Polarographic Wave Research Articles

Anodic Polaroqraphic Determination of lsradipine in Pharmaceutical Formulations

The anodic behaviour of isradipine was studied using cyclic voltammetry (CV), direct current (DCt) and differential-pulse (DPP) polarography. lsradipine exhibited well-defined anodic polarographic waves over the pH range of 4–8 in Britton-Robinson buffer (BRb). At pH 6, the analytical pH, the diffusion-current constant (Id) was 2.12 ± 0.42 (n = 4). The oxidation potential is −0.10 V vs AgIAgCl reference electrode with correlation coefficients of 0.9977 and 0.9948 in the DCt and DPP modes, respectively. The current-concentration plots were rectilinear over the ranges 5–14 µg/ml and 2.4–12 µg/ml using the DCt and DPP modes, respectively. The lower detection limit was 1.12 µg/ml (3.02 x 10−6 M) adopting the DPP mode. The proposed method was applied to commercial tablets and capsules, the % recoveries were 100.52 ± 1.267 and 99.4 ± 0.87 (n = 6) for the tablets and 101.3 ± 1.57 and 100.7 ± 2.10 (n = 6) for the capsules adopting both DCt and DPP modes, respectively. The number of electrons involved in the electrode process was accomplished and a proposal of the electrode reaction was presented.

Electroreduction of dipyridamole at mercury-coated platinum microelectrode

The electroreduction of Dipyridamole (DIP) was studied in 0.10 mol L-1 phosphate buffer solution (pH 3.0) on a mercury coated platinum microelectrode (Hg-ME), employing cyclic, linear sweep voltammetry and polarography techniques. The similarity between Hg-ME voltammetric profile and the sigmoidal polarographic waves both with a diffusion limited current is showed. Experiments with a hanging mercury drop electrode (HMDE) were performed in parallel to confirm the results obtained with Hg-ME, which indicated that the reduction occurs in two irreversible steps involving two electrons and two protons each step. The limiting diffusion current, concerning the first step, allows estimating the diffusion coefficient for DIP as being equal to 2.04 x 10-5 cm2 s-1.

Anodic polarographic determination of josamycin in formulations and spiked human urine

The anodic polarographic behaviour of josamycin (a macrolide antibiotic) has been studied using direct current (DC t) polarography and differential pulse polarography (DPP). In Britton–Robinson buffers (BRb) josamycin exhibited well-defined anodic polarographic waves in the pH range 2–8. In BRb of pH 6, the diffusion-current constant was 1.62 μA mmol –1 ( n = 6). The current–concentration plots are rectilinear over the range 10–50 and 5–40 μg/ml using the DC t and DPP modes, respectively, with a detection limit of 4.83 × 10 −6 M adopting the DPP mode. The method was applied to commercial tablets adopting both DC t and DPP modes, the recoveries % were 99.13 ± 2.22 ( n = 10) and 99.82 ± 1.82 ( n = 7), respectively. The method was further extended to the in vitro determination of josamycin in human urine, the recovery % ( n = 6) was 100.06 ± 2.84. The number of electrons involved in the electrode process could be accomplished and a proposal of electrode reaction was presented.

Equilibrium (NAD +/NADH) potential on poly(Neutral Red) modified electrode

The electrochemical regeneration of nicotinamide adenine dinucleotide (NAD +/NADH) has been one of the central subjects of bioelectrochemistry during past three decades. We report on the unique chemical electrocatalyst for NAD +/NADH regeneration based on electropolymerized Neutral Red. Using poly(Neutral Red) modified electrodes, the reversible polarographic waves of nicotinamide adenine dinucleotide reduction–oxidation and the equilibrium (NAD +/NADH) potential were observed. This was impossible using all known catalytic and mediator systems. The unique poly(Neutral Red) based electrocatalyst allowed us to determine the standard (NAD +/NADH) potential more precisely ( E ′≅0.59 V SCE, pH 6.0).

Analysis of Pharmaceuticals and Biological Fluids Using Modern Electroanalytical Techniques

A review of the principles and application of modern electroanalytical techniques, namely, cyclic voltammetry, linear sweep voltammetry, differential pulse voltammetry, differential pulse polarography, square wave voltammetry, square wave polarography, stripping voltammetric, and stripping polarographic techniques, is presented. The use and advantages of these techniques at different electrodes are discussed. The analytical applications of these techniques to pharmaceutical compounds in dosage forms and biological media are also discussed. Various selected studies on these subjects since 1995 are reviewed.

