Confining positve and negative ions with fast oscillating electric potentials

A technology of oscillating potential and ions, which is used in the field of mass spectrometers to achieve the effect of high signal-to-noise ratio

Active Publication Date: 2007-02-07
THERMO FINNIGAN
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However, conventional multipole trapping can only simultaneously confine particl...
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Abstract

Methods and apparatus for trapping or guiding ions. Ions are introduced into an ion trap or ion guide. The ion trap or ion guide includes a first set of electrodes and a second set of electrodes. The first and second sets of electrodes are arranged to define an ion channel to trap or guide the introduced ions. Periodic voltages are applied to electrodes in the first set of electrodes to generate a first oscillating electric potential that radially confines the ions in the ion channel, and periodic voltages are applied to electrodes in the second set of electrodes to generate a second oscillating electric potential that axially confines the ions in the ion channel.

Application Domain

Stability-of-path spectrometersPositive/negative analyte ion analysis/introduction/generation

Technology Topic

PhysicsVoltage +6

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  • Confining positve and negative ions with fast oscillating electric potentials
  • Confining positve and negative ions with fast oscillating electric potentials
  • Confining positve and negative ions with fast oscillating electric potentials

Examples

  • Experimental program(1)

Example Embodiment

[0025] figure 1 Shown is a mass spectrometry system 100 that operates in accordance with one aspect of the invention. The system 100 includes a precursor ion donor 110, a 2D multipolar ion trap 120, a reagent ion donor 130, and a controller 140. The precursor ion donor 110 is used to generate ions, which includes precursor ions. The ions generated by the precursor ion donor 110 are implanted into the 2D multipolar ion trap 120. The reagent ion donor 130 generates ions including reagent ions. The ions generated by the reagent ion donor 130 are also injected into the 2D multipolar ion trap 120. The 2D multipolar ion trap 120 forms a channel, in which precursor ions and reagent ions are applied to different electrodes in the ion trap 120 by the controller 140, and the oscillation potential generated by the periodically changing voltages is limited in the radial and axial directions. In the channel.
[0026] The precursor ion donor 110 includes: one or more precursor ion sources 112 to generate precursor ions from sample molecules such as larger biological molecules; and an ion transmission optical path 115 to guide the generated ions from the precursor ion source 112 To the ion trap 120. The precursor ions can be generated by electrospray ionization (ESI) technology, thermal spray ionization technology, field technology, plasma or laser desorption technology, chemical ionization technology or other technologies. The precursor ion may be a positive ion or a negative ion, and has one or more valences. For example, ESI technology is used to generate multivalent ions from larger molecules with multiple ionizable points.
[0027] The reagent ion donor 130 includes one or more reagent ion sources 132 to generate reagent ions from sample molecules; and an ion transmission optical path 115 to guide the generated ions from the reagent ion source 132 to the ion trap 120. During the interaction, the reagent ions can induce charge transfer from the reagent ions to other ions, such as the precursor ions provided by the precursor ion donor 110. The reagent ion can induce proton transfer or electron transfer to/or away from the precursor ion. For the positive precursor ion, the reagent ion can include perfluorodimethylcyclohexane (PDCH) or SF 6 Derived anions. For negative precursor ions, the reagent ions can be positive ions such as xenon ions. The choice of a particular reagent ion depends on the precursor ion and/or ion trap parameters.
[0028] For positive precursor ions, the reagent ion source 132 can use chemical ionization technology, ESI technology, thermal spray technology, particle bombardment technology, field technology, plasma or laser desorption technology to generate negative reagent ions. For example, in chemical ionization technology, negative reagent ions are generated by combining or separating in a chemical plasma, where the plasma includes neutral, positively charged and negatively charged particles such as ions or electrons. In chemical plasma, low-energy electrons can be captured by neutral particles to form a negative ion. The negative ions may be stable, or they may split into product ions including negative ions. The negative reagent ions can then be extracted from the chemical plasma by, for example, an electrostatic field. In another embodiment, the reagent ion source 132 uses other techniques to generate reagent ions. For example, you can select a suitable voltage and use ESI to generate positive or negative ions.
[0029] The ion transmission optical paths 115 and 135 transmit the ions generated by the precursor ion source 112 and the reagent source 132 to the multipolar ion trap 120. The ion transmission optical paths 115 and 135 may include one or more 2D multipole rod-shaped components such as quadrupole or octopole rod-shaped components so as to radially confine the transmitted ions in the channel. The ion transmission optical path 115 or 135 can only transmit positive ions or negative ions structurally, or select ions with a mass/charge ratio within a certain range. The ion transmission optical path 115 or 135 may include a lens, ion tunnel, plate or rod to accelerate or decelerate the transmitted ions. Alternatively, the ion transmission optical path 115 or 135 may include an ion trap to temporarily store the transmitted ions.
