High-throughput DESI-MS Screening Protocol

The DESI-MS experiments were conducted as described previously^{27 (link)}. A Biomek FX liquid handling robot (Beckman Coulter) was used to distribute reaction mixtures into master well plates (either 96 or 384 well plates, depending on the scope of the experiment). The 96-tip transfer pod (pod1) and the Span-8 transfer pod (pod2) were both utilized to generate the target set of reaction conditions. The final reaction concentration for all DESI-MS experiments was 50 mM (20–30 µL in the final 384 well master plate). A magnetic pin tool (V&P Scientific, Inc.) was interfaced with pod1 of the liquid handling robot and used to transfer 50 nL volumes of reaction mixtures from the master well plate to the porous PTFE surface for DESI-MS. A commercial DESI source (Prosolia, Inc.) and a Thermo LTQ linear ion trap were utilized to execute the DESI-MS experiment. Experiments were conducted in positive-ion mode (m/z 50–500) with pure methanol as the spray solvent (3 µL/min). Parameters for the mass spectrometer and speed of the DESI stage were optimized previously^{27 (link)}. In-house software was used to process the data and generate spreadsheets from which heat maps were prepared.