John R. Barr*
, Hercules Moura*, Anne E. Boyer*, Adrian R. Woolfitt*, Suzanne R. Kalb*, Antonis Pavlopoulos*, Lisa G. McWilliams†, Jurgen G. Schmidt‡, Rodolfo A. Martinez‡, and David C. Ashley*
Figure 3. High-performance liquid chromatography–electrospray ionization-tandem mass spectrometry chromatogram showing the botulinum neurotoxin (BoNT)-A substrate and product ions (CT, C-terminal; NT, N-terminal) from a reaction with 25 mouse lethal dose (MLD)50 BoNT-A. Each peptide has both a quantification ion (top trace) and a verification ion (lower trace). Isotopically labeled standards are added (traces not shown) as internal standards for quantification. The labeled peptides co-elute with their nonlabeled counterparts and are distinguishable by mass. Leucine enkephalin was included as a secondary reference compound and only 1 ion was monitored.