In situ generation and detection of methyl radical by voltammetry

In persulfate-acetate, dimethyl sulfoxide ortert-butyl alcohol systems,in situ generation and detection of methyl free radical are realized with voltammetry. It includes the following successive processes. The persulfate S2O 8 2− is polarographically reduced via one-electron addition to sulfate radical SO 4 −· , the SO 4 −· initiates chain reaction with acetate, dimethyl sulfoxide, ortert-butyl alcohol on the electrode surface to produce a methyl radical, and one-electron reduction of the methyl radical yields its polarographic reduction wave. In comparison with the known techniques such as ultraviolet radiolysis coupling with electron spin resonance, etc., the proposed method is simple, sensitive and selective.

Forward and reverse scans in square wave voltammetry applied to the first order CE mechanism: Ti(IV)/Ti(III) system in acidic oxalate media

A dimensionless analysis of the first order CE mechanism, whatever the rate of the charge transfer, in square wave voltammetry and incidentally in normal pulse voltammetry is presented. The quantitative description of the limiting cases of the mechanism and of the kinetic steady-state currents for reversible and irreversible electrochemical reactions, permits diagrams to be drawn, delimiting zones of preponderance for the various types of currents. Reverse scans (from the plateau towards the foot of the corresponding polarographic wave) are also studied and their interest in kinetic studies is discussed. In a subsequent experimental part, the kinetics of the Ti(IV)/Ti(III) system in acidic (HClO 4, H 2SO 4) oxalate media is investigated and the validity of the theoretical predictions is checked.

A New Approximate Formulation of the Koutecky Function

AbstractA new approximate formulation of the Koutecky function is proposed, with two new equations; one for the approximate calculation of the Koutecky function F(χ) in terms of its argument χ and the inverse χ=f [F(χ)]. Both use only two adjustable parameters, substantially more precise than the Smith‐McCord‐Hung and Oldham‐Parry formulations. The dependence χ=f [F(χ)] permits a more accurate general equation for polarographic waves to be deducted.

Stripping chronopotentiometry at scanned deposition potential (SSCP): Part 2. Determination of metal ion speciation parameters

Stripping chronopotentiometry at scanned deposition potential (SSCP) generates curves that are fundamentally different in form from classical polarographic waves. Still, despite their steeper slope and non-linear log plot, the shift in the SSCP half-wave deposition potential can be interpreted in a manner completely analogous to the DeFord–Hume treatment of polarographic waves. SSCP provides a reliable measure of metal speciation in the sample solution in the presence of simple ligands (i.e. those with non-distributed K and D values), even when there is relatively small ligand excess, and it is unaffected by induced metal adsorption. Data interpretation is not so straightforward for heterogeneous ligands: the presence of a range of metal complexes of slightly different stability and mobility flattens the SSCP wave as compared to the homogeneous case. The time dependent nature of the surface concentration of metal ion during deposition precludes straightforward rigorous interpretation of heterogeneous metal ion speciation.

A New Method of Analysis of Polarographic Waves

A method of analysis of polarographic waves of simple electrode processes is proposed. The quasi-reversible half-wave potential, Ec1/2, is involved in the determination of thermodynamic and kinetic parameters of electrode processes. This potential is determined very easily and with great precision. In order to facilitate the use of the method proposed, we have developed a computer program for Windows.

Stripping chronopotentiometry at scanned deposition potential (SSCP).: Part 1. Fundamental features

A rigorous theory for the shape and characteristics of (deposition potential) scanned stripping chronopotentiometry (SSCP) curves is presented. Their fundamental features are investigated and compared with those of dc polarograms. An equation is derived that fully describes the relationship between stripping time, τ, and deposition potential, E d, in the complete depletion regime at both a conventional HMDE and a microelectrode. This equation is explicit in the analytical signal, τ, and shows that for a reversible system the τ, E d waveform is basically different from the conventional polarogram. Specifically, it is distinctly steeper and does not conform to a linear log-plot. Still, the shift in half-wave potential in the presence of complexing agents, as well as the effect of a reduced diffusion coefficient for the metal complex species, can be interpreted straightforwardly, analogous to the DeFord–Hume expression for a polarographic wave.

