CN101789355B - Time-of-flight mass spectrometer with wide dynamic range, implementation method and application thereof - Google Patents

Abstract

The invention provides a time-of-flight mass spectrometer with a wide dynamic range, including an ion source, an ion extraction pulse electrode, an ion extraction lens, a vertical introduction time-of-flight mass spectrometer, an ion selective repulsion electrode, an MCP ion detector, and a high-speed data acquisition card and corresponding software. The method for improving the dynamic range of detection concentration realized by the above-mentioned instrument comprises the following steps: applying a pulse voltage with adjustable pulse amplitude, duty cycle and frequency on the ion extraction pulse electrode, i.e. ion extraction pulse; A pulse voltage with adjustable delay, pulse width and amplitude is applied to the ion selective repulsion electrode in the time mass spectrometer, that is, the ion selective repulsion pulse; the ion extraction pulse and the ion selective repulsion pulse are applied asynchronously. The instrument and method of the invention increase the dynamic range of the time-of-flight mass spectrometry detection concentration to more than 6 orders of magnitude, and can be applied to occasions where components with large concentration differences in the sample to be tested need to be detected simultaneously.

Description

A wide dynamic range time-of-flight mass spectrometry instrument and its realization method and application

technical field

The invention relates to analysis instrument detection technology, in particular to a time-of-flight mass spectrometry instrument with a wide dynamic range and its realization method and application.

Background technique

Time-of-flight mass spectrometer (TOFMS) determines the mass-to-charge ratio of different ions based on their flight time in vacuum. The analysis speed is fast and it can detect a single charge. The dynamic range of the time-of-flight mass spectrometer to measure the concentration is one of the main parameters of the time-of-flight mass spectrometer. In practical applications, due to the complexity of the components in the sample, it is usually necessary to measure some components whose content differs by more than 6 orders of magnitude at the same time. time-to-digital converter (TDC) for data acquisition, and TDC cannot simultaneously measure two ions with the same mass-to-charge ratio in the same detection cycle due to the existence of dead time, so for components with large concentrations, when more When two ions arrive at the detector at the same time in a very short time (for example, 2ns), the detector may think that there is only one ion, which causes a large measurement error. How to obtain the information of multiple ions while detecting a single ion is an important problem to be solved urgently for time-of-flight mass spectrometers. There are currently several methods for improving the dynamic range of ion detection efficiency, which will increase the cost and complexity of the instrument.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art, and provide a time-of-flight mass spectrometer with a wide dynamic range, simple structure, convenient realization and low cost.

Another object of the present invention is to provide a realization method of the time-of-flight mass spectrometer with wide dynamic range.

Another object of the present invention is to provide the application of the time-of-flight mass spectrometer with wide dynamic range.

The object of the present invention is achieved through the following technical solutions: a time-of-flight mass spectrometer with a wide dynamic range, comprising an ion source, an ion extraction pulse electrode, an ion extraction lens, a vertical introduction time-of-flight mass spectrometer, an ion selective repelling electrode, MCP (Microchannel Plate) ion detector, high-speed data acquisition card and corresponding software, the ion source is set at the front end of the ion extraction pulse electrode, the ion extraction pulse electrode is set at the front end of the ion extraction lens, and the rear of the ion extraction lens The end is set opposite to the vertical introduction time-of-flight mass spectrometer, and the ion selective repulsion electrode and MCP ion detector are set in the vertical introduction time-of-flight mass spectrometer. The high-speed data acquisition card is used to collect ion detection signals, and is set at the The position relative to the exit of the ion channel in an introductory time-of-flight mass spectrometer.

The ion source can be any ion source, including an electron bombardment source capable of continuously generating ions, a chemical ionization source, a glow discharge ion source, an electrospray source under atmospheric pressure, or a pulsed ion source, such as laser ionization source etc.

The ion extraction pulse electrode enables the ions generated by the ion source to obtain kinetic energy under the action of the pair of electrodes, and the voltage amplitude applied to the pair of electrodes determines the kinetic energy of the ions; the ion extraction pulse electrode can be used for different ion source forms different.

The ion extraction lens is a conventional electrostatic lens.

The vertical-introduction time-of-flight mass spectrometer can be a conventional vertical-introduction time-of-flight mass spectrometer; the ion-selective repeller electrode and the MCP ion detector are arranged therein.

The MCP ion detector is an ion detector composed of conventional two-chip MCP.

The high-speed data acquisition card is a TDC or a high-speed analog-digital converter (Analog-Digital Converter, ADC).

