Page:NIOSH Manual of Analytical Methods - 1018-1.pdf/3

 DICHLORODIFLUOROMETHANE, 1,2-DICHLOROTETRAFLUOROMETHANE, CHLORODIFLUOROMETHANE: METHOD 1018, Issue 1, dated 15 August 19 94, Page 3 of 4

CALIBRATION AND QUALITY CONTROL: 8.

9.

10.

Calibrate daily with at least five working standards. a. Pipet 20.0 mL methylene chloride into each of a series of bottles. Cap the bottles. b. Using a gas-tight syringe, add known amounts of analyte, e.g., 0.01 to 6 mL (0.0354 to 21.2 mg @ NTP) chlorodifluoromethane, or 0.01 to 6 mL (0.0495 to 29.7 mg @ NTP) dichlorodifluoromethane, or 0.01 to 6 mL (0.0699 to 41.9 mg @ NTP) 1,2dichlorotetrafluoroethane by bubbling the gas slowly through the methylene chloride. Gently shake the bottles. c. Analyze with samples and blanks (steps 11 and 12). d. Prepare calibration graph (area vs. mg analyte). Determine desorption efficiency (DE) at least once for each lot of sorbent used for sampling in the range of interest (step 8). Prepare three tubes at each of five levels plus three media blanks. a. Using a gas-tight syringe, inject a known amount of analyte (0.01 to 6 mL) through the septum of the DE apparatus unto a stream of nitrogen (ca. 20 mL/min) which carries the analyte into a large (400/200 mg) sorbent tube. Allow the nitrogen to flow an additional 30. b. Cap the tube. Allow to stand overnight. c. Desorb (steps 5 through 7) and analyze with working standards (steps 11 and 12) d. Prepare a graph of DE vs. mg analyte 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 1018-1. 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 methylene chloride, reanalyze and apply the appropriate dilution factor in calculations. Measure peak area. NOTE: The order of elution is chlorodifluoromethane, dichlorodifluoromethane, 1,2tetrafluoroethane. If analyzing for two or more of the compounds, a temperature rate of 5 °C/min is required.

CALCULATIONS: 13.

14.

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

EVALUATION OF METHOD: Validation this method for dichlorodifluoromethane and 1,2-dichlorotetrafluoroethane was done using packed column gas chromatographic techniques. The column was stainless steel 1.2 m x 6-mm OD, packed with 80/100 mesh Chromosorb 102. Chlorodifluoromethane was evaluated using the capillary NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94