CN118136492A - Method and system for improving resolution of a reflective time-of-flight mass spectrometer - Google Patents

Abstract

A method and system for improving resolution of a reflection type time-of-flight mass spectrometer applies positive pulse voltage and negative pulse voltage to a repulsion electrode plate and a lead-out electrode plate of an acceleration region of a mass analyzer respectively, so that ions of a sample enter a reflection region through a field-free region with certain acceleration kinetic energy; and applying sawtooth wave voltage to the electrode plate of the reflecting area of the mass analyzer to form a sawtooth wave electric field so as to strike ions on the detector, and outputting a mass spectrum signal diagram by the voltage signal output by the detector through data processing. The invention adopts a circuit with simple structure, reduces the dispersion of ions with different energy distribution and position distribution in a reflected electric field on the flight time by regulating and controlling the sawtooth wave voltage, and improves the resolution of mass spectrum signals.

Description

Method and system for improving resolution of a reflective time-of-flight mass spectrometer

Technical Field

The present invention relates to the field of mass spectrometers, and in particular to a method and system for improving the resolution of a reflective time-of-flight mass spectrometer.

Background

The main performance parameters of the mass spectrometer embody the analysis capability of a mass spectrometer, and mainly comprise parameters such as resolution, sensitivity, detection mass range, mass accuracy and the like. Wherein influencing time-of-flight mass spectrum resolution is mainly dependent on the time of flight of ions in the mass analyser and the time dispersion of ions during flight. The flight time T of the ions can be realized by prolonging the flight distance of the ions in a field-free region, and the time dispersion of the ions in the flight process is mainly related to the initial condition dispersion of vertically introduced ions, the stability of a power supply, the uniformity of an electrostatic field, an ion detector and other factors. The energies obtained in the acceleration zone are naturally different due to the presence of the initial spatial dispersion of the ions; the spatial dispersion of ions after entering the acceleration zone will continue to increase due to the initial energy dispersion.

In order to overcome the influence, in the existing flight time mass analyzer, ions far away from the acceleration direction obtain higher kinetic energy in an acceleration electric field by arranging two acceleration areas, so as to compensate the influence from ion space dispersion; ions with higher energy enter the reflecting area deeply in an ion reflection mode, so that the flight distance is increased, and the influence of different absolute values of initial energy of the ions can be compensated. Thus allowing ions of different initial positions and energies to reach the detector as simultaneously as possible before acceleration. The initial velocity and the ions in the opposite direction of the accelerating field require additional return time to return the velocity to zero and then to the original starting point, which is a form of initial energy dispersion. Compensation techniques can be employed to reduce the initial spatial dispersion and the energy dispersion, but the back-off time due to the ion thermal motion is uncompensated, and although the back-off time produces little energy dispersion (less than 0.01 eV), it becomes a major cause of limiting the resolution of time-of-flight mass spectrometry (TOF MS) when resolution is certain.

Disclosure of Invention

The main object of the present invention is to overcome the above-mentioned drawbacks of the prior art and to propose a method and a system for improving the resolution of a reflection time-of-flight mass spectrometer, in which the time distribution of ions of the same mass-to-charge ratio reaching the detector is relatively concentrated by means of a sawtooth wave reflected electric field, so as to reduce the time-of-flight dispersion and improve the signal resolution of the mass spectrum.

The invention adopts the following technical scheme:

the method for improving the resolution ratio of the reflection type time-of-flight mass spectrometer comprises the steps of respectively applying positive pulse voltage and negative pulse voltage to a repulsion electrode plate and a lead-out electrode plate of an acceleration zone of a mass analyzer, so that ions of a sample enter a reflection zone through a field-free zone with certain acceleration kinetic energy; and applying sawtooth wave voltage to the electrode plate of the reflecting area of the mass analyzer to form a sawtooth wave electric field so as to strike ions on the detector, and outputting a mass spectrum signal diagram by the voltage signal output by the detector through data processing.

Further, the reflection area comprises a first-stage reflection area and a second-stage reflection area, and the sawtooth wave voltage is respectively applied to the electrode plate of the first-stage reflection area or the electrode plate of the second-stage reflection area.

