The Kjeldahl method in analytical chemistry is a method for the quantitative determination of nitrogen contained in organic substances plus the nitrogen in inorganic ammonia and ammonium (NH 3 /NH 4 + ). Other forms of inorganic nitrogen, for instance nitrate , are not included in this measurement. This method was developed by Johan Kjeldahl in 1883 The method consists of heating a substance with sulphuric acid , which decomposes the organic substance by oxidation to liberate the reduced nitrogen as ammonium sulphate . In this step potassium sulphate is added to increase the boiling point of the medium (from 337 °C to 373 °C) . Chemical decomposition of the sample is complete when the initially very dark-coloured medium has become clear and colourless. The solution is then distilled with a small quantity of sodium hydroxide, which converts the ammonium s...
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