[0030] The multipole ion trap 120 includes a front plate lens 121, a rear plate lens 128, and one or more sections between the lenses 121 and 128. in figure 1 In the illustrated embodiment, the ion trap 120 includes a front section 123, a middle section 125, and a back section 127. The front lens 121 is formed with a front hole 122 to receive the ions transmitted from the precursor ion source 112 by the ion transmission optical path 115, and the rear lens 128 is formed with a rear hole 129 to receive the ions transmitted from the reagent ion source 132 by the ion transmission optical path 135 . Each segment 123, 125, and 127 includes a corresponding 2D multipole rod-shaped component, such as a quadrupole rod-shaped component including four quadrupole rod-shaped electrodes. Each multipole rod-shaped assembly can at least confine ions in a channel around the axis 124 of the ion trap 120 in a certain dimension. In this channel, the oscillating potential generated by the multipole rod electrode in the ion trap 120 and the voltage applied to the lenses 121 and 128 can be used to confine ions in one of the sections 123, 125, and 127 in the radial and axial directions. In multiple sections. In another embodiment, one or more of the sections 123, 125, and 127 may be implemented by independent 2D ion traps. in figure 1 In the illustrated embodiment, the first set of electrodes (which may include those electrodes corresponding to one or more of the front section 123, the middle section 125, and the rear section 127) are operationally capable of at least confining ions to the second ion channel In a one-dimensional space, thereby capturing or guiding the introduced ions. In this particular case, the first set of electrodes is used to confine ions in the ion channel in the radial direction. The first set of electrodes may include a plurality of rod-shaped electrodes. The second set of electrodes (which may include electrodes corresponding to the front lens 121 and the rear lens 128) can at least confine ions in the second dimensional space of the ion channel in operation. In this particular case, the second set of electrodes is used to confine ions in the ion channel in the axial direction. The second set of electrodes may include multiple rod-shaped electrodes or one or more end plate ion-transmitting electrodes. In this embodiment, the first and second groups of electrodes can operate to confine ions in three dimensions. Although in this particular example, the first and second sets of electrodes are discontinuous electrode sets, in another embodiment, the first and second sets of electrodes have common components (but they use different voltages to excitation). For example, the first set of electrodes may include a plurality of electrodes consisting of a front section 123, a middle section 125, and a rear section 127, while the second set of electrodes may include a plurality of electrodes consisting of a front section 123 and a rear section 127. The controller 140 applies a corresponding set of RF voltages 143, 145, and 147 to the multipole rod-shaped components in sections 123, 125, and 127, respectively, to generate an oscillating 2D multipole potential that moves the ions around the axis 124 is defined in the channel in the radial direction. In one embodiment, the controller 140 applies a set of main RF voltages to each of the rod-shaped components in the sections 123, 125, and 127. For a quadrupole assembly with two pairs of opposed rods, the set of main RF voltages may include a first RF voltage for the first pair of opposed rods, and a second RF voltage for the second pair of opposed rods Voltage, where the second RF voltage and the first RF voltage have the same frequency but opposite phases. Alternatively, the controller 140 can apply RF voltages 143, 145, and 147 of different frequencies or phases to the multipole rod-shaped components in different sections of the ion trap.
[0031] The controller 140 also applies RF voltages 141 and 148 to the front lens 121 and the rear lens 128, respectively. The RF voltages 141 and 148 may have a different frequency or phase from the RF voltages 143 and 147 applied to the rod-shaped components in the front section 123 and the rear section 128, respectively. The RF voltages 141 and 148 applied to the front lens 121 and the rear lens 128 generate an oscillating potential, which can axially move the positive and negative ions around the axis 124 while defining the corresponding ends of the channel. Will refer to later Figure 2A-2D To further describe how to confine the ions in the axial direction with the oscillating potential.
[0032] The controller 140 can apply different DC bias voltages 151-158 to the lenses 121 and 128 and the rod-shaped components in different sections of the ion trap 120. According to the sign of the DC bias applied in a certain section of the well 120, positive ions or negative ions can be axially confined in the section. For example, the positive precursor ions can be trapped in the front section 123 by applying a negative DC bias to the multipole in the front section 123 while applying a substantially zero DC bias to the middle section 125 and the front lens 121. Similarly, the negative reagent ions can be trapped in the rear section 127 by applying a positive DC bias to the multipole in the rear section 127 while simultaneously applying a substantially zero DC bias to the middle section 125 and the rear lens 121. . As reference later Figure 4-5F As described, by applying different DC bias voltages to different sections and lenses, positive and negative ions can be received or separated into the ion trap 120. The controller 140 may also apply additional AC voltage to the electrodes in the ion trap to eject ions from the ion trap 120 based on the mass/charge ratio of the ions.
[0033] Figure 2A It schematically shows how to confine the positive ions 210 and the negative ions 215 in a 2D multipole ion trap at the end section 230 next to the ion lens 220 at the same time. For example, the tip section 230 may be the front section 123 or the back end 127 of the ion trap 120, while the ion lens 220 may be the system 100 (see figure 1 The front lens 121 or the rear lens 128 in ).
[0034] The tip section 230 includes a 2D multipole rod-shaped component 232, which receives an RF voltage from an RF voltage source 240 to generate an oscillating 2D multipole potential, thereby radially confining positive ions 210 and negative ions 220 to the multipole The axis 234 of the polar ion trap. For example, the rod-shaped component 232 may be a quadrupole rod-shaped component that generates an oscillating 2D quadrupole potential around the axis 234.