Further, the positive pulse voltage, the negative pulse voltage and the sawtooth wave voltage are controlled by low-voltage pulse signals through energy coupling of a transformer; the positive pulse voltage, the negative pulse voltage and the sawtooth wave voltage are in time sequence correspondence.

A system for improving resolution of a reflective time-of-flight mass spectrometer acting on a reflective time-of-flight mass spectrometer, the reflective time-of-flight mass spectrometer comprising an EI ion source for ionization of a sample to produce ions, a mass analyzer provided with an acceleration zone, a field-free zone, and a reflection zone, a detector, and a signal acquisition and processing system, characterized in that: positive pulse voltage and negative pulse voltage are respectively applied to the repulsion electrode plate and the extraction electrode plate of the accelerating region, so that ions of a sample enter the reflecting region through a field-free region with certain accelerating kinetic energy; and applying sawtooth wave voltage to the electrode plate of the reflection area to form a sawtooth wave electric field so as to strike ions on the detector, and acquiring a voltage signal output by the detector by a signal acquisition and processing system to perform data processing and output a mass spectrum signal diagram.

Further, the device also comprises a sawtooth wave circuit, wherein the sawtooth wave circuit comprises a pulse unit and a charging and discharging unit, the pulse unit outputs a pulse signal under the control of a pulse control signal, the charging and discharging unit is connected with the output end of the pulse unit to charge and discharge at a certain rate under the action of the pulse signal, and the voltage output by the charging and discharging unit is gradually increased in the charging process to form a sawtooth wave signal.

Further, the charge-discharge unit comprises a resistor R1, a resistor R2, a resistor R24, a resistor R25, a resistor R26, a triode Q1, a triode Q2, a zener diode D7, an inductor L3, a capacitor C1, a capacitor C6 and a capacitor C7, wherein one end of the resistor R1 and one end of the diode D7 are connected with an isolation voltage HV4, the other end of the resistor R1 is connected with an emitter of the triode Q2, and the other end of the diode D7 is connected with a base of the triode Q2; one end of the resistor R24 is connected with the output end of the pulse unit, and the other end of the resistor R24 is connected with one end of the resistor R25, the base electrode of the triode Q1, the base electrode of the triode Q2 and one end of the resistor R25; the other end of the resistor R25 is connected with one end of the resistor R26, one end of the capacitor C6, one end of the capacitor C7 and one end of the inductor L3; the other end of the inductor L3 is input with an electrostatic voltage REF; the emitter of the triode Q1 is connected with one end of a resistor R2; the collector of the triode Q1, the collector of the triode Q2 and one end of the capacitor C1 are connected and output a sawtooth wave voltage U2; the other end of the resistor R2 and the other end of the capacitor C1 are connected to the other end of the resistor R25.

Further, the pulse signal output by the pulse unit controls the triode Q1 to act, so that the capacitor C1 charges and discharges at a certain rate, and in the process of charging the capacitor C1, the collector electrodes of the triode Q1 and the triode Q2 output a sawtooth wave voltage U2.

Further, the electrostatic voltage REF input from the other end of the inductor L3 is the electrostatic voltage of the reflection area.

Further, in the sawtooth wave circuit, the voltage values of the isolation voltage HV2 input by the pulse unit and the isolation voltage HV4 of the charge-discharge unit are fixed, and the resolution of the mass spectrum signal is adjusted by adjusting the value of the electrostatic voltage REF.

As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following advantages:

The invention applies positive pulse voltage and negative pulse voltage to the repulsion electrode plate and the extraction electrode plate of the acceleration region of the mass analyzer respectively, so that ions of a sample enter the reflection region through a field-free region with certain acceleration kinetic energy; and applying sawtooth wave voltage to the electrode plate of the reflecting area of the mass analyzer to form a sawtooth wave electric field so as to strike ions on the detector, and outputting a mass spectrum signal diagram by the voltage signal output by the detector through data processing. By adopting a circuit with a simple structure, the dispersion of ions with different energy distribution and position distribution in a reflected electric field on the flight time is reduced by regulating and controlling the sawtooth wave voltage, and the resolution of mass spectrum signals is improved.

