Determination of the Natural Dissolved Concentration of Zirconium in Seawater by Adsorptive Stripping Voltammetry

A voltammetric method was developed for zirconium determination as Zr(IV)‐cupferron‐oxalate‐diphenylguanidine complex based on adsorptive accumulation at the HMDE (E_peak=?0.95 V). The supporting electrolyte was a mixture of acetate/acetic acid (pH 4.6) and ammonium acetate (pH 5.7) solutions. E_ads=?0.6 V (vs. Ag/AgCl), t_ads=400 s, 10 mV s^?1 scan rate, and DP mode were the main parameters. The linear range was 0.033 to 3.3×10^?9 mol L^?1, and the LOD and LOQ (t_ads=400 s) were 0.77 and 1.6×10^?11 mol L^?1, respectively. The method was adequate for seawater samples, although not sufficiently sensitive for surface waters.     

Adsorptive anodic stripping voltammetry of zirconium(IV)-alizarin red S complex at a carbon paste electrode

A sensitive adsorptive anodic stripping procedure for the determination of trace zirconium at a carbon paste electrode (CPE) has been developed. The method is based on adsorptive accumulation of the Zr(IV)-alizarin red S(ARS) complex onto the surface of the CPE, followed by oxidation of adsorbed species. The optimal experimental conditions include the use of 0.10 mol · L⁻¹ ammonium acetate buffer (pH 4.3), ARS, an accumulation potential of 0.20 V (versus SCE), an accumulation time of 2 min, a scan rate of 200 mV · s⁻¹ and a second-order derivative linear scan mode. The oxidation peak for the complex appears at 0.69 V. The peak current is proportional to the concentration of Zr(IV) over the range of 1.0 × 10⁻⁹–2.0 × 10⁻⁷ mol · L⁻¹, and the detection limit is 3 × 10⁻¹⁰ mol · L⁻¹ for a 2 min adsorption time. The relative standard deviations (n = 8) for 5.0 × 10⁻⁸ and 5.0 × 10⁻⁹ mol · L⁻¹ Zr(IV) are 3.3 and 4.8%, respectively. The proposed method was applied to the determination of zirconium in ore samples with satisfactory results.     

Determination of Nanomolar Concentrations of Pb(II) Using Carbon Paste Electrode Modified with Zirconium Phosphated Amorphous Silica

A sensitive and selective method for the determination of Pb(II) with a zirconium phosphated silica gel (SiZrPH) modified carbon paste electrode has been developed. The measurements were carried out in three steps including an open circuit accumulation following by electrolysis of accumulated Pb(II) at the modified carbon paste electrode and differential pulse voltammetric determination. The analytical performance was evaluated with respect to the carbon paste composition, pH of solution at the accumulation step, pH and concentration of supporting electrolyte, electrolysis potential, accumulation time and electrolysis time. Two linear calibration graphs were obtained in the concentration ranges 2.5×10^?9 mol L^?1–5.0×10^?8 mol L^?1 and 5.0×10^?8 mol L^?1–5.0×10^?6 mol L^?1 with an accumulation time of 120 s. The detection limit was found to be 3.5×10^?10 mol L^?1. The effects of potential interfering ions were studied, and it was found that the proposed procedure is free from interferences of common interfering ions such as tin, thallium and etc. The developed method was applied to Pb(II) determination in a wastewater sample.     

Extraction and Spectrophotometric Determination of Zirconium(IV)

Abstract

A sensitive and selective method for the extraction and spectrophotometric determination of Zr(IV) with N-p-chlorophenyl-3,4-,5-trimethoxycinnamohydroxamic acid (PTCHA) has been developed. The binary complex of Zr(IV)-PTCHA is extracted from 2–6 M HCl into chloroform, having a maximum absorbance at 385 nm; molar absorptivity 2.1 × 10⁴ 1 mol^?1 cm^?1. A ternary complex with xylenol orange (Zr-PTCHA-XO) have been studied in chloroform-ethanol media, which absorbs at 540 nm; molar absorptivity 4.3 × 10⁴ 1 mol^?1 cm^?1. The present method is applied for the analysis of zirconium in standard samples.     

