This invention pertains generally to the field of ion storage and analysis technology and, particularly, to the ion storing components and mass spectrometry instruments which separate ions by characteristics such as mass-to-charge ratio, etc.
The family of alternating electric fields ion traps for ion storage and mass analysis includes 3-dimension rotational symmetric ion traps (3D-Rot.Sym.IT) and linear ion traps (LIT). In a 3-dimension rotational symmetric ion trap, ions are trapped around the center of the trap. Due to the space-charge effect, the number of ions which may be stored in a 3-dimension rotation symmetric ion trap is limited. Although a large number of ions can be successfully trapped inside a 3-dimension rotational symmetric ion trap, the severe charge-charge interaction between multiple ions will destroy the mass resolution in mass analysis procedure. In a linear trap, ions are stored around a middle axis of the trap. Accordingly, the number of trapped ions within a linear ion trap increases greatly under the same volume density of space charge. Previous research shows that a linear ion trap can trap more than 10 times the number of ions a same scale 3-dimension rotational symmetric ion trap can without obvious space charge effect, and more than a million ions can be trapped with a single ion injection procedure for the next step mass spectrometry analysis. But, under certain conditions, linear ion traps cannot meet all needs. For example, the electric signal of an ion stream in a linear ion trap still needs to be amplified by a high-gain electron multiplier for detection. For the detection of an infinitesimal analyte, the effective signal covered by noises millions folds of analyte cannot be detected. It is therefore necessary to develop greater storage ion traps.
It is known that the storage of trapped ions can be multiplied by simply arraying a group of linear ion traps (see, for example, US Patent Application Publication No. US2004/0135080A1). However, the cost of making a group of simply arrayed linear ion traps is relatively high. Furthermore, ions trapped within different linear ion traps in this type of array eject through corresponding outlet slits of respective ion traps. Accordingly, an ion detector with great receive surface is needed to receive simultaneous ion signals.
The aim of this invention is to provide a new ion trap array (ITA), with a simple geometry, to carry out parallel, multiplied axis ion storage. Ions stored inside the ITA can be one-off or selectively ejected out of the trap straightway and then be analyzed or detected by electric fields applied on the ITA.
An object of a first aspect of the present invention is to provide ion storage and analysis equipment including two or more rows of parallel placed electrode arrays. The electrode arrays consist of parallel bar-shaped electrodes. Different phases of high frequency voltages are added to adjacent bar electrodes to create a high frequency electric field in the space between two parallel electrodes of different rows of electrode arrays. Furthermore, multiple linear ion trapping fields are paralleled in the space between the different rows of electrode arrays. These linear ion trapping fields are adjacently open to one another without a real barrier.
Also, different phases of alternating current voltages are added on different bar electrodes to create an alternating electric field inside the space between two parallel electrodes of different rows of electrode arrays.
After ions are trapped inside the trapping regions, they will condense into a series of parallel narrow ion cloud strips. An object of a second aspect of the present invention is to provide an ion detection method for exciting, ejecting, and detecting ions in these ion cloud strips selectively, and rapidly ejecting the rest of the ions through the edges or the outlet slits of the electrode array boards.
On the basis of the schemes above, the ion storage and analysis equipment further includes a means for introducing low pressure collision gas which helps to reduce the kinetic energy of the trapped ions and focuses the axes in series, parallel to the bar electrodes mentioned above.
In these pelectrode arrays, the upper electrode arrays and the lower electrode arrays are planar paralleled and edges aligned up and down. Boundary electrodes are set around the volume enclosed by two adjacent rows of parallel electrode arrays.
The sizes of the bar electrodes on each electrode array are the same. The potentials of the boundary electrodes placed on the sides of electrodes array, paralleled to the bar electrodes, are the median of potentials of adjacent bar electrodes in the electrode arrays mentioned above.
The potentials of bar electrodes in the paralleled electrode arrays mentioned above are set according to the sequence: +V, −V, +V, −V, etc. The alternating voltage V contains at least one high frequency voltage component. The potentials of boundary electrodes paralleled to the bar electrodes mentioned above are set to zero.
Such as:
The voltage V is a pure high frequency voltage component.
Or, the voltage V contains a high frequency voltage component and a low frequency voltage component below 1000 Hz.
The invention further has groups of electric switches to create the high or low frequency voltages mentioned above by switching on and off rapidly.
Through holes, outlet slits, or outlet nets are placed on part of the boundary electrodes for ejecting ions out of the ITA.
Through holes, outlet slits, or outlet nets are placed on at least one part of the parallel electrodes arrays for ejecting ions out of the ITA.
The invention further comprises voltage generators and coupling equipment to create dipole fields between two adjacent rows of parallel electrodes arrays for ejecting ions out of the ITA.
