Quadrupole mass spectrometer and method of operation thereof

Claim 2

A quadrupole mass spectrometer comprising a quadrupole structure (13, 14, 16); means (22) for applying an RF voltage to said structure to form an electrostatic trapping field in said structure; ionizing means (18,18, 21) for ionizing a sample in said trapping field and forming sample ions with a mass range being trapped in said field; excitation means (25) for applying a pulse of energy to said trapped ions whose frequency distribution includes frequencies corresponding to the characteristic frequencies of motion for the ions of the range of mass-to-charge ratios to be analyzed to cause characteristic motion of said ions; and means (30) for detecting the image currents induced by the characteristic motion of said ions.

Claim 3

A quadrupole mass spectrometer as claimed in Claim 1, characterised in that said structure (13, 14, 16) defines a two dimensional trapping field.

Claim 4

A quadrupole mass spectrometer as claimed in Claim 1, characterised in that said structure (13, 14, 16) defines a three dimensional trapping field.

Claim 5

A quadrupole mass spectrometer as claimed in any preceding claim, characterised by means for applying a D.C. voltage along with the RF voltage to control the electrostatic trapping field so that the range of ion masses which are trapped is controlled.

Claim 6

A quadrupole mass spectrometer as claimed in Claim 3, characterised in that the quadrupole structure includes spaced end caps (14,16) and a ringe electrode (13), said means (22) for applying an RF voltage applying such voltage between the ring electrode (13) and at least one end cap (16) to form said three dimensional electrostatic field, said ionizing means comprising an electron gun for injecting ionizing electrons into said quadrupole structure to ionize a sample and form ions which are trapped in said field, said excitation means applying an excitation pulse to at least one of said end caps (14, 16) to cause characteristic motion of said trapped ions, and said detection means (30) being connected to at least one end cap (16) for detecting the characteristic motion of ions in said trap responsive to said excitation pulse.

Claim 7

A quadrupole mass spectrometer as claimed in Claim 5, characterised in that said means for applying excitation pulses to said two end caps (14, 16) and for detecting the current induced by the characteristic motion comprises a center tapped transformer (76).

Claim 8

A quadrupole mass spectrometer as claimed in Claim 2, characterised in that said quadrupole structure (41) includes spaced linear quadrupole rods and end plates (42, 43) closing the end of the structure, said means (22) for applying an RF voltage applying such voltage between said qualrupole rods; and by means (48) for applying a DC voltage between said end plates (42, 43) whereby said RF and DC voltages form said two dimensional electrostatic field, said excitation means (25) applying an excitation pulse to at least two of said quadrupole rods to cause characteristic motion of said trapped ions, and said detection means (30) being connected to at least two of said quadrupole rods for detecting the characteristic motion of ions in said trap responsive to said excitation pulse.

Claim 9

A quadrupole mass spectrometer as claimed in Claim 5, 6 or 7, characterised in the said excitation means (25) includes means for applying the excitation pulse across said two end caps (14, 16) or plates (42, 43) and said detection means includes means for detecting the characteristic motion current at both said end caps (14, 16) or plates (42,43).

Claim 10

A quadrupole mass spectrometer as claimed in any preceding claim, characterised in that said detection means comprises a high gain amplifier (26) and a digital to analog converter (27).

Claim 13

A method as claimed in Claim 10, characterised by the steps of expelling ions of unwanted mass from said trapping field, and applying a voltage to said structure which causes the ions to undergo collisionally induced dissociation, said excitation voltage including frequencies corresponding to the characteristic frequencies of motion of dissociated trapped ions in the range of mass-to-charge ratios to be analyzed.

Claim 14

A method as claimed in Claim 10 or 11, characterised in that the recorded ion current signals are processed to form a mass spectrum.

Claim 15

A method as claimed in Claim 10, 11 or 12, characterised in that the trapping field is a two dimensional electrostatic field.

Claim 16

A method as claimed in Claim 10, 11 or 12 characterised in that the trapping field is a three dimensional trapping field.