Determination of Zirconium and Vanadium in Natural Waters by Adsorptive Stripping Voltammetry in the Presence of Cupferron,Oxalic Acid and 1,3‐Diphenylguanidine

A sequential AdSV method based on the accumulation of Zr(IV) and V(V) as cupferron‐oxalic acid‐1,3‐diphenylguanidine (COD) complexes at the HMDE was used to determine traces of these metals in samples with different ionic strengths. DP mode, E_ads ?0.6 and ?0.2 V (vs. Ag/AgCl, 3 mol L^?1 KCl), t_ads 400 and 20 s and 10 and 60 mV s^?1 scan rates were used for Zr(IV) and V(V), respectively. E_peak were ?0.95 (Zr(IV)‐COD) and ?0.65 V(V(V)‐COD). The methodology was applied in samples of rivers, estuaries (in Germany and Brazil) and coastal and open seawater.     

Determination of Se(IV) in On‐Line System by Cathodic Stripping Voltammetry

A sensitive and selective on‐line voltammetric procedure for determination of traces of Se(IV) is presented. The pulsed potential accumulation was proposed for minimization of interferences of surface active substances and foreign ions. The calibration plot was linear from 1×10^?9 mol L^?1 to 4×10^?8 mol L^?1 for accumulation time of 180 s. The relative standard deviation was 6.1% (n=5) for a Se(IV) concentration of 1×10^?8 mol L^?1. The detection limit estimated from (3 σ) for an accumulation time of 180 s was about 4×10^?10 mol L^?1. The validation of the procedure proposed was made by a recovery tests for tap and river water samples.     

Simultaneous Determination of Dopamine and Ascorbic Acid Using the Nano‐Gold Self‐Assembled Glassy Carbon Electrode

Electrochemical behavior of dopamine (DA) was investigated at the gold nanoparticles self‐assembled glassy carbon electrode (GNP/LC/GCE), which was fabricated by self‐assembling gold nanoparticles on the surface of L ‐cysteine (LC) modified glassy carbon electrode (GCE) via successive cyclic voltammetry (CV). A pair of well‐defined redox peaks of DA on the GNP/LC/GCE was obtained at E_pa=0.197 V and E_pc=0.146 V, respectively. And the peak separation between DA and AA is about 0.2 V, which is enough for simultaneous determination of DA and AA. The peak currents of DA and AA were proportional with their concentrations in the range of 6.0×10^?8–8.5×10^?5 mol L^?1 and 1.0×10^?6–2.5×10^?3 mol L^?1, with the detection limit of 2.0×10^?8 mol L^?1 and 3.0×10^?7 mol L^?1 (S/N=3), respectively. The modified electrode exhibits an excellent reproducibility, sensibility and stability for simultaneous determination of DA and AA in human serum with satisfactory result.     

Voltammetric Determination of 3‐Nitrofluoranthene and 3‐Aminofluoranthene at Boron Doped Diamond Thin‐Film Electrode

The voltammetric behavior of 3‐nitrofluoranthene and 3‐aminofluoranthene was investigated in mixed methanol‐water solutions by differential pulse voltammetry (DPV) at boron doped diamond thin‐film electrode (BDDE). Optimum conditions have been found for determination of 3‐nitrofluoranthene in the concentration range of 2×10^?8–1×10^?6 mol L^?1, and for determination 3‐aminofluorathnene in the concentration range of 2×10^?7–1×10^?5 mol L^?1, respectively. Limits of determination were 3×10^?8 mol L^?1 (3‐nitrofluoranthene) and 2×10^?7 mol L^?1 (3‐aminofluoranthene).     

A Simple Approach to Simultaneous Electroanalytical Quantification of Acetaminophen and Tramadol Using a Boron‐doped Diamond Electrode in the Existence of Sodium Dodecyl Sulfate

The present work describes the individual, selective and simultaneous quantification of acetaminophen (ACP) and tramadol hydrochloride (TRA) using a modification‐free boron‐doped diamond (BDD) electrode. Cyclic voltammetric measurements revealed that the profile of the binary mixtures of ACP and TRA were manifested by two irreversible oxidation peaks at about +1.04 V (for ACP) and +1.61 V (for TRA) in Britton‐Robinson (BR) buffer pH 3.0. TRA oxidation peak was significantly improved in the presence of anionic surfactant, sodium dodecyl sulfate (SDS), while ACP signal did not change. By employing square‐wave stripping mode in BR buffer pH 3.0 containing 8×10^?4 mol L^?1 SDS after 30 s accumulation under open‐circuit voltage, the BDD electrode could be used for quantification of ACP and TRA simultaneously in the ranges 1.0–70 μg mL^?1 (6.6×10^?6–4.6×10^?4 mol L^?1) and 1.0–70 μg mL^?1 (3.3×10^?6–2.3×10^?4 mol L^?1), with detection limits of 0.11 μg mL^?1 (7.3×10^?7 mol L^?1) and 0.13 μg mL^?1 (4.3×10^?7 mol L^?1), respectively. The practical applicability of the proposed approach was tested for the individual and simultaneous quantification of ACP and/or TRA in the pharmaceutical dosage forms.     

