A simple on-line measurement system consisting of a conventional peristaltic pump, a HPLC-type heater, and a flow-through spectrophotometer is introduced for the determination of chemical oxygen demand(COD). The system was configured such that the reaction mixture in the highly concentrated sulfuric acid medium flowing through the PTFE reaction tubing was heated at 150℃ and the absorbance of dichromate was continuously monitored at 445 nm. The same oxidation principle as in the standard procedure was employed except the use of CoSO_4 as a new effective catalyst. To test the system, potassium hydrogen phthalate was selected as a COD standard material. With suitably optimized reaction condition, the applicable concentration range depends on the initial concentration of potassium dichromate in the oxidizing reagent. With 2.0×10-3 M and 5.0×10-4 M dichromate, the linear dynamic range was observed up to 400 ppm and 100 ppm, respectively. The standards in the linear ranges were shown to be completely oxidized, which was confirmed with sodium oxalate or Mohr`s salt. In all cases, the typical reproducibility for between-runs was 2% or less. The proposed measurement system provides the valuable information for the further development of automated analysis system based on the present standard procedure.

• 정형근(연세대학교 환경학과) | Hyung-Keun Chung (Dept. of Environmental Science & Technology Yonsei University)
• 차기철(연세대학교 환경학과) | Gi-Cheol Cha (Dept. of Environmental Science & Technology Yonsei University)