Correction factors are available in most C14 texts.A table showing isotopic fractionation of different substances in nature is shown here.
Fractionation also describes variations in the isotopic ratios of carbon brought about by non-natural causes.
For example, samples may be fractionated in the laboratory through a variety of means.
A d13C value, then, represents the per mille (part per thousand) deviation from the PDB standard.
PDB refers to the Cretaceous belemnite formation at Peedee in South Carolina, USA.
The extent of isotopic fractionation on the 14C/12C ratio which radiocarbon daters are seeking to measure accurately, is approximately double that for the measured 13C/12C ratio.
If isotopic fractionation occurs in natural processes, a correction can be made by measuring the ratio of the isotope 13C to the isotope 12C in the sample being dated.Recall that atoms are the basic building blocks of matter.Atoms are made up of much smaller particles called protons, neutrons, and electrons.The ratio is measured using an ordinary mass spectrometer.The isotopic composition of the sample being measured is expressed as delta13C which represents the parts per thousand difference (per mille) between the sample carbon 13 content and the content of the international PDB standard carbonate (Keith et al., 1964; Aitken, 1990).Scientists use a technique called radiometric dating to estimate the ages of rocks, fossils, and the earth.