[0035] The ion lens 220 receives the RF voltage from the RF voltage source 245 to generate an oscillating potential, which confines the positive ions 210 and the negative ions 215 in the axial direction. That is, the axially defined potential energy prevents the ions 210 and 215 from escaping the tip section 230 through the hole 225 in the ion lens 220. The axially limited electric potential has a different spatial distribution than the multi-pole electric potential generated by the component 232. The multipolar potential forms a substantially zero electric field at the shaft 234, and the axially defined potential forms a substantially non-zero electric field at least at a portion of the shaft 234 close to the ion lens 220.
[0036] The multipole rod assembly 232 includes a rod electrode that receives an RF voltage having a first frequency; and an ion lens 220 that receives an RF voltage having a second frequency. In one embodiment, there is a rational number between the first frequency and the second frequency. For example, the first frequency is basically an integer multiple or an integer fraction of the second frequency. Alternatively, the first frequency may also be any other multiple or fraction of the second frequency. Alternatively, the first and second frequencies may be substantially equal, and the ion lens 220 receives an RF voltage that is out of phase with the RF voltage received by the rod-shaped component 232. Generally, the rod-shaped assembly 232 receives multiple RF voltages in multiple phases. In a quadrupole rod-shaped component, the phase difference of the voltage received by adjacent rod-shaped electrodes is 180 degrees. In this way, the ion lens 220 can receive an RF voltage, which is 90 degrees out of phase (plus or minus) from each voltage received by the rod-shaped electrodes in the quadrupole rod-shaped assembly.
[0037] Figure 2B The illustrated coordinate system 250 schematically shows a trajectory 260, which is a typical movement trajectory of the positive ion 210 or the negative ion 215 when it approaches the ion lens 220. In the coordinate system 250, the ordinate 252 represents time, and the abscissa represents the axial distance of the ion along the axis 234 to the ion lens 220. The trajectory 260 shows the movement of the ions in the absence of background gas. If there are background gas molecules, the trajectory of the ion will be different. For example, smaller gas molecules dampen the movement of larger ions; or the trajectory of the ion may change randomly due to random collisions between the ion and the gas molecule.
[0038] The trajectory 260 includes three parts 262, 264, and 266. In the first trajectory portion 262, the ions only move in the multipolar potential, thereby confining the ions in the radial direction to approach the axis 234, where the multipolar potential forms a substantially zero electric field. Thus, along the axis 234, the ions can move axially at a substantially uniform velocity and approach the hole 225 in the ion lens 220. In the trajectory 260, this substantially uniform velocity is represented by the substantially constant slope of the first trajectory portion 262.
[0039] In the second trajectory portion 264, the ions are subjected to the electric field formed by the oscillating potential generated by the RF voltage applied to the ion lens 220. The electric field formed by the oscillating potential forces the ions to oscillate back and forth according to the frequency of the applied RF voltage. These oscillations experienced by the ions are represented by the wave-shaped trajectory in the second trajectory part 264. These waves can be described as rapid oscillations of ions around the center corresponding to the average position during several oscillations. Just like Figure 2B As indicated by the center trajectory 268, the movement of the center is slower and smoother than the movement of the ion itself.
[0040] The center trajectory 268 can be determined by an adiabatic approximation method. For details of the approximation method (including its application limitations), please refer to Dieter Gerlich in State-selected and stat-to-stateion-molecule reaction dynamics, Partl.Experiment "Inhomogeneous RFfields: A versatile tool for the study of processes with slow ion", editors Check-Yiu NG and Michael Baer, ​​Advances in Chemical Physics Series, Volume LXXXII, 1992 John Wiley & Sons. This adiabatic approximation method describes the rapid oscillation in the second trajectory portion 264 and the slow movement of the oscillation center along the central trajectory 268, respectively. For a particular ion, the central trajectory 268 can be described as if the ion has a pseudopotential V p (It is also called effective potential or pseudopotential), the pseudopotential V p Sign independent of time and ion charge. However, the pseudopotential V p It depends on the quality of the ion, the number of charges ("Z", which represents the net number and sign of the ion charge, Q=Ze), and the characteristics of the oscillating potential that causes rapid oscillation. For an oscillating potential used to generate the following electric field E(r, t), the electric field E(r, t) varies with the angular frequency ("Ω") and intensity E(r) at position r The following equation changes E(r,t)=E(r)cross(t), the pseudopotential V at position r p Given below
[0041] V p (r)=Ze E(r) 2 /(4mΩ 2 ) (Formula 1)
[0042] When the ion approaches the hole 225 along the axis 234, the lens 220 generates an electric field with increasing intensity E(r) and an increasing pseudopotential V according to Equation 1. p. Product Ze V p The negative gradient of is directed to the opposite of the lens 220 and the hole 225 formed by the lens 220, because the sign of the pseudopotential is the same as the sign of the ion charge. The negative gradient determines the direction and intensity of the average force on the ion. Under the action of this force, the ions move in the opposite direction as shown by the central trajectory 268 before reaching the hole 225. As a result, the ions are confined in the channel around the axis 234 along the axial direction by the oscillating potential generated by the RF voltage applied to the lens 220.
