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 NITRIC OXIDE and NITROGEN DIOXIDE: METHOD 6014, Issue 1, dated 15 August 1994 - Page 3 of 4

CALIBRATION AND QUALITY CONTROL: 11. Calibrate daily with at least six working standards to cover the range of 1 to 18 µg nitrite ion per 10mL sample. a. Analyze the working standards together with blanks and samples (steps 8 through 10 and steps 12 through 14). b. Prepare a calibration graph [absorbance vs. µg NO 2- per sample].

MEASUREMENT: 12. Set wavelength on the spectrophotometer to 540 nm. 13. Set to zero with reagent blank. 14. Transfer some of the sample solution from step 10 to a cuvette and record the absorbance.

CALCULATIONS: 15. From the calibration graph, determine the mass of NO 2- in each Tube A, W A (µg), and in the corresponding average blank, B A (µg). Similarly, determine the mass of NO 2- in each Tube C, W c (µg), and average blank, B c (µg). 16. Calculate the concentration, C NO2 (mg/m 3) of NO 2 in the volume of air sampled, V (L), applying the conversion factor 0.63:

NOTE: The conversion factor 0.63 represents the number of moles of nitrite ion produced by 1 mole of nitrogen dioxide gas. For NO or NO 2, gas concentrations above 10 ppm, use 0.5 as the conversion factor [7]. 17. Calculate the concentration, C NO (mg/m 3), of NO in the air volume sampled, V (L), applying the factor 0.652 (MW NO/MW NO 2-) and the conversion factor 0.63:

EVALUATION OF METHOD: Method S321, Nitric Oxide, was evaluated over the range of 11.1 to 47.7 ppm (13.8 to 58.5 mg/m 3) for 1.5-L samples, collected from dynamically generated test atmospheres [1,8]. The test concentration was verified with a direct reading instrument, Energetic Sciences Enolyzer. The 1.2 g oxidizer section was found adequate for a 60-min sampling time. NO samples had a mean recovery of 99.5% after 7 days storage at ambient temperature. Method S320, Nitrogen Dioxide, was evaluated over the range 3.0 - 11.6 ppm (5.8 to 21.6 mg/m 3) using 3.9-L samples [2,7]. When an atmosphere at 84% RH containing 11.59 ppm NO 2 was sampled at 0.064 L/min, 1.0% breakthrough occurred after 60 min and 2.4% breakthrough occurred after 180 min. Quantitative recovery was obtained for samples containing 47 µg NO 2 which were stored for 12 days at ambient conditions.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94