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

Improved Method for the Flow Injection Analysis of Chemical Oxygen Demand Using Silver Nitrate

On the flow injection analysis (FIA) of chemical oxygen demand (COD), silver salt was added as an oxidation catalyst for COD substances and a masking agent for halide to improve operating conditions of the FIA apparatus. Both of a proper concentration of potassium permanganate solution and 6.0 % sulfuric acid solution containing 0.1 % silver nitrate are individually pumped up with respective flow rates of 0.51 ml min(-l) and merged into a carrier stream. A 20 μ1 of sample solution is injected into the flow of sulfuric acid solution at just before the merging place. The sample mixed with the carrier solutions in a reaction manifol(polytetrafluoroethylene tubing: 0.5 mm i.d. x 30 m), is passed through a thermostated bath at 100 °c and led to a flow cell for the absorbance measurements at 525 nm. The absorbances are continuously recorded with time. The peaks in the recordings showed good reproducibility and the calibration obtained at a linear concentration range of 0 - 170 mg 1(-1) COD with glucose as standard. The detection limit and precision confirmed with this method were 5 mg 1(-1) and 0.8 %, respectively. Chloride ion up to 200 mg 1(-1) did not interfere without elimination of a silver chloride precipitate. By the present FIA method, several industrial waste water samples were analyzed at a sampling rate of about 40 samples per hour, and their apparent COD values were compared with those found by the manual JIS method. Both of the methods gave the similar results within an error range from -35 to +5 %