Determination of total nitrogen and phosphorus in soil by ion chromatography with conductivity detector following persulfate digestion method

This study introduces a new method to determine both TP and TN in one process, reducing the analytical cost and time. During this procedure, soil samples were digested in alkaline potassium persulfate (K2S2O8) at 150 °C for two hours in a reactor to convert organic N (including NH3/NH4+) and P species to the highest oxidation states NO3-, PO43-. After that, H2O2 removes the color of the digest, which could influence the efficiency of the analytical process. Finally, ions NO3- and PO43- were separated on the anion-exchange column and quantified by a conductivity detector. According to the spiked samples, which were made by mixing Bovine serum albumin (BSA) with organic nitrogen and triphenyl phosphate containing organic phosphorus with real soil matrix, the recovery of TN and TP was 85% and 97%, respectively. Both TN and TP linear concentration ranges were between 0.50 and 50 µg.mL-1. The results of relative standard deviation and limit of detection for TN were from 4.2%, and 0.31 mg.kg-1; and for TP were from 3.5%, and 0.25 mg.kg-1.