Isotopic pattern polyisotopic elements

Example The presence or absence of the polyisotopic element tin (Table 3.1) can readily be detected from its characteristic isotopic pattern. In case of tetrabutyltin, Ci6H3gSn, the lowest mass isotopic composition is CieHse Sn, 340 u. Due to the 16 carbon atoms, the isotopic abundance is about 17.5 %. This is superimposed on the isotopic pattern of elemental Sn, which becomes especially... 

Even if the analyte is chemically perfectly pure it represents a mixture of different isotopic compositions, provided it is not composed of monoisotopic elements only. Therefore, a mass spectrum is normally composed of superimpositions of the mass spectra of all isotopic species involved. [11] The isotopic distribution or isotopic pattern of molecules containing one chlorine or bromine atom is listed in Table 3.1. But what about molecules containing two or more di-isotopic or even polyisotopic elements While it may seem, at the first glance, to complicate the interpretation of mass spectra, isotopic patterns are in fact an ideal source of analytical information. 

The treatment of polyisotopic elements does not require other techniques as far as calculation or constmction of isotopic patterns are concerned. However, the appearance of isotopic patterns can differ largely from what has been considered so far and it is worth mentioning their peculiarities. 

In conventional mass spectra the isotope patterns deriving from the presence of polyisotopic elements are striking and quite noticeable. An excellent example is the ESP spectrum shown in Figure 17 for a compound with a C14H12NOFCI2 empirical formula. The zw/z 300 [M -I- H]" " and the m/z 269 neutral loss fragment (resulting from neutral loss of methylamine) clearly show CI2 isotope patterns which match well with simulations. The zzz/z 234... 

The characteristic abundance patterns resulting from the combination of more than one polyisotopic element can be calculated from the relative abundances of the different isotopes. The following polynomial expression gives the isotope distribution of a polyisotopic molecule ... 

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