Measuring Stable Isotopes

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What are isotopes?

Isotopes are atoms with the same number of protons and electrons but have different number of neutrons. This gives them different atomic weights for the same atomic number.

Stable isotopes do not degrade or decay over time, unlike an isotope such as C14 used in radiocarbon dating.

How are stable isotopes measured?

The isotopes of an element chemically behave very similarly to each other, although they will fractionate during certain processes. The end result is a shift in the isotopic ratio. It can tell you about where the material is from, what processes it has gone through, and to what extent it has changed.

The isotopic ratio is measured using an isotope ratio mass spectrometer (IRMS). There are two main types, or modes, of IRMS, dual inlet (DI) and continuous flow (CF) each with their own advantages to different applications. Stable isotope ratios are expressed in delta values relative to international scales. To calculate the ratio of an unknown sample you must compare it to a known reference.

The Stable Isotope Laboratory performs stable isotope analysis for carbon, nitrogen, sulphur, oxygen and deuterium by mass spectrometry.

This can be applied to many applications, such as geology, archaeology, environment, paleoclimate, food adulteration and agricultural research.