The method for improving the dynamic range of the detection concentration realized by the time-of-flight mass spectrometry instrument of the above-mentioned wide dynamic range comprises the following steps:

(1) Apply a pulse voltage with adjustable pulse amplitude, duty cycle and frequency on the ion extraction pulse electrode, that is, the ion extraction pulse. The magnitude of the pulse voltage amplitude determines the horizontal kinetic energy of the ions, which also determines the ratio of the ions finally detected by the MCP ion detector to the ions generated in the ion source; the pulse duty cycle determines the time ratio applied by the two different extraction kinetic energy modes , that is, the detection time of different concentrations of component ions is used to adjust the dynamic range width of the instrument; the pulse frequency is continuously adjustable from 0.1Hz to 1KHz.

(2) Apply a pulse voltage with adjustable delay, pulse width and amplitude to the ion selective repulsion electrode in the vertical introduction time-of-flight mass spectrometer, that is, the ion selective repulsion pulse. There is a certain delay between the application of the pulse and the modulation pulse of the analyzer, and the delay, pulse width and amplitude of the pulse depend on the mass-to-charge ratio and flight speed of the ions to be repelled and removed.

(3) The ion extraction pulse described in step (1) and the ion selective repulsion pulse described in step (2) are applied asynchronously.

Described step (3) specifically can be:

(3-1) When the concentration range of ions generated by simultaneous ionization has a large difference, the instrument alternately detects high and low concentration component ions according to the ion extraction pulse duty cycle. When in the mode of detecting low-concentration component ions, a low level is applied to the ion extraction pulse, and the ions obtain lower kinetic energy, so that the ions’ flight trajectories in the time-of-flight mass spectrometer just fall on the MCP ion detector. At this time, a pulse voltage will be applied to the ion selective repulsion electrode in the time-of-flight mass spectrometer to selectively repel high-concentration component ions from the MCP ion detector.

(3-2) When in the mode of detecting high-concentration component ions, a high level is applied to the ion extraction pulse electrode, and the ions obtain higher kinetic energy, while the ion selective repulsion electrode in the time-of-flight mass spectrometer does not apply The pulse voltage makes the flight trajectory of ions in the time-of-flight mass spectrometer deviate from the MCP ion detector, and only a certain proportion of ions reach the MCP ion detector to be detected, preventing MCP saturation. The greater the amplitude of the ion extraction pulse voltage, the smaller the percentage of detected ions, the smaller the pulse duty cycle, and the less time it takes to detect high-concentration component ions.

The time-of-flight mass spectrometer with wide dynamic range and the method for improving the dynamic range of detection concentration can increase the dynamic range of the time-of-flight mass spectrometer to more than 6 orders of magnitude from 100% to 0.0001%, and can be applied to the concentration difference in the sample to be tested Larger components need to be detected at the same time, such as the detection of trace organic pollutants in the atmosphere.

The working principle of the present invention is that the ion extraction pulse and the ion selection repulsion pulse are applied asynchronously. When detecting low-concentration component ions, a low level is applied to the ion extraction pulse, and the ions obtain lower kinetic energy, so that the ions’ flight trajectory in the time-of-flight mass spectrometer falls on the MCP ion detector. At this time, in A pulse voltage is applied to the ion-selective repelling electrode in the time-of-flight mass spectrometer to selectively repel high-concentration component ions out of the MCP ion detector. When detecting high-concentration component ions, a high level is applied to the ion extraction pulse electrode, and the ions obtain higher kinetic energy, while no pulse voltage is applied to the ion selective repulsion electrode in the time-of-flight mass spectrometer, so that the ions are in flight. The flight trajectory in the time-to-mass analyzer deviates from the MCP ion detector, and only a certain proportion of ions reach the MCP ion detector to be detected, preventing MCP saturation. The greater the amplitude of the ion extraction pulse voltage, the smaller the percentage of detected ions, the smaller the pulse duty cycle, and the less time it takes to detect high-concentration component ions.

Compared with the prior art, the present invention has the following advantages and effects:

(1) The ion horizontal kinetic energy can be continuously adjusted according to the ion extraction pulse amplitude. As long as the ion horizontal kinetic energy is adjusted, the proportion of ions arriving at the MCP ion detector can be adjusted to meet the detection requirements of different dynamic ranges.

(2) The detection time of different component ions can be continuously adjusted according to the ion extraction pulse duty cycle.

(3) Due to the reduction of adjustment parameters, MCP ion detectors, anodes and high-speed data acquisition cards do not need to be made into complex multi-channel modes, which greatly reduces costs.

