RU2458428C2 - Analyser for flight-type quadrupole mass-spectrometer with three-dimensional focusing - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: analyser has an electrode system and two electrodes which bound the electrode system on the z axis, with two holes in one of said electrodes for inlet and outlet of analysed ions. Coordinate values of the centres of the holes for inlet and outlet of ions on similar coordinate axes are equal in magnitude, but at least one pair of corresponding coordinate values has different signs.

EFFECT: high resolution and sensitivity of the mass-spectrometer.

3 dwg

Description

The invention relates to the field of mass spectrometry and can be used to create quadrupole mass spectrometers of the span type with high resolution and sensitivity.

A device for analyzing a quadrupole mass spectrometer (mass filter) [1] is known, which consists of four rod electrodes (circular or hyperbolic section) located along the z axis parallel to each other so that the system has two perpendicular planes of symmetry (xz plane and yz plane ) To the right and to the left of the electrode system along the z axis there are two (input and output) diaphragms having holes along the z axis for input and output of the analyzed ions.

The disadvantages of the known device when used in the three-dimensional focusing mode are the high requirements for the variation of the ion flux introduced into the analyzer at longitudinal speeds; difficulties in realizing the amplitude mode of scanning the mass spectrum during three-dimensional focusing, which is traditional for quadrupole mass spectrometers; a high level of spurious signal due to the alignment of the inlet and outlet for the input and output of the analyzed particles.

A device for the analyzer of a quadrupole mass spectrometer is known, which contains an electrode system, the working surfaces of which are described by the relations:

,

,

,

и

- отнесенные к x_a соответствующие координаты декартовой системы и x_a - наименьшее расстояние от точки x=y=z=0 до электродов анализатора в плоскости z=0, Р₀ - безразмерный параметр. Входная диаграмма, расположенная в плоскости z=0, имеет два отверстия для ввода и вывода анализируемых ионов. В известном устройстве практически полностью снимаются требования к разбросу вводимого в анализатор ионного потока по продольным скоростям [2]. В анализаторе известного устройства введенные в анализатор ионы совершают вдоль оси z возвратное движение, а поскольку вдоль оси z реализовано квадратичное распределение потенциала, то время пролета ионов через анализатор, выраженное в периодах высокочастотного поля, оказывается независимым от их начальной скорости по этой оси. К тому же реализация амплитудного метода развертки спектра масс в масс-спектрометре с известным устройством не вызывает затруднений.Where

,

and

are the corresponding coordinates of the Cartesian system referred to x _a and x _a is the smallest distance from the point x = y = z = 0 to the analyzer electrodes in the plane z = 0, P ₀ is a dimensionless parameter. The input diagram, located in the z = 0 plane, has two holes for input and output of the analyzed ions. The known device almost completely removes the requirements for the spread of the ion flux introduced into the analyzer along longitudinal velocities [2]. In the analyzer of the known device, the ions introduced into the analyzer return motion along the z axis, and since a quadratic potential distribution is realized along the z axis, the time of flight of ions through the analyzer, expressed in periods of a high-frequency field, turns out to be independent of their initial velocity along this axis. In addition, the implementation of the amplitude method of scanning the mass spectrum in a mass spectrometer with a known device is not difficult.

A disadvantage of the known device is the difficulty of separating the input and output ion streams in space and the uncertainty of the values of the geometric parameters that determine the geometry of the working surfaces of the analyzer electrodes, in which it is possible to implement a three-dimensional focusing mode.

The aim of the invention is to remedy these disadvantages of the prototype.

This goal is achieved by the fact that the analyzer quadrupole mass spectrometer span type with three-dimensional focusing contains an electrode system that includes four electrodes, the working surfaces of which are described by the relations:

и x_a - наименьшее расстояние от точки x=0, y=0, z=0 до электродов анализатора в плоскости z=0; x, y и z - координаты декартовой системы; P₀ - безразмерный параметр, который может принимать значения от 0 до 1, также анализатор содержит два электрода, ограничивающие электродную систему по оси z, один из которых расположен справа, а другой - слева от электродной системы. В одном из них выполнены два отверстия: одно для ввода анализируемых ионов в рабочий объем анализатора, а другое для вывода отсортированных ионов. Отличается анализатор тем, что значения координат центров отверстий для ввода и вывода ионов по одноименным координатным осям равны по модулю, но хотя бы одна пара соответствующих значений координат имеет разные знаки. При этом значение P₀ выбрано так, чтобы значение параметра

было кратно значениям параметров S_x и S_y, где S_x, S_y и S_z - целые числа, β_z - параметр стабильности движения анализируемого иона по оси z.Where

and x _a is the smallest distance from the point x = 0, y = 0, z = 0 to the analyzer electrodes in the plane z = 0; x, y and z are the coordinates of the Cartesian system; P ₀ is a dimensionless parameter that can take values from 0 to 1; the analyzer also contains two electrodes that limit the electrode system along the z axis, one of which is located to the right and the other to the left of the electrode system. Two holes are made in one of them: one for entering the analyzed ions into the working volume of the analyzer, and the other for outputting sorted ions. The analyzer differs in that the coordinates of the centers of the holes for input and output of ions along the coordinate axes of the same name are equal in absolute value, but at least one pair of corresponding coordinate values has different signs. In this case, the value of P _{0 is} chosen so that the value of the parameter

was a multiple of the values of the parameters S _x and S _y , where S _x , S _y and S _z are integers, β _z is the stability parameter of the motion of the analyzed ion along the z axis.

