This standard specifies the salicylic acid spectrophotometry used for determination of ammonia nitrogen in water.
This standard is applicable to the determination of ammonia nitrogen in groundwater, surface water, domestic sewage and industrial wastewater.
When the sampling volume is 8.0mL and a 10mm cuvette is used, the detection limit is 0.01mg/L, the lower limit of determination is 0.04mg/L and the upper limit of determination is 1.0mg/L (all expressed as N).
When the sampling volume is 8.0mL and a 30mm cuvette is used, the detection limit is 0.004mg/L, the lower limit of determination is 0.016mg/L and the upper limit of determination is 0.25mg/L (all expressed as N).
2 Method principle
In the presence of alkaline medium (pH =11.7) and sodium nitroprusside, ammonia and ammonium ions in water react with salicylate and hypochlorous acid ions to generate blue compounds, and the absorbance is measured with a spectrophotometer at 697nm.
3 Interference and its elimination
See Annex B for the possible interfering substances and their limits when this method is used for analysis of water samples.
Serious interference from aniline and ethanolamine is rare. The interference is usually caused by primary amine. It may also be caused by chloramine, excessive-high acidity and alkalinity as well as the inclusion of substance capable of reducing hypochlorous acid ions.
If the color of the water sample is too dark, the contained salt content is too high, the potassium tartrate does not have enough masking ability for metal ions in the water sample, or there are high concentrations of calcium, magnesium and chloride in the water sample, pre-distillation is required.
