The signal-to-noise issue in mass spectrometric analysis of polymers

Mass spectrometric approaches to polymer analysis become increasingly ineffective as the average molecular weight of the polymer increases. Why? The reasons are several-fold, and apply to both ESI and MALDI: the distribution of signal over an increasing number of different species, even for distributions of narrowest possible dispersity; each unique species has its own intensity broadened over a widening range of m/z values as polyisotopic contributions become more significant; individual signal width becomes larger as m/z increases; and solubility properties and solvent adducts can limit the analytical signal for polymer analysis. For MALDI analysis there is an additional reason: effective sample preparations require a certain weight percentage, causing the concentration of polymer in the matrix to drop. All these factors conspire to cause a signal-to-noise problem that fundamentally limits the ability of mass spectrometry to determine molecular weight distribution for high mass polymers.