OCTA-electrode linear ion trap mass analyzer

Abstract

An octa-electrode linear ion trap mass analyzer is formed by eight cylindrical electrodes and at least two end-cap electrodes. The inside surfaces of the eight cylindrical electrodes are free-form. The material of the octa-electrode linear ion trap mass analyzer is a conductive metal material or an insulating material plated with a conductive coating. The eight cylindrical electrodes are divided into four groups of cylindrical electrodes in total, each group of the four groups of cylindrical electrodes comprises two cylindrical electrodes, and each two groups of the four groups of cylindrical electrodes are parallelly placed. At least one through hole is provided with in the center of the end-cap electrode, and the two end-cap electrodes are respectively arranged at both ends of the cylindrical electrode.

Claims

1. An octa-electrode linear ion trap mass analyzer, comprising eight elongated electrodes and at least two end-cap electrodes, wherein in a cross section of each of the eight cylindrical electrodes, an outer side of the cross section has a approximately circular shape, and an inner side of the cross section toward an inner space of the octa-electrode linear ion trap mass analyzer comprises a protrusion extending towards the center of the octa-electrode linear ion trap; a material of the octa-electrode linear ion trap mass analyzer is a conductive metal material or an insulating material plated with a conductive coating; the eight elongated electrodes are divided into four groups of elongated electrodes, each group of the four groups of elongated electrodes comprises two elongated electrodes, and each two groups of the four groups of elongated electrodes are parallelly placed; at least one through hole is provided in a center of each electrode of the end-cap electrodes; the end-cap electrodes are respectively arranged at both ends of the eight elongated electrodes; and a slit is provided between the protrusions of at least one of the four groups of elongated electrodes.

2. The octa-electrode linear ion trap mass analyzer according to claim 1, wherein each of the end-cap electrodes is applied with a DC signal to form an axial bound field, and each elongated electrode of the eight elongated electrodes is applied with a radio frequency voltage to form a radial bound field.

3. The octa-electrode linear ion trap mass analyzer according to claim 1, comprising more than two end-cap electrodes, wherein a first end-cap electrode of the end-cap electrodes is located at a first end of a linear ion trap, wherein ions are injected from the first end, and the rest of the end-cap electrodes are arranged in order at a second end of the linear ion trap.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to illuminate other features, objects, and advantages of the present disclosure, the non-limiting embodiments is described in detail with reference to the following drawings.

(2) FIG. 1 is a schematic structural diagram of the first embodiment of the present disclosure.

(3) FIG. 2 is a schematic diagram of simulated mass spectrum peaks obtained when an octa-electrode triangular linear ion trap performs unidirectional ion ejection in the first embodiment.

(4) FIG. 3 is a schematic structural diagram of the second embodiment of the present disclosure.

(5) FIG. 4 is a schematic structural diagram of the third embodiment of the present disclosure.

(6) FIG. 5 is a perspective view of the present disclosure showing eight cylindrical electrodes and two end-cap electrodes.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(7) The present disclosure will be specifically described hereinafter with reference to specific embodiments. The following embodiments are described for facilitating those skilled in the art to further understand the present disclosure, but do not intend to limit the present disclosure in any way. It should be noted that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present disclosure, all of which belong to the protection scope of the present disclosure.

(8) As shown in FIG. 5, the octa-electrode linear ion trap mass analyzer of the present disclosure is formed by eight cylindrical electrodes and at least two end-cap electrodes, wherein the inner surface of the eight cylindrical electrodes is free-form, including circular arc, triangle, hyperboloid, etc., and the eight cylindrical electrodes are made of a conductive metal material or an insulating material plated with a conductive coating. The eight cylindrical electrodes can be identical or different. Each two cylindrical electrodes form a group, resulting in a total of four groups, with each two of them placed in parallel. The shape and size of at least two end-cap electrodes are not limited, including any polygonal shape such as a circle, square, hexagon, etc. The at least one end-cap electrode is provided with at least one through hole in the center, and the size and shape of the through hole not limited, including circle, square, hexagon, and other polygonal shapes. The surface of the end-cap electrode is flat, conical, arc or hyperboloidal. The two end-cap electrodes are arranged on the two ends of the cylindrical electrodes.

