Determination of Trace Amounts of Copper by Adsorptive Stripping Voltammetry

ABSTRACT

A technique is presented for the determination of trace amounts of copper(II) by adsorptive cathodic stripping voltammetry. The procedure is based on adsorptive accumulation of copper(II)-Alizarin Red S (ARS) complex on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the reduction current of the adsorbed complex at -0.16 V (vs. Ag/AgCl). The height of the copper -ARS reduction peak is linearly dependent upon the copper(II) concentration between 0.2-15 and 15-500 ng.ml^?1. The detection limit of the technique is 0.05 ng.ml^?1 copper(II) for a collection time of 1 minute. The method is free from most interferences. The procedure has been successfully applied to the determination of trace amounts of copper(II) in some analytical grade salts.     

Differential pulse cathodic stripping adsorption voltammetric determination of trace amounts of lead using factorial design for optimization

A sensitive cathodic stripping voltammetric method is developed for determination of lead(II), with adsorptive collection of complexes with Pyrogallol red (PGR) on to a hanging mercury drop electrode. After accumulation of the complex at −0.80 V vs. Ag/AgCl reference electrode, the potential is scanned in a negative direction from −0.20 to −0.50 V with differential pulse method. Then the reduction peak current for the lead(II)-PGR complex is measured at −0.39 V. The influence of reagent and instrumental variables was completely studied by factorial design analysis. The optimum analytical conditions for the determination of lead(II) were established. Under optimum conditions, lead(II) determined in the range of 0.1-30.0 ng ml⁻¹ with a limit of detection of 0.06 ng ml⁻¹. The method is successfully applied to determination of lead(II) in water sample.     

Trace determination of molybdenum by adsorptive cathodic stripping voltammetry

Molybdenum is determined by adsorptive cathodic stripping voltammetry in 0.15 M nitric acid solution containing 15 μM 2′,3,4′,5,7-pentahydroxyflavone (morin) as a ligand. In this medium, molybdenum is preconcentrated on a hanging mercury drop electrode and stripped cathodically in square-wave voltammetry mode, with a peak potential of -350 mV vs. Ag/AgCl (saturated KCl). The effect of various parameters (ligand concentration, supporting electrolyte composition, accumulation potential and collection time) on the sensitivity and linear range of the calibration curve are discussed. With controlled accumulation for 1 min, the detection limit (3σ) was 0.45 ng ml^?1 molybdenum and the calibration curve is linear up to 70 ng ml^?1. The procedure is applied to the determination of molybdenum in real samples with satisfactory results.     

Square-wave adsorptive stripping voltammetric determination of antihypertensive agent telmisartan in tablets and its application to human plasma

The adsorptive stripping voltammetry of telmisartan was investigated with a hanging mercury drop electrode. This compound produced a catalytic hydrogen wave at ?1.5 V in Britton Robinson buffer of pH 10.38, and the peak current increased with adsorptive accumulation at the electrode. Adsorptive stripping voltammetry with the catalytic hydrogen wave could provide a sensitive novel method for the determination of telmisartan. Various chemical and instrumental parameters affecting the monitored electroanalytical response were investigated and optimized for telmisartan determination. Under these optimized conditions the square-wave adsorptive stripping voltammetric (SW-AdSV) peak current showed a linear dependence on drug concentration over the range 0.05–3.00 μg/mL (1 × 10^?7?6 × 10^?6 M) (r = 0.999) with accumulation for 120 s at ?1.0 V vs. Ag/AgCl. The proposed electrochemical procedure was successfully applied for the determination of telmisartan in pharmaceutical tablets and human plasma. The results of the developed SW-AdSV method were comparable with those obtained by reported analytical procedures.     

Trace analysis of germanium

Summary The dp-polarographic and stripping voltammetric behaviour of germanium(IV) in the presence of various supporting electrolytes is discussed. Moreover, a highly sensitive adsorptive stripping voltammetric technique has been developed. The determination is based on the accumulation of germanium(IV)-diol complexes by adsorption at a hanging mercury drop electrode, followed by cathodic stripping voltammetry. Suitable for the complex forming reaction are catechol (1,2-dihydroxybenzol) and pyrogallol (1,2,3-trihydroxybenzol). By using pyrogallol the detection limit is 0.1 ng ml^–1 with a standard deviation of ±13%. A multistage combined procedure with adsorptive stripping voltammetry is described for the determination of germanium traces in ginseng and garlic. The results are compared with those using extraction-spectrophotometry and atomic absorption spectrometry.Dedicated to Prof. Dr. G. Schulze on the occasion of his 60th birthday     

Highly Selective Adsorptive Cathodic Stripping Voltammetric Determination of Uranium in the Presence of Pyromellitic Acid

