In order to model the entry of radical in emulsion copolymerization, a study of the oligomers present in the aqueous phase is necessary. In this work a new method for separation and characterization of the aqueous phase has been developed. MALDI-ToF-MS was found to be a powerful technique in order to characterize the oligomers present in the aqueous phase. It is for the first time that full chemical composition and molecular weight information of the oligomers present in the aqueous phase in emulsion copolymerization has been obtained. The methodology was shown to be semi-quantitative and several factors were studied, for example temperature effects, interference of latex particles present in serum of the aqueous phase and type of ionizing salt in MALDI. It was shown that the methodology works well, even though we are dealing with small quantities of oligomers and the possibility of mass discrimination in MALDI-ToF-MS.