution, which is able to improve mass transfer and facilitate adsorption hence enhance stripping response. A detection limit of 1.0 × 10−9 M (S/N = 3) could be obtained at an electrode temperature of 48 °C during 5 min accumulation, one magnitude lower than that at 28 °C (room temperature). This is the lowest value at carbon-based electrodes for rutin determination as we know. Such novel method was also successfully used to determine rutin in pharmaceutical tablets.

Simultaneous measurement of Pb, Cd and Zn using differential pulse anodic stripping voltammetry at a bismuth/poly(p-aminobenzene sulfonic acid) film electrode

Abstract A novel sensor was developed for simultaneous detection of Pb, Cd and Zn, based on the differential pulse anodic stripping response at a bismuth/poly(p-aminobenzene sulfonic acid) (Bi/poly(p-ABSA)) film electrode. This electrode was generated in situ by depositing simultaneously bismuth and the metals by reduction at −1.40 V on the poly(p-ABSA) modified electrode. Compared with the bismuth film electrode, the Bi/poly(p-ABSA) film electrode can yield a larger stripping signal for Pb, Cd and Zn. Under the optimum conditions, a linear response was observed for Cd and Zn in the range from 1.00 to 110.00 μg L−1 and for Pb in the range from 1.00 to 130.00 μg L−1. The detection limits of Pb(II), Cd(II) and Zn(II) were 0.80, 0.63 and 0.62 μg L−1, respectively. Finally this sensor had been applied to the simultaneous determination of Pb(II), Cd(II) and Zn(II) in river water samples and the results were quite corresponding to the value obtained by atomic absorption spectrometry.

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.

Carbon Paste Electrode Plated with Lead Film. Voltammetric Characteristics and Application in Adsorptive Stripping Voltammetry

AbstractA lead film plated in situ at a carbon paste support was tested as a novel, potential electrode for adsorptive stripping voltammetric determination of cobalt traces in an ammonia buffer solution. To show the practical applicability of the new electrode, a catalytic adsorptive Co system in a supporting electrolyte containing 0.1 M ammonia buffer, 5×10−4 M nioxime and 0.25 M nitrite was selected and investigated as a model solution. Pb and Co ions were simultaneously accumulated in situ on the electrode surface: Pb ions electrochemically at −1.3 V) and then at −0.75 V, at which potential the Co(II)‐nioximate complex was also pre‐concentrated via adsorption. Instrumental parameters, such as the time of nucleation and formation of Pb film deposits, the time of accumulation of the Co‐nioxime complex at the PbF/CPE, and the procedures of electrode regeneration, were optimized to obtain good reproducibility and sensitivity of the Co response. The optimized procedure yields favorable and highly stable stripping responses with good precision (RSD=3% for a 5×10−8 M Co) and good linearity (up to 5×10−7 M, coefficient of determination, R=0.996). The detection limit was 4×10−10 M Co (0.023 μg L−1) for an accumulation time of 120 s. The method enables the determination of Co in the presence of high excesses of Ni or Zn. The voltammetric data were correlated with the structural characterization by scanning electron microscopy (SEM) and X‐ray fluorescence spectroscopy (XRF).

Application of multiwalled carbon nanotubes for solid-phase extraction of organophosphate pesticide

Multiwalled carbon nanotube (MWCNT) was developed as a new sorbent for solid-phase extraction (SPE) of organophosphate (OP) pesticides. A combination of SPE with square-wave voltammetric (SWV) analysis resulted in a fast, sensitive, and selective electrochemical method for determination of OP pesticide using methyl parathion (MP) as a representative. Because of the strong affinity of MWCNT for phosphoric group, nitroaromatic OP compounds can strongly bind to the MWCNT surface. The macroporosity and heterogeneity of MWCNT allow extracting a large amount of MP less than 5 min. The stripping response was highly linear over the MP range of 0.05–2.0 μg/mL, with a detection limit of 0.005 μg/mL. The determination of MP in garlic samples showed acceptable accuracy. The fast extraction ability of MWCNT makes it promising sorbent for various solid-phase extractions.

Bismuth film electrodes for heavy metals determination

Bismuth film electrodes (BiFEs) have a potential to replace toxic mercury used most frequently for determination of heavy metals (Cd, Pb, Zn) by anodic stripping voltammetry. We prepared a graphite disc electrode (0.5 mm in diameter) from a pencil-lead rod and developed a nitrogen doped diamond-like carbon (NDLC) microelectrode array consisting of 50,625 microdiscs with 3 μm in diameter and interelectrode distances of 20 μm on a highly conductive silicon substrate as a support for BiFEs. The disc graphite BiFE was used for simultaneous determination of Pb(II), Cd(II) and Zn(II) by square wave voltammetry (SWV) in an aqueous solution. We found the optimum bismuth-to-metal concentration ratio in the solution to be 20. The dependence of the stripping responses on the concentration of target metals was linear in the range from 1 × 10−8 to 1.2 × 10−7 mol/L. Detection limits 2.4 × 10−9 mol/L for Pb(II), 2.9 × 10−9 mol/L for Cd(II) and 1.2 × 10−8 mol/L for Zn(II) were estimated. A bismuth-plated NDLC microelectrode array was used for Pb(II) determination by differential pulse voltammetry (DPV) in an aqueous solution. We found that the stripping current for bismuth-plated NDLC array was linear in the concentration range of Pb(II) from 2 × 10−8 to 1.2 × 10−7 mol/L. The detection limit 2.2 × 10−8 mol/L was estimated from a calibration plot.

