Differential pulse polarography and voltammetry of di-2-pyridyl ketone benzoylhydrazone

Summary The differential pulse polarographic (DPP) and voltammetric (DPV) behaviour of di-2-pyridyl ketone benzoylhydrazone (DPKBH), has been investigated over a wide pH range (2.1–11.5). The effect of various operational parameters on the reduction current are discussed and the mechanism of the electrode reaction is also included. Both methods DPP and DPV are applied for the analytical determination of this reagent and the detection limits are found to be 1.24 mol/l and 0.86 mol/l, respectively. The DPP behaviour of DPKBH in the presence of Pb(II), Cd(II) and Cu(II) is studied and the behaviour of the Cu(II)-DPKBH complex is fully investigated. The voltammetric determination of Cu(II), based on the accumulation of its complex at the hanging mercury drop electrode, is described. Statistical analysis of the calibration curve data is included.On leave from Assuit University, Egypt     

Determination of acipimox in capsules by differential pulse polarography

A differential pulse polarographic (DPP) method has been developed for the determination of acipimox in its pharmaceutical formulations. Using Sörensen buffer pH 6.0 as supporting electrolyte a single, irreversible peak occurred at –0.79 V vs an Ag/AgCl reference electrode. The peak height vs concentration plot was found to be linear over the range of 10^–6 to 6 × 10^–4 mol/l. The detection limit is 60ng/ml. The analysis of a series of 10 Olbetam® 250 mg capsules showed an overall standard deviation of ± 4.18 mg and a S_rel of ± 1.66%, respectively.     

The Use of Differential Pulse and D.C. Polarography in the Analysis of Solutions Containing Surfactants

Abstract

Peak currents in differential pulse polarography (DPP) are often used for quantitative analysis. In the presence of surfactants, peak currents depend not only on the concentration of the electroactive species, but also on that of the surfactant. In the presence of surfactants of biological origin, limiting currents obtained by d.c. polarography are often less sensitive to the effects of surfactants and are more suitable for quantitative analysis than DPP peak currents. Effects of surfactants on DPP curves were demonstrated for 4-nitrobenzoic acid in the presence of oligomers resulting from washing lignin preparations with water. In the study of adsorption of nitro compounds on lignin, d.c. polarographic curves yielded reliable adsorption isotherms whereas DPP peak currents indicated erroneously much stronger adsorption of nitro compounds on lignin.     

Resolution of global signals using ratio differential pulse polarograms: Determination of p-nitroaniline and p-nitrotoluene in their mixture

Ratio differential pulse polarograms obtained by dividing the multianalyte and single analyte signals are proposed as a tool for resolution of global signals and quantification of the analytes from a qualitatively known mixture by differential pulse polarography (DPP) and related electroanalytical techniques. The influences of shape and position of the resolving function (DP polarograms of individual analyte) on the efficiency of resolution are discussed on simulated and experimental results. The method is applied for the determination of p-nitroaniline (NA) and p-nitrotoluene (NT) from their mixture in N,N′-dimethylformamide solutions with 0.1 M tetrabutylammonium iodide as supporting electrolyte, using an external calibration diagram and internal standard addition methods. NA and NT give one-electron DP polarographic peaks with 93 mV of peak separation and, therefore, show significant overlapping which depends on the concentration ratio of NA and NT in the mixture. The method is especially suitable for quantification of one analyte in the presence of a large excess of another analyte, because by division the component in excess is removed and the pseudo-ratio DPP of the minor component is clearly revealed in a way which is not possible by deconvolution using polynomial division or deconvolution by Fourier transforms.     

Study of the electrochemical behaviour of amphetamine and its derivatives in aqueous solution

The polarographic behaviour of amphetamine-type drugs in acid and alkaline solutions was investigated. Differential pulse polarography (DPP) with a dropping mercury electrode (DME) was used to monitor these drugs in aqueous solution. DPP and cyclic voltammetry (CV) were also utilised to study the electrode process of some 2-phenylethylamines derivatised with 4-N,N-dimethylaminobenzaldehyde (Ehrlich’s reagent) and 2,4-dinitrofluorobenzene, known as Sanger’s reagent, respectively.     

