UV-Visible Spectroscopy for Kinetic Study of Fluorescein-Labeled Starch Adsorption at Ferric Chloride

Fateh Eltaboni, Abdelqader Imragaa
2016 Human Journals Research Article November   unpublished
Fluorescein 5(6)-isothiocyanate-starch (FITC-S) biopolymer was prepared via covalently attached fluorescein 5(6)-isothiocyanate (FITC) with starch. FITC-S with an average molecular weight length of 3x10 6 g/mol was formed upon precipitation in alcoholic solution. FITC-S showed absorption maxima at around 490 nm in aqueous medium. The adsorption of the photoactive starch onto ferric chloride (FeCl 3) was studied using UV-visible spectroscopy. Spectra of the adsorbed biopolymer were collected as
more » ... were collected as a function of time and as a function of concentration. Measurement of the peak intensities of the adsorbed FITC-S allowed adsorption isotherms and adsorption kinetics to be determined for biopolymer at different pH values. Unmodified Langmuir fitting for experimental data yielded a Gibbs free energy of adsorption () at pH 7, pH 9, and pH 11 of-55,-52and-51 kJ/mol, respectively, which correlate well with similar values determined modified Langmuir model. Kinetic analysis indicated that the adsorption of FITC-S was a pseudo-first-order process over pH range studied. Furthermore, the adsorption lifetime ( ad) was decreased to 46 min by decreasing the pH to 6.5., as the electrostatic attraction between starch and the oppositely charged ferric chloride was enhanced.