COMPARISON OF COMBUSTION AND KJELDAHL METHODS FOR DETERMINATION OF NITROGEN IN OILSEEDS

The recent development of combustion-type nitrogen analyzers capable of handling relatively large samples with semi-automatic operation offers a potential replacement for the Kjeldahl method for direct determination of nitrogen. Nitrogen analyses for canola seed, flaxseed, sunflower seed, mustard seed and soybeans on a LECO (St. Joseph, MI) FP-428 Nitrogen Analyzer were evaluated against results from the Grain Research Laboratory's (GRL) Kjeldahl system. The nitrogen analyzer gave significantly higher values than the Kjeldahl method, resulting in a correction of low values in the GRL Kjeldahl, caused by the inability to use mercury as catalyst. The standard error for results from the analyzer was comparable to that for the Kjeldahl method. The nitrogen analyzer also was faster than the Kjeldahl method and has less environmental impact. The combustion method has replace the Kjeldahl method for routine nitrogen determinations in oilseed surveys conducted by the GRL.