Sodium azide is added to the Omega™ modified polyethersulfone ultrafiltration membrane as a bacteriostatic preservative. As sodium azide inhibits cytochrome oxidase in the mitochondrial electron transport chain and can induce apoptosis, its presence in filtrates may have undesired effects on living cells or in in vivo studies. Sodium azide can also interfere with amine group-dependent conjugation reactions. If these or similar kind of problems are anticipated, a pre-rinse step can be performed to remove sodium azide from the membrane prior to filtering samples. Please note that the device should be used within 20 minutes of completing the pre-rinse step to prevent irreversible membrane damage due to dehydration.