Comparison of differential pulse and alternating current polarography in the soft-modelling study of the complexation of Cd(II) by the fragment Cys-Gly and by the phytochelatin (γ-Glu-Cys)<Subscript>2</Subscript>Gly

A comparison of a differential pulse polarographic with a phase sensitive alternating current polarographic study of the Cd-Cys-Gly and Cd-PC₂ systems [PC₂ being a phytochelatin of general structure (γ-Glu-Cys) _n -Gly, with n = 2] has been performed. The chemometric multivariate curve resolution method with alternating least squares was applied in the experimental data analysis. The results obtained by both polarographic techniques have made it possible to find out the formation sequences of the complexes and their final stoichiometries. The alternating current polarograms compared with the differential pulse ones show some differences (a new signal and an important shift of peak potentials), which anyway are consistent with some of the conclusions obtained by differential pulse polarography. This fact implies that although the alternating current polarography results need some corrections before data treatment, they provide extra information that complements the conclusions achieved by differential pulse polarography. Figure Voltammograms at ACP(−10°), ACP(−65°) and corrected ACP during the titration of a 10⁻⁵ mol L⁻¹ Cd(II) solution with PC₂ at pH 8.5 in 0.05 L⁻¹ Tris.     

Determination of cyanuric acid in swimming pool water by differential pulse polarography

A reliable differential pulse polarographic method is described for the determination of cyanuric acid (1,3,5-triazine-2,4,6-triol) in pool water. Cyanuric acid in the range 10^?5–10^?3 M is determined by means of the peak at ca. –60 mV (vs. Ag/AgCl/3 M NAcl). The high sensitivity of the polarographic technique allows ten-fold dilution of samples, thus avoiding matrix effects. It it shown that the peak can be attributed to formation of insoluble mercury(I) cyanurate, Hg₂(HC₃N₃O₃), at the mercury electrode.     

Differential pulse polarographic behaviour of thiazopyr herbicide and application to its determination in fruit juice and soil samples

A differential pulse polarographic method for the determination of the herbicide thiazopyr has been developed. The polarographic study of thiazopyr exhibited two well-defined cathodic peaks within the pH range of 1.0 to 8.0. The variation of pH and polarographic parameters indicated that the optimum conditions under which thiazopyr could be reduced were a pH 7.0 BR buffer solution, a reduction peak potential of ?1270 mV (vs. SCE), scan rate of 5 mV s^?1, pulse amplitude of 50 mV with pulse duration of 50 ms at an ambient temperature of 25 ± 3°C. The main reduction peak was characterised by cyclic voltammetry as being irreversible and diffusion-controlled. A linear relationship between the peak current and the concentration of thiazopyr was obtained in the range of 0.43–38.6 µg mL^?1, with a detection limit of 0.127 µg mL^?1. The proposed method was successfully applied to the determination of thiazopyr in spiked fruit juice and soil samples. The mean recoveries of the 19.8 µg g^?1 and 3.96 µg mL^?1 thiazopyr spiked to soil and orange juice were 20.2 ± 1.0 µg g^?1 and 3.84 ± 0.12 µg mL^?1, at 95% confidence level, respectively. The sufficiently good recoveries and low relative standard deviation (RSD) data confirm the high accuracy and precision of the proposed method. The interferences effects of several commonly used pesticides and inorganic species were also studied. Interfering effects were eliminated either by providing selectivity with pH, or using EDTA as complexing agent.     

Differential Pulse Polarographic Determination of Moxifloxacin Hydrochloride in Pharmaceuticals and Biological Fluids

Abstract

A simple, fast, sensitive and fully validated differential pulse polarographic (DPP) method for the determination of trace amounts of moxifloxacin in pharmaceutics, serum and urine is reported. Moxifloxacin exhibited irreversible cathodic peak over the pH 5.00–11.00 in Britton–Robinson (B–R) buffer. At pH 10.00 (the analytical pH), a well‐defined peak at ?1.61 V versus saturated calomel electrode was obtained. The current has been characterized as being diffusion‐controlled process. The diffusion current constant (i_d) was 1.48±0.12 and the current–concentration plot was rectilinear over the range from 5×10^?7 to 1×10^?4 M with correlation coefficient (n=10) of 0.995.

