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Removal of Nitrite Impurity from Nitrate Labeled with Nitrogen-15

Malone, John P., Stevens, R. James
Soil Science Society of America journal 1998 v.62 no.3 pp. 651-653
labeling techniques, titanium dioxide, potassium nitrate, soil analysis, oxidation, ultraviolet radiation, nitrites, biogeochemical cycles
Potassium nitrate labeled with ¹⁵N is often used as a tracer in studies of N dynamics in soil and water systems. Typically, 0.8% NO⁻₂ impurity has been found in the batches of K¹⁵NO₃ enriched to 99 atom % excess ¹⁵N that were purchased by our laboratory. Nitrite is an intermediate in several N cycling processes so its addition when adding NO⁻₃ could produce misleading results. We have developed a safe, simple, and inexpensive method to remove NO⁻₂ impurity from any NO⁻₃ solution in a water matrix. The principle is the oxidation of NO⁻₂ to NO⁻₃ by UV light in the presence of a heterogenous TiO₂ catalyst. A NO⁻₂ concentration of 0.2 mM in 100 mL of 0.2 M NO⁻₃ solution could be oxidized in 12 min using 0.5 g L⁻¹ TiO₂ in a specially constructed photoreactor with a 75-W UV facial tanning lamp. For the routine removal of NO⁻₂, use of the same TiO₂ concentration in a standard beaker worked equally well when the irradiation time was extended to 2.5 h. After irradiation, the TiO₂ is easily and totally removed from the solution by membrane filtration.