E. C. van Dalen

Linear potential-sweep voltammetry at a plane mercury- film electrode

Abstract A general treatment is given of linear potential-sweep voltammetry with a mercury-film electrode. The current-potential equations for both oxidizing and reducing potential-sweeps are considered. A mathematical approximation, useful for very thin mercury-films, is discussed, while the limiting case of zero film thickness is also considered. The effect of ohmic drop on the current-potential curves is given. The bearing of the results on experiment is pointed out.

Theory of anodic stripping voltammetry with a plane, thin mercury-film electrode

Abstract An approximate theory for anodic stripping voltammetry with a plane, thin (⩽ 100 micron) mercury-film electrode is presented. This approximate theory is valid only for slow rates of linear potential scan during the stripping of the reduced metal from the mercury, and for thin mercury films. There are important differences between anodic stripping peaks obtained with a thin mercury-film electrode and the peaks obtained under the conditions of the Sevcik-Randles theory. In the latter case the peak potential and the peak width are independent of the rate of potential change v, and of the mercury-film, thickness l (which is supposed to be infinite), but the peaks obtained with a mercury-film electrode show a variation of both the peak potential and the peak width with varying v and l. The peak width can be very small (ca. 40 mV), permitting a sharp separation of metals with closely adjacent half-wave potentials. For very thin mercury-films (⩽ 25 micron) the peak current is nearly proportional to the rate of potential change.

Chromatographic techniques using liquid anion exchangers : III. Systematic thin -layer chromatography of the elements in HCl systems☆

Abstract Using thin-layer chromatography on silica gel impregnated with Alamine 336, Amberlite La- i or Primene JM-T, the behavoiur of approx. 55 ions in an HCl system has been systematically investigated. Data have also been collected on the behaviour of most ions on the non-impreganted support. When comparing the R F spectra obtained with literature data concerning related methods, a satisfactory overall agreement is found. Moreover, for some elements tentative conclusions about the exchange mechanism are reached. The thin-layer technique previously described has been standardized and suitable apparatus developed. A number of successful separations are reported and in a few cases the advantages of these methods over those described in the literature are indicated.

Distortion of linear-sweep polarograms by ohmic drop

Abstract An exact computation of reversible linear-sweep polarograms at a plane electrode distorted by ohmic drop is presented. It follows from these calculations that ohmic drop causes a decrease of the peak current, a shift of even the corrected peak potential, and a considerable increase of the width of the peak, suggesting nonreversible behaviour. It is deduced that for quantitative studies of electrode processes, the use of a mercury-drop electrode (or other micro-electrodes of similar geometry) in conjunction with linear-sweep voltammetry should be avoided (even when using a three-electrode potentiostat) when the ohmic drop in the solution exceeds about 20/ n mV.

Chromatographic techniques using liquid anion-exchangers : II. Strong monobasic acid systems☆

Paper and thin-layer chromatography—which generally give analogous results—have been carried out in HNO3, HBr, HI, HSCN and HClO4 systems, using supports impregnated with high-molecular-weight amines and substituted ammonium salts. Based on results previously obtained in the HCl system, 5–7 liquid anion-exchangers were investigated, using approx. 10 cations for each acid system. The HBr and HI systems generally give results comparable to those found with HCl as an eluant. A more divergent picture is shown by HSCN, with which eluant it is preferable to use paper chromatography for the time being. The HNO3 system shows fairly low adsorption for most ions, but some interesting applications are outlined. Results with HClO4, on the other hand, are not particularly successful. The use of HI and HBr solutions containing some free I2 and Br2, respectively, has no unfavourable effects. The RF spectra in the HBr and HNO3 systems show good agreement with literature data on solid anion-exchangers. Most curves may be explained assuming an anion-exchange mechanism, adsorption to the support being important incidentally. The adsorption sequence previously reported for the liquid anion-exchangers appears to be reliable for general guidance.