(9) Among them, the length, width and height of the eight cylindrical electrodes are adjustable, that is, the electric field distribution in the space surrounded by the eight cylindrical electrodes is adjusted by changing the length, width and height of the eight cylindrical electrodes, the inner surface shape of the eight cylindrical electrodes, the relative position among the four groups of cylindrical electrodes and the voltage application mode, thereby obtaining a good ion storage and mass analysis performance.

(10) There is a slit between at least one of the four groups of cylindrical electrodes, and the width of the slit between the two cylindrical electrodes of each group can be adjusted as desired. The width of the slits can be identical or different. The relative positions of the four groups of cylindrical electrodes are independently adjustable.

(11) The end-cap electrode is applied with a DC signal to form an axial bound field, and the cylindrical electrode is applied with a RF voltage to form a radial bound field. The RF signal applied to each group of two cylindrical electrodes may be identical or different, which is settable depending on the actual expected effect. The application mode of the radio frequency voltage is arbitrary. The RF signals applied to the two cylindrical electrodes of each group may be identical or different, and the RF signals applied to the four groups of electrodes may be identical or different.

(12) When the number of end-cap electrodes is more than two, one of them is located at one end of the linear ion trap for ion injection, and the rest are sequentially arranged at the other end of the linear ion trap.

The First Embodiment

(13) The structure of the octa-electrode linear ion trap mass analyzer of the present disclosure is shown in FIG. 1. The first electrode 101, the second electrode 102, the third electrode 103, the fourth electrode 104, the fifth electrode 105, the sixth electrode 106, the seventh electrode 107, and the eighth electrode 108 are triangular electrodes, the entire linear ion trap is formed of eight surrounding triangular electrodes, and the application mode of the RF voltage is shown in FIG.1. The specific application mode of the radio frequency voltage is as follows: the first positive radio frequency signal +RF1 is applied to the third electrode 103, the fourth electrode 104, the seventh electrode 107, and the eighth electrode 108; the first negative radio frequency signal −RF1 of an equal amplitude and opposite phase is applied to the fifth electrode 105 and the sixth electrode 106; and the second negative radio frequency signal −RF2 is applied to the first electrode 101 and the second electrode 102. During the experiment, by means of changing the amplitude of the second negative radio frequency signal −RF2, the electric field distribution inside the ion trap can be changed, thereby affecting the moving trajectory and ejection direction of ions. In this embodiment, an octa-electrode triangular linear ion trap mass analyzer will be used to realize the unidirectional ejection of ions, so as to improve the efficiency of ion detection for the linear ion trap under the single detector mode. Assuming −RF2=(1−α) RF1, where the range of parameter α is [0, 1]. As the value of a changes, the ratio of the RF voltage applied to the first electrode 101 and the second electrode 102 changes, while the magnitude of the RF voltage applied to the other three groups of electrodes remains unchanged, and meanwhile, the proportion of multipole field components such as the quadrupole field and the hexapole field, etc. in the internal electric field changes, and the center of the quadrupole field inside the ion trap shifts. During the movement of ions in the trap, under the electric field force, the ions will move in a direction which is consistent with the direction of the electric field center shift, and finally achieve unidirectional ejection.

(14) In this embodiment, set the alpha value to 30%, that is −RF2=70% RF1, the center of the electric field will be biased toward the electrode to which a smaller voltage is applied, that is, a direction closer to the first electrode 101 and the second electrode 102. The center of motion of the ion is shifted, and the unidirectional ejection of ions is finally achieved.

(15) In this embodiment, by means of theoretical simulation, the octa-electrode triangular linear ion trap mass analyzer is used to realize the unidirectional ejection function of the ion trap, and the simulated mass spectrum peak generated therefrom is studied to analyze the performance thereof. Three kinds of ions with a mass-to-charge ratio (m/z) of 609, 610, and 611, respectively, each with a number of 100 for a total of 300, are placed in the center of the ion trap area, the RF voltage as described above is applied, and a dipole excitation signal AC is applied to the first electrode 101, the second electrode 102, the fifth electrode 105, and the sixth electrode 106 for ion excitation ejection. At this time, the movement center of the ions is biased toward the first electrode 101 and the second electrode 102, while the ions with m/z of 609 have been ejected out of the trap. The simulated mass spectrum peak obtained is shown in FIG.2, where there are three peaks, corresponding to ion peaks with m/z of 609, 610, and 611, the mass spectrum has a high and thin peak, and the half peak width (FWHM) is only 0.235, which proves that under the condition of unidirectional ion ejection, the octa-electrode triangular linear ion trap mass analyzer obtains a higher mass resolution and has good mass analysis performance.

