Atmosphere Level

Canopy Level

Leaf Level

Soil Level

Mass spec.

References

Mass Spectograph

Stable isotope concentrations of many biologically significant elements are measured by a large machine which performs gas isotope-ratio mass spectroscopy. Following is a very simple schematic of the concept behind gas isotope-ration mass spectroscopy for more details about the machines and the techniques of preparing material as well as their application a good book is Methods in Ecosystem Science. But in the meantime:

1. First, a carefully prepared sample is converted into a gas i.e. CO₂ which is ionized by the ion source (fig. 1) which makes each molecule positively charged.

2. These charged molecules are then sent through the flight tube. The bent flight tube has a magnet over it so that the charged molecules separate by their masses.

3. Heavier isotopes (i.e. ¹³C) bend less then lighter isotopes (i.e. ¹²C).

4. The molecules then hit Faraday collectors which have been calibrated to sense the differences in bend of each of the isotopes of interest, count the number of hits and give an R value. The process from there is described here.

(http://jan.ucc.nau.edu)