Differential Pulse Polarographic Peak Research Articles

A new and sensitive method for the determination of trace arsenic using differential pulse polarography

A new and simple differential pulse polarographic method has been developed for the trace determination of arsenic. When selenite was added into solutions of some ions such as copper, lead, cadmium, zinc, and chromium, their differential pulse polarographic peak decreased. A new reduction peak appeared at a more positive potential than the ion present and it was always higher than the corresponding reduction peak of the ion. Thus, we made use of this interference for the trace determination of As(III). By the addition of selenite onto As(III), a new As−Se intermetallic compound peak was formed at about −0.35 V (pH at about 1.0–2.0). The trace arsenic concentration could be determined simply from this peak by the addition of standard arsenic into a polarographic cell. In the presence of large amounts of selenite, 2 × 10−7 mol/L As(III) could be determined from this peak precisely. With the newly established method, the limit of detection was 1 × 10−8 mol/L (S/N = 3). Among the most common cations and anions, only Cd−Se and Pb−Se intermetallic compound peaks had an overlap with the As−Se peak. This interference could be eliminated simply by the addition of EDTA. This method was applied successfully for the determination of arsenic in a digested beer sample.

Electrochemical Analysis of Zinecard In Pharmaceutical And Biological Samples

Zinecard is used to prevent a toxic effect to heart caused by certain medicines that are used to treat cancer. Zinecard is also used to treat tissue damage caused by the leakage of certain medicines that are used to treat cancer. Differential pulse polarographic method developed for the quantitative determination of zinecard gives a peak at -0.32 V at DME. From the structural point of view zinecard contains a >C=Omoiety which can be electrochemically reduced at universal buffer (pH 4.0). Millicoulometric experiment is performed successfully in estimating the number of electrons and proton to understand reduction mechanism. The differential pulse polarographic peak was adequately well-resolved, reproducible and linear dependent with the zinecard concentration. For quantification the calibration plot for zinecard concentrations ranging between 1.0×10 -5 mol dm -3 to 1.0×10 -8 mol dm -3 at pH 4.0 was selected. The proposed differential pulse polarographic method was successfully applied to the determination of zinecard in pharmaceutical formulations and urine samples. Key words: Zinecard, DPP, pharmaceutical formulations and urine samples.

Binding of Cd2+ and Zn2+ with the Phytochelatin (γ‐Glu‐Cys)4‐Gly: A Voltammetric Study Assisted by Multivariate Curve Resolution and Electrospray Ionization Mass Spectrometry

AbstractThe complexation of Cd2+ and Zn2+ with the phytochelatin (γ‐Glu‐Cys)4‐Gly (PC4) is studied by Differential Pulse Polarography (DPP) assisted by Multivariate Curve Resolution with Alternating Least Squares (MCR‐ALS) and by Electrospray Ionization Mass Spectrometry (ESI‐MS). In the case of Zn2+, voltammetric results show the presence of an inert electroinactive Zn2+PC4 complex, which is confirmed by ESI‐MS. In the case of Cd2+, the unitary DPP peaks and the concentration profiles obtained by MCR‐ALS from DPP titrations of PC4 with Cd2+ suggest the formation of two electroactive Cd2+PC4 complexes. The first complex, with a 1 : 1 stoichiometry, shows a fixed DPP peak potential characteristic of a kinetically inert behavior. After further Cd2+ additions a second labile complex seems to be formed. This behavior is confirmed by ESI‐MS detection of CdPC4 and Cd2PC4 complexes.

