Study On The Methods For Determination Of Potassium Permanganate Index By Spectrometry And Seal Digest

China is a shortage of water resources country. Per capita water resources, which amount to 2500 m³, is only 1/4. of the world per capita consumption While a long time, the water using models of"exploitation - using - waste water discharge"leads to subject of water resources and water quality deterioration of the ecosystem destruction in most cities in China. More than 80 percent sewage without the effective treatment directly draw into the water, resulting in 1/3 polluted river, more than 90 percent of the urban waters is heavily polluted, of which the largest contributor to organic pollutants in China. Many of the large number of organic pollutants directly threaten the living environment and human health.As China's main surface water pollution index, Permanganate Index (COD_Mn), which generally reflects the contamination degree of reducibility substance (mainly organic pollutant) in waters, is an vital regular .monitoring index in the " Drinking Water Sanitary Standards" (GB5749-2006) which is already put into effect in 2007. At present, the national standard methods (GB11892-89) or the standard methods in "water and wastewater monitoring and analysis methods" (these two ways is equivalent) are adopted to determine permanganate index. The GB method or standard method of monitoring the water quality COD_Mn is in existence at the cost of energy consumption, time consuming, the operation tedious, low sensitivity, lower accuracy and precision and likely to cause secondary pollution of the environment and to meet the demand for batch processing and other shortcomings.Aiming at the disadvantages of GB method, the two new methods spectrophoto -metry and seal digestion are explored and studied to determine COD_Mn of surface water. In the thesis, the testing conditions are optimized through experiment. The opti -mized conditions of detecting COD_Mn by spectrophotometry and seal digestion me- thod are identified in surface water. And through statistical analysis of the test results, the analysis and evaluation is studied. The optimal analytical conditions under which COD_Mn was detected by spectrophotometry are achieved as follows: the total volume of reaction solution is 20 mL, the concentration of potassium permanganate (1/5 KMnO₄) is 0.0125 mol·L^-1, the addition of sulfuric acid (1+3) is 5 mL, heating tem- perature and time are100℃and 30 minutes, respectively. The method has high sensitivity and precision, the detection limit is only 0.085μg·L^-1, and the linearity of standard solution is excellent, the relative coefficient is 0.9993.The relative standard deviation of test results is less than 1.5 percent, relative error is between 0.46% and 1.25%, and the method has very high precision and accuracy. With the standard method of doing t-test, under 95% degree of confidence, the result meets the requirements. It shows that the COD_Mn values determined by the proposed method were in good agreement with those determined by the standard permanganate index method. Therefore, it can be used to analyse and detect COD_Mn .inâ… ^â…¤type of surface water and sanitary waste.The optimal analytical conditions under which COD_Mn was detected by seal digestion method are achieved as follows: the concentration of KMnO4 is 0.001000 mol?L-1, the addition of sulfuric acid (1+3) is 1 mL, heating temperature and time are150℃and 15minutes, respectively. The method has better sensitivity and precision, the detection limit is 1.67 mg?L-1, and the relative standard deviation of test results is between 1.28% and 1.61%, the relative error is between 5% and 6%, it demonstrates that the method has better precision and accuracy. With the standard method of t-test, under 95 % degree of confidence, t value meets the requirements. It shows that the COD_Mn values determined by the proposed method were in good agreement with those determined by the standard permanganate index method.Through experiments and technical and economic analysis comparing with other methods of COD_Mn, the study shows that spectrophotometry and seal digestion method put forward to the thesis have characteristic of simple and fast, high sensitivity and precision , stronger anti-interference capabilities, are two environment-friendly analysis methods. Therefore, the methods can be applied in domestic and promotion, can be simple and rapid monitoring of water COD_Mn to fully understand and achieve the situation of organic pollutants in the monitoring environment, if the methods put forward to the thesis is used, which can provide a lot of most timely and dependable information for surface water pollution detection and control.