Aqueous sulfur species determination using differential pulse polarography

Sulfur species play pivotal roles in biogeochemistry; however, quantification remains difficult because such species are transitory. Our objective was to determine the utility of using differential pulse polarography (DPP) to characterize soluble sulfur species of potential interest in agriculture and environmental quality. Polarographic responses for sulfide, disulfide, pentasulfide, sulfite, thiosulfate, tetrathionate, pentathionate, cysteine, and glutathione were determined. Sulfur in the compounds was categorized as cysteine-S, thiosulfate-S, nonpurgeable or purgeable sulfide-S, or sulfite based on characteristic polarographic responses for each respective category. Nonpurgeable sulfide-S, cysteine-S, and thiosulfate-S were polarographically separated using a pH 8.0 phosphate buffer. Nitrate/bicarbonate (pH 10.0) and acetate (pH 5.0) buffers were used to determine purgeable sulfide-S and sulfite, respectively. Sulfur in water extracts from cysteine-amended soils was quantified using the developed DPP method. Cysteine-, thiosulfate-, and sulfide-S were measured from these extracts without interferences during a 16-d incubation period. The developed DPP method provides qualitative and quantitative information concerning sulfur species in aqueous solutions and is potentially applicable to soil and sediment extracts.     

Trace determination of platinum-II. Analysis in ores by pulse polarography after fire-assay collection

A pulse-polarography method is described for the determination of traces of platinum in ores after fire-assay separation and preconcentration. The silver bead from the fire assay is dissolved and treated with ammonia and ethylenediamine to produce a sensitive catalytic polarographic wave. Measurement of the wave by differential pulse polarography allows determination of Pt with a detection limit of 0.0025 ppm. Platinum in ore samples was determined in the range 0.1-0.9 ppm and a correlation coefficient of 0.98 was obtained on comparison with AAS results.     

Trace analysis of vanadium as pentavalent vanadium using differential pulse polarography with a coupled catalytic homogeneous reaction

The differential pulse polarographic determination of the vanadium (V) ion coupled with a catalytic homogeneous reaction was carried out in a system containing the vanadium (V)-PAR complex and an oxidant in acetic/acetate buffer. On addition of the powerful oxidant, sodium bromate, the peak current for the reduction of the vanadium (V) complex was increased significantly by about 21 times. A calibration plot was found to be linear in the concentration range 0.05–0.25 g/ml and the detection limit was 5 ng/ml.     

Trace determination of dexamethasone sodium phosphate in pharmaceutical formulations by differential pulse polarography

A simple and rapid differential pulse polarographic method has been developed for the trace determination of dexamethasone sodium phosphate. A well-defined single peak with an Ep value of -1.14 V is obtained in acetate buffer (pH 5.0). The linearity is valid in the range 0.2-1.2 mg/25 mL ( r=0.9992) with minimum detection limit of 7.6x10(-6) M. The precision of the method developed is implied from the values of relative mean deviation, standard deviation and coefficient of variation, which are 2.44%, 0.014 and 3.5% respectively. Marketed formulations of dexamethasone sodium phosphate have been analysed by calibration and standard addition methods. Recovery experiments were found to be quantitative, and analysis to determine the mass per tablet was obtained within +/-0.2% of the expected market value. The studies have shown that the method is reproducible and accurate and can be used in the analysis of marketed formulations.     

Selection of optimum pH for the iodate determination using differential pulse polarography

The concentration of iodate in seawater samples was determined at various pH values using differential pulse polarography (DPP). The sensitivity for the iodate determination decreased rapidly below pH 7 and above pH 9. The decrease below pH 7 may be caused by conversion of iodate to iodide, followed by the successive formation of I₂ and I₃ ^–. The decrease above pH 9 is probably due to the combination of iodate and hydroxide. Theoretical calculations have demonstrated that the optimum pH for iodate determination is above pH 7.4 for Po₂ = 0.101 Pa.     

Selection of optimum pH for the iodate determination using differential pulse polarography

The concentration of iodate in seawater samples was determined at various pH values using differential pulse polarography (DPP). The sensitivity for the iodate determination decreased rapidly below pH 7 and above pH 9. The decrease below pH 7 may be caused by conversion of iodate to iodide, followed by the successive formation of I₂ and I₃ ^–. The decrease above pH 9 is probably due to the combination of iodate and hydroxide. Theoretical calculations have demonstrated that the optimum pH for iodate determination is above pH 7.4 for Po₂ = 0.101 Pa. Received: 14 July 1998 / Revised: 2 October 1998 / Accepted: 3 October 1998     

Direct determination of pentachlorophenol by differential pulse polarography

Differential pulse polarography at the dropping mercury electrode and differential pulse voltammetry at the carbon paste electrode are used for direct determinations of pentachlorophenol at concentrations down to 0.27 ppm. PCP is electrochemically reduced in phosphate buffers of pH 8 to produce a concentration-dependent current peak at —0.8 V vs. Ag/AgCl. The procedure requires only 15 min. Cyclic voltammetry at the hanging mercury drop electrode is used to evaluate the electrochemical reaction and to establish the reversibility of the PCP electrode reaction.     

