Continuous flow instrumentation for the automated measurement of ammonium and nitrate was developed at University of California, Davis. The method has been refined and adapted for routine analyses. Soil samples are extracted in 2N KCl and the extracts are mixed with an alkali solution to liberate ammonia (NH3). The instrument has two channels for simultaneous measurements of ammonia and nitrate. Reduction of nitrates to ammonia takes place in one channel. The amount of ammonia in each channel is then measured by a diffusion-conductivity method in which the ammonia gas is diffused through a micro-porous Teflon tube and then redissolved in water to form ammonium hydroxide. The measured conductivity of the ammonium hydroxide is directly related to the ammonium content of the samples. The method is both rapid and reliable.
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