RU2276426C1 - Method and device for sorting out charged particles by specific charge - Google Patents

Abstract

FIELD: mass spectrometry.

SUBSTANCE: mass analyzer built around confined ion trap and designed to improve consumer properties as well as to extend service life of mass spectrometers using hyperboloid electrode systems has hyperboloid butt-end electrode and plane-confined annular one, cylindrical shielding and focusing electrodes, as well as semitransparent flat correcting electrode. Charged particles are produced due to electron shock in space between annular and correcting electrodes beyond working space of mass analyzer. Ions are entered in analyzer under action of accelerating voltage across correcting and focusing electrode; period and phase of accelerating voltage are coordinated with those of variable field and with original coordinates and speeds of charged particles. Sorted out ions are brought out through annular electrode hole and through semitransparent correcting electrode under action of positive voltage across butt-end electrode.

EFFECT: enhanced efficiency of passing ions outside; enhanced parameters of device at limited peak values of high-frequency supply voltage.

2 cl, 2 dwg

Description

The invention relates to dynamic mass spectrometry and can be used to improve consumer properties and increase the life of mass spectrometers with hyperboloid electrode systems. In mass spectrometers with a three-dimensional ion trap, it is difficult to carry out external input of charged particles, and the analyzer requires braking gas and a supply voltage with an amplitude of tens of kilowatts. The resolution of a mass spectrometer on a monopolar ion trap is limited by nonlinear field distortions in the region of the hole in the ring electrode. The prototypes are a three-dimensional ion trap [1, 2] and a mass analyzer on a monopolar ion trap [3]. The technical task of the invention is to improve the analyzer of a monopolar ion trap, increase the efficiency of external input of ions, improve the analytical properties of hyperboloid mass spectrometers with limited amplitudes of the supply voltage.

The proposed method for mass-selective separation of charged particles is based on restricting the volume of the ion trap to the plane z = -z ₀₂ , z ₀₂ = (0.1-0.2) z ₀₁ and creating a square with a quadratic in the analyzer's working area 0≤z≤z ₀₁ distribution of potential. Under the influence of an alternating electric field, the ions of the analyzed mass m _o perform unipolar, close to periodic, oscillations along the z axis, and bipolar oscillations with a limited amplitude along the r axis. Charged particles of other masses m ≠ m ₀ in the working area of the proposed analyzer are unstable. As a device for separating charged particles by specific charge, a three-dimensional ion trap limited by a plane z = -z _{02 is used} with a cylindrical shielding electrode, a cylindrical focusing and flat translucent correcting electrode located behind the hole in the ring electrode.

A diagram of the electrode system of the mass analyzer on a limited ion trap is shown in Figure 1. The analyzer consists of two hyperboloid electrodes: end 1 and ring 2, shielding cylindrical electrode 3, cylindrical focusing electrode 4 and translucent flat correction electrode 5. The hyperboloid ring electrode 2 is bounded by the z = -z ₀₂ plane and forms part of the ion trap ring electrode. The parameters z ₀₁ , r ₀₁ and z ₀₂ are taken in accordance with r ₀₁ <0.2z ₀₁ , z ₀₂ ≤0.2z ₀₁ . The ion sorting region of analyzer 6 is in the form of a cylinder with a radius r ₀₁ , the base of the cylinder lie in the planes z = z ₀₁ and z = 0.

A single cycle of mass analysis consists of ionization, input, sorting and output of ions (Figure 2). During the entire analysis cycle, the potential of the ring electrode is U _k = 0, and the shielding electrode is U _e = (0.2-0.4) U _T , where U _T is the potential of the end electrode. The formation of ions by electron impact on the interval T _and takes place outside the working area of the analyzer in the space between ring 2, focusing 4 and correcting 5 electrodes. Ions are formed with initial coordinates z ₀ = - (0.1-0.2) z ₀₁ and thermal initial velocities.

