GMF Filters, like cellulose filters are depth filters; filtration is accomplished throughout the filter, not just on the surface. Glass microfiber filters are used when a high filtration efficiency is required and a high loading capacity is needed. GMF filters have particle retentions smaller than cellulose filters, down to 0.7um. Not only are glass microfibers used to filter fluids, they are used in air sampling equipment for collection of particulates and aerosols. Some GMF filters are designed to be heated to up to 550 deg for ignition of the sample in gravimetric determinations. Other applications include: liquid scintillation counting, radio immunoassay, analysis of water, analysis of wastewater, and filtration of hot gases and liquids. Quartz (SiO2) MF filters are used for air sampling in acidic gases, stacks, flues and aerosols, particularly at high temperatures. Whatman and Ahlstrom are two manufacturers of glass microfiber filters.