Whatman 6900-2504 PVDF GD/X 25 Sterile Syringe Filter, 25mm, 0.45 Micron (Pack of 50) 0.45m; ideal choice for the preparation of hard-to-filter samples Pigment-free polypropylene housing with a prefiltration stack Eliminates sample contamination Allows you to filter even the most difficult samples with less hand pressure Processes three to seven times more sample volume