Differential Pulse Polarographic and UV‐Vis Spectrophotometric Study of Inclusion Complexes Formed by 1,4‐Dihydropyridine Calcium Antagonists, Nifedipine and Nicardipine with β‐Cyclodextrin

AbstractThe formation of inclusion complexes of well‐known 1,4‐dihydropyridine calcium antagonists, such as nifedipine (NF) and nicardipine (NC), with β‐cyclodextrin (βCD) was investigated by differential pulse polarography (DPP) and UV‐vis spectrophotometry. The equimolar variation method indicated the formation of the NF‐βCD (1 : 1, M : M) and a NC‐βCD (1 : 1, M : M) inclusion complexes. Titrations using the DPP peak currents for NF and NC permitted one to determine formation constant values of (135±20) M−1 and (357±41) M−1 for NF‐βCD and NC‐βCD, respectively. For comparative purposes we have also applied phase solubility studies with spectrophotometric detection obtaining formation constant values of (129±5) M−1 and (385±19) M−1 for NF‐βCD and NC‐βCD, respectively. According to the DPP studies, we can postulate that the inclusion moiety were the nitroaromatic group, in the case of NF‐βCD, and the phenyl group on 3‐position of the 1,4‐DHP, in the case of NC‐βCD. The solubility of NF in water was increased about three times due to the formation of an inclusion complex with βCD. For NC the solubility was increased almost seven times.

Alternating Current Tensammetry of Tetraphenylborate (TPB) and its Application for Potassium Determination

AbstractAlternating‐current polarography of tetraphenylborate ion (TPB) in acetate buffer (pH 4 to 5) or 0.1 to 0.5 M NaCl produces a characteristic tensammetric (pseudocapacitive) peak at −0.95 V (vs. SCE). Within a limited range (till about 0.2 mM), the tensammetric peak current is proportional to the TPB concentration but it levels off at higher concentration. TPB concentration can also be determined within 5 to 50 μM by measuring the capacity current at −0.4 V or the differential pulse polarographic peak current at −0.85 V. The tensammetric peak current was used to determine the solubility of potassium tetraphenylborate in acetate buffer and sodium chloride solutions. Also, a method for amperometric back‐titration of potassium ion was worked out and applied to the analysis of mineral water.

Polarographic determination of propranolol in pharmaceutical formulation

Propranolol was reacted with nitric acid to give nitropropranolol and was then measured in Britton–Robinson solutions in the pH range 2.0–12.0 by differential-pulse polarography. Nitropropranolol gave rise to a well-resolved differential-pulse polarographic peak at pH 2.0. A linear calibration graph in the range 5.0×10 −7–5.0×10 −5 M and a detection limit of 5 nM was obtained. The relative standard deviation was 1.95% ( n=10) at 5×10 −6 M. The effect of common exceipient on the peak height was evaluated. The method was applied for the determination of the drug in the tablet dosage form.

Differential pulse polarographic determination of clotrimazole after derivatization with Procion Red HE-3B.

Clotrimazole was shown to react at room temperature in Britton Robinson buffer pH 2 with the reactive dye Procion Red HE-3B. The product exhibited a differential pulse polarographic peak at -0.38 V, which was well separated from the peaks of the reactive dye at -0.08, -0.80 and -0.95 V, and this allowed the indirect determination of clotrimazole in the presence of excess of the reactive dye. The method has been applied satisfactorily to the determination of clotrimazole in pharmaceutical formulations, calibration graphs are rectilinear up to at least 40 microg ml(-1). The detection limit was calculated to be 2.6 microg ml(-1) (3 sigma).

Voltammetric determination of N, N′-dinitrosopiperazine in simulated gastric juice

A voltammetric method has been developed for the determination of N, N′-dinitrosopiperazine (DNPZ) in simulated gastric juice. The method is based on measuring the differential pulse polarographic peak produced in pH 3 Britton Robinson buffer. A well defined, diffusion-controlled cathodic wave was obtained at −0.77 V versus Ag/AgCl over the range 0.4–24 μg/ml with minimum detectability (S/N=2) of 0.072 μg/ml (5×10 −7 M). The proposed method was successfully applied to study the possible in vivo production of the nitroso-derivatives of piperazine under the standard nitrosation reaction conditions recommended by WHO. The method has some distinct advantages over the reported GC methods.

