Study On The Method Of Field Detection Of Ammonia Nitrogen In Seawater

Ammonia nitrogen is one of the important biogenic elements in the seawater.Monitoring ammonia nitrogen in seawater is an important part of marine monitoring.In recent years,with the marine environment worsening,study for the determination of ammonia nitrogen content is getting more and more attention.In this thesis,Sodium Salicylic-Sodium Hypochlorite spectrophotometry(Sodium Salicylic method for short)and Ortho-phthalaldehyde fluorescence method(fluorescence method for short)were used to measure ammonia nitrogen content in seawater and two kinds of rapid field detecting method of ammonia nitrogen in seawater were established.It has laid an important theoretical foundation of developing automatic instrument for detecting ammonia nitrogen in seawater.The work in this thesis consists of the following parts:1.The best reagent ration of Sodium Salicylic method was determined by orthogonal experiment.That is the concentration of EDTA-Na2,sodium citrate and K2Fe(CN)5(NO)·2H2O in the mixed solution of sodium citrate was 25,200 and 5 g/L respectively and that of sodium salicylic and NaOH in sodium salicylic solution was50 g/L and 30 g/L respectively.In addition,effective concentration of NaClO was 1.4g/L.The reagent can be stable for 27 days at 6 ? under dark condition.2.The effects of pH,temperature and time on the color development of sodium salicylate method were studied.The results showed that the absorbance was maximum when the pH scale ranged from 10.26 to 10.49.In this experiment,the temperature and time of Sodium Salicylic method was 35 ? and 10 min respectively.3.Performance of Sodium Salicylate field detecting method was tested.The recovery of standard addition of ammonia nitrogen standard solution with concentration of 60 and 120 ?g/L was 99.3% and 96.7% respectively,which can meet the requirement of "marine monitoring standard".4.The Fluorescence spectrum characters were investigated.The effects of pH,temperature and time on the fluorescence intensity were studied.The result showed that the best excitation and emission wavelength of fluorescence was 362 nm and 421 nm respectively.The fluorescence intensity was maximum while the pH scale ranged from 10.2 to 10.5.In the experiment,the temperature and time of fluorometry method was 28 and 5 min respectively.5.Effect of enhanced sensitivity of Sodium Sulfite,Triton X-100 and brij35 on fluorescence reaction was studied.Then Sodium Sulfite was chosen as the sensitizing agent of fluorescence reaction.Reagent ration was determined by orthogonal experiment and that of 10 mL mixed fluorescence reagent was: 1mL OPA(40 g/L),3mL sodium sulfite(8 g/L).The pH value of buffer solution was 9.8.When adding only 5 mL mixed reagent into 10 mL water sample,good measurement effect can be achieved.The reagent can be stable for 35 days at 6 ?under dark condition.6.Performance of fluorescence field detecting method was tested.The recovery of standard addition of ammonia nitrogen standard solution with concentration of 60 and 120 ?g/L was 100.8% and 100.7% respectively.The detection limit of this method was 2.07 ?g/L.In conclusion,when using Sodium Salicylate method and fluorescence method to measure ammonia in seawater,the recovery rate is high.Compared with the current analysis methods used in ammonia analytical instruments,the two methods have advantages of no toxicity,good stability,low reagent consumption and high environmental friendliness and provide a new way for the rapid field analysis of ammonia nitrogen in seawater.