Determination of low chemical oxygen demand values in water by the dichromate semi-micro method

Authors:
  • JHJosef Hejzlar
    Josef Hejzlar
  • JKJiří Kopáček
    Jiří Kopáček
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Abstract
A semi-micro modification of the dichromate method for the determination of low concentrations (1–35 mg l–1) of the chemical oxygen demand is described. It is based on the experimentally established dependencies of the oxidation efficiency on the concentrations of H2SO4, K2Cr2O7 and Ag2SO4, and on the temperature and time of heating. The procedure involves increasing the concentration of H2SO4 and heating in closed test-tubes in a heating block at 170 °C for 40 min and the spectrophotometric determination of dichromate at 455 nm. The interfering effect of chloride, up to a concentration of 100 mg l–1, is masked by using a combination of HgSO4 and KCr(SO4)2. The modification has been tested on 30 samples of ground, tap, precipitation and surface waters and on 16 chemical compounds, and gives results comparable to those from a standard reflux method.