Nitrate in water was measured based on ion chromatography using a Metrohm 861 consecutive dual-suppressed ion chromatograph, which had a detection limit of 0.01 to 0.02 mg/L. Analysis was conducted using an SA-8 anion column and conductivity detector, with 0.24 mol/L Na2CO3 solution and 0.30 mol/L NaHCO3 solution at a ratio of 5.0 mL:10.0 mL as the eluent. The eluent was degassed and applied at a flow rate of 1.5 mL/min. The sample injection volume was 1 mL and samples were measured after direct injection.