RU158343U1 - DEVICE FOR TIME-SPAN MASS SPECTROMETER WITH SOURCE OF IONS WITH IONIZATION AT ATMOSPHERIC PRESSURE FOR SEPARATION AND REGISTRATION OF IONS OF ANALYZED SUBSTANCES - Google Patents

Abstract

1. The device of a time-of-flight mass spectrometer with an ion source with atmospheric pressure ionization for separation and registration of analyte ions in real time, containing an electrospray ion source, a vacuum transport system chamber with a differential pumping system with a nozzle and a skimmer, a radio frequency transport quadrupole, a system the diaphragm, as well as the high-vacuum chamber of the time-of-flight mass analyzer, which includes a lens system, an orthogonal accelerator, and ion mirrors o, span, detector, characterized in that on one side of the carrier flange there is a vacuum chamber of the conveying system, in which a tube is located between the nozzle and the first radio-frequency transport quadrupole, followed by a vacuum tight diaphragm, behind which a second radio-frequency transport quadrupole is installed, behind The lens system is located in front of the shut-off valve (gate), which separates all the further vacuum part of the time-of-flight mass spectrometer from the vacuum chamber of the importing system, an orthogonal pulse accelerator and a collimator are located behind the shut-off valve on the other side of the bearing flange, with the input diaphragm behind the valve and the output diaphragm in front of the orthogonal accelerator, the output of which is located along the symmetry axis of the drift gap and is directed towards the meshless mirror, the supporting flange is connected vacuum tightly to the vacuum chamber of the time-of-flight mass analyzer, made in the form of two six-electrode gridless mirrors, located

Description

This utility model relates to instruments for the qualitative and quantitative analysis of substances ionizable at atmospheric pressure, which together with the chromatograph implements the real-time chromatography-mass spectrometry method and are widely used in ecology, technology, pharmaceuticals, toxicology, medical practice, biotechnology and for research purposes. To implement the method of chromatography-mass spectrometry, instruments have been developed and used that combine a chromatograph and, as a highly sensitive detector, a time-of-flight mass spectrometer with an ion source with ionization at atmospheric pressure, by which the amount of the analyte in the chromatographic peak is estimated.

Known device Bruker Daltonics - maxis UHR - TOF Bruker Corporation, USA (URL: www.bruker.com.). As a mass spectrometer, a time-of-flight reflectron-type mass analyzer is used, in which the ion mirror is implemented as a two-stage (two-stage) ion mirror consisting of flat mesh capacitors spaced along the axis of the instrument and forming a second drift space. In addition, in order to obtain high resolution, the length of the first drift space was significantly increased, which led to an increase in the physical dimensions of the device in height up to 4 meters.

The described device has the following main disadvantage: the large size of the time-of-flight mass analyzer leads to a significant loss of sensitivity of the device. In such a complex and dimensional design, high-vacuum pumping of the mass analyzer is carried out only in the region of a pulsed orthogonal transducer, which leads to a pressure gradient and its deterioration towards the ion mirror in the analyzer space, and this in turn increases ion scattering and, accordingly, to a decrease in sensitivity. The decrease in sensitivity is also affected by the presence of grid electrodes, both in an orthogonal pulsed accelerator and in a two-stage ion mirror. With a transparency of the grid electrodes of the order of 0.9 and taking into account the number of these grids in the pulse accelerator and in the ion mirror, the total transparency of the mass spectrometer is of the order of 0.53, i.e. under all other conditions, the transmission of the mass spectrometer is halved.

The disadvantages of the described device include the distortion of the shape of the peaks in the mass spectra, which is associated with scattering on the grid electrodes of the mirror and, accordingly, with a decrease in resolution. It should be noted that the large dimensions of the mass analyzer chamber when the temperature changes by several degrees lead to significant changes in the size of the ion-optical path, which affects the analytical characteristics of the device, mainly the resolution. To eliminate this effect, the thermostabilization of the vacuum case of the mass analyzer was carried out, which significantly complicated the design and tightened the requirements for precision manufacturing of the ion-optical system. As a disadvantage, the dependence of the mass analyzer settings on the settings of the system for transporting the ion beam from the ion source to the pulsed orthogonal accelerator can be noted, which complicates obtaining the maximum parameters of the device.

