QUADRUPOLE MASS SPECTROMETER HAVING RESOLUTION VARIATION CAPABILITY

• US 3,784,814 A
• Filed: 03/12/1971
• Issued: 01/08/1974
• Est. Priority Date: 03/14/1970
• Status: Expired due to Term

• Current Assignee: Masahiko Sakimura, Tadashi Sakai, Yoichi Ino
• Original Assignee: Masahiko Sakimura, Tadashi Sakai, Yoichi Ino
• Inventors: Sakai, Tadashi, Ino, Yoichi, Sakimura, Masahiko
• Primary Examiner(s): Lindquist, William F.
• Application Number:
  US05/123,687
• Time in Patent Office: 1,033 Days
• Field of Search: 250/41.9DS
• US Class Current: 250/290
• CPC Class Codes: H01J 49/4215 Quadrupole mass filters H01J49/4225 takes precedence
• CPC Class Codes: H01J 49/429 Scanning an electric parameter, e.g. voltage amplitude or frequency

Abstract

A quadrupole mass spectrometer includes an ionization chamber, an ion detector, and a quadrupole structure having four electrodes extending therebetween. A d.c. voltage U and a high frequency voltage of amplitude V are linearly superimposed and are applied to the electrodes while maintaining the relationship U Alpha MV - K, where Alpha M denotes a critical U/V ratio. This constrains the mass peaks of a spectrum to be of substantially uniform shape. Variation of the parameter K permits the spectrometer resolution to be varied. In accordance with one aspect of the present invention, the d.c. voltage is maintained constant at values lower than the peak value of the stability curve for atomic hydrogen in a range of smaller values of the voltage amplitude V. The spectrum for atomic hydrogen can thereby be isolated.

Claims

1. A variable resolution system for a quadrupole mass spectrometer comprising an ionization chamber, an ion detector and a quadrupole structure having four electrodes extending between said detector and chamber;

said electrodes being symmetrically disposed with respect to the axis thereof;

means for electrically connecting alternate ones of said electrodes together to form two electrode pairs;

said electrode pairs having direct current potentials of an opposite polarity applied thereto;

wherein the improvement comprises;

a variable d.c. source for supplying a d.c. voltage of a magnitude U to said electrodes of said quadrupole structure, a high frequency sinusoidal voltage source for supplying a high frequency voltage of variable amplitude V to said electrodes, and means for varying the d.c. voltage U and the amplitude V of the high frequency voltage in a manner satisfying the relationship U Alpha MV K, where Alpha M denotes a critical U/V ratio at the limit of stable spectrometer response, and K denotes a constant determining the peak width Delta m of a mass spectrum determined by said spectrometer;

whereby all the mass peaks of the spectrum are characterized by a substantially identical shape.

2. A variable resolution system for a quadrupole mass spectrometer comprising an ionization chamber, an ion detector and a quadrupole structure having four electrodes extending between said detector and chamber;

said electrodes being symmetrically disposed with respect to the axis thereof;

means for electrically connecting alternate ones of said electrodes together to form two electrode pairs;

said electrode pairs having direct current potentials of an opposite polarity applied thereto;

wherein the improvement comprises;

a source of high frequency sinusoidal voltage of variable amplitude V;

means for producing a d.c. voltage proportional to the amplitude V of the high frequency voltage;

variable resistor means forming a voltage divider for said d.c. voltage and for providing a second d.c. voltage of a value Alpha MV, where Alpha M denotes a critical U/V ratio at the limit of stable spectrometer response;

means for biasing said second d.c. voltage of magnitude Alpha MV with a third d.c. voltage of magnitude -K, where K denotes a constant which determines the peak width Delta m of a mass spectrum; and

means for applying the high frequency voltage and the resultant d.c. voltage of magnitude Alpha MV-K to said electrodes of said quadrupole structure.

3. A variable resolution system for a quadrupole mass spectrometer comprising an ionization chamber, an ion detector and a quadrupole structure having four electrodes extending between said detector and chamber;

said electrodes being symmetrically disposed with respect to the axis thereof;

means for electrically connecting alternate ones of said electrodes together to form two electrode pairs;

said electrode pairs having direct current potentials of an opposite polarity applied thereto;

wherein the improvement comprises;

a source of high frequency sinusoidal voltage of variable amplitude V for application to said electrodes of said quadrupole structure;

means for generating a d.c. voltage U for connection to said electrodes which remains at a constant value of H for values of V, wherein O<

V <

or = K/ Alpha M-H and which varies in accordance with the equation U Alpha MV-K for a value of V in excess of K/ Alpha M-H, where Alpha M denotes a critical U/V ratio at the limit of stable sPectrometer response and K denotes a constant determining the peak width Delta m of a mass spectrum determined by said spectrometer;

means for varying the parameter K to vary peak width; and

means for varying the parameter H to establish said parameter H at a value smaller than the peak value of the stable spectral response for atomic hydrogen.

4. A variable resolution system for a quadrupole mass spectrometer comprising an ionization chamber, an ion detector and a quadrupole structure having four electrodes extending between said detector and chamber;

said electrodes being symmetrically disposed with respect to the axis thereof;

means for electrically connecting alternate ones of said electrodes together to form two electrode pairs;

said electrode pairs having direct current potentials of an opposite polarity applied thereto;

wherein the improvement comprises;

a source of high frequency sinusoidal voltage of the variable amplitude V;

means for generating a d.c. voltage proportional to the amplitude V of said high frequency voltage;

voltage divider means for deriving, by voltage division of said d.c. voltage, a second d.c. voltage of a value Alpha MV, where Alpha M denotes a critical U/V ratio at the limit of stable spectrometer response, means for biasing said second d.c. voltage with a third d.c. voltage of a value K, where K denotes a parameter that determines the peak width Delta m of a spectrum;

means for rendering said biased d.c. voltage Alpha MV - K equal to a null output for a value of V between zero and K/ Alpha M;

means for comparing the output from said rendering means with a constant voltage H and choosing the greater of the two as its output U, the value of H being chosen less than the peak value of the stable spectral response for atomic hydrogen and means for applying said output U and said high frequency voltage to the electrodes of the quadrupole structure.

5. A variable resolution system according to claim 4, further including means for varying the magnitude of the voltage H.