Drawings

FIG. 1 is a block diagram of a pulse circuit and saw tooth circuit of the present invention;

FIG. 2 is a graph of sawtooth voltage and positive pulse voltage waveforms;

FIG. 3 is a schematic diagram of the structure of a reflection time-of-flight mass spectrometer of the present invention;

FIG. 4 is a schematic diagram of a mass analyzer of the present invention;

FIG. 5 is a graph of a nitrogen mass spectrum signal with sawtooth applied in the first order reflection region;

FIG. 6 is a graph of a nitrogen mass spectrum signal with sawtooth applied in the second order reflection region;

Wherein:

10. An EI ion source; 20. a mass analyzer; 21. an acceleration region; 21a, repulsive electrode pieces; 21b, leading out an electrode plate; 22. a field-free region; 23. a reflection region; 23a, first stage reflection regions; 23b, second stage reflection regions; 30. a detector, 40, signal acquisition and processing system; 50. a positive pulse circuit; 60. a negative pulse circuit; 70. a sawtooth circuit.

The invention is further described in detail below with reference to the drawings and the specific examples.

Detailed Description

The invention is further described below by means of specific embodiments.

In the present application, the terms "first," "second," "third," and the like are used merely to distinguish between similar objects and not necessarily to describe a particular sequence or order, nor are they to be construed as indicating or implying a relative importance. In the description, the directions or positional relationships indicated by "upper", "lower", "left", "right", "front" and "rear", etc. are used for convenience of description of the present application based on the directions or positional relationships shown in the drawings, and are not intended to indicate or imply that the apparatus must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the scope of protection of the present application. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art according to the specific circumstances.

In addition, in the description of the present application, unless otherwise indicated, "a plurality" means two or more. "and/or", describes an association relationship of an association object, and indicates that there may be three relationships, for example, a and/or B, and may indicate: a exists alone, A and B exist together, and B exists alone. The character "/" generally indicates that the context-dependent object is an "or" relationship.

Methods for improving the resolution of a reflective time-of-flight mass spectrometer provide for relatively concentrated time distribution of ions of the same mass to charge ratio to the detector 30 by a sawtooth reflected electric field, thereby reducing time-of-flight dispersion and improving mass spectrum signal resolution. The method of the invention comprises the following steps: positive pulse voltage and negative pulse voltage are respectively applied to a repulsion electrode plate 21a and a lead-out electrode plate 21b of an acceleration region 21 of the mass analyzer, so that ions of a sample enter a reflection region 23 through a field-free region 22 with certain acceleration kinetic energy; a sawtooth wave voltage is applied to the electrode sheet of the reflection area 23 of the mass analyzer to form a sawtooth wave electric field so as to strike ions on the detector 30, and a voltage signal output by the detector 30 is subjected to data processing to output a mass spectrum signal diagram.

Referring to fig. 4, the mass analyzer of the present invention includes an acceleration region 21, a field-free region 22, a reflection region 23, and the like. Wherein the acceleration region 21 is provided with a repulsive electrode piece 21a, an extraction electrode piece 21b, a ground electrode, and the like, a positive pulse voltage is applied to the repulsive electrode piece 21a, and a negative pulse voltage is applied to the extraction electrode piece 21 b. The reflection region 23 includes a first-stage reflection region 23a and a second-stage reflection region 23b, and the first-stage reflection region 23a and the second-stage reflection region 23b are respectively provided with electrode pads, and a sawtooth wave voltage is respectively applied to the electrode pads of the first-stage reflection region 23a or the electrode pads of the second-stage reflection region 23 b.

The positive pulse voltage, the negative pulse voltage and the sawtooth wave voltage are subjected to energy coupling control by a low-voltage pulse signal through a transformer, and the time sequence among the positive pulse voltage, the negative pulse voltage and the sawtooth wave voltage corresponds.

Based on this, the present invention also proposes a system for improving the resolution of a reflection time-of-flight mass spectrometer, acting on a reflection time-of-flight mass spectrometer, comprising an EI ion source 10, a mass analyzer, a detector 30, and a signal acquisition and processing system 40, etc. The EI ion source 10 is used for ionizing a sample to generate ions, the mass analyzer 22 is provided with an acceleration region 21, a field-free region 22 and a reflection region 23, and positive pulse voltage and negative pulse voltage are respectively applied to a repulsion electrode plate 21a and a lead-out electrode plate 21b of the acceleration region 21, so that the ions of the sample enter the reflection region 23 through the field-free region 22 with certain acceleration kinetic energy; a sawtooth wave voltage is applied to the electrode sheet of the reflection area 23 to form a sawtooth wave electric field so as to strike ions on the detector 30, and the signal acquisition and processing system 40 acquires a voltage signal output by the detector 30 for data processing to output a mass spectrum signal diagram.

