Ascentis Express Guard Columns provide physical (filtration) and chemical protection for costly analytical columns without compromising the very high performance of Ascentis Express columns. These Ascentis Express guard columns are capable of continuous use at pressures up to 9000 psi (600 bar) with only hand-tightening. Guard cartridges are easily replaced without removing the guard column holder from the flow path. . Particle Size: 2.7 µm. Application(s): HPLC: suitable. Pore Size: 90 Å. . . Sigma-Aldrich 53501-U Ascentis Express C18 Guard Cartridge, 2.7 µm Particle Size, 2.1mm ID, 5mm Length, Pack of 3. Country of Origin : United States. Part Number : 1188M69EA. Pack of : 3.