The interactions between phenobarbital and activated carbon surfaces were studies in detail in this work. This was accomplished by utilizing different reagents to manipulate the surface polar functional group compositions of different activated carbons, and determining how those modifications changed phenobarbital adsorption. Oxidation of in activated carbon surface caused a systematic decrease in the basal carbon surface resulting ill a concurrent systematic decrease in the non-specific adsorption of phenobarbital. Even more interesting, it was shown for the first time that chemical reduction of some of the carbonyl-containing functional groups oil the activated carbon surface caused a significant increase ill the specific adsorption of phenobarbital without any significant effect oil the non-specific adsorption. These results support the notion that the OH groups on activated carbon Surfaces We the specific adsorption sites for phenobarbital from aqueous solutions, and that the basal carbon surface is the region where non-specific adsorption takes place. (c) 2005 Elsevier Inc. All rights reserved.