NITROGEN DIOXIDE: METHOD 6700, Issue 2, dated 15 January 1998 - Page 2 of 5 REAGENTS:
EQUIPMENT:
1. Absorbing reagent. Combine 1 part reagent grade triethanolamine (TEA) with 7 parts analytical grade acetone.* 2. Sulfanilamide solution. Combine 2 g sulfanilamide and 5 mL conc. H3PO4, and dilute to 100 mL with distilled water. 3. N-1-naphthylethylenediamine dihydrochloride (NEDA) solution. Dissolve 70 mg NEDA in 50 mL distilled water. 4. Combined reagent. Combine 1 part sulfanilamide solution, 1 part water, and 0.1 part NEDA solution. Protect from light and refrigerate. Stable ~ 1 month . 5. Sodium nitrite stock solution, 0.05 M. Accurately weigh 0.345 g NaNO2 (reagent grade). Dissolve in 100 mL deionized water. Protect from light and refrigerate. Stable 90 days. 6. Calibration stock solution. Dilute an aliquot of NaNO2 stock solution with distilled water (e.g.,1:50 dilution yields1 nanomole NO2-/µL). Prepare fresh immediately before use.
1. Sampler: See APPENDIX (Potential sources of equipment given in reference [1]): a. Acrylic tubing, 3/8-inch (9.5-mm) ID. b. Stainless steel screen, 40x40 mesh/inch (16x16 mesh/cm). c. Polyethylene cap, unflanged, ½-inch (12.7mm). d. Polyethylene cap, flanged, ½-inch (12.7mm). e. Pen clips, 0.48-inch (12.2-mm). f. Electrical tape, plastic. g. Stopcock grease. 2. Spectrophotometer, 540 nm, with 1-cm cuvettes. 3. Volumetric flasks and pipets for preparation of standards. 4. Mixer, vibration or vortex (optional). 5. Forceps.
- See SPECIAL PRECAUTIONS
SPECIAL PRECAUTIONS: Acetone is a fire hazard.
SAMPLING: 1. Attach the sampler with flanged cap down. Start sampling by removing flanged cap. Estimate appropriate sampling time such that the amount of NO 2 collected is in the range 1.2 to 80 ppm-h (0.13 to 8.5 µg NO2). 2. Terminate sampling by replacing flanged cap.
CALIBRATION AND QUALITY CONTROL: 3. Calibrate daily with at least six working standards over the range 0 to 40 nanomoles (0 to 1.84 µg) NO2- per 2.1 mL combined reagent. a. Prepare working standards from calibration stock solution immediately before use. b. Allow 10 min for color development. c. Transfer an aliquot of the working standard to a cuvette and analyze (steps 6 through 8). 4. Prepare a calibration graph (absorbance at 540 nm vs. NO 2 mass in nanomoles. NOTE: The absorbance of 40 nanomoles NO2 is approximately 1 absorbance unit. 5. Check dimensions of the sampler. If cross-sectional area divided by length (A t/L) of the sampler tube differs significantly from 0.10 cm, recalculate the diffusive collection rate (step 9).
MEASUREMENT: 6.
Remove flanged cap from samplers. Add 2.1 mL combined reagent directly into samplers.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
