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Nitrogen and Nitrogen-15 Analysis Using Automated Mass and Emission Spectrometers

Technical Advisory Committee Secretariat, FAO, Via delle Terme di Caracalla, 00100 Rome, Italy

D. L. Eskew

Plant Molecular Genetics, Univ. of Tennessee, Knoxville, TN 37901

* Corresponding author.

ABSTRACT

Analysis of large numbers of samples has been a major limitation in the use of ¹⁵N. Two new instruments—an automatic N analyzer coupled to a mass spectrometer (ANA/MS), and a microprocessor-controlled emission spectrometer (NOI-6e)—were therefore compared with a longer established procedure of the International Atomic Energy Agency Laboratories involving ¹⁵N analysis with a Micromass (MM) 602E mass spectrometer. For 10-mg plant samples ranging from natural abundance (NA) to 1.341 atom % ¹⁵N, the ANA/MS agreed with the MM 602E to within 0.002 atom %, and the NOI-6e to within 0.014 atom %. In the range 1.895 to 2.398 atom %, data from the ANA/MS and the NOI-6e agreed with the MM 602E within 0.022 and 0.093 atom %, respectively. Relative standard deviations (RSD) for six replications of a NA plant sample were: MM 602E, 0.22%; ANA/MS, 0.47%; NOI-6e, 2.3%. For a plant sample with 2.398 atom % ¹⁵N the RSDs were: MM 602E, 0.03%; ANA/MS, 0.08%, and NOI-6e, 0.3%. With finely ground soil samples (40 mg, 0.449 atom %) the RSD for ¹⁵N analysis with the ANA/MS was 0.30%. The ANA/MS was comparable to the Kjeldahl method (500-mg samples) for plant N analyses and was found suitable for routine ¹⁵N analysis of plant and soil samples, but additional care in sample grinding was needed. The NOI-6e analyzed ¹⁵N samples in one-tenth the time required with previous emission spectrometers and its precision would be adequate for many agricultural experiments. The lower precision is a limitation, however, for measuring the ¹⁵N content in soil samples.

Contribution of the Joint FAO-IAEA Programme, IAEA Laboratories, A-1400 Vienna, Austria, and the Australian Centre for International Agricultural Research, Canberra, Australia.

Received for publication February 21, 1990.