novel packing materials are provided for liquid chromatography and / or solid phase extraction columns which will allow direct injection of biological fluids . these packing materials have a hydrophilic exterior layer and a hydrophobic , charged or otherwise selective portion that forms an underlayer or is embedded in the hydrophilic layer . during a chromatographic process large water soluble biopolymers will be in contact with the hydrophilic outer layer and be shielded from interacting with the underlayer or embedded portion and elute unretained . small analytes , on the other hand , can be fully partitioned throughout the exterior and interior layers and are retained by hydrophobic or electrostatic interactions . using such packings the direct analyses of plasma or serum for drug analysis is demonstrated .