The shapes of the bar electrodes are planar, all main surfaces of the bar electrodes are parallel with each other.
On the basis of the schemes above, one or more rows of electrode arrays can be made of Printed Circuit Board (PCB).
The PCBs for planar electrode array construction contains multilayer PCBs with at least one surface layer designed for a planar electrode array shaped pattern.
As mentioned above, the manufacture of electrode arrays includes multilayer PCBs with electric components for mounting and pads for down-leads on at least parts of the electric conductive layers.
In this invention, the two rows of electrodes arrays can be made of two separate PCBs fixed together by several boundary electrode boards.
This invention also includes an ion detector to detect ejected ions. The detector should be located at the end of one of the ion trapping axis and outside the ITA.
This invention also includes an ion detector to detect ejected ions. The detector should be placed outside one of the boundary electrodes parallel to the ion trapping axes mentioned above.
This invention also includes an ion detector locate outside one column of the electrode array, which detects ions ejected out from this electrode array through silts or nets.
This invention also includes means to trap and analyze ions, which includes a parallel electrode arrays consisting of bar electrodes paralleled to each other. Alternating current (AC) voltages, with different phases, are assigned to the bar electrodes to create alternating electric fields between corresponding pairs of bar electrodes. Furthermore, multiple conjoint linear ion trapping fields are constructed in parallel in the space between the rows of electrode arrays. The ions can be trapped inside these fields and cooled down, then be separated and analyzed by their mass to charge ratio differences.
On the basis of the method above, the means to analyze ions includes assigning signals to the arrays to exclude all ions other than those having a certain mass to charge ratio, and then detecting the ejected ions one at a time.
A method of excluding ions includes superposing a low frequency signal, below 1000 Hz, beside high frequency AC voltages assigned to the electrode arrays, which makes ions trapped have maximal and minimal m/z ratios.
A method of excluding ions also includes adding a dipole excitation field between the parallel electrodes to eject certain m/z ions out by the resonance excitation between the ions' secular motion and the dipole field.
A method of detecting ejected ions one at a time includes decreasing the DC voltage on the electrodes at the end of the bars to educe the positive ions out through the slits or nets of the corresponding electrode, or increasing the direct current (DC) voltage on the electrodes at the end of the bars to educe the negative ions out through the slits or nets of the corresponding electrode, and then detecting the ion flow using ion detectors.
A method of detecting ejected ions one at time also includes applying an electric field parallel to the electrode array, which is called the X direction, to accelerate the ions and eject them out through either side of the array, and then detecting the ion flow using ion detectors.
A method of detecting ejected ions one at a time further includes applying an electric field vertical to the electrode array, which is called the Y direction, to accelerate the ions and eject them out through silts of either sides of the array, and then detecting the ion flow using ion detectors.
A method of ion separation includes scanning the voltage or frequency of the high radio frequency which is trapping the ions, and ejecting the ions following a sequence of m/z ratios. The detector outside the array receives a signal and forms a spectrum according to the m/z ratios.
The detector mentioned above is placed at the end of one of the ion trapping axis outside the parallel electrode array, and the ions can be ejected out through the silts or the nets on the boundary electrodes and enter into the detector mentioned above.
Furthermore, in this invention, adding an AC voltage between the parallel electrodes to form a resonance excitation field vertical to the electrode array to eject ions out follow the sequence of the m/z ratios by the resonance excitation between the ions' secular motion and the dipole field. The ions can pass through the silts in the electrode bars and reach the detector to be detected.
Also, in this invention, adding an AC voltage on adjacent bar electrodes of one of the bars to form a resonance excitation field parallel to the electrode array, which is the X direction, ejects ions following the sequence of the m/z ratios by the resonance excitation between the ions' secular motion and the dipole field. The ions can pass through the space between the electrode arrays and reach the detector to be detected.
When the AC voltage is produced by the groups of electric switches, the waveform is square wave.
When the number of electric switches groups which bring the square wave mentioned above is two, the phase difference between the square waves produced by two adjacent groups is 180 degrees.
If the number of electric switches groups mentioned above is greater than two, then the phase difference between the square waves produced by two adjacent groups is equal to the sum of 180 degrees and a certain increment, and both the periodic ion trapping fields and traveling wave fields are constructed in the space between the different rows of electrode arrays.
Furthermore, if the number of electric switches groups mentioned above is greater than two, and the phase difference between the square waves produced by two adjacent groups is equal to 180 degrees, but a modulation appears every N periodic wave length or phase, the modulation waves travel in the X direction.
The traveling wave fields mentioned above eject the ions out.
Each ion trapping unit, which comprises N bar electrodes with different phased AC voltages applied thereon and wherein N is equal to or greater than 1, can be optimized by adjusting the proportion of the voltages applied on each bars.
