| Water is the natural resource that people live on. Ocean is the largest water unit in the earth and covers 71 percentage of the earth. It occupies more and more important status in the development of the present society. In 21st century, the world is pacing a new era when people are willing to know, explore and protect the ocean. With the development of social economy, the ocean is polluted for most castofTs are discharged into the ocean directly or indirectly during manufacture and living. Along with our country entering WTO and the continuously speedy growth of the oceanic economy, protecting oceanic environment, maintaining oceanic ecosystem healthy, supervising and treating polluted water body, and preventing it to get further polluted have become the pressing problems that our country needs to solve urgently.In all kinds of contaminates, the organic contaminate is the fastest increasing and most serious one, Chemical Oxygen Demand is just the comprehensive index to valuate the degree of organic pollution. It's also the important parameter in supervising the water quality. It refers to the amount of the oxidants consumed by the reductive substances that can be easily oxidized by strong oxidants. (It should be converted into oxygen's mass concentration and be calculated by mg/L.) And it will be rather meaningful for oceanic pollution preventing and supervising to grasping and controlling the amount of COD in seawater in time.The automatic analytical method to determinating Chemical Oxygen Demand in seawater was established through experiments by adopting Flow Injection Spectrophotometry (FIS). It totally abandoned the traditional manual analytical method's disadvantages, operating complicatedly, easily causing artificial errors, consuming more time and reagents. It can easily realize the automatic online analysis of Chemical Oxygen Demand in seawater in real sense. And it is also a kind of green analysis method that is environmental benign, and has good analytical application prospect in oceanic analyzing and supervising field.The analytical flow path, oxidant and standard substance adopted in the method are all established through experiments. The reagents are less used and the oxidant has high oxidative percentage for the standard substance under the analytical conditions. The analytical conditions under which COD is determinated are established as follows: the concentration of KMnO4 in oxidative solution is 6.4 ×10-5 mol/L; the concentration of NaOH is 0.05 mol/L; the concentration of H2SO4 is 0.5 mol/L; the concentration of KI in 0.1% starch-KI solution is 0.025 mol/L; the reaction temperature is 95℃; the injection volume is 80ul; the velocity of carrier, H2SO4 and starch-KI solution is 0.30ml/min, 0.50ml/min and 050ml/min respectively; and the length of reaction coil L1, L2 and La is 15, 1.40 and 3.40m respectively. Under the analytical conditions, the precision, linearity and the detection limit are studied, and the results showed that the method has high sensitivity and precision, the linearity of standard solutions with salinity and without are both excellent within low concentration range; the detection limit is 0.084mg/L COD and is lower than that of the standard manual method. The results of referential experiments showed that the method has high anti-reference ability even when the concentration of standard solution is very low. The results of determination for practical water sample and the contrast between this method and the standard manual method indicated that the determination results are identical well, and this method is suitable to determinate the practical seawater.
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