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A Rapid Method for Total Nitrogen Analysis Using Microwave Digestion
Author(s) -
He X. T.,
Mulvaney R. L.,
Banwart W. L.
Publication year - 1990
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1990.03615995005400060019x
Subject(s) - kjeldahl method , microwave digestion , chemistry , digestion (alchemy) , microwave , chromatography , nitrogen , microwave oven , detection limit , organic chemistry , physics , quantum mechanics
A microwave digestion procedure recently proposed for total N analysis of soil using HF‐HCl, H 3 BO 3 , and H 2 O 2 was found to give much lower values than conventional Kjeldahl digestion in analysis of soil and plant samples and simple organic N compounds. An alternative microwave procedure was developed that involves Kjeldahl digestion with concentrated H 2 SO 4 and a K 2 SO 4 ‐catalyst mixture. With this procedure, digestion of five samples can be accomplished in 30 min. Complete recovery (≥98%) of N was obtained in analysis of several organic N compounds. Total N analyses of plant materials by the microwave Kjeldahl method agreed closely with those by conventional Kjeldahl digestion using an Al block; the microwave method gave somewhat lower results than the conventional method for surface soils with a high content of total N. Precision of the analysis was comparable for both methods. Recovery of N added to soil as NO 3 averaged 97% when the microwave procedure was modified to include a pretreatment with salicylic acid and sodium thiosulfate. Although much more rapid, the microwave Kjeldahl method is not necessarily more convenient than conventional digestion with an Al block because of the need for frequent loading and unloading of samples.