An electrochemical approach to the determination of dinobuton: a study of water samples

The electrochemical reduction behaviour of dinobuton was studied by employing advanced electrochemical techniques such as dc polarography, cyclic voltammetry, differential pulse polarography (DPP), controlled potential electrolysis and millicoulometry in universal buffers of pH ranging from 2.0 to 12.0. Polarographic and cyclic voltammetric studies of dinobuton showed that it is reduced in two six-electron steps in acidic medium and in two four-electron steps in basic medium. Polarographic waves are irreversible and diffusion controlled in nature and are precisely proportional to the concentration of dinobuton. A reduction mechanism is proposed on the basis of voltammetric results and reduction product analysis. The dependence of the DPP peak on various parameters was studied and the optimum conditions for the determination of dinobuton were found. Finally, the developed DPP method was applied to the determination of dinobuton in agricultural formulations and in spiked water samples. Evaluation by the standard addition method confirmed the accuracy of the analytical procedure.

Voltammetric determination of N-nitrosoderivatives of atenolol and propranolol in simulated gastric juice

A highly sensitive and simple voltammetric method is proposed for the determination of N-nitrosoatenolol (NA) and N-nitrosopropranolol (NP) in simulated gastric juice. The method is based on measuring the differential-pulse polarographic peak produced by NA and NP in Britton–Robinson buffers of pH 3 and 4 for NA and NP, respectively. Both compounds yielded diffusion-controlled current with diffusion–current constants of 7.23±0.03 and 9.46±0.06 for NA and NP, respectively. The current–concentration plots were rectilinear over the range 0.16–9.6 μg ml −1 with minimum detectability ( S/ N=2) of 0.015 μg ml −1 (5×10 −8 M) for NA; for NP the range was 0.08–8.0 μg ml −1 with minimum detectability ( S/ N=2) of 0.009 μg ml −1 (3×10 −8 M). The proposed method was successfully applied to study the possible in vivo production of the nitroso-derivatives under the standard nitrosation reaction conditions recommended by WHO. The method is characterized by simplicity and higher sensitivity as compared with the reported HPLC method.

Polarographic Complex Formation Curves for Fully Inert Metal-Ligand System

The ligands N,N,N′,N′-tetra-2-picolylethylenediamine (TPEN) and 1,4,7-tris(2-hydroxyethyl)-triazacyclononane (THETAC) were studied with BiIII, CdII and PbII by differential pulse polarography (DPP) at fixed total ligand to total metal concentration ratios and varied pH. These metal ions formed fully inert ML complexes with the ligands. It has been shown that the polarographic experimental and calculated complex formation curves (ECFC and CCFC), used previously for modeling of the fully labile metal-ligand systems and the refinement of stability constants of labile metal complexes, can be employed without any modification to study fully inert metal-ligand systems. The ECFC, in which a variation in a height of a labile DPP peak is converted into millivolts, appears to be a characteristic function for a particular metal-ligand system where the inert ML complex is formed. It has been demonstrated that the excess of the ligand is not required at all to obtain the reliable stability constant of an inert complex ML that can be polarographically either active or inactive. Stability constants found here are compared with the literature data.

Differential pulse polarography and electron spin resonance spectroscopy of nitroxyl free radicals used as ESR-spin probes

Differential pulse polarography (DPP) and electron spin resonance (ESR) were used to study the influence of substituents and of the pH of the medium on DPP peak potentials (electrochemical reduction) resp. k reduction (chemical reduction) of nitroxyl free radicals. The DPP peak potentials can be used to select the appropriate nitroxide spin label for relevant biochemical and biophysical applications.

A potentiometric and differential pulse polarographic study of Cd II with 1-hydroxyethylenediphosphonic acid

