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

Abstract

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 ...

Investigation of the gas phase reactivity of the 1-adamantyl radical using a distonic radical anion approach

“…It has been demonstrated that for low Q values (such as 0.25, used for these experiments) the effective temperature of ions held at zero collision energy inside an ion trap is approximately equivalent to the temperature of the buffer gas, and hence the temperature of the gas inlet to the trap itself. 31,32 Gronert has determined the effective temperature of ions contained within a three dimensional ion trap (from the same manufacturer as the linear trap employed herein) to be 310±20 K, by measurement of the equilibrium constant of a complexation reaction displaying very large temperature dependence. 32 Collision rates z have been calculated at 307 K by average dipole orientation (ADO) theory 33 using an available Fortran routine 34 to enable reaction efficiencies to be estimated.…”

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

“…The internal energy of ions in the trap can be characterized by a Boltzmann distribution and effective ion temperature [31]. Here the following equation was used to calculate the effective temperature [31]:…”

Vapor Treatment of Electrospray Droplets: Evidence for the Folding of Initially Denatured Proteins on the Sub-Millisecond Time-Scale

“…Typically, a sample is ionized via nano-ESI and then the metering valves are opened to introduce the reagent vapors as desired. In some cases, the charge states were difficult to resolve due to the presence of adducts (e.g., attached acid or base molecules), but these were easily removed using dipolar DC collision-induced dissociation (DDC-CID), a broad-band collisional activation technique [47][48][49].…”

“…When HCl vapors were introduced into the interface, higher charge state distributions (+27 to +14) of both apo-and holo-myoglobin were observed, as well as a third distribution at the +8 to +9 charge states that corresponded to myoglobin with two heme groups (Figure 8b). DDC CID [47][48][49] was used to clean-up the spectra in order to better determine the identity of the latter distribution. The observation of the three distinct myoglobin distributions (viz., apo-, holo-, and two heme versions) from a solution of holo-myoglobin prepared at basic pH, ionized in the positive mode, and exposed to acid vapors might be rationalized in several ways.…”