Quadrupole mass analyzer and method of mass analysis

Abstract

A quadrupole mass analyzer according to the present invention optimizes a stability band formation mode of a quadrupole system, so as to facilitate passing of ions and blocking of excessive ions, thereby improving the mass resolution without reducing the ion transmission efficiency. The solution of the present invention avoids the superimposition of high-frequency AC signals needed in the ion two-direction resonance frequency control in the prior art, and can effectively reduce the risk of quadrupole working performance reduction caused by the non-linear distortion of an RF voltage caused by bandwidth limitation in a fast RF circuit. In addition, a scanning speed of an ion-controlled electric field required by the quadrupole mass spectrometry can also be controlled faster because of reduction of limit bandwidth of various needed AC excitation signals. It is advantageous to obtain high-speed quadrupole scanning mass spectrometry performance.

Claims

1. A quadrupole mass analyzer, comprising: a first pair of rod electrodes placed in a first plane along an axial direction; a second pair of rod electrodes placed in a second plane along an axial direction, the second plane being perpendicular to the first plane so that the first pair of rod electrodes and the second pair of rod electrodes form a quadrupole; a DC power supply configured for providing a DC potential difference U between the two pairs of rod electrodes; an RF power supply configured for providing an RF voltage between the two pairs of rod electrodes, an amplitude of the RF voltage being V and a frequency being 0; a first AC frequency source configured for driving a first AC excitation voltage between the two pairs of rod electrodes, an amplitude of the first AC excitation voltage being smaller than the amplitude V of the RF voltage and being recorded as V.sub.ex1, a frequency of the first AC frequency source being .sub.ex1 different from ; and a second AC frequency source configured for linearly modulating the amplitude V of the RF voltage, at a modulation frequency being .sub.ex2.

2. The quadrupole mass analyzer of claim 1, wherein .sub.ex1 is equal to .sub.ex2.

3. The quadrupole mass analyzer of claim 1, wherein .sub.ex1 is twice .sub.ex2.

4. The quadrupole mass analyzer of claim 1, wherein V.sub.ex1/V is in a range of 0.001 to 0.02.

5. The quadrupole mass analyzer of claim 1, wherein /.sub.ex1 is an integer greater than or equal to 5.

6. The quadrupole mass analyzer of claim 1, wherein a modulation depth of the second AC frequency source to the RF voltage provided by the RF power supply is in a range of 90% to 110%.

7. The quadrupole mass analyzer of claim 1, wherein a modulation depth of the second AC frequency source to the RF voltage provided by the RF power supply maintains a linear relationship with an amplitude V.sub.ex1 of an excitation voltage generated by the first AC frequency source.

8. The quadrupole mass analyzer of claim 1, wherein the quadrupole mass analyzer comprises a third AC frequency source configured for driving a second AC excitation voltage between two pairs of rod electrodes, an amplitude of the second AC excitation voltage is smaller than the amplitude V of the RF voltage and is recorded as V.sub.ex3, and the frequency .sub.ex3 is different from .

9. The quadrupole mass analyzer of claim 8, wherein .sub.ex3 is equal to a positive value of A .sub.ex1+B, wherein A is a non-zero integer between 3 and 3, and B is a non-negative integer.

10. The quadrupole mass analyzer of claim 1, wherein a ratio of U to V is in a range of 0.167 to 0.172.

11. A method of mass analysis, applied to the quadrupole mass analyzer of claim 1, comprising: guiding ions to enter the quadrupole mass analyzer along an axial direction, wherein in the quadrupole mass analyzer, the RF power supply applies an RF voltage with the amplitude of V and the frequency of between the two pairs of rod electrodes, and the DC power supply applies the DC potential difference U between the two pairs of rod electrodes; the first AC frequency source applies the first AC excitation voltage with the amplitude of V.sub.ex1 and the frequency of .sub.ex1 between the two pairs of rod electrodes, and the first AC excitation voltage is superimposed on the RF voltage; the second AC frequency source generates a modulation signal with a modulation frequency of .sub.ex2, and modulates the amplitude V of the RF voltage by using the signal; maintaining a specific ratio among the amplitude of the RF voltage, the voltage amplitude of the first AC frequency source and the modulation amplitude of the second AC frequency source, so that the AC frequency sources are phase-coherent; and regulating the amplitude of the RF voltage to collect ions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following drawings form part of the present specification and are included to further demonstrate certain aspects of the invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein. The drawings described below are for illustration purposes only. The drawings are not intended to limit the scope of the present teachings in any way.

(2) FIG. 1 is a schematic structural diagram of a quadrupole and an application power supply in the background.

(3) FIG. 2 is a general diagram of a mass filter in the background, where a first common stability region (grey) shows the position of an operating line below the tip end of a stability line, and the stability region is formed by stability boundaries of Y and X motions marked on the drawing.

(4) FIG. 3 is a schematic diagram of stability islands, i.e., stability regions (grey), in the background under the influence of single AC excitation at the main RF frequency of 0.95, where the three main stability regions are marked as A, B and C; the boundary of the initial stability region is represented by a wide solid line, and the oblique operating line is represented by a thin solid line.

(5) FIG. 4A is a common stability diagram of a mass filter near the tip end of the first stability region in the background under the situation of two quadrupole excitations at the main frequency of 0.05. Excitation intensity is provided in the drawing. Stable motion regions are represented by grey, the boundary of the initial first stability region is represented by a thick black line, and the operating line passes through the end of stability. The excitations are at the same stage. The excitations are opposite.

(6) FIG. 4B is a common stability diagram of a mass filter near the tip end of the first stability region in the background under the situation of two quadrupole excitations at the main frequency of 0.05. Excitation intensity is provided in the drawing. Stable motion regions are represented by grey, the boundary of the initial first stability region is represented by a thick black line, and the operating line passes through the end of stability. The excitations are at the same stage. The excitations are opposite.

(7) FIG. 5 is a circuit schematic block diagram for forming an X-band stable mass filter band through RF amplitude modulation according to one embodiment of the present invention.

(8) FIG. 6 is a mass spectrogram formed by increasing a quadrupole excitation voltage to improve quadrupole resolution in an RF amplitude modulation-assisted quadrupole excitation method according to one embodiment of the present invention.

(9) FIG. 7 is a schematic diagram of a dependence relationship between the most possible resolution and the square of residence time in the traditional technical solution and the improved technical solution of the present invention.

(10) FIG. 8 shows influences of ion signal intensity under different mass spectrum resolution widths according to one embodiment of the present invention.

(11) FIG. 9A shows a stability diagram structure of an X-band under a unit resolution condition formed by simulating an RF amplitude-assisted quadrupole excitation method according to one embodiment of the present invention.

(12) FIG. 9B shows a stability diagram structure of an X-band under a high resolution condition formed by simulating an RF amplitude-assisted quadrupole excitation method according to one embodiment of the present invention.

(13) FIG. 9C shows a stability diagram structure of an X-band under an ultrahigh resolution condition formed by simulating an RF amplitude-assisted quadrupole excitation method according to one embodiment of the present invention.

(14) FIG. 10A is a high-resolution spectrogram formed by using melamine as an analyte through RF modulation and quadrupole excitation waveforms formed by adopting a self-compensation method according to one embodiment of the present invention.

(15) FIG. 10B is a high-resolution spectrogram formed by using sulfadoxine as an analyte through RF modulation and quadrupole excitation waveforms formed by adopting a self-compensation method according to one embodiment of the present invention.

(16) FIG. 10C is a high-resolution spectrogram formed by using verapamil as an analyte through RF modulation and quadrupole excitation waveforms formed by adopting a self-compensation method according to one embodiment of the present invention.

(17) FIG. 10D is a high-resolution spectrogram formed by using reserpine as an analyte through RF modulation and quadrupole excitation waveforms formed by adopting a self-compensation method according to one embodiment of the present invention.

