Semiautomated Determination of COD in Environmental Water Samples

A new method based on the principle of flow injection analysis is presented for the semiautomated determination of chemical oxygen demand (COD) in environmental water samples. The method is rapid and continuous, and suitable for the monitoring of COD in wastewaters. The apparatus used was simply constructed by parts commercially available for high performance liquid chromatography. Teflon tubing heated with a boiling water was used as a reactor and simultaneously used for mixing coils and transmission lines. The operating conditions were examined to apply the determination of COD in wastewaters by using glucose as a standard COD substance. The procedures recommended are as follows: Both 4.9x10(-4) M potassium permanganate and 6.7 % sulfuric acid solutions are individually pumped, 20 μl of a sample solution is injected into the flow of the sulfuric acid solution, and then mixed with a mixing joint. The mixed solution is transported to a flow cell situated in a spectrophotometer fixed at a wavelength of 525 nm, and decrements of absorbance are recorded. The peaks were reproducibly obtained at a concentration range of 10 - 200 mg-COD 1(-1). Chloride up to 1000 mg 1(-1) was not interfered at all. Various wastewater samples were analyzed by the proposed method at a sampling rate of 30 samples per hour, and the apparent COD values obtained were compared with the manual COD ones obtained by JIS method.