Application of nonresonance excitation to ion trap tandem mass spectrometry and selected ejection chemical ionization

Ion transfer and storage using inhomogeneous radio frequency (RF) electric fields in combination with gas-assisted ion cooling and focusing constitutes one of the basic techniques in mass spectrometry today. The RF motion of ions in the bath gas environment involves a large number of ion-neutral collisions that leads to the internal activation of ions and their effective "heating" (when a thermal distribution of internal energies results). The degree of ion activation required in various applications may range from a minimum level (e.g., slightly raising the average internal energy) to an intense level resulting in ion fragmentation. Several research groups proposed using the effective temperature as a measure of ion activation under conditions of multiple ion-neutral collisions. Here we present approximate relationships for the effective ion temperature relevant to typical operation modes of RF multipole devices. We show that RF ion activation results in near-thermal energies for ions occupying an equilibrium position at the center of an RF trap, whereas increased ion activation can be produced by shifting ions off-center, e.g., by means of an external DC electric field. The ion dissociation in the linear quadrupole ion trap using the dipolar DC ion activation has been observed experimentally and interpreted in terms of the effective ion temperature. ollisional activation of ions takes place in all practical mass spectrometry measurements, either as a side effect of a residual gas pressure, or for the specific purpose of collisional ion cooling, focusing or collision induced dissociation. Modeling of the collisionally induced ion activation process in mass spectrometry has been the focus of extensive study [1][2][3][4][5]. Of particular importance is the collisional activation of ions in radio frequency (RF) ion traps and guides, where a substantial bath gas pressure and long residence times result in large numbers of the ionneutral collisions [6]. Several research groups have proposed using the effective temperature as a measure of ion activation under conditions of multiple ionneutral collisions [7][8][9][10][11][12]. As such, the effective temperature concept proved to be very useful in the interpretation of ion activation data obtained for various mass spectrometry experiments, in particular in quadrupole ion trap experiments [8,9,[13][14][15]. Generally, the internal energy of ions produced at high pressures (e.g., by the electrospray ionization process) can be characterized in terms of effective ion temperature [16 -20]. The effective temperature T eff of an ion, moving in a bath gas under the influence of electric fields, can be expressed through the ion drift velocity V drift as follows:2 , where T is the gas temperature, and C T is a model dependent proportionality coefficient [9,12,21]. This approximation is applicable to conditions when the force acting on an ion is constant during a time interval longer than the ion velocity relaxation time (i.e., the drift motion approximation) [22]. In the lower ...

Section: Dipolar DC Activation Of Trapped Ionssupporting

confidence: 76%

Section: Discussionmentioning

confidence: 78%

Section: Dipolar DC Activation Of Trapped Ionsmentioning

confidence: 99%

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Collisional activation of ions in RF ion traps and ion guides: The effective ion temperature treatment

Tolmachev

Vilkov

Bogdanov

et al. 2004

“…Indeed, recent experiments suggest that very high internal energies can also be obtained for the singly charged precursor ion of leucine enkephalin when excited with single-or two-frequency excitation during mass acquisition (these results are subject of a future publication). We are currently establishing the effects of other instrumental variables-such as scan rate, ion number density, and the difference in frequency between the two excitation waveforms-on the fragmentation°behavior°of°ions° [44]. use of the ITSIM 5.0 software.…”

Section: Discussionmentioning

confidence: 99%

Dynamic collision-induced dissociation (DCID) in a quadrupole ion trap using a two-frequency excitation waveform: I. Effects of excitation frequency and phase angle

Laskay

Hyland

Jackson

2007

This study describes the application of a two-frequency excitation waveform to the end-cap electrodes of a quadrupole ion trap (QIT) during the mass acquisition period to deliberately fragment selected precursor ions. This approach obviates the need for a discrete excitation period and guarantees on-resonant excitation conditions without any requirement for resonant tuning; it is therefore faster than the conventional approach to collision-induced dissociation (CID) in QITs. The molecular ion of n-butylbenzene is used as thermometer molecule to determine the energetics of the new excitation procedure. The excitation waveform, consisting of two closely spaced sinusoidal frequencies, has an interference pattern that displays nodes and crests in the time domain. The energetics (determined by the product ion ratios of 91/92 Th) and CID efficiencies are highly dependent on the excitation amplitude, the relative position of the excitation frequencies in the Mathieu stability diagram, and whether the ions come into resonance during a node or crest of the excitation waveform. Under highly energetic conditions, ratios of 91/92 as large as 15 can be obtained at concomitant CID efficiencies of 10%, indicating internal energies in excess of 10 eV at the time of fragmentation. These extremely high internal energies far exceed the energetics achievable using conventional on-resonance excitation in QITs, indicating that the collisional heating rate is very fast in the new approach. Under less energetic conditions CID efficiencies as high as 70% are possible, which compares favorably with results obtained by conventional on-resonance excitation. Correlation analyses are used to determine the conditions that simultaneously optimize energetic and efficient fragmentation conditions. (J Am Soc Mass Spectrom 2007, 18, 749 -761) © 2007 American Society for Mass Spectrometry T he ever-increasing need for reliable mass spectrometric data drives researchers to develop increasingly sophisticated instruments that allow fast, cost-effective, and reproducible analysis of a wide variety of samples. Quadrupole ion traps (QITs) are of significant interest in the achievement of this goal because of their flexibility and excellent sensitivity. The ability to isolate precursor ions [1][2][3], effect fragmentation [4 -6], and to detect trapped ions in a variety of methods [7][8][9] makes QITs a very useful tool in many applications [10,11]. The design of faster, more sensitive ion traps that allow coupling with fast separation methods and overcome the necessity for resonance tuning is a major issue for QIT developers. The present study describes a small step toward the long-term goal of achieving fast, simple, and reliable tandem mass spectrometry (MS/MS).The use of QITs in tandem mass spectrometric experiments is made possible through on-resonance excitation [12], also known as axial modulation. Excitation is usually performed by matching the frequency of

“…CID in a QIT is usually implemented by applying a supplementary direct current (DC) potential [11][12][13] or alternating current (AC) potential [9,14,15] between a pair of trap electrodes and an auxiliary electric field is produced by the above potential. The mass-selected ions are excited by absorbing energy from the electric field and thus move close to the electrodes; therefore, the ion kinetic energy is increased [16].…”

Section: Introductionmentioning

confidence: 99%

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

Dang

Wang

et al. 2016

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.