National Institute for Occupational Safety and Health

“ The working range for NO is 1 to 50 ppm (1.3 to 61 mg/m 3) for a 1.5-L air sample. The working range for NO 2 is 0.5 to 25 ppm (1 to 47 mg/m 3) for a 3-L air sample. The lower sampling rate for NO is to allow collection of oxidized NO on the back sorbent section. At the lower rate, both NO and NO 2 may be determined simultaneously.
INTERFERENCES: Any compound that reacts with the colorimetric reagents will interfere. ”

“ SAMPLE PREPARATION: 5. Transfer the sorbent from Tube A and Tube C to separate 50-mL volumetric flasks. Discard glass wool plugs and oxidizer (Tube B) . 6. Add absorbing solution to sample in 50-mL volumetric and bring to the mark. 7. Stopper flask and shake vigorously for 30 sec. Allow solids to settle. 8. Pipet 10 mL of extracted sample into a 50-mL volumetric flask. NOTE: Start reagent blanks at this step. 9. Add 1.0 mL hydrogen peroxide solution, 10.0 mL sulfanilamide solution, and 1.4 mL NEDA solution. Mix thoroughly after each addition. 10. Allow 10 min for complete color development. ”

“ Pipets, 1-, 5-, 10-mL and other convenient sizes. Stopwatch.
SPECIAL PRECAUTIONS: Concentrated acid is corrosive to the skin and mucous membranes. Handle it only in a hood.
SAMPLING: 1. Calibrate the sampling pump with a representative sampler in line. 2. Immediately before sampling, break ends of sampler and attach to pump. NOTE: Nitrogen dioxide collects on the first tube (Tube A) , and is thereby separated from nitric oxide, which is oxidized by Tube B and then is collected on Tube C (adjacent to the sampling pump.) 3. Sample at an accurately known flow rate of 0.025 L/min ± 5%. ”