Differential pulse anodic stripping voltammetric determination of lead(II) with a 1,4-bis(prop-2'-enyloxy)-9,10-anthraquinone modified carbon paste electrode

A sensitive and selective method for the determination of lead(II) with a 1,4-bis(prop-2'-enyloxy)-9,10-anthraquinone (AQ) modified carbon paste electrode has been developed. The method is based on non-electrolytic preconcentration via complex formation with modifier, followed by an accumulation period with a negative potential (-1.5 V), and then by a proper anodic stripping. The analytical performance was evaluated with respect to the quantity of modifier in the paste, concentration of electrolyte solution, preconcentration time, lead(II) concentration, and other variables. A linear calibration graph was obtained in the concentration range 2.00x10(-9)-1.06x10(-5) M Pb(II) (n=21, r=0.9999) with 30 s preconcentration time. The detection limit was found to be 1x10(-9) M. For eight preconcentration/determination cycles, the differential pulse voltammetric response was reproduced with 5.0 and 3.7% relative standard deviations at 2.00x10(-8) and 2.00x10(-6) M Pb(II), respectively. Rapid and convenient renewal of electrode surface allows the use of a single modified electrode surface in multiple analytical determinations over several weeks. Many coexisting metal ions had little or no effect on the determination of lead(II). The developed method was applied to lead determination in waste waters.     

Differential pulse anodic stripping voltammetric determination of traces of copper with a tobramycin-Nafion modified electrode.

A Nafion-modified glassy carbon electrode incorporated with tobramycin for the voltammetric stripping determination of Cu2+ has been explored. The electrode was fabricated by tobramycin containing Nafion on the glassy carbon electrode surface. The modified electrode exhibited a significantly increased sensitivity and selectivity for Cu2+ compared with a bare glassy carbon electrode and the Nafion modified electrode. Cu2+ was accumulated in HAc-NaAc buffer (pH 4.6) at a potential of -0.6 V (vs. SCE) for 300 s and then determined by differential pulse anodic stripping voltammetry. The effects of various parameters, such as the mass of Nafion, the concentration of tobramycin, the pH of the medium, the accumulation potential, the accumulation time and the scan rate, were investigated. Under the optimum conditions, a linear calibration graph was obtained in the concentration range of 1.0 x 10(-9) to 5.0 x 10(-7) mol l(-1) with a correlation coefficient of 0.9971. The relative standard deviations for eight successive determinations were 4.3 and 2.9% for 1.0 x 10(-8) and 2.0 x 10(-7) mol l(-1) Cu2+, respectively. The detection limit (three times signal to noise) was 5.0 x 10(-10) mol l(-1). A study of interfering substances was also performed, and the method was applied to the direct determination of copper in water samples, and also in analytical reagent-grade salts with satisfactory results.     

Preconcentration at a carbon-paste electrode and determination by adsorptive-stripping voltammetry of rutin and other flavonoids

The non-Faradaic preconcentration behaviour of nine flavonoids (six flavones: fisetin, galangin, morin, quercetin, rhamnetin, rutin, and three flavanones: hesperidin, hesperitin, naringin) at a carbon-paste (nujol/graphite) electrode and the factors affecting it (pH, accumulation potential, presence of various surfactants) for their subsequent differential pulse voltammetric determination are examined. All flavones tested are readily accumulated on the carbon paste electrode resulting in a considerable signal enhancement making determinations feasible down to 10⁻⁸ − 10⁻⁷ M after preconcentration for 1–4 min. Flavanones are not preconcentrated so their lower determination limits are of the order of 10^-6 M. A simple voltammetric procedure for the determination of rutin in a multivitamin preparation is presented.     

Synthesis and preliminary analytical evaluation of the chemiluminescence from (4-[4-(dichloromethylsilanyl)-butyl]-4'-methyl-2,2'-bipyridyl)bis(2,2'-bipyridyl)ruthenium(II) covalently bonded to silica particles

This paper describes, for the first time, a simple and effective synthetic route for covalently bonding the chemiluminescence reagent, (4-[4-(dichloromethylsilanyl)-butyl]-4'-methyl-2,2'-bipyridyl)bis(2,2'-bipyridyl)ruthenium(II) onto silica particles. The subsequent preparation of chemically regeneratable detection cells and their preliminary analytical evaluation with both sequential injection analysis and flow injection analysis are also reported. Unoptimised analytical figures of merit were established for standard solutions of codeine and sodium oxalate with detection limits calculated from three times the standard deviation of the blank signal, of 1 x 10(-8) M and 3 x 10(-7) M respectively. The chemically immobilised reagent exhibited some intriguing solvent and kinetic effects, which are also briefly discussed.     

