NITRIC OXIDE and NITROGEN DIOXIDE: METHOD 6014, Issue 1, dated 15 August 1994 - Page 2 of 4 EQUIPMENT:
REAGENTS: 1. 2. 3. 4.
Triethanolamine, TEA, reagent grade. n-Butanol, reagent grade. Phosphoric acid, H 3PO 4, conc.,reagent grade.* N-(1-napthyl)ethylenediaminedihydrochloride, NEDA. 5. Sodium nitrite, NaNO 2. 6. Absorbing solution: Dissolve 15.0 g triethanolamine in ca. 500 mL deionized water, add 0.5 mL n-butanol, and dilute to 1 L. 7. H2O 2 solution, 0.02% (v/v): Dilute 0.2 mL of 30% H 2O 2 to 250 mL with deionized water. 8. Sulfanilamide solution: Dissolve 10 g sulfanilamide in 400 mL deionized water, add 25 mL conc. H 3PO 4, and dilute to 500 mL. 9. NEDA solution: Dissolve 0.5 g N-(1-napthyl) ethylenediamine dihydrochloride in 500 mL deionized water. 10. Calibration stock solution, 100 NO 2- µg/mL: Dissolve 0.1500 g NaNO 2 in 1 L deionized water.
See SPECIAL PRECAUTIONS.
1.
2. 3. 4. 5. 6. 7.
Sampler: Three glass tubes, 7-mm OD, flamesealed ends with plastic caps, with glass wool retainers: Tube A: 400 mg TEA-coated molecular sieve (type 13x, 30-40 mesh) Tube B: 800 mg oxidizer (chromate) to convert NO to NO 2. Tube C: Same as Tube A. Connect the tubes in series with flexible tubing. Position Tube C closest to the inlet of the sampling pump. Tubes are commercially available (SKC-226-40, or equivalent). Personal sampling pump, 0.025 to 0.2 L/min, with flexible connecting tubing. Spectrophotometer, UV-visible (540 nm), with cuvettes, 1-cm silica cuvettes. Beakers, borosilicate, 100-mL. Volumetric flasks, 50-mL and other convenient sizes. 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%. NOTE: If nitric oxide is not to be determined, a flow rate of up to 0.2 L/min may be used. 4. Cap the sampler and pack securely for shipment. Submit adequate numbers of field blanks and media blanks to the laboratory.
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. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
