Commissioning the digital mass-filter/ion-trap module for the MS SPIDOC prototype

Abstract

The combination of a linear quadrupole ion-filter and linear Paul trap operated with a rectangular guiding field for the filtering and accumulation of ions within the Mass Spectrometry for Single Particle Imaging of Dipole Oriented protein Complexes (MS SPIDOC) prototype [T. Kierspel et al., Anal. Bioanal. Chem., published online] is characterized. Using cationic caesium-iodide clusters, the ion-separation performance, ion accumulation, cooling, and ejection via in-trap pin electrodes is evaluated. Furthermore, proof-of-principle measurements are performed with 64 kDa multiply-charged non-covalent protein complexes of human hemoglobin and 804 kDa non-covalent complex of GroEL, to demonstrate that the module meets the criteria to handle high-mass ions which are the main objective of the MS SPIDOC project. The setup's performance is found to be in line with previous results from ion-trajectory simulations [F. Simke et al., Int. J. Mass Spectrom. 473 (2022) 116779].

Experimental Investigation of a Digital Quadrupole Inductively Coupled Plasma Mass Spectrometer for Elemental Analysis

“…This discrepancy occurs because the theoretical resolution is calculated without considering ion conditions and confirms that the resolution calculated from q /Δ q only provides a conservative estimate . In similar results, Simke et al observed a large deviation between calculated and measured resolutions with an increased duty cycle …”

“…Though unique characteristics of digital QMF are theoretically predicted and have been preliminarily explored, ,,, application of digital waveform QMF technology for ICP-MS has not yet been reported. In this work, we experimentally investigate a proof-of-principle digital quadrupole mass filter coupled to an ICP source for elemental analysis.…”

Increasing Isolation Efficiency Using a Segmented Quadrupole Mass Filter Operated with Rectangular Waveforms

“…For the digital quadrupole, the duty cycle can be changed which yields changes in the stability diagram − from which a mass filter − or ion trap − can be constructed. For a square wave (50.0/50.0 duty cycle), the stability diagram is very similar to a sinusoidal quadrupole mass filter with a low mass cut off at q = 0.712 versus q = 0.908.…”

“…While the resolving field in the digital mass filter is generated by the duty cycle and not a DC field, the principles of the delayed DC ramp can still be applied. A square waveform applied to the prefilter allows the ion to traverse the a = 0 axis within the stable region prior to entering the main rod section with a rectangular waveform which yields ion selection. ,, This method requires four independent waveform outputs between the pre and postfilters and main rod sections. Alternatively, the rectangular waveforms can be directly applied to the main rod section and then capacitively coupled to the pre and postfilters, , requiring only two independent waveform outputs.…”