FLIGHT TIME MASS SPECTROMETER

Description

[0001] The invention refers to the field of mass spectrometry with orthogonal injection of ions and can be used in solving problems of organic and bioorganic chemistry, immunology, biotechnology and medicine in the ionization of test substances by electron impact, "electrospray" and other methods.

[0002] The known analogue of time-of-flight mass spectrometer consists of a pulsed ion source, a field-free drift space, a reflecting system with a uniform electrostatic field (ion reflector) and an ion detector, in which time-of-flight focusing of ions in energy up to the second order is achieved (Karataev V.I., Mamyrin B.A., Shmikk D.V. A new principle of focusing ion packets in time-of-flight mass spectrometers / / Zhurnal Tekhnicheskoi Fiziki, 1971, v.41, pp. 1498-1501).

[0003] The main disadvantage of the known analogue is a relatively low resolution and sensitivity caused by the use of a uniform electrostatic field, formed in the accelerating gaps between flat fine-grained grids, in the ion source and a two-stage electrostatic mirror that acts as an ion reflector. Grid electrodes physically block part of the space for the passage of ions and also lead to a number of undesirable effects (the appearance of uncontrolled charges on the grids under the action of the ion flow, deflections of the grids when heated, etc.). For some of the ions that were scattered by the grids but reached the detector, the time-of-flight focusing conditions are not met, which directly leads to a decrease in the resolution of the device. In addition, uniform electrostatic fields, in principle, cannot provide spatial focusing of ions in the transverse direction, which leads to their loss in the ion package.

[0004] The closest in technical essence is a time-of-flight mass spectrometer, consisting of an ion source of the "electrospray" type, an orthogonal ion accelerator (pulser), including areas of accumulation and acceleration of ions, a field-free flight space, a two-stage electrostatic mirror and a detector. The pulser accumulation area is made in the form of a monopole that creates an inhomogeneous electrostatic field, which can significantly reduce the ion turn time for a weakly divergent beam, which has the effect of increasing the resolution by several times (Patent RU 2 381 591 C2, IPC H01J 49 / 40, published: 10.02.2010, Bull. No. 4).

[0005] The disadvantage of the prototype is a relatively low sensitivity caused by the fact that in the area of ion acceleration of the orthogonal accelerator (pulser) and two-stage electron mirror, acting as an ion reflector, uniform electrostatic fields, formed between flat fine-grained grids, are used.. Such fields, as indicated above, in principle cannot provide spatial focusing of ions in the transverse direction, which leads to their loss in the ion package, and the presence of fine-structured grids significantly aggravates the situation.

[0006] The objective of the invention is to increase the sensitivity of a time-of-flight mass spectrometer with orthogonal input of ions by improving the quality of spatial focusing of ions.

[0007] The technical result of the proposed invention is high sensitivity of the device

[0008] To achieve the claimed technical result, the invention provides a time-of-flight mass spectrometer consisting of an ion source of the "electrospray" type, an orthogonal ion accelerator (pulser), including areas of accumulation and acceleration of ions, a field-free flight space, a two-stage mirror and a detector, in accordance to claim 1. Advantageous embodiments of the invention are subject-matter of the dependent claims.

[0009] The invention is illustrated by numerical calculations and drawing.

[0010] The figure shows one of the possible versions of the proposed time-of-flight mass spectrometer with orthogonal input of ions in two projections (a in the XZ plane, b in the YZ plane).

[0011] The following notations are used: 1 is the ion source; 2, 3, 4 are gridless electrodes that create an inhomogeneous electrostatic field of two-dimensional symmetry in the region of ion acceleration; 5 is the position of the primary temporary focus z = z T formed by the orthogonal accelerator (pulser); 6, 7, 8 are gridless electrodes that create an inhomogeneous electrostatic field of transaxial symmetry (three-electrode transaxial mirror); 9 is the ion detector; U push is the pushing potential; U pull is the pulling potential; U acc is the accelerating potential.

[0012] The proposed time-of-flight mass spectrometer consists of an ion source 1 creating a continuous ion beam, an orthogonal ion accelerator (pulser), which includes areas of ion accumulation (from the plate with a potential U push to a grounded grid) and acceleration (the gap that includes a grounded grid, a grid with a pulling potential U pull and gridless electrodes 2, 3 and 4, made in the form of a pair of parallel plates separated by straight gaps), a field-free drift space (the gap between electrodes 4 and 6), a transaxial electrostatic mirror (gridless electrodes 6, 7, 8, made in the form of a pair of parallel plates separated by annular gaps) and detector 9.

[0013] The proposed device operates as follows. A continuous ion beam formed in source 1 enters the pulser accumulation region, where under the action of a pulsed potential U push an electrostatic field is created, which cuts out the ion package from the continuous beam and accelerates it orthogonally to the initial direction; the ion package falling into the ion acceleration region (pulser) with an inhomogeneous electrostatic field accelerates to energy qU acc , flies in a field-free span, reflects from the mirror with an inhomogeneous field, flies in a field-free space and hits the detector. It is assumed that the velocity vector of the ion package, as in the prototype, makes a small angle with the Z axis.

