PCM (Phase Contrast Microscopy):
Methodology for PCM Analysis - NIOSH 7400 & OSHA ID 160
Phase contrast microscopy is the method that is primarily used for estimating asbestos concentrations of airborne fibers. This method is quick and can be performed on-site for a rapid determination of concentrations of asbestos fibers in the air. Phase contrast microscopy does not positively differentiate between asbestos and other fibers. Positive identification of asbestos fiber must be performed using PLM (Polarized Light Microscopy) or Electron Microscopy (Method 7402)
Phase contrast microscopy, which was discovered by F. Zernike in 1932, is used to help the microscopist who has to observe sample preparations which give low contrast objects. The method enables the phase differences in a specimen to be converted to amplitude differences to give an image of good contrast. It requires the use of phase plate in the objective back focal plane and a phase ring in the condenser system and is usually used with a particular form of illumination.
Required Microscope Equipment: ML6500L, MT6500 & MT6800
Series Positive phase contrast microscope with 10X Brightfield and 40X phase objective, GIF (Green Interference Filter), Walton & Beckett Reticle Type-22G, and stage micrometer with 0.01mm divisions.
Required Test Slide:
The HSE/NPL Mark II Phase Shift Test Slide Checks or standardizes the visual detection limits of the phase contrast microscope. The HSE/NPL Test Slide consist of conventional glass microscope slide with seven sets of parallel line pairs of decreasing widths. The microscope must clearly resolve line pairs 1-3. Line pairs 4-5 must be at least partially visible. Line pairs 6-7 must be invisible. A microscope which fails to meet these requirements is either too low or high in resolution and cannot be used for asbestos identification. Meiji Techno does not sell this slide. In day to day operations it should be remembered that after checking the system for test slide visibility the microscope will need to be correctly adjusted for viewing the membrane filter deposit; this should only require a slight refocusing of the field iris image.