Liquid chromatography/mass spectrometry (LC/MS) with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) in the positive and negative ion modes was used for the characterization of a block copolymer consisting of methoxy poly(ethylene oxide) (mPEO), an ε-caprolactone (CL) segment and linoleic acid (LA), used as surfactant in water-based latex paints. Chromatographic separation was obtained based on the number of CL units in the polymer species and the presence of an mPEO and/or LA tail. Different ionization methods were found to be complementary and only their combination allowed the qualitative profiling of the chemical composition. The LC/MS method has proven valuable for following the reaction in time, as well as for comparison of different polymeric surfactants. Copyright © 2007 John Wiley & Sons, Ltd.