Improvement And Study On The Determination Method Of Ammonia Nitrogen And COD

The content of ammonia nitrogen is one of the critical indicators to reflect the water eutrophication of lakes and reservoirs.Nitrogen compounds easily cause eutrophication of water bodies,and different forms of nitrogen compounds via various chemical reactions in the water transform into ammonia nitrogen,which eventually result in the pollution of water system.The determination of ammonia nitrogen in water system mainly adopts the distillation-neutralization titration method.Experimental results show that the pH value of water sample has a direct influence on the accuracy of ammonia nitrogen determination and the most suitable pH is 7.Moreover,the relationship between the ammonia nitrogen content and distillate volume was also discussed.COD(Chemical Oxygen Demand)defined as the amount of oxygen equivalents consumed in the oxidation of organic compounds by strong oxidants,is regarded as an important index for representing the degree of organic pollution in water bodies.And it will be rather meaningful for preventing and supervising water pollution through grasping and controlling the COD values of water bodies in time.Due to the high price of silver catalyst,possible alternatives(MnSO4,CuSO4,and so on)were investigated in this paper.The results reveal that the catalytic efficiencyof CuSO4 was lower than Ag2SO4,but when the demand was not high or samples were quite easy to be oxidized,the above method still could be used practically.With the disadvantages of tedious preparation,low detection efficiency,long cycle analysis and reagents toxicity,common testing methods can not fully meet the testing requirements in actual work,or quickly provide test results when emergencies were occurred.In this paper,segment flow analysis was successfully used to determine the content of ammonia nitrogen and COD at the same time.Automatic segmented flow analysis is a continuous flow method of wet chemistry analysis in which a stream of reagents and samples,segmented with air bubbles is pumped through a manifold to undergo treatment such as mixing,heating,dialysis before enter a flow cell to be detected.Air segmentation can be used to eliminate cross contamination and mix different reagents well.The reaction mixtures are subsequently transferred to the built-in detection heads or separate external detectors.The measure signals are collected on a computer,where the data are processed.The results show that the linear correlation coefficient standard curve reached to 0.9999,and the recovery rate of standard addition was between 94.40 and 100.69%,which meet the demand of the experiment.Additionally,automatic segmented flow analysis has obvious advantages that is it can ensure the reliability of measured data when thesamples in large quantities.