Ion isolation and multigenerational collision-induced dissociation using the inverse Mathieu q scan.

RATIONALE: In a bid to develop a mass spectrometer using ac frequency scanning for ion isolation, ion activation, and ion ejection, we have developed scan functions for each process using the inverse Mathieu q scan.

METHODS: Ion isolation is accomplished by frequency hopping, that is, by skipping past the ranges of frequencies corresponding to the ions to be isolated during the frequency sweep. Multigenerational collision-induced dissociation is demonstrated by scanning the frequency of excitation from low to high so that multiple generations of product ions can be observed in the product ion mass spectra. Because the excitation frequency is scanned quickly across a large range, fragmentation of some precursor ions can be too limited. However, by first fixing the excitation frequency on the precursor ion and then scanning the frequency using the inverse Mathieu q scan, a higher abundance of product ions can be obtained.

RESULTS: Isolation of a single mass-to-charge (m/z) as well as nonadjacent m/z ions is demonstrated with isolation efficiency greater than 70%. Fragmentation of caffeine and noroxycodone is demonstrated, the latter of which shows multiple generations of product ions.

CONCLUSIONS: The results demonstrated here provide strong evidence that an ion trap mass spectrometer can be operated without using an rf amplitude ramp for any operation, and instead ac frequency scanning can be used for all mass-selective operations. Copyright © 2016 John Wiley & Sons, Ltd.