title: The influence of the adsorption of metoclopramide on the surface ionization of fumed silica.
abstract: The effect of adsorbed metoclopramide on the surface ionization of fumed silica was studied using potentiometric titration. Adsorption isotherms of metoclopramide to unionized and negatively-charged silica surfaces were generated and compared to the titration data. The adsorption of metoclopramide caused the silica surface charge to become more negative with increasing pH that was independent of ionic strength which suggested that specific adsorbate-surface interactions were occurring. Adsorption studies showed that metoclopramide adsorbs to the unionized silica surface. Ionization caused drug adsorption to increase which was consistent with at least two distinct surface adsorption sites. The ratio of the additional amount of metoclopramide adsorbed to the surface ionized group density determined from the titration curves was approximately unity which showed conclusively that the negatively-charged silanols constitute one of the surface adsorption sites. Potentiometric titration has been shown to be a useful technique for determining the number and types of adsorption sites on the silica surface.
authors.affiliation: College of Pharmacy, University of Iowa, Iowa City, IA 52242, USA. Electronic address: tuba331@yahoo.com.
authors.forename: Tuba
authors.initials: T
authors.lastname: Buyuktimkin
authors.affiliation: College of Pharmacy, University of Iowa, Iowa City, IA 52242, USA.
authors.forename: Dale Eric
authors.initials: DE
authors.lastname: Wurster
mesh_terms: D000327:Adsorption; D006863:Hydrogen-Ion Concentration; D008787:Metoclopramide / Q000737:chemistry*; D009994:Osmolar Concentration; D012822:Silicon Dioxide / Q000737:chemistry*; D012995:Solubility; D013499:Surface Properties
chemical_list: D012822:Silicon Dioxide; D008787:Metoclopramide
keywords: Fumed silica; Metoclopramide; Potentiometric titration; Silanol; Surface charge