@article {2402,
	title = {LINEAR QUADRUPOLES IN MASS SPECTROMETRY},
	journal = {Mass Spectrometry Reviews},
	volume = {28},
	number = {6},
	year = {2009},
	note = {ISI Document Delivery No.: 515CWTimes Cited: 5Cited Reference Count: 145Douglas, D. J.},
	month = {Nov-Dec},
	pages = {937-960},
	type = {Review},
	abstract = {The use of linear quadrupoles in mass spectrometry as mass filters and ion guides is reviewed. Following a tutorial review of the principles of mass filter operation, methods of mass analysis are reviewed. Discussed are extensions of quadrupole mass filters to higher masses, scanning with frequency sweeps of the quadrupole waveform, operation in higher stability regions, and operation with rectangular or other periodic waveforms. Two relatively new methods of mass analysis the use of "islands of stability" and "mass selective axial ejection" are then reviewed. The optimal electrode geometry for a quadrupole mass filter constructed with round rods is discussed. The use of collisional cooling in quadrupole ion guides is discussed along with ion guides that have axial fields. Finally, mass analysis with quadrupoles that have large distortions to the geometry and fields is discussed. An Appendix gives a brief tutorial review of definitions of electrical potentials and fields, as well as the units used in this article. (C) 2009 Wiley Periodicals, Inc., Mass Spec Rev 28:937-960, 2009},
	keywords = {2ND STABILITY REGION, axial fields, AXIAL-FIELD, CHARGED-PARTICLE, COLLISION-INDUCED DISSOCIATION, distorted fields, FRINGING FIELDS, ion guide, ION OPTICAL-PROPERTIES, linear, mass filter, mass scans, multipoles, OCTOPOLE FIELDS, QUADRUPOLE, quadrupole excitation, RADIO-FREQUENCY, RESOLUTION, SEPARATION MODE, STABILITY, TRAJECTORIES, VOLTAGE COMPONENT},
	isbn = {0277-7037},
	url = {<Go to ISI>://000271445200005},
	author = {Douglas, D. J.}
}
@article {2691,
	title = {Overcoming Field Imperfections of Quadrupole Mass Filters with Mass Analysis in Islands of Stability},
	journal = {Analytical Chemistry},
	volume = {81},
	number = {14},
	year = {2009},
	note = {ISI Document Delivery No.: 472MFTimes Cited: 2Cited Reference Count: 24Zhao, XianZhen Xiao, Zilan Douglas, D. J.},
	month = {Jul},
	pages = {5806-5811},
	type = {Article},
	abstract = {We have constructed, and tested as mass filters, linear quadrupoles with added hexapole fields of 4\%, 8\%, and 12\%, with and without added octopole fields. A hexapole field can be added to the field of a linear quadrupole by rotating the two y rods toward an x rod. This also adds an octopole field which can be removed by making the x rods greater in diameter than the y rods. In comparison to conventional quadrupole mass filters these rod sets have severely distorted quadrupole fields, with a mix of both even and odd higher spatial harmonics. They allow evaluating the performance of rod sets with strong geometric and field distortions as mass filters. Conventional mass analysis at the tip of the stability diagram has been compared to mass analysis using islands of stability. The stability islands are produced by applying an auxiliary quadrupole excitation field to the quadrupole. We show that with normal mass analysis at the tip of the stability diagram, the transmission, resolution, and peak shapes are relatively poor in comparison to a conventional rod set. However, the use of islands of stability dramatically improves the resolution and peak shape, and in some cases ion transmission, suggesting that mass analysis with islands of stability may provide a method to overcome a wide range of field imperfections in linear quadrupole mass filters.},
	keywords = {EXCITATION, FREQUENCIES, LINEAR ION-TRAP, OCTOPOLE FIELDS, SPECTROMETRY, TRANSMISSION},
	isbn = {0003-2700},
	url = {<Go to ISI>://000268135000029},
	author = {Zhao, X. Z. and Xiao, Z. L. and Douglas, D. J.}
}
@article {1441,
	title = {Linear quadrupoles with added hexapole fields},
	journal = {Journal of the American Society for Mass Spectrometry},
	volume = {17},
	number = {8},
	year = {2006},
	note = {ISI Document Delivery No.: 071YITimes Cited: 14Cited Reference Count: 26Konenkov, Nikolai Londry, Frank Ding, Chuanfan Douglas, D. J.},
	month = {Aug},
	pages = {1063-1073},
	type = {Article},
	abstract = {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 hexapole field can be constructed with round rods by rotating two rods (say the y rods) towards an x rod. Computer simulations are used to investigate the possibility of mass analysis with quadrupoles with added hexapole fields. We find that a quadrupole with an added hexapole field in the range 2-12\% can provide mass analysis provided the dc is applied with the correct polarity and value. When a rod set is constructed with round rods, other multipoles in the potential degrade the peak shape, resolution and transmission. The largest of these after the quadrupole and hexapole are a dipole and octopole term. With round rod sets, the peak shape can be improved by using different diameters for the x and y rod pairs to minimize the octopole term in the potential and by injecting ions at the field center where the dipole term is zero. Calculations of the boundaries of the stability diagram for this case show the boundaries move out, relative to those of a pure quadrupole field, but remain sharp.},
	keywords = {EXCITATION, ION-TRAP, MASS-SPECTROMETRY, OCTOPOLE FIELDS},
	isbn = {1044-0305},
	url = {<Go to ISI>://000239639400003},
	author = {Konenkov, N. and Londry, F. and Ding, C. F. and Douglas, D. J.}
}
@article {1097,
	title = {Linear ion traps in mass spectrometry},
	journal = {Mass Spectrometry Reviews},
	volume = {24},
	number = {1},
	year = {2005},
	note = {ISI Document Delivery No.: 888OJTimes Cited: 73Cited Reference Count: 145},
	month = {Jan-Feb},
	pages = {1-29},
	type = {Review},
	abstract = {Linear ion traps are finding new applications in many areas of mass spectrometry. In a linear ion trap, ions are confined radially by a two-dimensional (2D) radio frequency (RF) field, and axially by stopping potentials applied to end electrodes. This review focuses on linear ion trap instrumentation. Potentials and ion motion in linear multipole fields and methods of ion trapping, cooling, excitation, and isolation are described. This is followed by a description of various mass discrimination effects that have been reported with linear ion traps. Linear ion traps combined in various ways with three-dimensional (3D) traps, time-of-flight (TOF) mass analyzers, and Fourier transform ion cyclotron resonance mass spectrometers are then given. Linear ion traps can be used as stand alone mass analyzers, and their use for mass analysis by Fourier transforming image currents, by mass selective radial ejection, and by mass selective axial ejection are reviewed. (C) 2004 Wiley Periodicals, Inc.},
	keywords = {analysis, CYCLOTRON-RESONANCE, ELECTROSPRAY-IONIZATION, EXCITATION, EXTERNAL ACCUMULATION, FRINGING FIELDS, INVERSE FOURIER-TRANSFORM, ion traps, linear multipoles, mass, MOLECULE REACTION, OCTOPOLE FIELDS, OF-FLIGHT, QUADRUPOLE, RADIOFREQUENCY, RESONANCE, space charge, STORAGE ASSISTED DISSOCIATION, SYSTEM},
	isbn = {0277-7037},
	url = {<Go to ISI>://000226383800001},
	author = {Douglas, D. J. and Frank, A. J. and Mao, D. M.}
}
