Electroanalytical characterization of naphthenic acids

Naphthenic acid is the name for an unspecific mixture of several natural occurring carboxylic acids, which are present in crude oil and leads to corrosion problems within the oil refineries and to environmental problems, due to their toxicity. For these reasons, in the last years, there has been an increasing interest in the qualitative and quantitative determination of these acids, in the framework of the general topic of the characterization of carboxylic acids, involved in many fields, such as food processing and enology, electroplating, special-ink industry, metal surface treatments, pharmaceutical formulations, cosmetic products, wastewater treatments. The conventional methods [1] proposed so far (spectrophotometric ones; gas chromatography; mass spectrometry; capillary electrophoresis; HPLC) are partly inadequate to the task, particularly in the aim of elucidating the mechanism connected to the corrosion phenomena, not to mention their really limited sensitivity, time-consuming procedures and high costs. Electroanalytical techniques, in particular pulsed ones (square-wave voltammetry, differential-pulse voltammetry), offer a powerful, sensible, accurate and low-cost alternative. In this context, the present work proposes the electrochemical characterization and the electroanalytical determination in dimethylformamide of six commercially available naphthenic acids (naphthoic, cycloesilacetic, cyclopentylpropionic, cycloesanpropionic, cycloesancarboxylic, cyclopentancarboxylic), present individually or in mixtures. Different electrodes have been tested (Au, Pt, Glassy Carbon), in order to evaluate the best cathode material for the analysis.