Study of the electrochemical behaviour of amphetamine and its derivatives in aqueous solution

The polarographic behaviour of amphetamine-type drugs in acid and alkaline solutions was investigated. Differential pulse polarography (DPP) with a dropping mercury electrode (DME) was used to monitor these drugs in aqueous solution. DPP and cyclic voltammetry (CV) were also utilised to study the electrode process of some 2-phenylethylamines derivatised with 4-N,N-dimethylaminobenzaldehyde (Ehrlich’s reagent) and 2,4-dinitrofluorobenzene, known as Sanger’s reagent, respectively. Received: 19 March 1998 / Revised: 17 September 1998 / Accepted: 21 September 1998     

Electrode processes of the V(III)/V(II) and Eu(III)/Eu(II) systems in mixed water + acetone solvents

Rate constants of the electrode reaction V(III)+e⁻ → V(II) in water+acetone mixtures were determined. In the regions of irreversible and quasi-reversible behaviour we used polarographic and square-wave polarographic measurements, respectively. The values of the constant go through a minimum with increasing concentration of acetone. Following the published data for the Eu(III)/Eu(II) system (H. Elzanowska, Ph. D. Thesis, Warsaw, 1957), this behaviour was explained by the simultaneous reduction of differently solvated ions in the solution where, depending on the degree of electrode coverage, a partial resolvation at the electrode surface can occur. The calculated dependence of the rate constant on the solvent composition is in accord with experimental values.     

Enhanced sensitivity for the differential pulse polarographic determination of Mo(VI) based on adsorption catalytic current

A differential pulse polarographic (DPP) method based on the adsorption catalytic current in a medium containing chlorate and 8-hydroxyquinoline (oxine) is suggested for the determination of molybdenum(VI). Experimental conditions such as pH and the composition of supporting electrolyte have been optimized to get a linear calibration graph at trace levels of Mo(VI). The sensitivity for molybdenum can be considerably enhanced by this method. The influence of possible interferences on the catalytic current has been investigated. The sensitivity of the method is compared with those obtained for other DPP methods for molybdenum. A detection limit of 1.0 × 10^–8 mol/L has been found.     

Polarographic Studies on Se(IV) in Absence and Presence of Pb(II), Zn(II) and Sb(III) Ions in Aqueous N-(2-ACETAMIDO) Imino Diacetate Buffer Solutions

Abstract

The polarographic reduction and determination of selenite ions in absence and presence of a mixture of some cationic species such as, Pb(II), Zn(II) and Sb(III) in N-(2-acetamido) imino diacetate solutions, at constants of ionic strength 0.1 mol dm^?3 (KNO₃) and temperature 25°C was studied using direct current and differential pulse polarographic (DPP) techniques. It was shown that reduction of Se(IV) takes place along one, two or three waves depending on the pH value of the solution using the direct current polarographic measurements. The reduction of Se(IV) in N-(2-acetamido) imino diacetate buffer solutions was found to be reversible and involving six electron transfer process. Microcoulometric experiments was performed at the limiting current region of the different waves and at various pH values. Kinetic parameters and wave characteristics for the reduction of selenite ions have been calculated. A method for the analytical determination of selenite ions in either simple or quadruple mixture of ADA buffer solutions using DPP techniques are reported and discussed.     

A new simple sensitive differential pulse polarographic method for the determination of acrylamide in aqueous solution

A new simple sensitive differential pulse polarographic (DPP) method was investigated for the determination of acrylamide (AA) directly in a neutral aqueous solution. The AA showed a well-defined and well-resolved peak in pure aqueous LiCl at −1.84 V in the potential range from −1.6 V to −1.97 V at nitrogen pressure of 0.5 kg cm⁻². Among the various electrolytes studied, the AA showed good DPP response in the presence of LiCl and tetra methyl ammonium iodide, while it showed poor response in the presence of tetra butyl ammonium hydroxide and tetra butyl ammonium bromide due to their strong adsorption on the surface of electrode which hindered its reduction. The effect of LiCl concentration, the cyclic voltammetric response and the drop time study showed that AA exhibited an irreversible adsorptive electrochemical behavior. The good electrochemical response in pure aqueous medium suggested that hydrogen bonding might be involved which may favor the electrode reaction. Under optimized conditions, the peak current was linear in the entire concentration range from 0.2 mg L⁻¹ to 20 mg L⁻¹ with the correlation coefficient of R² = 0.9998. The method showed good reproducible results with R.S.D. of 0.3% (n = 16). The detection limit (LOD) was 27 μg L⁻¹. The influence of various interfering agents was also studied. The method was applied successfully for the quantification of AA in water samples without any interference effect from alkali metals.     

