2.2. Method

ZnPT determination in shampoo was performed using complexometric and potentiometric titrations. For the complexometric titration, 6.0 g of the sample were weighed and diluted in water (50 mL). Then, 2.5 mL of hydrochloric acid were added while heating and gently stirring for ten min. 0.5 mL of hydrogen peroxide was added, and the mixture was cooled simultaneously. pH was adjusted with an ammonia solution and 2.5 mL of buffer solution (pH = 10). Finally, the sample was titrated with EDTA (0.01 M) using eriochrome black T as an indicator. The equivalence point occurred when the color of the solution changes from violet to blue.

For the potentiometric titration, 6.3 g of the sample was weighed and transferred to the cell of the automatic titrator (Mettler Toledo, T70) along with 50 mL of water and 10 mL of fuming hydrochloric acid. The resulting sample was titrated with an iodine solution (0.05 M) where the final point of the titration was indicated by a platinum electrode (Mettler Toledo, DMI 140-SC). Constant stirring was ensured during the titration.