DETERMINATION OF MOLECULAR-WEIGHT DISTRIBUTIONS OF POLYMERS BY MALDI-FTMS

The advantages of matrix-assisted laser desorption/ionization (MALDI) and Fourier transform mass spectrometry (FTMS) are combined to create a powerful tool for the characterization of polymer samples. MALDI permits generation of intact, singly charged, high-mass (m/z 10(3)-10(4)) ions of polar and nonpolar analytes, while FTMS provides unique high resolution and mass accuracy. Use of a gated deceleration potential allows for FTMS detection of MALDI-generated ions. However, when a single delay time is used between desorption/ionization and restoration of normal trapping potentials, mass discrimination is apparent for broad polymer distributions, Here, an integral method for obtaining molecular weight distributions of polymers by MALDI-FTMS is presented. By means of a simple procedure of averaging time domain transients obtained from a series of polymer sample spectra recorded at systematically varied gated deceleration times, accurate polymer distributions are obtained. The technique is demonstrated with several poly(ethylene glycol) samples containing oligomers with masses covering a 10 kDa mass range.