Fig. 8
From: A European proposal for quality control and quality assurance of tandem mass spectral libraries
An example of near identical tandem mass spectra: phentermine- and methamphetamine spectra acquired on a QqTOF instrument. The spectra were taken from the WRTMD. Black dots indicate precursor masses that triggered the MS/MS spectra (hollow dot). At higher collision energy levels, the fragmentation mass spectra of these constitutional isomers show two identically-intense fragment ions, leading to ambiguous library search results. Cases such as these demonstrate that library matching has to be complemented by orthogonal information such as retention time for higher identification confidence