Comparison of various methods for the determination of total N in liquid effluents

A high temperature catalytic oxidation method (HTCO) was used to determine total dissolved nitrogen in different liquid effluents produced by agro-industry.This technique consists of catalysed combustion of the sample by direct injection in a furnace at 900 °C.Results obtained by HTCO were then compared with those determined by the Kjeldahl digestion method (TKN) and the dry combustion method (DCM) for freeze-dried effluents.The results obtained by HTCO within a concentration range of 10 to 800 mg N L -1 , were in good agreement with those obtained by TKN.Comparison with DCM method revealed large discrepancies which were probably due to the poor precision of this method and to the ammoniac-N losses occurring during the freeze-drying of samples.