Enhanced spectral analysis of C-TOF Aerosol Mass Spectrometer data: Iterative residual analysis and cumulative peak fitting

We present a method for an improved spectral analysis of datasets measured by a C-TOF Aerosol Mass Spectrometer. Using cumulative peak fitting and iterative residual analysis, multiple isobaric peaks can be separated. These algorithms are described and are tested in various simulations, which have been performed to determine the benefits and constraints of this method. A smog chamber example is presented to demonstrate the performance and constraints for real data, with an example focusing on m/z 43. In this case, two isobaric peaks can be separated (m/z 43.015 and m/z 43.043) and identified as C2H3O+ and C2H5N+ respectively. Indistinguishable isobaric interferences slightly shift the exact m/z ratios resulting in a worse mass accuracy as expected from the simulations. Nevertheless, a 50 ppm mass accuracy is achieved, which is an impressive value for the identification of two isobaric peaks separated by 0.65 full width half maximum for an instrument with a mass resolving power of only R = 1000. According to the simulations, a mass resolving power of at least 4000 would be necessary to quantitatively separate the expected isobaric interferences that are separated by a m/z difference of about 0.004 at m/z 43.