- January Edition -

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Endotoxin particles are very small. Removal strictly by size exclusion requires an Ultrafilter rated at 10,000 NMWL cutoff (0.005 microns). As a result, the filter requires high surface area and/or high pressure to achieve typical target flow rates. This technique is also impractical if a component of the solution being filtered might also be removed. 

A standard sterilizing grade filter (0.22 or 0.1 micron) will not remove endotoxin by size exclusion alone. Even an 0.03 micron filter is not sufficient to provide adequate endotoxin removal in most applications.

However, because endotoxins are negatively charged, a microporous filter can be surface-modified by applying a positive charge to the membrane to remove endotoxins by absorption. This technique allows smaller filtration area and lower pressures and will have much less chance of affecting solution components.

CPF 0.22 micron positively charged membrane filters have been validated to meet the most stringent endotoxin removal requirements. For more information on removing endotoxins, check out our blog on The Difference Between Sterilizing Fluids and Endotoxin Removal. 

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In every process, the final filter plays the most critical role in assuring that your filtrate meets expectations and requirements. It is typically the most expensive filter as well. The useful life span of a final filter will determine your change-out schedule and impact your filtration costs.