RU2557009C2 - Method and device for ions separation by specific charge with fourier transform - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to high-resolution mass-analyzers and may be used for perfection of analytical and commercial mass-spectrometers with Fourier transform. Proposed process consists in generation of intermittent oscillations in axes X and Y by combination of linear high-frequency and homogeneous static electric fields in semi-space x > 0. In this case plane x = 0 can be grounded in radio frequency to allow measurement of currents induced by oscillations of ions at high SNR. This mode of ions oscillations is implemented in the device composed of linear ion trap from radio frequency-grounded electrode 1 with constant positive potential in plane x = 0, electrode 2 in plane x = x_a with discrete-linear distribution of HF potential and in planes z = 0, z = z_a of electrodes 3, 4 with positive potential of several volts. Ions are fed into said trap via slit in electrode 1.

EFFECT: simplified design, decreased weight and sizes.

2 cl, 2 dwg

Description

The invention relates to the field of mass analysis of high-resolution substances and can be used to improve the analytical and commercial characteristics of Fourier transform mass spectrometric devices. The technical task of the invention is to improve the design, improve the mass-dimensional and commercial parameters of mass spectrometers with Fourier transform. Known devices of this type are ion-cyclotron resonance mass spectrometers (FT-ICR) [1] and Orbitrap electrostatic ion traps [2]. FT-ICR and Orbitrap mass spectrometry is one of the fastest growing methods for the analysis of chemical and biological substances due to its high resolution and accuracy of mass determination. However, due to the high cost of the instruments, and for the FT-ICR also the cost of maintenance, the possibilities of widespread use of Fourier transform mass spectrometers are limited. The proposed method and device allows you to create mass spectrometers with Fourier transform with all the advantages inherent in this class of devices, accessible to a wide consumer.

и двухмерного линейного высокочастотного (ВЧ).

, где

и

- единичные по осям X и Y вектора, E_m, ω, φ - амплитуда, частота и начальная фаза ВЧ поля, режима колебаний ионов по осям X и Y, близким к гармоническим, причем по оси X смещенным на величину x_c>x_m The proposed method for mass separation of ions by specific charge z = e / m, where e and m are the charge and mass of ions, consists of entering into the analyzer with the dimensions of the electrode system x _a , 2y _a , z _a along the axes X, Y, Z and creating in his work area 0≤x <x _a , | y | ≤0.25y _a , x _a ≤z <z _a -x _a under the action of a superposition of two electric fields - a uniform static

and two-dimensional linear high-frequency (HF).

where

and

are the unit vectors along the X and Y axes, E _m , ω, φ are the amplitude, frequency, and initial phase of the RF field, the mode of ion vibrations along the X and Y axes, which are close to harmonic, and along the X axis shifted by x _c > x _m

where x _m <x _a / 2, y _m <0.25y _a , φ _x , φ _y are the initial phases, which depend on the initial parameters of the ions and the rf field, Ω is the secular oscillation frequency proportional to the specific ion charge. The ion mass spectrum corresponding to the frequency spectrum Ω of their oscillations along the X axis is found by the Fourier transform induced on the ground plane along the HF surface located in the x = 0 plane.

It is known [3] that ion vibrations close to harmonic along the X and Y axes

накладывается однородное статическое электрическое поле

, которое смещает колебания ионов по оси X, происходящие под действием ВЧ поля, на величинуcan be performed in a two-dimensional linear RF field of a quadrupole analyzer. But since high-level RF potentials act on all the electrodes of the quadrupole analyzer, it is almost impossible to isolate the currents induced from them by a small number of current ions with a high signal / noise ratio. In the proposed method for a two-dimensional linear HF electric field

a uniform static electric field is applied

, which shifts the oscillations of ions along the X axis, occurring under the influence of an rf field, by

where U _n is the pseudopotential of the linear HF electric field [4], r ₀ is the geometric parameter of the quadrupole analyzer.

величину смещения установить больше амплитуды x_c>x_m, тогда колебания ионов под действием ВЧ поля будут происходить в полупространстве х>0 (Фиг.1).If using a static uniform field

the bias value is set to be greater than the amplitude x _c > x _m , then the oscillations of the ions under the influence of the RF field will occur in the half-space x> 0 (Figure 1).

