Amperometric titrations with rotated platinum electrode: Determination of hydrazine by potassium bromate

The reaction between hydrazine and potassium bromate is studied amperometrically at rotating platinum electrode. The bromate titration is performed at an applied e.m.f. of zero (versus S.C.E.) and in the presence of bromide and 1–5N sulfuric acid or 0.5–4N hydrochloric acid. Quantities ranging from 30 μg to 3 mg of hydrazine can be estimated accurately by this method. Determination of phenylhydrazine, Semicarbazide and other oxidizable materials on similar lines is suggested.     

Amperometric titration of cobalt and nickel with sodium diethyldithiocarbamate at zero applied voltage using rotating wire-platinum electrode

Analytical and Bioanalytical Chemistry -     

Voltammetric,potentiometric and amperometric studies with a rotated aluminum wire electrode : Amperometric titration of fluoride with aluminum

The rotated aluminum electrode is a suitable indicator electrode in the amperometric titration of fluoride, Fluoride in concentrations varying between 1.10^-4 and 2.10^-3M was titrated with a standard aluminum nitrate solution in aqueous buffer solutions (pH between 3.6 and 46) Equilibrium was established within 15 mim. The fluoride-aluminum ratio at the (true) end-point was found to increase from 2 2 in 10^-4M fluoride to 28 in. 2.10^-3M fluoride. The titration calculated from the stability constants of the various aluminum-fluoride complexes were found to be in excellent agreement with the experimental curves.From a practical point of view titration in an acetate buffer in 50% alcohol in the presence of 0 5 M potassium or sodium nitrate is recommended. The fluoride-aluminum ratio at the end-point was found to be 5 9 ± 0 1 and independent of the fluoride concentration.     

Determination of EDTA by catalytic amperometric and catalytic potentiometric titration at a small constant current

Summary Amperometric and potentiometric methods at a small constant current were developed to follow the course of catalytic titrations. In ammoniacal medium EDTA was determined by titration with 0.1 M copper(II) chloride in the presence of hydrogen peroxide as the indicator. Amounts of 42.26–126.87 mg of EDTA were determined with a maximal average deviation of 0.55 %. The results obtained are in good agreement with those of comparable methods.

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Bestimmung von ÄDTA mit Hilfe der katalytischen amperometrischen und der katalytischen potentiometrischen Titration bei kleinem konstantem Strom

Zusammenfassung Die amperometrische und die potentiometrische Methode bei kleinem konstantem Strom wurden für die Verfolgung katalytischer Titrationen ausgearbeitet. ÄDTA wurde in Ammoniakmedium mit 0,1 M Kupfer(II)-chlorid in Anwesenheit von Wasserstoffperoxid als Indicator titriert. Mengen von 42,26–126,87 mg ÄDTA wurden mit einer mittleren Abweichung von 0,55% bestimmt. Die Ergebnisse stimmen gut mit denen vergleichbarer Methoden überein.

The authors thank the SIZ for researchs of SAP Vojvodina for the partial financial support of the present work.     

Determination of electroinactive organic acids with LC and amperometric detection, using a PPy coated electrode

This paper reports on the amperometric detection of electroinactive sulfonic acids, organic acids and phosphate esters subsequent to chromatographic separation. The working electrode consisted of a 3 mm diameter glassy carbon electrode, coated with electrochemically deposited polypyrrole. The electrode was placed in a large volume wall jet cell, and a potential of +750 mV versus SCE was applied. The electroinactive analytes were detected as they induce a current, which originates from their effect on the doping of the polypyrrole coating. This allows sensitive detection of electrochemically inactive organic acids. Detection limits for sulfonic acids in LC with 4.6-mm ID columns (1 ml min(-1) flow rate) were 3 ng. The electrode had a linear response in the 1x10(-6) to 1x10(-3) M concentration range. The response time of the electrode was 3.6 s in a FIA set up. Peak heights are quasi independent on the flow rate, indicating that the phenomenon is not controlled by mass transfer in the diffusion layer. The electrode activity decreases to 50% after 24 h of continuous use. The electrode can be partly reactivated after application of a potential of -300 mV (versus SCE) for 1 h.     

Voltammetric,potentiometric and amperometric studies with a rotated aluminum wire electrode: Amperometric determination of fluoride with the raie

A simple and rapid amperometric method is described for the determination of traces of fluoride by measuring the anodic current at the RAIE at —0.75 V vs. SCE. In order to be independent of varying sensitivity of the RAIE, use is made of the standard addition technique. Proportionality between current and concentration is found between 0.2 and 6 p.p.m. of fluoride. Chloride, sulfate, nitrate, alkali and earth alkali ions do not interfere. Phosphate decreases the sensitivity but does not interfere. Aluminum ions interfere but can be made harmless by EDTA. Oxidising agents (including oxygen) must be removed. The method gives excellent results in potable and natural waters.     

