Automated Nitrogen-15 Analysis of Ammonium in Diffusion Disks by the Rittenberg Technique
1992
Liu, Y. P. | Mulvaney, R. L.
A recent development in ¹⁵N analysis of inorganic N in soil extracts involves diffusion of NH₃ into acidified glass-fiber disks in disposable specimen containers. A simple and convenient technique was developed for isotope-ratio analysis of the NH₄ in these disks using a mass spectrometer equipped with an automated Rittenberg apparatus (ARA-MS). For collection of diffused NH₃, the disks were treated with 10 µL of 1 M H₂SO₄. Following diffusion for 6 d, the disks, containing 50 to 150 µg of N, were transferred to a disposable plastic sample tray (96 wells per tray) and treated with 10 µL of 28.9 M (concentrated) HF, which digested the disks without affecting the tray. The tray was placed in a desiccator containing anhydrous CaSO₄, for drying of the digested disks in 1 to 3 d. Good agreement was obtained between ¹⁵N analyses of diffused and nondiffused NH₄-N when correction was made for isotopic dilution by NH₄ in the reagents used in diffusion. Trays containing the processed disks can be conveniently shipped to a service laboratory for analysis by ARA-MS. This study was a part of Project ILLU-15-0392, Illinois Agric. Exp. Stn.
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