If a mass selected ion containing multiple isotopes of an element fragments by loss of a neutral containing the element, the product ions wiU be observed as multiple peals. This 'isotopic duster' of peals, although of a different appearance than those found in normal mass spectra, also indicates the isotopic composition of the precursor ion. I481 229 389 468The presence of multi-isotopic elements such as chlorine and bromine in a compound is recognized by the 'isotopic clusters" produced in its normal mass spectrum, such as that of hexabromobiphenyl, Fig. l(a). Mass spectra from the decomposition of mass selected ions, such as those resulting from metastable2 or collisionally activated (CA)3 decompositions, also can show characteristic isotopic clusters ( Fig. l(b)).Although the contrasting appearances illustrated by Fig. l(a and b) apparently have not been reported previously, the effect producing the polyisotopic clusters of Fig. l(b) is the same as that pointed out by Beynon and co-workers in CA mass spectra of ions containing one I3C atom? The main reason the effect has not been reported previously is that the reverse geometry instruments used for years to measure CA spectra often do not give sufficient resolution for such high mass ion clusters. New instruments giving unit -628mass resolution (or better) in both mass analyzers, such as the tandem quadrupole' or tandem double focusing MS/MS instrument: provide abundance data on the individual cluster peaks indicative of their isotopic content. The CA spectrum of Fig. l(b) was obtained6 by mass selecting [C12H479Br381Br3]" (m/z 628) from the corresponding m / z 622-634 isotopic cluster of hexabromobiphenyl molecular ions formed in the ion source, Fig. l(a), yielding the single peak in the CA spectrum, Fig. l

No abstract

No abstract

No abstract

No abstract