Simultaneous determination of total nitrogen and total phosphorus in freshwater samples using persulfate digestion

The accuracy and precision of total nitrogen (T‐N) and total phosphorus (T‐P) determinations in freshwater samples by the simultaneous digestion method using an oxidizing reagent solution of NaOH‐K2S2O8 were assessed. Detection limits based on the blank test of nitrogen and phosphorus were 0.02 mgN/1 and 0.001 mgP/1, respectively. This simultaneous digestion method gave not only a high recovery and reproducibility over a wide range of various nitrogen and/or phosphorus compounds of known nitrogen and phosphorus compositions, but also high recoveries of nitrogen and phosphorus from standard reference materials, such as orchard leaves, pond sediment and chlorella. No significant difference was found between the determinations of T‐N and T‐P in freshwater samples by this method and those determined by the standard methods of T‐N and T‐P, respectively. This method should be useful for the routine analysis of T‐N and T‐P in freshwater samples containing particulate material and samples of low T‐N and/or T‐P concentration.