Isotopic Signatures

Synonyms

Isotopic fingerprinting

Definition

An isotopic signature (also isotopic fingerprint) is a ratio of stable or unstable isotopes of particular elements found in an investigated material. The atomic mass of different isotopes affects their chemical kinetic behavior, leading to natural isotopic separation process.

Expression

Stable isotope ratios are normally reported as δ values in units of parts per thousand (denoted as ‰, i.e., per mill) relative to a standard of known composition.

$$ {\delta} = \left( \text{R}_{\text{sample}} - \text{R}_{\text{reference}} \right) \left/ \text{R}_{\text{reference}} \right.$$

where R’s are the ratios of the¹⁸O/¹⁶O and D/H isotopes in case of water.

The difference between samples and references are usually quite small, δ values are, therefore, expressed in per mille differences (‰), that is, per thousand, δ(‰) = δ × 1,000.

$${{\delta }}\left( \text {}^0 /_{00} \right) = \left[ {{{{\left( {{{\text{R}}_{\text{s}}} - {{\text{R}}_{\text{r}}}}...