In light of the similar retention times, we were not completely
sure of the ink identity without MS. The use of LC–MS offers
additional information to identify counterfeit notes as well as the
possible structures of each dye component (for some compounds
with determined fragmentation patterns, their exact structures
could be identified) and their relative contents. This markedly
enhances the ability to identify the ink used in the counterfeit
notes. Therefore, in addition to the use of HPLC for the systematic
analysis of the various-color graphic inks on the counterfeit notes
that were seized from different locations, structural analysis of the
main dyes used in the inks was performed with LC–MS.