Millex-HV Syringe Filter Unit, 0.45 µm. Background Information. Available in 4, 13, 25, 33, and 50 mm diameters with a variety of membranes, Millex® sterile syringe filters are ideal for sterilizing organic solvents, aqueous solutions or air/gas. Many sample preparation methods specify Millex® filters because of their unsurpassed quality and