Chemical Mass Shifts in Ion Trap Mass Spectrometry: Experiments and Simulations

Multiple-stage tandem mass spectrometry was used to characterize the dissociation pathways for complexes composed of (1) the uranyl ion, (2) nitrate or hydroxide, and (3) water or alcohol. The complex ions were derived from electrospray ionization (ESI) ϩ . The abundance of the species was greater than expected based on previous experimental measurements of the (slow) hydration rate for UO 2 ϩ when stored in the ion trap. To account for the production of the hydrated product, a reductive elimination reaction involving reactive collisions with water in the ion trap is proposed. T he speciation and reactivity of uranium is a topic of sustained interest because species-dependent chemistry [1] controls processes ranging from nuclear fuel processing [2] to mobility and fate in the geologic subsurface [3,4]. The solution chemistry of uranium is dominated by the uranyl dication, UO 2 2ϩ , which is known to form complexes with a range of ligands [1]. Specific interaction with solvent will significantly influence the physico-chemical behavior of the uranyl ion and its complexes, and this has motivated investigations of complex composition and stability using infrared spectroscopy and extended X-ray absorption fine structure [5][6][7][8][9][10][11]. Unfortunately, explicit control over the interactions of solvent and nonsolvent ligands with the uranyl ion is difficult, which makes the study of species-dependent uranium behavior complicated. To gain a better understanding of the intrinsic interactions between different uranyl species and solvent, we have begun an investigation of uranyl-anion complexes in the gas phase using ion-trap mass spectrometry (IT-MS). Several recent reports have demonstrated that intrinsic metal and metal complex chemistry can be investigated by the (controlled) addition of reagent gas to an ion trap [12][13][14][15][16][17][18][19][20][21][22], or by way of the presence of H 2 O and other small molecule contaminants within the He bath gas used to collisionally cool ions and improve trapping efficiency [23][24][25]. The reactions of uranium ions in the gas phase have been the subject of several earlier investigations. Studies by , and by Schwarz and coworkers [30] have probed the reactions between U ϩ and UO ϩ and organic compounds such as alkanes and alcohols. Armentrout and Beauchamp [31] investigated the oxidation of U ϩ using small molecules such as O 2 , CO, CO 2 , COS, and

Section: Resultssupporting

confidence: 71%

Elucidation of the collision induced dissociation pathways of water and alcohol coordinated complexes containing the uranyl cation

Stipdonk

Anbalagan

Chien

et al. 2003

“…As a result, traditional rf amplitude sweeps have remained the favored method of ion trap operation. It is also theoretically possible to sweep the size of the device (r 0 ), but this is impossible in practice [16].…”

Section: Introductionmentioning

confidence: 99%

Experimental Characterization of Secular Frequency Scanning in Ion Trap Mass Spectrometers

Snyder

Pulliam

Wiley

et al. 2016

Self Cite

Abstract. Secular frequency scanning is implemented and characterized using both a benchtop linear ion trap and a miniature rectilinear ion trap mass spectrometer. Separation of tetraalkylammonium ions and those from a mass calibration mixture and from a pesticide mixture is demonstrated with peak widths approaching unit resolution for optimized conditions using the benchtop ion trap. The effects on the spectra of ion trap operating parameters, including waveform amplitude, scan direction, scan rate, and pressure are explored, and peaks at black holes corresponding to nonlinear (higher-order field) resonance points are investigated. Reverse frequency sweeps (increasing mass) on the Mini 12 are shown to result in significantly higher ion ejection efficiency and superior resolution than forward frequency sweeps that decrement mass. This result is accounted for by the asymmetry in ion energy absorption profiles as a function of AC frequency and the shift in ion secular frequency at higher amplitudes in the trap due to higher order fields. We also found that use of higher AC amplitudes in forward frequency sweeps biases ions toward ejection at points of higher order parametric resonance, despite using only dipolar excitation. Higher AC amplitudes also increase peak width and decrease sensitivity in both forward and reverse frequency sweeps. Higher sensitivity and resolution were obtained at higher trap pressures in the secular frequency scan, in contrast to conventional resonance ejection scans, which showed the opposite trend in resolution on the Mini 12. Mass range is shown to be naturally extended in secular frequency scanning when ejecting ions by sweeping the AC waveform through low frequencies, a method which is similar, but arguably superior, to the more usual method of mass range extension using low q resonance ejection.

“…Moreover, the nonlinear fields are regarded as the main factor in the degradation of the ion trap performance. For instance, the resultant nonlinear effects, such as ion delay ejection [31,32], nonlinear resonance [33,34], and frequency shift [35,36], are considered to be harmful to the mass resolution, sensitivity, and mass accuracy, respectively. With the in-depth study, the nonlinear fields have been found to be beneficial and have the potential to break the performance barrier and develop new operation modes of the ion trap.…”

mentioning

confidence: 99%

A Theoretical Method for Characterizing Nonlinear Effects in Paul Traps with Added Octopole Field

Xiong

Zhou

Zhang

et al. 2015

Abstract. In comparison with numerical methods, theoretical characterizations of ion motion in the nonlinear Paul traps always suffer from low accuracy and little applicability. To overcome the difficulties, the theoretical harmonic balance (HB) method was developed, and was validated by the numerical fourth-order Runge-Kutta (4th RK) method. Using the HB method, analytical ion trajectory and ion motion frequency in the superimposed octopole field, ε, were obtained by solving the nonlinear Mathieu equation (NME). The obtained accuracy of the HB method was comparable with that of the 4th RK method at the Mathieu parameter, q=0.6, and the applicable q values could be extended to the entire first stability region with satisfactory accuracy. Two sorts of nonlinear effects of ion motion were studied, including ion frequency shift, Δβ, and ion amplitude variation, Δ(C 2n /C 0 ) (n≠0). New phenomena regarding Δβ were observed, although extensive studies have been performed based on the pseudo-potential well (PW) model. For instance, the |Δβ| at ε=0.1 and ε=-0.1 were found to be different, but they were the same in the PW model. This is the first time the nonlinear effects regarding Δ(C 2n /C 0 ) (n≠0) are studied, and the associated study has been a challenge for both theoretical and numerical methods. The nonlinear effects of Δ(C 2n /C 0 ) (n≠0) and Δβ were found to share some similarities at q<0.6: both of them were proportional to ε, and the square of the initial ion displacement, z(0) 2 .