F. Vydra

Voltammetry with disc electrodes and its analytical application: II. Anodic stripping voltammetry of trace concentrations of silver and copper employing a glassy carbon electrode*

Summary The rotating GCE has been found to be a suitable electrode for anodic stripping voltammetry of submicro amounts of metal ions. Sharp mono peaks were obtained corresponding to the anodic dissolution of silver and copper in acidic, neutral and alkaline media. The effect of various factors (rotation velocity of the electrode during the deposition and stripping process ‘scan rate’ deposition potential and deposition time, composition of the supporting electrolyte) on the peak current and peak potential was studied. The peak height has been found to be a linear function of the concentration of the metal analyzed and the log of the peak potential to depend linearly on the concentration of silver and copper, respectively. The determination of trace amounts of silver (10−6–10−9 M) and copper (10−6–10−8 M) can be carried out in acidic, neutral or alkaline media. A procedure was established for the determination of micro amounts of silver in the presence of a large excess of copper. Ammonia/ammonium nitrate solution was employed as supporting electrolyte and when the concentration of copper was too high, the sample solution was replaced by a pure solution of ammoniacal buffer after the deposition step. 5×10−7 M silver solutions containing copper at a concentration of 5×10−3 M were analyzed successfully; the error did not exceed ±5%. The application of GCE in anodic stripping voltammetry is being further studied.

Voltammetry with disc electrodes and its analytical application: IX. The selectivity of the stripping determination of mercury and the determination of some metals in the presence of mercury at glassy carbon electrodes

Summary Mercury can be determined in the concentration range 10−6–5×10−8 using a.s.v. and the RDE prepared from glassy carbon. The determination can be carried out in the presence of a 10-fold excess of Cu, Pb, Zn, Ni, Co, and Cd in potassium thiocyanate medium or in a solution of sodium perchlorate pH=2. The determination of various metals in the presence of mercury in potassium thiocyanate medium is also discussed.

Voltammetry at disk electrodes and its analytical application: VI. A.C. Voltammetry at rotating disk electrodes and its application to stripping analysis

Summary A study has been made of the feasibility of using an a.c. voltammetric technique with rotating disk electrodes for analysis. Direct and inverse voltammetric techniques were studied for a number of metal ion-electrolyte systems at various electrode materials. The direct technique is valuable for quantitative analysis of reversible systems and qualitative analysis of semi-reversible systems. The stripping technique enables the oxidation peaks of difficultly analyzable systems such as silver in the presence of copper to be separated.Summary A study has been made of the feasibility of using an a.c. voltammetric technique with rotating disk electrodes for analysis. Direct and inverse voltammetric techniques were studied for a number of metal ion-electrolyte systems at various electrode materials. The direct technique is valuable for quantitative analysis of reversible systems and qualitative analysis of semi-reversible systems. The stripping technique enables the oxidation peaks of difficultly analyzable systems such as silver in the presence of copper to be separated.

Voltammetry at disk electrodes and its analytical application: Part VII. The use of the second harmonic alternating current technique for stripping analysis at rotating disk electrodes

Summary The second harmonic alternating current technique has been found to be particularly advantageous for stripping analysis with a glassy carbon electrode, and becomes especially sensitive when used in conjunction with a rotating disk electrode, Increased sensitivity results for all systems, and divalent elements give peaks comparable in height to monovalent elements. Divalent mercury could be analyzed at the 5×10−10 M level after only 10 min pre-electrolysis in thiocyanate media, comparing well with spectrometric techniques. Good results may be obtained employing simple commercial instrumentation.

New redox systems—II: Oxidation of cobaltII with ironIII chloride in 1:10-phenanthroline solutions

Abstract The oxidation of cobaltII with ironIII, in the presence of 1:10-phenanthroline, has been studied both potentiometrically and colorimetrically. From these studies it can be deduced that the course of the reaction is [Fe2(Phen)4(OH)2]4+ + 2Co(Phen)32+ + 2HPhen+ ⇌ 2Fe(Phen)32+ + 2Co(Phen)33+ + 2H2O (1) Conditions have been found in which the reaction proceeds quantitatively. Its utilisation in both macro and micro determination of cobalt is discussed.