(18) FIG. 11A is a waveform and frequency domain analysis diagram of an ideal waveform for generating an X-band according to one embodiment of the present invention.

(19) FIG. 11B is a waveform and frequency domain analysis diagram of an actual waveform for generating an X-band according to one embodiment of the present invention.

(20) FIG. 12 is a schematic diagram of order analysis of a modulated RF signal for forming an X-band and required high-order frequency component intensity according to one embodiment of the present invention.

(21) FIG. 13 is a schematic diagram for explaining an influence of unbalanced RF amplitude modulation on a quadrupole stability diagram according to one embodiment of the present invention.

(22) FIG. 14A is comparative schematic diagrams of a quadrupole structure containing no prerod structure, an edge field and an a-q stability diagram change in the prior art, where the upper part is a schematic structural diagram containing no quadrupole structure; the middle part is a schematic diagram showing changes along the axis and parameters through an edge field; the lower part illustrates changes of an a-q stability diagram represented by an arrow under the same parameters; and under the situation that the quadrupole has pre-parameters, the parameters in the stability region are always maintained.

(23) FIG. 14B is comparative schematic diagrams of a quadrupole structure in FIG. 14A improved by adopting a delayed DC slope technology, an edge field and an a-q stability diagram change in the prior art, where the upper part is a schematic structural diagram of a quadrupole containing a prerod structure; the middle part is a schematic diagram showing changes along the axis and parameters through an edge field; the lower part illustrates changes of an a-q stability diagram represented by an arrow under the same parameters; and under the situation that the quadrupole has pre-parameters, the parameters in the stability region are always maintained.

(24) FIG. 15A is comparative schematic diagrams of a quadrupole structure in a solution of a quadrupole containing prerods provided by Miseki et al. in 1993, an edge field and an a-q stability diagram change in the prior art, where the upper part is a schematic structural diagram of a quadrupole containing prerods; the middle part is a schematic diagram showing changes along the axis and parameters through an edge field; the lower part illustrates changes of an a-q stability diagram represented by an arrow under the same parameters; and in the drawing, it is supposed that the parameters in the quadrupole containing prerods are maintained consistent.

(25) FIG. 15B is comparative schematic diagrams of a quadrupole structure with prerod structure ion passing rate improved by modulating the amplitude of an RF voltage, an edge field and an a-q stability diagram change according to one embodiment of the present invention, where the upper part is a schematic structural diagram of a quadrupole containing prerods; the middle part is a schematic diagram showing changes along the axis and parameters through an edge field; the lower part illustrates changes of an a-q stability diagram represented by an arrow under the same parameters; and in the drawing, it is supposed that the parameters in the quadrupole containing prerods are maintained consistent.

DETAILED DESCRIPTION OF THE INVENTION

(26) Implementations of the present invention will be described below through specific examples, and a person skilled in the art may easily understand other advantages and effects of the present invention through the contents disclosed in this specification. The present invention may also be implemented or applied through other different specific implementations, and the details in this specification may be modified or changed without departing from the spirit of the present invention based on different points of view and applications. It should be noted that the embodiments in the present application and the features in the embodiments may be combined with each other under the situation of no conflict.

(27) The terms used in this specification generally have their ordinary meanings in the art, within the context of the invention, and in the specific context where each term is used. Certain terms that are used to describe the invention are discussed below, or elsewhere in the specification, to provide additional guidance to the practitioner regarding the description of the invention. For convenience, certain terms may be highlighted, for example using italics and/or quotation marks. The use of highlighting and/or capital letters has no influence on the scope and meaning of a term; the scope and meaning of a term are the same, in the same context, whether or not it is highlighted and/or in capital letters. It will be appreciated that the same thing can be said in more than one way. Consequently, alternative language and synonyms may be used for any one or more of the terms discussed herein, nor is any special significance to be placed upon whether or not a term is elaborated or discussed herein. Synonyms for certain terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification, including examples of any terms discussed herein, is illustrative only and in no way limits the scope and meaning of the invention or of any exemplified term. Likewise, the invention is not limited to various embodiments given in this specification.

(28) It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below can be termed a second element, component, region, layer or section without departing from the teachings of the present invention.

(29) It will be understood that, as used in the description herein and throughout the claims that follow, the meaning of a, an, and the includes plural reference unless the context clearly dictates otherwise. Also, it will be understood that when an element is referred to as being on, attached to, connected to, coupled with, contacting, etc., another element, it can be directly on, attached to, connected to, coupled with or contacting the other element or intervening elements may also be present. In contrast, when an element is referred to as being, for example, directly on, directly attached to, directly connected to, directly coupled with or directly contacting another element, there are no intervening elements present. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed adjacent to another feature may have portions that overlap or underlie the adjacent feature.

(30) It will be further understood that the terms comprises and/or comprising, or includes and/or including or has and/or having when used in this specification specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.

(31) Furthermore, relative terms, such as lower or bottom and upper or top, may be used herein to describe one element's relationship to another element as illustrated in the figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation shown in the figures. For example, if the device in one of the figures is turned over, elements described as being on the lower side of other elements would then be oriented on the upper sides of the other elements. The exemplary term lower can, therefore, encompass both an orientation of lower and upper, depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as below or beneath other elements would then be oriented above the other elements. The exemplary terms below or beneath can, therefore, encompass both an orientation of above and below.

(32) Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

(33) As used in this disclosure, around, about, approximately or substantially shall generally mean within 20 percent, preferably within 10 percent, and more preferably within 5 percent of a given value or range. Numerical quantities given herein are approximate, meaning that the term around, about, approximately or substantially can be inferred if not expressly stated.

(34) As used in this disclosure, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. As used herein, the term and/or includes any and all combinations of one or more of the associated listed items.

(35) The description below is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. The broad teachings of the invention can be implemented in a variety of forms. Therefore, while this invention includes particular examples, the true scope of the invention should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the invention.

(36) The existing technical solutions described in the background show that the use of multiple AC excitation voltages will bring about changes in the stability diagram. To facilitate the understanding about the principle of the present invention, a further discussion is described herein. For example, two AC excitation voltages are used in the prior art. As shown in FIG. 4A and FIG. 4B, when the excitation voltages q.sub.ex1 and q.sub.ex1 are at a specific frequency ratio, a stability band corresponding to X or Y-direction ion motion is generated outside the initial stability region. In fact, this is because the excitation voltages correspond to the q parameters of the two frequencies, i.e., when the ratio q.sub.ex2/q.sub.ex1 is fixed, the amplitudes generated at these frequencies by the solutions of the extended Mathieu equation of the ion motion in the X or Y direction are just offset, thereby producing an ion stability band similar to an optical diffraction fringe.

(37) It needs to be pointed out that not only can the ion motion terms produced by excitation voltages with two different frequencies be offset, but also when quadrupole excitation is applied in different ways, since different modes of excitation voltage application can produce different vibration frequencies, amplitudes and intensities in the X and Y directions. By using different modes of excitation voltage application and regulating the waveforms, amplitudes and phases of the excitation voltages, it is also possible to obtain a narrow stability band outside the stability region to improve the mass resolution of the quadrupole mass spectrometry.

(38) Without intent to limit the scope of the invention, examples according to the embodiments of the present invention are given below. Note that titles or subtitles may be used in the examples for convenience of a reader, which in no way should limit the scope of the invention. Moreover, certain theories are proposed and disclosed herein; however, in no way they, whether they are right or wrong, should limit the scope of the invention so long as the invention is practiced according to the invention without regard for any particular theory or scheme of action.

Embodiment 1

(39) In the embodiment of studying the influence of the quadrupole excitation signal with an operating frequency of .sub.ex on the stability diagram, the quadrupole excitation signal is not superimposed on the RF signal in the form of linear addition, but the quadrupole excitation signal is used as an amplitude modulation signal to modulate an amplitude of the initial RF signal in the form of multiplication operator.

