Jan Kaiser, How accurate do we know 13C/12C, 18C/16O and 17O ...
Jan Kaiser, How accurate do we know 13C/12C, 18C/16O and 17O ...
Jan Kaiser, How accurate do we know 13C/12C, 18C/16O and 17O ...
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<strong>How</strong> <strong>do</strong> <strong>we</strong> measure carbon <strong>and</strong> oxygen<br />
isotope ratios with mass spectrometers?<br />
Measure ion current ratios of sample relative to reference<br />
(NBS 19-CO 2 as st<strong>and</strong>-in for VPDB-CO 2 )<br />
m/z 44 12 C 16 O<br />
+<br />
2<br />
m/z 45 13 C 16 O<br />
+<br />
2<br />
12<br />
C 17 O 16 O +<br />
m/z 46 12 C 18 O 16 O + 13 C 17 O 16 O + 12 C 17 O<br />
+<br />
2<br />
45<br />
δ I<br />
=<br />
45<br />
I/<br />
I /<br />
45<br />
r<br />
44<br />
44<br />
I<br />
I<br />
r<br />
−1<br />
We assume that all minor isotopologues have the same<br />
relative ionisation efficiency. Then, the ion current delta<br />
is the same as the isotopologue delta.<br />
45 45<br />
δ I<br />
= δ<br />
=<br />
45<br />
R/<br />
R /<br />
45<br />
r<br />
44<br />
44<br />
R<br />
R<br />
r<br />
−1
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