Performance of Membrane Filters Used for TEM Analysis of Asbestos

Abstract

This article presents findings related to characteristics of membrane filters that can affect the recovery of asbestos and the quality of preparations for transmission electron microscopy (TEM) analysis. Certain applications and preparation steps can lead to unacceptable performance of membrane filters used in analysis of asbestos by TEM. Unless substantial care is used in the collapsing of mixed-cellulose ester (MCE) filters with an acetone hot block, grid preparations can suffer and fiber recoveries can be compromised. Calibration of the etching depth of MCE filters, especially at differing locations in an asher's chamber, is critical for reliable fiber recovery. Excessive etching of MCE filters with aerosol-deposited asbestos can lead to loss of short fibers, while insufficient etching of MCE filters with aqueous-deposited asbestos can, paradoxically, also lead to loss of short fibers. Interlaboratory precision on MCE filters is improved by aerosol-deposited asbestos, as opposed to aqueous deposition. In comparison, straightforward preparation, improved solvents, and reduced contamination make PC filters an increasingly acceptable alternative. Variations in the geometric configuration during application of carbon films can lead to fiber loss and unacceptable grid quality for either type of filter.

Keywords:

• asbestos
• membrane filter
• mixed-cellulose ester (MCE) filter
• polycarbonate (PC) filter
• transmission electron microscopy (TEM)

ACKNOWLEDGMENTS

Paul Baron, NIOSH–Cincinnati, provided substantial assistance on the design of the aerosol generator. George Matuczek of the Wadsworth Center's Instrumentation & Automation, fabricated the aerosol generator. Jon Roe, as summer student, assisted in preparation and analysis. Adrianna Verschoor improved the readability of this manuscript. Analyses were performed on electron-beam instruments in the Wadsworth Center Electron Microscopy Core, which was supported in part by an National Institutes of Health COBRE grant.