Stephen A. Lammert

Design, optimization and initial performance of a toroidal rf ion trap mass spectrometer

Abstract The design, optimization, and initial performance of a novel ion trap mass analyzer is reported. This analyzer geometry is based on the edge rotation of an ion trap cross-section into the shape of a torus. The advantages of this design are that for a given device analyzer radius (r0), significantly higher ion storage capacity than that obtained with a traditional three-dimensional quadrupole ion trap may be possible. Initial performance of this device was poor however, due to the significant contribution of additional nonlinear fields introduced by the rotation of the symmetrical ion trap cross-section. These nonlinear fields contributed to poor mass resolution and sensitivity as well as erratic ion ejection behavior. Using field analysis and ion trajectory simulation computer programs to guide the optimization, the geometry of this toroidal rf ion trap analyzer was modified in an attempt to correct for these nonlinear fields. These programs revealed that the original, symmetric toroid analyzer trapping field had a significant, sublinear component. Increasing the endcap separation and intentionally skewing the cross-sectional symmetry of the device minimized the field faults. Ion trajectory simulations indicated that the mass resolution and sensitivity of this asymmetric analyzer should be dramatically improved. Based on these results, an asymmetric version of the toroidal rf ion trap analyzer was constructed and this device has demonstrated unit mass resolution performance.

“Fast excitation” cid in a quadrupole ion trap mass spectrometer

Collision-induced dissociation (CID) in a quadrupole ion trap mass spectrometer is usually performed by applying a small amplitude excitation voltage at the same secular frequency as the ion of interest. Here we disclose studies examining the use of large amplitude voltage excitations (applied for short periods of time) to cause fragmentation of the ions of interest. This process has been examined using leucine enkephalin as the model compound and the motion of the ions within the ion trap simulated using ITSIM. The resulting fragmentation information obtained is identical with that observed by conventional resonance excitation CID. “Fast excitation” CID deposits (as determined by the intensity ratio of the a4/b4 ion of leucine enkephalin) approximately the same amount of internal energy into an ion as conventional resonance excitation CID where the excitation signal is applied for much longer periods of time. The major difference between the two excitation techniques is the higher rate of excitation (gain in kinetic energy) between successive collisions with helium atoms with “fast excitation” CID as opposed to the conventional resonance excitation CID. With conventional resonance excitation CID ions fragment while the excitation voltage is still being applied whereas for “fast excitation” CID a higher proportion of the ions fragment in the ion cooling time following the excitation pulse. The fragmentation of the (M+17H)17+ of horse heart myoglobin is also shown to illustrate the application of “fast excitation” CID to proteins.

A Lithographically Patterned Discrete Planar Electrode Linear Ion Trap Mass Spectrometer

We present a linear type radiofrequency ion trap mass spectrometer consisting of metal electrodes that are lithographically patterned onto two opposing planar ceramic substrates. An electric field for ion trapping is formed by applying specific voltage potentials to the electrode pattern. This technique represents a miniaturization approach that is relatively immune to problems with surface roughness, machining complexity, electrode misalignment, and precision of electrode shape. We also present how these traps allow a thorough study of higher order nonlinear effects in the trapping field profile and their effect on mass analyzer performance. This trap has successfully performed mass analysis using both a frequency sweep for resonant ion ejection, and linear voltage amplitude ramp of the trapping field. Better-than-unit mass resolution has been achieved using frequency sweep mass analysis. Mass resolution (m/Δm) has been measured at 160 for peaks of m/z values less than 100.

Improved Miniaturized Linear Ion Trap Mass Spectrometer Using Lithographically Patterned Plates and Tapered Ejection Slit

AbstractWe present a new two-plate linear ion trap mass spectrometer that overcomes both performance-based and miniaturization-related issues with prior designs. Borosilicate glass substrates are patterned with aluminum electrodes on one side and wire-bonded to printed circuit boards. Ions are trapped in the space between two such plates. Tapered ejection slits in each glass plate eliminate issues with charge build-up within the ejection slit and with blocking of ions that are ejected at off-nominal angles. The tapered slit allows miniaturization of the trap features (electrode size, slit width) needed for further reduction of trap size while allowing the use of substrates that are still thick enough to provide ruggedness during handling, assembly, and in-field applications. Plate spacing was optimized during operation using a motorized translation stage. A scan rate of 2300 Th/s with a sample mixture of toluene and deuterated toluene (D8) and xylenes (a mixture of o-, m-, p-) showed narrowest peak widths of 0.33 Th (FWHM). Graphical Abstractᅟ

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Double Resonance Ejection Using Novel RF Phase Tracking Circuitry in a Miniaturized Planar Linear Ion Trap Mass Spectrometer

RATIONALE Ion trap mass spectrometers are attractive due to their inherent sensitivity and specificity. Miniaturization increases trap portability for in situ mass analysis by relaxing vacuum and voltage requirements but decreases the trapping volume. To overcome signal/resolution loss from miniaturization, double resonance ejection using phase tracking circuitry was investigated. METHODS Phase tracking circuitry was developed to induce double resonance ejection in a planar linear ion trap using the β 2/3 hexapole resonance line. RESULTS Double resonance was observed using phase tracking circuitry. Resolution of 0.5 m/z units and improved signal-to-noise ratio (SNR) compared with AC resonant ejection were achieved. CONCLUSIONS The phase tracking circuitry proved effective despite deviations from a true phase locked condition. Double resonance ejection is a means to increase signal intensity in a miniaturized planar ion trap.