Hello, To measure the nitrite concentration in plasma-activated water (PAW), I used the following method: 10 mL of PAW + 200 µL of sulfanilamide (10 g/L). After 2 minutes of incubation, 200 µL of N-(1-naphthyl)-ethylenediamine dihydrochloride (1 g/L) was added, and after 20 minutes the absorbance was measured at 540 nm. The PAW samples showed an intense pink color, and the absorbance values of different samples ranged from 0.250 to 0.490.

My problem lies in the standard curve. I prepared different concentrations of sodium nitrite (up to 50 g/L) for the standard curve, but the color intensity and absorbance were much lower than those of the PAW samples. I would appreciate your guidance on this issue.

Thank you.