Brownlee Aquapore conventional columns built on a 7 m, 300 Angstrom pore size silica. The OD-300 and RP-300 are reverse-phase silicas modfied with C18 and C8, respectively. AX-300 is a weak anion exchanger that is composed of a crosslinked polyethyleneimine phase bonded on the silica surface. CX-300 is a weak cation exchanger that is composed of a polyamide coating containing carboxymethyl groups phase bonded on the silica surface. The reverse-phase columns are also available in microbore (1.0 mm i.d) for increased sensitivity and better compatibility with LC/MS interfaces.