Page:NIOSH Manual of Analytical Methods - 2520.pdf/2

 METHYL BROMIDE: METHOD 2520, Issue 2, dated 15 May 1996 - Page 2 of 5

REAGENTS:

EQUIPMENT:

1.	Eluant: methylene chloride, chromatographic grade.* 2.	Methyl bromide, 99.5%.* 3.	Calibration stock solution: To 4 mL of methylene chloride, add 12 µL dibromomethane. NOTE:	Other brominated compounds may be used if liquid at room temperature. 4.	Desorption stock solution: Bubble methyl bromide gas slowly into chilled eluant. Determine the methyl bromide concentration by comparison with calibration standards. 5.	Helium, prepurified, 99.995%. 6.	Oxygen, ultra purified, as reagent gas for plasma, 30 psi. 7.	Air, filtered. 8.	Dry ice, flaked, for chilling solvent.
 * See SPECIAL PRECAUTIONS.

1.	Sampler: two glass tubes, each tube, 10-cm long, 8-mm OD, 6-mm ID, containing 20/40 activated (600 °C) petroleum charcoal, first tube 400 mg, second tube 200 mg, held in place with silylated glass wool plugs; drying tube, glass, 9 g sodium sulfate. Tubes are connected in series with short pieces of plastic tubing. Pressure drop across sampler <3.4 kPa (2.5 cm Hg) at 1.0 L/min airflow. Tubes are commercially available (SKC, Inc.#226-38-02, or equivalent). NOTE:	If RH ≥50%, precede sampling train with drying tube. 2.	Personal sampling pump, 0.01 to 0.1 L/min, with flexible connecting tubing. 3.	Gas chromatograph, atomic emission detector (helium plasma), integrator or computer, and column (page 2520-1). 4.	Vials, 4- and 10-mL, glass, with PTFE-lined caps. 5.	Syringe, gas-tight, 10-mL. 6.	Microliter syringes, 10-µL, 50-µL, 100-µL, 250µL, 500-µL for preparing standard solutions. 7.	Pipettes, 2-mL, graduated in 0.1-mL increments.

SPECIAL PRECAUTIONS: Methylene chloride is a suspect carcinogen. Methyl bromide is a suspect carcinogen and is toxic by ingestion, inhalation, and skin absorption [4]. SAMPLING: 1.	Calibrate each personal sampling pump with a representative sampler in line. 2.	Break the ends of the sampling tubes immediately before sampling. Attach sampler to personal sampling pump with flexible tubing. NOTE:	Place drying tube in front of the sorbent train. 3.	Sample at an accurately known flow rate between 0.01 and 0.1 L/min for a total sample size of 1.0 to 5.0 L. NOTE:	Limit sample volume to 1.0 L if RH ≥ 50% and no drying tube is used. 4.	Separate the front and back tubes immediately after sampling. Cap the tubes. Pack securely in dry ice for shipment. Store at −10 °C until analysis. SAMPLE PREPARATION: 5.	Place the sorbent sections from each sampling tube in separate vials. Discard the glass wool plugs. 6.	Add 3.0 mL chilled eluant (methylene chloride) to each 400-mg section, and 2.0 mL chilled eluant to each 200-mg section. Immediately cap each vial. 7.	Allow to stand at least 30 minutes at room temperature with occasional agitation. Rechill before transferring to autosampler vials or diluting. NOTE:	Because of the volatility of the analyte, it is suggested that any dilutions be prepared at the

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition