CN210897194U - Ion signal detection device for time-of-flight mass spectrometer - Google Patents
Ion signal detection device for time-of-flight mass spectrometer Download PDFInfo
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- CN210897194U CN210897194U CN201922307719.0U CN201922307719U CN210897194U CN 210897194 U CN210897194 U CN 210897194U CN 201922307719 U CN201922307719 U CN 201922307719U CN 210897194 U CN210897194 U CN 210897194U
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Abstract
The utility model discloses an ion signal detection device for time of flight mass spectrograph. The device comprises a time-of-flight mass analyser, an electrode set, and a current or voltage measuring device; the electrode group is arranged at an ion leading-out end of the time-of-flight mass analyzer and consists of more than 2 electrodes which are mutually electrically insulated, and small holes are correspondingly arranged on other electrodes except the farthest electrode along the moving direction of the ions and used for the passing of the ions separated from the time-of-flight mass analyzer; wherein: when the electrode group is 2 electrodes, the current or voltage measuring device is directly connected with the 2 electrodes; when the electrode group is more than 3 electrodes, the working power supply is connected with the 2 electrodes nearest to the ions separated in the flight time mass analyzer, and the current or voltage measuring device is connected with the 2 electrodes farthest. The device of the utility model is simple in structure, it is with low costs, can realize the high sensitivity test of ion mass spectrum signal.
Description
Technical Field
The utility model relates to a mass spectrometry instrument technical field, concretely relates to an ion signal detection device for time of flight mass spectrograph.
Background
The time-of-flight mass spectrometer is one of the most commonly used mass spectrometry instruments, has high analysis speed and high sensitivity, and is a commonly used scientific instrument in scientific research and practical application. The method is widely applied in the fields of life science, material science, environmental monitoring, food safety, homeland safety and the like. The basic operating principle of a time-of-flight mass analyser is: the sample species being tested are ionized into ions using a suitable ion source and the sample ions are then introduced into the ion acceleration electrodes L1 and L2 of the time-of-flight mass analyzer. The ions are accelerated in the accelerating electrode and then enter a so-called ion free flight region having a length L3, equipotential, as shown in fig. 1. An ion extraction electrode is arranged at the other end of the ion free flight area, and an ion detector, generally a microchannel plate electron multiplier, is arranged at one side of the ion extraction electrode, which is far away from the ion free flight area.
The basic principle of time-of-flight can be described simply as follows: assuming that the mass of the sample ion is m, the charged charge is e, and the acceleration voltage applied to the ion in the acceleration electrode is V, the energy obtained after the ion is accelerated is: e ═ eV, this energy will be completely converted into the kinetic energy of the ion according to the law of conservation of energy, namely:
in the above formula, v is the velocity reached after the acceleration of the ions.
Therefore, the method has the advantages that,
assuming that the flight distance of the ion is L, the time required for the ion to fly the L distance is:
as can be seen from equation (2), the flight times are different for ions of different mass-to-charge ratios. Therefore, the time of flight of each ion is measured, and the mass-to-charge ratio of the corresponding ion can be calculated, which is the basic principle of time-of-flight mass spectrometry.
The ions finally reach the ion detector to be detected after passing through a flight area of the time-of-flight mass spectrum, and ion current/voltage signals corresponding to different flight times are recorded, so that a mass spectrogram of the analyzed sample is obtained, and chemical composition information of the analyzed sample is obtained. Briefly, time-of-flight mass spectrometry systems consist of three major components, namely, (1) an ion source that produces sample ions, (2) a time-of-flight mass analyzer that performs mass-to-charge ratio analysis on the ions, and (3) an ion detector and its signal processing system that can detect the ions.
The most commonly used ion detector in time-of-flight mass spectrometry instruments today is the so-called microchannel plate electron multiplier (MCP for short). It consists of a plurality of tiny channels, each constructed of a material with high secondary electron emission capability, and FIG. 2 is a schematic diagram of a microchannel plate electron multiplier. In use, a high voltage is applied across the microchannel plate electron multiplier, thereby creating an electric field within it. When ions separated by the time-of-flight mass analyzer collide under the electric field against the material surface of the microchannel plate electron multiplier, a plurality of secondary electrons will be generated. These secondary electrons will be accelerated and hit the surface of the multiplier at high speed under the action of the electric field generated by the operating voltage, generating more secondary electrons. This is repeated, and the electrons are accelerated and multiplied again and again in the multiplier, producing more and more secondary electrons. Finally, all secondary electrons pass through the final electron exit of the electron multiplier and are collected by electrodes arranged behind the electron multiplier, obtaining current signals corresponding to the incident ions, which can also be converted into voltage signals, eventually becoming mass spectra signals.
It is clear that electron multipliers are one of the essential components of all current time-of-flight mass spectrometry systems, including more complex mass spectrometry systems consisting of other types of mass analyzers, such as quadrupole mass analyzers, ion trap mass analyzers, etc., and time-of-flight mass analyzers, responsible for the tasks of mass spectrometers to record ion signals and obtain mass spectra.
Let the electron multiplication factor of a microchannel plate electron multiplier be 103Multiple multiplication, i.e. the number of secondary electrons generated by an ion gives a total number of 10 electrons3The final measured electron charge is then:
1.6×10-19×103＝1.6×10-16coulombs.
If 1000 ions of the same mass-to-charge ratio enter the ion detector at the same time per second, the resulting electron charge should theoretically be:
1000×1.6×10-19×103＝1.6×10-13coulombs.
The generated current is 1.6 × 10-13Coulomb 1 s 1.6 × 10-13Ampere is
Typically, two microchannel plate electron multipliers will be used in series in time-of-flight mass spectrometry, so the total electron signal produced by 1000 of its ions will be multiplied by 103*103＝106The resulting electron charge should therefore theoretically be:
1000×1.6×10-19×106＝1.6×10-10in amperes.
If this current is converted to a voltage, assuming that the resistance used is 100 ohms, the voltage that can be measured is: v100 x 1.6 x 10-10＝1.6*10-8In volts.
The microchannel plate electron multipliers currently used have several major problems: (1) all electron multipliers are aged due to aging of materials, and the consequence is that the electron multiplication efficiency is poorer and poorer, so that the obtained mass spectrum signals are weaker and weaker; therefore, all the electron multipliers of the microchannel plate have certain service lives; (2) different microchannel plate electron multiplier manufacturing companies, microchannel plate electron multipliers manufactured in different batches may have different final electron multiplication efficiencies due to differences in the materials or processes used, and thus when used as detected ion signals, may cause mass spectrum signals of equal ion content to have different magnitudes; (3) theoretically, the total amount of all secondary electrons generated by N ions should be equal to N times of that of one ion, but the secondary electron emission capability of all materials is limited, for example, a large number of electrons collide with the surface of a very small area of an electron multiplier in a very short time, the number of generated secondary electrons is difficult to be a simple multiple of that of the secondary electrons generated by one electron, so that the so-called signal "saturation" phenomenon of the ions is caused, and the quantitative analysis result is inaccurate. (4) The electron multiplier of the microchannel plate also often has a mass discrimination effect, that is, one ion with a large mass-to-charge ratio and a large volume is small, and the number of secondary electrons generated by the ion with a small volume is different, which finally causes the difference of the mass spectrum signal intensity generated by the large ion and the small ion with the same number, resulting in the inaccuracy of the quantitative analysis result. (5) The microchannel plate electron multiplier is a consumable product of the device in a flight time mass spectrum vacuum chamber, and is expensive and inconvenient to replace.
SUMMERY OF THE UTILITY MODEL
In order to solve the deficiencies existing in the above-mentioned existing ion detection technology, the utility model provides a novel an ion signal detection device for time of flight mass spectrograph. The device of the utility model is simple in structure, it is with low costs, can realize the high sensitivity test of ion mass spectrum signal.
The utility model discloses the ion of time of flight mass analysis ware is drawn forth the end and is set up several electrodes, and the ion that will be separated by time of flight mass analysis ware moves at a high speed between the electrode, obtains ion mass spectrum signal through measuring the produced electric current of the motion of ion between two electrodes. The basic process is as follows:
assuming that a single-charged ion separated by a time-of-flight mass analyzer is accelerated to 3000eV, the time taken for the single-charged ion to pass through two ion current detection electrodes at high speed is 10-8Second (i.e., 10 nanoseconds), the current produced is:
if 1000 ions with the same mass-to-charge ratio enter the ion current detection device at the same time, the final given electron current should theoretically be:
further, if this current is converted to a voltage, assuming that the resistance used is 100 ohms, the voltage that can be measured is 100 × 1.6.6 1.6 × 10-8＝1.6×10-6In volts.
The technical scheme of the utility model specifically introduces as follows.
The utility model provides an ion signal detection device for a time-of-flight mass spectrometer, which comprises a time-of-flight mass analyzer, an electrode group and a current or voltage measuring device; the electrode group is arranged at an ion leading-out end of the time-of-flight mass analyzer and consists of more than 2 electrodes which are mutually electrically insulated, and small holes are correspondingly arranged on other electrodes except the farthest electrode along the moving direction of the ions and used for the passing of the ions separated from the time-of-flight mass analyzer; wherein: when the electrode group is 2 electrodes, the current or voltage measuring device is directly connected with the 2 electrodes; when the electrode group is more than 3 electrodes, the working power supply is connected with 2 electrodes nearest to the ions separated in the flight time mass analyzer, and the current or voltage measuring device is connected with 2 electrodes farthest.
In the present invention, the time-of-flight mass analyser is a separate line time mass analyser or a combination of a time-of-flight mass analyser and another mass analyser.
The utility model discloses in, when the electrode group is 2 electrodes, through electric current or the voltage on the device test 2 electrodes of measuring current or voltage, obtain the mass spectrum signal.
Compare in traditional ion detection device, the utility model has the advantages of:
(1) because the microchannel plate electron multiplier is not used, the problems of aging and damage of the detector and the problem of service life of the ion detector are avoided;
(2) because the current signal generated by the ion movement is measured, the magnitude of the current signal is only related to the number of ions (assuming that the number of charges carried by the ions is equal), so that the problem that the multiplication efficiencies of the ions with different sizes are not equal is avoided;
(3) theoretically, the current generated by N ions is exactly equal to N times of the current generated by one ion, so that there is neither a so-called signal "saturation" phenomenon nor a so-called mass discrimination effect, i.e., the mass spectrum signal intensities generated by the same number of "large ions" and "small ions" (assuming that the number of charges carried by the "large ions" and the "small ions" is the same) are exactly the same, and the quantitative analysis result is accurate.
(4) Because the ion detector is not used, the maintenance and replacement of the ion detector do not exist, and the expenditure is saved.
Drawings
Fig. 1 is a schematic diagram of a conventional time-of-flight mass spectrometer.
FIG. 2 is a schematic diagram of the operation of a microchannel plate electron multiplier. FIG. 2(a) is a schematic structural diagram of a microchannel plate electron multiplier, and FIG. 2(b) is a schematic structural diagram of one microchannel in the microchannel plate electron multiplier.
Fig. 3 is a schematic diagram of an electrospray ionization-time-of-flight mass analyzer-ion signal detection system instrument system constructed according to the present technology.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings, which are not intended to limit the present invention.
Fig. 1 is a schematic diagram of a conventional time-of-flight mass spectrometer.
In fig. 1, 11 is sample ions entering between the time-of-flight mass spectrometer ion acceleration electrodes 12 and 13, which are generated by the time-of-flight mass spectrometer ion source and introduced between the acceleration electrodes 12 and 13. 12 and 13 are applied with different ion acceleration voltages, and 14 is another acceleration electrode, which is sometimes applied with a voltage of 0 volts (ground). Thus, under the action of the accelerating voltage, the ions will gain kinetic energy and eventually leave the grid on the electrode 14 into the ion free flight region 15. During the experiment the voltage on electrode 16 and the voltage on electrode 14 remain equal, so the ions will not be affected by any electric field forces between electrodes 14 and 15, the so-called free flight. Since ions of different mass to charge ratios will have different flight velocities, the time it takes for them to reach 16 will also be different. An ion detector, typically a microchannel plate electron multiplier, is arranged after 16 to measure the ion signal, it being apparent that the ion signals of different mass to charge ratios are time dependent, i.e. the mass to charge ratio of the corresponding ion can be deduced from the obtained time dependent ion signal. I.e. qualitative analysis.