Improvement of the chronopotentiometric method by the use of a potentiostat and a capacity-current addition device

Summary Due to many shortcomings in chronopotentiometry, it could never be considered as a reliable and sensitive method of analysis. With this present investigation it appeared possible to eliminate many difficulties by including a potentiostat as part of the apparatus (pre-electrolysis of small contaminations which would otherwise lengthen the transition time). Certain correction methods for the influence of the capacity current on the transition time were tested; the best results were obtained with the method of De Vries and that of Laity and McIntyre, but the applicability of these methods is limited. A method which is much easier and more generally applicable, is the electronic elimination of the effects by the automatic addition of the varying capacity current to the applied constant current. Solutions of thallium and lead in concentrations down to 10−5 M were measured with standard deviations as small as 1%, depending on the concentration.

The reactions of diphenylcarbazide and diphenylcarbazone with cations : Part II1. Extraction behaviour and spectra of the reagents

Abstract Extraction experiments in the carbon tetrachloride-water system for diphenylcarbazone above pH 7.5 give a value of (2.9 ± 0.3) ·10 -9 for the dissociation constant. At lower pH values the partition coefficients were found to be 7.5 for carbon tetrachloride-water and 39 for toluene-water in 0.1–1 M NaClO 4 . The solubility of the carbazone in water is 3.8·IO -4 M in acid perchlorate medium. Spectra of diphenylcarbazone in water, toluene and carbon tetrachloride, of the anion in water and of diphenylformazane in toluene are compared. In the infra-red spectrum the C=O band was present in the carbazone, but not in the sodium salt.

Ohmic drop distortion of anodic stripping curves from a thin mercury-film electrode

Abstract An exact treatment of the effect of uncompensated ohmic drop on anodic stripping curves from a plane, thin mercury-film electrode is given. The decrease in peak current caused by the ohmic drop can be 2.5–3 times larger than in the corresponding case of semi-infinite linear diffusion (“normal” linear-sweep voltammetry) Practical implications of the results, as well as the case of spherical micro-electrodes, are discussed briefly.

The reactions of diphenylcarbazide and diphenylcarbazone with cations : Part IV. Cations of Mn, Fe, Co, Ni, Cu, Zn, Cd, Sn And Pb

Abstract Of the cations mentioned in the title, only Pb(IV) and Sn(IV) do not react with diphenylcarbazone. The compositions of the carbazone complexes were determined by Jobs method; the formula proved to be M(HD) n according to the valence of the cation. Diphenylcarbazide forms metal complexes only after its oxidation to diphenylcarbazone. Oxidation of carbazide by the metal ion itself occurs with copper(II) and iron(III).

The nature of some metal-chloro anions present in the organic phase in reversed-phase chromatogrpahy involving liquid anion-exchanges

Abstract An analysis has been made of the metal-chloro species sorbed onto an impregnated thin layer in reversed-phase chromatography and extracted into the organic phase in liquid-liquid extractions, when using substituted quaternary ammonium chlorides or high-molecular-weight amine hydrochlorides. In all cases, i.e. irrespective of (1) the class of the anion-exchangers, (2) the concentration on Cl − in the aqueous phase and (3) the use of either HCl or LiCl as the source of Cl − , the sole metal-containing species present in the organic phase are CoCl 4 2− , CuCl 4 2− , MnCl 4 2− and FeCl 4 − . With Fe(III), however, in experiments involving the use of secondary or tertiary amine hydrochlorides, at low aqueous Cl − concentration an extra molecule of the exchanger is attached to the Fe(III)-containing species, which then may be formulated as R 2 R′HN + FeCl 4 − · R 2 R′HN + Cl − (R, alkyl; R′, alkyl or H). Desorption and decreasing extraction, which occur for many elements at high HCl—but not LiCl—aqueous concentrations, may be ascribed to the competitive sorption and extraction of the hydrogen dihalide anion HCl 2 − .