Page:NIOSH Manual of Analytical Methods - 1024.pdf/3

This page needs to be proofread.

1,3-BUTADIENE: METHOD 1024, Issue 2, dated 15 August 1994 - Page 3 of 8

CALIBRATION AND QUALITY CONTROL: NOTE: The accurate measurement of pure 1,3-butadiene gas by gas-tight syringe is a critical step in the calibration. Even a slight obstruction (e.g., flakes of PTFE from the plunger tip which obstruct the needle) can cause 1,3-butadiene to be liquified as the plunger is depressed, making delivery incomplete. Bracketing gas samples with water, as described below, allows the volume taken to be approximately verified, and assures complete delivery. The precision of the analysis of multiple independent standards is another indicator of the accuracy of the volumes taken. 9. Make up stock solutions in triplicate at three concentration levels, e.g., 200 µL of 1,3-butadiene gas in 1 mL solution, and both 200 and 50 µL of gas in 4 mL solution: a. Prepare a beaker and drying tube assembly as shown. Bubble 1,3-butadiene under the lower edge of the drying tube so that water is displaced and the gas is trapped in the tube. Plastic tubing Water Serum cap

Gas drying tube filled with water

Beaker

Water

b. Pipet 1 or 4 mL of methylene chloride into a 1- or 5-mL vial, cap, and thoroughly chill. c. Take a known amount (50 or 200 µL) of 1,3-butadiene from the drying tube with a 100- or 250-µL gas-tight syringe. Bracket the gas in the syringe with small amounts of water (5 to 10% of syringe volume) taken from the area above the serum cap before and after withdrawing the gas. Do not take water from inside the drying tube, since it may contain a significant amount of dissolved 1,3-butadiene. d. Slowly inject the 1,3-butadiene and water below the surface of the methylene chloride. e. Agitate and continue to chill the vial to complete dissolution. 10. Calibrate daily with media blanks and triplicate independent media standards of at least six levels ranging from, e.g., 0.5 to 200 µL 1,3-butadiene gas per sample: a. Break ends of larger sampler and attach to personal sampling pump with flexible tubing. b. Take pure gas (50 or 200 µL, as in step 9.c) for the higher levels, or 40 µL of stock solution for lower levels. c. Inject the gas and surrounding water plugs or the stock solution at a point inside the sampler near the glass wool plug while drawing clean air through tube at 0.05 L/min. Continue to draw air through the tube for 5 min or just until the stock solution evaporates. d. Seal tube with plastic caps. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition

This article is issued from Wikisource. The text is available under Creative Commons Attribution-Share Alike 4.0 unless otherwise noted. Additional terms may apply for the media files.