Aliphatic amines complex mixtures used in the synthesis of polybutenylsuccinimide dispersants can be qualitatively identified, after a mild saponification, by gas chromatography on a 5% diphenyl-94% dimethyl-1% vinylpolysiloxane WCOT capillary column through temperature programming. Dual detection with flame ionisation detector and thermoionic detector, sensitive only to nitrogen (and phophorus) compounds, is used. Examples are given for a commercial concentrate and for an engine motor oil.