JPH07240170A - Quadrupole mass spectrometric device - Google Patents

Abstract

PURPOSE:To automatically correct the measure shaft of a mass spectrometric curve resulted from the temperature change of the rod holder of a quadrupole. CONSTITUTION:The voltage V1 of the primary-side coil L1 of a transformer 15 and the phase difference G between the voltage and current of the primary- side coil L1 are detected, and a high frequency current to be supplied to the primary-side coil L1 is corrected on the basis of them. Thus, the heating of the rod holder of a quadrupole 17 is detected by the change of V1 and theta, and a proper RF voltage corresponding to it can be applied.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a quadrupole mass spectrometer.

[0002]

2. Description of the Related Art As shown in FIG. 7, a quadrupole mass spectrometer is provided with four electrode rods 41, 42, 43, 44 arranged rotationally symmetrically around the z-axis and at the outlet side thereof. It is composed of the ion detector 46 placed. Between the pair of electrode rods 42 and 44 arranged in the x-axis direction and the pair of electrode rods 41 and 43 arranged in the y-axis direction, a DC voltage U and a high frequency voltage Vcos
When (ω · t) is superimposed and applied, and ions are made incident on the center of the quadrupole along the z-axis, only ions with a specific mass determined by the voltages U and V pass through the quadrupole stably. It is possible to do so, and the ions 45 of other mass will diverge along the way. Therefore, by changing the voltages U and V while having a predetermined relationship with each other, it is possible to scan the mass passing through the quadrupole in order from light to heavy.

[0003]

In order to perform accurate mass analysis by the quadrupole mass spectrometer, it is necessary to arrange the four electrode rods (rods) 41, 42, 43, 44 correctly in axial symmetry. There must be. Therefore, conventionally, in the quadrupole mass spectrometer, four rods 41, 42, 43,
In order to prevent the positional deviation of 44 from each other, these ends were held by a pair of rod holders 48 made of ceramic.

However, the four rods 41, 42, 4
When a high frequency (about 1 MHz) is applied to 3, 44 as described above, a dielectric loss occurs in the ceramic rod holder 48 and heat is generated. As a result, the rod holder 48 expands, and as shown in FIG. 8, the central axis z of the quadrupole and each rod 4
The distance (radius of inscribed circle) r0 from 1, 42, 43, 44 changes. Further, the radius r0 of the inscribed circle also changes with changes in the ambient temperature. In this case, if the voltage (amplitude of) applied to the quadrupole is kept constant, the electric field E0 on the z axis, which is the passage of ions, changes according to r0, and accurate mass analysis can be performed. Disappear.

On the other hand, the rods 41, 42, 43, 4
4 and the rod holder 48 are selected so that the coefficients of thermal expansion of the rod holder 48 and the rod holder 48 have a certain constant relationship.
A method to prevent 0 from changing can be considered, but
In this case, it is not possible to use a material having good workability or a material having a small electrical loss, which causes a problem in terms of cost, performance, and the like. Further, even if the same material is used, the coefficient of thermal expansion varies among the individual units, which may cause an error in mass spectrometry.

The present invention has been made to solve such a problem, and an object thereof is to have a function of automatically correcting an error in mass spectrometry due to a temperature change of a rod holder or the like. It is to provide a quadrupole mass spectrometer equipped with the quadrupole mass spectrometer.

[0007]

SUMMARY OF THE INVENTION A quadrupole mass spectrometer according to the present invention, which has been made to solve the above-mentioned problems, provides a quadrupole connected to a secondary coil of a transformer with a predetermined target high-frequency voltage. In a quadrupole mass spectrometer equipped with a quadrupole drive circuit that controls the high-frequency current supplied to the primary coil of the transformer so that a is applied, a) detect the voltage of the primary coil of the transformer 1 Secondary side voltage detecting means, b) phase difference detecting means for detecting the phase difference between the voltage and current of the primary side coil of the transformer, and c) based on the detection result of the primary side voltage and phase difference, And a correction means for correcting the high-frequency current supplied by the quadrupole drive circuit.

[0008]

The quadrupole driving circuit is provided with means for detecting the voltage applied to the quadrupole, and the primary side coil of the transformer is arranged so that the quadrupole voltage becomes a predetermined target high frequency voltage. Controls the high frequency current supplied. However, when the ceramic rod holder that holds the four quadrupole rods generates heat due to the dielectric loss due to this high frequency, the dielectric constant (or dielectric loss tangent) of the rod holder changes, and the load capacity of the quadrupole changes. To do. Further, the load capacity of the quadrupole also changes with changes in the ambient temperature. Since the change in the load capacitance connected to the secondary coil of the transformer changes the voltage and phase difference of the primary coil, the primary side voltage detecting means and the phase difference detecting means detect these, The temperature change of the rod holder can be detected. It should be noted that it is sufficient to detect whether the phase difference is positive or negative.

