3M Empore extraction disk. SDB-XC is a poly (styrenedivinylbenzene) copolymer used as a reversed phase sorbent for solid phase extraction. SDB-XC is not bonded to silica but is a 100 percent copolymeric particle that is spherical, porous and cross-linked. It does not exhibit the secondary cationic (silanol) interactions and pH limitations common to bonded silica sorbents, so it offers more predictable and reproducible reversed phase interaction.