Determination of lead(II) in aqueous solution using carbon nanotubes paste electrodes modified with Amberlite IR-120

A new composite electrode is described for anodic stripping voltammetry determination of Pb(II) at trace level in aqueous solution. The electrode is based on the use of multiwalled carbon nanotubes and Amberlite IR-120. The anodic stripping voltammograms depend, to a large extent, on the composition of the modified electrode and the preconcentration conditions. Under optimum conditions, the anodic peak current at around ?0.57 V is linearly related to the concentration of Pb(II) in the range from 9.6?×?10^?8 to 1.7?×?10^?6 mol L^?1 (R?=?0.998). The detection limit is 2.1?×?10^?8 mol L^?1, and the relative standard deviation (RSD) at 0.24?×?10^?6 mol L^?1 is 1.7% (n?=?6). The modified electrode was applied to the determination of Pb(II) using the standard addition method; the results showed average relative recoveries of 95% for the samples analysed.

Electrochemical Determination of Citalopram by Adsorptive Stripping Voltammetry–Determination in Pharmaceutical Products

Abstract

The electrochemical behavior of citalopram was studied by square‐wave and square‐wave adsorptive‐stripping voltammetry (SWAdSV). Citalopram can be reduced and accumulated at a mercury drop electrode, with a maximum peak current intensity being obtained at a potential of approximately ?1.25 V vs. AgCl/Ag, in an aqueous electrolyte solution of pH 12. A SWAdSV method has been developed for the determination of citalopram in pharmaceutical preparations. The method shows a linear range between 1.0×10^?7 and 2.0×10^?6 mol L^?1 with a limit of detection of 5×10^?8 mol L^?1 for an accumulation time of 30 s. The precision of the method was evaluated by assessing the repeatability and intermediate precision, achieving good relative standard deviations in all cases (≤2.3%). The proposed method was applied to the determination of citalopram in five pharmaceutical products and the results obtained are in good agreement with the labeled values.     

Stripping voltammetry method for determination of manganese as complex with oxine at the carbon paste electrode with and without modification with montmorillonite clay

Oxine (8-hydroxyquinoline) was used as an efficient and selective ligand for stripping voltammetry trace determination of Mn(II). A validated square-wave adsorptive cathodic stripping voltammetry method has been developed for determination of Mn(II) selectively as oxine complex using both the bare carbon paste electrode (CPE) and the modified CPE with 7 % (w/w) montmorillonite-Na clay. Modification of carbon paste with montmorillonite clay was found to greatly enhance its adsorption capacity. Limits of detection of 45 ng l^?1 (8.19?×?10^?10 mol L^?1) and 1.8 ng l^?1 (3.28?×?10^?11 mol L^?1) Mn(II) were achieved using the bare and modified CP electrodes, respectively. The achieved limits of detection of Mn(II) as oxine complex using the modified CPE are much sensitive than the detection limits obtained by most of the reported electrochemical methods. The developed stripping voltammetry method using both electrodes was successfully applied for trace determination of Mn(II) in various water samples without interferences from various organic and inorganic species.     

Voltammetric determination of 17α-ethinylestradiol hormone in supply dam using BDD electrode

In this work, a simple method for electroanalytical determination of 17α-ethinylestradiol (EE2) hormone in natural waters was developed using a boron-doped diamond electrode (BDD). The analyses were performed using square wave voltammetry and the parameters were optimized. The results showed a well-defined irreversible oxidation peak (BR buffer 0.1 mol L^?1, pH 8.0) at +0.65 V (vs. Ag/AgCl). The voltammetric results showed also that the oxidation process is controlled by adsorption of species and indicated that there are two electrons involved. The obtained analytical curves for 17α-ethinylestradiol presented good linearity in the concentration range 9.9?×?10^?7 to 5.2?×?10^?6 mol L^?1 in utlrapure water and 7.9?×?10^?7 to 5.2?×?10^?6 mol L^?1 in natural water samples (supply dam). Detection limits (DL) obtained were between 2.4?×?10^?7 and 7.5?×?10^?7 mol L^?1 and quantification limits (QL) between 7.9?×?10^?7 and 2.5?×?10^?6 mol L^?1. The recovery experiments showed values between 86 and 114 % for spiked samples thus indicating the applicability of the electroanalytical methodology to quantify 17α-ethinylestradiol directly in natural water of supply Dam (Billings Dam in Diadema-SP. Brazil), without any preconcentration or derivatization.     

