A method is presented to test whether the conversion of the mass spectrum of a polydisperse analyte to its molecular mass distribution is quantitative. Mixtures of samples with different average molecular masses, coupled with a Taylor's expansion mathematical formalism, were used to ascertain the reliability of molecular mass distributions derived from mass spectra. Additionally, the method describes how the molecular mass distributions may be corrected if the degree of mass bias is within certain defined limits. This method was demonstrated on polydisperse samples of C60 fullerenes functionalized with ethylpyrrolidine groups measured by matrix assisted laser desorption/ionization time of flight mass spectrometry; however, it is applicable to a any polydisperse analyte and mass spectrometric method as long as spectrum resolution allows individual oligomers to be identified. Mass spectra of the derivatized fullerenes taken in positive ion mode were shown to give an accurate measured of the MMD while those taken in negative ion mode were not. Differences in the mechanisms for ion formation are used to explain the discrepancy.
Citation: Journal of the American Society for Mass Spectrometry
Pub Type: Journals
fullerene, mass spectrometry, molecular mass distribution, quantitative analysis, Taylor's expansion