Page:NIOSH Manual of Analytical Methods - 1611.pdf/2

 METHYLAL: METHOD 1611, Issue 2, dated 15 August 1994 - Page 2 of 3 REAGENTS: 1. 2. 3. 4. 5.

EQUIPMENT:

Hexane, chromatographic quality.* Methylal, reagent grade.* Nitrogen, purified. Hydrogen, prepurified. Air, filtered.



See SPECIAL PRECAUTIONS.

1. Sampler: glass tube, 7 cm long, 6-mm OD, 4mm ID, flame-sealed ends with 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 3mm 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 0.2 L/min, with flexible connecting tubing. 3. Gas chromatograph, FID, integrator and column (page 1611-1). 4. Vials, glass, 2-mL, PTFE-lined caps. 5. Syringe, 20-µL, readable to 0.1 µL. 6. Volumetric flasks, 10-mL. 7. Pipet, volumetric, 1.0-mL, with pipet bulb.

SPECIAL PRECAUTIONS: n-Hexane is extremely flammable (flash point = -22 °C). Methylal is also very flammable (flash point = -18 °C) and will attack some forms of plastics and rubber. Work with these only in a hood.

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 0.2 L/min for a total sample size of 1 to 3 L. Cap the samplers. Pack securely for shipment.

SAMPLE PREPARATION: 5. 6. 7.

Place the front and back sorbent sections of the sampler tube in separate vials. Discard the glass wool and foam plugs. Add 1.0 mL hexane to each vial. Attach cap to each vial. Allow to stand 30 min with occasional agitation.

CALIBRATION AND QUALITY CONTROL: 8.

9.

Calibrate daily with at least six working standards over the range 0.1 to 12 mg methylal per sample. a. Add known amounts of pure methylal to hexane in 10-mL volumetric flasks and dilute to the mark. Prepare solutions in the range 0.1 to 12 mg methylal/mL. b. Analyze together with samples and blanks (steps 11 and 12). c. Prepare calibration graph (peak area vs. mg methylal). 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