Single analyzer precursor scans using an ion trap

Precursor ion and neutral loss scans are general survey methods of tandem mass spectrometry (MS/MS) used for detecting structurally related compounds. Until now they have been performed in multiple analyzer instruments, e.g. triple quadrupoles and hybrid MS/MS instruments. Implementation of precursor ion scans in single mass analyzers would be advantageous in reducing instrument complexity.

Adoption of secular frequency scanning as a method of mass-selective excitation is shown to enable precursor scans in a single ion trap in a miniature mass spectrometer. A small supplementary alternating current (ac) signal is swept in frequency so as to cause mass-selective excitation of trapped ions. Simultaneously, a higher fixed amplitude ac signal is applied at the fixed secular frequency of a product ion, ejecting the mass-selected product ion and providing temporal data corresponding to a precursor ion spectrum.

Precursor scanning in a single ion trap is demonstrated using a mixture of three illicit drugs: cocaine, 3,4-methylenedioxyamphetamine (MDA), and 3,4-methylenedioxymethamphetamine (MDMA). Acquisition of the spectra as a function of the frequency of the product ejection waveform demonstrates that the signals acquired represent precursor ion scans.

Secular frequency scanning is a nonconventional method of mass scanning that in combination with product ion ejection enables precursor scans in single ion traps. This phenomenon is demonstrated here for a miniature linear ion trap, but the concepts described also apply to quadrupole mass filters. Copyright © 2016 John Wiley & Sons, Ltd.