Improved salicylic acid method for the determination of low concentration ammonia-nitrogen in seawater

The precision and applicability of water quality assessment methods for seawater analysis is significantly impacted by its high salinity,hardness and organic pollutant content. Ammonia-nitrogen is a crucial indicator in marine environmental monitoring and aquaculture, and its measurement also has problems such as low detection accuracy and complex procedures. This study presented an enhanced ammonia-nitrogen determination method based on salicylic acid spectrophotometry and an optimized non-ionic ammonia calculation method was developed and validated using actual seawater samples. The results showed that ammonia-nitrogen in seawater could react with sodium salicylate and sodium dichloroisocyanurate to form stable indole compounds at 25 ℃ with sodium nitroprusside as catalyst, creating a proportional relationship between ammonia-nitrogen and absorbance at 655 nm. The linear correlation coefficient was 0.999 1, with a range of 0.02-2.00 mg/L, and a coloration time of 10 minutes. The detection limit was 0.006 mg/L, and the lower limit was 0.024 mg/L. In seawater samples with ammonia-nitrogen of 0.20 and 1.00 mg/L, relative standard deviations were 3.70% and -0.50%, respectively, with recovery rates of 100.20% and 102.10%. By introducing a salinity correction term, the relational formula linking mass fraction of non-ionic ammonia in seawater to temperature, pH, and salinity was derived.