Because the signal intensity output by the electron multiplier of the microchannel plate is related to the number of incident ions, the quantity of ions with corresponding mass-to-charge ratios can be inferred according to the signal intensity of the ions, and the sample can be quantitatively analyzed.
FIG. 2 is a schematic diagram of the operation of a microchannel plate electron multiplier. Wherein: FIG. 2(a) is a schematic structural diagram of a microchannel plate electron multiplier, and FIG. 2(b) is a schematic structural diagram of one microchannel in the microchannel plate electron multiplier.
In FIG. 2(a), 21, 22, 23, 2n are a plurality of micro-channels constituting a micro-channel plate electron multiplier, each micro-channel having an independent ion detection function; in fig. 2(b), 201 is a sample ion separated by a time-of-flight mass analyzer, which will generate more than one secondary electron when it hits the channel surface. Assume 202, 203 as two secondary electrons, which will rapidly move and collide with the next surface of the channel under the operating voltage of the microchannel plate, generating more secondary electrons, such as 204, 205, 206, 207, etc. These secondary electrons will continue to be accelerated and multiply until the end of the microchannel. And measuring and recording an electronic signal output by the microchannel plate, namely a mass spectrum signal of the incident ions.
Fig. 3 is a schematic diagram of an electrospray ionization-time-of-flight mass analyzer-ion signal detection system instrument system constructed in accordance with the present technology. In fig. 3, 301 is sample ions produced by electrospray ionization, which pass through small holes in an electrode plate 302 and enter a vacuum system, where they are focused and transported by an ion guide 303 to the next stage, i.e., through an ion extraction aperture in an electrode 304 to the ion acceleration electrode region of the time-of-flight mass spectrum. 306, 307, and 308 are several ion accelerating electrodes of time-of-flight mass spectrometry, respectively. They accelerate ions 305 entering the acceleration region under the ion acceleration voltage of the time-of-flight mass spectrum and cause them to fly out of the acceleration region into the ion free flight region 309. Electrode 310 is the other electrode of the time-of-flight mass spectrum and will be held at the same voltage as electrode 308 so that the ions will not be subjected to any electric field forces in the free flight region 309. Since the ions accelerated by the same voltage have the same energy, the ions with different mass-to-charge ratios will have different flight velocities, and therefore the arrival times at the electrodes 310 will be different. After the electrode 310, i.e., away from the ion free flight region 309, two electrodes 311 and 312 will be positioned, and ions flying off the electrode 310 will continue to fly past the electrodes 311 and 312. The movement of ions between electrodes 311 and 312 will generate a current according to coulomb's law, and therefore a current signal corresponding to the movement of ions can be measured between electrodes 311 and 312, and this signal measured and recorded to obtain a mass spectral signal of the ions.
Claims (2)
1. An ion signal detection device for a time-of-flight mass spectrometer, comprising a time-of-flight mass spectrometer
An analyzer, an electrode set, and a current or voltage measuring device; the electrode group is arranged at an ion leading-out end of the time-of-flight mass analyzer and consists of more than 2 electrodes which are mutually electrically insulated, and small holes are correspondingly arranged on other electrodes except the farthest electrode along the moving direction of the ions and used for the passing of the ions separated from the time-of-flight mass analyzer; wherein: when the electrode group is 2 electrodes, the current or voltage measuring device is directly connected with the 2 electrodes; when the electrode group is more than 3 electrodes, the working power supply is connected with the 2 electrodes nearest to the ions separated in the flight time mass analyzer, and the current or voltage measuring device is connected with the 2 electrodes farthest.
2. The ion signal detection apparatus for a time-of-flight mass spectrometer of claim 1,
the time-of-flight mass analyser is a single line time mass analyser or a combination of a time-of-flight mass analyser and other mass analysers.
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