Anionic and cationic drug sorption on interpolyelectrolyte complexes.

Interpolyelectrolyte complexes of chitosan and poly(sodium 4-styrenesulfonate) [NaPSS] were synthesized and obtained in the form of solid particles, with two different sulfonate to aminium molar ratios: 0.7, resulting in particles with positive zeta potential (IPEC+), and 1.4, yielding particles with negative zeta potential (IPEC-). Both particles were characterized as potential drug sorbents using differently charged drugs: sodium cromoglycate (negatively charged), and tetracycline hydrochloride (positively charged). The adsorption isotherm for cromoglycate and tetracycline on IPEC+ was adequately described by the Langmuir model, while the IPEC- sorption of tetracycline followed the Redlich-Peterson isotherm without the occurrence of cromoglycate sorption. The sorption kinetics consisted of two processes, one fast and the other slow, which were correlated to purely surface-related interactions and processes that resulted in diffusion and/or destruction/rearrangement on the particle surface and subsurface, respectively. Charge build up equilibrium and kinetics were also monitored via zeta potential measurements, and the differences between mass drug uptake and particle charging were used to propose adsorption mechanisms for the systems studied in this work.

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

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.

Tetracycline adsorption on chitosan: a mechanistic description based on mass uptake and zeta potential measurements.

Adsorption phenomena occurring at the solid/liquid interface of chitosan particles are of extreme importance in the kinetics of drug release/upload as well as in effluent treatment by adsorption. In this work, equilibrium and kinetic aspects of protonated tetracycline adsorption on chitosan are explored using classic solution depletion method and zeta potential measurements. Equilibrium experiments showed that for solutions with tetracycline initial concentration of ca. 1.2 g L(-1), corresponding to a pH around 3, chitosan structure disrupted, as indicated by an increase in magnitude of tetracycline sorption. Adsorption and zeta potential isotherms before disruption suggested that the process of adsorption had a Langmuir character up to a point at which subsurface was exposed to adsorption; at this point, a second mode of sorption began: zeta potential tended to an equilibrium value, following Sips isotherm and tetracycline sorption had a linear dependence on its continuous phase concentration. The kinetics of tetracycline sorption suggested that sorption of tetracycline was divided between the sorption of protonated and non-protonated tetracycline; tetracycline in its non-protonated form seemed to rule the sorption of tetracycline.

The kinetics of adsorption of tetracycline on chitosan particles.

Experiments to monitor and characterize the kinetics of adsorption of tetracycline on chitosan particles are reported in this work. The same pseudo-order kinetics that has been widely used for describing the adsorption in systems related to wastewater purification and drug loading was used to treat the present data. As some unexpected results came out from the experiments, it was necessary a detailed deduction for this sort of kinetics to be carried out, so that approximations related to short and long times were obtained. Firstly it was shown that an apparently linear t/q(t) versus t relationship did not imply a pseudo-second-order sorption kinetics, differently of what has been repeatedly reported in the literature. It was found that this misinterpretation could be avoided by using non-linear regression. Finally, the adsorption of tetracycline on chitosan particles was analyzed, using the insights obtained from theoretical analysis, and the parameters generated were used to analyze to adsorption kinetics and to propose an adsorption mechanism.