Continuous-flow analysis of nitrogen compounds in environmental water using a copper–zinc reduction coil

•Copper–zinc reduction CFA method is cadmium-free and can determine nitrogen compounds.•Influence of metal precipitation can be removed by changing reagent conditions.•Copper–zinc reduction CFA method shows high accuracy in environmental water analysis. The copper–cadmium reduction method has been applied to determine nitrogen compounds in heavily contaminated environmental water. However, there is an international demand to reduce the use of cadmium because it is harmful to humans and environment. Hence, a copper–zinc reduction continuous flow analysis system without using cadmium was developed for nitrogen-compound determination. However, the effects of seawater contaminants on this analytical method remains unknown. Therefore, in this study, the effects of contaminants on the developed method are investigated, and the applicability of the method to environmental water analysis is examined. Resultantly, interference due to magnesium precipitation is confirmed; however, this could be prevented by adjusting the concentration of the analytical reagent, i.e.,. ethylenediaminetetraacetic acid disodium. The measurement of certified reference materials under the new conditions, with precipitation countermeasures, show good results, with an accuracy of over 96 %. Additionally, a recovery study using actual environmental water afforded good results, with recovery of >95 % for all samples. These results indicate that the proposed method is an excellent, cadmium-free analytical method capable of analyzing environmental water as effectively as conventional methods. [Display omitted]