@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 {604,
	title = {Quadrupole mass filters with octopole fields},
	journal = {Rapid Communications in Mass Spectrometry},
	volume = {17},
	number = {22},
	year = {2003},
	note = {ISI Document Delivery No.: 742BLTimes Cited: 16Cited Reference Count: 23},
	pages = {2495-2502},
	type = {Article},
	abstract = {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 greater in diameter than the other pair. For positive ions, resolution at half height of only about 200 is possible if the negative direct current (dc) output of the quadrupole power supply is connected to the smaller rods. If the positive dc output of the quadrupole power supply is connected to the smaller rods, the resolution improves dramatically; a resolution at half height of 5800 has been observed with a rod set with 2.6\% added octopole field. For negative ions the best resolution is obtained with the polarity of the dc reversed, i.e. with the negative dc applied to the smaller rods. These findings are unexpected in view of the literature that argues that to obtain high mass resolution with quadrupole mass filters, higher order multipoles must be kept as small as possible. Numerical simulations of peak shapes agree qualitatively with experiments. Simulation of the boundaries of the first stability region for positive ions shows that when the positive dc is applied to the smaller rods, the addition of a 2.0\% octopole field causes the boundaries to shift slightly but the boundaries are well defined, and the tip of the stability region remains sharp. When the positive dc is applied to the larger rods, the boundaries of the stability region move out and become diffuse. For instruments that require a rod set that can be used both as a linear trap and a mass filter, these rod sets may offer improved trap performance while still being capable of providing conventional mass analysis. Copyright (C) 2003 John Wiley Sons, Ltd.},
	keywords = {ELECTRODES, LINEAR ION-TRAP, OF-FLIGHT SYSTEM, PERFORMANCE, SPATIAL HARMONICS, SPECTROMETER},
	isbn = {0951-4198},
	url = {<Go to ISI>://000186495300007},
	author = {Ding, C. F. and Konenkov, N. V. and Douglas, D. J.}
}
