Determination of total nitrogen in aqueous samples using persulfate digestion

Determination of total nitrogen in aqueous samples after potassium persulfate digestion compared favorably in both precision and nitrogen recovery with determinations obtained using Kjeldahl digestion. The determination of total nitrogen (TN = inorganic and organic fixed nitrogen) has largely depended either on acid Kjeldahl digestion ( cf. Strickland and Parsons 1972) or on photo-oxidation (Armstrong et al. 1966) of nitrogenous organic compounds~ The former procedure is tedious to perform and yields a total Kjeldahl nitrogen (TKN) value that includes only or-. 1 This work was supported by NOAA Office of Sea Grant ( 04-6-158-44016 ), by the Ecosystems Center at the Marine Biological Laboratory, Woods Hole, Massachusetts, and by the Jessie Smith Noyes Foundation. Contribution 3791 from the Woods Hole Oceanographic Institution. ganic N and NH4+-N (not N02-and N03--N). The latter is less tedious and does include N02-and N03--N, but some compounds (e.g. urea and ethylenediaminetetraacetic acid-EDTA) have been reported to be refractory to this type of oxidation (Henriksen 1970; Afghan et al. 1971). In addition, a substantial investment in photo-oxidation equipment is necessary if large numbers of samples are processed. A persulfate oxidation technique for TN determination has also been developed ( Koroleff 1969, 1970). Koroleff found that while there is no single nitrogenous product of nonalkaline persulfate oxidation (presumably N03-, NOCl, and other compounds are produced), under alkaline conditions, N03-, readily reduced to N02for analysis, is the sole product. Thus, total /