Representation of Isotopic Abundances

Isotopic abundances are listed either as their sum being 100% or with the abundance of the most abundant isotope normalized to 100%. The latter is used throughout this book because this is consistent with the custom of reporting mass spectra normalized to the base peak (Chap. 1). The isotopic classifications and isotopic compositions of some common elements are listed below (Table 3.1). 

Bar graph representations are much better suited for visualization of isotopic compositions than tables, and in fact they exactly show how such a distribution would appear in a mass spectrum (Fig. 3.1). This appearance coined the term isotopic pattern. 

Note Some authors use the term isotopic cluster, which is incorrect, as cluster refers to an associate of more atoms, molecules, or ions of the same species, sometimes associated with one other species, e.g., [Ar ] , [(H20) H], and [I(CsI) ] are cluster ions. 

Classifi- Atomic Atomic Mass Isotopic Isotopic Relative 

Note Care has to be taken when comparing isotopic abundances from different sources as they might be conpiled using one or the other procedure of normalization. Never mix normalization modes in your calculations  

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