A very sensitive and selective adsorptive cathodic stripping procedure for trace measurement of uranium is presented. The method is based on adsorptive accumulation of the uranium‐pyromellitic acid (benzene‐1,2,4,5‐tetracarboxylic acid) complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. Influences of effective parameters such as pH, concentration of pyromellitic acid, accumulation potential and accumulation time on the sensitivity were studied. The peak current was proportional to the concentration of U(IV) up to 40 ng mL^?1 with a limit of detection of 0.136 ng mL^?1 with an accumulation time of 120 s. The range of linearity enhanced to 71.4 ng mL^?1and the detection limit improved to 0.058 ng mL^?1with accumulation times of 60 s and 300 s respectively. The relative standard deviation for 10 replicate determination of 4.76 ng mL^?1 U(IV) was equal to 2.7%. The possible interference by major cations and anions are investigated. The method was applied to the determination of uranium in some analytical grade salts, seawater and in synthetic samples corresponding to some uranium alloys with satisfactory results.     

Determination of furazolidone in urine by square-wave voltammetric method

A fast, simple and sensitive square-wave voltammetric (SWV) method for the determination of trace amounts of furazolidone (FZ) in urine is reported. A three-electrode system containing stationary mercury dropping (SMDE) working electrode, Pt auxiliary electrode and Ag/AgCl reference electrode was used throughout. Briton-Rabinson buffer solution is used as both pH adjusting agent and supporting electrolyte. The calibration graph showed good linearity in the concentration range of 20–900 ng ml^?1 of furazolidone with a regression coefficient of 0.9996. The equation Δ(i) = 0.0095C_FZ + 0.234 was used for calculation of furazolidone concentration in the sample solution, where C_FZ is the concentration of furazolidone in ng ml^?1 and Δ(i) is the difference between voltammogram peak currents of sample and blank solution. The RSD for 8 replicate measurements of a 60 ng ml^?1 solution and LOD of the proposed method were found to be 2.2% and 5.2 ng ml^?1, respectively. The procedure was successfully applied to the determination of furazolidone in urine samples.     

Determination of Copper by Adsorptive Stripping Voltammetry in the Presence of Calcein Blue

An electrochemical adsorptive stripping approach is presented for the trace measurement of copper in some real samples. The method is based on the reduction of Cu²⁺ at pH 5.5 calcein blue (CB) containing solution at ?250 mV (vs. Ag/AgCl), adsorption of Cu? CB complex on hanging mercury drop electrode (HMDE) and the voltammetric determination by further reduction to Cu⁺ at HMDE. Experimental optimum conditions were determined in the fundamental studies. At the experimental optimum conditions the adsorbed complex of Cu²⁺ and calcein blue gives a well defined cathodic stripping peak current at ?0.135 V, which has been used for the determination of copper in the concentration range of 0.02 to 15 ng/mL with accumulation time of 90 s. The relative standard deviation (RSD) for the determination of 0.5 and 6.0 ng mL^?1 were 2.60 and 1.94% respectively. (n=10). The method has been applied to the analysis of copper in analytical reagent grade salts and tap water, mineral water and drug samples with satisfactory results.     

Determination of azinphos-methyl by adsorptive stripping voltammetry

A very sensitive electrochemical stripping procedure for azinphos-methyl (Guthion) is reported. Accumulation is achieved by adsorption of the compound on a hanging mercury drop electrode. The adsorptive stripping response was evaluated with respect to accumulation time and potential, concentration dependence, electrolyte and other variables. The determination limit is 0.2 ng ml^?1 after 300 s accumulation and 0.4 ng ml^?1 after 180 s accumulation. The procedure was applied to spiked river water.     

Cathodic adsorptive stripping square-wave voltammetry of the anti-inflammatory drug meloxicam

The adsorptive behavior of the anti-inflammatory drug meloxicam was studied by cyclic, differentia-pulse and square-wave voltammetry on a hanging mercury drop electrode (HMDE). The drug was accumulated at HMDE and a well-defined stripping peak current was obtained at -1.42 V vs. Ag/AgCl (saturated KCl) electrode in acetate buffer solution (pH 5.0). A voltammetric procedure was developed for the determination of meloxicam using square-wave cathodic adsorptive stripping voltammetry (SW-CASV). The optimum working conditions for the determination of the drug were established. The analysis of meloxicam in human plasma was carried out satisfactorily.     

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.     