Determination of morphine at gold nanoparticles/Nafion® carbon paste modified sensor electrode

A novel and effective electrochemical sensor for the determination of morphine (MO) in 0.04 mol L(-1) universal buffer solution (pH 7.4) is introduced using gold nanoparticles electrodeposited on a Nafion modified carbon paste electrode. The effect of various experimental parameters including pH, scan rate and accumulation time on the voltammetric response of MO was investigated. At the optimum conditions, the concentration of MO was determined using differential pulse voltammetry (DPV) in a linear range of 2.0 × 10(-7) to 2.6 × 10(-4) mol L(-1) with a correlation coefficient of 0.999, and a detection limit of 13.3 × 10(-10) mol L(-1), respectively. The effect of common interferences on the current response of morphine namely ascorbic acid (AA) and uric acid (UA) is studied. The modified electrode can be used for the determination of MO spiked into urine samples, and excellent recovery results were obtained.     

Voltammetric Studies of Propylthiouracil at a Carbon-Paste Electrode Modified with Cobalt(II)-4-chlorosalophen: Application to Voltammetric Determination in Pharmaceutical and Clinical Preparations

A carbon-paste electrode chemically modified with a Schiff-base complex of cobalt (cobalt(II)-4-chlorosalophen, CoClSal) is utilized to investigate the voltammetric response of propylthiouracil (PTU). The mechanism of electrocatalytic oxidation of the compound is investigated by means of cyclic voltammetric studies applying various pHs to the buffered solutions. The modified electrode exhibits effective catalytic properties that lower the anodic overpotential and enhance the rate of electron transfer for the electrochemical oxidation of PTU. The results of the cyclic voltammetric (CV) and differential pulse voltammetric (DPV) techniques showed that the modified electrode exhibits good selectivity for discriminating between the anodic wave of PTU and some biological thiols (e.g. cysteine) which may be present in human serum samples. DPV is used as a very sensitive electroanalytical method for the detection of trace amounts of PTU in pharmaceutical and clinical preparations. The results showed that the anodic peak current for the analyte in DPV varies linearly with the concentration of PTU in the range of 7.5 × 10⁻⁶ to 7.5 × 10⁻⁴ M (RSD for the slope of calibration curve <4%, n = 6).     

Voltammetric behavior of some fluorinated quinolone antibacterial agents and their differential pulse voltammetric determination in drug formulations and urine samples using a β-cyclodextrin-modified carbon-paste electrode

A voltammetric determination of ofloxacin (OF), norfloxacin (NF), gatifloxacin (GF), and lomefloxacin (LF) at a β-cyclodextrin-modified carbon-paste electrode (CDMCPE) is described. A large increase in the peak currents was observed in cyclic voltammetry (CV) and differential pulse voltammetry (DPV) of OF, NF, GF, and LF at CDMCPE compared with a bare carbon-paste electrode (CPE). These increases in the peak currents were attributed to the complex formation of the quinone group of the drugs with β-cyclodextrin. CV studies indicate that the process is irreversible and adsorption-controlled. The experimental parameters which influence the peak current responses of OF, NF, GF, and LF were studied. The reduction peak currents of OF, NF, GF, and LF change linearly over the common concentration range from 3.2 × 10⁻⁸ to 2 × 10⁻⁵ M, with a common correlation coefficient and limit of detection of 0.9995 and 2.4 × 10⁻⁸ M, respectively, in pH 4.0 Britton-Robinson (BR) buffer at an accumulation time of 160 s. The interference of metal ions in the peak current response was also studied. The modified electrode exhibited good sensitivity and stability. The proposed method was applied to the determination of OF, NF, GF, and LF in both commercially available drugs and spiked human urine samples. The text was submitted by the authors in English.     