The proposed method was applied to commercial tablets and average percentage recovery was in agreement with that obtained by spectrophotometric comparison method. The method was extended to the in vitro determination of moxifloxacin in spiked human serum and urine.     

Polarographic determination of herbicide thifensulfuron methyl/application to agrochemical pesticide,soil, and fruit juice

A novel, sensitive, simple, fast, and fully validated differential pulse polarographic (DPP) method for the determination of trace amounts of thifensulfuron-methyl in pesticide formulation, soil, and orange juice is reported. This procedure was based on a highly sensitive peak formed due to the reduction of thifensulfuron-methyl on a dropping mercury electrode over the pH range 1.00–10.00 in Britton–Robinson buffer. The polarographic reduction exhibits only a single peak in the pH ranges pH?≥?3.0 and pH?≤?6.0 and pH?=?10.0 located at potential values of ?1.010, ?1.350, and ?1.610?V (vs. SCE), respectively. The single peak appeared as a maximum at pH 3.0 (?1.010?V) was well resolved and suitable to be investigated for analytical use. This peak showed quantitative increments with the additions of standard thifensulfuron-methyl solution under the optimal conditions, and the cathodic peak current was linearity proportional to the thifensulfuron-methyl concentration in the range of 2?×?10^?7–5?×?10^?5?M. The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 1.05?×?10^?7 and 3.50?×?10^?7?M, respectively, according to the relation k ?×?SD/b (where k?=?3 for LOD, k?=?10 for LOQ, SD is the standard deviation of the blank, and b is the slope of the calibration curve). The proposed method was applied to pesticide formulation (Harmony® Extra), and the average percentage recovery was in agreement with that obtained by the spectrophotometric comparison method, 97.82 and 102.6%, respectively. The method was extended to determination of thifensulfuron-methy in spiked soil and orange juice, showing a good reproducibility and accuracy with a relative standard deviation of 4.55 and 1.40%, and relative errors of +2.80 and +1.90%, respectively.     

The application of 2,4,6-trinitrobenzene-1-sulphonic acid in the differential pulse polarographic determination of amines

The differential pulse polarographic behaviour of 2,4,6-trinitrophenyl (TNP) derivatives of several primary amines and amino acids was investigated in the presence of sulphite ion. All the derivatives produced a polarographic peak for their complexes with sulphite (1 × 10^?2 M) in pH 8.0 phosphate buffer (0.05 M)/0.1 M potassium chloride. The derivatives of proteins and peptides did not give such a peak. A 5-min reaction time at room temperature (or 50°C for lysine) and pH 10.5 using 1 × 10^?4 M 2,4,6-trinitrobenzene-1-sulphonic acid provides the optimal conditions for the determination of 5 × 10^?6?2.5 × 10^?5 M amines. The relative standard deviation for determining 1 × 10^?5 M glycine (n = 5) was 1%.     

Differential pulse polarographic determination of some organotin(IV) compounds in dimethyl sulfoxide

The differential pulse polarographic behavior of two series of organotin(IV) compounds having the general formula R_xSnCl_{4 − x} (R = Me, Ph; x = 1, 2, 3, 4) has been investigated in DMSO. The peaks obtained are recommended for the trace determination of these compounds. Linear calibration curves are obtained over the concentration range 10⁻⁴ –10⁻⁶ M.     

Determination of Oxygen to Uranium Ratio in Uranium Dioxide Nuclear Fuel by Differential Pulse Polarography

A differential pulse polarographic method for determination of oxygen to uranium ratio in uranium oxides is fully described. An accuracy ?2.62% to +4.35% was achieved by calibrating the method against standard U₃O₃, replicate test runs with UO₂, gave a precision of ±4.59% or better. The method is now successfully used in routine analysis for UO² fuel.     

