Development of Nitric Acid Analysis with Copper-Zinc Reduction Coil Using Continuous Flow Analysis Method

Copper-cadmium reduced naphthylethylenediamine absorption spectrophotometry is one of the methods for analyzing nitrogen components in water, but it uses cadmium, a toxic substance, as a reducing agent. In this study, we developed a method to measure nitrogen components including nitrate nitrogen by reducing nitric acid and nitrite to ammonia using the copper-zinc reduction method with zinc instead of the copper-cadmium reduction method using continuous flow analysis（CFA）. Since the reagents used in the copper-zinc reduction inhibit the coloration of indophenol blue method, ammonia was separated from the inhibitors by an ammonia gas permeation method using a PTFE membrane filter to reduce the effect on the coloration. Comparison of the developed method with the conventional method showed that the lower detection limit of the instrument and the lower quantification limit of the developed method were equivalent to those of the conventional method. In addition, a good correlation was obtained by comparing the measurement results of actual samples such as seawater, environmental water, river water, and wastewater.