The retention of some open-chain diamines on a strong cation-exchange resin in ion chromatography as a function of their structure

This work reports the results of a study of the influence of the structure of some open-chain diamines on their retention in high-performance ion chromatography (HPIC). We examine a set of eight diamines, in which the N atoms are separated by two C atoms and are differently N- and C-alkyl substituted; four of these diamines have the same formula weight. In the other two sets, the diamines are different from each other, either in terms of the length of the alkyl chain between the N atoms or in terms of the length of the substituent(s) on the nitrogen atom(s). The mobile phase is a mixture of HClO4 0.100 mol/L, 0.160 < C(NaClO4) < 1.50 mol/L, and 0 < acetonitrile% < or = 15 (v/v). The amines are detected by integrated amperometry. Interpretation of experimental data shows that (a) elution occurs for both ionic and hydrophobic interactions and is dependent on all the components of the mobile phase, (b) the diamines are eluted in any case as dications, and (c) steric hindrance significantly influences elution times. Some examples of separation are proposed.