2.9. Zeta Potential

Zeta potential was measured from the original chitosan dissolved in 2% acetic acid and the modified chitosan after dissolution in water. Initial values of the pH of the original chitosan solution (3.71) and the modified chitosan (8.12) were determined before measurements with a one-electrode pH meter (WTW MultiLine P4, Xylem Analytics Germany). The pH of both solutions was adjusted to 3 with 0.01 or 0.1 N HCl correspondingly to avoid excessive dilution of the samples. Further titration was carried out under constant stirring with the use of 0.1 or 0.01 N NaOH in different pH regions in order to achieve minimal volume change due to the addition of titrant. The zeta potential values at specific pH were measured with a Zetasizer Nano ZS, Malvern Instruments (Malvern Panalytical, U.K.), and the results are presented as the average of three measurement.