Gel permeation chromatography (GPC) was utilised to control the progress of the reaction betweenN,N-dimethylpropylene-1,3-diamine (DMPDA) and triglycerides (fats). As per “ideal size exclusion mode”, the sample is separated into triglycerides (TGC), diglycerides (DGC), monoglycerides (MGC), and glycerine (GC), as the component groups with sufficiently different molecular weights. Moreover, the separation was obtained for MGC and amidoamines (AA), i.e. the reaction products, despite the fact that their molecular weights are the same in practice (Mw=348 and 358, respectively). The increased retention time for amidoamines was assumed to be accounted for by the additional adsorption effects in “adsorption mode”. Resulting from the overlapping of two types of chromatographic separation mechanisms, an analytical method was obtained which could be called “mixed mode” conditions.