The closest known technical solution for a similar purpose is the device used in the MX5311 chromato-mass spectrometric complex, developed at the Institute for Analytical Instrumentation of the Russian Academy of Sciences (URL: www.http: //Iairas.ru) [2], in which The first stage of the differential pumping together with air enters the ions “frozen” into a dense stream of gas, which, expanding, reduces the density of the ion beam and increases the angular divergence. The pressure in the first stage of differential pumping is of the order of several Torr. Next is a skimmer that separates the second stage of differential pumping and cuts out its central part from the total flow of expanded gas and ions. To transport a low-energy ion beam, a few electron-volts, and to “cool” it to reduce the energy spread of ions in the beam, which can reach 50 eV, and the ion distribution over the angle of 60 ° is determined by the solution of the inner angle of the skimmer, a radio frequency quadrupole with focusing is used ion beam at a pressure of the order of units mTorr in the second stage of differential pumping. The gas flow interacts with the ends of the rods of the radio-frequency quadrupole and forms shock waves. These factors lead to large losses of ion current and its uncontrolled scattering together with the carrier gas (air). After the radio-frequency quadrupole, a diaphragm system is located, one of which is installed tightly and vacuum separates the second stage of differential pumping from the high-vacuum chamber of the time-of-flight mass analyzer. The diaphragms are designed to form a narrow ion beam at the exit of the radio frequency quadrupole. Behind the diaphragms is a lens system that allows you to form the most parallel and narrow ion beam obtained from the radio frequency quadrupole and direct it to the inlet of the orthogonal pulsed accelerator, in which the continuous ion beam is converted to pulsed in the direction orthogonal to the continuous beam. The technical solution used to position the lens system and its settings relative to the orthogonal accelerator does not allow independent adjustment of the transporting system (the first and second differential pumping systems with incoming elements of ion optics) and the time-of-flight mass analyzer, which includes an orthogonal accelerator. The adjustment of the ion beam using the lens system affects the angular distribution of the beam and the parallelism of its axis to the repelling electrode of the orthogonal pulse accelerator, which affects the tuning of the time-of-flight mass analyzer and its analytical parameters - resolution and sensitivity. The ion impulses fall further into the transit space, reach the two-stage (two-stage) ion mirror, are reflected and, having passed the second part of their path in the transit space, enter the detector. A significant complexity in the design of the mass analyzer is the location on one carrier flange of an orthogonal pulsed accelerator, drift space, ion mirror and detector. In such a design, checking the parallelism of the axis of the lens system to the buoyant electrode of the orthogonal pulsed accelerator is not possible. The use of grid electrodes in an orthogonal pulsed accelerator and ion mirror leads to the general transparency of the mass spectrometer being about 0.53, i.e. under all other conditions, the transmission of the mass spectrometer is halved. In addition, the second stage of differential pumping is separated from the high-vacuum part of the device only by a diaphragm, the absence of a shut-off high-vacuum valve behind it in front of the vacuum chamber, which allows without maintenance of the mass analyzer to carry out technological maintenance of the nozzle and skimmer subjected to intense pollution during operation, significantly increases the time the device goes to operating mode after it is started.

The proposed utility model solves the following problems:

- reduction of ion current loss and its uncontrolled scattering along with gas;

- independent adjustment of the transporting system from the settings of the time-of-flight mass analyzer, including the orthogonal pulse ion accelerator;

- a significant simplification and reduction in time of assembly and alignment of the elements of the mass spectrometer (orthogonal pulse accelerator) and its maintenance, replacement of elements of the mass analyzer that have exhausted their working life, leading to deterioration of technical and analytical parameters, for example, a secondary electron multiplier;

- the possibility of vacuum tight separation of the vacuum chamber of the ion transport system from the high-vacuum chamber of the mass analyzer;

- increase in sensitivity and resolution.

