Fast Fourier Transform and autocorrelation function for the analysis of complex mass spectra

Abstract

Mass spectrometry is useful for structural investigation of molecules as it is able to give simultaneously molecular weight (MW) distributions, chemical functionalities and fragmentation and/or reaction growth paths. However, in the case of very complex mixtures it can be very difficult to interpret a mass spectrum and to individuate manually the gap among the peaks.In the present work, for the first time two mathematical methodologies, Fast Fourier Transform (FFT) and autocorrelation function (AF), have been applied to the mass spectra analysis of complex carbonaceous mixtures, like naphthalene pitch and asphaltenes, whose structure and MW are object of pitched debates in literature. The potentiality of this mathematical approach was shown for improving the spectra interpretation whichever the mass spectrometer used.It was found that in general FFT analysis is more accurate with denser peaks and lesser resolved spectra but fails in accuracy when few/sharp peaks are present. On the other hand, AF analysis is more accurate in the determination of main periodicities when the spectrum presents just few peaks and a higher resolution.Structures and MW have been derived for naphthalene pitch and asphaltenes, on the basis of the match of their FFT and AF spectra.Naphthalene pitch was found to be constituted of many compounds arriving up 1000Da, with different unsaturation degrees and the presence of naphthenic rings and aliphatic bridges.Asphaltenes have been found to present a polymeric structure with aromatic moieties with no more than 4–5 rings linked by aliphatic chains and their MW extending up to 1000Da.