MASS DISCRIMINATION IN THE ANALYSIS OF POLYDISPERSE POLYMERS BY MALDITIME-OF-FLIGHT MASS-SPECTROMETRY .1. SAMPLE PREPARATION AND DESORPTION IONIZATION ISSUES/

A study of the experimental effects on the matrix-assisted laser desor ption/ionization (MALDI) time-of-flight (TOF) mass spectrometric analy sis of polydisperse polymers is presented, based on a time-lag focusin g TOF configuration. Polydisperse polymers were simulated with the pre paration of multicomponent blends of polystyrene of narrow polydispers ity. Spectral collection was based on one sample preparation procedure . It is shown that many experimental parameters give rise to mass disc rimination in the signal generated from a mass spectral analysis of po lydisperse polymers. Several issues related to sample preparation and desorption/ionization are addressed in this work, rand the instrumenta l considerations such as ion focusing, transmission, and detection are presented in the following article of this issue. Ht is demonstrated that sample preparation and desorption/ionization can introduce seriou s mass biasing that appears to be due to the characteristics of the (M ALDI) process. Experimental procedures are discussed that allow for th e determination of this mass discrimination. Sample preparation guidel ines are suggested for the minimization of mass discrimination. It is stressed that,with our current understanding of the MALDI process, gre at care must be exercised in interpreting average molecular weights an d molecular weight distribution functions deduced from the direct MALD I analysis of polydisperse polymers.