Referring to fig. 1, the present invention further includes a positive pulse circuit 50, a negative pulse circuit 60, a sawtooth circuit 70, and the like. The positive pulse circuit 50 includes SN75372, resistor R3, resistor R4, resistor R5, resistor R6, resistor R7, resistor R8, resistor R9, resistor R10, resistor R11, resistor R12, resistor R13, fet Q3, fet Q4, transistor Q5, transistor Q6, transformer T1, transformer T2, diode D1, diode D2, capacitor C3, inductor L1, and the like. The SN75372 chip drives the following circuits respectively by two paths of pulse signals. Pulse signals output by the chip are coupled through transformers T1 and T2 to respectively control a triode Q5 and a triode Q6. Under the control of the pulse signal, when the transistor Q5 is turned on and the transistor Q6 is turned off, a high level is output, and when the transistor Q5 is turned off, the transistor Q6 is turned on and a low level is output, so that a positive pulse signal is formed.

The undershoot circuit 60 includes SN75372, resistor R27, resistor R28, resistor R29, resistor R30, resistor R31, resistor R32, resistor R33, resistor R34, resistor R35, resistor R36, resistor R37, field-effect transistor Q11, field-effect transistor Q12, transistor Q13, transistor Q14, transformer T5, transformer T6, diode D5, diode D6, capacitor C8, capacitor C9, inductor L4, and the like. The SN75372 chip drives the following circuits respectively by two paths of pulse signals. Pulse signals output by the chip are coupled through transformers T5 and T6 to respectively control a triode Q13 and a triode Q14. Under the control of the pulse signal, when the transistor Q13 is turned on and the transistor Q14 is turned off, a high level is output, and when the transistor Q13 is turned off, the transistor Q14 is turned on and a low level is output, so that a negative pulse signal is formed.

The sawtooth wave circuit 70 includes a pulse unit circuit that outputs a pulse signal under the control of a pulse control signal, and a charge-discharge unit. The pulse unit has a similar composition to the negative pulse circuit 60 and the positive pulse circuit 50, and includes SN75372, a resistor R14, a resistor R15, a resistor R16, a resistor R17, a resistor R18, a resistor R19, a resistor R20, a resistor R21, a resistor R22, a resistor R23, a field-effect transistor Q7, a field-effect transistor Q8, a triode Q9, a triode Q10, a transformer T3, a transformer T4, a diode D3, a diode D4, a capacitor C5, an inductor L2, and the like. The SN75372 chip drives the following circuits respectively by two paths of pulse signals. Pulse signals output by the chip are coupled through transformers T3 and T4 and then respectively control a triode Q9 and a triode Q10. Under the control of the pulse signal, when the transistor Q9 is turned on and the transistor Q10 is turned off, a high level is output, and when the transistor Q9 is turned off, the transistor Q10 is turned on and a low level is output, so that the pulse signal is formed.

The charge and discharge unit is connected with the output end of the pulse unit to charge and discharge at a certain rate under the action of the pulse signal, and the voltage output by the charge and discharge unit is gradually increased in the process of charging to form a sawtooth wave signal. The charging and discharging unit comprises a resistor R1, a resistor R2, a resistor R24, a resistor R25, a resistor R26, a triode Q1, a triode Q2, a diode D7, an inductor L3, a capacitor C1, a capacitor C6 and a capacitor C7, wherein one end of the resistor R1 and one end of the diode D7 are connected with an isolation voltage HV4, the other end of the resistor R1 is connected with an emitter of the triode Q2, and the other end of the diode D7 is connected with a base electrode of the triode Q2; one end of a resistor R24 is connected with the output end of the pulse unit, and the other end of the resistor R24 is connected with one end of a resistor R25, the base electrode of a triode Q1, the base electrode of a triode Q2 and one end of the resistor R25; the other end of the resistor R25 is connected with one end of the resistor R26, one end of the capacitor C6, one end of the capacitor C7 and one end of the inductor L3; the other end of the inductor L3 is input with an electrostatic voltage REF; the emitter of the triode Q1 is connected with one end of a resistor R2; the collector of the triode Q1, the collector of the triode Q2 and one end of the capacitor C1 are connected and output sawtooth wave voltage U2; the other end of the resistor R2 and the other end of the capacitor C1 are connected to the other end of the resistor R25.

