Comparison of continuous flow analysis and ion chromatography for determinations of nitrate, nitrite and phosphate ions in seawater and development of related seawater certified reference materials

Determinations of three nutrients (nitrate, nitrite and phosphate ions) in seawater were investigated by continuous flow analysis (CFA) based on colorimetry and ion chromatography (IC). The accuracies of those methods were examined by discussing their uncertainties. Although some of the nitrite and phosphate validations were not sufficient due to low concentrations, the results of nitrate agreed well with each other. While CFA is popular in this field, its comparison with IC was reported for the first time and contributed to an increase in the reliability of the analytical results. Finally, the investigation led to the development of three kinds of seawater certified reference materials (CRMs) of the National Metrology Institute of Japan (NMIJ) (NMIJ CRM 7601-a, 7602-a and 7603-a) for which the property values of nutrients including dissolved silica were given. The details of the development are described in the present paper.