соответствует пространственное распределение ВЧ потенциала в плоскости XOYTo the field

corresponds to the spatial distribution of the RF potential in the XOY plane

From (4) it follows that on the boundary x = 0 of the half-space x≥0, the HF potential is φ (0, y) = 0. With this in mind, to convert ion vibrations along the X axis into induced currents in the x = 0 plane, a grounded electrode 1 is installed (Fig. 1). Since the RF potential of electrode 1 is zero, the task of separating the ions induced by oscillations with frequencies Ω = βω / 2 (parameter β <0.63) and interference from the RF field with frequency ω is simplified. The introduction of ions into the working volume of the analyzer takes place from an external source, which generates a pulsed ion beam in the x = 0 plane, of duration t _n <π / 2ω, with coordinates | y | <h / 2, 0.2z _a <z <0.8z _a , and initial velocities ν ₀ and angles of entry | α | <90 °.

To bring ions to trajectories close to elliptical, centered at the point (x _c , 0) (Figure 1), the static field, starting from the moment of input of ions t = 0, changes exponentially E (t) = E ₀ ( 1-e ^{-t / τ} ), where the time constant τ is chosen depending on the mass range of the analyzed ions. After a time t> 3τ after input, the regime of ion oscillations periodic along the X and Y axes is established, the main components of which are harmonic components with frequencies Ω proportional to the specific charges of ions.

The formation of a superposition of static homogeneous and HF two-dimensional linear electric fields and the conversion of ion vibrations into induced currents in the proposed device is carried out using the electrode system shown in Fig.2. X device_a2y_az_a along the axes X, Y, X and with a working volume of 0≤x <x_a, | y | ≤0.25y_a, x_a≤z <z_a-x_a consists of electrodes 4 and 5 in the planes x = 0 and x = x_a rectangular shape with vertex coordinates (y_a, 0), (y_az_a), (-y_az_a), (-y_a, 0), the first of which is solid, grounded at a high frequency, with a slot of height h << y_a along the y axis and width z_u<z_a along the Z axis, and the second discrete, composed of uniformly with a step Δy << y_a Δy-s conductive strips distributed along the Y axis, where s << Δy is the gap between adjacent strips and two solid electrodes 6 and 7 in the planes z = 0 and z = z_a rectangular with vertex coordinates (0, y_a), (x_a, y_a) (x_a, -y_a), (0, -y_a) On the conductive strips of the discrete electrode 5 set high-frequency voltage u proportional to their number i_i= i · ΔVcos (ωt), where i = -n, ..., -1, 0, 1, ..., n are the numbers of strips, 2n + 1 is the number of strips of electrode 5, ΔV = V / n, ω is the frequency of the RF voltage . By direct current, the strips are grounded. On the electrode 4, after the ion input process, a constant voltage U₀forming a homogeneous electric field directed parallel to the X axis with intensity E₀= U₀/ x_a. Under the action of stresses u_i= i · ΔVcos (ωt) linearly distributed on the strips of the discrete electrode 5, a two-dimensional linear HF electric field is formed in the working volume with the projections of the strength on the X and Y axes

In the superposition of electric fields formed in the working volume, ions perform periodic oscillations along the X and Y axes, the secular components of which are described by expressions (1). There is no field along the Z axis in the working region and ions drift with thermal velocities v _Tz . To hold ions in the working volume in the planes z = 0 and z = z _a , electrodes 6 and 7 are installed with a positive locking potential U _s .

,

,

.The input of ions into the working volume of the analyzer is carried out through a slot 8 in the electrode 4 (Figure 2). During ion input, starting from the moment t = 0 of the beginning of the mass analysis cycle, an exponentially increasing voltage U = U ₀ (1-e ^{-t / τ} ), where τ≥2π / ω, under which accelerated the source of the pulse packet of the ions are transferred to periodic, close to elliptical trajectories 3 (Figure 1). When the uniform field reaches a steady-state value of E _{0, the} oscillations become periodic in nature with the center at the point (x _c , 0) and the period T _Ω = 2π / Ω, where

,

,

.

Oscillations of ions along the X axis induce 4 currents on the electrode, the main components of which are harmonic functions with frequencies Ω

where N is the number of ions with mass m. From the induced currents after their conversion to voltage and amplification, the mass spectrum of the analyzed ions is calculated using the Fourier transform procedure.

