This paper discusses the use of chemical derivatization methods for surface chemical composition analysis of diamond-like carbon (DLC) films synthesized through plasma-enhanced chemical vapor deposition with X-ray photoelectron spectroscopy (XPS). The main challenge in applying chemical derivatization reactions for titration of organic functional groups on the DLC surface is that sub-surface oxygenated species are not accessible to the derivatizing agent. As a simple approximation, a functional group that can be quantified unambiguously with XPS can be used as an internal reference to estimate the accessible-to-inaccessible ratio, and this information can be used to estimate the total amount of other functional groups from the chemical-derivatization-assisted XPS analysis. The use of this principle to obtain the surface composition of hydroxyl, ether, carbonyl, and carboxyl groups in the oxidized surface region of the DLC film was demonstrated. (C) 2011 Elsevier B. V. All rights reserved.