Determination of Nitrogen by Microdiffusion in Mason Jars: III. Nitrogen and Nitrogen-15 in Kjeldahl Digests

Diffusion methods for quantitative determination and isotope-ratio analysis of inorganic N in soil extracts were modified for use with Kjeldahl digests. The digest was diluted to 25 mL with deionized water, and an aliquot (to 6 mL) was transferred in a shell vial (17 mm dia., 60 mm long) to a 473-mL (1-pint) wide-mouth Mason jar containing 15 mL of 8 M NaOH. The NH₃ liberated by overturning the vial inside the sealed jar was collected for 48 h at room temperature (24 h with orbital shaking) in 3 mL of boric acid-indicator solution in a Petri dish, or in an acidified glass-fiber disk, suspended from the Mason-jar lid. Determinations of N and ¹⁵N by diffusion were in close agreement with analyses using conventional steam-distillation and concentration techniques.