Determination of isotope ratios for an element

Determination of isotopic abundance by mass spectrometry can give the geographic source of plant-based organic compounds or mineral compounds. Using the isotopic signature of a species leads to better precise results as the different dating methodologies based upon radioactivity. 

Isotope fractionation occurs during processes like evaporation or condensation and during chemical reactions. In the living world, isotopes of the same element can be differentiated by the biosynthetic pathways they follow. Furthermore, the rate at which a molecule crosses cellular membranes will depend of the molecule s isotopic distribution. For example, the isotopic ratio of natural vanillin is 

The detection of adulterated table oils, flavourings, limit juices as well as studies of plants metabolism and of numerous medical applications use isotopic abundance as an indicator. 

To evaluate variations in the ratio it is compared with an adopted 

In the presence of a mixture of two compounds A and B whose isotopic ratio distributions are respectively 5 and Sg, the experimental value for the total isotopic variation in the sample, results from the weighted combination of 5 and 8g. If x represents the fraction of B and (1 — x) the fraction of A, the following expression allows to calculate the percentages for A and B (16.27)  

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