Sensitive Differential Pulse Polarographic Determination of Molybdenum Using The New Catalytic System Mo(VI)‐Phenantroline‐Chlorate

It was found that in acidic chloride media the complex of Mo(VI) with 1,10‐phenantroline induces catalytic reduction of KClO₃. This catalytic effect can be utilized for sensitive differential pulse polarographic determination of Mo(VI) with a low detection limit of 2.9×10^?11 M (2.8 ng/L). The optimal Mo(VI) response was obtained at pH 2.8, in the presence of (6–12)×10^?5 M 1,10‐phenantroline and 2×10^?2 M KClO₃. The sensitivity was 1.73 nA/nM and the catalytic response was linear up to 7.5×10^?7 M Mo (VI). The interferences from inorganic ions and surface‐active substances were investigated. The results of the determination of Mo(VI) in CRM water sample showed good reproducibility (R.S.D. for standard solution is below 1.2% and for water samples is 8.9%) and accuracy of the elaborated catalytic polarographic method.     

Study on the determination of trace rhenium (VII) by the adsorption differential pulse polarography

The determination of trace rhenium (VII) by differential pulse polarography in the system of H₂SO₄-(NH_sOH)₂ · H₂SO₄-TeO^2?₄ is markedly improved by the addition of Nitron, which is adsorbed on the surface of mercury electrode. The limit of detection is down to 2 × 10¹⁰ M. The adsorptive peak potential is ?0.80 V (vs. SCE). In the ranges of 5 × 10¹⁰—10^?8, 1 × 10^?5—10^?7 and 1 × 10^?7—10^?6M, there are good linear relationships between the peak current increment and the concentration, of which the relative standard deviations are 9.5, 6.6, 1.8% respectively with the correlation coefficients of linear regression of 0.995–0.999. The results relating to this polarographic wave show that it is an adsorption-catalytic wave. The mechanism of the electrode reaction is discussed.     

Differential pulse polarographic determination of nitrate in environmental materials

Nitrate can be determined with reliable accuracy and sensitivity by differential pulse polarography utilizing the catalytic reaction between nitrate and uranyl ion in the presence of potassium sulphate. The differential pulse polarographic peak-height is proportional to nitrate concentration from 1 to 50 muM. The calculated detection limit for nitrate is 8 x 10(-7)M in pure aqueous solution. The method has been applied to determination of nitrate in fresh snow, and river waters and animal feeds.     

Differential Pulse Polarographic Determination of Orthophosphate in Nonaqueous Media

Abstract

The method is based on the polarographic behavior of 12-tungstophosphoric acid in nonaqueous media at the DME utilizing the differential pulse polarographic technique. In this procedure, orthophosphate is converted to 12-tungstophosphoric acid H₃ PW ₁₂ O ₄₀ by reacting with tungstate under acidic conditions and at 100°C. The H₃ PW ₁₂ O ₄₀ is extracted into 1-pentanol and its polarographic measurement is made in 1-pentanol-ethanoi mixture containing sodium perchlorate as supporting electrolyte. The differential pulse polarogram of H₃ PW ₁₂ O ₄₀ in this solution shows three peaks between 0.00 and -0.90 V vs. Ag/ AgCl. The most cathodic peak at -0.78 V exhibited the highest peak current value and was used for the analytical measurement. A linear calibration graph in the range 0.10 - 5.00 pg/ml P in the final solution was obtained. The method has a relative standard deviation of 0.90% at the 4 pg/ml P level and 1.32% at the 1 μg/ml P level in the final solution. Arsenate, borate and silicate do not interfere.     