The Second Embodiment

(16) As shown in FIG. 3, the eleventh electrode 501, the twelfth electrode 502, the thirteenth electrode 503, the fourteenth electrode 504, the fifteenth electrode 505, the sixteenth electrode 506, the seventeenth electrode 507, the eighteenth electrode 508 are arc electrodes. The entire linear ion trap is formed by eight surrounding arc electrodes. The RF voltage is applied in the manner shown in FIG. 3. As shown in FIG. 3, the RF voltage is applied as follows: the fifteenth electrode 505 and the sixteenth electrode 506 are applied with the first positive radio frequency signal +RF1, and the fourteenth electrode 504, the seventeenth electrode 507 are applied with the first negative radio frequency signal −RF1 of an equal amplitude and opposite phase, and the eleventh electrode 501, the twelfth electrode 502 are applied with a second positive radio frequency signal +RF2, and the thirteenth electrode 503 and the eighteenth electrode 508 are applied with a second negative radio frequency signal −RF2. During the experiment, by adjusting the amplitude of the second positive radio frequency signal +RF2, the electric field distribution inside the ion trap can be changed, and the movement trajectory and ejection direction of the ions can also be changed, similarly assuming RF2=(1−α) RF1. The purpose of this embodiment is also to change the electric field distribution inside the linear ion trap, and realize the unidirectional ejection of ions, by changing the application mode of the radio frequency voltage.

(17) The difference between this embodiment and the first embodiment is that the way of applying the unbalanced RF voltage is different. The voltage amplitude applied to four of the eight electrodes is different from the other four. The electric field on the left of the linear ion trap is weaker than that on the right, the center of the electric field is biased toward the weaker side. Using this voltage application mode, unidirectional ejection of ions under boundary excitation conditions can be achieved. Simply scanning the amplitude of the RF voltage enables the ions to be ejected, instead of applying extra excitation voltage AC, which will reduce the size and power consumption of the RF power supply, and of great significance to the miniaturization of the mass spectrometer.

The Third Embodiment

(18) As shown in FIG. 4, the twenty-first electrode 701, the twenty-second electrode 702, the twenty-third electrode 703, the twenty-fourth electrode 704, the twenty-fifth electrode 705, the twenty-sixth electrode 706, the twenty-seventh electrode 707 and the twenty-eighth electrode 708 are planar electrodes. The entire linear ion trap is formed by eight surrounding planar electrodes. The RF voltage is applied in the manner shown in FIG.4, and the RF voltage is applied as follows: the twenty-first electrode 701 is applied with the first positive radio frequency signal +RF1, the twenty-second electrode 702 is applied with the second positive radio frequency signal +RF2, and the twenty-third electrode 703 is applied with the third negative radio frequency signal −RF3, the twenty-fourth electrode 704 is applied with the fourth negative radio frequency signal −RF4, the twenty-fifth electrode 705 is applied with the fifth positive radio frequency signal +RF5, the twenty-sixth electrode 706 is applied with the sixth positive radio frequency signal +RF6, and the twenty-seventh electrode 707 is applied with the seventh negative radio frequency signal −RF7, and the twenty-eighth electrode 708 is applied with the eighth negative radio frequency signal −RF8.

(19) The radio frequency signal in this embodiment can apply any voltage value, and the applied radio frequency voltage value can be optimized by the electric field calculation software, to finally obtain a comparatively perfect quadrupole field. Besides, combinations of voltages with different values can be selected according to the requirements under different situations, to achieve certain functions. The embodiment is advantageous in that the radio frequency voltage applied to each electrode can be adjusted as desired, thus the radio frequency voltage can be applied flexibly and conveniently, and highly adjustable.

(20) The specific embodiments of the present disclosure have been described above. It should be understood that the present disclosure is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the appended claims, which does not affect the essence of the present disclosure.