Focussed microwave-assisted sample preparation: total phenol determination in petroleum refinery effluents by flow injection spectrophotometry

This paper reports the development of a new approach for total phenol distillation using a focussed microwave oven, aiming its determination in petroleum refinery effluents and sour waters. In the procedure, 25 ml of sample is distilled during 15 min at 210 W power. At these conditions, recoveries as high as 95% are obtained, making possible the determination of total phenol in the samples without any interference and in a time significantly lower than that required by the reference method. In the course of the research, the influence of the distilled volume was investigated and a Doehlert matrix was employed for the multivariate optimization of the irradiation power and time. Quantification of phenol was spectrophotometrically performed in a FIA system, exploring classical reaction of phenol with 4-amineantipyrine and ferricyanide. Aqueous standards solutions of phenol could be directly injected in the FIA system for calibration purposes, making the procedure very simple and low time-consuming. A detection limit of 10 μg l⁻¹ was achieved as well as a quantification limit of 33 μg l⁻¹, becoming the procedure very suitable to be applied in the control of total phenols in effluents from petroleum industry.