Differential analysis on precise determination of molecular weight of triblock copolymer using SEC/MALS and MALDI-TOF MS

Precise determination of the molecular weight of a poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) triblock copolymer (PEG-PTHF-PEG) using size-exclusion chromatography/multi-angle laser light scattering (SEC/MALS) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) was carefully investigated. The potential uncertainty factors for both SEC/MALS and MALDI-TOF MS were evaluated using cause-effect diagrams. The consistency of data between the two methods was then assessed by t-test. It was found that the data from SEC/MALS and MALDI-TOF MS were not consistent. For clarifying the differential results, titration was also employed to further measure the molecular weight of triblock copolymer. The result indicated that the data from titration was consistent with that of SEC/MALS, but not consistent with the data from MALDI-TOF MS. The result of MALDI-TOF MS was smaller and showed a deviation of about 10% from the SEC/MALS result. The reason for this difference was then further explored.