Determination of parabens in shampoo using high performance liquid chromatography with amperometric detection on a boron-doped diamond electrode

Methylparaben (MePa), ethylparaben (EtPa) and propylparaben (PrPa) have been widely used, among others, as chemical preservatives in cosmetics, drugs and foods. As these compounds are linked with allergies, dermatitis and estrogenic properties, it is necessary to control the concentration of these substances in different matrices. The aim of this paper are: to evaluate the electrochemical behavior of parabens on the boron-doped diamond (BDD) electrode and the development of a chromatographic method, with electrochemical detection (HPLC-ED), for determination of parabens in shampoo. A BDD (8000 ppm) electrode was adapted in a thin layer mode analytical cell consisting of a stainless steel and a platinum wire as reference and auxiliary electrodes, respectively. Chromatographic separations were obtained with a reversed phase C8 analytical column and a mobile phase of 0.025 mol L⁻¹ disodium phosphate, pH 7.0, and acetonitrile (40:60, v/v), delivered at a flow rate of 1.0 mL min⁻¹. Sample preparation was performed by solid phase extraction using C18 cartridges and acetonitrile for elution. Benzylparaben was employed as internal standard. The HPLC-ED method developed, using the BDD electrode, was validated for the determination of parabens in shampoos and presented adequate linearity (>0.999), in the range of 0.0125-0.500% (w/w), detectability 0.01% (w/w), precision (RSD of 2.3-9.8%) and accuracy (93.1-104.4%) and could be applied for routine quality control of shampoos containing MePa, EtPa and PrPa.     

Electrocatalysis by ad-atoms: Part IX. A fast parallel path for formaldehyde oxidation on a platinum electrode by oxygen adsorbing ad-atoms

The effect of various ad-atoms on formaldehyde oxidation was examined on a Pt electrode. Ad-atom species are found to be classified into two groups according to their way of affecting the electrode reaction: one consists of Cu, Ag, Tl, Hg, Pb, As, Bi, Te and Se, the other Ge, Sn and Sb. The enhancement effect of the former depends on the number of Pt sites occupied by an ad-atom of each species (S_M), which suggests to us that geometrical control of Pt site arrangement plays an important role in the enhancement. The latter group of ad-atoms adsorb oxygen atoms, and these oxygen atoms are considered to play an important role in this enhancement. The enhancement ratio by the latter group of ad-atoms is much greater than that by the former group. The enhancement by the latter group of ad-atoms is via a new rapid parallel path, which has not been found on a Pt electrode for formaldehyde oxidation.     

Theory of a.c. voltammetry at a rotating disk electrode: Part II. Quasi-reversible and irreversible redox-electrode reactions

Alternating current response at a rotating disk electrode to a small a.c. potential wave superimposed on the slowly changing d.c. potential is theoretically treated for an quasireversible and an irreversible redox-electrode process. Expressions for alternating current-d.c. potential curves are given for three types of a.c. signals, i.e., sinusoidal, rectangular and triangular waves. It is shown that the effect of the coupling of the diffusion layers due to hydrodynamics and a.c. polarization can be expressed in terms of a parameter which is defined by the ratio of the frequency of a.c. wave to that of the rotation of the electrode and Schmidt number.     

Determination of aminothiols by liquid chromatography with amperometric detection at a silver electrode: Application to white wines

Liquid chromatography coupled to a silver electrode based flow-through amperometric detector (LC-EC-Ag) was developed for the determination of aminothiols in white wines. The C18 reversed phase LC system operated in the isocratic mode at 0.7 mL min⁻¹ and used an acidic mobile phase composed of formic acid, EDTA, sodium nitrate, sodium hydroxide, and methanol 1% (v/v) at pH 4.5. The working electrode operated at 0.08 V vs Ag/AgCl, 3 M KCl and its manual cleaning was realized once a month by smoothing on a polishing cloth. The analyzed aminothiols were resolved and eluted within 4 min, and all standard curves were linear in the range 2 × 10⁻⁷–2 × 10⁻⁵ M. The analyzed wine samples needed no preparation other than dilution with the mobile phase. The concentration of cysteine (CYS), homocysteine (HCYS), glutathione (GSH) and N-acetylcysteine (NAC) in bottled white wines, determined by the method of standard addition, was found to be in the low μM range (0.2–2 mg L⁻¹) depending on the wine type and its age.     

