Sampling Using Filters
Filters include glass fiber filters, Teflon filters, mixed cellulose ester membranes, polyvinyl chloride filters, and treated filters and pads. Sampling with filters can be done open or closed faced. Open-faced sampling is done with three (3) piece cassettes with just the top of the cassette removed. Closed-faced sampling is performed with only the buttons removed from the cassette. Open-faced sampling is used in situations where even dispersal of the analyte over the filter is desired, such as in asbestos sampling or on certain coated filters such as for isocyanate sampling. Closed-faced sampling is performed in most cases of particulate sampling, which deposits the analyte near the center of the cassette.