Polyallylamine-supported pseudo-stationary phases for electrokinetic chromatography. Effect of alkyl chain length of the pseudo-stationary phase and methanol content of aqueous buffer on the separation of hydrophobic compounds

Polymeric pseudo-stationary phases having alkyl (C₈-C₁₆) and carboxylate groups were prepared from commercially available polyallylamine (PAA). PAA was first alkylated with an alkyl bromide, then reacted with methyl acrylate, followed by the hydrolysis of the ester functionality. The PAA-supported pseudo-stationary phases, especially those with long alkyl chains, provided high efficiencies for alkyl phenyl ketones and polynuclear aromatic hydrocarbons in a wide range of buffer-methanol mixtures. Migration times of the hydrophobic compounds, limited by the migration time of the carrier (t(C)) at low methanol content, showed a large increase at 40-60% methanol, and decreased due to the decrease in k' values at higher methanol content where large t(C) values were observed. The expansion of the migration time window occurred at a higher methanol content with the pseudo-stationary phase with the longer alkyl groups. Difference in the effect of methanol addition on the behavior of PAA derivatives with different alkyl groups can be attributed to the structural change of the polymeric pseudo-stationary phase resulting in the greater electrophoretic mobility relative to electroosmotic flow, and in turn large t(C) values. Simple preparation of the PAA-supported pseudo-stationary phase and the high efficiency will make electrokinetic chromatography using polymeric pseudo-stationary phases a promising tool for the separation of a wide range of compounds including very hydrophobic polynuclear aromatic hydrocarbons in simple water-methanol mixtures.