Studies on pollution of water and air dust of Benghazi using various analytical methods

Nondestructive neutron activation analysis has been used for the analysis of 17 out of 24 elements in 12 samples of air particulate matter collected from various localities in Benghazi. Both relative and monostandard methods were used. The neutron activation method was supplemented with graphite furnace atomic absorption, so that most toxic elements could be assayed in the same samples. Thus Cd, Cr, Cu, Mn, Ni, Pb, V and Zn could be analysed quantitatively in most of the samples. It has been found that contamination of the atmosphere of Benghazi with dust is largely due to heavy construction work in the city, action of wind on the surface of land around the city and the release of exhaust products from vehicles and airplanes. Particular contamination due to industrial activities was not noticeable. Results on samples from Benghazi were compared with those from Prague, Munich and Sendai.Research Project Studies on the environmental status change in Benghazi with special reference to water and air pollution, Research Center University of Garyounis, Benghazi, Libya.     

Mechanism and reaction rate of the Karl-Fischer titration reaction: Part II. Rotating ring-disk electrode measurements

A platinum disk-platinum ring electrode was used to investigate the kinetics of the oxidation of the monomethyl sulfite ion (which is the oxidizable species in the Karl-Fischer reagent) by triiodide and iodine, generated with controlled current at the disk electrode. The experimental conditions were such, that the technique for measurement of homogeneous pseudo-first order reactions could be used. The results are in reasonable agreement with those of the potentiometric investigations as described in part I. The reaction rate constant of triiodide is approximately 600 1² mol^?2 s^?1; for iodine the rate constant is approximately 7×10⁶.     

Amperometric immunoassay for the tumor marker neuron-specific enolase using a glassy carbon electrode modified with a nanocomposite consisting of polyresorcinol and of gold and platinum nanoparticles

Microchimica Acta - A glassy carbon electrode was modified with a redox-active nanocomposite consisting of polyresorcinol, gold nanoparticles (NPs) and platinum NPs. This nanocomposite possesses...     

Determination of vanadium(V) by direct automatic potentiometric titration with EDTA using a chemically modified electrode as a potentiometric sensor

A chemically modified electrode (CME) was prepared and studied as a potentiometric sensor for the end-point detection in the automatic titration of vanadium(V) with EDTA. The CME was constructed with a paste prepared by mixing spectral-grade graphite powder, Nujol oil and N-2-naphthoyl-N-p-tolylhydroxamic acid (NTHA). Buffer systems, pH effects and the concentration range were studied. Interference ions were separated by applying a liquid-liquid extraction procedure.The CME did not require any special conditioning before using. The electrode was constructed with very inexpensive materials and was easily made. It could be continuously used, at least two months without removing the paste.Automatic potentiometric titration curves were obtained for V(V) within 5 × 10⁻⁵ to 2 × 10⁻³ M with acceptable accuracy and precision. The developed method was applied to V(V) determination in alloys for hip prothesis.     

Ion chromatographic determination of sulfide and cyanide in real matrices by using pulsed amperometric detection on a silver electrode

The determination of free sulfide and cyanide by pulsed amperometric detection (PAD) at a silver-working electrode was improved through a deep de-oxygenation (at least 10 min) of both standard and real solutions containing the two analytes and adopting a two-potential waveform able to eliminate Ag working electrode fouling. The waveform stepped around the oxidation of Ag in the presence of 0.1-0.4 M hydroxyl ion, from -0.1 to 0.1 V versus saturated calomel electrode (SCE). The eluent composition (0.4 M NaOH plus 7.5 mM oxalate solution) allowed a very good column efficiency and selectivity. The presence of a polysulfide species was hypothesized in sulfide solutions that had not been de-oxygenated and aged. The polysulfide eluted just before sulfide and was confirmed by a chemical test with SO3(2-) producing the elimination of the polysulfide peak. Detection limits, according to the Hubaux-Vos method, were 1.0 and 2.0 microg/l for S2- and CN , respectively. We demonstrated good performance of the optimized method by repeatedly injecting standard solutions and by analyzing different real matrices. The method exhibited very good accuracy and repeatability (10 microg/l and a 500 microl injection loop, had a repeatability better than 3% for sulfide and 100 microg/l had a repeatability better than 1% for cyanide). The two-potential waveform ensured long-term stability of the electrode surface that required no manual polishing procedure for at least 1 month (20 analysis per day).