METHYL IODIDE: METHOD 1014, Issue 2, dated 15 August 1994 - Page 2 of 4 REAGENTS: 1. 2. 3. 4. 5. 6.
EQUIPMENT:
Toluene, reagent grade (distilled in glass). Methyl iodide, reagent grade.* Calibration stock solution, 250 mg/mL. Prepare in toluene. Nitrogen, purified. Hydrogen, prepurified. Air, compressed, filtered.
See SPECIAL PRECAUTIONS.
1. Sampler: glass tube, 7-cm long, 6-mm OD, 4-mm ID, flame-sealed ends and plastic caps, containing two sections of 20/40 mesh activated (600 °C) coconut shell charcoal (front = 100 mg; back = 50 mg) separated by a 2-mm urethane foam plug. A silylated glass wool plug precedes the front section and a 3-mm urethane foam plug follows the back section. Pressure drop across the tube at 1 L/min airflow must be less than 3.4 kPa. Tubes are commercially available. 2. Personal sampling pump, 0.01 to 1 L/min, with flexible connecting tubing. 3. Gas chromatograph, FID, integrator and column (page 1014-1). 4. Vials, glass, 2-mL, PTFE-lined caps. 5. Syringes, 10-µL, readable to 0.1 µL, 25-, 50and 100-µL. 6. Volumetric flasks, 10-mL. 7. Pipet, volumetric, 1-mL with pipet bulb.
SPECIAL PRECAUTIONS: Methyl iodide is an acute neurotoxin and may produce severe narcosis. It is a suspected carcinogen [4,5].
SAMPLING: 1. 2. 3. 4.
Calibrate each personal sampling pump with a representative sampler in line. Break the ends of the sampler immediately before sampling. Attach sampler to personal sampling pump with flexible tubing. Sample at an accurately known flow rate between 0.01 and 1 L/min for a total sample size of 15 to 50 L. Cap the samples. Pack securely for shipment.
SAMPLE PREPARATION: 5. 6. 7.
Place the front and back sorbent sections of the sampler tube in separate vials. Add 1.0 mL toluene to each vial. Attach cap to each vial. Allow to stand overnight with occasional agitation.
CALIBRATION AND QUALITY CONTROL: 8.
9.
Calibrate daily with at least six working standards over the range 0.01 to 5 mg methyl iodide per sample. a. Add known amounts of calibration stock solution, or a dilution thereof, to toluene in 10-mL volumetric flasks and dilute to the mark. b. Analyze together with samples and blanks (steps 10 through 12). c. Prepare a calibration graph by plotting peak area vs. mg methyl iodide. Determine desorption efficiency (DE) at least once for each lot of charcoal used for sampling in the calibration range (step 8). Prepare three tubes at each of five levels plus three media blanks. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