Stripping Voltammetry of Cerium(IIl) with a Chemically Modified Carbon Paste Electrode Containing Functionalized Nanoporous Silica Gel

This research introduces the design of an adsorptive stripping voltammetric method for the cerium(III) determination at a carbon paste electrode, chemically modified with dipyridyl‐functionalized nanoporous silica gel (DPNSG‐CPE). The electroanalytical procedure comprised two steps: the Ce(III) chemical accumulation at ?200 mV followed by the electrochemical detection of the Ce(III)/dipyridyl complex, using anodic stripping voltammetry. The factors, influencing the adsorptive stripping performance, were optimized including the modifier quantity in the paste, the electrolyte concentrations, the solution pH and the accumulation potential or time. The resulting electrode demonstrated a linear response over a wide range of Ce(III) concentration (1.0–28 ng mL^?1). The precision for seven determinations of 4 and 10 ng mL^?1 Ce(III) was 3.2% and 2.5% (relative standard deviation), respectively. The prepared electrode was used for the cerium determination in real samples and very good recovery results were obtained.     

High sensitive determination of trace amount of cobalt by catalytic adsorptive stripping voltammetry

A very sensitive and selective catalytic adsorptive cathodic stripping procedure for trace measurements of cobalt is presented. The method is based on adsorptive accumulation of cobalt-CCA (calcon carboxylic acid) complex onto a hanging mercury drop electrode followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. The reduction current is enhanced catalytically by nitrite. The effect of various parameters such as pH, concentration of CCA, concentration of nitrite, accumulation potential and accumulation time on the selectivity and sensitivity were studied. The optimum condition for the analysis of cobalt, include pH 5.2 (Acetate buffer), 2.1 μM clacon carboxylic acid, 0.032 M sodium nitrite and an accumulation potential of 0.05 V (versus Ag/AgCl). Under these optimum conditions and for an accumulation time of 60 s, the measured peak current at −0.480 V is proportional to the concentration of cobalt over the entire concentration range tested 0.003–2.0 ng ml⁻¹ with a detection limit of 1 pg ml⁻¹ for an accumulation time of 60 s and 2.0–10.0 ng ml⁻¹ for an accumulation time of 40 s. The relative standard deviations for ten replicate measurement of 0.5 ng ml⁻¹ of cobalt were 3.1%. The main advantage of this new system is the microtrace Co(II) determination by ASV. The method was applied to determination of cobalt in a water sample and some analytical grade salts with satisfactory results. Published in Elektrokhimiya in Russian, 2009, Vol. 45, No. 2, pp. 221–228. The article is published in the original.     

Adsorptive stripping voltammetric determination of the anti-inflammatory drug celecoxib in pharmaceutical formulation and human serum

Celecoxib is a cyclooxygenase inhibitor, that has been recently and intensively prescribed as an anti-inflammatory drug in rheumatic osteoarthiritis. A robust, highly reliable and reproducible square-wave (SW) adsorptive cathodic stripping voltammetric procedure was developed for the determination of celecoxib in pharmaceutical formulation and human serum. The analytical procedure was based on the reduction of the CN of the pyrazole ring of the drug molecule at the mercury electrode surface in Britton-Robinson buffer of pH 7.0. The SW adsorptive cathodic stripping voltammogram of celecoxib showed a single well-defined peak at −1.54 V (vs. Ag/AgCl/KCl_s) using an accumulation potential of −0.70 V, frequency of 120 Hz, scan increment of 10 mV and pulse amplitude of 25 mV. Repeatability was examined for 1×10⁻⁸ M CXB drug solution after 30 s pre-concentration and a mean recovery of 99.4±0.4% (n=5) was achieved. For 90 s preconcentration, a linear concentration range of 1×10⁻⁹-2×10⁻⁸ M CXB and a detection limit of 1.86×10⁻¹⁰ M were achieved. The proposed procedure was successfully applied for the determination of the drug in capsules and human serum with mean recoveries of 101.5±0.6 and 98.8±1.1%, respectively. A detection and quantitation limits of 1.0×10⁻⁹ M (0.4 ng ml⁻¹) and 4.7×10⁻⁹ M (1.3 ng ml⁻¹) were achieved for the determination of the drug in human serum. Moreover, the procedure was useful for study of the pharmacokinetic profile of celecoxib in a healthy volunteer after administration of a single oral dose (celebrex®, 200 mg).     

Electrochemical properties and square-wave voltammetric determination of pravastatin

The electrochemical reduction and adsorptive voltammetric behaviour of pravastatin have been studied by means of cyclic and square-wave voltammetry at a hanging mercury-drop electrode in electrolytes of different pH. Within the entire pH range (2.0–9.0) in Britton–Robinson buffer, pravastatin gave rise to a single voltammetric peak in the potential interval from −1.22 to −1.44 V, depending on pravastatin concentration. It was found that the reduction of pravastatin proceeds via a relatively stable intermediate, which is transformed to the final electroinactive product by a coupled chemical reaction or can be re-oxidized back to pravastatin. The rate of chemical transformation is controlled by the proton concentration. The electrode mechanism has the properties of a surface redox reaction. A sensitive analytical method for trace analysis of pravastatin based on the adsorptive stripping technique has been developed. The calibration plot was linear in the range 8×10⁻⁸–5×10⁻⁷ mol L⁻¹. Application of the square-wave voltammetric method to determination of pravastatin in a pharmaceutical dosage form, without sample pretreatment, resulted in acceptable deviation from the stated concentration.     