Polarographic determination of nanomolar concentrations of molybdenum(VI)

Summary Polarographic Determination of Nanomolar Concentrations of Molybdenum (VI) A new differential pulse polarographic method for the determination of Mo(VI) is described. Mo(VI) is first chelated by 7-nitro-8-hydroxychinoline-5-sulfonic acid at pH 1. The complex ion MoO₂L₂ ^2– formed is strongly adsorbed on the surface of a dropping mercury electrode. At a potential difference of 0.95 V the complex ion is reduced to a Mo(V)-complex, which is oxidized very fast by H_aq ⁺ providing the starting complex ion for repeated redox cycles. The net process consists in the catalytic reduction of H_aq ⁺ to 1/2 H₂ in the double layer. H₂ was detected by inductively coupled plasma atomic emission spectrometry. A modified preparation method for the chelating agent and its characterization are also described. The method was used for the determination of Mo(VI) in the surface water of Lake Zürich. An average value of 0.463±0.007 ng/g (4.83±0.07 nM) was calculated from 39 single values. The errors are the confidence intervals of the corresponding means at the 99% confidence level. The standard deviation and the practical detection limit were 0.016 and 0.031 ng/g, respectively, for single determinations on the average.     

Trace determination of TeO42?, TeO32?, AsO2? and VO3? by differential pulse polarography and resolution of binary and ternary mixtures of selected oxyanions

Summary A differential pulse polarographic method has been applied to the determination of trace concentrations of TeO ₄ ^2– , TeO ₃ ^2– , AsO ₂ ^– and VO ₃ ^– . The dependence of the differential pulse peak on various parameters was studied and optimum conditions for the analytical determination of these oxyanions were found. Limits of detection and quantitation have been calculated for the differential pulse polarographic determination of the investigated oxyanions. The selectivity of this technique for the determination of binary (TeO ₄ ^2– -TeO ₃ ^2– , TeO ₄ ^2– -AsO ₂ ^– and TeO ₄ ^2– -VO ₃ ^– ) mixtures and a ternary (TeO ₄ ^2– -TeO ₃ ^2– -AsO ₂ ^– ) mixture has also been reported.

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Spurenbestimmung von TeO ₄ ^2– , TeO ₃ ^2– , AsO ₂ ^– und VO ₃ ^– durch Differential-Puls-Polarographie und Trennung binÄrer sowie ternÄrer Gemische von ausgewÄhlten Oxyanionen

     

Differential Pulse and Cathodic Stripping Voltammetric Methods for the Determination of Aromatic Sulfones

Abstract

A cathodic stripping voltammetric method for the determination of aromatic sulfones was developed. The technique involved a conversion of the sulfone to a sulfinate by controlled potential electrolysis at a mercury pool electrode and a subsequent determination of the sulfinate by cathodic stripping at a silver electrode. The detection limit was 2 × 10^?7 M sulfone in 4:1 DMSO-H₂O.

The differential pulse polarographic method utilized direct reduction of the sulfone in a 3:2 DMSO-benzene solvent. Although the detection limit (4.6 × 10^?7 M) was higher than in the stripping method, the linear dynamic range was greater (500 vs. 25), the typical precision was better (0.5 v. 7% relative standard deviation) and the determinations were more rapid (20 vs. 90 min). In addition, fewer interferences are anticipated for the pulse polarography method.     

Polarographic and Voltammetric Assays of Sulfonamides as α‐Oxo‐γ‐Butyrolactone Arylhydrazones

Abstract

2‐Acetylbutyrolactone was characterized as a novel reagent of analytical potential in polarographic and voltammetric analyses. It forms α‐oxo‐γ‐butyrolactone arylhydrazones through Japp‐Klingemann coupling reaction with primary arylamines. α‐Oxo‐γ‐butyrolactone arylhydrazones possess an electro‐active site (azomethine center) that displays a cathodic activity at the mercury electrode. The protonated azomethine center of α‐oxo‐γ‐butyrolactone arylhydrazones is reduced by 2e/2H⁺ reaction to the hydrazo form. The differential pulse polarographic behavior of α‐oxo‐γ‐butyrolactone arylhydrazones was investigated in aqueous media ranging from pH 2 to 10.5. In aqueous acidic solution, α‐oxo‐γ‐butyrolactone arylhydrazones were shown to adsorb on a hanging mercury drop electrode and to be amenable to determination by adsorptive stripping voltammetry. Procedures for applying the polarographic and voltammetric methods to determination of sulfadiazine and sulfamethoxazole in pharmaceutical preparations have been developed. An analogous study on sulfas‐azo derivatives of ethyl acetoacetate was also considered. Furthermore, the differential pulse voltammetric method was adopted for determination of sulfamethoxazole in spiked plasma and urine samples. The recoveries turned out to be satisfactory, showing relative standard deviations from 2.4 to 4.6%.     