[0043] Due to pseudopotential V p It has the same sign as the charge number Z of the ion, so it can limit the positive ion 210 and the negative ion 215. Pseudopotential V p It depends on the ion mass m and the ion charge (Q=Ze). Based on this relationship, the same oscillating potential can be used to confine some ions while allowing other ions to pass.
[0044] Figure 2C In the example shown, a smaller ion 212 and a larger ion 214 move closer to the lens 220 in the tip portion 230. The ions 212 and 214 have the same charge and similar kinetic energy, but the mass of the larger ion 214 is greater than that of the smaller ion 212. The 2D multipole field generated by the RF voltage applied by the RF voltage source 240 to the multipole rod electrode 232 of the ions 212 and 214 is radially defined close to the axis 234. The RF voltage source 245 applies an RF voltage to the ion lens 220 to generate an oscillating electric field, which confines the smaller ions 212 while allowing the larger ions 214 to leave the tip portion 230 and pass through the aperture of the lens 220 225.
[0045] Figure 2D Shows schematically Figure 2C Pseudopotential for the example shown. In the coordinate system 270, the ordinate 272 represents the pseudopotential, and the abscissa 274 represents the axial distance from the lens 220 along the axis 234. The pseudopotential shown is formed by the same oscillating potential generated by the ion lens 220.
[0046] This oscillating potential forms a first pseudopotential 282 for the smaller ion 212 and a second pseudopotential 284 for the larger ion 214. Since these pseudopotentials are formed by the same oscillating potential, the electric field strength E(r) is the same for both (see Equation 1). Thus, the first and second pseudopotentials 282 and 284 have similar waveforms as a function of the axial distance ("r") from the lens 220. When the distance from the lens 220 is far, the pseudopotentials 282 and 284 are basically zero. As the corresponding ions continue to approach the lens 220, the pseudopotentials will continue to increase. The increasing pseudopotentials 282 and 284 form a potential barrier, that is, the maximum value of the corresponding pseudopotential on the ion trap axis 234. The first pseudopotential 282 forms a first potential barrier 283 which is higher than the second potential barrier 285 formed by the second pseudopotential 284. The difference in barriers 283 and 285 comes from the difference in mass/charge between the smaller ion 212 and the larger ion 214. For other ions with different mass and/or charge values, the pseudo-potential barrier can be determined by calculating the maximum value of Equation 1 on the axis 234.
[0047] The smaller ion 212 and the larger ion 214 have average energy levels 292 and 294, respectively. The average energy level can be obtained by averaging the ion energy in an oscillation potential period. In this example, the average energy levels 292 and 294 have comparable values. For smaller ions 212, the average energy level 292 is less than the corresponding barrier 283. Therefore, the smaller ion 212 is confined by the corresponding potential barrier 283 in the axial direction. After reaching the point where the average energy level 292 is substantially equal to the pseudopotential 282, the smaller ions 212 return away from the lens 220. However, for the larger ion 214, the average energy level 294 is greater than the corresponding potential barrier 285. Therefore, the larger ions 214 are not confined by the oscillating potential in the axial direction, and thus leave the tip portion 230 and pass through the hole 225.
[0048] The above-mentioned adiabatic approximation method and the corresponding pseudopotential have some limitations in their use. For example, the adiabatic approximation method can only be used when the electric field intensity |E(r)| is significantly greater than the change measured by the electric field gradient ("VE") multiplied by the characteristic amplitude of the fast oscillation. That is, if the electric field changes beyond the limit of one oscillation of a certain ion, the adiabatic is useless, and the pseudopotential cannot be used to describe the movement of the ion.
[0049] Based on this condition, when the mass of the ion is m and the charge is Z, and it is in an electric field of angular frequency Ω, the dimensionless adiabatic parameter ζ is
[0050] ζ=2Z|VE|/mΩ 2
[0051] Generally speaking, the adiabatic approximation method is effective when the adiabatic parameter ζ is approximately less than 0.3. The adiabatic parameter ζ is inversely proportional to the ion mass-to-charge ratio m/Z. That is, the larger the mass-to-charge ratio of the ion, the more effective the adiabatic approximation method is.
[0052] Near the pseudo-potential barrier on the axis of the quadrupole, trapped ions may experience unexpected linear, nonlinear, or parametric excitation, and may escape the quadrupole. If an appropriate RF electric field is used to capture these ions, this excitation can be avoided.
[0053] image 3 A method 300 is shown that performs quality analysis based on the above-mentioned technique. The method 300 is completed by a system including a 2D multipolar ion trap, in which positive and negative ions are as described above. Figure 1-2D As described, different oscillating potentials are defined along the radial and axial directions. For example, the system may include the system 100 ( figure 1 ), wherein an RF voltage can be applied to the front lens 121 or the rear lens 128 to confine positive and negative ions in the ion trap 120 in the axial direction. Alternatively, the method 300 may use the following reference Figure 6 with 7 The described segmented well is completed.
[0054] The system confines the precursor ions and reagent ions in the multipolar ion trap radially and axially through different oscillating potentials to induce the precursor ions to split into product ions (step 310). The precursor ions can be positive ions while the reagent ions are negative ions, and vice versa. The precursor ions and reagent ions are introduced into the same part of the channel formed by the multipolar ion trap, for example, see Figure 4-5F As described. In the channel, positive and negative ions are confined radially and axially by the oscillating electric potential.
