Since the discovery of carbon nanotubes (CNT), this material has been recognized as an attractive material because of its exceptional physical and chemical properties. CNT must be functionalized for most applications. However, the functional groups on the CNT are very complex. Here a simple acid-base titration is introduced to characterize the functionalized multi-wall carbon nanotubes (MWCNT). By using the principle component analysis (PCA) of a titration data set of 21 independent curves, we can calculate the density of Bronsted acid functional groups for each differently functionalized MWCNT. (C) 2015 Published by Elsevier B.V.