Determination of total nitrogen in sediments by using high-pressure bombs and ion chromatography

Abstract

The standard method for the determination of organic nitrogen in water samples has in the past been based on Kjeldahl's digestion technique which determines nitrogen in the triply negative state. In the presence of sulfuric acid, potassium sulfate, mercuric sulfate and a catalyst, amino nitrogen is converted to ammonium sulfate. Free ammonia and ammoniacal nitrogen are also converted to ammonium sulfate which can be determined spectrophotometrically, or by titration with a standard mineral acid. However, this method is time consuming and the accuracy is variable. An alternative method for the determination of organic nitrogen is the alkaline persulfate digestion technique which oxidizes all the nitrogen in the sample to nitrate as the sole product using potassium persulfate in a strongly alkaline environment under high pressure and temperature. In this paper, a methodology for total nitrogen determination in sediments is developed using 23 ml high-pressure bombs with potassium persulfate and sodium hydroxide. The determination of nitrogen as nitrate was made by using ion chromatography. Urea was used as the nitrogenous compound to calibrate the methodology, which was checked using the Kjeldahl method and showed good agreement.