The analysis of individual compounds present in complex mixtures is traditionally performed after application of a separation method such as LC or GC. Here, a novel method of direct structural elucidation without chromatographic separation is presented. In two-dimensional tandem mass spectrometry (2D MS/MS) one obtains data-independent MS/MS information over the full set of ion masses within a single scan. The experiment is done using a rectilinear quadrupole ion trap where the orthogonal excitation and ejection RF voltages are ramped, and each precursor ion is fragmented using a linear mass sweep vs. time. The intrinsic separation and dissociation of ions based on precursor m/z in the ion trap provides a highly efficient MS/MS analysis of each individual compound in a mixture within a 1 sec acquisition time. Molecular manipulations (e.g. online derivatizations) and ionic manipulations (e.g. collisional energy settings) provide additional information for structural elucidation and library matching. Online reactive ionization is used to quickly transform specific functional groups to increase the total information content of the 2D MS/MS fragmentation. This manipulation provides (i) functional group information related to reactivity and (ii) additional structural information on the derivatized compounds, which are structurally connected to the original compound. Katritzky reaction, alkylation, and nucleophilic substitution reactions will be demonstrated for a mixture containing amines, phenols, and carboxylic acids with two examples of each class. Changes in collision energy increase the information available from fragmentation patterns thus further facilitating structural elucidation. A synthetic Boolean subtracted spectrum before and after each manipulation combines information from molecular manipulations and MS/MS fragmentation pattern changes within one single spectrum in an attempt to enable automated analysis of compounds. Specific expert rules such as the shifts of precursor m/z, product ion m/z, neutral loss, and MS/MS prediction are being applied to the structural elucidation process. A small library of synthetic Boolean spectra is being created for future database searching.

Yanyang Hu

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