Simple and fast voltammetric procedure of U(VI) determination in the presence of high concentrations of surface active substances

In this work, a simple and fast procedure for elimination of interfering surface active substances and for U(VI) adsorptive stripping voltammetric determination was developed. The adsorption in the form of U(VI)-cupferron complexes was performed, because as it was proved before, U(VI) forms with cupferron stable complexes, which were employed in voltammetric procedures. The procedure is based on two steps: the first is an adsorption of surface active substances onto an Amberlite XAD-16 or XAD-7 resin and the second is a voltammetric determination of U(VI) with a pulsed potential of accumulation alternate –0.65–0.3 V with the frequency of 0.5 Hz and then the differential pulse voltammogram was recorded, whereas the potential was scanned from –0.65 to –1.2 V. The detection limit estimated from three times the standard deviation for a low U(VI) concentrations was equal to 1.7 × 10^?10 mol L^?1 (7.2 × 10^?8 g L^?1). The linear range of U(VI) was observed over the concentration range from 5.0 × 10^?10 mol L^?1 (2.1 × 10^?7 g L^?1) to 2.0 × 10^?8 mol L^?1 (8.5 × 10^?6 g L^?1) for an accumulation time of 60 s. The influence of different kinds of surfactants, such as non-ionic, cationic and anionic on the uranium voltammetric signal was studied. The results confirm the possibility of U(VI) determination in water samples containing high concentrations of surface active substances even up to 50 mg L^?1.     

Voltammetric analysis of Pb(II) in natural waters using a carbon paste electrode modified with 5-mercapto-1-methyltetrazol grafted on hexagonal mesoporous silica

A hexagonal mesoporous silica (HMS) functionalized with a 5-mercapto-1-methyltetrazole derivative was employed to prepare a chemically modified carbon paste electrode for Pb(II) detection in aqueous solution by square wave adsorptive stripping voltammetry. The optimal operating conditions were 5 min preconcentration time at pH 6.5, and 120 s electrolysis time in 0.2 mol L^?1 HCl. Under these conditions, the voltammetric signal increased linearly with the preconcentration time in the range 1 to 10 min and with the Pb(II) concentration in the range 1 to 100?µg L^?1. The electrode was reproducible and sensitive. Simultaneous determination of Pb, Cd and Cu was also carried out with the electrode. The accuracy of the method was validated by analysing Pb(II) in tap water and groundwater samples.     

Detection of Bisphenol A on a Screen-Printed Carbon Electrode in CTAB Micellar Medium

This work illustrates the effect of cetyltrimethylammonium bromide (CTAB) as an antifouling and pre-concentrating agent for electroanalytical measurement of bisphenol A (BPA) on a screen-printed carbon electrode. The calibration graphs are obtained for BPA from 1.0 × 10^?6 to 1.0 × 10^?5 mol L^?1 in B-R buffer pH 8.0 with addition of CTAB in a ratio of [CTAB]/[BPA] 2:1 and the limit of detection was 5.1 × 10^?8 mol L^?1. Nonylphenol can be also monitored by SWV at a potential 170 mV more positive than bisphenol A in B-R buffer pH 11.0 in the presence of CTAB. The method was successfully applied for BPA determination in river water and sewage without any pretreatment of the samples.     

Determination of folic acid by adsorptive stripping voltammetry at the static mercury drop electrode

Folic acid can be determined at nanomolar concentrations by controlled adsorptive accumulation of folic acid on a static mercury drop electrode held at ?0.3 V vs. Ag/AgCl followed by reduction of the surface species. In 0.1 M sulfuric acid, a cathodic scan gives peaks at ?0.47 v and ?0.75 V vs. Ag/Agcl; the latter peak provides greater sensitivity. Differential-pulse stripping is shown to be superior to normal-pulse and d.c. stripping. After a 5-min preconcentration, the detection limit is about 1 × 10^?10 M folic acid. The adsorptive stripping response is evaluated with respect to concentration dependence, preconcentration time and potential, solution acidity and the presence of gelatin and bromide. The relative standard deviation at the 5 × 10^?8 M level is 1.2%. This method is applied to the determination of folic acid in pharmaceutical tablets.     