[0055] Because they are all confined in the same part of the channel, the precursor ions and the reagent ions interact, and at the same time the charge is transferred from the reagent ions to the precursor ions. The charge transfer can induce the charge reduction of the multi-charged precursor ions or the polarity of the precursor ions can be reversed. The charge transfer can have an energy to split the precursor ion into two or more particles. The term "interaction" as used herein is used to refer to a chemical melon in which bonding, binding, separation, charge transfer, catalysis or other chemical reactions occur. The chemical reaction is usually a change or a transformation. The process may be the decomposition of a group of ions, the combination with other substances, and the exchange components with other ions. The term "interaction" does not include those interactions in which no transformation occurs, such as situations in which ions merely collide and/or disperse physically.
[0056] Generally speaking, when CAD is used alone in an ion trap, only the precursor ions are excited to split into product ions, and the generated product ions will not be stimulated to split further. However, in the reaction induced by the charge transfer, the reagent ion may also interact with the fragments of the precursor ion to further split or produce other products.
[0057] In another embodiment, the ion-to-ion interaction between the precursor ion and the reagent ion can be used for purposes other than splitting. For example, interactions with reagent ions can be used to reduce the charge in a mixture of precursor ions that have the same mass but are more or less charged. This reduction in charge allows the precursor ion to have an appropriate number of required charges. Reagent ions can also be used to reduce the charge of multi-charged product ions, such as those generated by certain highly charged precursor particles. The reduced charge of the product ion can simplify the mass analysis and the interpretation of the mass spectrum of the product ion formed. As with the simultaneous presence of positive and negative ions, if there are only positive ions or only negative ions, they can also be confined in the radial and axial directions by the oscillation potential and controlled in the ion trap.
[0058] The system removes reagent ions from the ion trap while retaining product ions (step 320). In order to retain the positive product ions and remove the negative reagent ions, a negative DC bias can be applied to the portion containing these ions. When these ions are exposed to a negative DC bias, the negative reagent ions are in an unstable state in the axial direction, while the positive reagent ions are in a stable state in the axial direction. In order to retain the negative product ions and remove the positive reagent ions, a positive DC bias can be applied to the same part. Alternatively, the reagent ions can be removed by resonance ejection, or they can be destabilized radially in the ion trap.
[0059] The system analyzes the product ions based on their mass/charge ratio (step 330). In one embodiment, the multipolar ion trap selectively releases product ions based on the mass/charge ratio of the product ions. The system uses one or more particle boosters to detect the released product ions and determine their mass/charge spectrum. In another embodiment, the released product ions can be directed to a mass analyzer, such as a time-of-flight analyzer, a magnetic, electromagnetic, ICR or quadrupole ion trap analyzer, or other mass analyzers, thereby Determine the mass/charge ratio of the product ion. The mass/charge ratio of the product ion can be used to reconstruct the structure of the precursor ion.
[0060] In another embodiment, reagent ions, precursor ions, or product ions can be further manipulated in the ion trap. For example, before analyzing the product ions (step 330), some product ions may be released from the ion trap.
[0061] Figure 4 A method 400 of using reagent ions to induce fragmentation of precursor ions is shown. The method 400 can be implemented by a system such as ( figure 1 The) system 100 is completed, which includes a segmented multipole ion trap having two or more parts, wherein the multipole rods form a channel to trap or guide ions.
[0062] The system releases and isolates the precursor ions into the multipolar ion trap (step 410). In order to isolate the positive precursor ions according to a specific mass/charge ratio, these positive ions need to be generated from the sample and released into the ion channel of the ion trap. Then, the ion trap releases sample ions whose mass/charge ratio is different from the mass/charge ratio of the selected precursor ion by, for example, resonance ejection. Thus, only the required precursor ions remain in the ion trap. Alternatively, the ion trap can receive sample ions while releasing some non-precursor ions.
[0063] The system moves the positive precursor ions into a first trap area of ​​the multipole ion trap (step 420). To this end, the system can apply a negative DC bias to the first part of the multipole, and apply a substantially zero or very small negative DC bias to the other parts.
[0064] The system releases negative reagent ions into a second trapping region of the multipolar ion trap (step 430). This second trap area is different from the first trap area in which the positive precursor ions are trapped. Negative and positive DC bias voltages are applied to the first and second parts, respectively, to generate an electrostatic potential barrier, thereby separating the positive ions in the first trapping region from the negative ions in the second trapping region. Alternatively, the first and second trapping regions may be separated by a third ion-free region formed by an oscillating potential generated by a suitable voltage applied to the electrode, which can form a pseudo Potential to confine and separate positive and negative ions into the channels of the ion trap in the axial direction.