Anodic Stripping Voltammetric Determination of Iron(II) at a Carbon Paste Electrode Modified with Dithiodianiline (DTDA) and Gold Nanoparticles (GNP)

A differential pulse anodic stripping voltammetric procedure was developed for the determination of trace amounts of iron(II) in the presence of iron(III) at a carbon paste electrode (CPE) modified with dithiodianiline and gold nanoparticle. At the pH working of 3.0, a wide concentration range from 0.1 nM to 100 nM was observed with the detection limit of 0.05 nM. The relative standard deviation for a solution containing 50 nM of iron(II) was found to be 3.11 % (n=9). Possible interferences from the coexisting ions were also investigated. The validity of the method and applicability of the sensor were successfully tested by determining of iron(II) in lentil, wheat seed and barley seed samples.     

Electrochemical investigation and determination of ceftazidime in pharmaceutical dosage forms and human urine

A voltammetric study of the oxidation of Ceftazidime (CEFT) has been carried out at the glassy carbon electrode by cyclic, differential pulse (DPV) and square wave (SWV) voltammetry. The oxidation of CEFT was irreversible and exhibited diffusion controlled process depending on pH. The oxidation mechanism was proposed and discussed. According to the linear relationship between the peak current and concentration, DPV and SWV voltammetric methods for CEFT assay in pharmaceutical dosage forms and human urine were developed. For analytical purposes, a well resolved diffusion controlled voltammetric peak was obtained in 0.1 M H₂SO₄ at 1.00 and 1.02 V for differential pulse and square wave voltammetric techniques, respectively. The linear response was obtained within the range of 4 × 10^?6?8 × 10^?5 M with a detection limit of 6 × 10^?7 M for differential pulse and 4 × 10^?6–2 × 10^?4 M with a detection limit of 1 × 10^?6 M for square wave voltammetric technique. The determination of CEFT in 0.1 M H₂SO₄ was possible over the 2 × 10^?6–1 × 10^?4 M range in urine sample for both techniques. The standard addition method was used for the recovery studies.     

Anodic oxidation of etodolac and its square wave and differential pulse voltammetric determination in pharmaceuticals and human serum

A voltammetric study of the oxidation of etodolac has been carried out at the glassy carbon electrode. The electrochemical oxidation of etodolac was investigated by cyclic, linear sweep, differential pulse and square wave voltammetry using glassy carbon electrode. Different parameters were tested to optimize the conditions for the determination of etodolac. The dependence of intensities of currents and potentials on pH, concentration, scan rate, nature of the buffer was investigated. For analytical purposes, a very well resolved diffusion controlled voltammetric peak was obtained in Britton-Robinson buffer at pH 2.15 for differential pulse and square wave voltammetric techniques. The linear response was obtained in the ranges of 2.10(-6)-8.10(-5) M with a detection limit of 6.8x10(-7) and 6x10(-6)-8x10(-5) M with a detection limit of 1.1x10(-6) M for differential pulse and square wave voltammetric techniques, respectively. Based on this study, simple, rapid, selective and sensitive two voltammetric methods were developed for the determination of the etodolac in tablet dosage form and human serum.     

Sequential potentiometric complexometric redox determination of iron(III) and cobalt(II) with application to alloys

A simple potentiometric method is presented for successive determination of iron(III) and cobalt(II) by complexometric titration of the iron(III) with EDTA at pH 2 and 40 degrees , followed by redox titration of the cobalt(II) complex with 1,10-phenanthroline or 2,2'-bipyridyl at pH 4-5 and 40 degrees , with gold(III). There is no interference in either determination from common metal ions other than copper(II), which severely affects the cobalt determination but can be removed by electrolysis. The method has been successfully applied to determination of iron and cobalt in Kovar and Alnico magnet alloys.     

Modification of carbon paste with congo red supported on multi-walled carbon nanotube for voltammetric determination of uric acid in the presence of ascorbic acid