(40) When .sub.ex and a frequency the source RF signal are at a non-integer ratio, for ions with different initial phases introduced into the quadrupole mass analyzer, the phase condition will cause the ion trajectories at the boundary of the stability region to turn back or excite, which usually results in periodic changes in the boundary of the stability diagram depending on the phase of ion implantation, as previously mentioned in the patent of Alan Schoen. The boundary vibration of the stability diagram will cause the stability of ion motion to be sequentially and periodically enhanced and weakened at different q values, resulting in a ringing phenomenon at the boundary of the obtained mass spectrum peaks.

(41) When .sub.ex and the frequency of the source RF signal are at an integer ratio, the situation will be similar to the previously mentioned patent of Kozo Miseki, making the stability diagram of the quadrupole mass analyzer become a series of stability island structures. In the instable mesh band separating the stability islands, the motion frequencies of ions in the X and Y directions are sequentially .sub.ex, 2.sub.ex, . . . , /2. The Mathieu equation of ion motion may be expressed as:

(42) $\begin{array}{cc}\frac{d^{2}x}{d{}^2}+\left[a+2q\mathrm{Cos}2\left(1+2q_{\mathrm{ex}}\mathrm{Cos}\left(2v+\right)\right)\right].Math.x=0& \left(6.a\right)\\ \frac{d^{2}y}{d{}^2}-\left[a+2q\mathrm{Cos}2\left(1+2q_{\mathrm{ex}}\mathrm{Cos}\left(2v+\right)\right)\right].Math.y=0& \left(6.b\right)\end{array}$
where the quadrupole amplitude modulation frequency coefficient is =.sub.ex/. When v=0.05, i.e., the frequency of the quadrupole amplitude modulation waveform is 1/20 of a source RF frequency, the two main bands respectively correspond to ion resonance frequencies of 1/20 and 19/20. Different from the traditional modulation method of directly linearly superimposing the quadrupole excitation voltage, the main vibration modes of ions in the Y and X directions are just opposite. That is to say, a modulation frequency of 1/20 can produce an ion resonance frequency of 1/20 in the Y direction. On the other hand, the superimposed quadrupole excitation voltage of 1/20 can also produce the ion resonance frequency of 1/20 in the Y direction, but the phase is just opposite. Therefore, the above two signals can be superimposed to offset the ion resonance frequency of 1/20 in the Y direction and form an instability band.

(43) To analyze the specific structure of the instability band, it is necessary to analyze the solution stability of the case where the RF amplitude modulation signal is applied and the quadrupole excitation voltage is superimposed simultaneously. At this time, the ion motion in the X-Y space satisfies the Mathieu equation as follows:

(44) $\begin{array}{cc}\frac{d^{2}x}{d{}^2}+\left[a+2q\mathrm{Cos}2\left(1+2q_{\mathrm{ex}2}\mathrm{Cos}\left(2v_2+{}_1\right)\right)+2q_{\mathrm{ex}1}\mathrm{Cos}\left(2v_1+{}_1\right)\right].Math.x=0& \left(7.a\right)\\ \frac{d^{2}y}{d{}^2}-\left[a+2q\mathrm{Cos}2\left(1+2q_{\mathrm{ex}2}\mathrm{Cos}\left(2v_2+{}_1\right)\right)+2q_{\mathrm{ex}1}\mathrm{Cos}\left(2v_1+{}_1\right)\right].Math.y=0& \left(7.b\right)\end{array}$
where the first AC frequency source is used for driving the first AC excitation voltage between two pairs of rod electrodes in a quadrupole system as shown in FIG. 1, an amplitude of the first AC excitation voltage is smaller than an amplitude V of the RF voltage and is recorded as V.sub.ex1; the frequency is different and is .sub.ex1; the superimposed quadrupole excitation frequency coefficient is v.sub.1=.sub.ex1/.

(45) In addition, the second AC frequency source is used for modulating the amplitude V of the RF voltage, the modulation frequency is .sub.ex2, and the modulation frequency coefficient v.sub.2=.sub.ex2/.

(46) A simpler method is to make the working frequencies of the two AC frequency sources be equal. At this moment, the frequencies of the excitation voltages of the two AC frequency sources may be expressed as a single frequency, such as v=0.05. Supposing that v=K/P K and P are integers and the common period of the periodic function in equation 7 is P, equation 7 is transformed to Hill equation (i.e., second-order linear differential equation containing the periodic coefficient). At this moment, a matrix method (such as [Konenkov, N. V.; Sudakov, M. Y.; Douglas, D. J. Matrix Methods for the Calculation of Stability Diagrams in Quadrupole Mass Spectrometry.//J. Am. Soc. Mass Spectrom. 2002, 13, 597-613]) and other mathematical methods may be used to resolve the q parameter distribution with stable trajectories, i.e., stability diagram.

(47) Because the change in the modulation amplitude is usually small and the amplitude of superimposed the quadrupole excitation AC signal is also small, the solution of the above equation can be obtained by adopting a perturbation method with parameters. When the amplitude parameter q.sub.ex1 is small such as smaller than 0.015, the product factor of the higher-order trigonometric terms of multiplicative modulation and additive modulation may be described by a linear function. At this moment, when the ratio q.sub.ex2/q.sub.ex1 is determined, stable quadrupole excitation offset of .sub.ex and /2-.sub.ex frequencies can be obtained. When .sub.ex in the Y direction is offset, the narrowband stability region of X-direction motion can be obtained, which is referred to as X-band. Contrarily, when .sub.ex in the X direction is offset, a narrowband stability region of Y-direction motion can be obtained, which is referred to as Y-band. Usually, q.sub.ex2/q.sub.ex1 needs to be controlled to be approximately 1.5 to deduct the vibration amplitude in the non-interest direction. For larger v values, the non-linear terms of the trigonometric function should be considered. Similar results can be obtained by adopting an approximation method. Another point is that, when the ratio q.sub.ex2/q.sub.ex1 is a smaller fixed value, the ratio q.sub.ex2/q.sub.ex1 produced by the X-band or Y-band is not related to v, which is determined by the characteristic of the expanded Taylor equation of the trigonometric function.

(48) Similarly, we can offset the instable motion in the Y direction by selecting other excitation frequencies to produce an X-band. For example, when q.sub.ex2/q.sub.ex1=1.63, v.sub.1=v and v.sub.2=1v, a narrow stability band result similar to that in FIG. 4A in the prior art can also be obtained. In fact, when the AC amplitude modulation frequency coefficient and the superimposed excitation frequency coefficient are set in the form of A .sub.ex+B, and when A is a natural number of which the absolute value is smaller than 4, the expanded equation of the ion motion frequency term can be better superimposed to eliminate the directional excitation of ions at the A .sub.ex frequency, thus forming a narrow instability band.

(49) When the quadrupole mass analyzer works, the set values of the RF voltage and a quadrupole DC amplitude are the scanning line a=2q passing through the vertex of the stability region. In a conventional mode, the mass resolution of the quadrupole is determined by the slope =U/V of the scanning line. In the stability band scanning mode, the slope of the scanning line is fixed, and the ions do not have a stable trajectory under the situation of no AC excitation voltage. At this moment, the mass resolution of the quadrupole is determined by the width of the stability band, and the width of the stability band is determined by the ratio q.sub.ex2/q.sub.ex1 of an AC amplitude modulation depth to the superimposed excitation voltage amplitude, or is recorded as the parameter AM2ratio (Amplitude-Modulation 2 parameter ratio). The theoretical mass resolution is R=q.sub.centre/q, where q=q.sub.1q.sub.2, which represents the distance between the two intersections of the scanning line and the stability region, where q.sub.centre is a median.

