An improved indirect preparation method for microscopy analysis of fibers collected on membrane filters
Airborne fibers and surface fibers are often sampled to obtain an assessment of exposure concentration levels. Fibers sampled may include asbestos, fibrous glass, cellulose, refractory ceramic fibers (RCF), mineral wool and others. Critical identificaiton of fibers often requires transmission electron microscopy (TEM) analysis. The preparation method for TEM usually involves the collapsing, carbon-coating and dissolution of the sampling filter, such that the airborne fibers are laminated on a carbon film for TEM examination. This preparation method, called direct preparation, is not always appropriate for airborne fiber samples. In some cases, an indirect sample preparation method must be employed, in which fibers are extracted from the original filter and redeposited on a new filter for subsequent preparation. Cases requiring indirect preparation include:
- Overloading of sample filter
- Need to analyze fibers adhered to sampling cassette interior surfaces
- Inhomogeneity of fiber deposition on sample filter
- Sample integrity compromised due to handling
- Improper cassette of filter used for sampling
Crankshaw, O., Adams, T. P., & Griffin, R. H. (1992). An improved indirect preparation method for microscopy analysis of fibers collected on membrane filters. Environmental Choices, Technical Supplement, 1(1), 22-25.