Page:NIOSH Manual of Analytical Methods - 1017.pdf/3

 TRIFLUOROBROMOMETHANE: METHOD 1017, 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. a. Add known volumes of trifluorobromomethane gas with a gas-tight syringe to 5.0 mL CH 2Cl2 in 10-mL volumetric flasks by slowly bubbling the gas through the liquid with the tip of the syringe needle near the bottom of the volumetric flask. Dilute to the mark. Use serial dilutions as needed to obtain trifluorobromomethane concentrations in the range 0.01 to 3.6 mg/mL. b. Analyze with samples and blanks (steps 11 and 12). c. Prepare calibration graph (peak area vs. mg trifluorobromomethane). Determine desorption efficiency (DE) at least once for each lot of sorbent used for sampling in the range of interest. Prepare three tubes at each of five levels plus three media blanks. a. Connect a large charcoal tube (400 mg/200 mg) to the outlet of the DE apparatus. Start nitrogen flow (ca. 200 mL/min) through the DE apparatus and into the charcoal tube. Inject a known amount (0.01 to 3 mL; 0.05 to 18 mg @ NTP) of trifluorobromomethane gas into the septum. Allow the N 2 flow to continue for 20 sec. b. Cap the tube. Allow to stand overnight at -10 °C. c. Desorb (steps 5 through 7) and analyze with working standards (steps 11 and 12). d. Prepare a graph of DE vs. mg trifluorobromomethane 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 1017-1. 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 an aliquot of the desorbed liquid with CH 2Cl2 reanalyze and apply the appropriate dilution factor in calculations. Measure peak area.

CALCULATIONS: 13.

14.

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

EVALUATION OF METHOD: Method S125 was issued on May 9, 1975 [2], and validated over the range 2890 to 11,500 mg/m 3 at 25 °C and 760 mm Hg using 1-L samples [1]. Generated concentrations were produced by calibrated gas flows and verified by a total hydrocarbon analyzer, standardized with gas standards. Overall precision, sr, was 0.065, with average recovery of 100%. Desorption efficiency was 0.81 in the range 3 to 12 mg per sample. Breakthrough (effluent = 5% of test concentration) occurred in 90 min when a concentration of 12,370 mg/m 3 was sampled at a rate of 0.046 L/min. The stability of trifluorobromomethane on charcoal was not determined. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94