RU2398308C1 - Method for mass-separation of ions based on time of flight and device for realising said method - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method for mass-separation of ions based on time of flight involves superposition of the ion formation region with the entrance aperture of a radio-frequency time-of-flight mass spectrometre. Analysed ions are accelerated and enter the drift space under the effect of an HF electric field. For this purpose, initial coordinates x₀ of the ions on the X axis are selected such that they are comparable to the amplitude y_m of oscillation of charged particles on the drift axis Y. To obtain high linearity of the electric field in the drift region of the ions, an electrode system which is closed in the XOY plane and consisting of three flat electrodes with discrete-linear distribution of potential and one flat earthed electrode with slits for entrance and outlet of ions is used.

EFFECT: improved ion inlet system and design of mass-analysers of the time-of-flight type with two-dimensional linear HF electric fields.

2 cl, 1 dwg

Description

The invention relates to the field of mass analysis of ions in two-dimensional linear RF fields and can be used to improve the analytical, design and technological characteristics of dynamic mass spectrometers. In radio-frequency time-of-flight mass spectrometers, when charged particles are formed in an ion source and transported to the analyzer input aperture due to the spread of the initial velocities, a temporary defocus of the ion packet occurs, the value of which is proportional to the initial coordinates y _{0 of the} particles along the Y axis, which reduces the resolution mass spectrometers [1]. The technical task of the invention is to improve the ion input systems and the design of time-of-flight mass analyzers with two-dimensional linear HF electric fields.

The problem is solved by combining the region of ion formation with the input aperture of the radio frequency time-of-flight mass analyzer. In this case, ions are formed in the input aperture (or transported into it) with the initial coordinates y ₀ ≈0 along the Y axis and x ₀ ≈x _a / 2 along the X axis, and then they are accelerated and introduced into the radio frequency drift space under the influence of the RF electric field of the analyzer time-of-flight mass spectrometer. A diagram of a time-of-flight mass analyzer with a two-dimensional linear HF electric field with the formation of ions in the input aperture is shown in the drawing.

The electrode system from flat with a discrete-linear distribution of the potential of electrodes 1, 2, 3 with a step Δφ and a flat one with slots for inputting the ion output of the grounded electrode 4 creates -x _a <x <x _a , 0 <y <y in the ion drift region _a two-dimensional linear RF field with potential distribution

The low-frequency (secular) components of the ion trajectories in a linear rf field at y≈0 and the initial phase of the rf field φ = π are described by the expressions

V, ω и φ - амплитуда, частота и фаза ВЧ питающего напряжения, m - масса анализируемых ионов. Из (2) видно, что при выполнении условияwhere ν _ox , ν _oy are the projections of the initial ion velocities on the X and Y axes,

V, ω and φ are the amplitude, frequency and phase of the RF supply voltage, m is the mass of the analyzed ions. From (2) it is clear that when the condition

vibrations of ions in the working area of the analyzer along the y-axis of the drift have a return character (see drawing), corresponding to vibrations of charged particles in a radio-frequency time-of-flight mass spectrometer [3].

. Таким образом из (2) следует, что ввод ионов в пространство дрейфа радиочастотного времяпролетного масс-анализатора может осуществляться без их ускорения в ионном источнике. Начальное ускорение ионов в этом случае происходит под действием компоненты E_y электрического поля анализатора, имеющей в первую четверть периода ВЧ поля при фазе φ=π положительное значениеCondition (3) is satisfied for all positive values of the projections of the initial ion velocities ν _oy ≥0 and negative values whose modulus does not exceed

. Thus, it follows from (2) that ions can be introduced into the drift space of the radio-frequency time-of-flight mass analyzer without their acceleration in the ion source. The initial ion acceleration in this case occurs under the action of the analyzer electric field component E _y , which has a positive value in the first quarter of the RF field period at the phase φ = π

The size x _a along the X axis of the radio-frequency time-of-flight analyzer should be selected taking into account the fulfillment of condition (3), and the value y _a based on the maximum amplitude of ion vibrations along the drift axis Y

where ν _{oy max} is the maximum value of the projection of the initial ion velocity on the Y axis.

Since the dimensions 2x _a , y _{a of the} electrode system along the X and Y axes are comparable, to obtain a high linearity of the field, the analyzer working area in the XOY plane must be closed, which is achieved by introducing electrode 3.

The proposed method and device for mass separation of ions by time of flight in two-dimensional linear HF electric fields can simplify the design of radio-frequency time-of-flight mass spectrometers and increase their resolution.

Literature

1. Mamontov E.V., Gurov V.S., Filippov I.V., Diaghilev A.A. A method of introducing charged particles into a radio frequency time-of-flight mass analyzer and a device for its implementation // Decision on the grant of a patent for an invention according to application No. 2007106273/28 (006819), 02/19/2007.

2. Mamontov E.V., Filippov I.V. The method of mass selective analysis of ions by time of flight and a device for its implementation // Patent No. 23237245. Priority of the invention 03.05.2006.

3. Mamontov E.V., Gurov V.S., Filippov I.V., Dyatlov R.N. The method of separation of charged particles by specific charge and device for its implementation // Decision on the grant of a patent for an invention according to application No. 2005124794/28, 03.08.2005.

Claims (2)

1. The method of mass separation of ions by time of flight, which consists in exposing the charged particles to a linear electric RF field, characterized in that the analyzed ions are formed in the input aperture of the mass analyzer of size Δx << x _a or transported to it with initial coordinates x ₀ ≈ х _а / 2, у _о ≈0, where х _а is the size of the analyzer along the X axis, and then accelerated in the direction of the Y axis and introduced into the drift space under the action of the two-dimensional linear HF electric field of the time-of-flight analyzer in certain phases of the HF field. 2. A device for mass separation of ions by time of flight, containing an electrode system for forming a two-dimensional electric RF field, characterized in that they use an analyzer of three flat electrodes with a discrete-linear step with Δφ pitch, two of which are sized a _and the Y axis are located in the planes x = ± x _a and are limited by the plane y = 0, and the third electrode with a size of 2x _and the X axis is located in the plane y = y _a , and the grounded fourth electrode with a size of 2 x _a along the X axis with a working surface of plane y = 0, and in h The fourth electrode has two slits Δx << x _a wide along the Z axis with the coordinates of the centers x _a / 2 and -x _a / 2 for input and output of ions.