Effect of citric acid and hydrochloric acid on the polarographic behaviour of tin: Application to the determination of tin(II) in presence of tin(IV) in the activating solutions of the electroless plating of polymers

A new method for the determination of tin(II) in presence of tin(IV) is described. The method is based on differential pulse polarography on the hanging mercury drop electrode (HMDE). The effect of citric acid and hydrochloric acid concentrations on the polarographic peaks of tin(II) and tin(IV) has been studied. In 1 M HCl, the total quantity of tin can be determined, as under these conditions, in the absence of complexing agents, eventual variations in the oxidation states, in any concentration ratio, do not affect the peak height and the peak potential. In 0.2 M HCl and 0.2 M citric acid, tin(II) can be determined selectively in presence of tin(IV), as under these conditions, tin(IV) does not present polarographic response, while a well-defined peak is observed for tin(II). The method is applied to determine tin(II) and total tin in the activating solutions of the electroless plating of polymers.     

Simultaneous Polarographic Determination of Lead (II) and TIN (II) by Multivariate Calibration

ABSTRACT

The polarographic waves of lead (II) and tin (II) overlap due to their similar reductive potentials and it is difficult to determine these two components simultaneously without a pre-separation. In this paper, differential pulse polarography (DPP) combined with multivariate calibration approaches, such as classical least squares (CLS), principal component regression (PCR) and partial least squares (PLS), were successfully applied to the resolution of overlapping polarographic waves of these two components in the concentration range of 0.05-3.50 mg 1^?1. Satisfactory quantitative results were obtained.     

Electrochemical and spectroscopic characterization of interaction between antimalarial drug cinchonine and human serum albumin at physiological pH

In the present study, the interaction between cinchonine (CCN) and human serum albumin (HSA) was investigated using differential pulse polarography (DPP), cyclic voltammetry (CV) and spectroscopic techniques in Britton-Robinson (B-R) buffer pH 7.4. CCN displayed a main cathodic peak at ?1.228 V (vs. Ag|AgCl|KCl_sat) on mercury working electrode. The addition of HSA into CCN sulfate solution resulted in the decrease of the main reduction peak current of CCN and no new peaks appeared. The decay in the peak current of CCN, after the addition of HSA, showed a decrease in free drug concentration and formation of a biocomplex. The peak current changes of CCN in the presence of HSA were followed by DPP to determine the binding parameters. The logarithm of binding constant and binding ratio between CCN and HSA were 6.128 and 1: 1, respectively. This interaction was also confirmed by UV-Vis and FTIR-ATR spectroscopic measurements.     

Direct current and differential pulse polarographic behaviour of benzylpenicilloic acid

The differential pulse and direct current polarographic behaviour of benzylpenicilloic acid (BPA) is discussed. In pH 9.2 borate buffer, the single anodic wave (E_{$\text{1}\text{2}$} = -0.25 V) obtained is diffusion-controlled at concentrations less than 2 × 10^-5 M but adsorptioncontrolled in 10^-4 M solution. Cyclic voltammetry at a hanging mercury drop electrode shows that the electrode reaction is reversible at pH 9.2. The differential pulse peak current is linearly related to concentration in the range 10^-6—2 × 10^-5 M. Penicillamine yields an anodic peak well separated from the BPA peak. Both substances may be determined in each other's presence. Intact penicillin decreases the BPA peak but the linearity between i_p and BPA concentration is maintained.     

Electrochemical behavior of 2'-halogenated derivatives of N,N-dimethyl-4-aminoazobenzene at mercury electrode.

The electrochemical behavior of 2'-halogeno-N,N-dimethyl-4-aminoazobenzene derivatives was investigated using various polarographic and voltammetric methods. The peak potentials of these derivatives were observed to shift towards negative values along with an increase in the pH. A reduction of the azo linkage took place via two electrons at pH > 4, but four electrons at pH < 4 in aqueous-ethanol mixtures. The standard rate constants were determined with (Laviron technique) or without (Nicholson technique) taking the adsorption phenomena into account. The diffusion coefficients were calculated from the cyclic voltammetric data using a method developed by Garrido. The amount of adsorbed substances and transfer coefficients for the electron transfer were also determined. A mechanism for the electrode reaction is proposed. These compounds can be quantitatively determined between 1 x 10(-5) M and 1 x 10(-7) with DPP and CV.     

