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Chemical oxygen demand (COD) is an important parameter in water-pollution control analysis. It is closely related to the organic contamination level of a water or wastewater sample. The Cr-COD method is used as the standard in USA and Taiwan. Compared to Japanese Mn-COD method, it has a higher detection limit and severe chloride ion interference because of the stronger oxidant and the longer digestion time. In order to reduce the chloride-ion interference, the mercury salt (e.g. HgSO4) is usually added to mask the chloride ion. On the other hand, the closed reflux-titrimetric method is recommended by the Standard Method to reduce the large amount of hazardous waste. 1 However, it still requires a long time (2 h) for the digestion step to be completed in this COD analysis, and the tolerance of the chloride ion interference is only up to 2000 mg Cl -/L.The objective of this research was to investigate the availability of a rapid procedure to determine the COD in water and wastewater by digesting samples in open vessels located in a focused microwave system followed by ferrous ammonium sulfate titration. The results obtained using this microwave system were also compared with those obtained by a closed reflux method described in the Standard Method. Experimental ApparatusA focused microwave system (Microdigest 3.6, Prolabo Corp.,

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