Page:NIOSH Manual of Analytical Methods - 7506.pdf/5

 BORON CARBIDE: METHOD 7506, Issue 2, dated 15 August 1994 - Page 5 of 7 CALCULATIONS: 12.

Calculate the concentration of boron carbide, C (mg/m 3), in the air volume sampled, V (L):

where:

Î x = normalized intensity for sample peak b = intercept of calibration curve ( ˆIxo vs. W) m = initial slope of calibration curve, counts µg f(T) =

R ln T 1 TR

= absorption correction factor (Table 1)

R = sin ( θAg)/sin ( θx) T = Î Ag/(average ˆI Ago ) = transmittance of sample Î Ag = normalized silver peak intensity from sample average ˆIAgo = normalized silver peak intensity from media blanks (average of six values) NOTE: For a more detailed discussion of the absorption correction procedure, see references [2] and [3].

EVALUATION OF METHOD: The method was developed using the secondary B 4C peak because the primary B 4C peak interferred with the primary peak of AgCl, which is usually found on silver filters [1]. B 4C that was previously ground, sieved through a 10-µm sieve and dried, was used to prepare 30 working standards on 25-mm silver filters in the range 20 to 2000 µg per filter (10 levels, three at each level). The detection limit was 50 µg per filter. The limit of quantitation was 100 µg per filter. The calibration graph had a linear correlation coefficient of 0.9999 and a pooled relative standard deviation of 0.04 (n = 24). Recovery was 0.92 with s r = 0.02 from five FWS-B (MSA Co.) filters spiked at the 600 µg level; the filters were ashed in a low temperature asher and were treated as described in SAMPLE PREPARATION.

REFERENCES: [1] NIOSH Manual of Analytical Methods, 2nd ed., Vol. 6, P&CAM 324, U.S. Department of Health and Human Services, Publ. (NIOSH) 80-125 (1980). [2] Leroux, J. and C. Powers. Direct X-Ray Diffraction Quantitative Analysis of Quartz in Industrial Dust Films Deposited on Silver Membrane Filters, Occup. Health Rev., 21, 26 (1970). [3] Williams, D. D. Direct Quantitative Diffractometric Analysis, Anal. Chem., 31, 1841 (1959).

METHOD WRITTEN BY: J. Palassis, NIOSH/DTMD.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94