HIGH-RESOLUTION END GROUP DETERMINATION OF LOW-MOLECULAR-WEIGHT POLYMERS BY MATRIX-ASSISTED LASER-DESORPTION IONIZATION ON AN EXTERNAL ION-SOURCE FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE MASS-SPECTROMETER

Matrix-assisted laser desorption ionization was performed on an extern al ion source Fourier transform ion cyclotron resonance mass spectrome ter equipped with a 7-T superconducting magnet to analyze end groups o f synthetic polymers in the mass range from 500 to 5000 u. Native, per deutero methylated, propylated, and acetylated polyethylene glycol and polyvinyl pyrrolidone with unknown end-group elemental composition we re investigated in the mass range up to 5000 u by using a 2,5-dihydrox ybenzoic acid matrix. A small electrospray setup was used for the depo sition of the samples. Two methods to process data were evaluated for the determination of end groups from the measured masses of the compon ent molecules in the molecular weight ranges: a regression method and an averaging method. The averaging method is demonstrated to allow end -group mass determinations with an accuracy within 3 mu for the molecu lar weight range from 500 to 1400 and within 20 mu for the molecular w eight range from 3400 to 5000. This is sufficient to identify the elem ental composition of end groups in unknown polymer samples.