Furthermore, each ion trapping unit, which comprises N bar electrodes with different phased AC voltages applied thereon and wherein N is equal to or greater than 1, can be joined up together because the number N is changed by changing the voltages applied on each of the bars, and ions trapped in different axes can be joined up together.
This invention also includes a means to trap and analyze ions which includes more than two parallel electrode arrays having bar electrodes paralleled to each other. AC voltages with different phases are assigned to the bar electrodes to create alternating electric fields between each pair of bar electrodes. Furthermore, multiple conjoint linear ion trapping fields are constructed in parallel in the space between the different rows of electrode arrays. Ions can be trapped inside these fields, cooled down, and then separated and analyzed by their mass to charge ratio differences.
According to the research, we find in the case mentioned above the electric field between two parallel electrode arrays is multi-repeated high frequency electric field that is primarily a quadrupole field. The isoline of the field is shown as (5) in
Also, several rows of parallel electrode arrays can form a more complex linear ion trap array system. As shown in
Case 1:
In this case, the ions are ejected and detected in the Z direction (axially).
Case 2:
It will be understood that the potential applied to opposite electrodes of the top and bottom array can be different, for example, a dipole excitation voltage can be applied between them to eject or excite ions.
Similar to other linear quadrupole ion traps, ions in the stability region can be trapped. If the potential applied on the electrodes are pure alternative current signal +V, −V, ions will be trapped mass selectively and a low mass-to-charge ratio cut-off will exist. This means ions with a mass-to-charge ratio lower than a particular value (low mass limit) will hit the electrodes and be lost. For example, if we want to detect a contaminated gas, whose molecular weight (M) is usually greater than that of air, we can adjust the low mass limit to a little less than (M) so ions of air molecular will be eliminated. The remaining ions in the trap are primarily from the contaminated gas and can be detected by the detector by decreasing the potential of electrode (3.6).
However, the method described above has low mass resolution and sensitivity. If we add a direct current voltage or a low-frequency voltage to the trapping voltage, then the stability region in a-q space has a certain upper limit of mass-to-charge ratio, which means ions whose mass-to-charge ratio are greater than the upper limit will hit the electrode array and be lost. Therefore, we can combine the two methods together. First ions are captured in the ion trap, then we can use the lower limit and upper limit of mass-to-charge ratio of the stability region to filtrate ions, and only ions with a particular mass-to-charge ratio remain in the ion trap. We can then detect ions using the above described method of ejecting ions. Since low-frequency signals can be coupled to trapping voltage using capacitors, in some situations it is advantageous to add a low-frequency AC voltage than to add a DC voltage to trapping voltage.
Another method of band-pass filtering of ions includes applying a dipole excitation electric field between the top and bottom electrodes. The dipole excitation signal will resonantly excite unwanted ions and these ions will be excited and hit the electrodes and be lost.
The examples given above are methods of ejecting unwanted ions and maintaining wanted ions in the ion trap. These are efficient methods to detect particular ions, but mass spectrum cannot be achieved efficiently by these methods. The mass-selective detection methods discussed below are simple methods to get a mass spectrum. Some of the methods are also can be used to capture ions mass-selectively.
Applications
Method A:
As shown in
In this method, coils (51, 52) are used to superpose a Y-directed dipole excitation electric field with a fixed frequency, ions are then excited by mass to charge ratio order, this electric signal coupled method is shown in
Method B
In this method, we use the structure shown in
Method C
Using structure similar to as shown in
Method D
Captured electric field and superposing dipole excitation electric field in the X direction are still needed in this method. As shown in
There are many ways to manufacture the electrode array. As shown in
As shown in
In the methods described above, a trapping region is formed by two electrodes (the top and the bottom) and only a single voltage is applied to the electrodes. As shown in
While each electrode unit is formed by several exiguous bar electrodes, the electric field generated can be optimized by adjusting +V to −V ratio in each exiguous electrode, such as superposing or eliminating certain multipole field as required.
Alternatively, ion trapping methods described above which apply one voltage, +V or −V, to one ion-captured unit incorporate several ion-trapping fields by applying proportional voltage to each electrode bar.
There are many ways to construct parallel electrode ion trap array that we can not enumerate everyone here. However, if the electric field mentioned above is achieved, the parallel electrode ion trap array may work modes. We just list some instances above. The ion trap array can easily provide more handle modes to experts in this domain. For example, after being selected subsistent ions can be detected by spectroscopic analysis or light dispersion method. Additionally, ions can also be transported to other spectrum analyze instrument, such as Time-Of-Flight, Ion Mobility Spectrum, OBITRAP etc. These applications should be considered as included in this patent.
Number | Date | Country | Kind |
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200610026283.2 | Apr 2006 | CN | national |
Number | Date | Country | |
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Parent | 12298968 | Jul 2009 | US |
Child | 14829454 | US |