(50) As shown in Table 1, a relationship between theoretical mass resolution and AM2ratio parameter is shown. This method is used for producing the mass resolution of the X-band, where the nondimensionalized frequency, i.e., the frequency ratio of the AC excitation voltage to the main RF voltage v=0.05. In the table, Q1 and Q2 are respectively the q values of the two edges forming the stability band, DeltaQ shows the width of the mass stability band. aA and qA are the coordinates of the top vertex of the stability band, the ratio determines the maximum kMax of the slope of the scanning line of the quadrupole, aB and qB are vertex coordinates of the stability island below, the ratio determines the minimum kMin of the slope of the scanning line of the quadrupole, and when it is below this value, the scanning line cuts off the stability island below to produce ghost peaks. According to the q difference width of the band, the limit mass spectrum resolution Theo. Res value under the corresponding conditions can be obtained.

(51) TABLE-US-00001 TABLE 1 Relationship between theoretical mass resolutions and AM2ratio parameters AC1/RF AM 2ratio Q 1 Q 2 DeltaQ aA qA kM ax 0 1.5646 0.236995 0.70598 0.167848 0.001 1.5617 0.70719 0.70502 0.00217 0.2369 0.70576 0.16782 0.002 1.5588 0.70783 0.70647 0.00136 0.23747 0.70682 0.167985 0.003 1.5559 0.70917 0.70835 0.00082 0.23807 0.70766 0.16821 0.004 1.553 0.70991 0.70937 0.00054 0.23865 0.70871 0.16838 0.005 1.5501 0.71123 0.71084 0.00039 0.23944 0.71038 0.16853 0.006 1.5472 0.71418 0.71394 0.00024 0.24065 0.71164 0.16908 0.007 1.5443 0.716045 0.715859 0.000186 0.241602 0.713142 0.169392 0.008 1.5414 0.717886 0.717761 0.000125 0.242599 0.714656 0.169731 0.009 1.5385 0.719889 0.719813 0.000076 0.2437 0.716502 0.170146 0.01 1.5356 0.72179 0.721738 0.000052 0.244596 0.718055 0.170319 0.011 1.5327 0.72384 0.723806 0.000034 0.245762 0.719695 0.170741 0.012 1.5298 0.725753 0.725726 0.000027 0.246251 0.722018 0.170529 0.013 1.5269 0.727757 0.727737 0.00002 0.247919 0.723339 0.171371 0.014 1.524 0.729761 0.729746 0.000015 0.249182 0.724978 0.171855 0.015 1.5211 0.731765 0.731754 0.000011 0.249934 0.727119 0.171866 AC1/RF aB qB Km in Theo.RES 0 0.001 0.23595 0.70704 0.16686 325.394 0.002 0.23589 0.70783 0.16698 519.9632 0.003 0.23646 0.70917 0.16671 864.3415 0.004 0.23679 0.71046 0.16665 1314.148 0.005 0.23727 0.712139 0.16659 1823.167 0.006 0.23778 0.71419 0.16647 2975.25 0.007 0.23828 0.716045 0.166387 3857.498 0.008 0.239102 0.717886 0.166533 5742.588 0.009 0.239672 0.719889 0.166464 9471.728 0.01 0.240515 0.72179 0.16661 13880.07 0.011 0.24132 0.72384 0.166694 21288.9 0.012 0.242204 0.725753 0.166864 26879.23 0.013 0.243161 0.727757 0.167072 36387.35 0.014 0.243992 0.729761 0.167173 48650.24 0.015 0.245017 0.731765 0.167415 66523.62

(52) From the table, it can be learned that, when AM2ratio is set to a corresponding proper value, the higher the combination of excitation voltage and the modulation amplitude, the higher the resolution can be obtained. It needs to be noted that, when the slope =U/V of the scanning line is too small, the scanning line will pass through the stability region to produce ghost peaks. By setting the working conditions of the quadrupole mass analyzer according to the above parameters in the table, the maximum mass resolution up to approximately 66,000 can be obtained. Herein, the frequency ratio /.sub.ex1 of the RF power supply to the first AC frequency source is an integer greater than or equal to 5. Because cheap available solutions can be easily found for the divide-by-2, divide-by-5 and divide-by-10 frequency dividers, the condition of divide-by-20 frequency division, i.e., v=0.05, is usually adopted. A modulation depth of the second AC frequency source for forming the RF amplitude modulation to the output voltage of the RF power supply is in a range of 90% to 110%. Usually, the modulation depth of the second AC frequency source to the output voltage of the RF power supply and the amplitude V.sub.ex1 of the excitation voltage generated by the first AC frequency source maintain a linear relationship.

Embodiment 2

(53) Table 2 shows combinations of AC amplitude modulation frequency coefficients v.sub.2 causing the production of the X-band and superimposed excitation frequency coefficients v.sub.1 and frequency ratios thereof, which are arranged according to frequency from low to high. Table 3 shows simulation of the quadrupole in a traditional mode under the situation of an X-band. All amplitudes are zero peaks.

(54) TABLE-US-00002 TABLE 2 Combinations of AC amplitude modulation frequency coefficients O I II III IV V VI v.sub.1= v v v 1 v 1 v 1 + v 1 + v v.sub.2= v 1 v 1 + v 2 v 2 + v 2 v 2 + v q.sub.ex2/ 1.54 1.63 1.72 3.31 3.45 4.55 3.38 q.sub.ex1=

(55) TABLE-US-00003 TABLE 3 Simulation of the quadrupole in a traditional mode under the situation of an X-band. DC RF AC-1 AC-2 AMRF % Frequency, KHz 0 1200 60 1130 60 Conventional 141.69 V 844.33 V 0 0 Xband-Prior Art 144.33 V 857.25 V 6.85 V 20.16 V Xband-AMRF 144.19 V 856.47 V 6.85 V 0 +/2.48%

(56) According to Table 1 above, by using amplitude modulation RF in combination with the quadrupole excitation voltage to form an X-band to perform quadrupole mass analysis scanning, a very high mass resolution can be obtained. However, it needs to be noted that this is only a theoretical numerical simulation situation in an infinite long quadrupole. In actual application, as mentioned above, the mass resolution is first restricted by the residence time of ions in the quadrupole, which will correspondingly become poor in a finite long rod. For example, we use a quadrupole with an electric field radius of r.sub.0=4 mm and length of 200 mm for simulation. First the influence of the field distortion at both ends of the rod system is not considered, and the electric field along the quadrupole is set as a pure quadrupole field (hyperboloidal electrode) to ignore the high-order field effect at both ends. When the quadrupole works under the condition of an RF frequency of 1.2 MHz, ions of 609 Da can obtain a mass resolution of 10,000 in the traditional mode. The corresponding power supply is set according to the condition in Conventional in Table 3. In a new operating mode, we select another condition in Table 2, and an amplitude of the corresponding AC excitation voltage is expressed by Xband-AMRF in Table 3. Under this condition, the ion mass resolution of reserpine with a mass of 609 is also approximately 10,000. To analogize the prior art of Sudakov et al., their conditions are transcribed in Xband-Prior Art.

(57) From the above table, it can be learned that, when an amplitude modulation mode is used, the second excitation voltage of 1.14 MHz in the prior art can be avoided, which is very helpful for the design of the drive power supply of the high-resolution quadrupole mass analyzer, because in this case, if the second excitation voltage of 1.14 MHz is used, its amplitude will also be acquired by the control circuit through sampling feedback because its frequency is very close to the main RF frequency. Since a rectifying circuit is usually used in sampling feedback, its feedback depth is usually reflected as the absolute value of instantaneous high frequency RF signal. However, an amplitude of the second excitation voltage of 1.14 MHz is higher and will form a beat frequency pattern with the rectification value of the initial RF signal, which makes the feedback value of the feedback circuit fluctuate at phases of different RF and AC, and is very disadvantageous to form a stable RF signal.

