Reducing nitrate, how to determine the generated nitrogen by gas chromatography, and what are the determination conditions?

It has been reported that nitrate ions were first reduced to nitrite ions, then nitrite ions were reduced to nitrogen oxides or nitrogen or even ammonia, and then transferred to gas phase for determination. Japanese Patent PublicationNo. 55-65 157 firstly reduced nitrate ions into nitrite ions with zinc powder in neutral or weakly alkaline solution, then introduced the generated aqueous solution of nitrite ions into the chromatographic column of a gas chromatograph, reduced it with sulfamic acid or a salt containing sulfamic acid to generate nitrogen, loaded a nitrogen detector with nitrogen-free helium gas, quantified the nitrogen by gas chromatography, and converted the measured nitrogen amount into nitrate nitrogen content. This method produces quantitative nitrogen in two steps, and the determination time is long. Because the determination procedure is complex and difficult to master, the precision and accuracy of the determination results are low.