These problems are solved due to the fact that the known device containing an electrospray ion source, a vacuum chamber of a transport system with a differential pumping system with a nozzle and a skimmer, a radio frequency transport quadrupole, a diaphragm system, as well as a high-vacuum chamber of a time-of-flight mass analyzer, which includes a lens system , orthogonal accelerator, ion mirror, span, detector, equipped with: bearing flange, on one side of which there is a vacuum chamber conveyor a system consisting of a nozzle and a first radiofrequency transporting quadrupole, between which there is a tube, and behind the first quadrupole there is a vacuum tight diaphragm, behind which a second radiofrequency transporting quadrupole is installed, followed by a lens system located in front of the shut-off valve (gate), which separates the vacuum tightly the entire further vacuum part of the time-of-flight mass spectrometer from the vacuum chamber of the conveying system, behind the shut-off valve on the other side of the carrier flange is located an orthogonal impulse accelerator and a collimator with the inlet diaphragm behind the valve and the outlet diaphragm in front of the orthogonal impulse accelerator, the outlet of which is located on the axis of symmetry of the drift gap and directed toward the meshless mirror, are placed, the bearing flange is connected tightly to the vacuum chamber of the time-of-flight mass -analyzer made in the form of two six-electrode gridless mirrors located opposite each other, extended along the direction of drift and symmetrically and the drift gap, at the end of the drift gap there is a detector on a separate flange, the detector input is on the axis of symmetry and is oriented in the opposite direction of the output of the orthogonal accelerator.

The utility model is illustrated in figure 1, which presents a 2-D model of the inventive device of a time-of-flight mass spectrometer with an ion source with ionization at atmospheric pressure for separation and registration of ions of the analyzed substances. The proposed device contains a high-vacuum chamber of the mass analyzer (1), to which a conveying system (2) and a detector (3) are mounted on a separate bilateral carrier flange and on a separate flange. Inside the high-vacuum chamber, symmetrically to the axis of the drift gap (4), there are two gridless six-electrode mirrors (5, 6). The conveying system is presented in more detail in figure 2, which presents its 2-D model. The vacuum chamber of the conveying system (2) is tightly fastened to the double-sided bearing flange (1). The other end face of the vacuum chamber of the conveying system is vacuum tightly closed by a flange (3), on which an electrospray ion source is attached from the atmosphere side (4), and a nozzle (5) is installed in the center of the flange, which separates the atmospheric pressure region from the forevacuum region of the first differential pumping stage, in which the first radio-frequency transporting quadrupole (6) is located, connected to the nozzle exit by a tube (7). Behind the first transporting quadrupole, a vacuum tightly mounted diaphragm (8) is located, separating the second stage of differential pumping, in which the second radio-frequency transporting quadrupole (9) and the lens system (10) are located. Behind the lens system there is a shut-off valve (gate) (11) that separates the second stage of differential pumping from the high-vacuum chamber of the mass analyzer (figure 1, position 1). A collimator (12) and an orthogonal pulse accelerator (13) are mounted behind the shut-off valve, attached to the supporting double-sided flange from the side of the high-vacuum chamber of the mass analyzer. On the supporting double-sided flange are high-voltage high-vacuum electrical connectors (13) for supplying voltage to the orthogonal pulse accelerator.