(58) However, when we use the modulation solution provided by the present invention, since the AC voltage of 1.14 MHz is avoided, only 60 KHz modulated and superimposed AC waveform signals appear in the whole system. At this moment, because 60 KHz is far from the frequency band 1.2 MHz, very simple high-pass and low-pass filters can perfectly realize the superimposition of mixing signals on the quadrupole. At the same time, it is easy to remove the influence of the excitation signal. Furthermore, we can even offset the influence of spurious noise in the circuit by actively generating reverse 60 KHz signals.

(59) As shown in FIG. 5, a circuit schematic block diagram capable of effectively forming an X-band stable mass filter band through RF amplitude modulation, where a mass control signal 501 is mixed with a signal from a first AC source 521 through an adder 511, the intensity of the superimposed AC signal source is modulated by a first excitation voltage signal source 503 through a multiplier 512, the formed mixed control signal is superimposed with the signal of a resolution control DC voltage source 502 for controlling quadrupole DC intensity respectively through a forward superimposer 513 and a reverse superimposer 514, and the signals are respectively applied to a quadrupole electrode pair 500A and a quadrupole electrode pair 500B through an additive amplifying circuit. When the bias voltage of the quadrupole pair needs to be corrected, the above output DC voltage may be biased by a biasing DC voltage source 504 through an additive amplifying circuit 515 and an additive amplifying circuit 516.

(60) At the same time, to effectively control the modulation amplitude of the quadrupole RF signal, the second AC source 505 forms an amplitude modulation signal, a excitation voltage may be amplified through a frequency selective amplifier 517, such as 60 KHz in the drawing. This waveform forms a modulated amplitude signal on a multiplier circuit 520 with the output of the above mass control signal at the frequency selective amplifier 519 of 1.2 MHz, so that the signal can transfer RF energy to a secondary amplifying coil 532 and a secondary amplifying coil 533 through a primary coil 531 of a resonant transformer, thus generating a combination of AC and RF signals for constraining ions.

(61) It needs be further pointed out that, in the synthesis of RF amplitude modulation signal and superimposed quadrupole excitation voltage signal, the pass bandwidth of various multipliers is limited. Some solutions may be adopted to overcome these problems, such as by introducing a second frequency selective amplifier 518 to introduce other signal frequencies. The combination of 505, 517 and 518 may also be implemented by other means in some cases, such as multiple mixer networks or chips, or direct waveform synthesis of the above frequency combination.

(62) When an ion beam composed of ions with similar mass number moves in a quadrupole, it will have a random distribution of approximately 0.1 mm in transverse motion. Because all ions fly in the direction of the quadrupole with the same energy, they also fly for the same time. The time that ions enter the quadrupole is from 0 s to 20 s for uniform distribution, so the ions entering the quadrupole are not only in all possible RF phases, but also in all phases of the AC excitation voltage. Finally, the ions will reach a normal distribution, where the transverse energy standard deviation is 0.025 eV, which is equivalent to the thermal motion energy of ions at 320 K. At each time of simulation, we set 10,000 ions with the same mass and energy. For other conditions, we randomly distribute them. When they hit the quadrupole or disappear or are transmitted to the other end of the quadrupole, the simulation stops. Then we record the number of ions transmitted, and then set ions with another mass number to simulate till different peak shapes are formed as shown in the drawing. In practice, the quadrupole works in another way, i.e., scanning RF and DC voltages, and the nominal mass of ions can be obtained from the RF voltage. Therefore, compared with the real experiment, in the simulation herein, the peaks of both low mass number and high mass number will appear.

(63) It can be learned that, even under the situation of the lowest mass resolution, a lot of ions (approximately half) are lost. This is caused by the initial distribution of ion velocity and position. Adjusting to increase the ratio of the quadrupole excitation voltage to the main RF intensity can make the resolution of the mass analyzer increase rapidly. As shown in FIG. 6, a mass spectrogram formed by increasing a quadrupole excitation voltage to improve quadrupole resolution in an RF amplitude modulation-assisted quadrupole excitation method is illustrated, and the resolution is gradually improved.

(64) When simulation is performed in a traditional mode (i.e., without AC excitation voltage), the theoretical mass resolution is also 10,000 at the maximum ion passing efficiency, but the mass resolution is more and more affected by the ion flying time. Since the peak shape in this mode is well known, there is a very serious tailing on the side of the high mass number. The maximum mass resolution can be obtained from equation (5).

(65) As shown in FIG. 7, a relationship between mass resolution and periodic motion period number n2 in two modes of quadrupole excitation for forming an X-band (701, the RF amplitude modulation-assisted quadrupole excitation method of the present invention, and 702, forming an X-band through two additional assisted quadrupole excitation voltages in the prior invention) is illustrated. To compare the improvement of the method, a curve 703 indicates a mass resolution relationship of the quadrupole without any quadrupole excitation in the traditional method.

(66) The simulation results are shown in FIG. 7, where the mass resolution is in proportion to the square of the periodic motion period number. In the traditional mode, the mass resolution is only 500 at 100 RF periods. Contrarily, the mass resolution of 9,000 can be obtained by scanning with the X-band.

(67) Here's an explanation. Obviously, compared with the traditional mode, the instable motion speed of instable motion ions near the X-band of the boundary of the stability region is higher, and they disappear faster when they hit the quadrupole. When the frequency v is low, the two AC excitation voltages with frequencies v.sub.1=v and v.sub.2=1v modulate the ion trajectories, which leads to the instability of motion in the X-direction outside the X-band. The RF frequency and parameters q.sub.ex1 and q are also used in equation (7) for comparison. If a smaller frequency v is used for replacing , q.sub.ex1 will become very large, which will make it difficult to realize the actual voltage. In the above simulation, v=0.05. However, because the effective value of q.sub.ex1 will resonate with the modulation envelope of RF, it can be enlarged by 400 times after 20 periods in fact. That is to say, when q.sub.ex1=0.0068, the effective value of actual q is 2.72, which also corresponds to the region with high q value in Mathieu equation. Therefore, the instable motion of ions is more intense. The ions can be separated after only a few of RF periods. For higher separation period numbers, the effective q value for ion separation will further increase. At this moment, the actual ion separation effect is similar to the situation of the fourth stability region using q=27.2 in [Wei Chen, B. A. Collings, and D. J. Douglas, High-Resolution Mass Spectrometry with a Quadrupole Operated in the Fourth Stability Region,//Anal. Chem. 2000, 72, 540-545]. In our simulation, the instable ions with a mass difference of 0.08 can be enabled to hit the quadrupole and disappear within only 100 RF periods, so as to obtain higher resolution.

(68) Therefore, the X-band is similar to a region with a high q value when the frequency v is low. The influence of this method on the resolution of ions with a mass of 609 under different resolution widths is shown in FIG. 8.

(69) In FIG. 8, the method of using RF amplitude modulation to superimpose the quadrupole excitation voltage shown by 801, compared with the method of the traditional quadrupole mass analyzer shown by 802 and the result of the double quadrupole excitation superposition method of Saudakov shown by curve 804, can achieve the enhancement of signals under each resolution situation. Especially as shown by the improved rate curve of the new method shown by 803 compared with the traditional method, by adopting this method, the resolution efficiency of the quadrupole mass analyzer to the ions can be significantly improved indeed and higher ion transport efficiency can be obtained, especially under the situation of high resolution.

