The selection of a particular filter type for a specific application is invariably the result of a compromise of many factors. These factors include cost, availability, collection efficiency, analytical requirements and the ability of the filters to retain its filtering properties and physical integrity under the ambient sampling conditions. The sampling methodology adopted will determine the type of filter required. Recognized methodologies such as HSE or NIOSH analytical methods must be consulted. A suitable backing pad is required to support the filter disk in the cassette.

Due to the hygroscopic nature of most filters, it is necessary to quantify any variation in their moisture content. Reference filters are thus used in the weighing procedure as follows:

A maximum allowable variation of 0.05mg in the mass of filters in three consecutive weighings of the same filter, is allowed. Should these three measurements vary by more than the value mentioned above repeated mass determination must be performed.

An important step in ensuring accurate results and records is the correct marking and preparation of filters.

Filters