Square‐Wave Voltammetric Determination of Paraquat at Carbon Paste Electrode Modified with Hydroxyapatite

The voltammetric behavior of paraquat was investigated at hydroxyapatite‐modified carbon paste electrode HAP‐CPE in K₂SO₄. A method was developed for the detection of the trace of this herbicide, based on their redox reaction. The reduction peaks of paraquat were observed around ?0.70 V and ?1.00 V (vs. SCE) in square‐wave voltammetry. Experimental conditions were optimized by varying the accumulation time, apatite loading and measuring solution pH. Calibration plots were linear under the optimized parameters over the herbicide's concentration range 8–200×10^?7 mol L^?1, with a detection and quantification limits about 1.5×10^?8 mol L^?1 and 6.4 10^?8 mol L^?1, respectively.     

Anodic stripping voltammetric determination of silver ion at a carbon paste electrode modified with carbon nanotubes

A carbon paste electrode (CPE) was modified with multi-wall carbon nanotubes and successfully applied to the determination of silver ion by differential pulse anodic stripping voltammetry. Compared to a conventional CPE, a remarkably improved peak current response and sensitivity is observed. The analytical procedure consisted of an open circuit accumulation step for 2?min in ?0.4?V, this followed by an anodic potential scan between +0.2 and?+?0.6?V to obtain the voltammetric peak. The oxidation peak current is proportional to the concentration of silver ion in the range from 1.0?×?10^?8 to 1.0?×?10^?5?mol?L^?1, with a detection limit of 1.8?×?10^?9?mol?L^?1 after an accumulation time of 120?s. The relative standard deviation for 7 successive determinations of Ag(I) at 0.1???M concentration is 1.99%. The procedure was validated by determining Ag(I) in natural waters.

Multi‐responses Methodology Applied in the Electroanalytical Determination of Hair Dye by Using Printed Carbon Electrode Modified with Graphene

This paper describes a rapid and sensitive method for determination of the hair dye Basic Blue 41 in wastewater samples using screen‐printed carbon electrodes modified with graphene (SPCE/Gr). The method is based on the reversible reduction of azo groups of the dye at potential of ?0.23 V/?0.26 V, where both the anodic and cathodic currents increased 1,300 % when compared to screen‐printed carbon (SPCE) and glassy carbon electrodes (GCE). The optimization of a square wave voltammetric method was performed by means of 2³ factorial design, Doehlert matrix and multi‐response assays, and the best parameters were: frequency (54.8 Hz), step potential (6 mV), pulse amplitude (43.7 mV) and pH 4.5. The analytical curve was constructed from 3.00×10^?8 to 2.01×10^?6 mol L^?1, with detection and quantification limits of 5.00×10^?9 and 1.70×10^?8 mol L^?1, respectively. The repeatability of the method evaluated for 10 consecutive measurements at concentrations of 1.70×10^?7 mol L^?1 and 1.70×10^?6 mol L^?1, showed relative standard deviation of 3.56 and 0.57 %, respectively. The sensor based in SPCE/Gr was successfully applied in wastewater samples collected from a drinking water treatment plant and validated by comparison with HPLC‐DAD method with good accuracy.     

Use of Tin (IV) Porhyrins as Ionophores for the Construction of Phthalate‐Selective Electrodes: Influence of the Structure and Membrane Composition on their Response Properties

