Equilibrium and kinetic aspects of sodium cromoglycate adsorption on chitosan: Mass uptake and surface charging considerations

• Cromoglycate ion is adsorbed on chitosan by electrostatic or hydrophobic interactions.
• Adsorption isotherms show that below a critical temperature, hydrophobic interactions prevail.
• Sorption kinetics may be divided into slow and fast processes.
• Slow processes are related to the mobility of groups on chitosan surface.
• Fast processes are related to the adsorption of cromoglycate on chitosan.

Chitosan has more and more been suggested as a material for use as adsorbent in the treatment of effluents as well as in the synthesis of drug-loaded nanoparticles for controlled release. In both cases, a good understanding of the process of adsorption, both kinetically and in terms of equilibrium, has an importance of its own. In this manuscript we study the interaction between sodium cromoglycate, a drug used in asthma treatment, and chitosan. Equilibrium experiments showed that Sips (or Freundlich–Langmuir) isotherm described well the resultant data and adsorption possibly occurred as in multilayers. A model based on ordinary reaction-rate theory, compounded of two processes, each one with a correlated velocity constant, described the kinetics of sorption. Kinetic and equilibrium data suggested the possibility of surface rearrangement, favored by the increase of temperature.

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