ENDGROUP ANALYSIS OF POLYETHYLENE-GLYCOL POLYMERS BY MATRIX-ASSISTED LASER-DESORPTION IONIZATION FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE MASS-SPECTROMETRY

Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) by external injection of matrix-assisted laser desorbed and ionized ( MALDI) polymers offers good possibilities for characterization of low molecular weight homopolymers (MW range up to 10 kDa). The molecular m asses of the molecular weight distribution (MWD) components of underiv atized and derivatized (dimethyl, dipropyl, dibutyl and diacetyl) poly ethylene glycol (PEG) 1000 and 4000 were measured by MALDI-FTICR-MS. T hese measurements have been performed using a commercial FTICR spectro meter with a home-built external ion source. MALDI of the samples with a 2,5-dihydroxybenzoic acid matrix in a 1000:1 matrix-to-analyte mola r ratio produces sodiated molecules in a sufficient yield to trap the ions in the ICR cell. The masses of the molecular weight distribution of PEG components were measured in broad-band mode with a mass accurac y of <5 ppm in the mass range around 1000 u and within 40 ppm accuracy around 4000 u. From these measurements, the endgroup mass of the poly mer was determined by correlation of the measured component mass with the degree of polymerization. The masses of the PEG endgroups have bee n determined within a deviation of 3-10 millimass units for the PEG100 0 derivatives and 10-100 millimass units for the PEG4000 derivatives, thus confirming the identity of the distal parts of the model compound s.