The pulse signal output by the pulse unit controls the triode Q1 to act, so that the capacitor C1 is charged and discharged at a certain rate, and the collector electrodes of the triode Q1 and the triode Q2 output sawtooth wave voltage U2 in the process of charging the capacitor C1. The constant current circuit formed by the zener diode D7 and the resistor R1 regulates the rising slope and linearity of the sawtooth wave, and the resistor R2 provides a discharge loop for the capacitor C1. Resistor R1 controls the charge rate of capacitor C1, i.e., the slope of the ramp up of the sawtooth wave, and circuit R2 provides a discharge loop for capacitor C1.

In fig. 1, HV1 of the positive pulse circuit 50, HV2 input at the end R19 of the sawtooth wave circuit 70 and HV4 connected to the end of the diode D7 are positive voltages, and HV3 connected to the end R37 of the negative pulse circuit 60 is negative high voltage. The electrostatic voltage REF input at the other end of the inductor L3 is the electrostatic voltage of the reflection area 23, that is, the electrostatic voltage of the first reflection area or the second reflection area, and HV4 is the isolation voltage taking REF as the reference potential. In the sawtooth wave circuit 70, the voltage values of the isolation voltage HV2 input by the pulse unit and the isolation voltage HV4 of the charge-discharge unit are fixed, and the resolution of the mass spectrum signal is adjusted by adjusting the value of the electrostatic voltage REF so that the resolution of the mass spectrum signal is optimal.

The pulse output OUT1 of the positive pulse circuit 50 is a positive pulse voltage output, the positive pulse output is U1 in fig. 4, the repulsive electrode piece 21a applied to the acceleration region 21, the pulse output OUT3 of the negative pulse circuit is a negative pulse voltage output, the negative pulse is U3 in fig. 4, and the repulsive electrode piece 21b applied to the acceleration region 21. The ground electrode of the acceleration region 21 is grounded for preventing penetration of the electric field.

As shown in fig. 5 and 6, a saw-tooth voltage is applied to the electrode sheet of the first stage reflection region 23a or the second stage reflection region 23b, respectively. As shown in fig. 5, in the method of superimposing the 40V sawtooth wave voltage on the basis of the electrostatic voltage of the first-stage reflection region 23a as the reference potential, the bottom peak-type broadening of the mass spectrum signal of nitrogen gas is smaller than in the conventional method of applying the electrostatic charge, and as shown in fig. 6, the bottom peak-type broadening of the mass spectrum signal of nitrogen gas is smaller and the peak "trailing" phenomenon is alleviated by superimposing the 50V sawtooth wave voltage on the basis of the electrostatic voltage of the second-stage reflection region 23b as the reference potential, as compared with the case of directly applying the electrostatic charge.

The foregoing is merely illustrative of specific embodiments of the present invention, but the design concept of the present invention is not limited thereto, and any insubstantial modification of the present invention by using the design concept shall fall within the scope of the present invention.

Claims (9)

1. A method for improving resolution of a reflective time-of-flight mass spectrometer, characterized by: positive pulse voltage and negative pulse voltage are respectively applied to a repulsion electrode plate and a lead-out electrode plate of an acceleration region of the mass analyzer, so that ions of a sample enter a reflection region through a field-free region with certain acceleration kinetic energy; and applying sawtooth wave voltage to the electrode plate of the reflecting area of the mass analyzer to form a sawtooth wave electric field so as to strike ions on the detector, and outputting a mass spectrum signal diagram by the voltage signal output by the detector through data processing.

