Fisherbrand™ IB™ Model Serum Filter For Glass, Plastic Collection Tubes (327859_PK) 100/PKFisherbrand IB Model Serum Filter allows you to store serum up to 7 days when it is essential to prevent any exchange of ions. One way valve permits a physical gap to be created between the serum plasma and clot, and prevents backflow into the primary collection tube. Use with glass or plastic collection tubes. Technique reduces second centrifugation, tube labeling and sample preparation time. Allows direct sampling into automatic laboratory equipment