Adsorptive Stripping Analysis of Riboflavin at Electrically Heated Graphite Cylindrical Electrodes

Electrically heated graphite cylindrical electrodes (HGCEs) made from ground pencil leads have been used to perform adsorptive stripping square wave voltammetry (SWV) measurements of trace riboflavin (RF). The SWV stripping peak current was significantly enhanced with increasing the electrode temperature only during preconcentration step. This enhancement was due to the forced thermal convection induced by heating the electrode rather than the bulk solution. It is the thermal convection that has the ability to improve mass transfer and facilitate adsorption thus enhance stripping responses. It was found that the detection limit of 5×10−9 M (S/N=3) could be obtained at an electrode temperature of 72 °C during 5 min accumulation, more than one magnitude lower than that at 22 °C (room temperature), the sensitivity could be enhanced ca. eight or four folds for two different RF concentration ranges. So it is possible to develop a new highly sensitive method to determine riboflavin at HGCEs. Such HGCEs were also successfully used to determine RF in multivitamin tablets.

Validated Polarographic Methods for the Determination of Certain Antibacterial Drugs

Two simple, precise, inexpensive and sensitive voltammetric methods for the determination of lomefloxacin (LFX), sparfloxacin hydrochloride (SFX), gatifloxacin (GFX), and moxifloxacin (MFX) were developed. The present methods were first used to explore the adsorption behavior of the four investigated antibacterial agents at a hanging mercury dropping electrode (HMDE), by a direct method and secondly by a modification via their complexation with PdCl(2). For the direct method, drugs were accumulated on HMDE, and a well-defined reduction peak was obtained in Britton-Robinson buffer of pH 7 for LFX and SFX, and pH 6 for GFX and MFX. The adsorptive stripping response was evaluated as a function of some variables such as the scan rate, pH, accumulation time and potential. For the modified method, the adsorptive behavior of Pd(II)-4-quinolone complexes at the HMDE developed a strippining voltammetry peak at a more negative potential than that of the free Pd(II) ions (-1.05 V). The limits of detection (LOD) were 2 x 10(-8) M, while the limits of quantification (LOQ) were 6 x 10(-8) M for the investigated drugs. The methods were applied to the determination of LFX, SFX, GFX, and MFX in biological samples and pharmaceutical preparations, and also compared with the official reference methods. Complete validation of the proposed methods was also done.

Complexing capacity profiles of naturally occurring ligands in Tempranillo wines for Cu and Zn: An electroanalytical approach for cupric casse

Complexing capacity of naturally occurring ligands in Vitis vinifera (Tempranillo variety) wines has been studied with respect to two target metals (Cu and Zn) by differential pulse anodic stripping voltammetry (DPASV). Eight commercial wines of two certified brands of origin (CBO) and a young wine along its vinification process were monitored. Conditional stability constants and total complexing ligand(s) concentration(s) have been calculated for both metals. Discussion of the particular electrochemical responses for Cu and Zn for all samples is presented. A follow-up of the Cu stripping response allowed differentiating a commercial wine from one under processing related to the cupric casse phenomenon. Interaction of Cu with two molecular forms of cyanidin has been theoretically modeled at natural wine pH.

Differential Pulse Adsorptive Stripping Voltammetric Determination of Chlorpyrifos at a Sepiolite Modified Carbon Paste Electrode

An adsorptive stripping voltammetric (AdSV) method for the determination of organophosphorus insecticide chlorpyrifos at a bare carbon paste electrode (CPE) and clay modified carbon paste electrode (CMCPE) was developed. A systematic study of various experimental conditions, such as the pH, accumulation variables and composition of a modifier on the adsorptive stripping response, were examined by using differential pulse voltammetry. A significant improvement was observed in the sensitivity by using the present method with CMCPE. When CMCPE was used, a linear response was obtained over the concentration range 0.0001–2.0 ppm with lower detection limit of 0.00008 ppm, at an accumulation time of 80 s. The interference from other herbicides and ions on the stripping signal of the compound was also evaluated. The described method was applied to estimate the chlorpyrifos in environmental samples.

Utilising gallium for enhanced electrochemical copper analysis at the bismuth film electrode

A sensitive anodic stripping voltammetric procedure at the bismuth film electrode (BFE) for trace analysis of copper (II) in the presence of gallium is presented. The new protocol circumvents the problems of overlapping stripping signals between copper and bismuth that previously hampered the analysis of copper at the BFE. The results illustrate that the addition of gallium not only improves the reproducibility of the bismuth stripping signal but also facilitates much improved resolution between the stripping signals of bismuth and copper. Investigations into the effect of gallium on the stripping response of copper and bismuth were studied showing a 4:1 gallium:copper mole ratio produces optimum signals from bismuth and copper indicating a possible stoichiometric relationship. Optimisation of other key variables including electrolyte composition, accumulation parameters and appropriate waveform settings were studied and optimised. The optimised procedures show a range of linear calibration plots (R2>0.994) ranging from 2 to 500μgL−1 and the relative standard deviation for a solution containing 100μgL−1 copper was 3.7% (n=10). Utilising an accumulation time of 300s the limit of detection was 1.4μgL−1(S/N=3). This technique was successfully applied to the analysis of copper in tap water representing the first successful copper determination in real samples using the BFE.