A novel high-capacity ion trap-quadrupole tandem mass spectrometer

Abstract

We describe a prototype tandem mass spectrometer that is designed to increase the efficiency of linked-scan analyses by >100-fold over conventional linked-scan instruments. The key element of the mass spectrometer is a novel high ion capacity ion trap, combined in tandem configuration with a quadrupole collision cell and a quadrupole mass analyzer (i.e. a TrapqQ configuration). This ion trap can store >10 6 ions without significant degradation of its performance. The current mass resolution of the trap is 100-450 full width at half maximum for ions in the range 800-4000 m/z, yielding a 10-20 m/z selection window for ions ejected at any given time into the collision cell. The sensitivity of the mass spectrometer for detecting peptides is in the low femtomole range. We can envisage relatively straightforward modifications to the instrument that should improve both its resolution and sensitivity. We tested the tandem mass spectrometer for collecting precursor ion spectra of all the ions stored in the trap and demonstrated that we can selectively detect a phosphopeptide in a mixture of non-phosphorylated peptides. Based on this prototype instrument, we plan to construct a fully functional model of the mass spectrometer for detecting modification sites on proteins and profiling their abundances with high speed and sensitivity.

A high-resolution multi-reflection time-of-flight mass spectrograph for precision mass measurements at RIKEN/SLOWRI

“…flat trap side) is slightly larger than that of the entrance side, while the horizontal inter-rod gap is slightly smaller. The asymmetric configuration generates a potential gradient [45] to push the ions toward the flat trap when DC biases are superimposed on the taper trap RF signals.…”

High-capacity ion trap coupled to a time-of-flight mass spectrometer for comprehensive linked scans with no scanning losses

“…The high-capacity tapered geometry ion trap (“Qtap”) used in this work has been discussed in detail previously 33. Hence, only a brief description will be provided here.…”

“…The ion trap is driven by an independent RF power supply (RF frequency 333 kHz) and a secondary, low-voltage resonance ejection RF is set at 265 kHz. These frequency values were found empirically based on the optimal combination of resolution, sensitivity, and the m/z range of the ion trap 33. The secondary RF is only applied to one pair of rods as shown in Fig.…”

“…1. The purpose of the tapered geometry is to create an electric potential that closely approximates a linear quadrupole at any point along its z axis, with the field radius scaling as a function of position on the z axis as previously described 33. This geometry results in an effective potential well, with steeper walls at the ends of the trap, and shallower well towards the center, thus forcing the ions towards the center of the trap when the RF voltages are ramped.…”

“…After the fill time, the main and ejection RF amplitudes are ramped over a period of 1 s to 600 V and 6 V, respectively. These time-varying potentials cause ions to be ejected sequentially as a function of mass through a slit in one of the connecting quadrupole rods 33. During the ejection process, lighter ions at the ends of the trap are swept towards the center first.…”