Experimental We dissolved polypropylene glycol HO (C 2 H 4 O) n H, polyethylene glycol monolauryl ether HO (C 2 H 4 O) n C 12 H 25 , and polyoxyethylene monocetyl ether HO (C 2 H 4 O) nC 16 H 33 in methanol (10 mg/mL). We used α-cyano-4-hydroxycinnamic acid (α-CHCA; 10 mg/mL in methanol) and sodium trifluoroacetate (NaTFA; 10 mg/mL in methanol) as matrix and cationizing agent, respectively. The sample, α-CHCA, and NaTFA were mixed at 1:10:1 (v/v/v), spotted on a target plate, and air dried. Product-ion spectra were acquired in positive-ion mode using JMS-S3000 SpiralTOF™ with the TOF–TOF option. We analyzed the data using msRepeatFinder version 3.0.