NITROUS OXIDE: METHOD 6600, Issue 2, dated 15 August 1994 - Page 2 of 3 REAGENTS: 1. 2.
EQUIPMENT:
Nitrous oxide, 99%, compressed.* NOTE: Required in field for calibration. Air, uncontaminated.
See SPECIAL PRECAUTIONS.
1. Spectrophotometer: infrared analyzer, transportable, long pathlength (0.5 to 40 m, as needed for concentration range measured), wavelength 4.48 µm, sample cell of known volume. NOTE: Readout drift should be less than 5% full-scale/8-h. 2. Pump to circulate air samples through the spectrophotometer sample cell; flow rate ca. 1 sample cell volume/min. 3. Syringes, gas-tight, 0.1-, 0.5- and 1-mL. 4. Regulator for nitrous oxide. 5. Strip chart recorder, compatible with spectrophotometer (optional). 6. Personal sampling pump, 0.1 to 4 L/min, capable of bag filling, with flexible connecting tubing; and plastic bags, inert and impermeable, clean, various sizes, capacity ≥2 times spectrophotometer cell volume (optional; for TWA samples). 7. Plastic tubing (optional; for remote, real-time analysis).
SPECIAL PRECAUTIONS: Nitrous oxide supports combustion. Shipment of compressed calibration gas must comply with 49 CFR 1992 regulations regarding shipment of hazardous materials.
SAMPLING: 1.
Select one of the following sampling modes according to the desired form of the data: a. Ambient air. Pump ambient air at ca. 1 cell volume/min through the spectrophotometer sample cell. NOTE 1: Record and integrate the continuous spectrophotometer output signal if data are to be expressed as TWA concentration. NOTE 2: Remote air samples may be transported to the spectrophotometer with the use of plastic tubing and a vacuum pump and analyzed in the same manner as ambient air samples. b. Integrated air samples for TWA determinations. (1) Evacuate a clean plastic bag. (2) Attach the plastic bag to a personal sampling pump and pump the air to be sampled into the bag at a rate calculated to fill the bag over the duration of the sampling period. Terminate sampling before the bag is 80% full. NOTE: The flow rate must remain within ± 5% of the initial setting throughout the sampling period. (3) Analyze the bag sample within 2 h after completion of sampling to minimize loss of analyte by adsorption and permeation.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
