Prediction of collective characteristics for ion ensembles in quadrupole ion traps without trajectory simulations

Abstract. The ion enhanced activation and collision-induced dissociation (CID) by simultaneous dipolar excitation of ions in the two radial directions of linear ion trap (LIT) have been recently developed and tested by experiment. In this work, its detailed properties were further studied by theoretical simulation. The effects of some experimental parameters such as the buffer gas pressure, the dipolar excitation signal phases, power amplitudes, and frequencies on the ion trajectory and energy were carefully investigated. The results show that the ion activation energy can be significantly increased by dual-direction excitation using two identical dipolar excitation signals because of the addition of an excitation dimension and the fact that the ion motion radius related to ion kinetic energy can be greater than the field radius. The effects of higher-order field components, such as dodecapole field on the performance of this method are also revealed. They mainly cause ion motion frequency shift as ion motion amplitude increases. Because of the frequency shift, there are different optimized excitation frequencies in different LITs. At the optimized frequency, ion average energy is improved significantly with relatively few ions lost. The results show that this method can be used in different kinds of LITs such as LIT with 4-fold symmetric stretch, linear quadrupole ion trap, and standard hyperbolic LIT, which can significantly increase the ion activation energy and CID efficiency, compared with the conventional method.

Section: Theoretical Methodssupporting

confidence: 61%

Section: Theoretical Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Theoretical Study of Dual-Direction Dipolar Excitation of Ions in Linear Ion Traps

Dang

Wang

et al. 2016

“…Rhodamine 575 cations formed in the electrospray ionization region are focused into the QIT by a series of ion optics. The ions are trapped inside an "ideal" geometry [18] QIT by a radiofrequency field (983 kHz) where they are irradiated by a laser beam that is normal to the ion beam axis. When collecting fluorescence, the photons emanating from one aperture of the ring electrode of the QIT are counted while the ions are irradiated.…”

Section: Methodsmentioning

confidence: 99%

Fluorescence and photodissociation of rhodamine 575 cations in a quadrupole ion trap

Sassin

Everhart

Dangi

et al. 2009

The fluorescence and photodissociation of rhodamine 575 cations confined to a quadrupole ion trap are observed during laser irradiation at 488 nm. The kinetics of photodissociation is measured by time-dependent mass spectra and time-dependent fluorescence. The rhodamine ion signal and fluorescence decay are studied as functions of buffer gas pressure, laser fluence, and irradiation time. The decay rates of the ions in the mass spectra agree with decay rates of the fluorescence. Some of the fragment ions also fluoresce and further dissociate. The photodissociation rate is found to depend on the incident laser fluence and buffer gas pressure. A s an alternative to collision-induced dissociation, surface-induced dissociation, infrared multiphoton dissociation, or direct UV/visible dissociation of biomolecular ions, there has been interest in labeling biomolecules with a chromophore tag to enhance photoactivation efficiency and selectivity. For example, Brodbelt and colleagues studied photodissociation mass spectra to sequence peptides labeled with both infrared absorbers [1] and UV chromophores [2]. Fluorophore labeling is also used in fluorescence resonant energy transfer (FRET) experiments, in which the acceptor/donor interactions of two attached fluorophores depend on the distances between them and therefore can provide conformational information [3][4][5][6]. In gas-phase work, Parks and coworkers [7][8][9][10] and Zenobi and coworkers [11,12] investigated the fluorescence of trapped molecular ions commonly used as fluorescent molecular probes of biomolecules. Both groups attached fluorescent probes to peptide cations for the purposes of investigating gas-phase FRET [8,11].Chromophore and fluorophore labeling experiments both rely on energy transfer from the absorbing moiety to another part of the biomolecule, either via intramolecular vibrational energy transfer or via radiative or electronic interactions. To understand the initial absorption process and the efficiency of photoactivation, it is of interest to investigate the photophysics and chemical dynamics of the absorption, fluorescence, and dissociation processes in the fluorescent dye molecules themselves in the gas phase. This work investigates the competition between fluorescence and photodissociation of rhodamine dye cations in a quadrupole ion trap. The ion trap is an ideal device for measuring chemical reactions that have slow reaction rates or processes that have long-lived intermediate states because of its ability to store a population of thermalized ions in the same location for extended periods of time. The photodepletion rate of the rhodamine cations is determined here by two independent methods: by directly observing the fluorescence photons and by recording the ion mass spectra. The resulting decays obtained by both methods are compared as a function of pressure, laser fluence, and irradiation time. The mechanism of rhodamine cation photodissociation at 488 nm is discussed.Several other groups have directly measured fluorescence from ions in...

“…As this displacement occurs, the ions visit areas of higher rf field where they can absorb power from the drive rf. Ion kinetic energies are increased in this overall process both as a result of the increase in velocity associated with the secular motion as well as the increase in velocities associated with power absorption from the drive rf, sometimes referred to as 'rfheating' [8]. Collisions with the bath gas at the elevated velocities associated with resonance excitation serve as means for conversion of kinetic energy to internal energy, thereby resulting in heating of the ions to the point where they may undergo fragmentation.…”

Section: Introductionmentioning

confidence: 99%

Dipolar DC Collisional Activation in a “Stretched” 3-D Ion Trap: The Effect of Higher Order Fields on rf-Heating

Prentice

McLuckey

2012

Applying dipolar DC (DDC) to the end-cap electrodes of a 3-D ion trap operated with a bath gas at roughly 1 mTorr gives rise to 'rf-heating' and can result in collision-induced dissociation (CID). This approach to ion trap CID differs from the conventional single-frequency resonance excitation approach in that it does not rely on tuning a supplementary frequency to coincide with the fundamental secular frequeny of the precursor ion of interest. Simulations using the program ITSIM 5.0 indicate that application of DDC physically displaces ions solely in the axial (inter end-cap) dimension whereupon ion acceleration occurs via power absorption from the drive rf. Experimental data shows that the degree of rf-heating in a stretched 3-D ion trap is not dependent solely on the ratio of the dipolar DC voltage/radio frequency (rf) amplitude, as a model based on a pure quadrupole field suggests. Rather, ion temperatures are shown to increase as the absolute values of the dipolar DC and rf amplitude both decrease. Simulations indicate that the presence of higher order multi-pole fields underlies this unexpected behavior. These findings have important implications for the use of DDC as a broad-band activation approach in multi-pole traps.