JP2004200082A - Mass spectrometry device and its adjustment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mass spectrometry device capable of easily matching an impedance which can be automated with simple construction , and to provide an adjustment method thereof. <P>SOLUTION: The mass spectrometry device is composed of a multipole electrode and its driving power circuit, and the driving power circuit is constructed of an oscillation circuit for oscillating a high frequency signal of a prescribed frequency, a high frequency transformer, a high frequency transformer driving circuit for supplying a high frequency current to the primary coil of the high frequency transformer by amplifying the high frequency signal, and a DC power source for superimposing a positive and a negative DC voltage to each of two secondary coils connected to the multipole electrode. On the mass spectrometry device, equipped with a mass filter making the ion with optional mass charge ratio pass according to the size of high frequency voltage impressed on the multipole electrode, and its adjustment method, a frequency variable mechanism of high frequency current is provided, and impedance is matched by changing the frequency in a prescribed range, and mass spectrometric analysis is carried out basing on the frequency at that time. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a mass spectrometer provided with a multipole electrode mass filter and a method for adjusting the mass spectrometer, and particularly to a mass spectrometer which can easily achieve accurate impedance matching with high accuracy and can be automated with a simple configuration. Equipment related.
[0002]
[Prior art]
The structure and measurement principle of a mass spectrometer equipped with a mass filter will be described using a quadrupole mass spectrometer, which is most commonly used, as an example.
FIG. 2 is a schematic diagram showing a structure of a quadrupole mass spectrometer, and FIG. 3 is a schematic circuit diagram showing an example of a driving power supply circuit for a high-frequency voltage applied to a quadrupole electrode.
[0003]
As shown in FIG. 2, the mass spectrometer 21 includes an ion source (ion generation unit) 23, a quadrupole electrode (analysis unit) 24, and a detector arranged inside a vacuum chamber 22 provided with an exhaust device 26. (Detection unit) 25, atoms and molecules are ionized by the ion source 23, and only ions having a predetermined mass-to-charge ratio M (= mass m / charge z) are applied to the electrodes by the high-frequency voltage applied to the quadrupole electrode. After passing through the inside, the amount is quantified by the detector 25 as a charge amount.
[0004]
The analysis unit 24 includes (U + Vcosωt) and − (U + Vcosωt) for the quadrupole electrode 7 in which four metal electrode rods are arranged in parallel, and for each pair of two opposing electrode rods. And a driving power supply circuit for applying a voltage. Here, U is a DC voltage, and V is a high frequency peak voltage having a frequency f. That is, the driving power supply circuit includes an oscillation circuit 1 for oscillating a high-frequency signal of a predetermined frequency, a high-frequency transformer 3, and a high-frequency transformer driving circuit 2 for amplifying the high-frequency signal and supplying a high-frequency current to the primary winding of the high-frequency transformer 3. And DC power supplies 5 and 6 for superimposing positive and negative DC voltages on each of the two secondary windings connected to the quadrupole electrode 7. Impedance matching is established between the two secondary windings. (Refer to Japanese Patent Application Laid-Open No. H10-69880). 4 is a capacitor.
[0005]
When (U + Vcosωt) and − (U + Vcosωt) are applied to the quadrupole electrode 7 by this drive power supply circuit, a rectangular hyperbolic electric field is formed in the electrode, and a specific mass-to-charge ratio M (= m / z) ) Can pass through the vicinity of the center axis of the electrode rod and reach the detector, while ions having other mass-to-charge ratios diverge and do not reach the detector.
[0006]
Here, assuming that U / V is constant, Equation (1) is established between the detected mass-to-charge ratio M and the high frequency. By fixing the frequency f (usually 1 to several MHz) and sweeping the amplitude (peak to peak value) V of the high-frequency voltage, it is possible to quantitatively analyze ions having a small mass-to-charge ratio from large ions.
M = V / (κf ² r ₀ ² ) (1)
here,
M: mass-to-charge ratio (= m / z)
κ: fixed value r ₀ : radius of the inscribed circle of the electrode rod cm
It is.
[0007]
[Problems to be solved by the invention]
In the above-described mass filter, the impedance of the electrode is shifted when the maintenance is performed, so that the power loss increases, the mass-to-charge ratio range that can be swept becomes narrow, and high-precision quantitative analysis cannot be performed. Therefore, after maintenance or replacement with a new mass filter, it is necessary to adjust the capacitance Cv of the variable capacitor 8 to achieve impedance matching. That is, the capacitance Cv is adjusted so that the expression (2) is satisfied.
f = 1 / (2π × (Lt (Cq + Cv)) ^1/2 ) (2)
here,
Cq: capacitance of quadrupole electrode 7,
Cv: capacitance of variable capacitor 8,
Lt is a secondary inductance of the high frequency transformer 3.
