Towards a Quantitative Interpretation of Polymer Distributions from MALDI-TOF Spectra

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Abstract

The importance of proper conversion of MALDI-MS signals into the number of polymers with a certain mass increment (by taking into account a nonconstant conversion factor) is demonstrated with calculated Schulz-Zimm and Poisson distributions. Measurements of two narrow polystyrene standards were used to investigate the influence of measurement conditions (laser intensity, matrix) and data processing (signal conversion, baseline construction). We observed the following effects: (a) slightly broader distributions with DCTB as matrix at a given laser intensity in comparison to those obtained with all-trans-retinoic acid, (b) changes in the relative intensities of several peaks in a sample, and (c) a nonlinear baseline in the low molar mass region in most of the cases. Therefore, the implications of an assumed linear baseline instead of the correct one on the results were scrutinized experimentally and by simulations. In all, measurement of narrow distributions turned out to give reasonable results. Based on the assumption that the polymer standards can be described by Poisson distributions, overlap conditions between two distributions are rephrased. An alternative possibility of how mass discrimination could be determined, in principle, is presented, too.

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