Simultaneous Determination of Iron,Copper, and Cadmium by Adsorptive Stripping Voltammetry in the Presence of Thymolphthalexone

A novel, sensitive and selective adsorptive stripping procedure for simultaneous determination of iron, copper and cadmium is presented. The method is based on the adsorptive accumulation of thymolphthalexone (TPN) complexes of these elements onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan using differential pulse modulation. The influences of control variables on the sensitivity of the proposed method for the simultaneous determination of iron, copper and cadmium were studied using the Derringer desirability function. The optimum analytical conditions were found to be TPN concentration of 2.0 μM, pH of 9.5, and accumulation potential at ?0.4 V vs. Ag/AgCl with an accumulation time of 60 s. The peak currents are proportional to the concentration of iron, copper and cadmium over the 1–80, 0.5–100 and 1–100 ng mL^?1 ranges with detection limits of 0.5, 0.4 and 0.9 ng mL^?1_, respectively. The R.S.D. at a concentration level of 20 ng mL^?1 of iron, copper and cadmium were 2.5%, 0.9% and 1.5% (n=6), respectively. The procedure was applied to the simultaneous determination of iron, copper and cadmium in the tap water and some synthetic samples with satisfactory results.     

Adsorptive Stripping Square-Wave Voltammetry of Creatine

ABSTRACT

An adsorptive stripping square-wave voltammetric method for quantitative determination of creatine is developed. The basic redox properties of creatine are investigated by means of square-wave and cyclic staircase voltammetry. Creatine undergoes an irreversible reduction in neutral and acidic medium at a hanging mercury drop electrode. The square-wave voltammetric response of creatine depends on the parameters of the SW excitation signal as well as on the concentration and type of the supporting electrolyte, the accumulation time and the potential and pH of the medium. The optimal experimental conditions for quantitative determination of creatine are as follows: supporting electrolyte 0.1 mol/L KNO₃ buffered with 0.1 mol/L acetate buffer to pH = 4 and accumulation potential -1.2 V. The optimal SW parameters found are: frequency f = 120 Hz, amplitude E _sw = 30 mV, and scan increment dE = 4 mV. A detection limit of 6.6 x 10^?8 mol/L creatine was obtained after 30 s preconcentration period at accumulation potential -1.2 V. The correlation coefficients of the calibration curves at concentration levels of 10^?7 to 10^?5 mol/L creatine are greater than 0.99. The results of recovery tests range from 92.18% to 102.51%.     

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 sensing of triclosan in the presence of cetyltrimethylammonium bromide using a cathodically pretreated boron-doped diamond electrode

ABSTRACT

In the present study, a simple, cheap and sensitive electrochemical method based on a cathodically pretreated boron-doped diamond (CPT-BDD) electrode is described for the detection of triclosan with the cationic surfactant (cetyltrimethylammonium bromide, CTAB) media. The oxidation of triclosan was irreversible and exhibited an adsorption controlled process. The sensitivity of the adsorptive stripping voltammetric measurements was significantly improved with addition of CTAB. Using square-wave stripping mode, a linear response was obtained for triclosan determination in Britton-Robinson buffer solution at pH 9.0 containing 2.5 × 10^?4 M CTAB at around + 0.67 V (vs. Ag/AgCl) (after 30 s accumulation at open-circuit condition). The method could be used in the range of 0.01–1.0 μg mL^?1 (3.5 × 10^?8–3.5 × 10^?6 M), with a detection limit of 0.0023 μg mL^?1 (7.9 × 10^?9 M). The feasibility of the proposed method for the determination of triclosan in water samples was checked in spiked tap water.     

Determination of the pesticide Chlorpyrifos by cathodic adsorptive stripping voltammetry

The adsorption behavior and differential pulse cathodic adsorptive stripping voltammetry of the pesticide Chlorpyrifos (CP) were investigated at the hanging mercury drop electrode (HMDE). The pesticide was accumulated at the HMDE and a well-defined stripping peak was obtained at –1.2 V vs Ag/AgCl electrode at pH 7.50. A voltammetric procedure was developed for the trace determination of Chlorpyrifos using differential pulse cathodic adsorptive stripping voltammetry (DP-CASV). The optimum working conditions for the determination of the compound were established. The peak current was linear over the concentration range 9.90 × 10^–8– 5.96 × 10^–7 mol/L of Chlorpyrifos. The influence of diverse ions and some other pesticides was investigated. The analysis of Chlorpyrifos in commercial formulations and treated waste water was carried out satisfactorily