Fig. 1. Calibration curves using nitrate (■), ammonium (●), and urea (▲) working standards (500–10,000 mg L−1 N) prepared without (a) and with (b) the presence of 5% (v/v) H2O2.
Fig. 1. Calibration curves using nitrate (■), ammonium (●), and urea (▲) workingstandards (500–10,000 mg L−1 N) prepared without (a) and with (b) the presence of5% (v/v) H2O2.