Direct isotope dilution analysis with a radioactive

2 Direct isotope dilution analysis with a radioactive label 

In these types of isotopic analyses, the same compound as that to be measured is used where one of the atoms in it has been replaced by a radionuclide. 

To measure a molecular compound X present in a sample, a quantity of the labelled compound X (the reference tracer) is added to a precise quantity of the sample. The specific activity (see Section 17.5) of this tracer is represented by Aj (activity in Bq per unit of mass) whUe A is the specific activity after dilution and calculated from a very small aliquot of the spike sample isolated by a fractionation technique as recrystallization or chromatography 

Ax is smaller than Aj because the quantity of (the tracer implemented) is mixed with the quantity wjx of non-labelled compound. On the other hand, the overall activity is conserved, which is translated by the following expression  

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