Determination of total phenols in waters and wastewaters using flow injection with electrochemical detection; an alternative to the standard colorimetric procedure

A new flow injection (FI) method using a dual electrochemical detector is described for the analysis of total phenols in water and wastewater samples. The method relies upon in-line oxidative electrochemical removal or elimination of interferences at an upstream large surface area (coulometric) electrode combined with oxidative detection of all phenols at an amperometric electrode. Using the ESA dual electrode high sensitivity cell and a phosphate buffer carrier stream (pH 6.8), the ideal potentials were found to be +0.35 V for the coulometric electrode and +0.78 V for the sensing amperometric electrode. The method is fast, with sampling frequencies around 60 h−1 and precision is typically 0.1–4%. Several synthetic aqueous samples were analysed by the FI and colorimetric methods and compared with results obtained using reversed-phase liquid chromatography (LC). More reliable data were obtained for samples containing para-substituted phenols and nitrophenols with plots of FI vs. LC data resulting in correlation coefficients of r2 = 0.71 and r2 = 0.79, respectively, whereas the standard colorimetric method vs. LC data gave correlation coefficients of r2 = 0.29 and r2 = 0.04, respectively. The method was applied to the analysis of five industrial wastewaters.