2D MS/MS Spectra Recorded in the Time Domain Using Repetitive Frequency Sweeps in Linear Quadrupole Ion Traps.

Ion trap mass spectrometers have emerged as powerful on-site analytical platforms, in spite of limited mass resolution, due to their compatibility with ambient ionization methods and ready implementation of tandem mass spectrometry (MS/MS). When operated at constant trapping voltage, ions can be activated at their secular frequencies and all MS/MS experiments can be performed, including the two-dimensional tandem mass scan (2D MS/MS scan) in which all precursor ions and their subsequent product ions are both identified and correlated. In the new method of performing this 2D MS/MS experiment presented here, the precursor ions are excited by a nonlinear (inverse Mathieu q) frequency sweep while the resulting product ions are identified by their ejection time within a repeating orthogonally applied nonlinear (inverse Mathieu q) frequency sweep. This resulting compact representation contains the total fragmentation behavior of a collection of ionized compounds and captures detailed chemical information efficiently (typically in 1 s). The approach is implemented using a simple single mass analyzer instrument. This methodology was tested on three different multicomponent mixtures: drugs of abuse, peptides, and fentanyl analogs. The data are compared with those obtained by more common MS/MS scan methods.