Page:NIOSH Manual of Analytical Methods - 6009.pdf/3

 MERCURY: METHOD 6009, Issue 2, dated 15 August 1994 - Page 3 of 5 the BOD bottle must be 100 mL. To prevent possible loss of mercury during transfer, place the pipet tip below the surface of the liquid in the BOD bottle.

CALIBRATION AND QUALITY CONTROL: 10.

11.

12.

Prepare a minimum of two series (six levels each) of working standards covering the range 0.01 to 0.5 µg Hg per aliquot by adding known amounts of the intermediate standard to BOD bottles containing enough 1% nitric acid to bring the final volume to 100 mL. Analyze the working standards together with the samples and blanks (steps 13 through 16). Analyze full set of standards at the beginning of the run, and a second set at the end of the run. Additional standards may be run intermediately during the analysis to confirm instrument response. Prepare calibration graph (peak height vs. solution concentration, µg/sample).

MEASUREMENT: 13. 14. 15. 16.

Zero the spectrophotometer by removing the bubbler from the BOD bottle, allowing the baseline on the recorder to stabilize. Place the bubbler in a BOD bottle containing 0.5 µg mercury in 100 mL 1% nitric acid. Adjust the spectrophotometer so that it will give a 75% to full-scale deflection of the recorder. Vent the mercury vapor from the system. Analyze standards, samples and blanks (including media blanks). a. Remove the bubbler from the BOD bottle. b. Rinse the bubbler with deionized water. c. Allow the recorder tracing to establish a stable baseline. d. Remove the stopper from the BOD bottle containing the next sample to be analyzed. Gently swirl the BOD bottle. e. Quickly add 5 mL 10% stannous chloride solution. f. Quickly place the bubbler into the BOD bottle. g. Allow the spectrophotometer to attain maximum absorbance. h. Vent the mercury vapor from the system. i. Place the bubbler into an empty BOD bottle. Continue venting the mercury until a stable baseline is obtained. j. Close the mercury vent.

CALCULATIONS: 17. 18.

Calculate the amount of mercury in the sample aliquot (W, µg) from the calibration graph. Calculate the concentration C (mg/m 3), of mercury in the air volume sampled, V (L):

Where: Vs = original sample volume (step 8; normally 50 mL) Va = aliquot volume (step 9; normally 20 mL) B = average amount of mercury present in the media blanks

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