Nucleosil is one of the first standard silica gel phases for HPLC. It consists of a completely porous spherical silica gel with a very pure and uniform SiO2 structure. It is considered an extremely reliable choice for analytical and preparative routine use. The pore width can vary from 50 to 4000 Å and available particle sizes are 3 μm, 5 μm, 7 μm and 10 μm. The NH2 phase is an amino-propyl-modified SiO2 structure.