Retention of some ethylenediamine oligomers in reversed-phase chromatography

Abstract The retention behaviour of four ethylenediamine oligomers containing two, three, four and five monomer units was studied in reversed-phase thin-layer chromatography using various alcohols, salts, acetic acid and ammonia as eluent additives. It was established that with salt-free eluents the oligomers showed very high retention. The retention decreased with increasing salt concentration in the eluent. This phenomenon may be due to the dissociation-suppressing effect of the salts and/or to the competition for the free silanol groups on the silica surface uncovered by the impregnating agent. The salts with higher activity coefficients had a greater effect on the retention whereas lower dielectric constants of the alcohols decreased their influence on the retention. The results suggest that to obtain the minimum retention of ethylenediamine oligomers (and probably other polyamines), the use of a salt with a high activity coefficient and organic mobile phases with high dielectric constants can be recommended.