Page:NIOSH Manual of Analytical Methods - 5700.pdf/3

FORMALDEHYDE ON DUST/FIBERS: METHOD 5700, Issue 1, dated 15 August 1994 - Page 3 of 5 SAMPLE PREPARATION: 7.

If gravimetric weighing is done, post-weigh the entire cassette (see NMAM 0500 [7]) then return the cassette to the screw-cap bottle.

8.

Transfer 8-mL distilled water to the LDPE screw-cap bottle containing the cassette. Use tweezers (two) to disassemble cassette which is immersed in water, remove all cassette pieces (shake off excess water) leaving the filter and dust in the bottle. Transfer the resulting solution to a 20-mL scintillation vial and rinse the screw-cap bottle with an additional 2 mL of distilled water. Replace the cap on the vial and then place the vial in a 37 °C water bath for four hours. Remove from the bath and allow to cool 1/2 hour. Filter through a 0.45 µm pore size filter into another bottle.

CALIBRATION AND QUALITY CONTROL: 9. 10.

11. 12. 13.

Prepare a calibration stock solution by dilution of 1 mL of 1 mg/mL formaldehyde stock solution to 100 mL with distilled water. Pipet aliquots of calibration stock solution (e.g., 40, 200, 750, 2000, 5000, and 10000 µL) into 10-mL volumetric flasks to prepare working standards. Higher level standards, if needed, can be prepared by using different dilutions of the formaldehyde stock solution. Add distilled water to bring the volume of each working standard to 10 mL. Analyze working standards together with samples and blanks (steps 14 through 17). Prepare calibration graph of area vs. amount (µg) of formaldehyde per sample (10-mL total volume).

MEASUREMENT: 14.

15. 16. 17.

Transfer a 1-mL aliquot of the solution from step 8. to a 5-mL vial containing 3-mL of an 2,4dinitrophenylhydrazine/acetonitrile solution (1.3 mg/mL). Add one drop 1 N perchloric acid (to catalyze the reaction to form the corresponding hydrazone), cap the vial and shake it gently for several seconds. Set liquid chromatograph to conditions given on page 1. Inject 15-µL sample aliquot. Measure peak area. NOTE 1: If peak area is greater than the highest standard, take a smaller aliquot of the remaining unreacted sample solution, dilute to 1 mL with distilled water and analyze (steps 14 through 17) and apply appropriate dilution factor in the calculations. NOTE 2: For optimum results, all samples containing over 400 µg/mL should be diluted and reanalyzed, since the maximum amount of formaldehyde that can react with 3.9 mg of 2,4-dinitrophenylhydrazine is 590 µg.

CALCULATIONS: 18.

19.

Determine mass, µg, of formaldehyde (W) found in the sample and the average media blank (B) from the calibration graph. Use the appropriate aliquot factor (e. g., 1 mL aliquot/original volume from step 14) and the total sample volume (10-mL) unless corrected for in calibration plot (step 13). NOTE: Include dilution factor for any sample which exceeded the highest calibration standard. Calculate concentration, C, of formaldehyde from dust in the air volume, V (L).

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