Activation of oligonucleotide polyanions using collisions, electrons and photons in a timsOmni platform

We describe here various ion activation experiments realized in the Omnitrap™ platform integrated on the timsOmni ^TM mass spectrometer for the analysis of oligonucleotides in the negative ion mode. The activation methods include resonance collision-induced dissociation ( _R CID), electron detachment dissociation (EDD), infrared laser multiple-photon activation (IRMPD) and UV laser photodissociation (UVPD). Special emphasis is given to EDD, either as a standalone technique or in conjunction with vibrational re-activation of the ion radicals. We describe EDD on standard 6-mer DNA sequences that have been extensively characterized on other instruments, followed by a comparison of several activation approaches for the phosphorothioate-based oligonucleotide therapeutics Fomivirsen, and concluding with the fragmentation analysis of 46-mer DNA and RNA. EDD alone already provides excellent sequence information on Fomivirsen, but MS ³ combinations such as EDD- _R CID or EDD-IRMPD proved even more effective, including for the 46-mer DNA (less prone to fragmentation than RNA) at a relatively low charge state. The diversity of ion activation combinations available on the Omnitrap platform is demonstrated by an MS ⁴ experiment investigating the fate of a • and z • radical fragments produced by EDD.