(70) When the quadrupole is applied with the AC excitation voltage, the produced field distortion is much smaller. A pure quadrupole electric field is formed by an ideally symmetric and parallel hyperboloidal rod on an infinite length. However, in practice, this is impossible, and the quadrupole is often processed into a cylindrical rod. In the traditional mode, the ratio of the radius R of the rod to the radius r.sub.0 of the electric field is generally 1.12 to 1.13, so as to offset the influence of field distortion and achieve better performance at the same time. Although the influence of non-linear field distortion is very small, it will seriously influence the performance of the quadrupole, resulting in peak distortion, tailing and loss of ion transmission. When the quadrupole works at a high resolution, these problems become more serious. Other distortions such as rod dislocation, rod bending, rod shape distortion, surface irregularity or surface contamination will bring more unpredictable influences. When an additional AC excitation voltage is applied, many of these influences are weakened or even disappear. Experiments [X. Zhao, Z. Xiao and D. J. Douglas, Overcoming field imperfections of quadrupole mass filters with mass analysis in islands of stability, Anal. Chem. 81, 5806, (2009)] confirm this. Because the quadrupole mass analyzer solution in this method is also based on quadrupole AC excitation, this method can also have the small mechanical structure and size of analyzer devices, and resist dirt.

Embodiment 3

(71) In this embodiment, a commercial quadrupole mass spectrometry instrument (Shimadzu Corporation, LCMS2020) is modified. The length of the main rod of the quadrupole in the instrument is 200 mm, and the incircle radius is 4 mm. By adopting several different voltage settings, stability diagrams of transmission regions of ions under an X-band can be drawn, as shown in FIGS. 9A-9C.

(72) FIGS. 9A-9C respectively show stability diagram structures of an X-band formed under a unit resolution, a high resolution and an ultra-high resolution by simulating an RF amplitude-assisted quadrupole excitation method.

(73) From FIGS. 9A-9C, it can be learned that, in FIG. 9A, when VAC/VRF=0.0042, for reserpine ions with a mass number of 609, the resolution can reach 1431, and at the time, the transmission efficiency of the quadrupole mass analyzer is 33%; as shown in FIG. 9B, if this value is increased to approximately 2 times, the resolution of these ions can reach 7780 and is approximately increased by 5.5 times, while the transmission efficiency can reach 15% and is decreased by only half; and as shown in FIG. 9C, when VAC/VRF reaches 0.012, a very good resolution result can be obtained, and in the simulation results, a resolution of 22,000 or more can be obtained at passing efficiency of 2.8%.

(74) In the experiment, by simultaneously modulating the RF voltage of the modified quadrupole mass analyzer system according to the above parameters and compensating the applied excitation voltage, the preliminary results prove the superiority of the method of forming an X-band through an RF amplitude modulation-assisted quadrupole excitation method.

(75) Table 4 below gives results of comparison between the conventional U-V scanning method and the RF amplitude modulation-assisted quadrupole excitation method. Specifically, results of comparison between conventional QMS resolution and AMX band signals with similar or better FHWM resolution are shown.

(76) TABLE-US-00004 TABLE 4 Results of comparison between the conventional U-V scanning method and the RF amplitude modulation-assisted quadrupole excitation method Prior art Present invention Existing Sensitivity Sensitivity Test conditions test (signal (signal of the present condition FHWM Intensity) FHWM Intensity) invention U-V 0.65 0.91 0.648 0.934 Based on of the existing test scanning condition, additionally mode under applying a 60 KHz, 72 mV condition of modulation signal to the mass 1.2 MHz RF control input voltage terminal voltage of the quadrupole, and additionally applying a 2.8 V 60 KHz quadrupole excitation signal between the two pairs of quadrupoles at the same time 0.53 0.792 0.501 0.833 Based on of the existing test condition, additionally applying a 60 KHz, 86 mV modulation signal to the mass control input voltage terminal of the quadrupole, and additionally applying a 3.2 V 60 KHz quadrupole excitation signal between the two pairs of quadrupoles at the same time 0.44 0.318 0.397 0.549 Based on of the existing test condition, additionally applying a 60 KHz, 99 mV modulation signal to the mass control input voltage terminal of the quadrupole, and additionally applying a 3.7 V 60 KHz quadrupole excitation signal between the two pairs of quadrupoles at the same time 0.34 0.176 0.343 0.441 Based on of the existing test condition, additionally applying a 60 KHz, 132 mV modulation signal to the mass control input voltage terminal of the quadrupole, and additionally applying a 4.6 V 60 KHz quadrupole excitation signal between the two pairs of quadrupoles at the same time 0.319 0.085 0.306 0.279 Based on of the existing test condition, additionally applying a 60 KHz, 142 mV modulation signal to the mass control input voltage terminal of the quadrupole, and additionally applying a 5.0 V 60 KHz quadrupole excitation signal between the two pairs of quadrupoles at the same time 0.235 0.038 0.231 0.098 Based on of the existing test condition, additionally applying a 60 KHz, 152 mV modulation signal to the mass control input voltage terminal of the quadrupole, and additionally applying a 5.5 V 60 KHz quadrupole excitation signal between the two pairs of quadrupoles at the same time 0.152 0.0098 0.152 0.0172 Based on of the existing test condition, additionally applying a 60 KHz, 188 mV modulation signal to the mass control input voltage terminal of the quadrupole, and additionally applying a 6.2 V 60 KHz quadrupole excitation signal between the two pairs of quadrupoles at the same time

(77) From the table, it can be learned that, basically, under the condition that the resolution is 0.1 to 0.4 unit mass, approximately 2 to 3 times of signal enhancement brought by the RF amplitude modulation-assisted quadrupole excitation method are observed. For example, when the unmodified quadrupole analyzer scans the peak shape of reserpine, if a unit mass resolution is obtained, under the condition of RF of 1.2 MHz, the relative signal intensity that can be obtained by the instrument is 0.91. However, if the resolution is expected to be improved to 0.3 FHWM, the signal intensity of the ions will drop to approximately 0.085, which will cause the overall signal sensitivity of the instrument to be reduced by one order of magnitude. When a cascade mass spectrometer with two quadrupoles is used, the signal sensitivity of the instrument will be reduced by two orders of magnitude. However, if a 60 KHz, 142 mV modulation signal is additionally applied to the mass control input voltage terminal of the quadruple based on of the original equipment, and a 5.0 V 60 KHz quadrupole excitation signal is additionally applied between two pairs of quadrupoles at the same time, the signal intensity similar to FHWM can reach 0.279. The pass rate is reduced only by half order of magnitude relative to the original condition. If this method is used, when a 60 KHz, 152 mV modulation signal is additionally applied to the mass control input voltage terminal of the quadrupole based on of the original equipment, and a 5.5 V 60 KHz quadrupole excitation signal is additionally applied between two pairs of quadrupoles at the same time, the signal intensity of 0.098 can be obtained. Relative to the signal intensity of 0.085 in the high-resolution mode of the original unmodified instrument, the signal intensity is improved by 15%, but the mass resolution width of ions can be improved by approximately 0.23 unit mass.

(78) The above method proves that the RF amplitude modulation method has the potential possibility of higher resolution. A simpler modification solution is to modulate the RF signal by using only a 60 KHz RF modulation signal. Since this waveform can be regarded as a carrier signal, the low frequency part of the signal can be fed back and rectified out on the error amplifier fed back by the quadrupole power supply, so a 60 kHz waveform signal will also be generated. Usually, this signal is controlled to the output of the high-voltage DC generator circuit of the quadrupole power supply through a resistive divider, so this modulation can be correspondingly used as a quadrupole AC excitation waveform. By adjusting the ratio of the resistive divider, the formed RF modulation envelope waveform and quadrupole AC excitation waveform can be completely phase-aligned under an appropriate RF modulation voltage. By using this method, only a large RF modulation voltage is needed to produce a good X-band mass filter structure. FIG. 10D shows that, when the phase delay is well compensated under the voltage corresponding the mass number 609 of reserpine, the resolution of the main peak of reserpine can rise to the width of only 0.05 unit mass, while only of signals under a unit mass resolution condition are attenuated when compared with the conventional mode. This result is even better than the result obtained by using a high-resolution and high-precision quadrupole mass analyzer with a larger field radius, such as 6 mm. Similar results can also be obtained for ions with other mass-charge ratios. However, due to the nonlinear relationship brought by this modulation and demodulation solution, an incomplete quadrupole excitation offset will be formed in the motion of ions in the Y-direction, and slight resolution attenuation will be caused, which is also shown in the front trailing characteristics of the mass spectrum peak pattern.

