The Bremner Contribution to N-15 Isotope Ratio Analysis.

Jack Bremner started work at Iowa State in 1959 on an ‘inherited mass spectrometer’ to carry out research to improve the methodology of ¹⁵N analysis. In the early 1960s he showed that both the amount of NH₄ and the time required for isotope-ratio analysis of NH₄ could be greatly decreased by modification of the techniques normally required for this analysis. It was possible to obtain accurate and precise isotope-ratio values with as little as 40µg of NH₄-N and to perform more than 50 ¹⁵N analyses in a normal working day. The most important advance in ¹⁵N-tracer methodology since that time has been the development of automated mass spectrometers and optical emission spectrometers for ¹⁵N analysis. Jack carried out this research on ‘Determination and isotope-ratio analysis of different forms of nitrogen in soils: 1-7’, with Art Edwards (1965), H.H. Cheng (1966),  Dennis Keeney (1966, 1967), and J. Silva (1966). The ¹⁵N-tracer work was continued with papers by Darrell Nelson (1968, 1970), Ali Tabatabi (1969, 1978), and Roland Hauck (1976, 1982). A concluding statement in one of Jack’s papers states: “It should be pointed out that even if it were possible to determine the δ ¹⁵N of the nitrate derived from every nitrate-producing surface soil and subsoil in a region under study, it would still be impossible to calculate a reliable δ ¹⁵N value for soil-derived nitrate entering surface water in this region. Calculation of this value would require information that is impossible to obtain, including the percentage contribution of each surface soil and subsoil in the study region to the nitrate entering the surface water.”