The proposed device operates as follows. From the ion source of the electrospray (4, Fig. 2), the ions together with gas (air) through the nozzle (5, Fig. 2) fall into the tube (7, Fig. 2) and the ions “frozen” into the laminar gas flow enter the the area of influence of the radio-frequency field of the first transport radio-frequency quadrupole (6, Fig. 2), while the gas is pumped out between the rods of the quadrupole, and the ions are picked up by the high-frequency field and when the gas density decreases along the flow, they are held by the radio-frequency field, while the background pressure in the first stage of the differentialPumping out is 1-5 Torr. The distance between the ends of the tube and the end of the quadrupole assembly is 1 mm, the inner diameter of the tube is 5.9 mm, and the inscribed diameter in the quadrupole assembly is 6 mm. The frequency of the radio-frequency field supplied to the quadrupole side is 1 MHz, and the amplitude of the electric field is of the order of 300-310 V, which does not narrow the range of transmitted masses of ions. The maximum amplitude of the radio frequency voltage is limited by the possibility of electrical breakdown, and the frequency allows for the stable movement of ions at intermediate pressures. A constant voltage, adjustable in the range from - 50 to 100 V, is necessary for controlling the ion energy, is applied to the diaphragm (8, Fig. 2). The diameter of the hole in the diaphragm is 2 mm, which makes it possible to obtain a background pressure of the order of 3-10 mTorr in the second stage of differential pumping. and limit the divergence of the continuous ion beam upon admission to the second transport radio frequency quadrupole (9, figure 2). A high-frequency voltage with a frequency of 5 MHz and an amplitude of up to 2 kV is supplied to the second transport quadrupole, which ensures the transmission of ions in a wide mass range. The use of a second radio frequency transport quadrupole increases the transport of a low-energy ion beam. The radio-frequency confinement of the ion beam on the axis of the second transport quadrupole in combination with collision with neutral gas molecules and transferring part of the kinetic energy to them leads to cooling and radial compression, which in turn significantly improves both the transmission of the beam from the source and the parameters of the ion beam at the input to orthogonal pulse accelerator. The diameter of the formed ion beam at the exit of the second transporting radio-frequency quadrupole can be reduced to 1 mm., The energy spread in this case is units of electron-volts. The phase volume of the ion beam decreases with minimal ion loss, which allows a significant gain both in the sensitivity of the device as a whole (by one or two orders of magnitude) and in its resolution. The lens system (10, FIG. 2) allows focusing of the ion beam and its deflection to compensate for inaccuracies in the manufacture and assembly of ion optics of the transport system as a whole. The ion beam is focused on the inlet of the collimator (12, Fig. 2). A high-pressure shut-off valve is installed between the collimator and the lens system (11, Fig. 2), which, on the one hand, allows non-stop pumping of the high-vacuum region of the mass analyzer to carry out routine maintenance related to cleaning the nozzle and tube at atmospheric pressure, and, on the other hand, is an element of the ion-optical system (grounded electrode). This technology allows you to significantly, at times reduce the time the device goes to operating mode after maintenance. The use of a collimator, in which the diameter of the input aperture is 2.4 mm and the output aperture, in front of the orthogonal pulse accelerator, is 1.2 mm, allows independent electrical and vacuum settings of the conveying system from the settings of the orthogonal pulse accelerator (13, Fig. 2), working as part of a mass analyzer. The parameters of a continuous ion beam entering an orthogonal pulsed accelerator are: diameter 1.5 mm, total angular spread of 2 °, and energy 16 eV. The pulsed orthogonal accelerator is made in a gridless version of the control electrodes, and the buoyancy field strength is about 300 V / mm. The amplitude of the pulse voltage supplied to the ejection electrode of the orthogonal accelerator is 1.5 kV. A continuous ion beam entering an orthogonal pulsed accelerator under the influence of a pulsed electric field is accelerated in the direction orthogonal to the axis of entry of the continuous beam in the form of a packet of ions. The pulse repetition rate is consistent with the accelerator filling speed with a continuous beam, which allows almost 100% use of the ion beam. The ion packet enters the drift gap (4 FIG. 1). A controlled constant electric voltage supplied to the electrodes that make up the orthogonal accelerator allows deflecting packets of charged particles in the plane of ion mirrors. The parameters of the ion beam in an orthogonal pulsed accelerator are determined by the characteristics of the vacuum part of the conveying system and the specified mode of operation of the mass analyzer. To supply voltage to the orthogonal pulse accelerator on the carrier flange (1 of Fig. 2) are high-vacuum high-voltage connectors that can withstand operating voltages up to 10 kV. The energy of charged particles in the drift gap in the direction of the mirrors is 7 keV. Packets of charged particles in the plane of ion mirrors (5, 6 of Fig. 1) perform a zigzag motion, reflected in parallel six-electrode gridless mirrors. At the same time, packets of charged particles move in the direction orthogonal to the movement of the packets between the mirrors, which is determined by the deflecting voltage on the electrodes of the orthogonal pulse accelerator. The value of the deflection voltage should provide an integer number of oscillations of the ion packets between the mirrors in the drift gap, so that the packets of separated ions fall on the input plane of the detector (3 of Fig. 1), oriented in the opposite direction to the exit plane of the orthogonal pulse accelerator. The exit planes of the orthogonal accelerator and detector input are located on the axis of the drift gap between the meshless ion mirrors. Meshless ion mirrors provide fourth-order focusing of the time of flight in energy, spatial isochronism in the second aberration order, and effective retention of the small width of the ion beam during multiple reflections of charged particles. The detector (3 of Fig. 1) is a secondary electron multiplier with a time constant of less than 2 nanoseconds. The converted and amplified ion current flows through a high-vacuum connector to a broadband amplifier for recording it using a high-speed ADC.

