SURFACE INTERACTION OF ALUMINUM HYDROXIDE GEL WITH ORGANIC COMPOUNDS
Abstract
The zero point of charge (ZPC) of an aluminum hydroxide gel determines the surface interaction with adsorbate molecules. At pH values below the ZPC, the aluminum hydroxide gel exists as a predominantly positive surface. While at pH values above the ZPC, a predominantly negative surface exists. Sodium dioctyl sulfosuccinate (NaDSS), an anionic compound, reacts strongly with the aluminum hydroxide gel at pH values below the ZPC of the aluminum hydroxide gel and reduces the extent as well as the rate of acid reactivity of the aluminum hydroxide gel. Mannitol, a non-ionic compound, does not interact as strongly as NaDSS, however, the interaction is also pH-dependent and can be related to the surface charge. Mannitol is more extensively adsorbed at pH values above the ZPC of the aluminum hydroxide gel than at pH values below the ZPC. When mannitol interacts with aluminum hydroxide gel, the rate of acid neutralization is decreased. The decrease in the rate of acid neutralization is directly related to the concentration of mannitol until 1.5 molar. In the presence of 2 molar mannitol the rate of acid neutralization increases. This may be due to the critical solute-solvent aggregation phenomenon. Inositol, methanol, ethanol, and glycerol fail to alter the rate of acid neutralization. Infrared analysis indicated that inositol does not react with the aluminum hydroxycarbonate gel. Thus, the pH-stat technique is useful to screen compounds that might interact with aluminum hydroxide gel. Infrared analysis shows that hydrogen bonding is the main mechanism by which mannitol interacts with the aluminum hydroxycarbonate gel. An aging study indicated that mannitol containing aluminum hydroxide gel samples maintained the extent of acid reactivity. The samples containing inositol failed to maintain the extent of acid reactivity with time. The relationship between the pH of an aluminum hydroxide gel and the ZPC will influence the viscosity of the system. At the ZPC of an aluminum hydroxide gel, the viscosity is at its maximum. If the pH of the sample is away from the ZPC, a less viscous system will result.
Degree
Ph.D.
Subject Area
Pharmacology
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