Analytical accuracy and environmental impact of nitrogen compound determination via absorption spectrophotometry using a copper–zinc reduction coil

The determination of nitrogen compounds in the environment is essential for sustainable nitrogen management. However, conventional analyses of environmental water, which often contains numerous foreign substances, typically rely on cadmium —a hazardous material. In this study, we propose an absorption spectrophotometric method using a copper–zinc reduction coil and evaluate its applicability to environmental water analysis as well as its potential for reducing environmental impact. The proposed method achieved a high recovery rate (>89%) in environmental water recovery tests and exhibited a strong correlation with the copper–zinc reduction continuous flow analysis method in measurement results. Although seawater samples were affected by contaminants, measurements of seawater certified reference materials showed accuracies within 120%, indicating that the method is applicable when dilution is used to mitigate contaminant effects. Furthermore, the proposed method demonstrated a markedly lower environmental impact than the conventional copper–cadmium reduction absorption spectrophotometric method. These findings indicate that the copper–zinc reduction coil absorption spectrophotometric method combines low environmental impact with performance comparable to conventional analytical techniques, making it suitable for environmental water analysis.