An examination of MCE filter morphology and implications on preparation and analysis of air samples for asbestos

ABSTRACT

Morphological imperfections of mixed-cellulose ester filters and their possible influence on sample preparation and analysis of asbestos were examined. Filters were identified with large regions of non-porous “dead zones” which could negatively affect fiber deposition and, therefore, fiber recovery and analysis by Transmission Electron Microscopy (TEM). As these imperfections are effectively erased during the preparation of the sample, they may not be readily observed by TEM. Un-collapsed filters as well as those collapsed using dimethylformamide (DMF) and two acetone techniques were examined. In order to minimize negative sampling and analytical bias, it is suggested that MCE samples be collapsed utilizing a 35% DMF solution, etched with a correctly calibrated low-temperature etcher, carbon coated using a rotating and tilted stage, and analyzed with a strong analyst-independent grid square opening randomization scheme.

KEYWORDS:

• Acetone
• AHERA
• air cassettes
• asbestos
• dimethylformamide
• fiber
• low-temperature plasma etcher
• MCE
• mixed-cellulose ester filters
• scanning electron microscopy
• SEM
• TEM
• transmission electron microscopy

Acknowledgments

The authors would like to thank Dr. Xianliang Zhou, New York State Department of Health, for his guidance and assistance in the preparation of this article. The Electron Microscopy Core of the Wadsworth Center for their maintenance of the Leo 1550vp Scanning Electron Microscope.