n-BUTYL MERCAPTAN: METHOD 2525, Issue 2, dated 15 May, 1996 - Page 3 of 3 b. Inject calibration stock solution (2 to 20 µL) containing a known amount of n-butyl mercaptan directly onto front sorbent section with a microliter syringe. c. Cap the tube. Allow to stand overnight. d. Desorb (steps 5 through 7) and analyze together with working standards (steps 11 and 12). e. Prepare a graph of DE vs. µgn-butyl mercaptan recovered. 10. Analyze three quality control blind spikes and threeanalyst spikes to ensure that the calibration graph and DE graph are in control.
MEASUREMENT: 11. Set gas chromatograph according to manufacturer's recommendations and to conditions given on page 2525-1. Inject sample aliquot manually using solvent flush technique. Vent the acetone peak so that it will not extinguish the flame in the detector. NOTE: If peak area is above the linear range of the working standards, dilute with acetone, reanalyze and apply the appropriate dilution factor in calculations. 12. Measure peak area.
CALCULATIONS: 13. Determine the mass, µg (corrected for DE) ofn-butyl mercaptan found in the sample front (W f) and back (Wb) sorbent sections, and in the average blank front (B f) and back (Bb) sorbent sections. NOTE: If Wb > Wf /10, report breakthrough and possible sample loss. 14. Calculate concentration, C, ofn-butyl mercaptan in the air volume sampled, V (L):
C
Wf
Wb
Bf V
Bb
, mg/m 3.
EVALUATION OF METHOD: 3 This method was validated over the range 17 to 74 mg/m at 22 C and 759 mm Hg using a 1.5-L sample [1]. Overall precision, rT, was 0.062 with an average recovery of 0.98. The concentration ofn-butyl mercaptan was independently determined from the syringe delivery rate and dilution flow rates. Desorption efficiency was 0.90 in the range 28 to 110 µg per sample. The breakthrough volume (effluent concentration = 5% of influent concentration) was 4.0 L; this was determined by sampling humid air (94% relative humidity), containing 74 mg/m3 n-butyl mercaptan at 0.023 L/min.
REFERENCES: [1] NIOSH [1977]. Backup data report for S350, prepared under NIOSH Contract 210-76-0123. [2] NIOSH [1978]. n-Butyl mercaptan: Method S350. In: Taylor DG, Ed. NIOSH manual of analytical methods, 2nd. ed., V. 4. Cincinnati, OH: National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No.78-175. [3] General Electric [1982]. Material safety data sheet, #504 Butyl Mercaptan, General Electric Co., Schenectady, N.Y. 12305. [4] NIOSH [1981]. NIOSH/OSHA Occupational health guidelines for occupational hazards. U.S. Department of Health and Human Services, DHHS (NIOSH) Publication No. 81-123, available as GPO Stock #017-033-00337-8 from Superintendent of Documents, Washington, DC 20402. METHOD REVISED BY: James E. Arnold, NIOSH/DPSE. Method S350 was originally validated under NIOSH Contract 210-76-0123.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 5/15/96
