Mass selective notch filter with quadrupole excision fields

A method for selectively removing a target ion with a specific mass-to-charge ratio from an ion beam;

• comprising:
• driving the electrical potential of four electrodes of a quadrupole as two pairs of opposite polarities with an oscillating voltage which is a superposition comprising a rf quadrupole frequency component and an excision frequency component, the target ion having a dominant resonant frequency in response to the rf quadrupole frequency component, the rf quadrupole frequency being selected to cause ions above a selected mass-to-charge ratio to be guided along the quadrupole, the excision frequency being selected to be twice the dominant resonant frequency of the target ion to cause the target ion to resonate and be removed from the ion beam which is directed to traverse from an inlet end to an outlet end of the quadrupole.

A method for selectively removing a target ion with a specific mass-to-charge ratio from an ion beam, comprising:

• driving the electrical potential of four electrodes of a quadrupole with an oscillating voltage which is a superposition comprising a rf quadrupole frequency component and an excision frequency component, the rf quadrupole frequency component being provided by a first oscillator and the excision frequency component being provided by a second oscillator, the oscillators being connected in series and to the electrodes in two pairs such that any two oppositely facing electrodes of the quadrupole form a pair having the same electrical potential with each other but oscillatingly different from the electrical potential of the other pair, the rf quadrupole frequency being selected to cause ions above a selected mass-to-charge ratio to be guided along the quadrupole, the excision frequency being selected to cause the target ion to resonate and be removed from the ion beam which is directed to traverse from an inlet end to an outlet end of the quadrupole, while allowing ions above a selected mass-to-charge ratio and different from the mass-to-charge ratio of the target ion to remain in the ion beam traversing through the quadrupole.