Abstract: The complex salt components in seawater or other salty water will lead to turbidity or precipitation in the measurement of ammonia nitrogen by using Nessler's reagent colorimetric method. In this study, the interference of calcium and magnesium ions in seawater was eliminated by adjusting the dosage of potassium sodium tartrate as masking agent according to seawater samples with different salinity. The results indicate that 1% potassium sodium tartrate solution can be used for the determination of ammonia nitrogen in samples with salinity below 17.3‰ while 2% can be used for the samples with salinity between 4.5‰ to 34.1‰ under experimental conditions. The detection range of the approach was 0.1~8.0mg.L^-1,detection limit was 0.03mg.L^-1. The spiked recoveries of samples ranged from 96% to 105%, and the standard deviation of parallel samples was under 3.94%. The approach has the advantages of simple operation, wide linear range, good performance in sensitivity and accuracy.

Key words: Nessler's reagent, Spectrophotometry, Seawater, Ammonia nitrogen, Potassium sodium tartrate