Oxidation efficiency of different oxidants of persulfate method used to determine total nitrogen and phosphorus in solutions

Its speed, safety, and convenience have made the persulfate oxidation method popular in recent years for determining total N and Pin natural water, soil solution and soil extracts. However, the compositions of the oxidizing reagent (i.e., the concentrations of K2S2O8 and NaOH in oxidizing reagent) used by different researchers varied. In this study, a standard urea solution was used as a sample to evaluate the oxidation efficiency of the various oxidants. The oxidizing reagent chosen was also used to determine the total nitrogen (N) in 0.5 mol L-1 K2SO4 soil extracts and total phosphorus (P) in pure compound, compared to the traditional digestion method. Results showed that the efficiency of an oxidizing reagent depend not only on the amounts of K2S2O8, but also on the NaOH concentration in the oxidizing reagent. The pH values in the oxidizing process played an important role in converting the other forms of N to nitrate. The oxidizing reagent of 3% K2S2O8 in 0. 15 mol L-1 NaOH solution used to digest total N in 0.5 mol L-1 K2SO4 extracts of soils gave similar values to that measured by traditional Kjeldahl digestion methods (r = 0.997, P < 0.01); and total P in sodium ribonucleate solution determined by this method was also comparable to that by the H2SO4-HCIO4 digestion methods. Therefore, we recommend this composition as a suitable oxidizing reagent to determine the total N and P in sample solution simultaneously.