|Application Note: Integrity Test Troubleshooting - Beyond Rewet and Retest|
|Filter Integrity Test Methods|
|Sterilizing-grade Durapore® 0.22 µm Hydrophobic Filters|
|What is the compatibility of Durapore with high pH solutions?||The upper recommended pH limit for Durapore membranes is 10. At pH >10, the hydrophilization layer of the membrane may become subject to hydrolysis. The extent of hydrolysis is a function of time, temperature , concentration and time of exposure. Upon exposure to high pH, the hydrophylization layer can swell which could result in a loss of permeability or flux. The hydrolysis of the hydrophilic layer will also lead to increased extractables from the membrane.|
|What are Millipore's general recommendations for filtering high pH solutions?||For applications involving pH > 10, Millipore recommends the use or our PES membranes Express SHF or Express SHC. For information on these filters :
Express SHF: http://www.millipore.com/catalogue.nsf/docs/C8873
Express SHC: http://www.millipore.com/catalogue.nsf/docs/C9146
|How can I differentiate filter plugging due to air bubbles, particulates, surface tension, inappropriate filter size, etc.?||Air locking will occur when filtration is initiated without adequate venting or when air bubbles become trapped in fluid lines. Air will pass easily through a dry hydrophillic or hydrophobic filter. However, when a filter is wet and air is applied to a surface, the air will remain until it is manually moved upstream by venting or until the bubble point of the filter is reached. Bubble point is defined as the pressure at which gas displaces liquid for the largest set of filter pores and is able to flow through the pores. Air locking reduces the effective filtration area of the filter and thus reduces the flow rate.
Surface tension refers to the strong cohesive forces present between molecules at the surface of a liquid. The higher the surface tension, the more force is required to force fluid through the membrane..
Innapropriate filter size will can cause a filter to plug prematurely. Filter pore size is chosen based on the application. If the application requires a sterile fluid, than a 0.22 micron membrane would be used for standard solutions that have bacterial bioburden. A 0.1 micron filter would be used for applications where mycoplasma is a concern. Where virus contamination is a concern, ultrafiltration would be required. The selection of a filter pore size that is smaller than that required for the application will cause a decrease in filter capacity and an increase in cost.