SKC Filter Selection Guide

Understanding The Difference Between Membrane and Depth Filters

Membrane Filters — Membrane filters are made typically of MCE, PVC, copolymers, polycarbonate, silver, gelatin, or PTFE. They are precision cast into sheets, therefore, the pores are consistent and pore size ratings are more precise. During sampling small particles pass through the pores in membrane filters leaving larger particles on the surface of the filter. A high amount of particles on the surface of a membrane filter can clog the pores causing particles that would normally pass through to be retained on the surface such as what commonly occurs during asbestos sampling.

Depth Filters — Depth filters are constructed usually of fibrous materials such as glass or quartz fibers. The multiple layers of randomly oriented fibers in depth filters cause their pore size to be inconsistent and undefined, therefore, a pore size rating for a depth filter is typically approximate (nominal). Particles collected with depth filters are captured within the pathways of the fibrous material. Depth filters are typically more economical and tolerate higher temperatures.

 

Material	Abbr.	Common Pore Sizes	Main Properties	Air Sampling Applications
Mixed Cellulose Ester	MCE or MEC	0.45 µm 0.8 µm 1.2 µm 5.0 µm	Hydrophilic Readily soluble for atomic absorption analysis Readily rendered transparent for transmitted light microscopy Dissolve and clear easily	Metal dust analysis Asbestos and man-made fibers
Polyvinyl Chloride (Pure Homopolymer) GLA-5000	PVC or PH-PVC	0.5 µm 0.8 µm 5.0 µm	Hydrophobic Non-oxidizing surface Silica-free Low ash Low tare weight for gravimetric analysis	Gravimetric analysis Hexavalent chromium
Polytetrafluoroethylene (Teflon)	PTFE	0.5 µm 1.0 µm 2.0 µm 5.0 µm	Hydrophobic Inert to solvents, acids, and bases Autoclavable	Alkaline dusts Polynuclear aromatics Pesticides Isocyanates
Polycarbonate	PC	0.3 µm 0.4 µm 0.8 µm	Hydrophobic Microscopically smooth surface Straight-through pores Extremely thin (10 - 20 µm) and transparent Autoclavable	Scanning electron microscopy Asbestos fibers
Silver	AG	0.45 µm 0.8 µm	Wide solvent compatibility Higher temperature tolerance Autoclavable Uniform porosity and thickness	Bromine Asbestos by TEM Silica by x-ray diffraction
Glass Fiber	GF or FG	Liquid Nominal Rating 1.0 µm	Partially hydrophobic Higher temperature tolerance Autoclavable High particulate retention	Pesticides Coarse gravimetric Isocyanates Ethylene glycol
Quartz	QZ	Liquid Nominal Rating 1.2 µm	Same as fiber glass Low level metals content High temperature 300 C Autoclavable	Gases Aerosols PM10 Diesel particulates
Cellulose	CEL	Nominal	Autoclavable Uniform strength Ashless (Type 40)	AA HPLC

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This page was last modified March 22, 2006