RESEARCH ON AUTOMATION OF A REDUCTIVE DISSOLVED ORGANIC NITROGEN ANALYZER

The accurate classical batch method of Duursma (1961), based on the co nversion of Dissolved Organic Nitrogen (DON) into NH3, is used as a ba sis for a new automatic DON analyser. After testing different possibil ities through mechanical automation of the original batch technique, i n which the conversion is preceded by the degassing of NH3 and drying of the sample, the procedure of autoanalyses has been selected. This p rocedure was simplified to the extent that a compact unit could be con structed, which would easily be applicable on board ship. The automati c method has a conversion phase in which in principle only DON is diss ociated to NH4+, whereas both NO2- add NO3- are not reduced. This requ ires selective conditions and particularly high silver purity for the reactor. Consequently, a total reduction, including NO2- and NO3- is a lso possible, applying an efficient metal catalyst. Using distilled wa ter, the accuracy of the method is at the level of 3 mu M (0.05 mg N/l ), whereas the percent conversion of DON into NH3 is estimated between 80 and 100%, depending on the applied reference compounds. The method is applicable to both fresh and sea water.