Voltammetry with disk electrodes and its analytical application: VIII. The cyclic voltammetry of copper(II) at the glassy carbon rotating disk electrode

Summary The cyclic voltammetry of copper(II) at the glassy carbon rotating disk electrode has been studied in a number of media with a view to its usefulness in analytical applications. It has been found that, while Cu 2+ is generally reduced to Cu 0 , the stripping scan does not necessarily result in reoxidation to Cu 2+ , the reaction often ending with oxidation of Cu 0 to monovalent copper. This phenomenon has been related to the degree to which monovalent copper, produced at the electrode surface, remains adsorbed long enough to undergo further reaction, which is, in turn, strongly affected by the medium.

Sorption of ferroïn on silica and its analytical use

Abstract Sorption of ferroin on silica is studied and the influence of pH, volume, ionic strength, flow rate, particle size and pore size of silica, and the presence of EDTA and citric acid on the sorption is found. This has led to the development of procedures for the determination of traces of iron in nickel, chromium, molybdenum and tungsten, and the possibility of other uses of silica for the separation of metals is discussed.

The voltammetry of ethylenediaminetetraacetic acid (EDTA) and related compounds on a rotating platinum electrode

Summary The behaviour of EDTA, ethylenediamine, iminodiacetic, 1,2-diaminocyclohexanetetraacetic, nitrilotriacetic, ethyleneglycol-bis-(2-aminoethylether)tetraacetic, diethylenetriaminepentaacetic, and triethylenetetraminehexaacetic acids was studied on a rotating platinum electrode. These substances, with the exception of ethylenediamine and iminodiacetic acid, yield anodic voltammetric waves on a platinum electrode, the heights and half-wave potentials of which are dependent upon pH and the composition of the solution. The probable mechanism of the electrode reactions is given.

Selective determination of trace quantities of silver using sorption of Ag(NH3)2+ on silica

Abstract It is possible to adsorb silver, in the form of Ag(NH3)2+, quantitatively on silica from solutions of pH higher than 8.5, even in the presence of EDTA. Conditions are described for the determination of trace amounts of silver in the presence of gram amounts of copper, mercury, cadmium, zinc, nickel, bismuth and iron.

Voltammetry with disk electrodes and its analytical application: X. The voltammetry and electrochemical stripping analysis of gold in aqueous and nonaqueous media

Abstract Cyclic voltammetry of AuCl 4 − was studied in the medium of aqueous hydrochloric acid and in non-aqueous media using the rotating disc electrode made from glassy carbon. Cyclic voltammetry in nonaqueous medium was carried out after the extraction of gold from the aqueous solution 4 M HNO 3 with 60% TBP in benzene. The reduction of gold in this medium takes place up to the potential at which the evolution of hydrogen starts. Gold was determined by stripping voltammetry down to the concentration 10 −7 to 5×10 −6 M and by stripping chronopotentiometry down to 3×10 −7−5 ×10 −6 M . The metals in the concentration 5×10 −3 M : In 3+ , Fe 3+ , Co 2+ , Cd 2+ , Mn 2+ , Pb 2+ , Zn 2+ , Ag + and other metals which are not extracted by TBP do not interfere with the stripping chronopotentiometric determination of gold (10 −6 M ) carried out under optimum conditions. The error of the determination did not exceed ±3%. The determination of gold with an error of ±5% can be carried out in the presence of 3.5×10 −4 M Bi 3+ , 3×10 −4 M Sb 3+ and 2.5×10 −4 M Hg 2+ . Pt 4+ interfered when its concentration was higher than the gold concentration. Pd 2+ did not interfere up to the concentration 3×10 −4 M .