Rapid Determination Of Chemical Oxygen Demand Based On Micro-spectrometer

Chemical oxygen demand is an important indicator of water organic pollutionmeasurement, which refers to the equivalent oxygen calculated through the amount ofoxidant consumed to digest reducing substances in the water, to be counted as mg/L.The general method for COD determination in water quality monitoring is thepotassium dichromate method and the potassium permanganate method. The former oneapplies for higher contamination of sewage and industrial waste water monitoring,while the later one is used for less polluting groundwater, surface water and drinkingwater analysis. However, these methods need high temperature, high pressure, strongacid and prolonged digestion, which all limit the application of the field monitoring.What’s more, under such a rapid development of the economic society, water qualityhas impact on the production and living of people’s lives all the time. Therefore, find asimple, fast COD determination method for timely water quality monitoring isimminent.In the present paper, base on spectroscopy we study the COD determinationmethod as following:First，based on the rapid digestion using hydroxyl radicals of high oxidationpotential at normal temperature, we have developed a new method of CODdetermination through the competitive consumption of hydroxyl radicals betweenreducing substances and an extra dye. According to the correlation between digestion ofreducing substances and dye, COD colorimetric determination has been achieved by theabsorbance change of dye before and after the digestion. With dye screening andcondition optimization, COD can be determined within15min by this method. Resultsobtained from our method were consistent with the standard method when applying todetermination of the actual water samples.Then, study of a miniaturized COD measurement technique, according to theabove method combined with the micor-spectrometer. Examine the sensitivity, recoveryand reagent life, compared with the determination results in Shimadzu UV-2450, whichare comparable. When the COD value ranges in the1~30mg/L, our method shows agood linear relationship, with a detection limit0.85mg/L. And when the technologyapplied to the determination of the actual water samples, the results are consistent withthose of the GB method.At last, based on the organic matter in the ultraviolet area absorbing certain wavelengths of characteristics combined with micro-spectrometer, and modellingthrough the multiple linear regression and principal component regression, we study adirect UV spectroscopy COD determination method. By examining the multiplecoefficient of determination and root mean square error of prediction (RMSEP) toevaluate the accuracy of the model, the results show that both of the models couldachieve the goal of explaining the concentration variation by the regression line.Besides, the RMSEP values of both models are relatively small, indicating that the twomodels have strong predictive abilities. The two prediction models were then applied tothe simulative waste water, and the results show that both models could predict well.What’s more, PCR was relatively better in prediction than MLR, in terms of examiningthe multiple coefficient of determination and root mean square error of prediction.