A chemically modified carbon-paste electrode (CPE) is prepared by incorporating congo red (CR) immobilized on multi-walled carbon nanotube (MWCNT). The results show that CR is effectively immobilized on the surface of MWCNT under the ultrasonic agitation in aqueous solution and further incorporating the nafion. The prepared electrode, due to the electrostatic repulsions between the CR and ascorbate anion, is capable to mask the response of the ascorbic acid (AA) completely and provide an effective method for the detection of minor amounts of uric acid (UA) in the presence of high concentrations of AA. On the other hand, an increase in the microscopic area of the electrode by addition of MWCNT together with the electrocatalytic activity caused to a significant enhancement in the voltammetric response to UA. Optimization of the amounts of composite modifier in the matrix of CPE is performed by cyclic and differential pulse voltammetric measurements. The modified electrode shows a linear response to UA in the range of 1.0 × 10⁻⁷–1.0 × 10⁻⁴ M with a detection limit of 1.0 × 10⁻⁸ M. The electrode exhibits excellent accuracies for the determination of UA in the presence of high concentrations of AA (a recovery of 97.6%). The response of the electrode toward sulfhydryl compounds such as cysteine, penicillamine, and glutathione is not considerable. This reveals a good selectivity for the voltammetric response toward UA. The effective electrocatalytic property, ability for masking the voltammetric responses of the other biologically reducing agents, ease of preparation, and surface regeneration by simple polishing together with high reproducibility and stability of the responses make the modified electrode suitable for the selective and sensitive voltammetric detection of sub-micromolar amounts of UA in clinical and pharmaceutical preparations.     

Differential Pulse Voltammetric Determination of Local Anesthetics Heptacaine,Carbisocaine and Pentacaine at DNA Modified Screen‐Printed Electrode

A procedure for the differential pulse voltammetric determination of three local anesthetics (Heptacaine, Carbisocaine and Pentacaine) at a screen‐printed electrode surface modified with the dsDNA layer is described. The detection limits obtained after 120 s drug accumulation from 0.01 M phosphate buffer solution pH 6.96 are 0.02 μM (Pentacaine) and 0.03 μM (Carbisocaine and Heptacaine). The method was applied to the determination of Carbisocaine in spiked serum.     

Adsorption voltammetry of the copper(II) 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complex

The voltammetric determination of copper(II), based on adsorptive accumulation of the Cu(II)-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (S-Br-PADAP) complex on a hanging mercury drop electrode, is reported. The complex can be accumulated at the electrode at constant potential in 0.1M ammonium nitrate/ammonia buffer solution, and its reduction wave observed by scanning the potential in the negative direction, in the differential pulse mode. The calibration graph for copper is linear over the range 0.05-0.5muM, with accumulation for 5 min at -0.20 V. The adsorption of the complex is discussed and compared with that of copper complexes with several other pyridylazo derivatives.     

Trace measurements of the antineoplastic agent methotrexate by adsorptive stripping voltammetry

An extremely sensitive voltammetric method is presented for trace measurement of the cancer chemotherapy drug methotrexate. The method is based on controlled adsorptive preconcentration of methotrexate on the hanging mercury-drop electrode, followed by voltammetric determination of the surface species. Cyclic voltammetry was used to explore the interfacial behaviour. The adsorptive stripping response was evaluated with respect to preconcentration time and potential, pH, concentration dependence, stripping mode, possible interferences, and other variables. The detection limit found was 2 x 10(-9)M (5-min preconcentration), the response was linear, and the relative standard deviation (at the 1.6 x 10(-7)M level) 2.2%. Sensitive adsorptive stripping measurements were also obtained by use of a carbon-paste disk electrode. Applicability to urine analysis is illustrated.     

Simultaneous Voltammetric Determination of Uric Acid and Ascorbic Acid Using a Carbon‐Paste Electrode Modified with Multi‐Walled Carbon Nanotubes/Nafion and Cobalt(II)nitrosalophen

A composition of multiwalled carbon nanotube (MWCNT), Nafion and cobalt(II)‐5‐nitrosalophen (CoNSal) is applied for the modification of carbon‐paste electrode (CPE). The pretreated MWCNT is well dispersed in the alcoholic solution of Nafion under the ultrasonic agitation, and the resulted suspension is used as modifier (with 10% w/w) in the matrix of the paste electrode. The prepared electrode further modified by addition of 3 wt% of CoNSal. The resulted modified electrode is used as a sensitive voltammetric sensor for simultaneous determination of uric acid (UA) and ascorbic acid (AA). The electrode showed efficient electrocatalytic activity in lowering the anodic overpotentials and enhancement of the anodic currents. This electrode is able to completely resolve the voltammetric response of UA and AA. The effects of potential sweep rate and pH of the buffer solution on the response of the electrode, toward UA and AA, and the peak resolution is thoroughly investigated by cyclic and differential pulse voltammetry (CV and DPV). The best peak resolution for these compounds using the modified electrode is obtained in solutions with pH 4. The ΔE_p for UA and AA in these methods is about 315 mV, which is considerably better than previous reports for these compounds. A linear dynamic range of 1×10^?7 to 1×10^?4 M with a detection limit of 6×10^?8 M is resulted for UA in buffered solutions with pH 4.0. The voltammetric response characteristics for AA are obtained as, the linear range of 5×10^?7 to 1×10^?4 M with the detection limit of 1×10^?7 M. The voltammetric detection system was very stable and the reproducibility of the electrode response, based on the six measurements during one month, was less than 3.5% for the slope of the calibration curves of UA and AA. The prepared modified electrode is successfully applied for the determination of AA and UA in mixture samples and reasonable accuracies are resulted.     

