PACKING MATERIALS WITH SURFACE BARRIERS, CONTROLLED DISTRIBUTION AND TOPOGRAPHY OF LIGANDS FOR SAMPLE CLEANUP AND ANALYSIS OF BIOLOGICALLY-ACTIVE SOLUTES IN HPLC

Various types of, so-called, restricted access packings have been developed for sample clean-up and analysis of biologically active solutes by means of HPLC. The unique feature of these packings is that they prevent the access of matrix components such as protein whilst selectively retaining the drug components and their metabolites. This results from the fact that the particles of the packings possess a surface barrier for large solutes at the external or internal surface area and exhibit a controlled gradient in the chemical surface composition. They are grouped, according to their particle structures, into internal-surface reversed phases (ISRP), shielded hydrophobic phases (SHP), semi-permeable surfaces (SPS), dual zone phases (DZP) and mixed functional phases (MFP). The structural characteristics and the chromatographic properties of these packings are reviewwed, especially with regard to their use in the assaying of drugs.