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     

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.     

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.     

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.     

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

     

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.     

Simultaneous determination of the isomers of nitrophthalic acid by differential pulse polarography

A differential pulse polarographic method has been developed for simulataneous determination of isomers of nitrophthalic acid. In ammonia buffer (1.0 M), the peak potentials for the reduction of 4-and 3-nitrophthalic acids are ?0.54 and 0.67 V vs. SCE, respectively. Response of peak current vs. concentration of each isomer is linear over three orders of magnitude change in concentration. The detection limit for both 4-and 3-nitrophthalic acid is 0.2 mg l^?1. A typical sample can be analyzed for both isomers of nitrophthalic acid in less than 15 min.     

Employment of differential pulse polarography and adsorptive voltammetry for the determination of some sulfonamides

Reduction of sulfonamides in mineral acids was investigated using fast scan differential-pulse polarography (FSDPP). The optimal medium for sulfadimidin, sulfamethoxydin and sulfamethoxypyridazin is 0.01–0.02M HCl, while for phthalazol it is 1M HCl and the latter compound can be selectively determined in the presence of other sulfonamides. Adsorptive properties on the Hg-electrode were analytically used in the case of sulfamethoxypyridazin and phthalazol. Relative standard deviation of all determinations did not exceed 8%.     

N-nitrosamines and differential pulse polarography

Differential pulse polarography is a versatile and sensitive technique which yields both qualitative and quantitative information about N-nitrosamines. The ability of the technique to carry out determinations in-situ permits the study of anchimeric, metabolic, and mechanistic properties in addition to phenomena such as kinetics and transnitrosation.     

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.     

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.     

The electrochemical behaviour of copper proteins using differential pulse polarography

Copper proteins involving either isolated centres (horse liver alcohol dehydrogenase with Cu(II) at the active site, cupric complex of BSA and porcine ceruloplasmin) or binuclear cuprous (Limulus polyphemus deoxyhemocyanin, Cu(I) complex with disulphides in BSA) or cupric sites (Limulus deoxymethemocyanin) were studied by means of DPP in buffered media. The reduction of the binuclear sites was directly observable in the polarograms. The reduction responses of the isolated cupric centres were promoted either by EDTA or in a weakly acidic buffered medium at pH 5.4 to 5.6. Electroactive ternary complexes (e.g. Cu(II): protein: EDTA) permitting a bridged electron transfer are proposed to be the key intermediates in the promoted electroreduction of cupric centres.     

Characterisation of human foetal liver Zn-metallothioneins using differential pulse polarography

A study on electrochemical characterisation of three isoforms of human foetal liver Zn-metallothioneins, labelled MT-0, MT-1 and MT-2, has been performed by using differential pulse polarography (DPP). Two different peaks, attributed to two different Zn complexes with metallothioneins, have been detected. The electrochemical behaviour is similar for the three studied isoforms. Studies on the addition of Cd(2+) and Zn(2+) as well as studies as a function of pH have been carried out. The association and dissociation equilibria of metal ions with MTs are reversible in the studied pH range. The behaviour of Zn complexes in human foetal liver Zn-metallothioneins is comparable to the Cd complexes obtained using other mammalian Cd, Zn-metallothioneins, particularly as a function of pH.     

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.     

Direct and indirect methods for the determination of vitamin K3 using differential pulse polarography and application to pharmaceuticals

Two methods for the determination of vitamin K(3) have been developed. Vitamin K(3) in its oxidized form is determined by direct and indirect methods. Its standard solution was prepared by the indirect method using Ti(III) as reducing agent. For this purpose vitamin K(3) (menadion) in a clinical injection solution, which is in its hydroquinone form in the presence of sulfite, is oxidized with oxygen. In 0.2 M HAc and 0.02 M HCl electrolyte vitamin K(3) and Ti(IV) have reduction peaks at -0.58 V at -0.82 V respectively. The reaction between Ti(III) and vitamin takes place quantitatively in a medium of 0.2 M HAc and 0.002 M HCl. After the reduction, the reaction product Ti(IV) is followed from its polarographic peak at about -0.82 V. The most important result in this work is that, with this method vitamin K(3) can be standardized and after standardization this solution can be used for the direct determination in routine analysis with a very simple and fast method, using only the peak at -0.71 V in 0.2 M HAc medium. Both direct and indirect methods have been used for the determination of Vitamin K(3) in a clinical injection solution. The limit of quantification (LOQ) was 1.5x10(-6) M and in both methods the detection limit found was 7x10(-7) M.     

The determination of phenobarbital and diphenylhydantoin in blood by differential pulse polarography

A sensitive differential pulse polarographic assay was developed for the determination of phenobarbital or diphenylhydantoin in blood. The assay involves the selective extraction of the compound into chloroform from whole blood buffered to pH 7.0. After suitable “clean-up” of the sample, each compound is nitrated in 10% potassium nitrate in sulfuric acid at 25° for 1 h. The nitro-derivatives are extracted into ethyl acetate, and the residues are dissolved in 1 M phosphate buffer (pH 7.0) or 0.1 M sodium hydroxide for phenobarbital and diphenylhydantoin, respectively; the solutions are deoxygenated, and analyzed by differential pulse polarography. The overall recovery of phenobarbital and diphenylhydantoin from blood was 72.3% ±6.5 (s_r) and 76.7 ±2.3 (s_r) respectively. The sensitivity limit is 1–2 μg ml^-1 of blood for both compounds. A modified assay for the determination of both compounds in blood with t.l.c. separation was also developed.     

Studies on some cadmium mixed ligand complexes using differential pulse polarography

Differential pulse polarography was used to study the mixed ligand complexes of imidazole and some dicarboxylate anions namely, oxalate, tartrate and malonate with Cd(II) at constant ionic strength (mu = 1, NaNO(3)) at 25 +/- 0.1 degrees . It has been found that the reduction of complexes is reversible and diffusion-controlled. Three mixed complexes are formed with malonate (or oxalate) whereas four mixed complexes are formed with tartrate. The overall stability constants for each system were calculated and discussed.