The proposed technical solutions allow us to improve the design of the device from the point of view of simplifying its technological maintenance and use, increase the sensitivity of the device with ultra-high resolution of the device and thereby achieve a decrease in the detection threshold and the accuracy of determining the mass of the analyzed ions.

Information sources

1. Bruker Daltonics - maxis UHR instrument - TOF Bruker Corporation, USA (URL: www.bruker.com.

2. Device MX5311 IAP RAS Russia (URL: www.http: //Iairas.ru), A.H. Arseniev M.A. Gavrik, M.Z. Muradymov, A.A. Kayumov. Research and optimization of the system for transporting ion fluxes in electro-gas-dynamic fields from a region with atmospheric pressure to a high-vacuum region of a mass analyzer // Scientific Instrument Making, 2010, V. 20, No. 4, P. 120-126 (prototype).

Patent holder:

Alpha Limited Liability Company (RU)

Authors: Krasnov Nikolay Vasilievich (RU)

Limited Liability Company “BIAP” (RU)

Authors: Monakov Alexander Georgievich (RU), Muradymov Marat Zarifovich (RU)

Claims (3)

1. The device of a time-of-flight mass spectrometer with an ion source with atmospheric pressure ionization for separation and registration of analyte ions in real time, containing an electrospray ion source, a vacuum transport system chamber with a differential pumping system with a nozzle and a skimmer, a radio frequency transport quadrupole, a system the diaphragm, as well as the high-vacuum chamber of the time-of-flight mass analyzer, which includes a lens system, an orthogonal accelerator, and ion mirrors o, span, detector, characterized in that on one side of the carrier flange there is a vacuum chamber of the conveying system, in which a tube is located between the nozzle and the first radio-frequency transport quadrupole, followed by a vacuum tight diaphragm, behind which a second radio-frequency transport quadrupole is installed, behind The lens system is located in front of the shut-off valve (gate), which separates all the further vacuum part of the time-of-flight mass spectrometer from the vacuum chamber of the importing system, an orthogonal pulse accelerator and a collimator are located behind the shut-off valve on the other side of the carrier flange, with the inlet diaphragm behind the valve and the outlet diaphragm in front of the orthogonal accelerator, the outlet of which is located along the symmetry axis of the drift gap and is directed towards the meshless mirror, the supporting flange is connected vacuum tightly to the vacuum chamber of the time-of-flight mass analyzer, made in the form of two six-electrode gridless mirrors, located s face each other, extended along the drift direction and symmetrically with the axis of the drift interval, the end of the drift gap detector located on a separate flange, the detector input is on the symmetry axis and is oriented in the opposite direction the output of the orthogonal accelerator. 2. The device according to p. 1, characterized in that the ion source is a source with chemical ionization at atmospheric pressure. 3. The device according to claim 1, characterized in that the ion source is a source with photo-ionization at atmospheric pressure, and a blanker is located in the span in front of the detector.

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