Fundamental study of the adsorption of 1-pentanol, ribofravin and thioctic acid on a gold electrode.

Abstract

The adsorption of 1-pentanol, ribofravin and thioctic acid on a gold electrode was studied by measuring diffferential capacity-potential curves. The differential capacity was measured by a phase sensitive ac polarograph (Fuso Model 332 and 333). The frequency used was 25 Hz and the amplitude was 5 mV. The gold electrode was prepared by sealing a commercially available gold wire in a glass tube. The cyclic voltamograms for riboflavin and thioctic acid are shown in Fig. 1. The voltamogram for riboflavin has a clear reduction peak and an oxidation peak on a gold electrode as on a mercury electrode. Although the voltamogram for thioctic acid has no clear peak, reduction steps can be observed. 1-Pentanol was not reduced or oxidized on a gold electrode as was on a mercury electrode. Differential capacity-potential curves for 1-pentanol, riboflavin and thioctic acid are shown in Figs. 2∼4. A depression of the differential capacity in the presense of 1-pentanol and thioctic acid was observed over the whole potential range investigated (Figs. 2 and 4). At around -0.5, V peaks due to reduction were observed for riboflavin. In the negative potential range, adsorption was also observed, which means that leucoflavin is also adsorbable. The isotherms for these compounds fit the Langmuir isotherm. The free energy of adsorption for 1-pentanol, riboflavin and thioctic acid were 14.6∼18.8, 33.9∼36.8 and 34.7∼38.9 kJ/mol, respectively.