EXPRESS: Precursor/Fragment Ion Identification from Bulk Analysis of a Mixture through Two-Dimensional Correlation...

The identification of analytes in complex mixtures with mass spectrometry (MS) is often complicated by isobaric overlap, adduct/fragment formation, isotopic distributions, and competitive ionization. Common analysis methods such as chromatography-coupled MS and tandem-MS require physical separation or isolation of analytes prior to mass analysis. This work demonstrates that two-dimensional correlation techniques, used widely in optical spectroscopy, can be adapted to MS to identify precursor and fragment ion pairs from the direct analysis of a two-component mixture, obviating the need for sequential separation or isolation of analytes. A mathematical framework is presented to threshold correlation-derived metrics to predict whether two mass-spectral signals arose from the same molecular origin. Single-analyte spectra derived from the time-averaged mass spectrum of the mixture with these metrics were identified through the National Institute of Standards and Technology (NIST) MS Search 2.2 software with greater than 90% accuracy. Though presented here for data acquired with direct analysis in real time (DART) mass spectrometry, these methods can be directly applied to other mass-spectral datasets that have a time-dependent signal, including metabolomics, petroleomics, natural organic matter, forensics, and chemical reaction monitoring.