Water Column Total Nitrogen Determination Method

Total nitrogen is an important indicator which reflects pollution concentration of water bodies and lakes,reservoirs eutrophication,so accurate determination of total nitrogen in water is very important.In this paper,existing defects of the national standard method of alkaline potassium persulfate degistion-UV spectrophotometric for the determination of TN in Water(GB11894-89)were analysed,digestion environment was optimized and a new accurate method for the determination of the total nitrogen in water was proposed combining spectrophotometric method with phenol disulfonic acid.It is shown that the regression equation is A=0.0011+0.3962 c,the correlation coefficient r is 0.9999,the molar absorption coefficient is 4.04×10⁴ L.mol^-1·cm^-1,the identification limit is 0.02 mg/L,the average recovery is 98%～102%,and the relative standard deviations of them are all under 5%in new method.It is shown that the new method greatly improved the accuracy and stability of the determination,and the characteristics of sensitivity,accuracy,precision are remarkable.In this paper,the experimental result contains three aspects below:1.The alkaline potassium persulfate degistion-UV spectrophotometric method(GB11894-89)is adopted to determine TN in water bodies now.Through the practical application,many shortcomings were found.Such as,by using colorimetric tube,the grinding mouth cypriot is difficult to open and might be poped up;temperature is difficult to control and is instable by using pressure steam sterilizer or civilian pressure cookers as the digestion vessel;NH₄⁺-N is easy to escape by form of ammonia which make the accuracy,stability and reproducibility of the test reduced in digestion process;unthoroughly digestion and oxidant decomposition can affect the determination of absorbance,the reproducibility of the determination by dual-wavelength is poor and results are bigger than the true value,and so on.2.By using high-pressure reactor as the digestion containers,it had a good performance in obturation,so the improvement dramatically ameliorated digestion environment and the conversion rate,and the precision and accuracy of test were improved.It is shown that the temperature is the key factor in digestion,and there is little difference between the results of high-pressure reactor put in steam oven or portable medical sterilizer.3.A new method was proposed based on the alkaline potassium persulphate digestion-spectrophotometric method for the determination of TN in water and spectrophotometric method with phenol disulfonic acid for determination of nitrogen.The new method apply high-pressure reactor replacing the colorimetric tube to optimize digestion environment, then determine the nitrate in digestion liquid by using spectrophotometric method with phenol disulfonic acid,thus it can determine TN in different water samples accurately.It is shown that the sensitivity,linear relationship and relative error of new method comply with the technical requirements of environmental monitoring.It optimizes the digestion process and improves the accuracy and stability of the determinationand and efficiency of work.