What type of filter is used in personal air sampling for PCM analysis?

The correct answer is 25 mm mixed cellulose ester filters. These filters are specifically chosen for personal air sampling in the analysis of asbestos because they provide a good balance of collection efficiency and air flow resistance, which is essential for accurately capturing airborne asbestos fibers.

Mixed cellulose ester filters are composed of cellulose acetate and cellulose nitrate, which enhances their ability to capture fibers in the desired size range for PCM (Phase Contrast Microscopy) analysis. They exhibit the necessary physical properties to ensure that dust and fiber capture is optimized while maintaining a reasonable air flow during sampling.

In addition to their efficiency in collecting asbestos fibers, the 25 mm size is optimal for personal sampling devices, as it allows for manageable airflow while still filtering out the relevant particulate matter effectively. This ensures that sampling results are both reliable and representative of the exposure level to asbestos.

The other types of filters listed may not provide the right conditions or efficiency needed for effective asbestos sampling and analysis, which is why they aren't suitable for this specific application.