[0008]
However, this adjustment operation has a problem that skill is required and time is required because a current value largely shifts due to a slight change in capacitance as approaching the matching point. In addition, since a high-withstand-pressure air variable capacitor is used as the variable capacitor 8, the drive power supply circuit is large and expensive. Further, automatic control requires an actuator or the like that mechanically changes the capacity, and has a problem that the control mechanism is complicated and large.
[0009]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides a mass spectrometer that can easily perform impedance matching and that can be automated with a simple configuration and a method of adjusting the mass spectrometer. The purpose is to: That is, by realizing an adjustment method and a small and inexpensive adjustment mechanism that can achieve impedance matching easily and with high accuracy even by a non-expert, it is possible to always perform stable high-precision mass analysis. It is an object of the present invention to provide a mass spectrometer with reduced cost.
[0010]
[Means for Solving the Problems]
A mass spectrometer according to the present invention is a mass filter including a multipole electrode and a driving power supply circuit, wherein the driving power supply circuit includes an oscillation circuit that oscillates a high-frequency signal of a predetermined frequency, a high-frequency transformer, and the high-frequency A high-frequency transformer drive circuit for amplifying a signal and supplying a high-frequency current to a primary winding of the high-frequency transformer, and a DC power supply for superimposing positive and negative DC voltages on each of two secondary windings connected to the multipole electrode In a mass spectrometer equipped with a mass filter that allows ions having an arbitrary mass-to-charge ratio to pass through according to the magnitude of the high-frequency voltage applied to the multipole electrode, a frequency variable mechanism for the high-frequency current is provided, The multipole electrode is impedance-matched by changing the frequency within a range, and mass analysis is performed at the frequency at that time.
By adopting a configuration in which the frequency of the high-frequency signal is changed instead of changing the capacitance of the variable capacitor to perform matching, impedance matching can be performed extremely easily and with good reproducibility.
[0011]
The frequency variable mechanism compares the phases of two high-frequency signals and outputs a voltage or current according to the difference, a loop filter that cuts high-frequency components from the output of the phase comparator, and the filter A voltage-controlled oscillator that outputs a high-frequency signal having a frequency corresponding to the output voltage of the voltage-controlled oscillator, and an output of the oscillation circuit connected to a first input of the phase comparator. Is preferably fed back to the second input of the phase comparator via the variable frequency divider, and wired so as to be input to the high-frequency transformer driving circuit. It can be realized, and the size and the price can be reduced.
[0012]
Further, a converter for A / D-converting an output current of the control circuit and the high-frequency transformer drive circuit is provided, and the control circuit sends a signal for changing a frequency division ratio to the variable frequency divider according to an output of the converter. It is more preferable to adopt a configuration in which the output is output from the converter and the frequency division ratio of the variable frequency divider is changed until the output is minimized.Thus, it is possible to realize fully automatic impedance matching. In addition, by performing the adjustment constantly, not only when the mass filter is replaced, it is possible to always perform high-accuracy mass analysis more stably.
It is preferable that a frequency divider is arranged between the oscillation circuit and the first input. By disposing the frequency divider, the width of change (resolution) of the frequency can be further reduced, and more accurate impedance matching can be performed.
[0013]
In the present invention, the control circuit has a memory in which the relationship between the true value M ₀ of the mass-to-charge ratio with respect to any ion and the frequency f ₀ is stored in advance, and the mass-to-charge ratio obtained using the frequency ft after the matching is obtained. The difference ΔM between the ratio value M and the true value M ₀ is calculated, and the reference axis of the mass-to-charge ratio is corrected by ΔM. That is, after performing the matching operation, the reference axis of the mass-to-charge ratio is automatically corrected, and accurate data can be displayed.
