F. Verbeek

Determination of traces of bismuth, copper and lead in cadmium by pulse polarography

Traces of bismuth, copper and lead impurities in metallic cadmium and cadmium salts were determined, without separation, by pulse polarography. In chloride medium, these metals can be determined down to 4.10−8, 3.10−8 and 10−6M, respectively, i.e., 8.10−6, 2.10−6 and 2.10−4% in metallic cadmium, when analysing 1 M solution; 4.10−7% Cu can be detected in 5 M solutions. In acetate buffer, the sensitivity for bismuth and copper is about 2.10−8M or, respectively, 4.10−6 and 10−6% in cadmium. In ethylenediamine, down to 10−8M lead or 2.10−6% in cadmium can be determined. The reciprocal tolerance was investigated for copper and bismuth in chloride and acetate solutions, and for copper and lead in ethylenediamine solutions. Finally, the method was applied to the analysis of various cadmium products commercially available and gave satisfactory sensitivity and resolution.

The determination of traces of thallium in cadmium by pulse polarography

Summary Traces of thallium in cadmium and cadmium compounds have been determined by pulse polarography. A direct method, without previous separation, allows the determination of about I p.p.m. at pH 4.25 in the presence of a 10% molar excess of EDTA with respect to cadmium. After separation by co-precipitation with manganese dioxide, thallium could be determined in an acetate buffer-EDTA mixture down to 0.008 p.p.m. thallium in cadmium for a sample weight of 10 g and a final volume of 10 ml. Both methods were applied satisfactorily to the analysis of a number of synthetic and commercially available cadmium products.

Study of the solubility of antimony in mercury by cyclic and stripping voltammetry

Abstract The solubility of antimony in mercury has been studied by cyclic and stripping voltammetry in solutions of Sb(III) in 4 M HCl. The solubility has been evaluated at 8.57×10−4 mol l−1 or 1.27×10−3 at. % at 25°C which agrees well with solubility values derived from data reported by other authors at different temperatures. A solubility heat (Hsol) of 16.7 kJ mol−1 was calculated.

Specific adsorption of Sb(III) ions at mercury electrodes in 4 M H(Cl, ClO4)

Abstract A dc polarographic and cyclic voltammetric study has been made of the reduction of Sb(III) ions from 4 M HCl, 1 M HCl + 3 M HClO 4 and 0.1 M HCl + 3.9 M HClO 4 solutions. Reversible behaviour was observed, accompanied by significant specific adsorption of Sb(III) ions on the mercury electrode. Double potential step chronocoulometry was employed to determine the extent of adsorption which correlates better with the amount of adsorbed Cl − ions than with the potential or electronic charge of the electrode. From this correlation and the distribution of the complex species in solution it is concluded that SbCl 3 or SbCl 4 − is the adsorbing species.

The stability of some lanthanide complexes with itaconate in aqueous solutions

Summary A potentiometric study has been made of the complexes formed between lanthanide ions and itaconate in aqueous solution at 25°C and unit ionic strength in sodium perchlorate. The experiments were carried out for ligand concentrations below the mononuclear boundary and it is proved that under these conditions positively and negatively charged mononuclear protonated lanthanide itaconate complexes exist. Several calculation techniques were applied to identify these complexes and to evaluate their stability. The concentration of the free ligand was obtained by the titration method of Osterberg. Based upon these calculation techniques a computer program was developed for the treatment of the experimental data.

Potentiometric determination of the dissociation constants of itaconic acid

Summary The dissociation of itaconic acid was investigated potentiometrically at ionic strength I =1 in NaClO 4 at 25.000±0.02°C in the concentration range 0–50 m M . The two dissociation constants were calculated by both a graphical and a computer method. The values reported are p K A 1 =3.629±0.002 and p K A 2 =4.988±0.0001. For concentrations > 50 m M , polynuclear proton itaconate complexes are observed.

Electrochemical reduction of the lanthanide ions: Part I. First reduction step of ytterbium(III) in acidic 1 M NaClO4 solution

Abstract The reduction of Yb(III) to Yb(II) in 1 M NaClO 4 in the pH range 1.9–6.6 was studied by d c. polarography, cyclic voltammetry and electrode impedance measurements as a function of frequency and electrode potential. It results that the d.c. reversible reduction is followed by a homogeneous chemical reaction and is accompanied, by an irreversible process which is attributed to a lowering of the overpotential of the reduction of the hydrogen ions. Values of the rate constant and transfer coefficient pertaining to the charge transfer step were deter mined.

Determination of traces of zinc and manganese in cobalt by pulse polarography

Summary A pulse polarographic method for determining traces of zinc and managanese in cobalt and its compounds is described. Interference due to the reduction of the cobalt matrix was eliminated by a prior separation on an anion exchange resin. The yield was controlled with the radio-isotopes, 65Zn and 54Mn, and a quantitative recovery was obtained for both elements. After separation, zinc was determined in an acetate medium; for managanese, 0.1 M lithium chloride was chosen as supporting electrolyte. A blank value prevented the attainment of the pulse polarographic detection limit for zinc and manganese, being about 10−8 M for both elements. The method enables as little as 0.15 p.p.m. of zinc and 0.03 p.p.m. of manganese to be determined in a 1 g sample. A number of analyses carried out on synthetic and various commercially available cobalt samples showed satisfactory sensitivity and accuracy.

The determination of traces of indium in cobalt by pulse polarography

Summary A pulse polarographic method is described for determining traces of nickel in cobalt, and its compounds, without separation. The detection limit in pyridine is as low as 1 p.p.m in metallic cobalt, and 0.25 p.p.m. in cobalt compounds, while in potassium thiocyanate these limits are decreased to 0.25 and 0.06 p.p.m., respectively. The method was applied to the analysis of synthetic and commercially available cobalt samples and showed satisfactory sensitivity at various nickel levels.

The determination of traces of bismuth in cobalt by colorimetry after electrolytic separation and by pulse polarography

Abstract Traces of bismuth (down to 3 · 10 −5 %) in cobalt were determined colorimetrically with dithizone after a prior separation of the bismuth onto a mercury cathode using controlled potential analysis and subsequent anodic stripping of the amalgam. The quantitative character of the method was controlled by pulse polarography. The conditions, (i.e., cathode potential, electrolysis time, acidity, bismuth concentration) for electrodeposition of micro-quantities were investigated. Interferences from cobalt, mercury, tin(II), thallium(I), indium and lead are discussed. Analogous analyses of traces of bismuth in cobalt without preliminary separation (down to 6 · 10 −6 %) were performed with a pulse polarograph using the standard-addition method.