Page:NIOSH Manual of Analytical Methods - 6006.pdf/3

 DIBORANE: METHOD 6006, Issue 2, dated 15 August 1994 - Page 3 of 4

9.

10.

b. Analyze with samples and blanks (steps 11 and 12). c. Prepare calibration graph (response vs. µg boron). Determine desorption efficiency (DE) at least once for each lot of impregnated charcoal in the range of interest. Prepare three tubes at each of five levels plus three media blanks. a. Place 100 mg impregnated charcoal (e.g., unused front sorbent section) in a vial and screw on the septum cap. b. Flush the gas-tight syringe with inert gas (e.g., N 2). Inject a known amount (0.1 to 5 mL) of diborane gas mixture with the syringe into the vial. Treat two parallel blanks in the same manner except that no diborane is added. c. Allow the vials to stand overnight. d. Desorb (steps 5 through 7) and analyze with working standards (steps 11 and 12). e. Prepare a graph of DE vs. µg boron recovered. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and DE graph are in control.

MEASUREMENT: 11. 12.

Set spectrometer to conditions on page 6006-1 and as specified by the manufacturer. Analyze standards and samples. NOTE: If response is above the range of the standards, dilute the sample solution with 3% H2O 2, reanalyze, and apply the appropriate dilution factor in the calculations.

CALCULATIONS: 13.

14.

Determine the mass, µg (corrected for DE) of boron found in the sample front (W f) and back (W b) sorbent sections, and in the average media blank front (B f) and back (B b) sorbent sections. NOTE: If W b > W f/10, report breakthrough and possible sample loss. Calculate concentration, C, of diborane in the air volume sampled, V (L):

where: 1.28 = the stoichiometric conversion factor from boron to diborane. EVALUATION OF METHOD: The method was tested by analyzing 18 samples, prepared by spiking 100 mg of impregnated charcoal with 6.7, 13.4 or 26.8 mg of diborane gas representing the equivalent of 120-L air samples at 0.05, 0.1 and 0.2 ppm [2]. Desorption efficiency was determined to be 0.889, 0.964, and 0.994 at these three concentrations, respectively. After analysis, the precision at the three concentrations was 8.4, 4.0, and 3.8%, respectively. Test atmospheres at 0.05, 0.1, and 0.2 ppm were generated using diborane gas. The samples were collected at 1 L/min for 2 hours in charcoal tubes containing 100 mg front/50mg back of impregnated charcoal. Eighteen samples were collected, and were desorbed one day later. The backup sections of the samples at 0.2 ppm were analyzed also. Six additional generated samples at 0.1 ppm were stored and analyzed seven days later. The average recovery of the 18 samples was 95.2%, pooled Sr = 2.7%. No trace of diborane (boron) was found in the backup section. The seven-day storage stability samples indicated an average recovery of 101.6 ± 2.1%. Breakthrough tests were conducted with a generated test atmosphere at 1.9 ppm with four impregnated charcoal tubes. The sample volume was 120 L. The average collection efficiency in the front sections was 99.8 ± 0.3%. Breakthrough occurred in only two samples indicating 0.6 and 0.2% breakthrough. An additional breakthrough study was conducted with a generated test atmosphere containing 0.34 ppm diborane at a relative humidity of 60 to 70%. Two impregnated charcoal tubes were collected after NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94