2. A method for improving resolution of a reflective time-of-flight mass spectrometer according to claim 1, wherein: the reflection area comprises a first-stage reflection area and a second-stage reflection area, and the sawtooth wave voltage is respectively applied to the electrode plate of the first-stage reflection area or the electrode plate of the second-stage reflection area.

3. A method for improving resolution of a reflective time-of-flight mass spectrometer according to claim 1, wherein: the positive pulse voltage, the negative pulse voltage and the sawtooth wave voltage are controlled by low-voltage pulse signals through energy coupling of a transformer; the positive pulse voltage, the negative pulse voltage and the sawtooth wave voltage are in time sequence correspondence.

4. A system for improving resolution of a reflective time-of-flight mass spectrometer acting on a reflective time-of-flight mass spectrometer, the reflective time-of-flight mass spectrometer comprising an EI ion source for ionization of a sample to produce ions, a mass analyzer provided with an acceleration zone, a field-free zone, and a reflection zone, a detector, and a signal acquisition and processing system, characterized in that: positive pulse voltage and negative pulse voltage are respectively applied to the repulsion electrode plate and the extraction electrode plate of the accelerating region, so that ions of a sample enter the reflecting region through a field-free region with certain accelerating kinetic energy; and applying sawtooth wave voltage to the electrode plate of the reflection area to form a sawtooth wave electric field so as to strike ions on the detector, and acquiring a voltage signal output by the detector by a signal acquisition and processing system to perform data processing and output a mass spectrum signal diagram.

5. A system for improving resolution of a reflection time-of-flight mass spectrometer as recited in claim 4, wherein: the device comprises a pulse unit, a charge-discharge unit and a sawtooth wave circuit, wherein the sawtooth wave circuit comprises the pulse unit and the charge-discharge unit, the pulse unit outputs a pulse signal under the control of a pulse control signal, the charge-discharge unit is connected with the output end of the pulse unit to charge and discharge at a certain rate under the action of the pulse signal, and the voltage output by the charge-discharge unit is gradually increased in the charging process to form a sawtooth wave signal.

6. A system for improving resolution of a reflection time-of-flight mass spectrometer as recited in claim 4, wherein: the charging and discharging unit comprises a resistor R1, a resistor R2, a resistor R24, a resistor R25, a resistor R26, a triode Q1, a triode Q2, a voltage stabilizing diode D7, an inductor L3, a capacitor C1, a capacitor C6 and a capacitor C7, wherein one end of the resistor R1 and one end of the diode D7 are connected with an isolation voltage HV4, the other end of the resistor R1 is connected with an emitter of the triode Q2, and the other end of the diode D7 is connected with a base electrode of the triode Q2; one end of the resistor R24 is connected with the output end of the pulse unit, and the other end of the resistor R24 is connected with one end of the resistor R25, the base electrode of the triode Q1, the base electrode of the triode Q2 and one end of the resistor R25; the other end of the resistor R25 is connected with one end of the resistor R26, one end of the capacitor C6, one end of the capacitor C7 and one end of the inductor L3; the other end of the inductor L3 is input with an electrostatic voltage REF; the emitter of the triode Q1 is connected with one end of a resistor R2; the collector of the triode Q1, the collector of the triode Q2 and one end of the capacitor C1 are connected and output a sawtooth wave voltage U2; the other end of the resistor R2 and the other end of the capacitor C1 are connected to the other end of the resistor R25.

7. A system for improving resolution of a reflective time-of-flight mass spectrometer as defined in claim 6, wherein: the pulse signal output by the pulse unit controls the triode Q1 to act, so that the capacitor C1 is charged and discharged at a certain rate, and in the process of charging the capacitor C1, the collector electrodes of the triode Q1 and the triode Q2 output sawtooth wave voltage U2.

8. A system for improving resolution of a reflective time-of-flight mass spectrometer as defined in claim 6, wherein: the electrostatic voltage REF input from the other end of the inductor L3 is the electrostatic voltage of the reflection area.

9. A system for improving resolution of a reflective time-of-flight mass spectrometer as defined in claim 6, wherein: in the sawtooth wave circuit, the voltage values of the isolation voltage HV2 input by the pulse unit and the isolation voltage HV4 of the charge-discharge unit are fixed, and the resolution of the mass spectrum signal is adjusted by adjusting the value of the electrostatic voltage REF.