(79) As shown in FIGS. 10A-10D, effects of high-resolution spectrograms formed for analytes with different mass numbers when RF modulation and quadrupole excitation waveforms are formed by adopting a self-compensation method are illustrated.

(80) In the above device, the best X-band mass peak width is restricted to approximately 0.08. The reason for restricting higher resolution is that a higher RF modulation voltage such as higher than 0.25 V will produce asymmetric envelope waveforms in the current circuit. Although this phenomenon can hardly be learned in the signal displayed by an oscilloscope, it can be revealed by Fourier transform. In this case, the RF signal is different from the additional quadrupole AC waveform and cannot be fully compensated. In the next embodiment, we will show how to overcome this problem.

Embodiment 4

(81) In this embodiment of the present invention, we further improve the system to overcome the influence of asymmetric quadrupole excitation waveforms caused by electronic restrictions.

(82) FIGS. 11A and 11B are waveform and frequency domain analysis comparison diagrams of an ideal waveform 121 and an actual waveform 122 for generating an X-band.

(83) As shown in FIG. 11A, the waveform 121 shows a waveform that is theoretically inferred to form a perfect X-band. It can be found by Fourier transform that the main frequency of the waveform superimposed with amplitude modulation and accompanied by a proper reverse quadrupole excitation signal contains a quadrupole DC component which causes ion instability, a quadrupole excitation component with 1/n frequency division ratio and a high-frequency quadrupole AC component with 1-1/n frequency division ratio produced by amplitude modulation. If we observe carefully, we can also learn that there are very few of 2/n frequency divided signals. This is due to the high-order term produced by the prosthaphaeresis of the triangular function. However, to view from the amplitude, the power of the high-order components of the second or higher order is only 0.01 times or less of that of the first order. In the actual waveform, we can learn that the components of the 2/n frequency divided signal are increased obviously. At this moment, the signal will cause doubling of the ionic movement duration frequency in all directions in the sense of ion vibration. However, n frequency components are not correspondingly learned in this signal at high frequency bands. Therefore, the doubled-frequency motion of ions in the Y direction is not effectively offset, and an ideal Y-direction instability band cannot be suppressed at this moment.

(84) To resolve this problem, an ideal solution is to introduce an additional amplitude modulation signal with 2/n frequency division ratio, which can be learned through the analysis of the RF envelope band. Least-square fitting is performed to the pure RF signal superimposed with 1-1/n dividing frequency. As shown FIG. 12, the left figure illustrates a waveform data diagram of a modulation RF signal for forming an X-band based on a divide-by-20 frequency excitation signal, and order analysis of the envelope line is performed thereto. First, 1/n dividing frequency illustrated in the middle figure, i.e., the main waveform of the amplitude modulation signal corresponding to 1/20f.sub.RF can be obtained. After deducting the amplitude modulation signal component of 1/n dividing frequency from this waveform, it can also be learned in the right figure that it further contains 2/n dividing frequency, i.e., an amplitude modulation signal corresponding to 1/10f.sub.RF.

(85) Contrarily, if a 2/n dividing frequency term is introduced into the amplitude modulation signal, a motion frequency component of 1-2/n dividing frequency can also be formed in the spectrum of ion motion, and this component can be used for offsetting the original 2/n dividing frequency component formed by the electronic imperfection.

(86) Similarly, this additional frequency component .sub.ex3 can also be designated as a positive value equal to A .sub.ex1+B, where A is a non-zero integer between 3 and 3, and B is a non-negative integer. These frequencies respectively correspond to the fundamental frequencies of the main RF voltage and quadrupole AC excitation voltage frequencies, and ion motion frequency characteristics caused by higher harmonics. The situation that the absolute values of A and B are 1 corresponds to fundamental frequency superimposition. If the quadrupole field type contains higher-order fields, such as an octupole field produced by symmetry breaking in the X-Y direction, or a hexapole field caused by single pole position offset, they respectively correspond to the situation that the absolute values of A and B are 2 and 3. By introducing an excitation voltage of a frequency component .sub.ex3 corresponding to these conditions, the clarity of the boundary of the formed stability band and the additional ion motion frequency component formed by the above waveform imperfection can be further corrected, and the resolution performance of the quadrupole mass spectrometry can be further improved.

(87) Another method of improving the peak shape of the quadrupole is to deliberately introduce an RF amplitude modulation ratio which is greater or smaller than the balanced quadrupole excitation voltage condition in Table 2. FIG. 13 is used for explaining an influence of unbalanced RF amplitude modulation on a quadrupole stability diagram.

(88) Herein, numeral references 1301, 1302 and 1303 are respectively X stability band shapes obtained at low, normal and high RF amplitude modulation ratios, and the RF amplitude modulation ratios AM2ratio are respectively 1.50, 1.5356 and 1.58. It can be learned that, when the RF amplitude modulation ratio applied to the quadrupole deviates from an ideal compensation value, the X stability band will be split, because of the ionic trajectory vibration influenced by RF modulation and the incomplete offset of the quadrupole excitation condition at the splitting position. The expansion of the trigonometric function product term in Mathieu equation 7.a/7.b formed by amplitude modulation will produce second-order and other higher-order additive terms, which will produce sharper lower edges of the splitting position. When the scanning line 1304 passes through these lower edges, the effective width of the actually formed X stability band becomes narrower. For example, when the RF amplitude modulation ratio is 1.50 and the slope of the scanning line is 0.1694, by cutting the lower edge of the split X stability band 1301, a mass resolution of 18,272 can be obtained for ions of reserpine with a mass of 609. When the same scanning line is used to pass through the fully compensated stability band 1302, the mass resolution is only 13,880. It can be learned that, when the RF modulation ratio and the higher-order frequency term of the effective quadrupole excitation voltage are reasonably configured, the mass resolution obtained by the method provided by the present invention is higher than that obtained by other prior methods of forming the stability band or island structure based on quadrupole excitation.

Embodiment 5

(89) In the prior art, when a high-order stability region with a high q value is used, although a mass resolution of 14,000 can be obtained in the experimental report, since the sensitivity is too low, it is difficult to realize commercialization in the actual application. In the traditional mode, because of the existence of the edge field at the introducing end of the quadrupole, the ion loss in this method is too great. At the introducing end of the quadrupole, the contents of DC and RF are lower than that inside the quadrupole, and the ion motion becomes more instable. However, due to the existence of transverse motion, ions need to undergo very great ion sputtering to cross the edge field. In the quadrupole, the edge field exponentially decreases along the quadrupole and maintains 2r.sub.0 (the radius of the electric field of the quadrupole) in a distance. For a quadrupole with an electric field radius of 5 mm and a length of 200 mm, the edge field accounts for 5% of the total length. For ions which move for 100 RF periods, they will undergo five periods in the edge field, which will result in ion loss. In the traditional mode, the resolution is only 500 when the motion time is the same. To achieve a higher mass resolution, it is necessary to increase the ion motion time, and the time in the edge field will increase correspondingly, which will lead to the decrease of sensitivity. If an X-band is used at this moment, a high mass resolution can also be obtained even the motion time is 100 RF periods. Since the vertex of the stability region is only modified, compared with the traditional mode, the ion transmission efficiency will decrease.

(90) Especially when a high resolution is required, the edge field brings a big problem. To overcome this problem, a DC delay technology was invented [W. M. Brubaker, D. Burnham, and G. Perkins, J. VAC. Sci. Technol, 8 (1971), 273-274].

