Experimental Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV, 12 mol% 3HV, M n =1.4×10 5 g mol -1 , ĐM=2.5) was from Sigma-Aldrich (St. Louis, MO, USA) while all other chemicals and solvents were from Wako pure chemicals (Osaka, Japan) unless otherwise mentioned. 1 μL of PHBV (1 mg mL −1 in THF) was drop-casted on a disposable MALDI target plate (Hudson Surface Technology, NJ, USA). 1 μL of sodium hydroxide in methanol-d4 at 10 mg mL −1 was further deposited and left to air-dry. The excess alkaline reagent was washed with distilled water. 1 μL of 2,4,6-trihydroxyaceto-phenone (Protea Biosciences, WV, USA) in THF at 20 mg mL −1 was applied on the sample spot. Mass spectra were recorded with a JMS-S3000 SpiralTOF™ mass spectrometer. Plots were computed using msRepeatFinder 3.0 from the peak list exported using MSTornado.