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SIRA boils down to one simple idiom - you are what you eat.
It may be obvious to some, but everything from wood to beef is made up of the elements they eat/consume. These elements have stable isotopes that are location-specific analysing them allows our scientists to decode where produce originated from.
Take water for example. Water is made up of hydrogen and oxygen. Both hydrogen and oxygen have heavier versions that are stable isotopes (i.e. they have not decayed since they were formed billions of years ago!). There are different amounts of heavy hydrogen and heavy oxygen in water depending where you are in the world.
The amount of heavy hydrogen, also known as Deuterium or 'D', varies from place to place.
For example in the middle of the ocean, roughly 1 hydrogen atom in every 6240 atoms would be heavy hydrogen. In Scotland, this ratio would be very different as there is less heavy hydrogen in Scottish water.
In the South of England there is more heavy hydrogen in the water than there is in Scotland. Elsewhere the ratio of Deuterium to Hydrogen would be different again. We can exploit this natural variation as a tool to track organic materials (e.g. food, timber, clothing).
For meat samples we typically analyse up to 8 signatures per sample, the more signatures that are known to correlate with geography/provenance, the better the resolution the results have.
Some products, such as bottled water, do not require as many signatures for origin authentication.
SIRA results are taken from Isotope Ratio Mass Spectrometry (IRMS). Food/products are chemically broken down, injected into a mass spectrometer (see right) and the relative abundance of its constituent stable isotopes are measured by their deflection through a magnetic field.
The abundance of the products' stable isotopes is compared to a standard. For water this is Vienna Standard Mean Ocean Water (VSMOW). Results are expressed as a parts-per-thousand ratio (units = ‰).