A nanoporous ruthenium oxide framework for amperometric sensing of glucose and potentiometric sensing of pH

We report on a carbon ionic liquid electrode modified with a composite made from Nafion, graphene oxide and ionic liquid, and its application to the sensitive determination of rutin. The modified electrode was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. It shows excellent cyclic voltammetric and differential pulse voltammetric performance due to the presence of nanoscale graphene oxide and the ionic liquid, and their interaction. A pair of well-defined redox peaks of rutin appears at pH 3.0, and the reduction peak current is linearly related to its concentration in the range from 0.08 μM to 0.1 mM with a detection limit of 0.016 μM (at 3σ). The modified electrode displays excellent selectivity and good stability, and was successfully applied to the determination of rutin in tablets with good recovery.

Electroanalysis at modified carbon-paste electrodes containing natural ionic polysaccharides

The strong affinity of natural ionic polysaccharides for certain metal ions is exploited in the design of a new class of voltammetric sensing devices. In particular, carbon-paste electrodes containing pectic and alginic acids are used for the nonelectrolytic collection and subsequent voltammetric determination of copper and lead, respectively. Cyclic and differential pulse voltammetry are used to quantify the accumulated ions. The response is characterized with respect to modifier loading, preconcentration period, metal concentration, reproducibility, possible interferences and other variables. Titrimetric experiments illustrate the potential of polysaccharide electrodes for speciation work. Preliminary data are also given for analogous measurements of copper at heparin-modified electrodes. Detection limits are 1 mug/ml and the relative standard deviation is 4.8%.     

Highly sensitive adsorptive stripping voltammetric method for the ultra-trace determination of chromium(VI).

A rapid differential pulse adsorptive stripping voltammetric method has been developed for the ultra-trace determination of chromium using 2,2'-bipyridine. The base electrolyte used is 0.1 M NH4Cl (pH 6.0). The peak current was found to increase substantially with the addition of nitrite ions. A well-defined peak was observed at -1.3 V. Parameters, like concentration of the ligand, concentration of nitrite ion, accumulation potential, accumulation time, rest period, drop size, scan rate, pulse amplitude etc. have been optimized. Under the optimum conditions, the 3 sigma detection limit was found to be 0.02 ppb (3.8 x 10(-10) M). The method is highly selective and sensitive, and has been applied to the determination of Cr(VI) in spiked water, effluents and ore samples.     

Indirect Determination of Trace Copper(II) by Adsorptive Stripping Voltammetry with Zincon at a Carbon Paste Electrode

Traces of copper(II) can be determined by adsorptive stripping voltammetry using 2‐carboxy‐2′‐hydroxy‐5′‐sulfoformazyl benzene (Zincon) as complex forming reagent. First in phosphate buffer pH 6.4, copper(II)‐Zincon complex was adsorbed on carbon paste electrode (CPE) with an accumulation potential of 0.6 V. Following this, adsorbed complex was oxidized and detected by differential pulse voltammetric (DPV) scan from 0.6 to 1.0 V. The effective parameters in sensor response were examined. The detection limit (DL) of copper(II) was 1.1 μg/L and relative standard deviations (RSDs) for 10 and 200 μg/L Cu(II) were 1.81 and 1.03%, respectively. The calibration curve was linear for 2–220 μg/L copper(II). The resulting CPE does not use mercury and therefore, has a positive environmental benefit. The method, which is reasonably sensitive and selective, has been successfully applied to the determination of trace amount of copper in water and human hair samples.