[0014]
An adjustment method of the mass spectrometer of the present invention is a mass filter including a multipole electrode and a driving power supply circuit thereof, wherein the driving power supply circuit oscillates a high-frequency signal of a predetermined frequency, a high-frequency transformer, A high-frequency transformer drive circuit that amplifies the high-frequency signal and supplies a high-frequency current to a primary winding of the high-frequency transformer; and a power supply that superimposes positive and negative DC voltages on each of two secondary windings connected to the multipole electrode. In a mass spectrometer, comprising a mass filter that allows ions having an arbitrary mass-to-charge ratio to pass according to the magnitude of the high-frequency voltage applied to the multipole electrode, the output current of the high-frequency transformer drive circuit is monitored. The impedance of the multipole electrode is adjusted by changing the frequency of the high-frequency signal so that the output current is minimized. I do.
[0015]
Furthermore, the output of the oscillation circuit is connected to a first input of a phase comparator that compares the phases of two high-frequency signals and outputs a voltage or a current according to the difference, and outputs the output of the phase comparator to a high-frequency signal. Connected to a voltage-controlled oscillator that outputs a high-frequency signal having a frequency corresponding to the magnitude of the input voltage via a loop filter that cuts components, and outputs the output of the voltage-controlled oscillator via a variable frequency divider to the phase comparator Of the variable frequency divider while gradually increasing or decreasing the frequency division ratio while monitoring the output current of the high frequency transformer drive circuit. The time at which the output current is minimized is determined by changing the frequency in step (1), and this time is set as an impedance matching point.
The present invention can be applied to a mass spectrometer having a quadrupole, hexapole, octupole, or 16-pole multielectrode.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a block diagram showing a configuration example of a quadrupole mass filter according to the present invention, which is composed of a quadrupole electrode 7 and a driving power supply circuit thereof.
As shown in FIG. 1, the drive power supply circuit for the quadrupole electrode according to the present embodiment is configured to change the frequency of the high-frequency voltage applied to the quadrupole electrode to achieve matching. An automatic impedance adjusting circuit 10 is arranged between the high frequency transformer driving circuit 2 and the high frequency transformer driving circuit 2. The automatic impedance adjustment circuit 10 includes a frequency variable mechanism 20 that changes the frequency of a high-frequency current flowing through a high-frequency transformer and a control unit that determines whether impedance matching is successful or not and controls the frequency variable mechanism 20.
[0017]
The frequency variable mechanism 20 compares the phases of the fixed frequency divider 17 and the two high-frequency signals, outputs a voltage or current corresponding to the difference, and cuts high-frequency components from the output of the phase comparator. It comprises a loop filter 12 and a voltage controlled oscillation (VCO) circuit 13. The output of the VCO circuit is connected to the second input of the phase comparator 11 via the variable frequency divider 16, and the output is fed back to the phase comparator. Output from the circuit 13.
With such a circuit configuration, assuming that the oscillation frequency f of the oscillation circuit 1 is f / L in the fixed frequency divider (division ratio L) and the frequency division ratio of the variable frequency divider is N, the VCO circuit 13 Is f · N / L. Therefore, for example, if the frequency division ratio of the variable frequency divider 16 is increased by one, the output frequency of the VCO circuit 13 is increased by f / L, and the frequency division ratio is increased in a range corresponding to the frequency range to be swept. Can be changed. Further, by using a fixed frequency divider having a large frequency division ratio, the width of frequency change can be reduced, so that matching can be achieved with higher accuracy.
[0018]
On the other hand, the control unit determines whether impedance matching is successful or not based on the converter 14 for A / D converting the output current of the high frequency transformer drive circuit and the A / D converted data, and based on the determination result, the variable frequency division. And a control circuit 15 for changing the frequency division ratio of the circuit 16.
[0019]
Next, a procedure for adjusting impedance matching for the mass filter of FIG. 1 will be described.
In the configuration of the mass filter shown in FIG. 1, the output current of the high-frequency transformer drive circuit 2 is minimized when the impedance is matched. Therefore, while monitoring this output current, the frequency is increased or decreased with a certain width, and the output current is reduced. May be adjusted so as to obtain the frequency at which the minimum value is obtained. Specifically, this is performed as follows.
[0020]
First, the frequency division ratio range of the variable frequency divider 16 is set in accordance with the frequency sweep range, and the control circuit 15 is turned on. Assuming that the frequency f oscillated from the oscillation circuit 1 is f / L in the fixed frequency divider (division ratio L) 17 and the frequency division ratio of the variable frequency divider 16 is N, the output frequency of the VCO circuit 13 is f · N / L. At this time, the output current of the high frequency transformer driving circuit 2 is A / D converted by the converter 14 and stored in the memory of the control circuit 15. The control circuit 15 sends a frequency division ratio change signal to the variable frequency divider 16 to change the frequency division ratio to (N + 1). As a result, the output frequency of the VCO circuit 13 becomes f · (N + 1) / L, and increases by f / L. The output current of the high frequency transformer drive circuit at this time is A / D converted and output to the control circuit 15. The control circuit 15 compares, for example, the data stored in the memory with the newly sent data, and updates the content of the memory if the size of the data is smaller. Sends the ratio change signal. As a result, the frequency division ratio of the variable frequency divider becomes (N + 2), and the output frequency of the VCO circuit 13 becomes f · (N + 2) / L.
