Page:NIOSH Manual of Analytical Methods - 5036.pdf/3

 TRIMELLITIC ANHYDRIDE: METHOD 5036, Issue 2, dated 15 August 1994 - Page 3 of 4 k.

6.

Rinse the beaker two or three times with small amounts of methanol and combine the rinsings in the test tube. l. Evaporate the methanol in the test tube to dryness. Derivatization: a. Add 125 µL of BF 3/methanol to each sample or standard tube and screw the cap tightly. b. Place in a water bath (97 °C) for 20 min. c. Remove the tube and allow to cool to room temperature. d. Add 50 µL of diethyl ether to the tube. Screw the cap on and shake mildly. e. Add 50 µL of pentane, replace cap and shake mildly. f. Add 50 µL of pyridine, replace cap and shake mildly. g. Allow to stand for a few minutes until the white material precipitates.

CALIBRATION AND QUALITY CONTROL: 7.

8.

9.

Prepare at least six working standards over the range of 19.2 to 96 µg (10 to 50 µL) of trimellitic anhydride. a. Add known amounts of calibration stock solution to test tubes. b. Derivatize according to step 6. c. Prepare a calibration graph (peak area vs. µg analyte). Determine recovery (R) for each lot of filters used for sampling in the concentration range of interest (step 7). Prepare three filters at each of five levels plus three media blanks. a. Spike aliquots of calibration solution onto the center of each filter. Allow to dry overnight. b. Extract and derivatize (steps 5 and 6) and analyze (steps 10 through 12). Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration and recovery graphs are in control.

MEASUREMENT: 10. 11. 12.

Set gas chromatographic conditions as given on page 5036-1. Inject a 5 µL aliquot. Measure peak area.

CALCULATIONS: 13. 14.

Determine the mass of trimellitic anhydride, µg (corrected for recovery), for sample (W) and average media blank (B). Calculate the concentration of trimellitic anhydride, C (mg/m 3) in the air volume sampled, V(L):

EVALUATION OF METHOD: The extraction efficiency was evaluated over the range of 19.2 to 96 µg/sample levels with an average recovery of 103.3% and a measurement precision of 0.087.

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