Quadrupole mass analyzer and method of operation in RF only mode to reduce background signal
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United States of America Patent
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Feb 27, 2001
Grant Date -
N/A
app pub date -
Jan 28, 1999
filing date -
Jan 28, 1999
priority date (Note) -
Expired
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Abstract
A method of and apparatus for mass analysis utilizes two quadrupole rod sets located in a vacuum chamber, this first rod set is intended to collimate the ions with an RF-only voltage. An RF-only voltage to the second quadrupole rod set and this is operated so that desired ions having a mass-to-charge ratio giving a q value of substantially 0.907 gain additional axial kinetic energy upon leaving the second quadrupole rod set. These desired ions are then detected by separating the ions with increased axial kinetic energy. It has been discovered that the pressure within the first quadrupole rod can be adjusted to enhance separation between ions gaining the additional axial kinetic energy and other ions, the pressure times the length in the first quadrupole rod set can be in the range 4.times.10.sup.-2 torr-cm. to 1.6.times.10.sup.-1 torr-cm.
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