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Appendix C: Sample Filter Characteristics and Applications

Type Characteristics Application
Glass-fibre High flow rates, high efficiencies, low pressure drops, high solids capacity, good wet strength. Can withstand very high temperatures. Fragile: care must be taken in handling for gravimetric work. Levels of background contaminants vary according to grade/type. Relatively inexpensive. Gravimetric measurements, particularly with high-flow samplers. Binder-free glass-fibre filters used for sampling and analysis of organics (eg, polycyclic aromatic hydrocarbons (PAHs)). Grades with low acid-soluble contaminant levels used if metals analysis required. Quartz type used for sulphate or nitrate analysis.
Mixed cellulose ester, cellulose nitrate or cellulose acetate Low levels of metal contaminants. Easily oxidised and destroyed during extraction and digestion. Can be cleared for optical microscopy examination. Susceptible to moisture. Relatively inexpensive. Chemical analysis of metal content of particulates by atomic absorption spectroscopy, auger emission spectroscopy, fluorescence, infrared and X-ray diffraction analysis. Determination of airborne fibre (eg, asbestos) concentrations.
Polyvinyl chloride Low moisture pick-up. Resistant to concentrated acids and alkalis. Gravimetric analysis. Sampling of particulates for analysis of silica, quartz, carbon black.
Polytetrafluoroethylene Naturally hydrophobic but some grades treated to render hydrophilic. Relatively inert and unreactive. Resistant to most chemicals, including high-performance liquid chromatography (HPLC) solvents. Expensive. Sampling of particulates for ultraviolet or HPLC analysis. Sampling of PAHs.
Nylon Resistant to many chemicals, including organic solvents. Flexible, durable and tear-resistant. Sampling of gaseous species (eg, hydrogen chloride).
Silver membrane High collection efficiency, uniform pore size. Expensive. Sampling of crystalline substances for analysis by X-ray diffraction. Sampling of gaseous species (eg, halogens).
Cellulose High flow rates, low pressure drops, collection efficiencies of some grades poor. Low impurity levels. Ashless grades available. Cheap. Ashing of samples to determine organic content. Washing of samples on filter to determine water-soluble component.
Polycarbonate Some grades virtually transparent: no clearing necessary for optical microscopy. Non-hygroscopic: equilibrium with water vapour not necessary before weighing. Resistant to many solvents. Low ash content. Sampling of particulates. Examination by optical microscopy. Ashing of samples to determine organic content.