(91) As shown in FIGS. 14A and 14B, the upper figure illustrates a schematic structural diagram during entering into a quadrupole, the middle figure illustrates corresponding changes during passing through edge fields a and q along a z axis of a quadrupole, and the bottom figure illustrates a change of the stability diagram represented by an arrow under the same parameters. In the drawings, it is supposed that the parameters in the quadrupole containing prerods are maintained consistent.

(92) In this technology, a small section of rod (referred to as prerod) is required to be additionally placed at the front end of the quadrupole. The main quadrupole has both RF voltage and DC voltage, but the prerod has only RF voltage. Therefore, there is no DC component when the ion beam enters the prerod. The edge field of the RF electric field of the prerod gradually increases from 0. Only when the ions enter the main quadrupole, the ions experience the electric field containing a DC component. Therefore, parameters a and q will be maintained stable in the first region, and the ion sputtering in the edge field will be minimized. This technology is shown in FIG. 8, from which it can be learned that, when ions enter the main quadrupole for analysis from the prerod region, the ions in the a, q parameter space first enter the deep position of the stability region due to the gradual enhancement of the edge RF quadrupole field, with the q value being increased, and then the ions in the gap between the prerod and the main rod finally reaches the top end of the stability region due to the enhancement of the edge DC quadrupole field, with the a value being increased, resulting in mass resolution. The ions in the whole process move in the stability diagram to avoid ion loss. However, in the case of using the prior X-band for ion mass separation, the difference between the effect of the X-band method and the effect of the traditional method using this improved method lies in that, when the ions move in front of the X-band which is very close to the vertex, the ions pass through a narrow instability band. At this moment, when the ions are located at the tail end of the edge field, i.e., the position where the prerod and the main rod are separated, if the experience time is long, serious ion beam scattering will be caused, resulting in ion loss.

(93) FIGS. 15A and 15B are used for comparatively describing the improvement of the ion pass rate of the prerod structure through RF voltage amplitude modulation in the present invention.

(94) As shown in FIG. 15A or 15B, the upper figure illustrates a schematic structural diagram during enter into a quadrupole, the middle figure illustrates a change during passing through edge fields a and q along a z axis of a quadrupole, the bottom figure illustrates a change of the stability diagram represented by an arrow under the same parameters. In the drawings, it is supposed that the parameters in the quadrupole containing prerods are maintained consistent.

(95) In the previous patent solution of X-band separation, since RF and two excitation voltage signals having a frequency division relationship of 1/n and 1-1/n are applied to the quadrupole, when the AC signal of the main rod is additionally applied to the prerod through a capacitance network, since the 1-1/n high-frequency AC excitation voltage signal (AC2) is very similar to the initial RF signal, it is difficult to avoid coupling it to the prerod.

(96) At this moment, the stability diagram structure of ions in the prerod is restored to the stability island structure proposed by Miseki et al. in 1993, as shown in the lower figure of FIG. 15A. When ions pass through the instability band between islands, the ions will be scattered and a part of the pass rate will be lost.

(97) However, in the present solution, since the frequencies of the RF amplitude modulation signal and the quadrupole excitation signal are only a fraction of the main RF frequency, the AC excitation signal on the prerod can be isolated through a simple band-pass filter (such as RC network). At this moment, the stability region structure formed when ions pass through the prerod is illustrated in the lower figure of FIG. 15B, and the ion beam in the instability band between the stability islands is prevented from being diverged.

(98) Using the modulation method to form the X-band for ion separation has another significant advantage that the vibration amplitude of the ions is only changed in the X-direction. As mentioned above, near the X-band, the Y-direction motion of ions along the scanning line is maintained stable. In the traditional mode, the scanning line sweeps through the vertex of the stability region, and the q value of the side with a low mass number is high, and instable motion will be caused in the X direction. At the same time, instable motion will be caused on the side with a high mass number in the Y direction. Considering that the sensitivity of a mass spectrometer is determined by the initial position of ions, the initial energy distribution and the time of transmission to the detector, the requirement for ions which can pass through the quadrupole mass analyzer stably is that the motion of the ions in any X or Y direction at any moment is required to be smaller than r.sub.0.sup.2. From FIG. 3, it can be learned that this is also related to the ion separation of the stability island A. However, due to the instable motion of the ions in the X and Y directions, the ion transmission loss is too great, so the application of the traditional mode is restricted in practice. Comparatively, the restriction in the use of the X-band is only in one direction, i.e., X direction, while the motion in the Y direction is stable. In the prior art such as in the solution of Alan Schoen, two dipole excited electric fields are needed to form a pass-band, which will destroy the symmetry of the electric field. The solution of Sudakov et al. needs a high-frequency AC excitation signal, which is difficult to be generated and decoupled from the main RF signal, so it will lead to signal distortion to influence ion transmission. As described above, with the application of the AC excitation voltage and the RF amplitude modulation signal, a stability band can appear, and fast ion mass separation can also be realized. When the low-frequency AC excitation voltage is used, it only takes several periods to enable the instable ions to hit the quadrupole and disappear. In the traditional mode, more than 100 RF periods are needed, and there is also the influence caused by the non-linear field distortion. The use of stability islands will avoid such influence. The characteristics of the stability band formed by applying two AC excitation voltages according to the present invention are also described herein.

(99) To sum up, according to the present invention, by using the stability band for scanning, the mass resolution of the quadrupole can be significantly improved, and there is no significant ion transmission loss. The reasons are as follows:

(100) 1) The ion mass separation is faster. By using the low-frequency AC excitation voltage, it takes only a few of periods to enable the instable ions to hit the quadrupole and disappear. In addition, a mass resolution of more than 10,000 can be obtained.

(101) 2) The ion mass separation only occurs in one direction, which improves the sensitivity.

(102) 3) The instability band for ion mass separation only appears near the apex of the first stability region, so the DC delay technique can be used to improve the sensitivity.

(103) 4) Both the RF amplitude modulation signal and the AC excitation voltage can be low-frequency signals with frequencies which are several times to tens of times less than the frequency of the main RF signal, so it is easy to decouple the generation and regulation from the initial RF control circuit, which is conducive to the realization of the stability of the system.

(104) 5) No additional high-frequency AC excitation voltage is required, and it is not influenced by the non-linear field distortion of the edge of the analytic rod.

(105) The above embodiments and calculation results in the present invention are all implemented under the situation of a frequency v=0.05, which more conforms to reality, i.e., there are five low-frequency excitation periods in 100 RF periods. This process is also relatively easy to realize experimentally, because divide-by-2, divide-by-5 and divide-by-10 frequency dividers with low phase noise can be commercially purposed, and the cost of using this device to form a mass filter band is relatively low. In fact, similar amplitude modulation mass filter bands can also be obtained by adopting other frequency division parameters.

(106) Also as shown in Table 1, when the frequency values are all in a range of 0 to 0.2, under the situation that the ratio of the excitation voltage amplitudes is equal, the results are similar. As described above, the quadrupole can use the values of the AC excitation voltage and the modulation amplitude in Table 2. In actual application, other means may also be introduced to apply more than two AC excitation voltages, such as by adding a third AC excitation voltage, or improving the RF power supply to combine with the AC excitation voltage. Such improvements should be considered as technical solutions derived from the present invention and are hereby declared.

(107) The above embodiments are only used for exemplarily describing the principles and effects of the present invention, instead of limiting the present invention. Any person skilled in the art may modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by a person skilled in the art without departing from the spirit and technical thought disclosed by the present invention shall still be covered by the claims of the present invention.

(108) Some references, which may include patents, patent applications and various publications, are cited in a reference list and discussed in the description of this invention. The citation and/or discussion of such references is provided merely to clarify the description of the invention and is not an admission that any such reference is prior art to the invention described herein. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference.