Membrane Filters

• Depth filters comprise fibers or fibrous materials that trap particles as they pass through the tortuous path between fibers.
• Membrane filters, also called screen filters, have pores of a certain size that allow only smaller particles to pass through.

More on Membrane filters

Membranes, or membrane filters, can be validated for 100% retention of contaminants larger than their pore size. These filters are placed at the furthest possible point in a system to remove the last remaining traces of resin fragments, carbon fines, colloidal particles, microorganisms or other undesirable contaminants. For example, 0.22 µm Millipore membrane filters, which can be validated for quantitative bacterial retention, are routinely used to sterilize intravenous solutions, serum, and antibiotics.

Membrane filters are made by processes that result in a regular porous matrix. Examples of membrane filters include microporous membranes, track-etched membranes, ultrafiltration membranes, and RO membranes. This represents a wide capability for filtration ranging from small particles down to ions. Because of how they are manufactured, membrane filters exhibit virtually no sloughing off during filtration.

Membrane filters can be characterized as sterilizing-grade if the microorganism being filtered is larger than the pore size. The microorganism will collect on the upstream surface of the filter as the sample is processed. For prolonged usage, the filter should be validated for preventing penetration of the microorganism through the membrane as it grows.

Membrane filters are further classified as:

• Microporous Filters
• Ultra Filters
• Reverse Osmosis Filters