The complexation of the ligand 1-hydroxyethylenediphosphonic acid (HEDP) with Cd II was studied by differential pulse polarography (DPP) and glass electrode potentiometry (GEP) at fixed total ligand to total metal concentration ratios and varied pH values. Labile and non-labile metal complexes were analysed simultaneously by the use of a polarographic experimental complex formation curve (ECFC) and the calculated complex formation curve (CCFC). Complex formation curves were used for modelling of the metal–ligand system and the refinement of stability constants. The ECFC, in which experimental parameters of only labile DPP peak are included (a shift in the peak potential and a variation in the peak height) appears to be a characteristic function for a full metal–ligand model (labile and non-labile parts of a metal–ligand system). The CCFC is a theoretical curve calculated for the assumed metal–ligand model from mass-balance equations. The final model of metal species formed is the one, which is confirmed by these two experimental techniques, and for which stability constants of metal complexes obtained from DPP and GEP differ the least. Six cadmium complexes M(H 4L), M(H 2L), M 2L, ML (all labile), ML 2 (non-labile), and ML(OH) (labile) and their stability constants as log β found from DPP 25.04±0.06, 19.56±0.02, 12.67±0.03, 7.26±0.02, 10.39±0.06 and 10.93±0.04, respectively, are reported. Results obtained from GEP are also reported and they differ from polarographic results only within the experimental errors typical for these techniques.

A differential pulse polarographic study of bismuth III complexes with macrocyclic ligands 1,4,7,10-tetraazacyclododecane and 1,4,7,10-tetrakis (2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane. An out-of-cell determination of stability constants of polarographically active and inactive bismuth complexes at fixed ligand to metal ratio and various pH values

The ligands 1,4,7,10-tetraazacyclododecane (cyclen) and 1,4,7,10-tetrakis (2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane (THP-cyclen) were studied with Bi III by differential pulse polarography (DPP) at the fixed total ligand to total metal concentration ratio and various pH values at 25°C and an ionic strength of 0.5 mol dm −3. The out-of-cell technique was used for the stability constant determination, as the equilibrium of the Bi III–cyclen and Bi III–THP-cyclen systems in aqueous solution is very slow. A polarographic speciation technique based on the data interpretation of a labile part of the metal–ligand system was used. The stability constants of the ML complexes, as log K 1, were estimated to be 23.45±0.05 and 21.25±0.05 for Bi III–cyclen and Bi III–THP-cyclen, respectively. The influence of neutral alcoholic oxygen donors on the stability constants is discussed and results obtained in this work are compared with the literature data. The presence or absence of the DPP peaks of reduction of polarographically non-labile complexes Bi III–cyclen and Bi III–THP-cyclen is related to their crystallographic structures.

Differential Pulse Polarographic Analysis of Chlorpyrifos Insecticide

The differential pulse polarographic (DPP) behavior of chlorpyrifos (CP) was investigated over a wide range of pH (pH 1.8–pH 10.1). CP compound displays a well-resolved cathodic reduction peak at −1.2 V (vs. Ag/AgCl) (pH 3.2). This peak probably corresponds to the reduction of the CN centre of the pyridyl moiety. The effect of solution and operational parameters on the sensitivity of the DPP peak was carefully examined in order to select the optimum conditions for determination of the CP compound. Under the optimum conditions the reduction response gives a linear calibration plot over a concentration range of 9.70 × 10−7–6.92 × 10−6 M and the detection limit was found to be 8.7 × 10−7 M. The effects of some diverse metal ions, anions and some other organophosphorus insecticides on the determination of CP compound were studied. The applicability of DPP for determination of the CP insecticide in a commercial sample as well as in some irrigation water (treated waste water and underground water) was detected.

Inosine reduction study at low pH by a combination of electrochemical methods

The reduction process of inosine on a mercury electrode has been studied by differential pulse polarography (DPP), elimination polarography (EP), and potentiostatic macroelectrolysis. The measurable reduction signal of inosine can give only DPP and EP and can be measured only in the pH range between 1.4 and 2.5. For pH values below this limit the hydrogen evolution makes the measurement irreproducible, while for pH values above this limit the hydrogen reduction current totally overlaps the inosine signal. The elimination of the charging and kinetic current with the conservation of the diffusion current by EP application revealed the inosine reduction wave. The concentration dependence of this wave indicates the inosine association resembling the micelle formation or phase transition with a critical concentration around 0.1 mM. The EP wave corresponds to the reduction of inosine monomer. The DPP peak appears in more negative potentials than the EP wave and corresponds to catalytic hydrogen reduction. The reduction scheme for inosine monomer based on the results of EP and of the analysis of macroelectrolysis reduction products leads to a reduction scheme with four electrons and four protons and with the breaking of the pyrimidine ring. The inosine associates, inosine and the inosine reduction product are responsible for the hydrogen reduction catalysis. The process in the associates occurs by the recombination of hydrogen atoms travelling along the train of stacked hypoxanthine molecules in one associate. With respect to the known similarity of the reaction processes of purine derivatives, the present study can serve as a base for the interpretation of their electrochemical behavior.

