Determination of the Natural Abundances of the Stable Isotopes of 15 N and 13 C by Mass Spectrometry: A Simplified Manual Method for the Preparation of N 2 and CO 2

Small variations in the natural abundance of stable isotopes are becoming widely acknowledged as important in explaining both ecosystems and physiological processes, but there are considerable technical problems of sample preparation. Conflicting claims for precision also confuse the potential user. To recover both N2 and CO2 from samples of plant tissues, we use a combustion method which is simpler than some previously described methods in that: 1 It uses a relatively low vacuum in the preparation line. 2 It uses activated charcoal for capturing N2. 3 It does not require separate freezing of CO2 and