Chemical Oxygen Demand (COD) and Nitrate concentration data are of vital importance in coastal water quality monitoring. The traditional method for monitoring these two parameters is a chemical method that consumes chemical reagent. The drawbacks of these chemical methods are the waste they generate, and the difficulty in implementing in-situ long term monitoring. A new instrument based on an optical method to measure Chemical Oxygen Demand and Nitrate concentration without reagent is described in this paper. According to the different water quality, optical path length of flow cell is variable in this system. A 10 mm path length is selected in this paper. And a Y type of structure of quartz optical fibers is used for real-time compensation. Concentration calculation principle is based on the analysis of absorption spectrum and partial least square method. Comparison between model calculation and experimental data is also discussed in detail with several test samples. The implementation of standard test and measurements for the collected water samples is presented in this paper.
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