Improved diffusion methods for determination of inorganic nitrogen in soil extracts and water

Diffusion methods previously developed for inorganic-N analysis of soil extracts were modified to improve reliability, increase the dynamic range, extend the scope of applications. and simplify the processing of samples for N-isotope analysis. In these methods, the soil extract is treated with MgO, or MgO plus Devarda's alloy, in a 473-ml (1-pint) wide-mouth Mason jar to convert NH4+-N, NO3--N, and/or NO2--N to NH3-N. The NH3 thereby liberated is collected in H3BO3-indicator solution in a Petri dish suspended from the Mason-jar lid and determined quantitatively by acidimetric titration. With the modifications described, analyses can be performed on 10- to 100-ml samples of water, 0.5 M K2SO4, 1 M KCl, 2 M KCl, or 4 M KCl, at temperatures between 20 and 30 degrees C. Recovery from 10 or 20 ml was quantitative in 18-80 h with up to 4 mg N; recovery from 50 or 100 ml was quantitative in 3-13 days with up to 2 mg N. Removal of H3BO3 for N-isotope analysis by the Rittenberg process was effected using methanol. Mason-jar diffusion methods are much simpler and more convenient than conventional steam distillations. Comparative studies showed that quantitative determinations are more accurate and precise by diffusion than by distillation.