An investigation of the properties of a ''shielded'' phase for the solid phase extraction of acidic and basic compounds

The extraction properties of Hisep, a novel bonded phase for solid phase extraction, have been investigated using a number of acidic and basic analytes and compared with those of a conventional ODS bonded material. Marked differences in extraction properties for the test analytes propranolol, anisic acid and ICI 128436 from aqueous buffer were noted between the two materials. Thus, extraction onto the ODS material was by both ionic and reversed-phase mechanisms whilst retention on the Hisep phase appeared to be mediated predominantly by reversed-phase hydrophobic interactions. The presence of dog plasma had no effect on the extraction of propranolol but did reduce the extraction efficiencies observed for anisic acid and ICI 128436 in a pH dependent manner.