Rotating Ring Disk Voltammetry Research Articles

Sensitivity and selectivity of the electrochemical detection of the copper(II) complexes of bioactive peptides, and comparison to model studies by rotating ring-disc electrode

Post-column reaction of peptides with Cu(II) can be used for the electrochemical detection of peptides as their biuret complexes. Understanding of the behavior (sensitivity at the anode and cathode in the dual-series electrochemical detector) of the system is facilitated through the observation of the rotating ring disc voltammetry of some model compounds. In operation, the anodic signal from the oxidation of the Cu(II)-peptide to the Cu(III) form can be used to detect peptides, or the downstream cathode can be used to detect the Cu(III) form. The signals appear at about 0.4 V (anode) for tetra- and longer peptides, 0.65 V for tripeptides. The anode signal is augmented by tyrosine (oxidation at 0.4–0.5 V) and tryptophan (0.5–0.6 V). If the cathode is used as the detector in a two working electrode cell, the sensitivity depends on the stability of the Cu(III) product. This is peptide dependent, but the signal is significant and useful analytically. Twenty-three bioactive peptides in two groups, naturally electrochemically active and naturally electrochemically silent, and several model compounds have been studied. Both naturally electrochemically active peptides (contain tyrosine and/or tryptophan) and naturally electrochemically silent peptides have been studied. Chromatography with an acetonitrile gradient has been used to separate the peptides in each group. Detection limits are for non-electroactive peptides in the range of 16–100 fmol (10- μl injection 1.6–10 n M, 100 μl injection 0.16–1.0 n M), and for electroactive peptides in the range of 6–40 fmol (0.6–4.0 n M for a 10- μl injection and 60–400 p M for a 100- μl injection). A tryptic digest of bovine cytochrome c is easily seen at 100 n M.

The anodic behaviour of tin in sulphuric acid solutions

The anodic dissolution and partial passivation of tin in 4.5–8 M sulphuric acid solutions has been studied using rotating ring—disk voltammetry. In the region of active dissolution a Tafel slope of 1/(30 ± 3) mV −1 was measured. This value was found to be independent of acid concentration. A reaction mechanism is presented to explain this slope. It was found that tin dissolves both in the active and partly passive potential region in the form of bivalent tin. Oxidation to the tetravalent state seems to occur only at high anodic potentials. Oxygen evolution starts only at potentials above 3 V (vs. Hg 2SO 4/Hg). Analysis of the passivating film formed on the electrode surface using SEM, XRD, XPS and SIMS showed that the film is mainly tin oxide, SnO, mostly in an amorphic form.

Electrochemical and optical studies of silicon dissolution in ammonium fluoride solutions

The mechanisms involved in the (photo)dissolution of silicon in fluoride solutions are discussed. Several methods, including intensity modulated photocurrent spectroscopy, in situ ir spectroscopy, rotating ring disc voltammetry and ellipsometry, have been used to examine the anodic dissolution process. The valence state of the dissolving silicon has been determined under different conditions, and the optical properties of the surface have also been characterized. The generation of hydrogen has been linked in the case of n-Si to intensity dependent photocurrent multiplication, and in the case of p-Si it has been related to different etching regimes. The current oscillations observed during the anodic dissolution of p-Si are also discussed.

Electrogenerated chemiluminescence. 30. Electrochemical oxidation of oxalate ion in the presence of luminescers in acetonitrile solutions

The electrochemical oxidation of oxalate at a platinum electrode in acetonitrile solutions as studied by cyclic and rotating-ring disk voltammetry and controlled potential coulometry shows an irreversible two-electron oxidation at ca. 0.3 V vs. SCE to CO2 with no intermediates detectable by these techniques. The oxidation of oxalate in the presence of several fluorescers (such as rubrene, 9, IO-diphenylanthracene, and the bipyridyl chelates of ruthenium(l1) and osmium(l1)) does not produce light, but emission characteristic of the fluorescer occurs during the simultaneous oxidation of the additive and oxalate. Studies of the conditions for emission in the presence of thianthrene and naphthalene lead to a mechanism for the oxidation of oxalate and the excitation process based on oxidation of oxalate to CzO4-., which undergoes rapid decomposition to COz and C02--. The C02-e can transfer an electron to the additive molecule to produce a radical anion, which can then undergo an ecl annihilation reaction with the electrogenerated radical cation. There has been much interest in the intense chemiluminescence which results from the reaction of oxalyl chloride or oxalate esters and hydrogen peroxide in the presence of fluorescent compounds in nonaqueous solvents.’-3 In the proposed mechanism for these processes, the reaction between the oxalate ester and H202 produces the dioxetanedione (1) as an