Voltammetric determination of nitrosocimetidine in simulated gastric juice.

To develop a voltammetric method for the determination of nitrosocimetidine in simulated gastric juice (SGJ). Measurement of the polarographic wave of the nitroso derivative at the dropping mercury electrode in 0.1 m HCl. A well-defined diffusion-controlled cathodic wave was obtained at -0.34 V vs. Ag/AgCl electrode. The current-concentration relationship was found to be rectilinear over the range 10-80 microg/mL and 2-50 microg/mL with percentage recovery of 101.24 +/- 0.79 and 100.79 +/- 0.56 for the direct current (DCt) and differential pulse polarography (DPP) modes, respectively, with a minimum detectability (S/N=2) of 0.16 microg/ml (5.6 x 10-7 m) using DPP mode. The proposed method was successfully applied to study the nitrosation of cimetidine in SGJ.

Preconcentration with membrane cell and adsorptive polarographic determination of formaldehyde in air

The present paper describes a procedure that formaldehyde in air was preconcentrated in a membrane cell and its content was determined by adsorptive polarography. First the formaldehyde in air samples was preconcentrated in a membrane cell using water, then the formaldehyde reacted with 2,4-dinitrophenyl hydrazine to form 2,4-dinitrophenyl hydrazone, which can be adsorbed at the mercury electrode and yields a sensitive adsorptive polarographic wave. Over the range 6.0×10 −10–5.0×10 −6 M, the peak currents are linearly proportional to the concentration of formaldehyde, the detection limit is 2.0×10 −10 M.

Study and Application of Polarographic Catalytic Wave of Chlordiazepoxide in the Presence of Persulfate

AbstractPolarographic catalytic wave of chlordiazepoxide in the presence of K2S2O8 was studied in aqueous and DMF/H2O mixed solutions. The results showed that a single reduction wave in alkaline medium was the reduction of the N = C bond in 1,2‐position of chlordiazepoxide via an intermediate free radical in two one‐electron successive additions. When K2S2O8 was present, the free radical of the N = C bond was oxidized to regenerate the original, producing a parallel catalytic wave of chlordiazepoxide. It was determined that the apparent rate constant kf of the oxidation reaction was 3.2 × 103 mol−1·L·s−1. Using the catalytic wave the trace of chlordiazepoxide can be determined by linear‐potential scan polarography. In NH3/NH4Cl (pH 10.2 ± 0.1, 0.12 mol/L)/K2S2O8(0.016 mol/L) supporting electrolyte, the second‐order derivative peak current of the catalytic wave was rectilinear to chlordiazepoxide concentration in the range of 3.20 × 10−8‐1.60 × 10−7, 1.60 × 10−7‐1.44×10−6 and 1.44×10−6‐1.44x 10−5 mol/L, respectively. The limit of detection was 9.0×10−9 mol/L.

Differential Pulse Polarographic Determination of Procymidone in Formulations and Wine

The dicarboximide fungicide procymidone was studied systematically by using direct current polarography, cyclic voltammetry, differential pulse polarography (DPP), controlled potential electrolysis, and millicoulometry in the universal buffer medium with dimethylformamide as the solvent. Procymidone exhibited a single well-defined polarographic wave in the pH range 2.0-6.0, leading to the formation of the hydroxy compound. The overall reduction process was diffusion-controlled and adsorption-free. The variation of half-wave potential with pH, the concentration of the analyte, and other experimental conditions are described. The reduction mechanism proposed is an overall 4-electron process, in which the dicarboximide group is reduced. DPP was used to determine procymidone in agricultural formulations and wine at the optimum conditions found; a detection limit of 2.4 x 10(-9) M was estimated. The results obtained by the proposed method were also compared with those obtained by other methods.

Determination of Nitrite in Foods by Single-Sweep Polarography

In an acid medium, nitrite diazotized with p-rosaniline and then coupled with 8-hydroxyquinoline in a weak alkaline medium produces azo compounds. The azo compounds produce a very sensitive polarographic wave at -0.70 V (versus the saturated calomel electrode). The height of the peak is linear with the concentration of nitrite in the range of 5 x 10(-9) to 5 x 10(-7) g/mL. The detection limit is 3 x 10(-9) g/mL. The electrochemical characteristics of the polarographic wave are also discussed. The method was used to determine nitrite in sausage. The results agree well with those obtained by spectrophotometry.

