Isotopic signature

Carbon isotopes

For example, different sources and sinks of methane have different affinity for the ¹³C isotopes, which allows distinguishing between different sources by the ¹³C/¹²C ratio in methane in the air.

Similarly, carbon in inorganic isotope analysis of their flesh and bone collagen. Similarly, marine fish contain more ¹³C than freshwater fish, with values approximating the C4 and C3 plants respectively.

salt domes originates from carbon dioxide formed by oxidation of petroleum, which due to its plant origin is ¹³C-depleted.

The fossil fuels like coal or petroleum, where the ¹⁴C originally present has decayed below detectable limits. The amount of ¹⁴C currently present in a sample therefore indicates the proportion of carbon of biogenic origin.

Nitrogen isotopes

The ratio of ¹⁵N/¹⁴N presents a characteristic distinction between herbivores and carnivores, as the movement up along the food chain tends to concentrate the ¹⁵N isotope, by 3-4‰ with each step of the food chain (terrestrial plants, with the exception of legumes, has the isotopic ratio 2-6‰ of N). The tissues and hair of vegans therefore contain significantly lower percentage of ¹⁵N than the bodies of people who eat mostly meat. Isotopic analysis of hair is an important source of information for archaeologists, providing clues about the ancient diets; a terrestrial diet produces a different signature than a marine-based diet and this phenomenon has been used in analysing differing cultural attitudes to food sources.

Oxygen isotopes

Oxygen comes in two variants as well. The ratio of ¹⁸calcium carbonate secreting organisms, such sediments prove a chronological record of temperature and salinity of the water in the area.

Radioactive isotopes

Pu/²³⁹Pu are also different for fusion and fission nuclear weapons, which allows identification of hot particles of unknown origin.

Forensics use

With the advent of stable isotope ratio mass spectrometry, isotopic signatures of materials find increasing use in forensics, allowing disguising the origin of otherwise similar materials and tracking the materials to their common source. For example the isotope signatures of plants can be to a degree influenced by the growth conditions, including moisture and nutrient availability. In case of synthetic materials, the signature is influenced by the conditions during the chemical reaction. The isotopic signature profiling is useful in cases where other kinds of profiling, eg. characterization of impurities, are not optimal.

A study was published demonstrating the possibility of determination of the origin of a common brown PSA packaging tape by using the carbon, oxygen, and hydrogen isotopic signature of the backing polymer, additives, and adhesive[1].