In the input interval T _in under the action of the positive potential U _in the focusing and correcting electrodes, the ions are accelerated and introduced into the working area of the analyzer. During input, a voltage that is periodic with a period of T ₁ acts on the end electrode, which creates an alternating RF field in the analyzer's working area. Upon completion of the input, the ions of the analyzed mass m ₀ acquire coordinates z ₀₀ = (0.8-0.9) z ₀₁ and initial velocities close to zero. The fulfillment of these conditions ensures the capture and retention by the RF field of the ions of the analyzed mass m _o during sorting. At T _B = (5-7) T, the confinement conditions are satisfied for all the initial phases of the RF field. Sorting of charged particles occurs on the interval T _c under the action of a periodic with a period T HF voltage U _T (t) on the end electrode. The transition from the input mode to the sorting mode is carried out by changing the period of the RF voltage T = (0.9-0.99) T ₁ . During ion sorting, a voltage U _{K is} set at the correction electrode. _{By the} magnitude and sign of U _K, one can change the distribution of the potential φ (z, r) in the working area of the analyzer near the coordinate origin and thereby establish various modes of mass-selective sorting and ion retention. _By changing U _{K, it is} also possible to control the parameters of the mass analyzer - resolution and sensitivity. The trajectories of the analyzed ions during sorting are close to periodic. The number of retained ions and the shape of the mass peaks of the analyzer depends on the spread of the initial coordinates z _{0 of the} ions and the amplitude U _{m of the} RF voltage. Depending on U _m , a threshold effect is observed. For U _m <U _{p, the} sensitivity and resolution of the analyzer strongly depends on U _m , and for U _m > U _{p they} practically remain constant. The threshold voltage is U _p = 100-200 V. This allows to achieve high analytical parameters of mass spectrometers with limited amplitudes of the RF voltage.

Sorted ions of mass m ₀ on the interval T _p under the action of the positive potential U _p on the end electrode are removed from the analyzer through the hole in the ring electrode and are fed to the registration system. The mass sweep is carried out by changing the frequency of the RF voltage at a constant amplitude U _m .

The proposed method for introducing and sorting charged particles by specific charge and a device for its implementation make it possible to exclude the formation of dielectric films on the field-forming electrodes of the analyzer, to obtain high analytical properties of mass spectrometers with limited RF voltage amplitudes, and to improve the technological and operational characteristics of devices.

The method of separation of ions by specific charge and a device for its implementation are illustrated by drawings:

Figure 1 - electrode system of the analyzer,

Figure 2 - time diagram of the voltages at the electrodes of the analyzer and the trajectory of particles along the z-coordinate.

Information sources

1. E.P. Sheretov. Hyperboloid mass spectrometers. Measurement, control, automation. 1980, N 11-12.

2. R.E. March, Int. J. Mass. Spectrom. Ion Processes 118/119, 71 (1992).

3. E.V. Mamontov, D.A. Ivlev. Method for separating ions by specific charge and device for its implementation. Patent for invention No. 2159481, 2000.

Claims (2)

1. The method of separation of charged particles by specific charge, which consists in exposing the charged particles to an alternating electric field of a three-dimensional hyperboloid analyzer with parameters Z ₀₁ , r ₀₁ , where z ₀₁ and r ₀₁ are the radii of the boundary equipotentials along the coordinates z and g, characterized in that by restricting the analyzer’s working space along the z coordinate to z ≥ -Z ₀₂ , where z ₀₂ = (0.1-0.2) z ₀₁ , in the Z ₀₁ ≥z≥0 part of the analyzer workspace, a field with a quadratic potential distribution is created, and in part 0≥z≥-z ₀₂ with potential distribution different from quadratic, and charged particles with initial coordinates z ₀ = -0.2z ₀₁ , r <r _{01 are} affected by an alternating electric field with a period T ₁ , and then with a period T = (0.9-0.95) T ₁ . 2. A device for separating charged particles by specific charge, containing an electrode system of hyperboloidal end and ring electrodes of an ion trap, characterized in that the hyperboloidal end face and limited by the plane z = -z ₀₂ , where z ₀₂ = (0, 1-0,2) z ₀₁ ring electrodes of a three-dimensional ion trap with parameters Z ₀₁ ≤0,2r ₀₁ , where z ₀₁ and r ₀₁ are the radii of the boundary equipotentials along the coordinates z and r, and a shield electrode in the form of a cylinder is installed along the boundaries of the hyperboloid electrodes , a and a hole in the ring electrode is a translucent flat electrode with a diameter of d _k ≥4r ₀₁ and a cylindrical electrode with a diameter of d _r ≥4r ₀₁ and a height of h = r ₀₁ .

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