[0065] The system enables the positive precursor ions and the negative reagent ions to move into the same trapping region of the multipolar ion trap to induce fragmentation of the precursor ions (step 440). If the DC bias voltage separates the ions in the first trapping region from the ions in the second trapping region, the system can move the positive and negative ions into the first and second trapping regions by removing the DC bias. In the absence of DC bias, positive and negative ions can be simultaneously captured by the oscillating potential into the ion trap. Figure 1-2D As described, the ions are axially confined in the ion channels of the ion trap. If the first and second capture areas are separated by the third capture area, in which there is an oscillating potential in the third capture area that confines the precursor ions and reagent ions in the axial direction, then the system changes or turns off the oscillating potential to make Precursor ions or reagent ions or precursor ions and reagent ions pass through the middle third region. Since the precursor ions and the reagent ions are confined in the same trap area or the same multiple trap areas of the ion trap, they interact to form a charge transfer reaction (ion-ion reaction), thereby splitting the precursor ions.
[0066] Figure 5A-5E An embodiment of the method 400 is schematically shown in which negative reagent ions and an oscillating potential defined along the direction are used. In this example, a 2D multipole ion trap 500 forms an ion channel around axis 502. The well 500 includes a front lens 503, a front section 504, a middle section 505, a rear section 506, and a rear lens 507. Each segment 504-506 includes a corresponding set of multipole rods, which are used to receive an RF voltage (the frequency of which is about 1.2MHz, for example) to generate an oscillating multipole potential to confine the ion around the axis 502 in the radial direction. In the channel. In addition, the lenses 503 and 507 can also receive RF voltage to confine ions in the ion channel in the axial direction. In ion trap 500, DC bias can be applied to any of the components 503-507. In the ion trap 500, only 0.001 Torr of helium gas can dissipate or dampen the ions.
[0067] in Figure 5A The positive sample ions 511 are released into the ion trap 500. The sample ions 511 include those with different masses and one or more positive charges. The sample ions 511 can be formed by ESI or other ionization techniques.
[0068] These sample ions are released into the ion trap through the hole in the front lens 503 and converge in a trap area in the middle section 505. During the release process, different DC bias voltages can be applied to different components of the ion trap 500 as shown by the schematic line 510. The front lens 503, the front section 504, and the middle section 505 receive negative DC biases 513, 514, and 515, respectively. The negative bias voltages 513, 514, and 515 are gradually increased, such as -3 volts, -6 volts and -10 volts respectively, so that the generated electrostatic field can force the positive sample ions 511 to gather toward the middle section 505. The rear section 506 receives a positive DC bias 516, such as +3 volts, so that the generated electrostatic field can prevent the sample ions 511 from escaping from the middle section through the rear lens 507, where the rear lens 507 receives a substantially zero DC bias, such as approximately less than 30mV bias voltage.
[0069] Figure 5B The case of isolating the precursor ions from the sample ions 511 captured in the middle section 505 of the ion trap 500 is shown. In addition to the RF voltage, an AC voltage is applied to the multipole rod in the middle section 505 to generate a multipole electric field. The electric field generated by the AC voltage enables the trap to release ions whose mass/charge ratio is different from the selected precursor ions, while leaving only the precursor ions in the trap 500.
[0070] The schematic line 520 shows the DC bias applied to different components in the well 500 during the isolation process. The front lens 503 and the rear lens 507 have substantially zero DC bias voltages 523 and 527, respectively. The middle section 505 has a negative DC bias, such as -10V. The front section 504 and the rear section 506 are respectively negative DC bias voltages 524 and 526, whose values ​​are smaller than the bias voltage 525 so that the generated electrostatic field axially confines the positive ions in the trap area in the middle section 505.
[0071] Figure 5C The movement of precursor ions 531 from the middle section 505 in which the precursor ions 531 are isolated to the front section 504 is shown. As shown by the schematic line 530, the DC bias 535 of the middle section 505 is approximately -10V. A DC bias voltage 534 that exceeds the DC bias voltage 535 on the middle section 505 is applied to the front section 504, so that the positive precursor ions 531 move from the middle section 505 to the front section 504. The DC bias voltage 534 is approximately -13V, for example. As a result, an electrostatic field is generated, which moves the positive precursor ions 531 from the middle section 505 to the front section 504. The front lens 503 has a substantially zero DC bias 533 to generate an electrostatic field that can prevent positive precursor ions from escaping from the front lens 503 from the front section 504. The rear section 506 and the rear lens 507 have a negative bias voltage 536 and a substantially zero bias voltage 537, respectively, so that the generated electric field can move the positive precursor ions to the front section 504 and prevent them from escaping through the rear lens 507.
[0072] Figure 5D It is shown that the negative reagent ions 541 are released into the middle section 505 while the positive precursor ions 531 remain in the front section 504 of the ion trap, that is, two trapping regions are shown therein. The reagent ions 541 are generated by chemical ionization or any other suitable ionization technique. The negative reagent ions are released into the ion trap through the hole in the rear lens 507 and are collected in the middle section 505. During the release process, as shown by the schematic line 540, different DC bias voltages are applied to different parts of the ion trap 500. The rear lens 507, the rear section 506, and the middle section 505 receive positive DC biases 547, 546, and 545, respectively. The positive bias voltages 547, 546, and 545 become larger and larger, such as +1V, +3V, and +5V, respectively, so that the generated electric field can move the negative reagent ions 541 to the middle section 505. In the middle section 505, the reagent ions collide with the background gas and are captured.