Therefore, the target high frequency voltage of the quadrupole and the voltage of the primary coil when the mass number detected by the quadrupole is made correct by using a sample having a known mass pattern in advance. And the relationship with the phase difference. This relationship is stored, the voltage and phase difference of the primary coil of the transformer are detected by both detection means during actual measurement, and the voltage applied to the quadrupole is the target high-frequency voltage corresponding to them. By correcting the control target of the quadrupole drive circuit so that, the correct mass number can always be analyzed.

[0010]

EXAMPLE A quadrupole mass spectrometer which is an example of the present invention will be described with reference to FIGS. The quadrupole analyzer of the present embodiment is obtained by adding various circuits for RF voltage correction described later to the conventional quadrupole analyzer. Therefore, first, the part of the conventional quadrupole mass spectrometer will be described. The quadrupole 17 composed of four rods is connected to the secondary coil L2 of the transformer 15. A high frequency (RF) current is applied to the primary coil L1 of the transformer 15 by the oscillator 11, the modulator 12 and the RF amplifier 13, whereby a high frequency (RF) voltage is generated in the secondary coil L2 and the quadruple coil is generated. Pole 17
Applied to. The RF voltage applied to the quadrupole 17 is detected by the rectifying / smoothing circuit 16 and fed back to the modulator 12 via the error amplifier 21. Therefore, by applying the target RF voltage to the error amplifier 21, the RF voltage applied to the quadrupole 17 can be controlled.
Target RF applied to error amplifier 21 for mass scanning
The voltage is generated by the CPU 30 so as to change with time. Ions that have passed through the quadrupole 17 are detected by the ion detector 18
And is recorded by the recorder 20 via the detector amplifier 19 with the mass axis synchronized with the scanning of the target RF voltage as the horizontal axis (FIG. 4). In order to simplify the explanation,
In FIG. 1, a circuit for generating a DC voltage applied to the quadrupole 17 is not shown.

In the quadrupole mass spectrometer of this embodiment, the voltage detector 22 for detecting the voltage of the primary coil L1 of the transformer 15 and the primary coil L1 are added to the above conventional circuit. A phase difference detector 14 is provided for detecting the phase difference between the voltage and the current at. Also, the target R of the quadrupole
As a circuit for correcting the F voltage, an adder 23, a multiplier 24, and an RF correction D / A converter 26 are added. Hereinafter, the operation principle and actual operation of the quadrupole mass spectrometer of this embodiment will be described.

As described above, when the RF voltage is applied to the quadrupole 17, the rod holder generates heat due to the dielectric loss of the ceramic rod holder, and the distance between the rods (r0 × in FIG. 8).
2) changes. Further, the distance between the rods also changes due to changes in the ambient temperature. As a result, the peak of the ion passing through the quadrupole 17 deviates from the point representing the true mass of the ion on the horizontal axis (mass axis) of the recorder (dotted line in FIG. 4). In the quadrupole analyzer of the present embodiment, attention is paid to the fact that the dielectric constant of the rod holder changes as the temperature of the rod holder rises, and by detecting this as an index, the deviation is properly corrected. It is a thing.

The quadrupole 17 in which four electrodes (rods) are held by a rod holder which is a dielectric can be represented as a resistance R and a capacitance C as shown in FIG. When the load resistance R and the load capacitance C change due to the temperature change of the rod holder, the primary coil L1 of the transformer 15
The input impedance seen from will change. L
The relationship between the voltage V1 applied to 1 and the RF voltage V2 applied between the two pairs of rods of the quadrupole 17 is as follows. V1 = j · ω · C {R + j · (ω · L-1 / (ω · C))} · V2 (L is the mutual inductance of the coils L1 and L2)

From this equation, V is to the change in load capacitance C and load resistance R when attempting to keep | V2 | constant.
The value of 1 and the phase difference θ between the voltage V1 and the high frequency current flowing through L1 are as shown in the graph of FIG. This graph shows that changes in the load capacitance C and the load resistance R are
Primary voltage V1 and its phase difference θ (as shown in FIG.
Indicates that it is symmetric with respect to the minimum point, and can be known by detecting (identifying the direction by the phase difference θ).

Therefore, in the quadrupole mass spectrometer of the present embodiment, first, before analyzing an unknown sample, a sample having a known mass pattern is used to shift the mass number due to the temperature change of the quadrupole 17. A correction amount for correction is determined. That is, a known sample is input to the quadrupole 17 so that each peak of the curve recorded by the recorder 20 comes to the correct position on the horizontal axis (mass axis) of the recorded graph (that is, in FIG. 4). Correct the target RF voltage so that the dotted curve moves correctly to the solid curve). By changing the temperature around the quadrupole 17, at various temperatures,
The correction amount of the target RF voltage and the values of the primary voltage V1 and the phase difference θ at each temperature are detected. The correction amount of the target RF voltage thus determined is stored in the memory 31 in combination with V1 and θ.

