Stable Isotopes – General principle

It is well known that the elements occur in various forms, which differ only in the numbers of neutrons called isotopes. Most of them are radioactive but some heavy isotopes are stable as well. The building blocks of life – hydrogen, oxygen, carbon, nitrogen and sulphur – exist in various heavy forms, which are notified as stable isotopes. The ratio of these isotopes to one another differs from material to material and from region to region. Therefore, the stable isotope method is a universal, non-radioactive analytical tool to test the authenticity e.g. the origin, food webs (including feeding conditions) and adulteration. In detail, there is a well-known pattern of ²H/ ¹H and ¹⁸O/¹⁶O in the meteoric water as well as in the ground water. Every material including plants and animals gets a significant fingerprint in the tissue water depending on the local tap water. The pattern of ²H/¹H and ¹⁸O/¹⁶O in the meteoric water depends mainly on temperature, landscape altitude and distance from the sea (continental effect). Adding the remaining stable isotopes of the elements of life (C, N, S) further information is available. Soils show different isotope ratios of ¹⁵N/¹⁴N and ³⁴S/³²S depending firstly on the natural geological composition and secondly on the cultivation. For example, the isotopic composition of fertilizers varies from their type (organic nitrogen or synthetically produced from air nitrogen, sulphur of volcanic or biological origin). Finally, the ¹³C/¹²C isotope ratio of plants depends on the type of metabolism and of local climatic conditions. In result plants as maize (C4-plants) show different ¹³C/¹²C ratios to wheat (C3-plants).
Plants implement these isotope signatures in their organic tissue; afterwards those signatures will be transferred to animals via food web. These stable isotopic signatures deliver various information of the geographical origins of the plants and animal products (e.g. meat, eggs, milk), the feeding conditions (proportion of maize) and the organic status.
As an addition, the strontium isotopes (⁸⁷Sr/⁸⁶Sr) show potential to describe the geological age of the soil, which show us a link for the origin of food products as well. Still yet, the analytical price of strontium isotopes is high. Therefore, it is normally used as an additional parameter.

Reliability of the stable isotopic results

Stable isotopic methods are recognized and accepted in court cases^[1] and recommended in various international guidelines for tracking the origin of products. For instance, they are referenced in the UNDOC guidelines for ivory and EU guidelines for timber tracking.

[1] Camin F. Boner M. et al (2017) Stable isotope techniques for verifying the declared geographical origin for food in legal cases. Trends in Food Science & Technology. 64, 176-187.

Limitations of isotope analysis

While stable isotopic analysis provides valuable information about origin, agricultural growing conditions, feeding and environmental conditions, it has its limitations. The method relies on established reference data, and while these can be refined, there may be other locations with similar isotopic signatures. Thus, while it is possible to confirm with high probability whether a sample matches reference data, there may be exceptions. This exclusion principle can be strong enough to challenge the validity of origin claims but should be used with the understanding of its inherent limitations.

Our Technology

Agroisolab is using various isotopic mass spectrometers and is one of the largest stable isotopic laboratories in the world.
In order to achieve a high reproducibility and linearity of the measurement results, we use the best isotope mass spectrometers in the market currently available from NU Instruments, because only that company use a powerful method in which the mass beams can be extra focused separately on the triple mass detector before detection.
In combination with our patented high-hemperature-hardware working on a temperature of 1550 °C in pyrolysis and our unique Zero-Blank-Revolver-Autosampler with heated sampling chamber, Agroisolab offers a unique potential to measure isotopes like hydrogen or oxygen in organic.