Nitrate Interference in Total Kjeldahl Nitrogen Determinations and Its Removal by Anion Exchange Resins,

摘要

The standard methods for analysis of water and waste samples are under continual review to assure that the most accurate results possible are obtained. If a chemical interference in an important analytical procedure is discovered it must be evaluated and if necessary a procedure modification made to circumvent the interference. The interference of nitrate with the determination of total Kjeldahl nitrogen (TKN) was investigated. TKN losses of greater than 90% were observed in solutions containing a nitrate-nitrogen concentration ten times the TKN level. The loss was found by infrared spectroscopy to be occurring due to nitrate and ammonia decomposition to nitrous oxide at the elevated TKN digestion temperatures. Prevention of the nitrate interference in TKN analyses was found to be possible only by removal of nitrate prior to TKN analysis. Several anion-exchange resins in the chloride form were found effective in this removal. Samples containing known TKN levels and high nitrate concentration when treated by these resins prior to TKN analysis gave nearly 100% TKN recovery on TKN analysis.