Adsorptive Cathodic Stripping Voltammetric Method for Determination of Gallium Using an In Situ Plated Lead Film Electrode

The in situ plated lead film electrode was proposed for the first time for adsorptive stripping voltammetric determination of gallium in water samples. The method was based on simultaneous lead film formation and Ga(III)‐cupferron complex preconcentration at ?0.7 V and its cathodic stripping during the potential scan. The composition of the supporting electrolyte, cupferron concentration, conditions of lead film formation, potential and time of accumulation were studied in detail. Under optimum conditions the limit of detection was 3.8×10^?9 mol L^?1. The proposed procedure was validated in the course of Ga(III) determination in waste water certified reference materials.     

Cathodic Stripping Voltammetry Determination of Ceftiofur Antibiotic in Formulations and Bovine Serum

Abstract

A sensitive and reliable stripping voltammetry method was developed to determine the presence of Ceftiofur antibiotic drug. This method is based on the adsorptive accumulation of the drug at a hanging mercury drop electrode and then the initiation of a negative sweep that yielded well‐defined cathodic peaks at ?0.65 V (1 C) and ?1.00 V (2 C) vs. Ag/AgCl reference electrode. To achieve high sensitivity, various experimental and instrumental variables were investigated such as supporting electrolyte, pH, accumulation time and potential, drug concentration, scan rate, convection rate, and working electrode area. The monitored adsorptive current of peak 1 C was directly proportional to the concentration of Ceftiofur; it shows a linear response in the range from 0.50×10^?8 to 8.00×10^?8 mol L^?1 (correlation coefficient=0.998); and the limit of detection is 6.00×10^?10 mol L^?1 at an accumulation time of 300 s. The applicability of this approach was illustrated by the determination of Ceftiofur in pharmaceutical preparations and bovine serum.     

Catalytic Adsorptive Stripping Voltammetry at a Carbon Paste Electrode for the Determination of Amiodarone

Voltammetry using solid electrodes usually suffers from the contamination due to the deposition of the redox products of analytes on the electrode surface. The contamination has resulted in poor reproducibility and overelaborate operation procedures. The use of the chemical catalysis of oxidant on the reduction product of analyte not only can eliminate the contamination of analyte to solid electrodes but also can improve the faradaic response of analyte. This work introduced both the catalysis of oxidant K2S2O8 and the enhancement of surfactant Triton X-100 on the faraday response of amiodarone into an adsorptive stripping voltammetry at a carbon paste electrode for the determination of amiodarone. The method exhibits high sensitivity, good reproducibility and simple operation procedure. In 0.2 mol·L^-1 HOAc-NaOAc buffer （pH=5.3） containing 2.2×10^-2 mol·L^-1 K2S2O8 and 0.002% Triton X-100, the 2.5th-order derivative stripping peak current of the catalytic wave at 0.3 V （vs. Ag/AgCl） is rectilinear to amiodarone concentration in the range of 2.0×10^-10-2.3×10^-8 mol·L^-1 with a detection limit of 1.5×10^-10 mol·L^-1 after accumulation at 0 V for 30 s.     

Removal, preconcentration and spectrophotometric determination of U(VI) from water samples using modified maghemite nanoparticles

Arsenazo III modified maghemite nanoparticles (A-MMNPs) was used for removing and preconcentration of U(VI) from aqueous samples. The effects of contact time, amount of adsorbent, pH and competitive ions was investigated. The experimental results were fitted to the Langmuir adsorption model in the studied concentration range of uranium (1.0 × 10^?4–1.0 × 10^?2 mol L^?1). According to the results obtained by Langmuir equation, the maximum adsorption capacity for the adsorption of U(VI) on A-MMNPs was 285 mg g^?1 at pH 7. The adsorbed uranium on the A-MMNPs was then desorbed by 0.5 mol L^?1 NaOH solution and determined spectrophotometrically. A preconcentration factor of 400 was achieved in this method. The calibration graph was linear in the range 0.04–2.4 ng mL^?1 (1.0 × 10^?10–1.0 × 10^?8 mol L^?1) of U(VI) with a correlation coefficient of 0.997. The detection limit of the method for determination of U(VI) was 0.01 ng mL^?1 and the relative standard deviation (R.S.D.) for the determination of 1.43 and 2.38 ng mL^?1 of U(VI) was 3.62% and 1.17% (n = 5), respectively. The method was applied to the determination of U(VI) in water samples.     

