Determination of selenium(IV) and tellurium(IV) by differential pulse polarography

Differential pulse polarographic methods for the determination of selenium(IV) and tellurium(IV) in nitric acid medium are described. The peak current is maximal when 0.25M nitric acid medium is used, the DPP peaks for Se(IV) and Te(IV) being at -0.54 and -0.8 V vs. Ag/AgCl respectively. The peak current is a linear function of selenium concentration over three ranges, 5.1 x 10(-6)-1.3 x 10(-5), 1.27 x 10(-5)-1.27 x 10(-4) and 1.27 x 10(-4)-7.60 x 10(-4)M Se(IV), with different slopes. The plot for Te(IV) is linear over the range 0.78 x 10(-6)-9.40 x 10(-5)M.     

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.     

Development of an electroanalytical methodology using differential pulse voltammetry for amiloride determination

Journal of Solid State Electrochemistry - In this work, an analytical electrochemical method was developed using a glassy carbon electrode (GCE) for the determination of amiloride (AMI). To study...     

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     

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).     

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.     

The determination of chromium(VI) in natural waters by differential pulse polarography.

A method utilizing differential pulse polarography for the determination of chromium(VI) in natural water is described. Additions of 0.62 μg Cu(II) ml^-1 and 0.55 μg Fe(III) ml^-1 did not interfere with the determination of 0.050 μg Cr(VI) ml^-1. The natural water samples containing chromium(VI) were buffered to approximately pH 7 with 0.1 M ammonium acetate and 0.005 M ethylene diamine and analyzed. Natural water samples of chromium content from 0.035 μg ml^-1 to 2.0 μg ml^-1 may be analyzed directly without further preparation. The detection limit is 0.010 μg ml^-1.     

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.     

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.     

Differential pulse polarographic determination of trace selenium(IV) and molybdenum(VI) using the catalytic hydrogen wave

In the presence of selenium(IV) and molybdenum(VI) a new polarographic peak appears which corresponds to a hydrogen catalytic wave. By differential pulse polarography a single, sharp peak at about -1.1 V is obtained, allowing trace determination of selenium(IV) and molybdenum(VI) in the range 1x10(-6)-5.0x10(-9) M with a linear calibration and a detection limit of 1.5x10(-9) M. The optimum conditions are found to be 0.1 M KNO(3) and a pH of about 3.2 (Britton-Robinson buffer). There is no serious interference from some ions when present at 1.0-40 times that of molybdenum. At higher amounts of interfering ions the interference is eliminated by the addition of EDTA.     

Determination of methylviologen (Paraquat) by differential pulse polarography

Summary Determination of Methylviologen (Paraquat) by Differential Pulse Polarography The second reduction wave of methylviologen (Paraquat) has been studied at pH 2 by different polarographic techniques. The limiting current is diffusion-controlled. Evidence for dimerization of the radical formed in the first reduction step has been obtained. The n values for the reduction process have been calculated at concentration levels where the dimer and the monomer predominate. Paraquat can be determined by differential pulse polarography in the 6.0×10^–5–4.0×10^–7 M concentration range, the limit of determination being 1.7×10^–7 M. The method has been applied to paraquat determination in commercial herbicides.     

Differential pulse polarographic determination of selenium(IV) in whole blood using the catalytic hydrogen wave

The selenium content in blood was determined using the hydrogen catalytic peak. This peak at -1.1 V was obtained in the presence of selenium and molybdenum at pH values of 1-4 in different buffers. For the determination of selenium, the Mo(VI) concentration has to be approximately 100-200 times higher than the selenium present. The linear domain range of selenium is 1x10(-6)-5x10(-9) M. The interference of zinc is eliminated by the addition of EDTA at pH 3.5 acetate buffer. The method was applied to 1.0 ml of digested blood, and 620+/-44 mug l(-1) Se and 7.15 mg l(-1) Zn could be determined with a 90% (n=6) confidence interval.     

Microwave digestion of fish tissue for selenium determination by differential pulse polarography

In KIO(3)NH(3)NH(4)Cl medium, the selenium complex Se(O)SO(2-)(3), resulted from the reaction of selenite and sulphite in acid solution, gave a catalytic wave, which was applied to the determination of selenium in fish by differential pulse polarography. The sample was decomposed using the HNO(3)/H(2)SO(4)/H(2)O(2) digestion mixture in a closed PTFE digestion vessel with microwave heating. The detection limit was 0.06 mug/dm(3). The calibration curve was linear up to 8 mug/dm(3). Selenate present was reduced with hot hydrochloric acid to selenite. The recoveries of the selenite and selenate in two spiked samples investigated ranged from 91 to 104%. The NIES CRM No. 6 mussel was analyzed and the results obtained agreed well with the reference value (reference value: 1.5 mug/g; found: 1.43 +/- 0.05 mug/g). The results obtained by differential pulse polarography were in good agreement with those found by hydride generation atomic absorption spectrometry.     

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 chromium(VI) in waste water and industrial effluents by differential pulse polarography

A method for the determination of chromium(VI) in water and waste water is described. Interfering cations are separated by co-precipitation with aluminium from the phosphate-buffered solution. Differential-pulse polarographic measurement of chromium(IV) in the same background solution at pH 10 or 12 provides a lower limit of determination of 30 μg l⁻¹ Cr(VI). No significant losses of chromium(VI) occur in the precipitation step; chromium(VI) is not susceptible to reduction by waste-water constituents at the moderate pH maintained throughout the procedure. The polarographic characteristics of chromium(VI) in phosphate-buffered solution are discussed.     

Study of the conditions for the determination of metamitron by differential pulse polarography

Summary The electrochemical behaviour of the herbicide 4-amino-3-methyl-6-phenyl-1,2,4 triazine-5(4H)-on (Metamitron) is studied in aqueous medium using voltammetric techniques, with the ionic strength adjusted to 0.1 mol/l in sodium perchlorate and using a Britton-Robinson buffer. Two reduction waves on the mercury drop electrode appear, at –0.49 V the first and the second folded at –0.95 V and –1.05 V. The system is identified as irreversible and fundamentally controlled by diffusion. Using differential pulse polarography the detection limit reached was 0.02 mg · l^–1 for the first wave with an error of less than 2%. Thus a method is proposed for the determination of Metamitron in soil, with a detection limit of up to 0.02 g/g.

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Untersuchung der Bedingungen zur Metamitronbestimmung durch Differential-Puls-Polarographie

     

Simultaneous determination of SO(2), NO and NO(2) in air by differential pulse polarography

The method of Garber and Wilson for SO(2) determination has been tested on real samples of air. The results demonstrate the possibility of simultaneous determination of SO(2), NO and NO(2) in the sample. Detection limits as low as 7 mul/m(3) for SO(2) and about 50 mul/m(3) for nitric oxides can be reached.     

Determination of germanium(IV) in perchloric acid solution by a.c. polarography and differential pulse polarography in the presence of 3,4-dihydroxybenzaldehyde

Germanium(IV) at trace levels can be determined in perchloric acid solution containing 3,4-dihydroxybenzaldehyde by alternating current and differential pulse polarography with dropping mercury and hanging mercury drop electrodes. The results are comparable by the two methods. The possible interferences of some elements are discussed. The serious interference of lead(II) can be prevented by addition of EDTA in hydrochloric acid medium. Interference of selenium can be avoided by precipitation with potassium iodide. The method is applied to silver—germanium alloys.