[0073] The front section 504 receives a negative DC bias 544 such as -5V, thereby capturing the positive precursor ion 531 and separating it from the negative reagent ion 541 in the middle section 505. The front lens 503 receives a positive DC bias 543, such as 3V, so that the generated electric field can prevent the precursor ions 531 from escaping from the front end 504 through the hole of the front lens 503.
[0074] Figure 5E It is shown that the positive precursor ions 531 and the negative reagent ions 541 are mixed in all the parts 504, 505, and 506 of the multipolar ion trap 500 along the axis 502. As shown by the schematic line 550, each of the parts 504, 505, and 506 have substantially the same DC bias, such as a substantially zero DC bias 558, so that positive and negative ions can move along the axis 502. The same DC bias is also applied to the front lens 503 and the rear lens 507.
[0075] Beside the lenses 503 and 507, the positive precursor ions 531 and the negative reagent ions 541 are axially confined along the axis 502 by the oscillating potentials 553 and 557 generated by the RF voltage applied to the front lens 503 and the rear lens 507. For example, the front lens 503 and the rear lens 507 both receive an RF voltage with a frequency of approximately 600 kHz and an amplitude of approximately 150 V, which is approximately half of the RF frequency applied to the rod electrode. Thus, the precursor ion 531 and the reagent ion 541 are confined in the same cavity and the same capture area, and the interaction between them can induce the charge transfer and splitting of the precursor ion. In this case, the capture area includes segments 504, 505, and 506. Charged fragments (such as product ions) can be confined in the axial direction by the same oscillating potentials 553 and 557 like precursor ions and reagent ions.
[0076] Figure 5F It is shown that the negative reagent ions 541 are removed from the ion trap while the positive product ions 561 are retained. As shown schematically by the curve 560, adding a negative DC bias voltage 565 to the middle section 505 while adding substantially zero DC bias voltages 561 and 568 to the front section 504 and the rear section 506 respectively, the negative reagent ions 541 can be added. Remove from trap 500. The electric field generated by the DC bias voltages 561, 565, and 568 can cause the negative reagent ions 541 to depart toward the front lens 503 and the rear lens 507, and confine the positive product ions 561 in the middle section 505. In order to remove the reagent ions through the lenses 503 and 507, no DC bias or RF electric field needs to be applied to the lenses. After the reagent ions are removed, the product ions can be analyzed by, for example, selectively releasing product ions having different mass/charge ratios. Alternatively, the product ions can be further manipulated in the ion trap.
[0077] In some examples shown here, the front, middle, and back sections 504, 505, and 506 have always been described corresponding to the capture area, but in fact they do not need to correspond directly. For example, as described above, an ion trap that is structurally divided into three sections can also be structurally provided with one, two or three trapping regions, and each trapping region includes one or more regions of the ion trap. segment.
[0078] Figure 6 Another embodiment is schematically shown, in which an oscillating potential can be used to confine positive and negative ions in a segmented multipolar ion trap 600 in both the radial and axial directions. The multipolar ion trap 600 includes a front section 610, a middle section 620, and a rear section 630, which form a channel around an axis 601. Each segment 610, 620, and 630 includes a multipole rod-shaped component, such as a quadrupole rod-shaped component including two pairs of opposed rod-shaped electrodes. Alternatively, the rod-shaped component may be a six-pole, eight-pole or more pole component including three, four or more pairs of opposed rod-shaped electrodes. In each section 610, 620 and 630, Figure 6 Both schematically show a pair of opposed rod electrodes, namely, the rod electrodes 612 and 614 in the front section 610, the rod electrodes 622 and 624 in the middle section 620, and the rod electrodes 632 and 634 in the rear section 630. .
[0079] In the middle section 620, the opposing rod electrodes 622 and 624 receive the same-phase RF voltage V1 to generate an oscillating multipolar potential such as a quadrupole potential together with other rod electrodes in the middle section 620. The resulting oscillating multipole potential confines the ions in the radial direction to approach the axis 601, where the multipole potential forms a substantially zero electric field.
[0080] In the front section 610, the opposing rod electrodes 612 and 614 receive the same RF voltage as the rod electrodes 622 and 624 in the middle section 620 to generate an oscillating multipolar potential together with the other rod electrodes in the front section 610. The confining ion is close to the axis 601. In addition to the RF voltage V1, the rod-shaped electrodes 612 and 614 also receive another RF voltage V2 that is substantially inverse to the voltage V1 of the opposed rod-shaped electrodes 612 and 614. Therefore, the rod-shaped electrodes 612 and 614 also generate an oscillating bipolar potential in the front section 610. The bipolar potential will form a substantially non-zero electric field in at least a part of the axis 601 of the front section 610. In this way, the oscillating bipolar potential confines the positive ions and negative ions captured in the middle section 620 in the axial direction. The other opposed rod electrodes in the front section 610 can also generate an oscillating bipolar potential. For different opposing rods in the front section 610, the bipolar potentials can have the same or different oscillation frequencies, and for the same frequency, they can also be in phase or out of phase with each other.