Differential Pulse Polarographic Determination of Nitrate in AUT Solution

A differential pulse polarographic method for the determination of nitrate ion has been developed. With 0.5 M CaCl₂ as supporting electrolyte, NO^?₃ is reduced to give a peak with E_1/2=–1.836 Volt vs. the Ag/AgCl electrode. The differential pulse polarographic peak height is proportional to the nitrate concentration from 20 to 60 ppm. The detection limit for nitrate is 2 ppm in pure aqueous solution. In the determination of 40 ppm nitrate a relative precision (relative standard deviation) of less than 2% was achieved. Nitrite interferes seriously and should be absent if accurate results are required. The method has been applied to the determination of nitrate in Ammonium Uranyl Tricarbonate (AUT) Solution, results obtained by this method are compared to those obtained by ion chromatography. The agreement between the two sets of results suggests that the DPP method can be used with a fair degree of confidence.     

Polarographic Detection of Arenediazonium Ions. Optimization of the Method and Application for Investigating Dediazoniation Mechanisms

The use of differential pulse polarography (DPP) at the dropping mercury electrode (DME) to detect and to investigate the mechanisms for decomposition of arenediazonium ions, ArN₂⁺, under different experimental conditions is discussed. The effect of a number of experimental and instrumental parameters on the polarographic peaks of a model arenediazonium ion was explored and representative applications to investigate their reaction mechanisms are given. The composite data shows that DPP provides an alternative, relatively cheap, technique to monitor ArN₂⁺ decomposition in, for example, opaque systems where, for obvious reasons, spectroscopic detection does not work; meanwhile in homogeneous systems, DPP complements the results obtained by employing spectroscopic or chromatographic techniques. In addition, a variety of valuable mechanistic information such as detection of transient intermediates or estimation of the binding constants of aryl radicals with macromolecular systems, that otherwise cannot be easily obtained, is readily available by using DPP.     

Application of principal component regression to the determination of Captopril by differential pulse polarography with no prior removal of dissolved oxygen

As shown in this paper, multivariate calibration in general and principal component regression (PCR) in particular allow the determination of Captopril by differential pulse polarography (DPP) in the presence of oxygen despite the overlap between their polarographic bands. Electrochemical parameters (pulse amplitude, pulse delay and drop time) are optimized from response surfaces using PCR to determine the relationship between the variables to be optimized and the relative square error of prediction (RSEP), which was adopted as the parameter to be minimized. The proposed method is quite fast and inexpensive as a result of the decreased analysis times and sparing use of the inert gas. It was applied to the determination of Captopril in synthetic samples and a commercially available pharmaceutical preparation, with relative errors and confidence intervals <2.5% and 2.0%, respectively. It should be noted that the sample can be analysed directly following dissolution in water without the need to remove the excipients.     

Trace determination of platinum-I. A catalytic method using pulse polarography

Experimental conditions are given for the development of a well-defined catalytic polarographic wave for PT(II) after chelation with ethylenediamine. Direct-current polarographic studies of the wave characteristics indicate that it is of the catalytic hydrogen type, sensitive to pH changes, temperature, and electrode characteristics. By differential pulse polarography a single, sharp peak at -1.62 V is obtained, allowing trace determination of Pt(II) in the range 0.01-1.0 ppm with a linear calibration and a detection limit of 0.003 ppm. The catalytic wave is shown to suffer little interference from other platinum-group metals at 1:1 concentration ratio to Pt, except for Rh(III).     

Estimation of cephalosporin antibiotics by differential pulse polarography

Differential pulse polarographic (DPP) method of determination of cephalosporins has been developed based on the electrochemistry of the azomethine group in the drugs in universal buffers of pH 2.0-12.0. Quantitative measurements were successful in the concentration range of 1.0 x 10(-5) M-2.5 x 10(-8) M, the lower concentration representing the detection limit by DPP. The described procedure has been applied for the determination of these drugs individually in pharmaceutical formulations and urine samples as well as for simultaneous determination in a single run.