SU1742901A1 - Ion-cyclotron mass spectrometer - Google Patents

Abstract

Use: in scientific instrumentation, namely in the technique of mass spectrometry and mainly in the study of the mechanisms and kinetics of ionic molecules of ry reactions, precision measurement of ion masses, analysis and identification of substances and their mixtures. SUMMARY OF THE INVENTION: The end holding electrodes are made of two outer 1 (2) and inner 3 (4) parallel-installed grid electrodes at a distance smaller than the size of the elementary cell of the grid and 1/2 offset from each other, , 8,9,10 and end electrodes have ring-shaped holding electrodes 5, 6, the ring electrodes 5 and 6 and the outer grid electrodes 1, 2 of holding, are connected to a source of opposite voltages, and the internal grid electrode is en. 3 il. w w y

Description

The invention relates to a technique of mass spectrometry and is mainly used in the field of research into the mechanisms and kinetics of ionic molecules of ry reactions, precision measurement of ion masses, analysis and identification of substances and their mixtures.

Ion-cyclotron resonant mass spectrometers are known that contain a measuring cell with lateral detection and excitation electrodes and two retarding end electrodes that are connected to a constant voltage source with a sign that matches the sign of the ions under study. In such mass spectrometers, functionality is limited by the ability to hold and examine only either positive or negative ions in the measuring cell at a time.

The closest to the present invention is an ion-cyclotron resonant mass spectrometer containing a measuring cell with an ion source, side excitation and detection electrodes and composite end electrodes, each of which consists of two parallel external and internal electrodes, and the internal electrodes are made of mesh and are grounded .

However, the functionality of the device is limited by the ability to retain only ions of the same polarity in the measuring cell. Ion retention is carried out under static conditions of crossed electric and magnetic

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fields, and in the measuring cell it is impossible to simultaneously hold positive and negative ions. The functionality of the device does not allow to investigate ion-molecular reactions involving ions of different signs,

The aim of the invention is to expand the functional capabilities of the instrument due to the possibility of simultaneously holding and studying ions of a different sign in the measuring cell of the spectrometer.

The goal is achieved by the fact that in a well-known ion-cyclotron resonant mass spectrometer containing a measuring cell with an ion source, side excitation and detection electrodes and composite end electrodes, each of which consists of two parallel external and internal electrodes, and the internal electrodes are made of mesh and grounded, annular holding electrodes are additionally installed between the side electrodes and the end electrodes, and the ring holding electrodes and external end electrodes are connected to sources of reference voltages of opposite sign.

FIG. 1 shows a general view of the proposed device; FIG. 2 is a longitudinal te4eHne; in fig. 3 is a graph of the potential distribution of the electric field U along the axis of the measuring cell, where h is the distance between the end grid electrodes, 2 is the distance between the centers of the annular holding electrodes.

The measuring cell of the spectrometer contains: 1,2 - external end electrodes; 3,4- internal end grid electrodes; 5, b - annular holding electrodes; 7, 8 — side excitation electrodes; 9,10 - lateral detection electrodes; 11 - ion source; 12, 13 are sources of reference voltages of internal annular holding electrodes; 14, 15 are sources of reference voltages of external holding electrodes.

The device works as follows.

Permanent potentials from the reference sources 12-15 are supplied to the outer end electrodes 1, 2 and to the ring holding electrodes 5, 6. In this case, a configuration of electric fields is created in the measuring cell of the spectrometer, which retains both positive and negative ions. The ion source 11 creates a bundle of positive and negative ions in the measuring cell of the spectrometer. For positive ions

(at the polarity of the reference stresses indicated in FIG. 1) the retention takes place in the center of the measuring cell in an electric field approximated by a hyperboloidal, the retention of negative ions is carried out in close proximity to the end grid electrodes due to their reflection from the highly inhomogeneous electric field created

0 external and internal end electrodes. The side excitation electrodes 7, 8 are connected to an alternating radio frequency voltage generator with a frequency equal to the cyclotron frequency c of the test

5 ions to excite their cyclotron movement.

As a result of the action of alternating voltage, a rotating ion bundle is formed in the cell of the spectrometer, which

0 creates an induced charge on the lateral detection electrodes 9, 19. The induced current through the differential amplifier of the electronic system enters the data processing system and is represented as

5 of the mass spectrum of the ions contained in the measuring cell of the spectrometer, while the peaks of the positive and negative ions are different in their position in the mass spectrum, since they differ by a magnitude corresponding to the mass of the electron.

Expansion of the functionality of the device, i.e., the ability to hold and study oppositely charged ions in the measuring cell,

5 is achieved by installing ring-shaped holding electrodes, as well as their appropriate connection to the sources of reference voltage.

The escape of ions from the measuring

0 cells in the transverse direction prevents the presence of a magnetic field B, the retention of ions in the direction of the magnetic field lines is accomplished by creating a special distribution of the electric field (Fig. 3) by applying opposite polarities Ui and Ua on the end external electrodes and annular retention electrodes. Areas of localization of positive and

0 negative ions are indicated by AI and A2, respectively. The retention of positively charged ions occurs in an electrostatic field created by the potential of the ring-shaped holding electrodes Ua.

5 The retention of negatively charged ions occurs as a result of the action of a force directed to the center of the cell on the side of a highly inhomogeneous electric field and determined by a potential difference between the outer and inner end electrodes near the inner end grid electrodes.

Let us now consider the conditions of retention of ions in the process of detection, i.e., after their cyclotron motion is excited. The positively charged ions are retained by the hyperboloidal electric field created by annular retention electrodes 5,6. Negatively charged ions are pushed out by a hyperboloidal field to the periphery of the measuring cell, where they fall into a spatially non-uniform field created by the outer and inner end electrodes. In the case when the distance between the outer and inner end electrodes is less than the size of the elementary cell of grid I, in the middle of the elementary cells of the internal grid electrodes there is a noticeable sag of potential caused by the potential on the external grid retention electrode. In the measuring cell at its periphery, the configuration of the electric fields is periodic with period I. When rotating negatively charged ions with a cyclotron frequency ok in a plane perpendicular to the magnetic field, the conditions of their retention will be reflected from periodically repeating regions of the retarding potential:

 - dt

Vn ftfc Rc where Vn is the diverting velocity of the ion in the direction of the retention mesh electrodes; L is the diameter of the wires of the grid electrodes; Rc is the radius of the cyclotron rotation of the ions.

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For typical values of Vn, corresponding to the energy of the frontal movement of 1 eV, and cyclotron velocities Vc Rc ftJb. corresponding to energies of 10–100 eV, the retention condition (1) is certainly fulfilled.

The use of the invention will expand the analytical capabilities of ion-cyclotron resonance mass spectrometry for analyzing substances and their mixtures due to

0 simultaneously obtaining the mass spectrum of the studied mixture in both positive and negative ions, and also allows one to study the poorly studied region of ionic and ionic molecular reactions with the participation of oppositely charged ions.

Claims (1)

The invention The ion cyclotron mass spectrometer containing a measuring cell with 0 by an ion source, side excitation and detection electrodes, and composite end electrodes, each of which consists of two parallelly installed external and internal, with which the internal electrodes are made of grids and are grounded, in order to enhance the functionality of the device by simultaneous analysis in measuring A cell of ions of a different sign, between the side electrodes and the end electrodes, is additionally fitted with ring-shaped holding electrodes, with the ring holding electrodes and external end electrodes connected to sources of opposite-voltage reference voltages. /five, FIG. / Fie.2