The above operation is repeated until the output of the A / D converter 14 becomes minimum. That is, until the output of the A / D converter increases before and after the frequency division ratio is changed, the frequency at the time of the increase or the frequency obtained by subtracting the change (f / L) becomes the frequency ft at which impedance matching can be achieved. . In this manner, the impedance matching point can be automatically detected.
[0021]
After this adjustment, the matched high-frequency current of the frequency ft is supplied to the high-frequency transformer 3 and the multiple electrodes, and mass analysis is performed. Accordingly, stable high-precision mass spectrometry can be performed without power loss. However, since a frequency different from that at the time of shipping the device is used, the mass-to-charge ratio can be understood from the relationship shown in Expression (1). M will be deviated from the true value M _0.
The following operation is performed to correct this shift. In matched frequency ft, for ^example, 14 ^{N +} calculated value Mt of mass-to-charge ratio of the difference from the relationship between the value _{M 0} of the frequency _{f 0} and the true mass-to-charge ratio, the true value _{M 0 ΔM} (= Mt−M ₀ ), and the reference axis of the mass-to-charge ratio is corrected by ΔM. This will give a true mass to charge ratio. In order to do this automatically, after performing automatic impedance matching, the reference axis of the mass-to-charge ratio can be automatically calculated and corrected automatically by the CPU. Can be displayed.
[0022]
In the above embodiment, the fixed frequency divider is disposed between the oscillation circuit and the phase comparator, and the frequency increase in one step is reduced to achieve high-precision impedance matching. May be omitted in some cases. Further, it goes without saying that a variable frequency divider may be used instead of the fixed frequency divider.
A general-purpose IC commercially available as a PLL circuit can be used as the feedback loop including the phase comparator, the loop filter, and the VCO circuit. As the loop filter, for example, an RC filter such as a lag-type LPF or a lag-lead-type LPF is used.
[0023]
In the above description, an example using a quadrupole electrode has been described. However, if a DC voltage and an AC voltage are superimposed and applied, a multipole of a hexapole, an octupole, and a 16-pole is used. The same can be applied to a mass filter using electrodes. These mass filters include a tandem mass spectrometer (MS / MS) that combines a plurality of quadrupole mass spectrometers (QMS), and a gas chromatograph mass spectrometer (GC / MS) that separates sample components in advance and performs mass analysis. MS), liquid chromatograph mass spectrometer (LC / MS) having another chromatography means, or induction plasma mass spectrometer (ICP-MS), secondary ion mass spectrometer (SIMS), etc. Can be.
[0024]
【The invention's effect】
As is apparent from the above description, according to the present invention, unlike a conventional case where a large and expensive variable capacitor is used, for example, a general-purpose PLL-IC is used to change the frequency to achieve matching. By doing so, it is possible to automate impedance matching with a simple configuration and to perform automatic adjustment of the mass spectrometer. As a result, it is possible to provide a mass spectrometer capable of realizing reduction in size, weight, cost, and energy saving.
[Brief description of the drawings]
FIG. 1 is a schematic circuit diagram illustrating a configuration example of a mass filter according to the present invention.
FIG. 2 is a schematic configuration diagram of a quadrupole mass spectrometer.
FIG. 3 is a schematic circuit diagram of a mass filter.
