Forwarding WTC air monitoring scope for final review, Aug 2002

NYC 9/11 Public Portal Document

n. 763, Subpt. E, App. A 40 CFR Ch. I <7-1-00 Edition) that has been distilled in glass or filtered or strips on the same microscope slide, taking deionized water Is satisfactory for this pur­ ct>re to rinse and wet-wipe the scalpel blade pose. Reagents must be fiber-free. and tweezers before handling a new sample. b. Polycarbonate preparation method— The filter strips should be Identified by etch­ chloroform. ing the glass slide or marking the slide using c. Mixed Cellulose Ester (MCE) preparation a marker Insoluble In water and solvents. method—acetone or the Burdette procedure After the filter strip has been cut from each (Ref. 7 of Unit III.L.). filter, the residual parts of the filter must be 7. TEM specimen preparation from poly­ returned to the cassette and held in position carbonate filters. by reassembly of the cassette. The cassette a. Specimen preparation Jaboratoiy. It is will then be archived for a period of 30 days most important to ensure that contamina­ or returned to the client upon request. tion of TEM specimens by extraneous asbes­ e. Carbon coating of filter strips. The glass tos fibers Is minimized during preparation. slide holding the filter strips Is placed on the b. Cleaning of sample cassettes. Upon re­ rotation-tilting device, and the evaporator ceipt at the analytical laboratory and before chamber is evacuated. The evaporation must they are taken Into the clean facility or lam­ be performed in very short bursts, separated inar flow hood, the sample cassettes must be by some seconds to allow the electrodes to cleaned of any contamination adhering to cool. If evaporation is too rapid, the strips of the outside surfaces. polycarbonate filter will begin to curl, which c. Preparation of the carbon evaporator. If will lead to cross-linking of the surface ma­ the polycarbonate filter has already been terial and make it relatively Insoluble in carbon-coated prior to receipt, the carbon chloroform. An experienced analyst can coating step will be omitted, unless the ana­ Judge the thickness of carbon film to be ap­ lyst believes the carbon film is too thin. If plied, and some test should be made first on there is a need to apply more carbon, the fil­ unused filters. If the film is too thin, large ter will be treated in the same way as an particles will be lost from the TEM speci­ uncoated filter. Carbon coating must be per­ men, and there will be few complete and formed with a high-vacuum coating unit. undamaged grid openings on the specimen. If Units that are based on evaporation of car­ the coating is too thick, the filter will tend bon filaments In a vacuum generated only by to curl when exposed to chloroform vapor an oil rotary pump have not been evaluated and the carbon film may not adhere to the for this application, and must not be used. support mesh. Too thick a carbon film will The carbon rods should be sharpened by a also lead to a TEM image that is lacking In carbon rod sharpener to necks of about 4 mm contrast, and the ability to obtain ED pat­ long and 1 mm In diameter. The rods are in­ terns will be compromised. The carbon film stalled in the evaporator in such a manner should be as thin as possible and remain in­ that the points are approximately 10 to 12 tact on most of the grid openings of the TEM cm from the surface of a microscope slide specimen intact. held in the rotating and tilting device. f. Preparation of the Jaffe washer. The pre­ d. Selection of filter area for carbon coat­ cise design of the Jaffe washer is not consid­ ing. Before preparation of the filters, a 75 ered Important, so any one of the published mm X 50 mm microscope slide is washed and designs may be used, A washer consisting of dried. This slide is used to support strips of a simple stainless steel bridge is rec­ filter during the carbon evaporation. Two ommended, Several pieces of lens tissue ap­ parallel strips of double-sided adhesive tape proximately 1.0 cm X 0.5 cm are placed on the are applied along the length of the slide. stainless steel bridge, and the washer Is Polycarbonate filters are easily stretched filled with chloroform to a level where the during handling, and cutting of areas for fur­ meniscus contacts the underside of the mesh, ther preparation must be performed with which results In saturation of the lens tis­ great care. The filter and the MCE backing sue, See References 8 and 10 of Unit III.L. filter are removed together from the cassette g. Placing of specimens Into the Jaffe and placed on a cleaned glass microscope washer. The TEM grids are first placed on a slide. The filter can be cut with a curved piece of lens tissue so that individual grids scalpel blade by rocking the blade from the can be picked up with tweezers. Using a point placed In contact with the filter. The curved scalpel blade, the analyst excises process can be repeated to cut a strip ap­ three 3 mm square pieces of the carbon-coat­ proximately 3 mm wide across the diameter ed polycarbonate filter from the filter strip. of the filter. The strip of polycarbonate filter The three squares are selected from the cen­ Is separated from the corresponding strip of ter of the strip and from two points between backing filter and carefully placed so that It the outer periphery of the active surface and bridges the gap between the adhesive tape the center. The piece of filter is placed on a strips on the microscope slide. The filter TEM specimen grid with the shiny side of strip can be held with fine-point tweezers the TEM grid facing upwards, and the whole and supported underneath by the scalpel assembly is placed boldly onto the saturated blade during placement on the microscope lens tissue in the Jafie washer. If carbon- slide. The analyst can place several such coated grids are used, the filter should be

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