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Quantitative Reduction and Inclusion of Plant Tissue Nitrates in Kjeldahl Digestion
Author(s) -
Goyal Sham S.,
Hafez Ahmed A.
Publication year - 1990
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1990.00021962008200030027x
Subject(s) - kjeldahl method , chemistry , digestion (alchemy) , metal , metal ions in aqueous solution , zinc , nitrogen , nuclear chemistry , inorganic chemistry , chromatography , organic chemistry
This study was prompted by controversy over the accuracy of the existing predigestion methods to include NO 3 ‐N in Kjeldahl digestion. A system for quantitative reduction of NO − 3 to NH + 4 using the Zn metal and Cu 2+ in 2 M H 3 PO 4 was developed and was used as a predigestion treatment. Using four different acids in a Zn metal and Cu ion system, the efficiency of NO 3 reduction was found to be depenndent on the acid type and its concentration. The Cu ions catalyze the Zn‐acid reaction and improved reproducibility compared to treatments with no Cu 2+ added. Four milliters 2 M H 3 PO 4 containing 40 mg Cu 2+ as CuCl 2 ˙2H 2 O and 0.3 g Zn recovered 100% of the NO − 3 ‐N in plant materials containing as high as 2.51% NO − 3 –N (200 mg sample). Tissues containing higher levels of NO − 3 –N may be analyzed using smaller size sample, e.g. 150 mg. The digestion procedure includes acidified H 2 O 2 treatment at low temperature to solubilize unused Zn and partially oxidize plant organic matter to control foaming and frothing. Small digestion tubes (50‐mL) and a digestion block were used for greater efficiency. The method is simple, highly reproducible and convenient.