Differential pulse polarographic behaviors of p-nitrosodimethylaniline: Application for microdetermination of NADH

The differential pulse polarographic behavior of p-nitrosodimethylaniline has been investigated in Britton-Robinson buffer and phosphate buffer. The peak obtained at pH 8.0 is recommended for the trace determination of this compound, with an experimental detection limit of 18 ppb (1.2 × 10^?7M) in simple aqueous solution. The method is also applied for the indirect microdetermination of NADH. The experimental detection limit of NADH is shown to be 1.05 × 10^?6M.     

The Polarographic Determination of Fluvoxamine Maleate

Abstract

In this study, the polarographic behaviour and the optimum polarographic conditions for the determination of fluvoxamine using DC, DP and SIAP techniques are described based on the reduction on the DME. The experiments were conducted in the aqueous supporting electrolyte containing 0.2 M KCI, 20% ethanol (v/v) and 0.2 M buffer solution. Single waves were obtained at various pH values. The limiting currents were decreased and E_1/2 values were linearly shifted to more negative potentials with an increase of pH. The system was irreversible at both the acidic and the basic medium and was controlled by adsorption at pH 4.2 and by diffusion at pH 8.03. The variation of the limiting current against temperature was found to be 1.1 μA°C. Good calibration relations were obtained for DC (direct current), DP (differential pulse) and SIAP (superimposed increasing amplitude pulse) techniques. The determination of fluvoxamine in a pharmaceutical preparation, Faverin® Tablets containing 50 mg of fluvoxamine, were tested. The results were compared to those of UV-spectrophotometric method. In the analysis of a single 50 mg tablet, the relative standard deviation (S_rel) are found to be between ±0.5 and ±1.0 for the techniques employed for filtered and unfiltered solutions. The polarographic techniques used for the determination of fluvoxamine seem to be accurate, rapid and practical. Therefore, the suggested method may be promising in the routine analysis.     

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.     

Method validation in quantitative electrochemical analysis of colchicine using glassy carbon electrode

A cathodic differential pulse voltammetric determination of colchicine was validated using a glassy carbon electrode in HClO₄/H₃PO₄ 0.01 M. Colchicine gives an irreversible, diffusion-controlled peak at −862 mV vs. Ag/AgCl reference electrode. The cathodic peak is strongly influenced by a more alkaline environment with a shift towards more negative potentials. Method optimization was carried out in parallel for three types of electrodes (glassy carbon, mercury film and bismuth film coated glassy carbon). The cathodic peak current is higher using film-coated electrodes, but shows poorer intra-day reproducibility and a longer analysis time due to film renewal. Thus, a bare glassy carbon electrode was used to determine colchicine in the concentration range of 2.4 − 50 μg mL⁻¹ (R ² = 0.9998, n = 5), with a calculated detection limit of 0.80 μg mL⁻¹. The proposed method was characterized according to ICH Harmonized Tripartite Guidance Q2(R1) by validation parameters (selectivity, linearity, accuracy, fidelity, limit of detection, limit of quantification) and it was successfully applied for the determination of colchicine from tablets, without the interference of the excipients. The method’s performances were evaluated and compared with both a known polarographic method and the official quantitative spectrophotometric determination from the Romanian Pharmacopoeia, Xth edition, respectively.