[0081] In the rear section 630, the RF voltage received by the opposed rod electrodes 632 and 634 is the same as that of the opposed rods 612 and 614 in the front section 610. As a result, the opposing rods 632 and 634 in the rear section 630 will also generate: an oscillating multipolar potential to confine ions in the radial direction to approach the axis 601, and an oscillating bipolar potential that confines the ions in the axial direction. In the middle section 620. Since the oscillating potential energy simultaneously confines positive ions and negative ions, the ion trap 600 can be used in operation to induce ion-ion interactions and corresponding splits in the middle section 620.
[0082] Figure 7 Another embodiment is schematically shown, in which both positive and negative ions can be confined in a segmented multipolar ion trap 700 by an oscillating potential in the radial and axial directions. The multipole ion trap 700 includes a front lens 703, sections 704-709, and a rear lens 710. Each section 704-709 includes a multi-pole rod-shaped component, such as a quadrupole or higher-order multi-pole electrode component, to trap or guide ions around an axis 702 into an ion channel.
[0083] The multi-pole ion trap 700 can respectively receive the first group of ions and the second group of ions in operation, and then confine them in the same section or the same multiple sections of the ion trap 700 to induce the two groups of ions to interact . For example, the first group of ions may include precursor ions, while the second group of ions include reagent ions. The first group of ions may be received through the front lens 703 and stored in the section 705, and the second group may be received through the rear lens 705 and stored in the section 708.
[0084] The oscillating potential generated by the multipoles in the sections 706 and 707 can separate the first group of ions from the second group of ions. For example, different oscillating bipolar potentials can be generated in the sections 706 and 707 to confine ions in the first and second groups in the axial direction, respectively. Thus, the ions in the section 705 can be manipulated separately from the ions in the section 708. For example, the precursor ions may be spatially isolated from the first group of ions in the section 705, while the reagent ions may also be spatially isolated from the second group of ions in the section 708.
[0085] The oscillating potentials in sections 706 and 707 can be adjusted to move ions from section 705 to 708, and vice versa. For example, in addition to the bipolar potential, a quadrupole potential may be generated in the sections 706 and 707 to guide the ions between the sections 705 and 708. The oscillating potential generated by the front lens 703 and the rear lens 710 or the bipolar potential generated in the sections 704 and 709 can confine positive and negative ions near the two ends of the ion trap 700 in the axial direction.
[0086] In one embodiment, a segmented well, such as Figure 7 In the ion trap 700 shown, the ion-ion reaction occurs in the first stage. A weaker pseudo-potential barrier is formed to separate the precursor ions and reagent ions from the second section, which has a lower on-axis DC bias potential. Since the ion-ion reaction will generate product ions in the first stage, some product ions may have a sufficiently large mass/charge ratio and thermal kinetic energy to pass through this weaker pseudo-potential barrier and penetrate into it. In the second paragraph, here, these ions are buffered after collision and may be trapped. As a result, these product ions are removed from the first section and are no longer exposed so as not to further react with reagent ions. Such removal of product ions can reduce the neutralization of product ions and the resulting loss. The method steps of the present invention can be completed by one or more programmable processors, which execute a computer program to operate on input data and generate output, thereby realizing the functions of the present invention. These method steps and the device of the present invention can also be implemented by logic circuits with specific functions, such as FPGA (field programmable gate array) or ASIC (application-specific integrated circuit). to fulfill.
[0087] Processors suitable for executing a computer program include, for example, general-purpose and special-purpose microprocessors, and any one or more processors in any type of digital computer. Generally speaking, the processor will receive commands from a read-only memory or a random access device or both. The main components of a computer are a processor used to execute instructions and one or more memories used to store instructions and data. Generally speaking, a computer also includes or is operatively connected to one or more mass storage devices such as magnetic disks, magneto-optical disks, or optical disks to receive data therefrom, or transfer data to save data. Information carriers suitable for embedding computer program instructions and data include various forms of non-volatile memory, such as semiconductor storage devices such as EPROM, EEPROM and flash memory devices, magnetic disks such as internal hard disks or non-detachable hard disks, magneto-optical disks, and CD-ROM and DVD-ROM discs, etc. The processor and the memory can also be provided with or integrated in logic circuits with specific functions.
[0088] In order to be able to interact with the user, the present invention can be implemented on a computer that has: a display device such as a CRT (Cathode Ray Tube) or LCD (Liquid Crystal Display) monitor to display information to the user, as well as a keyboard and one-point access A device such as a mouse or trackball allows the user to provide input to the computer. Other devices can also be used to interact with the user. For example, the feedback provided to the user can be any form of perceptible feedback, such as visual feedback, auditory feedback, or tactile feedback. The user's input can also be in any form such as Sound, language, or touch are received.
[0089] A number of embodiments of the present invention have been described above. However, it can be seen that there are many variations within the concept and scope of the present invention. For example, the steps in the aforementioned method can be performed in a different order and still achieve the desired result. The aforementioned technology can be applied to other ion traps or guides, such as: crankshaft ion guide, which forms a curved ion channel for trapping or guiding ions; planar RF ion guide (planar multipole trap) and RF cylindrical ion tube. In addition to segmented ion traps, the above technique can also be implemented with multiple separated ions.

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