Mass selectivity of dipolar resonant excitation in a linear quadrupole ion trap

Abstract

The excitation contour, S(q), introduced here, is a useful tool for studying the ejection process. The excitation strength, excitation time and buffer gas pressure interact in a complex way but, when set properly, a mass resolution R0.5 of at least 10,000 can be obtained at a mass-to-charge ratio of 609.

Mass resolution of linear quadrupole ion traps with round rods

“…Dipolar resonant excitation of ions with an auxiliary waveform is widely used for mass‐selective ejection of ions from quadrupole ion traps . Douglas and Konenkov proposed an approach to describe the resonant dipolar or quadrupolar excitation processes of ions in linear quadrupole ion traps in which ions are characterized by Gaussian distributions of the initial positions and velocities. Numerical simulations of the motion of ions in a quadrupole field together with ion excitation with an auxiliary dipole field or various forms of quadrupole excitation were used.…”

Dipole Excitation: A New Method for Mass Analysis with a Quadrupole Mass Filter

“…The coefficient A 1 is the normalized (dimensionless) amplitude of the dipole spatial harmonics of the 2D electric field induced by the dipole excitation in x or y for a given round rod set. For a round rod set with r/r 0 = 1.13 (where r is the round rod radius) A 1 = 0.7982 ≈ 0.8 [24]. For a pure quadrupole field we take A 1 = 1.…”

“…It is also possible to use resonances on the next higher harmonics with frequencies [24]. For example, for the excitation lines with β y = 0.01 and β x = 0.99 near stability boundaries (Figure 1), the required frequencies are ω y = 1.005 Ω and ω x = 1.495 Ω (k = 1) and ω y = 0.995Ω and ω x = 1.505 Ω (k = − 1).…”

“…The equations of ion motion in the x and y directions with dipole excitation can be written with dimensionless variables [13,24] as…”

“…The use of dipole resonant excitation of the ions was first proposed by Fischer in 1959 [13]. Much later, dipole excitation of ion oscillation found broad application in linear and 3D ion traps for mass selective detection of ions [14][15][16][17][18][19][20][21][22][23][24][25]. The oscillation frequencies of ions in a quadrupole field, ω u , are given by ω u = (2n + β u )Ω/2, where u is x or y, n = 0, ± 1, ± 2 … and Ω is the angular frequency of the main quadrupole rf.…”