Selecting Filters for Particle Monitoring

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For comprehensive details on all micron filtration membranes and depth filters available, visit Laboratory Filtration.

This page addresses the characteristics of each membrane as they pertain specifically to particle monitoring. Click on the membrane type for details:

MF-Millipore™ (Mixed Cellulose Esters) Membrane Filters

Featured Membrane:
MF-Millipore™ Membrane Filters
Mixed Cellulose Esters

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MF-Millipore™ membrane filters are composed of a biologically inert mixture of cellulose acetate and cellulose nitrate. They are available in a variety of diameters and surface configurations to meet a wide range of application needs. MF-Millipore™ membranes have set the standard for analytical and laboratory applications. They are recommended for a variety of analytical applications. For gravimetric analysis by the ashing technique, incineration at 820 °C or addition of HNOyields a negligible ash weight of less than 0.45% of the initial filter weight. For particle analysis by light microscopy, the standard MF-type filter has a refractive index of 1.51 and is easily rendered transparent when placed in standard immersion oil.
Chemical Compatibility
MF-Millipore™ filters are compatible with dilute acids and bases, aliphatic and aromatic hydrocarbons, and non-polar liquids. They are not compatible with ketones, esters, ether-alcohol, nitro-paraffins or strong acids and bases.
Thermal Stability
They are recommended for applications below 75°C.
Matched-Weight Membranes
Type AA (0.8 µm) and HA (0.45 µm) MF-Millipore™ membrane filters, matched in pairs to within ± 0.1 mg, are available in 37 mm (AA) and 47 mm (AA and HA) diameters. Used for gravimetric analysis of particle contamination by the matched-weight filter method, these products eliminate the need to preweigh the test filter. Testing accuracy and speed are greatly improved. Matched-weight filters are also available in convenient, preloaded plastic cassette configurations (37 mm Type AA filters only).
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Isopore™ Track-Etched (PC) Membrane Filters

Featured Membrane:
Isopore™ Membrane Filters
Polycarbonate membrane for microscopy and visual analysis

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Isopore™ track-etched polycarbonate membrane filters have uniform, cylindrical pores. They are especially recommended for scanning and transmission electron microscopy, as particles are collected on the smooth surface of the membrane. Applications include particulate analysis and retention testing of microporous filters.
Surface Retention Characteristics
Isopore™ membranes have cylindrical pores that pass straight through the membrane (perpendicular to membrane surface). Their even and random distribution contributes to uniform sample distribution over the membrane surface. All particles larger than the actual pore size are captured on the membrane surface. This absolute retention on a microscopically smooth surface makes it possible to determine the amount and type of particles in either liquids or gases.
Track-Etched Membranes for Particle Analysis
For Isopore™ membranes, no clearing is necessary for most transmitted light microscopy. For transmission electron microscopy, sample replication is straightforward. For scanning electron microscopy, a conductive coating is the only sample preparation needed.
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Fluoropore™ and Mitex™ (PTFE) Membrane Filters

Featured Membrane:
Isopore™ Membrane Filters
Polycarbonate membrane for microscopy and visual analysis

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Fluoropore™ membrane filters are PTFE (polytetrafluoroethylene) bonded to high-density polyethylene to improve handling. Fluoropore™ membranes are also available without the polyethylene backing. These “unlaminated” membranes are supplied only in the 0.5 µm pore size, 47 mm diameter discs. They are suitable for use with strong solvents, and at high temperatures that would otherwise soften the backing material. They must be used in the standard glass filter funnels. Mitex™ membrane filters are PTFE without a backing material and are unaffected by many liquids. These membranes are hydrophobic and can only be used with gases or non-aqueous fluids unless they are prewet with low-surface-tension fluid such as methanol.
Chemical Compatibility
Both filter types are biologically and chemically inert, and will meet extreme conditions of chemical compatibility and temperature. Fluoropore™ membrane is compatible with strong solvents, acids, and bases. (Exceptions are aromatic hydrocarbons at temperatures in excess of 80°C). Mitex™ membrane is compatible with organic solvents, concentrated acids, and bases within a wide thermal range.
Thermal Stability
Fluoropore™ membranes are stable up to 130°C. Mitex™ membranes are stable at temperatures in the range of +260°C to -100°C.
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Silver Membrane Filters (Pure Silver)

These silver membrane filters are composed solely of metallic silver. The pure silver composition makes them an ideal collection media for analysis of crystalline silica by X-ray diffraction techniques. They are also suited for analysis of organics by other instrumental analyses. Silver filters are referenced in several methods in the NIOSH Manual of Analytical Methods, for collecting airborne contaminants and sample preparation.

To ensure reproducible and reliable sampling data for any of the above applications, Merck Silver Membrane Filters are quality control tested to meet exacting standards for porosity, flow rate, thickness, as well as lot-to-lot consistency.

Merck silver membrane filters are available in a 0.45 µm pore size.

Merck:/Freestyle/BI-Bioscience/Filters-Particle-Monitoring/A030 Images/MB2-01[867-ALL].jpgDurapore® (Polyvinylidene Fluoride) Membrane Filters

Durapore® membrane filters are designed for strength, flexibility and broad chemical compatibilities. They cannot be rendered transparent by the standard clearing procedures.

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Broad Chemical Compatibilities

Durapore® membranes are compatible with many chemicals with the exception of concentrated ketones, amines, and esters. Hydrophilic Durapore® is recommended for aqueous samples. The hydrophobic version is recommended for organic samples.

Durapore® hydrophilic and hydrophobic discs are available in a variety of pore sizes, including 0.10, 0.22, 0.65 and 5.0 µm (nominal). They are also available in various diameters and surface configurations.

Merck:/Freestyle/BI-Bioscience/Filters-Particle-Monitoring/A030 Images/MB1911-01[861-ALL].jpgPVC Membrane Filters

These filters are composed of pure medical-grade PVC and are used for monitoring airborne silica, carbon black and quartz particulates. PVC membrane filters are available in a 5.0 µm pore sizes.

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Merck:/Freestyle/BI-Bioscience/Filters-Particle-Monitoring/A030 Images/MB5-02[877-ALL].jpgGlass Fiber Filters Without Binders

These filters are composed of borosilicate microfiber glass without binder resin and are used for environmental, gravimetric, and biochemical applications. They retain structural integrity without weight loss when ignited to 550 °C after sample filtration. You can render them transparent by immersing them in benzene, ethyl alcohol, or other solvent with the same refractive index.

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Merck:/Freestyle/BI-Bioscience/Filters-Particle-Monitoring/A030 Images/MB5-02[877-ALL].jpgOther Depth Filters
Type AP40 Microfiber Glass Discs (for analysis only) without Binder Resin


Type AP40 Microfiber Glass Discs (for analysis only) without Binder Resin These filters are composed of borosilicate microfiber glass and are used for determination of volatile suspended matter in contamination analysis of wastewater and industrial effluents and aerosol sampling. Since these filters contain no binders, they retain structural integrity without weight loss when ignited at 550°C after sample filtration.

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Type AP10 Absorbent Pads

Also called nutrient pads, these are made of pure white cellulosic material resembling blotting paper. They are used as filter supports in Merck cassettes, and for microbiological culturing when saturated with growth medium and placed under the test filters in Petri dishes.
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Type AP30 Thick Support Pads

Identical material to Type AP10, but much thicker. Used as filter supports in Merck contamination analysis cassettes, where the increased thickness is required for adequate support against high sampling pressures.