Asbestos optical microscopy

Asbestos can be determined by several analytical techniques, including optical microscopy, electron microscopy, X-ray diffraction (XRD), light scattering, laser microprobe mass analysis, and thermal analysis. It can also be characterized by chemical analysis of metals by atomic absorption, X-ray fluorescence, or neutron activation techniques. Electron microscopy methods are, however, commonly applied for the analysis of asbestos in environmental matrices. 

Limit of aluminum Limit of aluminum Absence of asbestos (IR, XRPD, optical microscopy)... 

Applications of Optical Microscopy in Analysis of Asbestos and Quartz... 

Optical Microscopy is a powerful tool in industrial hygiene for the analysis of asbestos, quartz or other substances. Electron microscopy and specialized techniques in optical microscopy such as ultraviolet, infrared, and fluorescence, although important, will not be considered in this paper. 

Various means of particle identification are possible with optical microscopy. These include dispersion staining for identification of asbestos particles [44] and the use of various mounting media [45], Proctor et. al. [46,47] dispersed particles in a solidifying medium of Perspex monomer and hardener. This was poured into a plastic mold that was slowly rotated to ensure good mixing. Microscope analyses were carried out on thick sections a lower size limit of 5 p,m was due to contamination. 

Optical microscopy (OM), polarized light microscopy (PLM), phase contrast microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) are the methods normally used for identification and quantification of the trace amounts of asbestos fibers that are encountered in the environment and lung tissue. Energy-dispersive X-ray spectrometry (EDXS) is used in both SEM and TEM for chemical analysis of individual particles, while selected-area electron diffraction (SAED) pattern analysis in TEM can provide details of the cell unit of individual particles of mass down to 10 g. It helps to differentiate between antigorite and chrysotile. Secondary ion mass spectrometry, laser microprobe mass spectrometry (EMMS), electron probe X-ray microanalysis (EPXMA), and X-ray photoelectron spectroscopy (XPS) are also analytical techniques used for asbestos chemical characterization. 

Phase-contrast optical microscopy (PCOM) is used mainly for assessment of the refractive index in comparison with liquids of standard index. Next PCOM is widely used to measure fiber concentration. Before examination of the sample, acid treatment may be used to remove carbonates from cement matrices, or organic solvents may be necessary to remove plastic binder materials. OM operates at magnifications of only 400 x and will not resolve fibers below 0.25 pm in diameter. Furthermore, PCOM caimot distinguish asbestos fibers from other fibers (e.g., gypsum, mineral wool, fiberglass, cellulose, etc.). 

Dixon, W.C., Applications of Optical Microscopy in Analysis of Asbestos and Quartz, Analytical Techniques in Occupational Health Chemistry, edited by D.D. Dollberg and A.W. Verstuyft. Wash. D.C. American Chemical Society, (ACS Symposium Series 120) 1980. pp. 13-41. 

Workplace exposure is usually assessed by personal sampling in which a known volume of air is sucked through a membrane filter which is subsequently prepared for examination by phase-contrast optical microscopy, and respirable fibres counted using predetermined rules (HSE, 1990). 0.5 0.2 f/ml control limits for chrysotile and amphibole asbestos exposure respectively has been introduced in the UK, and a 2f/ml maximum exposure to MMMF has been agreed, running in parallel with a 5mg/m gravimetric limit. 

In order to define the extent of emissions from automotive brakes and clutches, a study was carried out in which specially designed wear debris collectors were built for the dmm brake, the disk brake, and the clutch of a popular U.S. vehicle (1). The vehicle was driven through various test cycles to determine the extent and type of brake emissions generated under all driving conditions. Typical original equipment and aftermarket friction materials were evaluated. Brake relines were made to simulate consumer practices. The wear debris was analyzed by a combination of optical and electron microscopy to ascertain the asbestos content and its particle size distribution. It was found that more than 99.7% of the asbestos was converted to a nonfibrous form and... 

More advanced methods of optical and electron microscopy may be used to determine whether a fiber that meets the size and shape requirements is in fact an asbestos fiber. This can be done most definitively by transmission electron microscopy (TEM), which allows observation and measurement of fiber size and shape for even the smallest asbestos fibers. TEM also provides the opportunity for positive identification through elemental analysis by energy-dispersive X-ray analysis... 

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