The proposed device can significantly improve the electrical and mechanical parameters of a quadrupole span mass spectrometer with triple focusing:

- significantly (almost three times) reduce the length of the analyzer;

- almost completely remove the restrictions on the permissible spread of the introduced ion flux along the longitudinal velocities, which will significantly increase the introduced ion flux and, accordingly, the sensitivity of the mass spectrometer;

- significantly reduce the influence of the transition region of the analyzer on the parameters of the input ion flux, which will lead to an increase in the resolution of the mass spectrometer:

- even with a decrease in the length of the analyzer, increase the speed of the ions introduced into the analyzer, which will increase the sensitivity of the device and, most importantly, significantly increase the stability of the ion source over its service life (and increase the life of the entire device);

- use the amplitude scan mode of the mass spectrum;

- reduce the amplitude of the RF voltage applied to the electrodes of the analyzer, i.e. power supply to the analyzer of RF generators.

Figure 1 shows the cross sections of the electrodes of the proposed analyzer device in the xz and yz planes and the corresponding projection of the trajectory of the analyzed ion introduced and displayed in the plane of the input diaphragm through the input and output holes, the coordinates of the centers of which along the coordinate axes of the same name coincide modulo, but opposite in sign. The ion trajectories were calculated when a pulse antiphase voltage (meander) was applied to the analyzer electrodes with a range of 200 V; x _a = 6 mm; the length of the electrode system 78.3 mm; P ₀ = 0.00195. The coordinate of the center of the inlet along the x axis is + 4 mm, and the outlet is 4 mm. Accordingly, the y axis is +0.7 mm and -0.7 mm. Through the inlet, ions were introduced parallel to the z axis with a longitudinal velocity corresponding to an energy of 4.62 eV. Figure 1 shows that when using the proposed device in the three-dimensional focusing mode, it is possible to separate the input and output ion flows in the plane of the input diaphragm by more than 8 mm, which is quite enough for the practical implementation of the invention.

Figure 2 illustrates the shape of the mass peak obtained by numerical simulation for a quadrupole span mass spectrometer with three-dimensional focusing using the proposed analyzer device. On figa peak is presented on a linear scale as the dependence of the coefficient of transmission of the ion flux (from the inlet to the outlet) in% of the value of coefficient a ₂ , and on figb - the same peak is presented on a logarithmic scale and in relative units.

where U is the amplitude of the pulse voltage in Volts, T ₀ is the period of the RF voltage in seconds, e = charge in Coulomb and m is the ion mass in kg. In the calculations, the ion flux was introduced into the analyzer at an angle of 10.6 degrees to the z axis in the yz plane through an opening with a diameter of 0.3 mm and was discharged through an opening with a diameter of 0.3 mm. In this case, the ion flight time through the analyzer is 70 periods of the RF field. 2A is a table illustrating the dependence of resolution on the level at which resolution is determined. It can be seen that almost below the level of 0.01 up to the level of 0.00001, the resolution remains almost constant, which is an undoubted advantage of the proposed device. Figure 3 shows the mass peaks calculated when ion streams having an energy of 1-5.55 EV, 2-2.57 EV are introduced into the analyzer, differences in longitudinal energies reaching 70% of the average ion energy. It is seen that with such a significant difference in longitudinal energies, the shape of the mass peak does not undergo significant changes.

Thus, numerical simulation showed that the use of the proposed analyzer device in a quadrupole span mass spectrometer with triple focusing allows you to:

- remove restrictions on the allowable spread of the ion flux introduced into the analyzer along longitudinal velocities and, due to this, increase the resolution and sensitivity of the mass spectrometer;

- reduce the length of the analyzer several times;

- even with a decrease in the length of the analyzer, increase the longitudinal velocity of the introduced ions, which improves the stability of the ion source and increases the life of the entire device.

Bibliographic data

1. Paul W., Reinchard H.P., von Zahn U. Das elektrische Massenfilter als Massenspectrometer und Isotopentrener // Z. fur Physik. 1958. No. 152. S.143-182.

2. AC USSR No. 589573, publ. 01/25/78. Bull. Number 3.

Claims (1)

An analyzer of a quadrupole mass spectrometer of a span type with three-dimensional focusing, containing an electrode system including four electrodes, the working surfaces of which are described by the relations

Where

x _a is the smallest distance from the point x = 0, y = 0 and z = 0 to the analyzer electrodes in the plane z = 0;
x, y and z are the coordinates of the Cartesian system,
P ₀ is a dimensionless parameter that can take values from 0 to 1;
and two electrodes bounding the electrode system along the z axis, one of which is located to the right and the other to the left of the electrode system, two holes are made in one of them: one for introducing ions into the working volume of the analyzer, and the other for outputting sorted ions, different the fact that the coordinates of the centers of the holes for input and for output of ions along the coordinate axes of the same name are equal in absolute value, but at least one pair of corresponding coordinate values has different signs, and the value of P _{0 is} chosen so that the parameter

is a multiple of the parameters S _x and S _y , where S _x , S _y and S _z are integers, β is the stability parameter of the motion of the analyzed ion along the z axis.

Images