CEL LULO SE INS ULA TIO N: ME TH OD 7404, Issue 1, dated 1 5 Ma rch 2003 - page 3 of 6 SAMPLE PREPARATION: 7. Mount the entire 25-mm filter directly on a carbon disk planchet by painting the planc het w ith a colloidal grap hite paint and im m ediate ly laying the filter, glossy(sam ple) side up, on the planchet. The sam ple num ber is scratched into the back of the planchet prior to mou nting the filter. 8. The planchet is th en placed in a labeled petri dish and perm itted to dry com pletely. 9. W hen dry, place sa m ple in a spu tter co ater a nd d epo sit, following manufacturer’s instructions, a heavy metal conductive coating on the sample.
CALIBRATION AND QUALITY CONTRO L: 10. Microscope adjustments. Follow the manufacturer’s instructions. At least once daily use an SEM performance standard, such as the NIST traceable U1011. Record in log book the results of the exa m ination of this s tand ard. 11. If more rigorous magnification calibration is needed, use a diffraction grating replica. a. Insert a m ounted diffraction grating replica into the sam ple cham ber. b. Obta in a secondary electron image of the replica and m easure the distanc e (m m ) between the same relative pos ition (e.g., between left edg es) of two widely-sepa rated lines on the grating replica . c. Mea sure the distance separated lines on the grating replica. Count the number of spaces between the lines. d. Calculate the true m agnification(M)
where: X = total distance (mm ) between the two grating lines; G = calibra tion co nsta nt of the gra ting rep lica (lines/m m ) Y = number of grating replica spaces counted.
MEASUREMENT: 12. Use s econd ary electron detector( at ~15KeV) and scan the filter at low m agnification (~100X). Observe the particulate loading. If the filter is not evenly loaded, it should not be analyzed (see note 4 below) 13. Adjust m agnification to ~1200X and find the center of the filter using the X-Y m anipulators. Fields are exa m ined at regular intervals from the cente r of the filter along a trave rse in one direction. 14. Determine the area of the viewing field at this magnification using the inscribed or overlain calibrated sca le. 15. Count fibers in each field; distinguish, based upon morphology, between cellulose and other fiber types and make note of the relative proportion of fibrous to non-fibrous material in the field. 16. Counting rules: (Modified A rules, NIOSH Method 7400).[2] a. Count any fiber longer than 5 :m (see note 2 below for exceptions) i. Count only fibers longer than 5 :m . Measu re an d rec ord len gth of fibers . ii. Count only fibers with a length-to-width ratio equal to or greater than 3:1. b. For fibers which cro ss th e bo und ary of the view ing field: i. Use the X -Y m anipulators as neede d, to follow and m easure the en tire length of any fibers that meet the criteria of rule a above. Return to original viewing field before moving to the nex t field. ii. Re ject and d o no t count all othe r fibers . c. Co unt enou gh viewing fields to yield at leas t 100 cellulos e fibers. C oun t a m inim um of 40 fields. d. W hen selecting fields, ensure that fields do not contain fibers counted and measured from a prev ious field. NOT E 1: W hen analyzing a viewing field, continuously scan a range of focal planes by moving the focus k nob to observe and m eas ure fibers which ha ve do no t lie flat on the filter.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