Simultaneous Determination of Synthetic Dyes Tartrazine, Allura Red and Sunset Yellow by Differential Pulse Polarography and Partial Least Squares. A Multivariate Calibration Method

Synthetic azo dyes, such as tartrazine, sunset yellow and allura red have sensitive polarographic waves in solution (pH 9.2). However, the dyes polarographic waves are seriously overlapped making their simultaneous determination difficult without previous sample preparation. The aim of this work was to apply partial least squares (PLS) multivariate calibration to such commonplace electrochemical technique as differential pulse polarography (DPP) for the simultaneous determination of the dye's three component mixture at trace levels (0.05–1.00 μmol/L). The method has been applied in the determination of these synthetic dyes in commercial food products.

Electrochemical behavior of 5-bromosalicylaldehyde isonicotinoylhydrazone

Electrochemical behavior of 5-bromosalicylaldehyde isonicotinoylhydrazone has been studied at dropping mercury and glassy carbon electrodes by employing DC polarography and cyclic voltammetry in Britton-Robinson buffers (pH 2-10). The compound exhibits two polarographic waves in solutions of pll 2-10. In cyclic voltammetric studies, the hydrazone exhibits two cathodic peaks in acid solutions (pH 4.0) and one cathodic peak in alkaline solutions (pH 8.0). The electrode reactions are attributed to the reductive cleavage of =N-N- linkage and the reduction of amide formed in the cleavage.

A POLAROGRAPHIC STUDY OF TL+, PB2+ AND CD2+ COMPLEXES WITH DICYCLOHEXANO-18-CROWN-6 IN SOME BINARY MIXED SOLVENTS

The complexes of Tl+, Pb2+ and Cd2+ cations with the macrocyclic ligand, dicyclohexano-18-crown-6\linebreak(DC18C6) were studied in water/methanol (H2+O/MeOH), water/1-propanol (H2+O/1-PrOH), water/acetonitrile (H2+O/AN), water/dimethylformamide (H2+O/DMF), dimethylformamide/acetonitrile (DMF/AN), dimethylformamide/methanol (DMF/MeOH), dimethylformamide/1-propanol (DMF/1-PrOH) and dimethylformamide/nitromethane (DMF/NM) mixed solvents at 22 °C using differential pulse polarography (DPP), square wave polarography and conductometry. In general, the stability of the complexes was found to decrease with increasing concentration of water in aqueous/non-aqueous mixed solvents with an inverse relationship between the stability constants of the complexes and the concentration of DMF in non-aqueous mixed solvents. The results show that the change in stability of DC18C6.Tl+, vs the composition of solvent in DMF/AN and DMF/NM mixed solvents is apparently different from that in DMF/MeOH and DMF/1-PrOH mixed solvents. While the variation of stability constants of the DC18C6.Tl+ and DC18C6.Pb2+ complexes vs the composition of H2+O/AN mixed solvents is monotonic, an anomalous behavior was observed for variations of log Kf vs the composition of H2+O/1-PrOH and H2+O/MeOH mixed solvents. The selectivity order of the DC18C6 ligand for the cations was found to be Pb2+ > Tl+ > Cd2+.

Square Wave Voltammetric-Thermodynamic Study of the Interaction Between Heavy Metal Ions and Some Macrocyclic Ligands in Water*

The interaction between Cd2+ and Pb2+ ions and 18-crown-6 (18C6), 1,10-diaza-18-crown-6 (C22) and 1,7-diaza-15-crown-5 (C21) were studied in water solvent at 25, 35, 45 and 55°С using square wave voltammetric technique. The stoichiometry and stability of the complexes were determined by monitoring the shift in half-wave or peak potential of the polarographic waves of metal against the ligand concentration. Thermodynamic parameters such as ΔG, ΔH and ΔS were obtained by using a polarographic double wall cell in which the temperature could be fixed to ±0.1°C. The results of all experiments show 1 : 1 complexes, but in addition to 1 : 1 ratio, a 2 : 1 ratio of ligand to cation is also obtained for C22–Pb2+ complex. The selectivity order for 18C6 and C22 is Pb2+ > Cd2+. The thermodynamic data ΔG, ΔH and ΔS values show that the complexes are stabilized by both the enthalpy and entropy terms, but C22–Pb2+ complex is stabilized by only enthalpy term.