Scanning a triple quadrupole mass spectrometer for doubly charged ions

Single Analyzer Neutral Loss Scans in a Linear Quadrupole Ion Trap Using Orthogonal Double Resonance Excitation

In this follow-up paper to our previous work on single analyzer precursor ion scans in a linear quadrupole ion trap (Snyder, D. T.; Cooks, R. G. Single analyzer precursor ion scans in a linear quadrupole ion trap using orthogonal double resonance excitation. J. Am. Soc. Mass Spectrom. 2017, DOI: 10.1007/s13361-017-1707-y), we now report the development of single analyzer neutral loss scans in a linear quadrupole ion trap using orthogonal double resonance excitation. Methodologically, there are three key differences between single analyzer precursor ion scans and neutral loss scans under constant radiofrequency (rf) conditions: (1) in the latter experiment, both excitation and ejection frequencies must be scanned, whereas in the former the ejection frequency is fixed, (2) the need to maintain a constant neutral loss while incrementing both precursor and product ion masses, complicated by the complex relationship between secular frequency and mass, requires use of two simultaneous frequency scans, both linear in mass, and (3) because the ejection frequency is scanned, a third ac signal occurring between the ac excitation and ac ejection frequency scans must also be applied and scanned in order to reject artifact peaks caused by ejection of unfragmented precursor ions. Using this methodology, we demonstrate neutral loss scans on a commercial linear ion trap using mixtures of illicit drugs and acylcarnitines. We also demonstrate neutral loss scanning on a Populus deltoides leaf and on a lignin sample, both significantly more complex mixtures.

Unimolecular and collision-induced reactions of doubly charged porphyrins

Results from a tandem mass spectrometry (MS/MS) study, obtained with a reverse-geometry mass spectrometer, of the unimolecular and collision-induced reactions of doubly charged free-base and metal containing alkyl-substituted porphyrins formed by electron ionization are reported. These doubly charged porphyrin ions dissociate to yield both singly and doubly charged product ions via a number of reactions. This article classifies the major reactions observed, illustrating each with the appropriate spectra. Supplementary data from the same porphyrins, acquired with a tandem quadrupole MS/MS instrument, are also presented. The potential utility of some of these reactions as new methods for porphyrin analysis is discussed.