Experimental Sample information and preparation conditions are shown in Table 1. PEG1500 was dissolved in water at a concentration of 10 mg/mL. Each matrix was dissolved in THF at a concentration of 10 mg/mL. NaI used as the cationization agent was dissolved in THF at a concentration of 1 mg/mL. Next, the PEG1500, NaI and matrix solutions were mixed together 1:1:2 (1:1:4 for DIT) by volume. Afterwards, 0.75 μL of this mixture was placed on the hairline finish stainless steel plate (MTP format, 384 spots for samples and 96 spot for calibrant). Finally, the dried sample was measured using the JMS-S3000 SpiralTOF MS system. We also obtained SEM images for each crystal condition with the JSM-7600F.