HYDROGEN CYANIDE: METHOD 6010, Issue 2, dated 15 August 1994 - Page 4 of 5 NOTE 1:
17. 18. 19.
To avoid possible loss of HCN, add the oxidizing agent before proceeding to the next sample. NOTE 2: Do not prepare more samples than can be analyzed within the 30-minute maximum time for color development. After at least 5 min. standing (but not longer than 15 min), starting with the reagent blank, add 1.0-mL barbituric acid-pyridine coupling reagent. Mix. Adjust sample volume to 25 mL with deionized-distilled water and allow to stand at least 12 min (but not longer than 30 min) for color development. Read absorbance at 580 nm in a 1-cm light path cuvette on a spectrophotometer. If sample absorbance is outside the range of the calibration standards, take an aliquot, re-analyze (steps 12 through 19), and apply the appropriate aliquot factor in calculations.
CALCULATIONS: 20. 21.
22.
Calculate the mass, µg, of CN - in aliquot analyzed. Apply the appropriate aliquot factor to calculate the mass, µg, of CN - in the original 10-mL solution. Determine the mass, µg CN - (corrected for DE), found in the sample front (W f) and back (Wb) sorbent sections and in the average media blank front (B f) and back (Bb) sorbent sections. If Wb > Wf/10, report breakthrough and possible sample loss. Calculate concentration, C, of HCN in the air volume sampled, V(L).
where 1.039 = conversion factor, CN - to HCN EVALUATION OF METHOD: The method was evaluated by sampling the test atmospheres of HCN generated from a compressed mixture of HCN in nitrogen [1]. The range of HCN concentration was equivalent to 2 to 15 mg/m3 for a 3-L air sample. Twenty-two samples collected at 0.2 L/min for 15 minutes ˆ rT of 0.076 with nearly 100% recovery. Breakthrough occurred indicated overall precision S after 40 minutes of sampling at the flow rate of 0.2 L/min at an HCN concentration of 148 mg/m3. Sample tubes spiked with solutions of KCN and analyzed after storage, indicated that the samples of cyanide ions were stable on the tube for at least 2 weeks. Analysis of 22 tubes which were spiked with KCN standard solutions in the range 10 to 50 µg indicated a recovery of nearly 100% with a pooled precision of 0.041. Desorption efficiency may be poor below 10 µg CN - [6]. REFERENCES: [1] Williamson, George. "Method Development Protocol and Backup Data Report on Hydrogen Cyanide" Internal NIOSH/MRSB Report, Unpubl. NIOSH (1988). [2] Williamson, George. "Analysis of Air Samples on Project 166 (Firesmoke) on HCN; Sequence NIOSH/MRSB-6366A, Unpubl. NIOSH, (1988). [3] Lambert, J. L., Ramasamy, J., and J. V. Paukstelis, "Stable Reagents for the Colorimetric Determination of Cyanide by Modified Konig Reactions," Analyt. Chem., 47, 916-918 (1975). [4] DataChem Laboratories, NIOSH Sequence #6837-K (unpublished, March 21, 1990). [5] NIOSH/OSHA Occupational Health Guidelines for Chemical Hazards, U.S. Department of Health and Human Services. Publ. (NIOSH) 81-123 (1981), available as stock #PB 83-154609 form NTIS, Springfield, VA 22161. [6] DataChem Laboratories, User Check, NIOSH Sequence #6837-J (unpublished, March 19, 1990).
METHOD WRITTEN BY: George Williamson, NIOSH/DPSE. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
