Ultraviolet COM.BUSTION of Dissolved Organic Nitrogen Compounds in Lake Waters1

Abstract

Ultravioletcombustion of lake waters combined with sensitive spectrophotometric NO, + NO,-N and NH,-N analyses offers a loo-fold increase in sensitivity over the micro-Kjeldahl method for total dissolved organic nitrogen.The procedure permits quantification of two organic nitrogen fractions in lake waters based on the relative rate and amounts of labile NH4-N and refractory NOa + NO,-N released. Combustions of water from six 1,akes under uniform conditions disclosed widely different amounts of the two fractions and increased amounts of the refractory fraction with increased depth in one lake. Duration of combustion, pII, and adequate oxygen affected ultraviolet combustions of Ircshwater samples and must be controlled to achieve uniform results. A recommended procedure for freshwaters consists of 1.5-3 hr of combustion with continuous oxygenation at pH 4.0 buffered with boric acid.Additions of organic carbon as glucose and glycine or tryptophanc to standard solutions and natural lake samples demonstrated that the rate of nitrogen release and the final combustion product expression were a function of: 1) the molecular nature of the dissolved organic nitrogen compound ( DONC), 2) the concentration of total dissolved organic carbon ( TDOC ) , and 3 ) the inorganic s,alt concentration.Use of this procedure in comparing lakes of different trophic status should permit investigation of the role of DONC and its decomposition in primary production processes of lake ccosystcms.

Nitrogen and phosphorus dynamics in hot desert streams of Southwestern U.S.A.

“…At 10 sites where ammonium analyses were not performed, total inorganic nitrogen was estimated 3 0 5 from nitrate plus an amount of nitrogen equivalent to mean percentage of ammonium in all other samples (6%, n = 42) . Total dissolved nitrogen was analyzed in selected samples as nitrate and ammonium after four hours of ultra-violet oxidation (Manny et al 1971) .…”

Dissolved Organic Matter in Lakewater: Characteristics of Molecular Weight Size-Fractions and Ecological Implications

“…There were no additions of H202, boric acid, or 02, made to lakewater fractions prior to combustion that would accelerate or facilitate the combustion process itself, or increase the efficiency of the oxidation (see Manny et al 1971). …”

Determination of organically combined chlorine in high molecular weight aquatic organics

“…Low recoveries of chlorine from chloroform are probably due to evaporation from solution before and during irradiation; the reflux condensers were not completely effective in retaining the chloroform in the reaction vessel. UV irradiation has been used by several investigators (5)(6)(7)(8)(9)(10) to decompose aqueous organics for elemental analysis (organic carbon, nitrogen, phosphorus, and iron). In the studies cited, the rate of destruction of organic material was found to be a function of flux of light in the sample, temperature of the sample during irradiation, TOC of sample, and the presence of sensitizers such as Hg.…”