1982 Volume 31 Issue 9 Pages 517-523
A useful and sensitive system has been developed for the fully automated flow injection analysis by connecting a cheap commercial personal computer. The system has successfully been applied to continuously measure the micro amount of chemical oxygen demand (COD) in river waters. Both a potassium dichromatesulfuric acid solution and water are separately pumped up with a double reciprocating micro-pump. A 500 μl sample is injected into the flow of water with an automatic sample injector, and the solutions are merged into a carrier stream. The COD substances in samples are oxidized by dichromate for 20 min in a reaction manifold, made of poly (tetrafluoroethylene) tubing (0.5 mm i. d. × 50 m) and heated at 120 °C. The resulting solution is led into a spectrophotometric detection at 445 nm. COD values are automatically measured with this computer system by directly analyzing absorbance data, obtained via an interface unit having an analog/digital converter from the spectrophotometer. The BASIC can easily be used for computer programing. D-Glucose was used as a standard substance for calibration curves using peak heights or peak areas. A sampling rate of 10 samples h-1 could be achieved, and the detection limit and precision were 0.5 mg l-1 and 2 %, respectively. For river water samples at a COD level of (12) mg l-1, COD values obtained from peak heights were comparable to those obtained with the Japanese standard method.
