Characterization of immobilized Rhoeo discolor (L’Hér.) hance leaf extract in alginate-chitosan membrane as a pH indicator

An easy, simple and eco-friendly pH indicator from immobilized Rhoeo discolor leaf extract on alginate-chitosan membrane was developed. Rhoeo discolor leaf extract in ethanol was immobilized in the alginate-chitosan membrane by entrapment technique. The membrane was prepared at a pH of 5.2 with a mass ratio of alginate and chitosan of 1:1. Then, the immobilized extract in the membrane was tested in a pH solution of 2 to 8. The resulting pH indicator was characterized by UV-Vis and FTIR spectroscopy. Furthermore, biodegradability tests in soil medium was carried out. The color change was observed at pH 2 to 8. FTIR spectra showed that interaction of alginate and chitosan in membrane was occurred through electrostatic interaction between carboxylate group and protonated amine, while the immobilized membraned showed no additional functional groups that indicated there is no chemical interaction between leaf extract and alginate-chitosan membrane. The leaf extract was trapped in a three-dimensional network of alginate-chitosan membrane. Biodegradability test on soil medium for 21 days showed a membrane degradation of 23.07%. Therefore, the obtained pH indicator is suitable for eco-friendly pH testing tool.