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 CYANIDES, aerosol and gas: METHOD 7904, Issue 2, dated 15 August 1994 - Page 4 of 4 stability study involving six samples at the OSHA standard concentration level indicated a 92.4% average recovery for the one-day old samples and a 92.6% for eight-day old samples. A collection efficiency study at twice the OSHA standard level, which included backup bubblers, indicated that an average of 99.8% of HCN was collected in the first bubbler. The HCN air generated concentrations were independently confirmed by a titration method [3]. KCN: Method S250 was issued on January 30, 1976 [5]. A set of six weighed KCN samples in the range of 1.8 to 2.5 mg KCN per filter indicated a 97% recovery and a 3.8% measurement precision [2]. Spiking with aqueous or basic solutions of KCN proved unsuccessful (low recovery) because of the cyanide instability in the presence of water and CO 2. Test atmospheres of KCN were generated by atomization of an aqueous solution (162 g/L) of KCN into a dry airstream. Eighteen KCN samples collected in 0.1 N NaOH at 1.5 L/min for 60 min indicated overall precision, SˆrT, of 0.103. Collection was accomplished with cellulose ester membrane filters followed with backup bubblers. The collection efficiency at twice the OSHA level was 100.0% on the filters. Cyanide salts are known to decompose in moist air with liberation of HCN. This instability was determined with two sets of six samples at the one and two times the OSHA level. Each of the samples which were twice the OSHA level were connected with two backup bubblers. Both sets indicated a loss of 16.5%.

REFERENCES: [1] Perkins, J.B., D.G. Tharr, J. Palassis, D.B. Fannin, and P.M. Eller, Case Studies: Reduction of Blank Values in the Determination of Particulate Cyanides. Appl. Occup. Environ. Hyg. 5:836-837 (1990). [2] Documentation of the NIOSH Validation Tests, S250, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-185 (1977). [3] Backup Data Report for Hydrogen Cyanide, S288, available as "Ten NIOSH Analytical Methods, Set 5," Order No. BP 287-499 from NTIS, Springfield, VA 22161. [4] NIOSH Manual of Analytical Methods, 2nd. ed., V. 4, S288, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 78-175 (1978). [5] Ibid, V. 3, S250, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-157-C (1977). [6] Ibid, V. 1, P&CAM 116, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-157-A (1977). [7] Criteria for a Recommended Standard...Occupational Exposure to Hydrogen Cyanide and Cyanide Salts, 5-9, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-108 (1976). [8] NIOSH Research Report-Development and Validation of Methods for Sampling and Analysis of Workplace Toxic Substances, U.S. Department of Health and Human Services, Publ. (NIOSH) 80-133 (1980).

METHOD REVISED BY: J. Palassis, NIOSH/DTMD; S250 and S288 originally validated under NIOSH Contracts CDC-99-74-45 and 210-76-0123, respectively.

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