Transcript Technical Supplement 2A. figures.ppt

Fig. A. Relationships between d values and atom %13C. Top: natural abundance range of d values that correspond to
about 1.08 to 1.12%13C. Bottom: larger range of atom % values, 0-10%13C, corresponding to a larger range in d values.
Note that no 13C (% 13C = 0) corresponds to -1000o/oo d value (see text for explanation). Isotope depleted samples thus
have a lower limit (-1000o/oo), but isotope enriched samples have no upper limit, as evident in the next figures.
Fig. B. Relationships between d values and atom %13C, continued. Top: larger range of atom % values, 050%13C. Note the relationship between atom % and d starts to become visibly non-linear at higher enrichments.
Bottom: largest range of atom % values 0-100%. At high enrichments >90% 13C, d and atom % are related in a
very non-linear fashion.
Fig. C. Nitrogen isotopes in N2 gas samples at different 15N enrichments. Modern mass spectrometers collect three
isotopomers (isotope varieties) of N2 that have masses 28 (14N14N), 29 (15N14N and 14N15N) and 30 (15N15N). In
natural samples, most N is 14N with only small amounts of 15N, so most N2 exists as mass 28 with minor amounts as
mass 29 and very, very minor amounts as mass 30. However, this can change when scientists start adding 15N to
samples, increasing the fraction that is 15N while simultaneously decreasing the amount that is 14N. Eventually, when
there is no 14N, all N is present as mass 30. At intermediate mixtures of 14N and 15N, both masses 29 and 30 are
important carriers of 15N and both these masses need to be measured and considered when keeping track of 15N
amounts.
Fig. D. Nitrogen isotopes in N2 gas samples at different 15N enrichments, continued from previous Fig. 2.6. Top:
In most usual d measurements, only the mass 28 (14N14N) and mass 29 (15N14N) isotopomers are considered,
because the mass 30 (15N15N) contributions are very, very minor. But at higher 15N enrichments, considering only
masses 28 and 29 will underestimate actual amounts of 15N, as shown in the previous Fig. 2.6. The problem is
that much 15N is in mass 30 for enriched samples, and this is ignored in most d calculations. Bottom: Estimated
error in d for enriched samples when mass 30 is ignored.
Fig. E. Correction factors (o/oo) for d values measured at relatively small 15N enrichments, <2000o/oo. For
example, at 1% 15N (about 1750o/oo d15N), one needs to add about 8.8o/oo to the normal measured d value to
obtain the correct d15N value, when the normal d value is calculated from the mass 28 and mass 29 ion
beams without including the mass 30 ion beam.