Page:NIOSH Manual of Analytical Methods - 1612.pdf/3

 PROPYLENE OXIDE: METHOD 1612, Issue 2, dated 15 August 1994 - Page 3 of 4 CALIBRATION AND QUALITY CONTROL: 8.

9.

10.

Calibrate daily with at least six working standards over the range 0.01 to 3 mg propylene oxide (PrO) per sample. a. Add known amounts of PrO or calibration stock solution to CS 2 in 10-mL volumetric flasks and dilute to the mark. b. Analyze together with samples and blanks (steps 11 and 12). c. Prepare calibration graph (peak area vs. mg PrO). Determine desorption efficiency (DE) at least once for each lot 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 (1 to 20 µL) of DE 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. mg PrO 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 gas chromatograph according to manufacturer's recommendations and to conditions given on page 1612-1. Inject sample aliquot manually using solvent flush technique or with autosampler. NOTE: If peak area is above the linear range of the working standards, dilute with CS 2, reanalyze, and apply the appropriate dilution factor in calculations. Measure peak area.

CALCULATIONS: 13.

14.

Determine the mass, mg (corrected for DE) of PrO 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 PrO in the air volume sampled, V (L):

EVALUATION OF METHOD: Method S75 was issued on February 14, 1975 [3], and validated over the range 121 to 482 mg/m 3 at 24 °C and 766 mm Hg using a 5-L sample [1]. Overall precision, SˆrT, was 0.085, with an average recovery of 94.4% at the OSHA standard level. Desorption efficiencies averaged 0.88, 0.95, and 0.96 at 0.6, 1.2, and 2.4 mg propylene oxide per sample, respectively. Breakthrough (5% on back section) occurred at 45 min when sampling an atmosphere of propylene oxide containing 484 mg/m 3 in dry air at 0.185 L/min. At this time, the front section contained 4 mg propylene oxide. Breakthrough in humid air and storage stability were not determined.

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