Esi l tune mix

For targeted MS/MS, all ions were analyzed by IM and then m/z species related to DP = 1 and DP = 5 [M+Li]⁺, [M+Na]⁺, [M+K]⁺, [M+Rb]⁺, and [M+Cs]⁺ oligomer adducts were mass isolated for CID (IM-MS/MS). For IM, the trap fill time was set to 60,000 μs and 200 μs for trap release time. For CID, a stepped voltage ramp was used with increments of 10 V between 0 – 100 V (laboratory frame). The IM-MS was tuned and mass calibrated using a commercially-available tuning mixture (ESI-L Tune Mix, Agilent).

A timsTOF fleX (Bruker Daltonics, Bremen, Germany) with a dual ESI-MALDI source was used to acquire all MALDI IMS data.^{30 (link)} A SmartBeam 3D 10 kHz frequency tripled Nd:YAG laser (355 nm) was tuned to provide the optimal signal with the beam scan activated to produce a 16 μm × 16 μm footprint and 8 μm × 8 μm footprint for 20 and 10 μm spatial resolution imaging, respectively. The local laser power was set to 49 or 71% for 20 μm spatial resolution and decreased to 40% for 10 μm (attenuator offset: 0%). Shots remained consistent at 200 per pixel for all experiments. The additional height of the mount and Cryofilm was accounted for by a Galvo scanner offset focus adjustment. The MS was operated in qTOF mode with TIMS deactivated. ESI-L Tune Mix (Agilent Technologies, Santa Clara, CA, USA) was directly infused for mass calibration prior to data acquisition. Positive ion mode data were acquired from m/z 300 to 1500. Additional MS parameters are included in the Supporting Information (Table S1).