[0014] The invention is based on the results of a numerical calculation of two new electron-optical elements: 1) a four-electrode immersion objective, consisting of a flat electrode combined with a grid electrode with the pulling potential U pull , and three gridless electrodes 2, 3 and 4; 2) a three-electrode transaxial mirror, consisting of gridless electrodes 6, 7 and 8.

[0015] The parameters of the four-electrode immersion objective, which determine the conditions for formation of a primary temporary focus at the field boundary and a parallel ion beam in two mutually perpendicular directions, are given in Table 1. Table 1. Parameters of the four-electrode immersion objectiveV 2 / U acc V 3 / U acc V 4 / U acc l / d acc z T / d acc 0.2514.3310.732.69

[0016] Here V 2 , V 3 , V 4 are the potentials at electrodes 2, 3 and 4, l is the length of electrodes 2 and 3, and z = z T is the location of the primary temporary focus. In this case, the geometric dimensions are given in d acc units - the distance between the plates of the gridless electrodes of the immersion objective, and the potentials on the electrodes are given in units of the accelerating potential U acc = V 4 (drift potential). The origin of coordinates coincides with the plane of the electrode with the pulling potential U pull .

[0017] In order to use these data for any values of the pulling potential U pull and accelerating potential U acc = V 4 , the potential ratios are given in dimensionless values V i / U acc (i = 2,3,4) at the value of the potential U pull = 0 at the first electrode. For U pull ≠ 0 potentials on electrodes 2, 3 and 4 will be determined by the equality: V i * = U pull + V i i = 2 , 3 , 4 .

[0018] The parameters of the three-electrode transaxial mirror, which determine the conditions for the time-of-flight focusing of ions in energy up to the third order inclusive, simultaneously with the spatial focusing of a parallel ion beam in two mutually perpendicular directions in the focal plane of the mirror z = z F , are presented in Table 2. Table 2. Parameters of the three-electrode transaxial mirrorV 6 / U acc V 7 / U acc -V 8 / U acc l / d M R / d M -z F / d M 10.03800.4160.82213.16.36

[0019] Here l is the length of the middle (seventh) mirror electrode, R is the length of the radius of curvature of the gap between electrodes 6 and 7 of the mirror, z = z F is the position of its focal plane, and d M is the distance between the plates of the mirror electrodes. The origin of coordinates is aligned with the middle of the gap between electrodes 7 and 8.

[0020] To provide operation of the above modes of the pulser and ion reflector, which ensure high sensitivity of the proposed mass spectrometer, the number of gridless electrodes forming an inhomogeneous electrostatic field, both in the pulser ion acceleration region and in the transaxial electrostatic mirror, must be at least three. With a larger number of electrodes, the reflecting electrode of the transaxial mirror located after the gridless electrodes can be made in the form of a half ring, which will make the mass spectrometer more compact.

[0021] Thus, the advantage of the proposed invention is high sensitivity of the device.

Claims

1. Time-of-flight mass spectrometer, consisting of an ion source of the electrospray type, an orthogonal ion accelerator pulser, including an area of accumulation and an area of acceleration of ions, a field-free flight space, a transaxial electrostatic mirror and a detector (9), characterized in that: . - the area of ion acceleration includes a four-electrode immersion objective, consisting of a grid electrode with a pulling potential (Upull) and three or more gridless electrodes (2, 3, 4) in the form of a pair of parallel plates separated by straight gaps, creating an inhomogeneous electrostatic field of two-dimensional symmetry; and - the electrostatic mirror consists of three or more gridless electrodes (6, 7, 8) in the form of a pair of parallel plates separated by annular gaps, which create an inhomogeneous electrostatic field of transaxial symmetry.

2. Time-of-flight mass spectrometer according to claim 1, characterized in that: - ratios of parameters of the immersion objective are equal to: l / dacc = 0.73 and V2 / Uacc = 0.251, V3 / Uacc = 4.33, and V4 / Uacc = 1, if Upull = 0, wherein V2, V3, V4 are potentials on the three gridless electrodes (2, 3, 4) of the immersion objective; l is a length of the first and second (2, 3) of the three gridless electrodes (2, 3, 4) of the immersion objective; and dacc is a distance between the plates of the three gridless electrodes (2, 3, 4) of the immersion objective; and - ratios of parameters of the electrostatic mirror are equal to: l / dM = 0.822, R / dM = 13.1, V6 / Uacc = 1, V7 / Uacc = 0.038, and V8 / Uacc = -0.416, wherein V6, V7, V8 are potentials on the three gridless electrodes (6, 7, 8) of the electrostatic mirror; l is a length of the middle (7) of the three gridless electrodes (6, 7, 8) of the electrostatic mirror; R is a length of a radius of curvature of the electrostatic mirror; and dM is a distance between the plates of the three gridless electrodes (6, 7, 8) of the electrostatic mirror.

3. Time-of-flight mass spectrometer according to claim 2, characterized in that the parameters of the immersion objective are equal to V i ∗ = U pull + V i with (i = 2, 3, 4), wherein V 2 ∗ , V 3 ∗ , , V 4 ∗ are the potentials on the three gridless electrodes (2, 3, 4) of the immersion objective, if Upull ≠ 0.