(4) Reduce the number of large groups of ions that finally reach the MCP ion detector, avoid the occurrence of the saturation state of the MCP ion detector, prevent high-speed data acquisition cards, such as time-to-digital converter TDC dead time limitations, and improve instrument quantification Accuracy.

Description of drawings

Fig. 1 is the instrument structure and schematic diagram of the present invention.

Figure 2 is a pulse timing diagram.

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example

Fig. 1 shows the principle and structure of the present invention. It can be seen from Figure 1 that the device includes three parts: electron bombardment ion source, ion extraction lens, and vertical introduction time-of-flight mass spectrometer.

The electron bombardment ion source includes: bombardment electron beam 1 , ion extraction pulse electrode 2 , and ion extraction grid 3 .

The ion extraction lens 5 is a conventional electrostatic lens, which introduces the ions 4 generated by the electron bombardment ion source into the vertical introduction time-of-flight mass spectrometer.

The vertical introduction time-of-flight mass spectrometer is a conventional vertical introduction time-of-flight mass spectrometer with an ion-selective repeller electrode 11 added.

The described vertical introduction time-of-flight mass spectrometer is composed of: vertical introduction repulsion electrode 6, ion collector 7, acceleration region 8, field-free flight region 9, reflection region 10, ion selective repulsion electrode 11 and MCP ion detector 13 compositions.

The ion-selective repeller electrode 11 may be, but not limited to, two parallel electrodes.

The ions 4 generated by the bombardment of gas molecules by electrons 1 emitted by the electron gun obtain a certain kinetic energy under the action of the ion extraction pulse electrode 2, and are continuously introduced into the vertical introduction time-of-flight mass spectrometer by the ion extraction lens 5.

In the vertical introduction time-of-flight mass spectrometer, the pulse voltage (frequency generally greater than 10000 Hz) introduced vertically to the repeller electrode 6 will introduce the ions into the acceleration zone 8 and start timing. After the ions are accelerated, they enter the field-free flight zone 9 and pass through the reflection zone. The 10 reflections are finally detected by the MCP ion detector 13 .

When detecting low-concentration components, the ion extraction pulse low-level region 17 as shown in Figure 2, the voltage applied to the ion extraction pulse electrode 2 just makes the ions reach the MCP ion detector 13 within the time of flight, as shown in Figure 1 Ion flight trajectory 14 is shown. At this time, in order to prevent the high-concentration component ions from saturating the MCP, a pulse voltage needs to be applied to the ion-selective repulsion electrode 11. When the high-component ions reach the electrode, they are pushed out of orbit and absorbed by the instrument wall.

When detecting and detecting high-concentration components, the ion extraction pulse high-level region 18 as shown in Figure 2, the voltage applied on the ion extraction pulse electrode 2 will make all ions have a higher level of kinetic energy, and its ion flight trajectory is as shown in the figure 1, so that only a certain percentage of ions reach the MCP ion detector 13 to be detected, while other ions are absorbed by the instrument wall. During this process, no pulse voltage was applied to the repelling electrode 11 .

Specific application examples:

For example, according to the National Air Pollutant Comprehensive Emission Standard (GB16297-1996), the limit value of toluene in air pollutant emission sources of existing pollution sources is 60 mg/m ³ . This is equivalent to detecting 14.6 ppm of tiny components in a gas with air as the background. The difference in component concentration ratio between nitrogen and toluene is 78%: 14.6ppm is about 50000 times. That is: there is only 1 toluene molecule in every 50,000 nitrogen molecules.

From the standard electron bombardment source spectrum of toluene, we know that its characteristic peak mass-to-charge ratios are 91 and 92. In view of this situation, when it is necessary to detect low-concentration toluene gas, all ions with a mass-to-charge ratio in the range of 17-44 can be pushed away from the orbit by using the ion-selective repeller electrode 11 during the flight of the ions.

When it is necessary to detect high-concentration gases such as nitrogen, oxygen, argon, and carbon dioxide at the same time, a higher voltage is applied to the ion extraction pulse electrode 2, and the duty ratio is about 1:100, so that only part of the ions reach the MCP ion detector 13, thereby Saturation of the MCP ion detector 13 is avoided.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (9)

