Forwarding WTC air monitoring scope for final review, Aug 2002

NYC 9/11 Public Portal Document

Environmental Protection Agency Pt. 763, Subpt. E, App. A placed carbon-coated side down. The three the conditions that should be used. This Is excised squares of filters are placed on the one area of the method that requires further same piece of lens tissue. Any number of sep­ evaluation. Insufficient etching will result In arate pieces of lens tissue may be placed In a failure to expose embedded filters, and too the same Jaffe washer. The lid is then placed much etching may result in loss of particu­ on the Jaffe washer, and the system is al­ late from the surface. As an Interim meas­ lowed to stand for several hours, preferably ure, it is recommended that the time for overnight. ashing of a known weight of a collapsed fil­ h. Condensation washing. It has been found ter be established and that the etching rate that many polycarbonate filters will not dis­ be calculated In terms of micrometers per solve completely in the Jaffe washer, even second. The actual etching time used for a after being exposed to chloroform for as long particular asher and operating conditions as 3 days. This problem becomes more seri­ will then be set such that a 1-2 pm (10 per­ ous if the surface of the filter was overheated cent) layer of collapsed surface will be re­ during the carbon evaporation. The presence moved. of undissolved filter medium on the TEM 11. Place the slide containing the collapsed preparation leads to partial or complete ob­ filters into a low-temperature plasma asher, scuration of areas of the sample, and fibers and etch the filter, that may be present in these areas of the g. Transfer the slide to a rotating stage in­ specimen will be overlooked; this will lead to side the bell Jar of a vacuum evaporator. a low result. Undissolved filter medium also Evaporate a 1 mm x 5 mm section of graphite compromises the ability to obtain ED pat­ rod onto the cleared filter. Remove the slide terns. Before they are counted, TEM grids to a clean, dry, covered petrl dish, must be examined critically to determine h. Prepare a second petrl dish as a Jaffe whether they are adequately cleared of resid­ washer with the wicking substrate prepared ual filter medium. It has been found that from filter or lens paper placed on top of a 6 condensation washing of the grids after the mm thick disk of clean spongy polyurethane initial Jaffe washer treatment, with chloro­ foam. Cut a V-notch on the edge of the foam form as the solvent, clears all residual filter and filter paper. Use the V-notch as a res­ medium In a period of approximately 1 hour. ervoir for adding solvent. The wicking sub­ In practice, the piece of lens tissue sup­ strate should be thin enough to fit into the porting the specimen grids is transferred to petrl dish without touching the lid. the cold finger of the condensation washer. i. Place carbon-coated TEM grids face up and the washer Is operated for about 1 hour. on the filter or lens paper. Label the grids by If the specimens are cleared satisfactorily by marking with a pencil on the filter paper or the Jaffe washer alone, the condensation by putting registration marks on the petrl washer step may be unnecessary. dish lid and marking with a waterproof 8. TEM specimen preparation from MCE marker on the dish lid. In a fume hood, fill filters. the dish with acetone until the wicking sub­ a. This method of preparing TEM speci­ strate is saturated. The level of acetone mens from MCE filters Is similar to that should be Just high enough to saturate the specified in NIOSH Method 7402. See Ref­ filter paper without creating puddles. erences 7. 8. and 9 of Unit III.L. J. Remove about a quarter section of the b. Upon receipt at the analytical labora­ carbon-coated filter samples from the glass tory. the sample cassettes must be cleaned of slides using a surgical knife and tweezers. any contamination adhering to the outside Carefully place the section of the filter, car­ surfaces before entering the clean sample bon side down, on the appropriately labeled preparation area. grid In the acetone-saturated petrl dish. c. Remove a section from any quadrant of When all filter sections have been trans­ the sample and blank filters. ferred, slowly add more solvent to the wedge- d. Place the section on a clean microscope shaped trough to bring the acetone level up slide. Affix the filter section to the slide to the highest possible level without dis­ with a gummed paged reinforcement or other turbing the sample preparations. Cover the suitable means. Label the slide with a water petrl dish. Elevate one side of the petrl dish and solvent-proof marking pen. by placing a slide under It. This allows drops e. Place the slide in a petrl dish which con­ of condensed solvent vapors to form near the tains several paper filters soaked with 2 to 3 edge rather than in the center where they mL acetone. Cover the dish. Wait 2 to 4 min­ would drip onto the grid preparation. utes for the sample filter to fuse and clear. G. TEM Method f. Plasma etching of the collapsed filter is required. 1. Instrumentation. 1. The microscope slide to which the col­ a. Use an 80-120 kV TEM capable of per­ lapsed filter pieces are attached Is placed In forming electron diffraction with a fluores­ a plasma asher. Because plasma ashers vary cent screen inscribed with calibrated grada­ greatly in their performance, both from unit tions. If the TEM is equipped with EDXA It to unit and between different positions in must either have a STEM attachment or be the asher chamber, it is difficult to specify capable of producing a spot less than 250 nm

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NYC-WTC_000139306