This paper's proposal was to study the pH influence on protein exclusion in restricted access carbon nanotubes (RACNT), obtained by chemical modification of carbon nanotubes (CNT) using concentrated acid oxidizing agent (HNO3-65 % v/v). Oxidized CNT were coated with a layer of bovine serum albumin (BSA), resulting in RACNT-BSA. The isoelectric points of CNT, oxidized CNT, RACNT-BSA, BSA, and cross-linked BSA were determined by potentiometric titration. Percolating the BSA solutions at a concentration of 3 mu g mL(-1), in a phosphate buffer at a pH range from 2.2 to 7.0, by RACNT-BSA inside SPE cartridges, we studied the interactions among them. Solubilized BSA adsorbed in the RACNT-BSA surface at a pH range near the Ip (3.5-5.2), while in the other studied pH ranges this did not occur, which is mainly governed by electrostatic phenomena.