Abstract
The usual method of preserving the samples for NO2-N analysis in a strong acid condition was found to be unsuitable because NO2-N decreases with time. This decrease rate after 24 hr was found to be 3% at pH 4.0, 22% at pH 3.5. and 55% at pH 2.0 for 20.0 ppm of NO2-N. Decrease rate of NO2-N at pH 2.0 was found to be different according to its initial concentration. The rates after 27 hr were 9.5% with 2.0 ppm of NO2-N, 30.5% with 10.0 ppm, 34.5% with 20.0 ppm, 28.0% with 50.0 ppm, and 25.5% with 100.0 ppm of NO2-N. NO2-N in water and wastewater did not change by the addition of 40 mg/liter of HgCl2, 5 ml/liter of CHCl3, or 5 ml/liter of CH2Cl-CH2Cl. When NO2-N is to be analyzed within 24 hr of sampling, it is recommended that the sample be preserved at 5°.
