A model for energy transfer in inelastic molecular collisions applicable at steady state or non-steady state and for an arbitrary distribution of collision energies

The mass-selective manipulation of ions at elevated pressure, including mass analysis, ion isolation, or excitation, is of great interest for the development of mass spectrometry instrumentation, particularly for systems in which ion traps are employed as mass analyzers or storage devices. While experimental exploration of high-pressure mass analysis is limited by various difficulties, such as ion detection or electrical discharge at high-pressure, theoretical methods have been developed in this work to study ion/neutral collision effects within quadrupole ion traps and to explore their performance at pressures up to 1 Torr. Ion trapping, isolation, excitation, and resonance ejection were investigated over a wide pressure range. The theoretically calculated data were compared with available experimental data for pressures up to 50 mTorr, allowing the prediction of ion trap performance at pressures more than 10 times higher. (J Am Soc Mass

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confidence: 99%

Ion trap mass analysis at high pressure: A theoretical view

Song

Smith

et al. 2009

“…C ollision induced dissociation (CID) remains by far the most common method used for ion activation in tandem mass spectrometry (MS/ MS) experiments [1,2]. During CID, the internal energy of a parent ion is increased through inelastic collision(s) with a target gas, resulting in the dissociation of parent ions.…”

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confidence: 99%

High amplitude short time excitation: A method to form and detect low mass product ions in a quadrupole ion trap mass spectrometer

Cunningham

Glish

Burinsky

2006

Collision induced dissociation (CID) in a quadrupole ion trap mass spectrometer using the conventional 30 ms activation time is compared with high amplitude short time excitation (HASTE) CID using 2 ms and 1 ms activation times. As a result of the shorter activation times, dissociation of the parent ions using the HASTE CID technique requires resonance excitation voltages greater than conventional CID. After activation, the rf trapping voltage is lowered to allow product ions below the low mass cut-off to be trapped. The HASTE CID spectra are notably different from those obtained using conventional CID and can include product ions below the low mass cut-off for the parent ions of interest. . During CID, the internal energy of a parent ion is increased through inelastic collision(s) with a target gas, resulting in the dissociation of parent ions. CID is the result of two distinct events; parent ion activation (collisional activation) and parent ion dissociation [3]. The appearance of an MS/MS spectrum, both product ion formation and abundance, is a function of the amount of energy deposited into the parent ion during the activation period [4,5]. Activation times for CID in rf trapping instruments typically range between 10 and 50 ms; however, CID can be accomplished using much shorter activation times in these instruments [6].For rf trapping instruments, the Mathieu parameters q z , (proportional to the applied fundamental ac rf voltage), and a z , (proportional to the applied dc voltage) determine if ions of a given mass-to-charge will be trapped. Typically, and in these experiments, rf trapping instruments are operated at a z ϭ 0, so theoretically ions with q z values from 0 to 0.908 are trapped. As the mass-to-charge value of an ion increases, its q z value decreases. Thus, the mass-to-charge value corresponding to a q z value of 0.908 is the minimum mass-to-charge value of ions trapped and is termed the low mass cut-off (LMCO).Each ion held by the trapping field exists in a pseudo potential well with the well depth proportional to the q z for each mass-to-charge value. Hence, smaller mass-tocharge ions, which have larger q z values, exist in deeper wells than larger mass-to-charge ions, which have smaller q z values [7]. To implement CID, a q z value is selected that allows the kinetic energy of the parent ion to increase via power absorption from a supplementary resonance excitation voltage without exceeding the pseudo potential well depth. Typical q z values for CID in quadrupole ion traps range from 0.2 to 0.3 and supplementary resonance excitation voltages with amplitudes greater than 1 V are not generally utilized [8]. A trade-off in the selection of the q z value for CID is that product ions with mass-to-charge values below the LMCO will not be trapped. This means that product ions with mass-to-charge values less than ϳ25-30% of the parent ion mass-to-charge are not observed in the MS/MS spectrum.Previous research conducted using "fast excitation" CID has shown that collisional activation can be accom-

“…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].…”

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confidence: 99%

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

Tolmachev

Vilkov

Bogdanov

et al. 2004

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 ...