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- Donald J Douglas, Nikolai V Konenkov
- Rapid communications in mass spectrometry : RCM
- 2002

The influence of the ratio of the rod radius, r, to field radius, r(0), on the peak shape for a linear quadrupole mass filter constructed with round rods has been investigated. The expansion of the potential in multipoles, phi(N),Phi(x, y) = sum(infinity)(N=0)A(N)phi(N)/r(N)(0) has been considered, and the peak shape and resolution have been determined by… (More)

- Michael Sudakov, Nikolai V Konenkov, Donald J Douglas, Tatiana Glebova
- Journal of the American Society for Mass…
- 2000

Resonant quadrupole excitation of ions confined in a radio frequency quadrupole field with angular frequency omega by an excitation signal with angular frequency omega has been investigated theoretically. It is shown that the spectrum of excitation frequencies has considerable structure which corresponds to different orders of excitation. The resonance… (More)

- Chuanfan Ding, Nikolai V Konenkov, Donald J Douglas
- Rapid communications in mass spectrometry : RCM
- 2003

The performance of quadrupole mass filters with added octopole fields in the range 2.0-4.0% has been investigated. The added fields are much greater than those normally added to conventional rod sets by mechanical tolerances or construction errors. Quadrupole rod sets with added octopole fields were constructed with round rods by making one pair of rods… (More)

- Nikolai V Konenkov, Michael Sudakov, Donald J Douglas
- Journal of the American Society for Mass…
- 2002

The theory of the computer calculation of the stability of ion motion in periodic quadrupole fields is considered. A matrix approach for the numerical solution of the Hill equation and examples of calculations of stability diagrams are described. The advantage of this method is that it can be used for any periodic waveform. The stability diagrams with… (More)

- Nikolai V Konenkov, Frank A Londry, Chuanfan Ding, Donald J Douglas
- Journal of the American Society for Mass…
- 2006

Linear quadrupoles with added hexapole fields are described. The shifts in ion oscillation frequency caused by the addition of a hexapole field are calculated within the effective potential model. Methods to construct linear quadrupoles with added hexapole fields with exact electrode geometries and with round rods are discussed. A quadrupole with added… (More)

- Donald J Douglas, Nikolai V Konenkov
- Rapid communications in mass spectrometry : RCM
- 2014

RATIONALE
For mass analysis, linear quadrupole ion traps operate with dipolar excitation of ions for either axial or radial ejection. There have been comparatively few computer simulations of this process. We introduce a new concept, the excitation contour, S(q), the fraction of the excited ions that reach the trap electrodes when trapped at q values near… (More)

- Hui Qiao, Cong Gao, Dunmin Mao, Nikolai V Konenkov, Donald J Douglas
- Rapid communications in mass spectrometry : RCM
- 2011

Methods to reduce mass shifts caused by space charge with mass-selective axial ejection from a linear quadrupole ion trap are investigated. For axial ejection, dipole excitation is applied to excite ions at q ≈ 0.85. The trapping radiofrequency (rf) voltage is scanned to bring ions of different m/z values into resonance for excitation. In the fringing field… (More)

- Nikolai V Konenkov, Xianzhen Zhao, Zilan Xiao, Donald J Douglas
- Journal of the American Society for Mass…
- 2007

Mass analysis with linear quadrupole mass filters is possible by forming "islands" in the stability diagram with auxiliary quadrupole excitation. In this work, computer simulations are used to calculate stability boundaries, island positions, and peak shapes and ion transmission for mass analysis with linear quadrupole mass filters that have added octopole… (More)

- Nikolai V Konenkov, A N Korolkov, Marat Machmudov
- Journal of the American Society for Mass…
- 2005

Modulation of the voltages applied to a quadrupole mass filter (QMF), either RF or RF and DC, leads to splitting of the stability region into islands of stability. The ion optical properties, such as transmission, resolving power and peak tails of the first upper stability islands have been investigated by numerical simulation of ion trajectories. The… (More)

- Donald J Douglas, Nikolai V Konenkov
- Rapid communications in mass spectrometry : RCM
- 2012

RATIONALE
If too many ions are stored in a linear quadrupole ion trap, space charge causes the oscillation frequencies to decrease. Ions therefore appear at higher apparent mass-to-charge ratios in a mass spectrum. To further understand this process, we have used trajectory calculations of ions to determine mass shifts.
METHODS
Two models of the ion cloud… (More)