Fig. 1.

The optimization of mobile phase condition and the concentration of oxidation reagent. a The effects of phosphate salt (PS) and TBAP on the resolution (R) and the retention time (RT) of nitrate. The black Y-axis and curve represent the effect of PS and TBAP on R, and the blue Y-axis and curve represent the effect of PS and TBAP on RT. b The resolution and the retention time of nitrate declined with pH. c A greater amount of acidic potassium permanganate was added to the solutions, and the worse of the peak shape of nitrate was generated (a–g represent different volumes of acidic potassium permanganate were added into 250 μL of the solution with nitrite). a: 1 μL; b: 2 μL; c: 4 μL; d: 10 μL; e: 20 μL; f: 40 μL; g: 80 μL