A new and direct method for the trace element determination in cauliflower by differential pulse polarography

Using the DPP polarograms of wet digested cauliflower sample in acetate buffer at pH values of 2, 4 and 6, Fe, Zn, Mo, Se, Cr, Cd, Pb, Ti and Cu quantities were determined. The best separation and determination conditions for Zn, Se and Mo was pH 2; for Cr, Zn, Mo and As was pH 4; for Pb pH 6, for Ti, Cu and Fe was pH 6-7 EDTA, for Cd pH 2 EDTA and for lead pH 6, all in acetate buffer. The trace element ranges for cauliflowers from two different seasons were (first figure for winter, the second for summer) for Se 120-250 μg g⁻¹, Fe 70-85 μg g⁻¹, Cu 320-150 μg g⁻¹, Ti 90-120 μg g⁻¹, Cr 130-630 μg g⁻¹, Zn 90-550 μg g⁻¹, Mo 170-230 μg g⁻¹, Cd 20 μg g⁻¹ (in winter) and Pb 130-300 μg g⁻¹ in dry sample. Cd was under the detection limit in summer. The length of digestion time had no effect on the recovery of copper, iron, molybdenum and zinc between 15 and 3 h of digestion.     

Cathode ray polarography and differential pulse polarography of the catalytic molybdenum(VI) wave

The optimum conditions of electrolyte composition and pH were studied for the cathode ray polarography (c.r.p.) of the catalytic molybdenum(VI) wave; 1–2 M potassium nitrate at pH 1.6–2.2 is optimum, the detection limit is 3 × 10^-9 M (0.3 ppb) molybdenum(VI). Equal molar concentrations of foreign electroactive substances do not interfere at the potential of the molybdenum wave and 500-fold amounts of these can be tolerated if their c.r.p. peaks are separated from the molybdenum wave by 0.1 or 0.2 V. Similar conditions were used for the differential pulse polarography of the catalytic wave. The detection limit is 2 × 10^-8 M (2 ppb). being limited in part by lead impurities which contribute to the background.     

A study of mixed ligand complexes using differential pulse polarography

Differential pulse polarography was used to study the mixed ligand complexes of trimethylenediamine (TMDA) and oxalate (OX) with Cd(II) at constant ionic strength (μ = 1, NaNO₃) at 25°C. It has been found that the reduction of complexes is reversible and diffusion-controlled. Three mixed complexes, [Cd(TMDA)(OX)], [Cd(TMDA)(OX)₂]^2? and [Cd(TMDA)₂(OX)], are formed. Their overall stability constants are: log β₁₁ = 6.78, log β₁₂ = 7.53 and log β₂₁ = 8.20, respectively.     

Some electroanalytical aspects of using pulse polarography for determination of Ge(IV)

Summary Presented data give some informations of analytical importance as a result of pulse polarographic investigations of Ge(IV) in KCl solutions within pH range 3–12 at Ge concentration from 1×10^–4 to 2.5×10^–6 M. It was shown that Ge(IV) can be polarographically active in acidic solution but its reduction interferes with hydrogen gas development. The addition ofp-quinone enables the determination of Ge(IV) without this interfering effect.Suggested explanation of the observed changes in polarographic curves dependent on pH and Ge concentration based on the existence of several polarographically active forms.

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Elektroanalytische Bemerkungen zur pulspolarographischen Bestimmung von Ge(IV)

Zusammenfassung Unsere Ergebnisse bieten einige Informationen über die pulspolarographische Bestimmung von Ge(IV) in KCl-Lösungen innerhalb pH 3–12 und bei Ge-Konzentrationen zwischen 10^–4 und 2,5×10^–6 M. Es wurde gezeigt, daß Ge(IV) in saurer Lösung polarographisch aktiv ist, seine Reduktion aber durch Wasserstoff-Entwicklung gestört wird. Der Zusatz vonp-Chinon beseitigt diese Störung. Die Änderung der polarographischen Kurven je nach Ge-Konzentration und pH beruht vermutlich auf der Existenz verschiedener polarographisch aktiver Formen.