Catalytic Adsorptive Stripping Voltammetric Procedure for Determination of Total Chromium in Environmental Materials

A sensitive catalytic adsorptive stripping voltammetric procedure for determination of traces of total chromium in environmental samples is reported. The method is based on the preconcentration of a Cr(III)? H₂DTPA complex by adsorption at the HMDE from an acetate buffer solution at the potential ?1.0 V vs. Ag/AgCl. Total chromium was determined as Cr(III) after reduction of Cr(VI) to Cr(III) by NaHSO₃. In order to stabilize the signal of Cr(III) the measurements were performed at 5 °C. The calibration graph for chromium for an accumulation time of 60 s was linear in the range from 5×10^?10 to 5×10^?8 mol L^?1. The relative standard deviation for a chromium concentration of 1×10^?8 mol L^?1 was 3.9% (n=5). The detection limit for accumulation time of 60 s was about 8×10^?11 mol L^?1. The validation of the procedure was performed by the analysis of the certified reference materials.     

Surfactant-intercalated smectite modified electrode: sensitive electrochemical detection of methyl orange dye

This work describes the use of organosmectite modified electrode to evaluate the electrochemical behaviour and to develop an electroanalytical procedure for the determination of methyl orange (MO) dye in natural water. Organosmectites were prepared by intercalation of hexadecyltrimethylammonium cations at various ratios into the interlayer of smectite. The synthesised organosmectites were characterised by various physicochemical techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. An amperometric sensor based on organosmectite as electrode modifier for MO sensing purposes was then evaluated by means of clay-film modified electrode using square wave voltammetry (SWV). The electrochemical procedure for MO analysis by stripping voltammetry involves two successive steps: accumulation of MO at open circuit conditions followed by a voltammetric detection in a same medium by the SWV technique. The peak current obtained (after 5 min preconcentration of 15 µmol L^?1 MO solution) on a glassy carbon electrode coated by a thin film of the modified clay was more than 2.5 times higher than that exhibited by the same substrate covered by a film of the pristine clay. Under optimised conditions, a linear calibration curve for MO was obtained in the concentration range from 0.1 to 1.6 µmol L^?1, leading to a detection limit of 4 × 10^?8 mol L^?1 (signal-to-noise ratio equal to 3). The interfering effect of various inorganic and organic ions likely to influence the stripping determination of the MO was also examined. To further validate application of this sensor, the proposed method was successfully used to the determination of MO in natural water with satisfactory results.     

Adsorptive stripping voltammetry of nickel at a bare glassy carbon electrode

A bare glassy carbon electrode is applied to nickel determination by adsorptive stripping voltammetry in the presence of dimethylglyoxime as a complexing agent. A procedure of nickel determination and electrode regeneration was proposed. The calibration graph for Ni(II) for an accumulation time of 120?s was linear from 2?×?10^?9 to 1?×?10^?7?mol?L^?1. The detection limit was 8.2?×?10^?10?mol?L^?1. The relative standard deviation for a solution containing 2?×?10^?8?mol?L^?1 of Ni(II) was 4.1%. The proposed procedure was applied for Ni(II) determination in certified water reference materials.     

Determination of Cysteine in the Presence of Copper in Diluted Alkaline Electrolyte by Adsorptive Stripping Voltammetry at the Mercury Film Electrode

Abstract

A stripping method for the determination of cysteine in the presence of copper at the submicromolar concentration levels is described. The method is based on controlled adsorptive accumulation of cysteine at mercury film electrode followed by linear cyclic voltammetry scan measurement of the surface species. Optimum experimental conditions were found to be the use of a 1×10^?3 M NaOH solution, an accumulation potential of ?0.50 V and a scan rate of 200 mV. s^?1. The response of cysteine is linear over the concentration range 0.04–0.20 ppm. For an accumulation time of 15 minutes, the detection limit was found to be 0.9 ppb (7.4×10^?9 M). The more convenient relation to measuring the cysteine in presence of metals, and others amino acids were also investigated. The utility of the method is demonstrated by presence of casein and ATP.     

