Abstract The Romanian standard for the analytical method for phenols measurements in aquatic media was subject of internal validation procedure, adapted to the specific concentration domain of the laboratory. Method performance criteria were investigated on standard samples measurements: selectivity, linearity domain, precision, accuracy, limit of detection, limit of quantification androbustness. The validated method was further used on real samples of domestic and industrial wastewaters from the Wastewater Treatment Plant of Brasov, Romania. As a novelty, even not required in the Romanian standard, sources of uncertainties were identified, and uncertainty was estimated for both measurements on standard and wastewater samples. The results showed that the method is suitable for phenolic compounds determination from wastewaters, with a very low uncertainty level.