Kendrick analysis and complex isotopic patterns: a case study with the compositional analysis of pristine and heated polybrominated flame retardants by high-resolution MALDI mass spectrometry

Abstract

The Kendrick analysis has been used for the processing and visualization of mass spectra from polymers containing C, H, O and/or Si atoms with simple isotopic patterns (monoisotope = lightest isotope = most intense isotope for short chains). In case of heteroatoms with complex isotopic patterns, the impact of the chosen isotope on the point alignments in the Kendrick plot has not been commented yet. Rich isotopic patterns also make the evaluation of the mass and nature of the repeating unit and end-groups more difficult from the mass spectrum in case of unknown samples due to the number of peaks and the absence of monoisotopic peak. With a polybrominated polycarbonate as running example, we report that horizontal point alignments are obtained in a Kendrick plot using the mass of the most abundant isotope instead of the monoisotopic mass as usually done. Rotating the plot (“reverse Kendrick analysis”) helps to accurately evaluate the mass of the most abundant isotope of the repeating unit, as well as the nature of the brominated neutral expelled upon gentle heating (debromination or dehydrobromination). The whole procedure is later applied for the characterization of an unknown polybrominated flame retardant in an industrial formulation before and after heating.