Tin(IV) porphyrins derivatives were used as ionophores for phthalate selective electrodes preparation. The influence of ionophore structure and membrane composition (amount of incorporated ionic sites) on the electrode response, selectivity and long‐term stability were studied. Poly(vinyl chloride) polymeric membranes plasticized with o‐NPOE (o‐nitrophenyloctylether) and containing Sn(IV)‐tetraphenylporphyrin (TPP) dichloride (Sn(IV)[TPP]Cl₂) or Sn(IV)‐octaethylporphyrin (OEP) dichloride (Sn(IV)[OEP]Cl₂), and in some cases incorporating lipophilic cationic (tetraocthylammonium bromide ‐ TOABr) and anionic (sodium tetraphenylborate – NaTPB and potassium tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate‐KTFPB) additives, were prepared and their potentiometric characteristics compared. Both ionophores are shown to operate via a neutral mechanism, and the addition of 10 mol % of lipophilic quaternary ammonium salt derivative to the membrane is required to achieve optimal electrode performance. The potentiometric units prepared, with Sn(IV)[TPP]Cl₂ (Type A) or Sn(IV)[OEP]Cl₂ (Type B) without additives, presented a slope of ?52.8 mV dec^?1 and ?58.8 mV dec^?1 and LLLR of 9.9×10^?5 mol L^?1 and 9.9×10^?6 mol L^?1, respectively. The units prepared using the same metalloporphyrins and incorporating 10% mol TOABr presented a slope of ?55.0 mV dec^?1 and ?57.8 mV dec^?1 and LLLR of 5.0×10^?7 mol L^?1 and 3.0×10^?7 mol L^?1. Their analytical usefulness was assessed by potentiometric determinations of phthalate in water and industrial products providing results that presented recoveries of about 100%.     

Chemometric Strategies to Develop a Nanocomposite Electrode for Simultaneous Determination of Ascorbic Acid,Dopamine, and Uric Acid

A simple and sensitive method for simultaneously measuring dopamine (DA), ascorbic acid (AA), and uric acid (UA) using a poly(1‐aminoanthracene) and carbon nanotubes nanocomposite electrode is presented. The experimental parameters for composite film synthesis as well as the variables related to simultaneous determination of DA, AA, and UA were optimized at the same time using fractional factorial and Doehlert designs. The use of carbon nanotubes and poly(1‐aminoanthracene) in association with a cathodic pretreatment led to three well‐defined oxidation peaks at potentials around ?0.039, 0.180 and 0.351 V (vs. Ag/AgCl) for AA, DA, and UA, respectively. Using differential pulse voltammetry, calibration curves for AA, DA, and UA were obtained over the range of 0.16–3.12×10^?3 mol L^?1, 3.54–136×10^?6 mol L^?1, and 0.76–2.92×10^?3 mol L^?1, with detection limits of 3.95×10^?5 mol L^?1, 2.90×10^?7 mol L^?1, and 4.22×10^?5 mol L^?1, respectively. The proposed method was successfully applied to determine DA, AA, and UA in biological samples with good results.     

Determination of Blasticidin S in Spiked Rice Using SW Voltammetry with a Renewable Silver Amalgam Film Electrode

Blasticidin S (BS) was determined in spiked rice samples by square wave voltammetry (SWV) and square wave stripping voltammetry (SWSV) using a cyclic renewable silver amalgam film electrode (Hg(Ag)FE). It was found that the compound can act as an electrocatalyst. In Britton? Robinson buffer at pH 7.0 a signal connected with the hydrogen evolution reaction was detected at ?1.2 V versus Ag/AgCl. Validation of the method was carried out. The detection and quantification limits were found to be 2.13×10^?8 mol L^?1; 7.10×10^?8 mol L^?1 for SWV and 2.65×10^?9 mol L^?1; 8.85×10^?9 mol L^?1 for SWSV, respectively.     

Simultaneous Determination of Thallium and Lead on a Chemically Modified Electrode with Langmuir– Blodgett Film of a p‐tert‐Butylcalix[4]arene Derivative

A new voltammetric sensor, Langmuir–Blodgett (LB) film of a p‐tert‐butylcalix[4]arene derivative modified glassy carbon electrode, was designed and successfully used in simultaneous determination of Tl⁺ and Pb²⁺ by square‐wave anodic stripping voltammetry. Under the optimum experimental conditions, this newly developed sensor reveal good linear response for Tl⁺ and Pb²⁺ in the concentration range of 3×10^?8–4×10^?6 mol L^?1 and 2×10^?7–2×10^?5 mol L^?1 respectively. The detect limits are 2×10^?8 mol L^?1 for Tl⁺ and 8×10^?8 mol L^?1 for Pb²⁺. Using proposed method, Tl⁺ and Pb²⁺ in environment samples were determined with satisfactory results.     

