A HIGH-TEMPERATURE CATALYTIC-OXIDATION TECHNIQUE FOR DETERMINING TOTAL DISSOLVED NITROGEN

A high-temperature catalytic oxidation method for determination of tot al dissolved N has been developed and tested on soil solution and thro ughfall. Unlike methods generally used for total dissolved N, this met hod is rapid, quantitative, and does not require use of strong acids o r bases. The technique couples a commercially available chemiluminesce nt N detector with the combustion furnace of a commercially available C analyzer. An aqueous sample is combusted in an ultra pure oxygen env ironment at 680 degrees C, converting all forms of N to nitric oxide, which then reacts with ozone. The product, metastable NO2, is measured chemiluminescently by the N detector. The method is appropriate for s amples collected in studies of forest soil solution and throughfall, h aving a method detection limit of 0.03 mg L(-1) total N, and a range f rom 0.03 to 10.0 mg L(-1). Tests of several organic and inorganic N-co ntaining compounds showed recoveries >90% for concentrations up to 5.0 mg N L(-1). Urea was the only compound tested with recoveries <90%. N umerous field samples were analyzed and compared with results obtained using persulfate oxidation and high-temperature oxidation (uncatalyze d oxidation at 1100 degrees C). Results from this high-temperature cat alytic oxidation method compare well with persulfate oxidation and hig h-temperature oxidation.