Voltammetric study of nimesulide and its differential pulse polarographic determination in pharmaceuticals

AbstractNimesulide, N‐(4‐nitro‐2‐phenoxyphenyl)methanesulfonamide is an antiinflamatory analgesic agent that is both reducible at the mercury electrode and oxidizable at the glassy carbon electrode. Nimesulide in hydroalcoholic solution, presents cathodic response in a wide range of pH (2–12), both, by differential pulse and tast polarography techniques. The obtained results show only one main well‐defined peak or wave in all the pH range studied. This peak (or wave) corresponds to the nitro group reduction in position 4. The voltammetric oxidation shows one well‐resolved signal in all the pH range studied. This anodic signal could be attributed to the methylsulfonamide group oxidation. For analytical purposes, a very well resolved diffusion controlled differential pulse polarographic peak obtained at pH 7 was selected. This peak was used to develop a new method for the determination of nimesulide in pharmaceutical dosage forms. The recovery study (104.8% with a RSD of 1.3%) shows that the method is sufficiently accurate and precise to be applied in the individual tablet assay of commercial samples.

Pulse polarography of soybean trypsin inhibitor in the presence of dithiothreitol

The redox system of reduced and oxidized dithiothreitol, DTT(SH) 2/DTT(S-S), was followed in the presence of bovine pancreatic trypsin inhibitor (BPTI) from buffer solution pH 8.8 using differential pulse polarography (DPP). The reduction of -S-S- bonds in protein with DTT(SH) 2 was investigated either in absence or in the presence of denaturant such as guanidine hydrochloride (Gdn-HCl). From the analysis of -SH and -S-S- DPP peak current intensities, the kinetic of BPTI unfolding was estimated. It was found that the reaction rate is one order of magnitude higher when denaturant is present, indicating that the lifetime of the corresponding intermediary is shortened.

Voltammetric study of ketorolac and its differential pulse polarographic determination in pharmaceuticals

A differential pulse polarographic method for the quantitative determination of ketorolac is described. Ketorolac is an antiinflamatory-analgesic agent that is directly electroreducible at the mercury electrode. The polarographic reduction is due to the reduction of the benzoyl moiety in the ketorolac molecule. For analytical purposes, a very well resolved diffusion controlled differential pulse polarographic peak obtained at pH 9 was selected. This peak was used to develop a new method for the determination of ketorolac in pharmaceutical dosage forms. Recovery study shows that the method is sufficiently accurate and precise to be applied in the individual tablet assay of commercial samples.

Cadmium-binding properties of glutathione: A chemometrical analysis of voltammetric data

The complexation of glutathione (GSH) by Cd 2+ has been investigated as a model for the coordination chemistry of Cd 2+ by thiol-containing peptides. Experimental data obtained by differential pulse polarography (DPP) for different Cd 2+-to-GSH concentration ratios at fixed pH have been globally analyzed by the recently proposed multivariate curve resolution (MCR) method. Polarograms from experiments at fixed Cd 2+-to-GSH concentration ratios but changing pH values have been univariately deconvoluted at each pH value. In both cases, the obtained single DPP peaks can be associated to specific electrode processes. The results obtained in this work, together with structural data from the literature, allow us to propose a model for the complexation of Cd 2+ by GSH involving the formation of Cd(GSH) 2 and Cd 2(GSH) 2 complexes. Moreover, a scheme for the electrode process is also proposed.