Electroosmotic flow mobilities in open and packed capillaries with spermine and other amine flow modifiers

The effect of some cationic amines (spermine, spermidine, hexamethonium bromide and tetramethylammonium bromide) on the mobility of electroosmotic flow (EOF) in open fused-silica capillaries was studied. The EOF was found to be significantly reduced with spermine and spermidine and to a lesser extent with hexamethonium bromide. Tetramethylammonium bromide was found to be ineffective as a flow modifier. Spermine (10-20 mu M) gave a stable reduced EOF at pH 2.50, while 400-500 mu M was required at pH 7.0. In a silica-packed capillary, higher concentrations of spermine were required to significantly change the EOF (up to 1 mM). The very low absorption coefficients (M-1 cm(-1)) of spermine [epsilon(200)=250, epsilon(210)=35] and spermidine [epsilon(200)=118, epsilon(210)=3] at low UV wavelengths makes them useful as surface-charge modification agents when using UV detection, and their low conductivity makes them suitable for use with conductivity detection.