Voltammetry Combined with on-Line HPLC for the Electro-Oxidation of Formamidine Disulfide

Abstract

Formamidine disulfide is an important oxidation product of thiourea, the electro-oxidation mechanism is not well understood. Herein, the electro-oxidation of formamidine disulfide was studied by on-line HPLC combined with voltammetry. The sampling process on the electrode surface is controlled by a microporous sampler placed at the electrode interface while scanning, which allowed the electro-oxidation products to be detected at a given potential. The dependence of electrode product and electrode potential was determined, the main electro-oxidation products of formamidine disulfide are thiourea, formamidine sulfinic acid, cyanamide, and elemental sulfur.In this study, We use on-line HPLC combined voltammetry to study the electro-oxidation of formamidine disulfide, the convective mass transfer control technique was applied to determine the electrode intermediates involved in the electrochemical reaction at a given potential. Similar to the RDE or RRDE technology, forced mass transfer control technology was introduced by sampling pump, but the direction of the mass transfer was rather different from the RDE or RRDE. The key of the forced mass transfer control technology is the rate control of the sampling pump. When the sampling rate of the pump is low, the mass transfer process on the electrode surface is not strong enough and the sampling too little affects the HPLC analysis, the excessive sampling rate of the pump has a great influence on the electrochemical voltammetry curve. A qualitative and quantitative analysis of electrode interface species can be carried out by on-line HPLC and electrochemical techniques, and the distribution of products with electric potential can be obtained more directly.Combining voltammetry with on-line HPLC technique provided a effective approach for detecting the products on the surface of electrode formed at a given potential. In addition, when the intermediate products are produced on the electrode surface, sampling at the electrode interface causes a decrease in concentration, resulting in an increase in the peak current with the increase of the sampling speed. If the species in the solution reacts electrochemically, sampling near the electrode interface enhances the mass transfer process and the material in the bulk solution diffuses to the electrode surface faster, thus the peak current increases with the increase of the sampling speed, until reaching a plateau. Thus, as exemplified by the qualitative and quantitative analysis of the electro-oxidation products of TU2 2+, sampling using a microporous sampler on the platinum electrode surface allows in situ detection of the species and concentration changes on the electrode surface. Figure 1