Page:NIOSH Manual of Analytical Methods - 6603.pdf/2

 CARBON DIOXIDE: METHOD 6603, Issue 2, dated 15 August 1994 - Page 2 of 3 REAGENTS: 1. 2. 3. 4.

EQUIPMENT:

Carbon dioxide,* 99% or higher purity Nitrogen,* purified Helium,* purified Air*, filtered, compressed



See SPECIAL PRECAUTIONS.

1. Portable gas chromatograph (GC), with thermal conductivity detector, column (p. 6603-1), and 5-mL gas sampling loop. 2. Strip chart recorder, if appropriate. (Many GCs have built-in data-handling capabilities) 3. Personal sampling pump, 0.02 to 0.1 L/min or other rate suitable for filling sample bag, with flexible connecting tubing. 4. Sample bags, five-layer, 2- to 20- L, or other appropriate sizes, fitted with a metal valve and hose bib (Calibrated Instruments, 731 Saw Mill Rd., Ardsley, NY 10502, or equivalent). 5. Gas-tight syringes, 10 mL and other convenient sizes for making standards and GC injections if GC is not equipped with gas sampling loop. 6. Calibrated rotameters, for standards preparation. 7. Label tape and marking pens for labelling bags.

SPECIAL PRECAUTIONS: Shipment of compressed must comply with 49 CFR 171-177, DOT regulations regarding shipment of hazardous materials.

SAMPLING AND MEASUREMENT: 1.

2.

3.

Start GC and recorder (if applicable) and allow to warm up according to manufacturer's instructions. NOTE: A straight baseline should be attained at the highest sensitivity likely to be used. Select one of the following sampling modes: a. Spot sample. Draw air sample into the gas sampling loop of the GC with the on-board sampling pump, if supplied. Alternatively, inject an aliquot of air to be sampled into the GC with a gas-tight syringe. NOTE: A large contributor to random error in the method is imprecision of replicate injections. To improve precision: (1) use a gas sampling loop for injections if available; (2) make at least three replicate determinations per sample; (3) use an injection volume large enough to be precisely readable, and consistent with that used in calibration. b. Integrated air sample for TWA determination. (1) Evacuate a clean sample bag using the inlet port of a personal sampling pump. NOTE: To reduce memory effects and contamination, use only previously unused sample bags. (2) Attach the sample bag to the outlet port of the personal sampling pump with a minimum length of flexible tubing. (3) Pump the air sample into the bag at a rate calculated to fill ≤80% of the sample bag capacity over the sampling period. NOTE: The flow rate must be known to ±5% throughout the sampling period. (4) Within 24 hours after completion of sampling, introduce an aliquot of the sample into the GC (as in step 2a). Obtain the carbon dioxide peak height of the injected sample. NOTE: Under these conditions, carbon dioxide elutes at about 2 min, after oxygen and nitrogen. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94