Qualitative and quantitative determination of a humic model compound in microbial cultures by cyclic voltammetry

The humic model compound, anthraquinone-2,6-disulfonate (AQDS), was characterized and measured in microbial cultures by cyclic voltammetry (CV). Under the experimental conditions, the formal reduction potential (E(o')) of the couple AQDS/AHQDS was found to be of -0.520 V vs. SCE (standard calomel electrode) at pH value of 7.0. Control experiments showed that there were no interferences of the culture medium or the microbial consortium on the quantitative determination of the quinone. The linear equation E(o') = -0.294 - 0.032 pH was found, showing that the pH used (7.0-7.8) did not affect significantly the AQDS determination by CV and AHQDS was the predominant hydroquinone formed. A calibration curve was obtained by plotting current response versus AQDS concentration with a linear correlation (r = 0.999) from 0.2 to 10 mM of AQDS. This technique was applied in a denitrifying culture to establish kinetic profiles for AHQDS formation coupled to acetate and p-cresol oxidation. CV results showed that organic matter oxidation by the denitrifying sludge was stoichiometrically associated to AQDS reduction into AHQDS-. CV was shown to be a useful tool for monitoring oxidation/reduction processes of quinones occurring in complex microbial media.