COMPARATIVE BEHAVIOR OF DIFFERENT REVERSED-PHASE PACKINGS WHEN EQUILIBRATED WITH CETYLTRIMETHYLAMMONIUM BROMIDE

The saturation of different reversed-phase HPLC C-18 packings with the cationic surfactant cetyltrimethylammonium bromide (CTA) and its subsequent elution in net aqueous eluants, has been studied. The distribution of the surfactant between the mobile and stationary phases indicates a mixed retention mechanism. Under conditions of saturation, the total amount of CTA retained in different commercial packings is inversely related to the density of coating (mu moles C-18/m(2)), and for a given packing depends on the temperature and degree of ageing. When deionised water or a phosphate buffer was passed through the column saturated with CTA, part of it was eluted with the mobile phase, but there was always an amount of CTA that did not elute with aqueous eluants; this uneluted CTA was a constant quantity depending on the eluant, packing characteristics and temperature. When columns were equilibrated with CTA, there was a shift in the eluant ph which was related with the life of these packings working in the presence of CTA.