Electrochemical Study of Interaction Between Clozapine and DNA and Its Analytical Application

Abstract

The interaction between clozapine (CLZ) as an orally administrated antipsychotic drug with double stranded calf thymus DNA (dsDNA) was investigated at electrode surface using differential pulse voltammetry (DPV). Activated carbon paste electrode (CPE) was modified with dsDNA and used for monitoring the changes of the characteristics peak of CLZ in 0.05 M acetate buffer (pH 4.3). The adsorptive stripping voltammetry on dsDNA‐modified carbon paste electrode (dsDNA‐CPE) was used for determination of very low concentration of CLZ. Under optimal conditions, the oxidation peak current is proportional to CLZ concentration in the range of 7×10^?9?1.2×10^?6 mol l^?1 with a detection limit of 1.5×10^?9 mol l^?1 for 180 s accumulation time by DPV. The proposed dsDNA‐CPE was successfully used for determination of CLZ in human serum samples with recovery of 97.0±2.5%.     

Determination of Folic Acid by Adsorptive Stripping Voltammetry at a Lead Film Electrode

An adsorptive stripping voltammetric procedure for the determination of folic acid at an in situ plated lead film electrode was described. Formation of lead film on a glassy carbon substrate and accumulation of folic acid was performed simultaneously from an acetate buffer solution of pH 5.6 at the potential ?0.88 V. The measurements were carried out from aerated solutions. The calibration graph for an accumulation time of 300 s was linear from 2×10^?9 to 5×10^?8 mol L^?1. The detection limit was 7×10^?10 mol L^?1, the relative standard deviation for 2×10^?8 mol L^?1 of folic acid was 3.9%. The proposed procedure was applied to folic acid determinations in pharmaceutical preparations.     

Determination of Polyethylene Glycol Monoester Acrylate and Polyethylene Glycol Diester Acrylate Using Reversed-Phase High-Performance Liquid Chromatography

A procedure was developed for the determination of polyethylene glycol monoester acrylate (PEGMA) and polyethylene glycol diester acrylate (PEGDA) by reversed-phase high performance liquid chromatographic (RP-HPLC) with UV detector. Sample was well separated on an SinoChrom ODS-BP (C-18) column (200 × 4.6 mm i.d., 5 μm) with mobile phases composed of acetonitrile-phosphate buffer solution (0.05 mol · L^?1 pH = 6.86) in the ratio of 42:58 (v/v). The PEGMA and PEGDA were detected by UV detector at 205 nm, and quantitatively analyzed with an external standard of methyl acrylate. For PEGMA, the linear response ranged from 0.40 × 10^?5 mol · L^?1 to 2.00 × 10^?3mol · L^?1 (r² > 0.999), the detection limit was 0.12 × 10^?5 mol · L^?1, the recovery rate was found to be 93.4%–99.7%. For PEGDA, the linear response ranged from 0.20 × 10^?5 mol · L^?1 to 1.00 × 10^?3mol · L^?1 (r² > 0.999), the detection limit was 0.04 × 10^?5 mol · L^?1, the recovery rate was found to be 99.1% ～ 105.8%. This quantitative method can also be used in the HPLC analysis of other α,β-unsaturated esters.     

Catalytic Adsorptive Stripping Voltammetry of Cobalt in the Presence of Nitrite at an In Situ Plated Bismuth Film Electrode

For the first time an in situ plated bismuth film electrode has been applied to catalytic adsorptive stripping voltammetry of cobalt in the presence of nitrite. At optimised conditions bismuth film was plated before each measurement for 30 s at ?1.0 V from a sample solution with the added supporting electrolyte and Bi(III) in the form of its complex with tartrate. The calibration graph for Co(II) for an accumulation time of 120 s was linear from 5×10^?10 to 1×10^?8 mol L^?1. The detection limit was 1.1×10^?10 mol L^?1. The proposed procedure was applied for Co(II) determination in certified water reference material.