[Explanation of symbols]
1 oscillator circuit,
2 High frequency transformer drive circuit,
3 High-frequency transformer,
4 capacitors,
5 Negative DC power supply,
6 Positive DC power supply,
7 quadrupole rods,
8 Variable capacitors,
10 Impedance automatic matching mechanism,
11 phase comparator,
12 loop filter,
13 VCO (voltage controlled oscillator) circuit,
14 A / D converter,
15 control circuit (CPU),
16 variable frequency divider,
17 divider,
20 frequency variable mechanism,
21 quadrupole mass spectrometer,
22 vacuum chamber,
23 ion sources,
24 analysis part,
25 detectors,
26 Exhaust device.

Claims (9)

What is claimed is: 1. A mass filter comprising a multipole electrode and a driving power supply circuit, comprising: an oscillation circuit for oscillating a high-frequency signal having a predetermined frequency; a high-frequency transformer; and a high-frequency transformer for amplifying the high-frequency signal. A high-frequency transformer drive circuit for supplying a high-frequency current to the primary winding of the multi-pole electrode, and a DC power supply for superimposing positive and negative DC voltages on each of the two secondary windings connected to the multi-pole electrode. In a mass spectrometer equipped with a mass filter that allows ions of an arbitrary mass-to-charge ratio to pass according to the magnitude of the high-frequency voltage applied to the electrode,
A mass spectrometer, wherein a frequency variable mechanism for the high-frequency current is provided, the frequency is changed within a predetermined range, impedance matching of the multipole electrode is performed, and mass analysis is performed at the frequency at that time. The frequency variable mechanism compares the phases of two high-frequency signals and outputs a voltage or current according to the difference, a loop filter that cuts high-frequency components from the output of the phase comparator, and the filter A voltage-controlled oscillator that outputs a high-frequency signal having a frequency corresponding to the output voltage of the voltage-controlled oscillator, wherein an output of the oscillation circuit is connected to a first input of the phase comparator, 2. The mass spectrometer according to claim 1, wherein an output of the mass analyzer is fed back to the second input of the phase comparator via the variable frequency divider and input to the high frequency transformer drive circuit. A control circuit and a converter for A / D converting an output current of the high frequency transformer drive circuit are provided, and the control circuit sends a signal for changing a frequency division ratio to the variable frequency divider in accordance with an output of the converter. 3. The mass spectrometer according to claim 2, wherein the frequency division ratio of the variable frequency divider is changed until the output of the converter is minimized. 4. The mass spectrometer according to claim 2, wherein a frequency divider is arranged between the oscillation circuit and a first input of the phase comparator. The control circuit has a memory in which the relationship between the true value M ₀ of the mass-to-charge ratio for any ion and the frequency f ₀ is stored in advance, and the value M of the mass-to-charge ratio obtained using the frequency ft after the matching is obtained. 5. The mass spectrometer according to claim 3, wherein a difference ΔM between the absolute value and the true value M ₀ is calculated, and the reference axis of the mass-to-charge ratio is corrected by ΔM. The mass spectrometer according to any one of claims 1 to 5, wherein the multipole electrode is a quadrupole, a hexapole, an octupole, or a hexapole. A mass filter comprising a multipole electrode and a driving power supply circuit thereof, wherein the driving power supply circuit oscillates a high-frequency signal of a predetermined frequency, a high-frequency transformer, and a high-frequency transformer that amplifies the high-frequency signal. A high-frequency transformer drive circuit for supplying a high-frequency current to the primary winding, and a power supply for superimposing positive and negative DC voltages on each of the two secondary windings connected to the multipole electrode. A mass filter that passes ions of an arbitrary mass-to-charge ratio depending on the magnitude of the high-frequency voltage to be applied,
Mass spectrometry, wherein, while monitoring the output current of the high-frequency transformer drive circuit, the frequency of the high-frequency signal is changed so that the output current is minimized, thereby achieving impedance matching of the multipole electrode. How to adjust the device. The output of the oscillation circuit is connected to a first input of a phase comparator that compares the phases of two high-frequency signals and outputs a voltage or a current according to the difference, and cuts the output of the phase comparator to cut high-frequency components Connected to a voltage-controlled oscillator that outputs a high-frequency signal having a frequency corresponding to the magnitude of the input voltage through a loop filter, and outputs the output of the voltage-controlled oscillator to the second of the phase comparator via a variable frequency divider. The frequency is fed back to the input and input to the high-frequency transformer driving circuit, and the output current of the high-frequency transformer driving circuit is monitored, and while gradually increasing or decreasing the dividing ratio of the variable frequency divider, the frequency in a predetermined range is increased. The method for adjusting a mass spectrometer according to claim 7, wherein a time point at which the output current is minimized is obtained by changing the time point, and this time point is set as an impedance matching point. For any ion, it obtains a difference between the value M and the true value M ₀ of the mass-to-charge ratio to be determined at a frequency after the alignment, and correcting the reference axis of the mass-to-charge ratio in the difference ΔM A method for adjusting the mass spectrometer according to any one of claims 7 to 8.

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