A 100 mg L− 1 sodium dodecylsulfate (SDS) stock solution was used for the preparation of analytical standard solutions throughout the ex- perimental work. This solution was prepared by dissolving 10.0 mg of SDS reagent (Vetec, Rio de Janeiro, Brazil) in approximately 10 ml of water. After total dissolution of the solid, the mixture was transferred to a 100 ml volumetric flask and the volume was completed to the mark with water. Stock solutions of SDS were prepared daily as well as the analytical standard solutions, which were prepared by conve- nient dilution of the stock solution. SDS was used in this work as a model anionic surfactant because the substances belonging to this class of surfactants present very similar structure and same reactivity of this compound.