Use of diffusion to determine inorganic nitrogen in a complex organic matrix

Serious interference can arise in carrying out quantitative or isotopic analyses of inorganic N in samples having a high content of labile organic N. Studies to evaluate existing Mason jar diffusion methods for interference by a high concentration of various amino acids and amino sugars showed the need to minimize the diffusion period. This was accomplished by increasing the volume of H3BO3-indicator solution (to 7 mt). and by carrying out diffusions from a fixed volume (10 mt) with a high salt concentration (4 M KCI), Quantitative recovery (greater than or equal to 98%) of 4 mg of NH4-N was achieved in the presence of 10 mg of organic N, either in 18 h at 25 degrees C, or in 1.5 h by heating on a hot plate at 45 to 50 degrees C, Under the same conditions, complete recovery of NO3-N and NO2-N was achieved in the presence of 4 mg of organic N by increasing the amount of Devarda's alloy from 0.3 to 1.5 g, The modified diffusion methods were much more accurate and precise than conventional steam distillation techniques for inorganic N analysis of animal waste or other complex samples treated with labeled NH4-N, NO3-N, or NO2-N. Recovery of the labeled N by diffusion ranged from 96 to 107%, and the coefficient of variation was usually <2%. The isotopic analyses from these diffusions were usually accurate to within 4%, as determined by isotope-dilution calculations. The latter finding provides ample evidence that no interference arises from labile organic N.