     

Quantitative determination of the non-entrapped chlorothiazide in the presence of liposomes using differential pulse polarography

Differential Pulse Polarography (DPP) was used for the quantitative determination of the free and adsorbed (non-entrapped) chlorothiazide (CHT) in the presence of liposomes. It was found that CHT polarographic signal depends both on the concentration of multilamelar (MLV) liposomes, due to its adsorption on the liposomal surface, and on their size. Calibration plots of CHT concentration versus current density, at pH 7.4, in the presence of different liposomes concentrations were constructed. Based on these curves the non-entrapped chlorothiazide was determined. Results were compared to those obtained from the application of conventional procedure i.e. chromatographic separation of CHT from liposomes followed by UV spectrophotometric determination. Both techniques were found to be comparable with respect to their accuracy, with a relative error of 0.47%. Determination of the drug using DPP was faster.     

The determination of trace levels of aluminium by differential pulse polarography

The direct determination of aluminium in aqueous solutions by differential pulse polarography is described. If the pH is carefully controlled to 4.00 ± 0.01, there is a linear relationship between the peak height of the polarographic wave and the aluminium concentration up to 2.5 × 10^-5 mol dm^-3. The coefficient of variation is about 4% at the 10^-5 mol dm^-3 level. With increasing aluminium concentrations, the relationship ceases to be linear, and above 9 × 10^-5 mol dm^-3, the peak splits, probably because of hydrolysis and polymerisation. Na⁺, NH₄⁺, Mg²⁺ and Ca²⁺ interfere at levels 100 times greater than that of the aluminium whereas Fe²⁺, Fe³⁺, Cu²⁺, Zn²⁺, Ni²⁺, NO₃^-, ClO₄^-, Cl^- and SO₄^2- do not interfere.     

Differential pulse polarography of some benzodiazepines and their determination in urine

A differential pulse polarographic method has been applied to the determination of diazepam, oxazepam, nitrazepam and flurazepam down to 2 x 10(-7)M (0.14 mug/ml). The method can also be used with biological materials such as urine, without prior extraction. Only a 2-ml volume of urine is necessary.     

Rapid-flow analysis using differential pulse polarography with automatic sampling

Differential pulse polarography is used in a rapid-flow analysis system for automated determination of lead, zinc and ascorbic acid in acetate-buffered sample solutions, without the need for sample deaeration. By use of a nitrogen-segmented buffer stream at high flow-rates, high-speed sampling at up to 180 samples/hr can be obtained at a flow-rate of 22.8 ml/min through a polarographic flow-cell fitted to the dropping mercury electrode. A linear calibration range of approx. 0.1 x 10(-4)-1.0 x 10(-3)M is found for lead, zinc and ascorbic acid, with respective detection limits of 4.0, 0.8 and 0.2 x 10(-6)M, limited by the high base-line current and high noise-level. Vitamin C tablets can be routinely analysed without prior separation steps, provided the sample and wash solutions are matched in electrolyte composition. A precision of better than 1% RSD is obtained at a sampling rate of 120/hr.     

A new sensitive method for the determination of trace mercury by differential pulse polarography: Application to raw salt sample

A new indirect differential pulse polarographic (DPP) method is established for the trace determination of mercury(II). Because of its toxic effects on human health, trace determination of mercury is very important. An indirect method had to be used since no polarographic peak is observed in its direct determination. According to the standard potentials, the reaction between Sn(II) and Hg(II) was found suitable. The peak of Sn(II) at about ?0.40 V is sharp, high and very reproducible, which enables the determination of low concentrations of Hg(II). For this purpose, to a known amount of Sn(II) present in the polarographic cell (acetic acid, HAc, pH 1–2), the unknown Hg(II) sample is added and the quantitative reaction takes place directly in the cell. The Hg(II) concentration is calculated simply from the decrease of the Sn(II) peak. The limit of detection (LOD) was found as 2 × 10^?7 M for S/N = 3. Interferences of some common cations, such as Fe, Cd, Cu, Zn and Pb and anions have been investigated. Only Pb had an overlapping peak with Sn(II). This peak overlap was eliminated simply by working at pH 2 (HAc electrolyte), because of the shift of the Pb peak in the Ac complex to ?0.7 V. This method was successfully applied to synthetic samples and raw salt sample taken from a salt lake in Turkey.     

Determination of bacitracin by differential pulse polarography.

Differential pulse polarograms of pharmaceutical-grade bacitracin exhibit a well-defined double wave at the dropping mercury electrode over the entire pH range 1–8. The current is diffusion-controlled and proportional to the concentration as well as to the biological activity of the sample. The concentration of bacitracin and of zinc—bacitracin can be determined by pulse polarography with a standard deviation less than 2%. The biologically inactive oxidation product (bacitracin F) is reduced at less negative potentials and can easily be determined in the presence of the biologically active components of bacitracin.