Determination of ammonia

The concentration of produced NH₃ was spectrophotometrically determined by the indophenol blue method with modification⁶⁶. First, a certain amount of electrolyte was taken out from the electrolytic cell and diluted to the detection range. Then, 2 mL of solution was removed from the diluted electrolyte. Subsequently, 2 mL of a 1 M NaOH solution containing 5 wt% salicylic acid and 5 wt% sodium citrate was added to the aforementioned solution, followed by the addition of 1 mL of 0.05 M NaClO and 0.2 mL of 1.0 wt% C₅FeN₆Na₂O (sodium nitroferricyanide) solution. After 2 h at room temperature, the absorption spectrum was measured by using a UV–vis spectrophotometer (UV-2600). The formation of indophenol blue was determined using the absorbance at a wavelength of 655 nm. The concentration–absorbance curve was made using a series of standard ammonium chloride solutions.