Analysis of poly(ethylene glycol) using matrix-assisted laser desorption/ionization-mass spectrometry: Novel matrix systems using ultraviolet light absorber and stabilizer

Abstract

UV absorbers of orthohydroxyphenyl benzotriazole derivatives and a UV stabilizer (Tinuvin 770) as the matrix system were applied to analysis of poly(ethylene glycol) (PEG) using matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) and investigated. An N2 laser (337nm) was used as the light source. Various UV absorbers of Tinuvin 234, Tinuvin 326, Tinuvin 327, Tinuvin 328, and Tinuvin 329 were used as the matrix. The analytical results were compared with the results of using 2,5-dihydroxybenzoic acid (DHB), the most common matrix for MALDI-MS analysis of PEG. The MALDI-MS spectrum of PEG obtained using Tinuvin 328 or Tinuvin 329 showed higher ionization efficiency than that obtained using DHB. However, by adding Tinuvin 770 to DHB, the ionization efficiency notably enhanced. In contrast to this, for the UV absorbers, the ionization efficiencies were strikingly reduced by adding Tinuvin 770. The increased ionization efficiency of the co-matrix system of DHB+Tinuvin 770 was explained by the formation of the complex of DHB with Tinuvin 770, which improved flexibility of the matrix and enhanced compatibility with PEG. Formation of the complex of the UV absorber with Tinuvin 770 blocked the alcohol group of the UV absorber to remarkably reduce the intermolecular interactions between the matrix and PEG.