High Steric Selectivity. Shim-pack GIS C18-P is designed with a polymerically bonded octadecy group, which provides high steric selectivity for separation of planar and non-planar compounds. It achieves complete baseline separation of structurally similar compounds such as vitamin D2 and D3 because of the planarity recognition capability. Shim-pack GIS C18-P is also ideal for the HPLC analysis of 16 PAH compounds listed as target pollutants by the U.S. EPA. Bonded Phase Octadecyl Groups, Particle Size 3 ?m, 5 ?m, Pore Size 10 nm, Surface Area 450 m2/g, Carbon Loading 29 %, End-capping No, pH Range 2 - 7.5, USP Code L1.