When the unknown sample is analyzed, the voltage V1 of the primary coil L1 detected by the voltage detector 22 and the phase difference θ detected by the phase difference detector 14 are determined by the multiplexer 25 and the A / D. CPU 3 via converter 28
Input to 0. The CPU 30 reads the corresponding correction amount from the memory 31 based on these detected values V1 and θ. Then, the CPU 30 causes the predetermined target RF voltage V
2 is sent to the error amplifier 21 via the RF setting D / A converter 27, and the correction amount read from the memory 31 is R
It is sent to the multiplier 24 via the F correction D / A converter 26. In the multiplier 24, the RF setting D / A converter 27
Based on the scanning information (V2) input from, the correction amount is multiplied by a coefficient corresponding to the detected mass at the present time. This is because the deviation between the peak and the mass axis increases as the detected mass increases. The correction amount generated in the multiplier 24 is added to the target RF voltage V2 from the RF setting D / A converter in the adder 23 and input to the error amplifier 21. As a result, the mass peaks of the unknown sample are always output accurately from the recorder without any deviation from the mass axis.

A second embodiment of the present invention will be described with reference to FIGS. The quadrupole mass spectrometer of the present embodiment does not use the multiplier 24, the adder 23, the RF correction D / A converter 26 and the like as in the first embodiment, but the correction amount stored in the memory 31. Based on the above, the CPU 30 directly inputs the corrected target RF voltage to the error amplifier 21. Further, even when the correction amount is detected by the known sample, the detection curve is input from the detector amplifier 19 to the CPU 30 so that the CPU 30
Automatically calculates the correction amount and stores it in the memory 31.

The operation of the CPU 30 in this embodiment is shown in FIG.
The flowchart will be described. First, correction data collection work is performed (FIG. 6A). Here, the temperature around the quadrupole 17 is raised from room temperature (step S1), and a sample having a known mass pattern is analyzed while being kept at that temperature (step S2). The CPU 30 detects the peak of the detection curve input from the ion detector 18 via the detector amplifier 19, and corresponds to the actual mass number of each peak and the target RF voltage applied to the quadrupole 17 at that time. A correction amount of the target RF voltage is calculated based on the difference from the mass number (step S3). Then, the primary voltage V1 and the phase difference θ when the RF voltage added with the correction amount thus calculated is applied to the quadrupole 17 are input (step S4),
Memory 3 in combination with the correction amount (or corrected RF voltage)
Store in 1. After performing such a process step by step up to the upper limit of the temperature that can be considered by the rod holder (step S
5), the correction data collection process is ended.

Next, when performing analysis of an unknown sample, FIG.
As shown in (b), first, a predetermined initial target RF voltage is applied to the quadrupole 17 (step S11), and the primary voltage V1 of the coil L1 and the phase difference θ detected at that time are input (step S12). ). Then, the correction amount corresponding to the detected V1 and θ is read from the memory 31, and the RF voltage applied to the quadrupole 17 is corrected accordingly (step S13). After that, by performing the measurement (step S14), the output curve having no deviation from the mass axis can be obtained in the recorder 20.

In this embodiment, the number of circuits added to the conventional quadrupole mass spectrometer is small, and the device of the present invention can be constructed at a relatively low cost. Further, rather than a simple multiplication, it is possible to perform a complicated correction that more accurately reflects the relationship between the mass axis and the RF voltage.

[0021]

According to the quadrupole mass spectrometer of the present invention,
It is possible to automatically correct the deviation of the mass axis of the detection curve due to the change of the ambient temperature or the heat generation of the rod holder, and always output the accurate detection curve that coincides with the mass axis.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a quadrupole mass spectrometer that is a first embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of a circuit around a quadrupole.

FIG. 3 is a graph showing changes in primary voltage and phase difference due to changes in quadrupole capacitance and resistance.

FIG. 4 is a plan view showing a shift of a mass peak recorded in a recorder.

FIG. 5 is a block diagram showing the configuration of a quadrupole mass spectrometer that is a second embodiment of the present invention.

FIG. 6 is a flowchart showing the flow of processing performed by the CPU of the quadrupole mass spectrometer of the second embodiment.

FIG. 7 is an explanatory diagram illustrating the principle of mass spectrometry using a quadrupole.

FIG. 8 is a front view of the quadrupole unit.

[Explanation of symbols]

 11 ... Oscillator 12 ... Modulator 13 ... RF amplifier 14 ... Phase difference detector 15 ... Transformer 16 ... Rectifying / smoothing circuit 17 ... Quadrupole 18 ... Ion detector 19 ... Detector amplifier 20 ... Recorder 21 ... Error amplifier 22 ... Voltage detector 23 ... Adder 24 ... Multiplier 25 ... Multiplexer 26 ... RF correction D / A converter 27 ... RF setting D / A converter 28 ... A / D converter 30 ... CPU 31 ... Memory

Claims (1)

[Claims] 1. A quadrupole drive circuit for controlling a high frequency current supplied to a primary coil of a transformer so that a predetermined target high frequency voltage is applied to a quadrupole connected to a secondary coil of the transformer. In the quadrupole mass spectrometer provided, a) the phase difference between the primary side voltage detecting means for detecting the voltage of the primary side coil of the transformer and b) the phase difference between the voltage and the current of the primary side coil of the transformer. A phase difference detecting means for detecting; and c) a correcting means for correcting the high frequency current supplied by the quadrupole drive circuit based on the detection result of the primary side voltage and the phase difference. Polar mass spectrometer.