The method and device based on the formation of a superposition of a static homogeneous and radio-frequency two-dimensional linear electric fields and the creation of a periodic ion oscillation regime can significantly improve the design, mass-dimensional and commercial characteristics of Fourier transform mass spectrometers.

Literature

1. A.G. Marshall, C.L. Hendrickson and G.S. Jackson, “Fourier transform ion cyclotron resonance mass spectrometry: a primer” // Mass spectrum. Rev. 17, 1998, p. 1-35.

2. Makarov A.A. U.S. Patent 5.886.346 1999.

3. E.B. Mamontov, D.V. Kiryushin // ZhTF, 2012, t 82, issue 9, p. 63-68.

4. R.H. Dawson. Quadrapole Mass Spectrometry and its Applications. American Institute of Physics, New York, 1995.

и ВЧ двухмерного линейного

электрических полей. 1 - заземленная по ВЧ поверхность с щелью 2 для ввода ионов, 3 - траектория ионов.Figure 1 - Trajectories of ions with initial coordinates x ₀ = 0, | y ₀ | <h / 2, velocities ν in a superposition of constant uniform

and treble two-dimensional linear

electric fields. 1 - RF ground plane with a slot 2 for introducing ions, 3 - ion path.

Figure 2 - The electrode system for the formation of a superposition of a constant homogeneous and HF linear in x and y coordinates of the electric fields.

1 - grounded by high-frequency electrode, 2 - discrete electrode of conductive strips, 3, 4 - locking electrodes, 5 - slot for inputting ions.

Claims (2)

1. The method of separation of ions by specific charge with Fourier transform, which consists in creating a periodic oscillation mode of ions introduced into the working volume of the analyzer with the dimensions of the electrode system x _a , y _a , z _a along the X, Y, Z axes, measuring induced on the analyzer electrodes currents and calculating mass spectra using the Fourier transform, characterized in that the periodic oscillations of the ions along the X and Y axes create under the influence of a superposition of the analyzer formed in the working volume 0≤x <x _a , | y | ≤0.25y _a , x _a ≤ z <z _a -x _a static uniform along the axis X and a high-frequency electric field linear along the X and Y axes, and during the introduction of ions into the working volume of the analyzer, the intensity of a uniform electric field increases from 0 to the set value according to the exponential law. 2. Device for separating ions by specific charge with Fourier transform, containing an electrode system for introducing ions into the working volume 0≤x <x _a , | y | ≤0.25y _a , x _a ≤z <z _a -x _a analyzer with dimensions x _a , 2y _a , z _a along the X, Y, Z axes and create a regime of periodic ion oscillations in it, characterized in that they use an electrode system of electrodes 1 and 2 in the planes x = 0 and x = x _{a of} rectangular shape with coordinates vertices (y _a , 0), (y _a , z _a ), (-y _a , z _a ), (-y _a , 0), the first of which is solid, grounded at a high frequency, with a gap of height h << y _a along the Y axis and a width z _u <z _a along the Z axis, and T discrete, made up of conductive strips of width Δy-s distributed uniformly with a step Δy << y _a along the Y axis, where s << Δy is the gap between adjacent strips, and two solid electrodes 3 and 4 in the planes z = 0 and z = z _a rectangular in shape with the coordinates of the vertices (0, y _a ), (x _a , y _a ), (x _a , -y _a ), (0, -y _a ), and a high-frequency voltage u _{i is} applied to the conductive strips of electrode 2 = V _i cosωt, where V _i = i · ΔV, i = -n, ..., -1, 0, 1, ..., n are the numbers of strips, 2n + 1 = 2y _a / Δy is the number of strips of electrode 2, ΔV is the difference in high-frequency voltages between adjacent strips, ω is the frequency of high-frequency voltage yazheniya, the electrodes 3, 4 is fed constant positive value of the voltage of a few volts, and electrode 1, starting from the time t = 0 start cycle of mass analysis is fed exponentially increasing voltage U = U ₀ (1-e ^{-t / τ)} , where τ≥2π / ω, then through the gap in the electrode 1 during the interval 0 <t <π / ω, a ribbon stream of the analyzed ions with a width z _u and a thickness h is introduced into the working volume and, after a time t> 3τ, the currents induced on the electrode 1 are measured with frequencies inversely proportional to the masses of ions.

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