Quadrupole storage mass spectrometry of mono- and dimethylalkanes

Monomethyl and dimethylalkanes with one, two, three, four, five, and seven methylene groups separating the methyl branches were synthesized and analyzed by magnetic sector and quadrupole storage (ion trap) mass spectrometry. The spectra produced by the magnetic sector instrument were in good agreement with previously reported data, whereas the ion trap spectrometer produced ions resulting from cleavages adjacent to the branching points, markedly different than those from the magnetic sector instrument. Fragmentation patterns show that the ion trap mass spectrometer can be used to characterize branched alkanes in nanogram and subnanogram quantities.