Extremely Strong pi-pi Interactions. The extremely unique phase characteristics of Shim-pack GIST Phenyl are critical to resolving compounds that could not be separated with a C18 or C8 phase column. In addition to pi-pi interactions, Shim-pack GIS Phenyl provides hydrogen bonding secondary interactions, which results in retaining polar compounds at the same time. As the phenyl groups are directly bonded to the silica gel, Shimpack GIS Phenyl is also capable of the analysis of structural isomers due to its high stereo-selectivity. Bonded Phase Phenyl Group, Particle Size 2 ?m, 3 ?m, 5 ?m, Pore Size 10 nm, Surface Area 350 m2/g, Carbon Loading 10 %, End-capping No, pH Range 2 to 7.5, USP Code L11.