ACRYLONITRILE: METHOD 1604, Issue 2, dated 15 August 1994 - Page 3 of 4 b. c.
Analyze together with samples and blanks (steps 11 and 12). Prepare calibration graph (peak area vs. µg acrylonitrile). NOTE: Compare the peak areas of the working standards with a 0.1 mg/mL reference standard prepared from stabilized (undistilled) acrylonitrile in hexane. When the concentration of the working standards starts to decrease, prepare new working standards. 9. Determine desorption efficiency (DE) at least once for each batch of charcoal used for sampling in the calibration range (step 8). Prepare three tubes at each of five levels plus three media blanks. a. Remove and discard back sorbent section of a media blank sampler. b. Inject a known amount of calibration stock solution 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. µg acrylonitrile recovered. 10. Analyze three quality control blind spikes and three analyst spikes to insure 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 1604-1. Inject sample aliquot manually using solvent flush technique or with autosampler. NOTE 1: If peak area is above the linear range of the working standards, dilute with eluent, reanalyze and apply the appropriate dilution factor in calculations. NOTE 2: Under these conditions t r for acrylonitrile is ca. 8.5 min. 12. Measure peak area.
CALCULATIONS: 13. Determine the mass, µg (corrected for DE) of acrylonitrile 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. 14. Calculate concentration, C, of acrylonitrile in the air volume sampled, V (L):
EVALUATION OF METHOD: Method S156 [2] was validated at levels of 0.48, 0.95, and 1.91 mg per sample, using samples of acrylonitrile prepared both by sampling standard atmospheres generated by calibrated syringe drive and by spiking standard solutions in hexane on to the charcoal [6]. After the OSHA standard for acrylonitrile was lowered to 2 ppm, the method was evaluated by NIOSH at levels of 8.6 and 16.6 µg per sample (desorption solvent 2% acetone in CS 2), using samples from gas bag atmospheres and by spiking the charcoal with standard solutions of acrylonitrile in hexane [1]. At the higher levels (> 16 µg), the recoveries of acrylonitrile averaged 94% and the Sr was 0.06. At the lower level (8.6 µg), the recovery for the two sets of samples prepared from standard atmospheres averaged 79% with a Sr of 0.14. The sample set prepared by spiking charcoal at the lower level had a recovery of 94%. The parity between the recoveries of samples obtained from test atmospheres and from liquid spikes at the lower level suggested a possible problem with accuracy at this level [1]. Samples were found to be stable for at least seven days at room temperature [1,6]. Several breakthrough studies have been reported. At 80% relative humidity, breakthrough occurred after 184 minutes (36.7 L) sampling 8 mg/m 3 at 0.2 L/min [7]. Breakthrough did not occur after sampling dry air at 92 mg/m 3 at 0.2 L/min for 4 hours [6]. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
