Commercial or in-house libraries are applied for confirmation or to build MRM methods. However, CID shows limitations with regard to the number and the specificity of the fragments for a given analyte, which depends on the collision energy. This can challenge the unambiguous identification of known analytes or characterization of unknowns. The use of orthogonal activation techniques, such as electron activation dissociation or ultraviolet photodissociation, in the same LC run for additional structural information would be, therefore, of interest. UVPD, on the other hand, is based on photon absorption at chromophores, causing fragmentation near the absorption site, direct dissociation, or at weaker points along the molecule via internal vibrational redistribution . However, these mechanisms can lead to diverse fragments.