@article{
 title = {Collisional focusing effects in radio frequency quadrupoles.},
 type = {article},
 year = {1992},
 identifiers = {[object Object]},
 pages = {398-408},
 volume = {3},
 websites = {http://www.ncbi.nlm.nih.gov/pubmed/24243050},
 month = {5},
 id = {2bc944d8-39cd-38ab-ada0-074f9b6dacfd},
 created = {2015-05-08T02:33:55.000Z},
 file_attached = {true},
 profile_id = {f8c267c4-4c39-31dc-80fa-3a9691373386},
 group_id = {63e349d6-2c70-3938-9e67-2f6483f6cbab},
 last_modified = {2015-05-08T10:56:33.000Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {true},
 hidden = {false},
 abstract = {The transmission of ions through a conventional two-dimensional radiofrequency-only (rf) quadrupole has been studied for comparatively high operating pressures between 5 × 10(-4) and 1 × 10(-2) torr. Measurements of signals from mass-resolved analyte ions and total ion currents show that, provided the initial injection ion energy is low (1-30 eV), the ion transmission observed through a small aperture at the exit of the rf quadrupole first increases as the gas pressure increases, reaching a maximum at - 8 × 10(-3) torr before decreasing at higher pressures. This is in direct contrast to the expectations of classical scattering. This "collisional focusing" appears to be analogous to effects seen in three-dimensional ion traps. The collisional focusing increases with the mass of the ion (not mass-to-charge ratio) for masses up to at least 16,950 u. The collisional focusing of the ions is found to be accompanied by significant losses of axial kinetic energy. A Monte Carlo simulation of the energy loss process is reported that can provide agreement with the observed losses for reasonable collision cross-sections. The results suggest that operation of rf quadrupoles at relatively high pressure may find practical application in sampling ions from high (e.g., atmospheric) pressure ion sources.},
 bibtype = {article},
 author = {Douglas, D J and French, J B},
 journal = {Journal of the American Society for Mass Spectrometry},
 number = {4}
}

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Measurements of signals from mass-resolved analyte ions and total ion currents show that, provided the initial injection ion energy is low (1-30 eV), the ion transmission observed through a small aperture at the exit of the rf quadrupole first increases as the gas pressure increases, reaching a maximum at - 8 × 10(-3) torr before decreasing at higher pressures. This is in direct contrast to the expectations of classical scattering. This \"collisional focusing\" appears to be analogous to effects seen in three-dimensional ion traps. The collisional focusing increases with the mass of the ion (not mass-to-charge ratio) for masses up to at least 16,950 u. The collisional focusing of the ions is found to be accompanied by significant losses of axial kinetic energy. A Monte Carlo simulation of the energy loss process is reported that can provide agreement with the observed losses for reasonable collision cross-sections. The results suggest that operation of rf quadrupoles at relatively high pressure may find practical application in sampling ions from high (e.g., atmospheric) pressure ion sources.","bibtype":"article","author":"Douglas, D J and French, J B","journal":"Journal of the American Society for Mass Spectrometry","number":"4","bibtex":"@article{\n title = {Collisional focusing effects in radio frequency quadrupoles.},\n type = {article},\n year = {1992},\n identifiers = {[object Object]},\n pages = {398-408},\n volume = {3},\n websites = {http://www.ncbi.nlm.nih.gov/pubmed/24243050},\n month = {5},\n id = {2bc944d8-39cd-38ab-ada0-074f9b6dacfd},\n created = {2015-05-08T02:33:55.000Z},\n file_attached = {true},\n profile_id = {f8c267c4-4c39-31dc-80fa-3a9691373386},\n group_id = {63e349d6-2c70-3938-9e67-2f6483f6cbab},\n last_modified = {2015-05-08T10:56:33.000Z},\n read = {false},\n starred = {false},\n authored = {false},\n confirmed = {true},\n hidden = {false},\n abstract = {The transmission of ions through a conventional two-dimensional radiofrequency-only (rf) quadrupole has been studied for comparatively high operating pressures between 5 × 10(-4) and 1 × 10(-2) torr. Measurements of signals from mass-resolved analyte ions and total ion currents show that, provided the initial injection ion energy is low (1-30 eV), the ion transmission observed through a small aperture at the exit of the rf quadrupole first increases as the gas pressure increases, reaching a maximum at - 8 × 10(-3) torr before decreasing at higher pressures. This is in direct contrast to the expectations of classical scattering. This \"collisional focusing\" appears to be analogous to effects seen in three-dimensional ion traps. The collisional focusing increases with the mass of the ion (not mass-to-charge ratio) for masses up to at least 16,950 u. The collisional focusing of the ions is found to be accompanied by significant losses of axial kinetic energy. A Monte Carlo simulation of the energy loss process is reported that can provide agreement with the observed losses for reasonable collision cross-sections. 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