Targeted MS/MS spectra were acquired after isolating a specific user-defined RNA isoform using 5 m/z width quadrupole isolation. Collisional activation was carried out using normalized collisional energy values (NCE) ranging from 15 to 30, dependent on the precursor charge state, and a q value of 0.14. 213 nm UVPD using the onboard Nd:YAG laser (CryLas, 2.5 kHz) was performed using 20-80 laser pulses (8 to 32 ms). a-EPD spectra were gathered by re-isolating a charge-reduced precursor produced after 20 pulses of 213 nm UVPD, and subsequently activating with CID at an NCE of 15.