Catalytic Adsorptive Stripping Voltammetry of Germanium(IV) in the Presence of Gallic Acid and Vanadium(IV)‐EDTA

A highly sensitive and selective catalytic adsorptive cathodic striping procedure for the determination of trace germanium is presented. The method is based on adsorptive accumulation of the Ge(IV)‐gallic acid (GA) complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species. The reduction current is enhanced catalytically by addition of vanadium(IV)‐EDTA. The optimal experimental conditions include the use of 0.03 mol/L HClO₄ (pH1.6), 6.0×10^?3 mol/L GA, 3.0×10^?3 mol/L V(IV), 4.0×10^?3 mol/L EDTA, an accumulation potential of ?0.10 V(vs. Ag/AgCl), an accumulation time of 120 s and a differential pulse potential scan mode. The peak current is proportional to the concentration of Ge(IV) over the range of 3.0×10^?11 to 1.0×10^?8 mol/L and the detection limit is 2×10^?11 mol/L for a 120 s adsorption time. The relative standard deviation at 5.0×10^?10 mol/L level is 3.1%. No serious interferences were found. The method was applied to the determination of germanium in ore, mineral water and vegetable samples with satisfactory results.     

Effect of Pulse Width of Square Potential to Remove Silver Interference in the Determination of Mercury(II)

A graphite electrode modified with silver (Ag‐CPE) has been applied to detect mercury(II) using differential pulse voltammetry (DPV). Under optimized conditions, the calibration curve is linear in the range from 5.0×10^?8 mol L^?1 to 1.0×10^?4 mol L^?1 of mercury(II). The detection limit was found to be 3.38×10^?8 mol L^?1 with a relative standard deviation (RSD) of 2.25 % (n=8). The proposed method was successfully applied for the detection of mercury(II) in leachate samples. The Ag‐CP composites were characterized using X‐ray diffraction (XRD), BET adsorption analysis and scanning electron microscopy (SEM).     

An Experimental Design for Simultaneous Determination of Carbendazim and Fenamiphos by Electrochemical Method

This study is aimed to develop an electroanalytical methodology using a boron‐doped diamond electrode (BDD) associated with experimental design in order to determine simultaneously and selectively carbendazin (CBZ) and fenamiphos (FNP) pesticides. In previous studies oxidation peaks were observed at 1.10 V (CBZ) and 1.20 V (FNP), respectively, with characteristics of irreversible processes controlled by diffusion of species (in pH 2.0 (CBZ) and pH 3.5 (FNP)) using a BR buffer 0.1 mol L^?1 as support electrolyte. The differences between the potentials for both pesticides, (about 100 mV) indicate the possibility of selective determination of FNP and CBZ. However, employing an equimolar mixture of analytes, the peaks overlap to form a single oxidation peak. Thus, we used a 3⁴ full factorial design with four parameters to be analyzed in three levels, in order to obtain the optimized parameters for the separation of the peaks. The best separation conditions were pH 5.0, square wave frequency of 300 s^?1, pulse amplitude of 10 mV and scan increment of 2 mV. These parameters were used to obtain the calibration curves of CBZ and FNP. For CBZ the analytical curve was obtained in the concentration range of 4.95×10^?6 to 6.90×10^?5 mol L^?1 with good sensitivity and linearity (0.175 A/mol L^?1 and 0.999, respectively). The limits of detection (LOD) and quantification (LOQ) were 1.6×10^?6 mol L^?1 and 5.5×10^?6 mol L^?1, respectively. For FNP the linear concentration interval was 4.95×10^?6 to 3.67×10^?5 mol L^?1, with a sensitivity of 0,207 A/mol L^?1 and linearity of 0.996. The LOD and LOQ were 4.1×10^?6 mol L^?1 and 13.7×10^?6 mol L^?1, respectively. Using these experimental conditions it was possible to separate the oxidation peaks of CBZ (E_p=1.08 V) and FNP (E_p=1.23 V). The electroanlytical method was applied in lemon juice samples. The recovery values were 110.0 % and 92.5 % for CBZ and FNP, respectively. The results showed that the developed method is suitable for application in foodstuff samples.     

Determination of Trace of Cobalt in Complex Matrices by Adsorptive Stripping Voltammetry at a Lead Film Electrode

An adsorptive stripping voltammetric procedure for the determination of cobalt in a complex matrices at an in situ plated lead film electrode was described. The procedure exploits the enhancement effect of a cobalt peak observed in the system Co(II)–nioxime–piperazine‐1,4‐bis(2‐ethanesulfonic acid)–cetyltrimethylammonium bromide. The calibration graph was linear from 5×10^?10 to 2×10^?8 mol L^?1 and from 1×10^?10 to 1×10^?9 mol L^?1 for the accumulation times 120 and 600 s, respectively. The detection limit (based on the 3 σ criterion) for Co(II) following accumulation time of 600 s was 1.1×10^?11 mol L^?1. The interference of high concentrations of foreign ions and surfactants was studied.