Enhancement of Ion Activation and Collision-Induced Dissociation by Simultaneous Dipolar Excitation of Ions inx- andy-Directions in a Linear Ion Trap

Abstract

Collision-induced dissociation (CID) in linear ion traps is usually performed by applying a dipolar alternating current (AC) signal to one pair of electrodes, which results in ion excitation mainly in one direction. In this paper, we report simulation and experimental studies of the ion excitation in two coordinate directions by applying identical dipolar AC signals to two pairs of electrodes simultaneously. Theoretical analysis and simulation results demonstrate that the ion kinetic energy is higher than that using the conventional CID method. Experimental results show that more activation energy (as determined by the intensity ratio of the a4/b4 fragments from the CID of protonated leucine enkephalin) can be deposited into parent ions in this method. The dissociation rate constant in this method was about 3.8 times higher than that in the conventional method under the same experimental condition, at the Mathieu parameter qu (where u = x, y) value of 0.25. The ion fragmentation efficiency is also significantly improved. Compared with the conventional method, the smaller qu value can be used in this method to obtain the same internal energy deposited into ions. Consequently, the "low mass cut-off" is redeemed and more fragment ions can be detected. This excitation method can be implemented easily without changing any experimental parameters.

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

“…It has been recognized that the ion moving radius (i.e., the r i value) by dual-direction excitation method is greater than that by conventional single-direction excitation method [26]. This also can be seen from Supplementary Figure S1 (see Supplemental Information), which shows the comparison of ion trajectory with the above two methods by direct numerical simulations (the simulation method is described in the following section).…”

“…As a consequence, the ion average energy is improved (the average energy with single-direction and dual-direction excitation method are 1.7eV and 2.8 eV, respectively). Because the well depth in the xy plane is greater than that in either x-or y-direction [26], ions can still be trapped.…”

“…The ion circulates about central axis of the trapping field because of the rotating supplemental resonant field and the ion kinetic energy can be increased by this method. Dang et al [26] recently introduced a method that can enhance the ion activation and CID in a LIT by employing two identical dipolar AC signals. In this method, ions are excited in two radial coordinate directions simultaneously and mainly move along the diagonal direction of the trapping region.…”

Linear ion trap with added octopole field component: the property and method

“…Several ITs with different geometries were built and tested according to the simulation results, such as sCRIT‐0, sCRIT‐3 and sCRIT‐4. All experiments were performed on a homebuilt three‐stage differential pumping vacuum system as described previously . Ions from an electrospray ionization (ESI) source were first introduced into a quadrupole ion guide through a skimmer and then proceeded through a lens into the sCRIT.…”

“…All experiments were performed on a homebuilt three-stage differential pumping vacuum system as described previously. [18,38,39] Ions from an electrospray ionization (ESI) source were first introduced into a quadrupole ion guide through a skimmer and then proceeded through a lens into the sCRIT. A voltage of 4 kV for ESI was used.…”