1. A time-of-flight mass spectrometer with wide dynamic range, characterized in that: comprise ion source, ion extraction pulse electrode, ion extraction lens, vertical introduction time-of-flight mass spectrometer, ion selective repelling electrode, MCP ion detector, High-speed data acquisition card and corresponding software, the ion source is set at the front end of the ion extraction pulse electrode, the ion extraction pulse electrode is set at the front end of the ion extraction lens, and the rear end of the ion extraction lens is connected with the vertical introduction time-of-flight mass spectrometer The relative setting of the instrument is set in the vertical introduction time-of-flight mass spectrometer. The ion selective repulsion electrode and the MCP ion detector are set. The high-speed data acquisition card is used to collect ion detection signals and is set in the vertical introduction time-of-flight mass spectrometer. The relative position of the exit of the channel. 2. The time-of-flight mass spectrometry instrument of wide dynamic range according to claim 1, characterized in that: said ion source comprises an electron bombardment source, a chemical ionization source, a glow discharge ion source, an electric ion source under atmospheric pressure, which can continuously produce ions. Spray source, or pulsed ion source. 3. The time-of-flight mass spectrometer of wide dynamic range according to claim 1, characterized in that: the ion is drawn out from the pulse electrode, so that the ion generated by the ion source obtains kinetic energy under the action of the pair of electrodes, and the applied voltage of the pair of electrodes The amplitude determines the kinetic energy of ions; the ion extraction pulse electrode has different forms for different ion sources. 4. the time-of-flight mass spectrometry instrument of wide dynamic range according to claim 1, is characterized in that: described ion extraction lens is conventional electrostatic lens; Described MCP ion detector is the ion detector that conventional two-chip MCP forms . 5. the time-of-flight mass spectrometry instrument of wide dynamic range according to claim 1, is characterized in that: described vertical introduction time-of-flight mass spectrometer is a conventional vertical introduction time-of-flight mass spectrometer; ion selective repelling electrode and The MCP ion detector is arranged therein. 6. The time-of-flight mass spectrometer with wide dynamic range according to claim 1, characterized in that: the high-speed data acquisition card is a TDC or a high-speed analog-to-digital converter. 7. A method for improving the detection concentration dynamic range realized by the time-of-flight mass spectrometry instrument of wide dynamic range according to claim 1, is characterized in that comprising the steps: (1) Apply a pulse voltage with adjustable pulse amplitude, duty cycle and frequency on the ion extraction pulse electrode, that is, the ion extraction pulse; the magnitude of the pulse voltage determines the horizontal kinetic energy of the ion, and also determines the final MCP ion. The ratio of the ions detected by the detector to the ions generated in the ion source; the pulse duty cycle determines the time ratio applied by two different extraction kinetic energy modes, that is, the detection time of different concentration component ions, which is used to adjust the dynamic range width of the instrument; (2) Apply a pulse voltage with adjustable delay, pulse width and amplitude on the ion selective repulsion electrode in the vertical introduction time-of-flight mass spectrometer, that is, the ion selective repulsion pulse; when the pulse is applied, it is modulated with the analyzer pulse There is a certain delay, the delay of the pulse and the pulse width and amplitude depend on the mass-to-charge ratio and flight speed of the ions that need to be repelled and removed; (3) The ion extraction pulse described in step (1) and the ion selective repulsion pulse described in step (2) are applied asynchronously; Described step (3) is specifically: (3-1) When the concentration range of ions generated by simultaneous ionization has a large difference, the instrument alternately detects high and low concentration component ions according to the ion extraction pulse duty cycle; when it is in the detection mode of low concentration component ions, in A low level is applied to the ion extraction pulse, and the ions obtain lower kinetic energy, so that the flight trajectory of the ions in the time-of-flight mass spectrometer falls on the MCP ion detector. At this time, the ion selection in the time-of-flight mass spectrometer A pulse voltage will be applied to the repulsion electrode to selectively repel high-concentration component ions out of the MCP ion detector; (3-2) When in the mode of detecting high-concentration component ions, a high level is applied to the ion extraction pulse electrode, and the ions obtain higher kinetic energy, while the ion selective repulsion electrode in the time-of-flight mass spectrometer does not apply Pulse voltage, so that the flight trajectory of ions in the time-of-flight mass spectrometer deviates from the MCP ion detector, and only a certain proportion of ions reach the MCP ion detector to be detected to prevent MCP saturation; the greater the amplitude of the ion extraction pulse voltage, the more detected The smaller the ion percentage, the smaller the pulse duty cycle, and the less time it takes to detect high-concentration component ions. 8. The method according to claim 7, characterized in that the frequency of the ion extraction pulse in step (1) is continuously adjustable from 0.1 Hz to 1 KHz. 9. The application of the time-of-flight mass spectrometry instrument with wide dynamic range according to claim 1, characterized in that: it is applied to occasions where components with large concentration differences in the sample to be tested need to be detected simultaneously.

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