JP4305832B2 - Multipole mass spectrometer - Google Patents

Description

  The present invention relates to a multipole mass spectrometer, and more particularly to a multipole mass spectrometer capable of performing stable measurement without the intensity and position of a measured peak changing over time.

A structure and measurement principle of a quadrupole mass spectrometer as an example of a multipole mass spectrometer will be described with reference to FIGS.
FIG. 2 is a conceptual diagram showing the structure of a quadrupole mass spectrometer, and FIG. 3 is a schematic circuit diagram showing an example of a drive power supply circuit that applies a high-frequency and DC superimposed voltage to the quadrupole.
As shown in FIG. 2, the mass spectrometer 21 includes an ion source (ion generator) 23, a quadrupole (analyzer) 24, and a detector (which are disposed inside a vacuum chamber 22 having an exhaust device 26. Detection unit) 25, atoms and molecules are ionized by the ion source 23, and only ions having a predetermined mass number M (= mass m / charge number z) are applied to the quadrupole by a high frequency and a DC voltage. The amount passes through the inside and is quantified as a charge amount by the detector 25.

  The analysis unit 24 applies (U + Vcosωt) and − (U + Vcosωt) to each of the quadrupole 7 in which four metal electrode rods are arranged in parallel and two opposing electrode rods. And a drive circuit to be applied. Here, U is a DC voltage, V is a high-frequency peak voltage of frequency f, and ω = 2πf. That is, the drive circuit includes an oscillation circuit 1 that oscillates a high-frequency signal having a predetermined frequency, a high-frequency transformer 3, a high-frequency transformer drive circuit 2 that amplifies the high-frequency signal and supplies a high-frequency current to the primary winding of the high-frequency transformer 3. DC power sources 5 and 6 for superimposing positive and negative DC voltages connected to each of the two secondary windings connected to the quadrupole 7, and impedance matching between the two secondary windings. A variable capacitor 8 is attached for this purpose. Reference numeral 4 denotes a virtual grounding capacitor. The stabilizing voltage source 9 is a supply voltage source for the high-frequency transformer driving circuit 2.

  When (U + Vcosωt) and − (U + Vcosωt) are applied to the quadrupole 7 by this driving circuit, a right-angle hyperbolic electric field is formed in the electrode, and only ions having a specific mass number are located at the center of the electrode rod. It can pass through the vicinity of the axis and reach the detector 25, and ions having other mass numbers diverge and do not reach the detector.

  Here, if U / V is constant and the frequency f (usually 1 to several MHz) is fixed, a proportional relationship is established between the mass number of the detected ions and the high-frequency voltage V. Accordingly, by continuously sweeping the high-frequency voltage V, it is possible to perform quantitative analysis from ions having a small mass number to ions having a large mass number.

The high-frequency transformer drive circuit 2 that handles high frequencies and the high-frequency generator of the high-frequency transformer 3 are sealed in the metal shield 10. The high-frequency transformer drive circuit 2 is generally composed of a high-frequency amplifier circuit or a switching circuit, which causes power loss and generates heat. Similarly, in the high frequency transformer 3, heat is generated due to loss due to wire resistance of the transformer winding (copper loss) and loss due to magnetic flux passing through the core (iron loss). An air cooling fan 11 is attached.
Furthermore, in the high-frequency transformer driving circuit, a circuit configuration for performing a stable measurement by correcting a deviation from the linearity of the swept high-frequency voltage caused by the variation in the ambient temperature has been studied.
JP 2002-33073 A

    However, the above quadrupole mass spectrometer has a problem that the reliability of measurement is greatly lowered depending on how it is used. For example, unlike the case where the mass number is continuously swept, if the mass number is changed intermittently, the peak value and position measured may be different immediately after that and after a predetermined time has elapsed. In particular, after switching from a small mass number ion to a large ion number, the larger the difference in mass number, the more the waveform and position of the detected peak tend to change more. It disappeared and it was necessary to retune the circuit.

These phenomena are thought to be caused by the fact that the amount of heat generated in the circuit section varies depending on the mass number. That is, the high-frequency power applied to the quadrupole 7 is expressed by the equation (1), and as the mass number M to be measured increases, the power input to the quadrupole increases, and conversely, the smaller mass number. Then, the electric power becomes small.
P = k · C · M ² · f ⁵ · r ₀ ⁴ / Q (1)
k: constant P: RF power (W) applied to the quadrupole
C: Quadrupole capacitance (μF)
M: Mass number (= mass m / charge number z)
f: High frequency (MHz)
r ₀ : radius of the quadrupole inscribed circle (cm)
Q: Sharpness of the current peak when the quadrupole capacitance and the high-frequency transformer secondary winding resonate

  Here, the conversion efficiency η represented by the ratio (P / Pi) between the power Pi supplied from the stabilized voltage source 9 to the high-frequency transformer drive circuit 2 and the power P input to the quadrupole 7 is generally Is about 50 to 60 (%), and the remainder (40 to 50%) is heat. Therefore, for example, when the circuit is tuned by adjusting the variable capacitor 8 at a small mass number (for example, M = 4), the measurement can be stably performed at that mass number. When the mass number is changed to a large mass (for example, M = 200), the amount of heat generation increases, and the inductance of the high-frequency transformer 3 changes due to this heat, resulting in resonance detuning. As a result, the high-frequency voltage is considered to cause a disturbance in the waveform attributed to the superposition of harmonics and the like, causing fluctuations in mass resolution and peak displacement. On the contrary, even when the tuning is performed after the temperature is stabilized at M = 200, the same phenomenon occurs when the value is changed to M = 4 and further changed to M = 200 again.

  Therefore, the present inventor arranged a heater in the metal shield 10 and changed the energization amount to the heater according to the value of the mass number so that the amount of heat generated in the shield was constant. It was confirmed that even when switching between the two, the phenomenon that the peak changes over time or the position shifts is alleviated and stabilized.

  The present invention has been completed by further study based on such knowledge, and high-accuracy mass spectrometry can be obtained even immediately after changing the mass number of ions, and highly reliable measurement without change over time. An object of the present invention is to provide a multipole mass spectrometer that can be used.

A multipole mass spectrometer according to the present invention includes a multipole, an oscillation circuit that oscillates a high-frequency signal having a predetermined frequency, a high-frequency transformer, amplifies the high-frequency signal, and supplies a high-frequency current to a primary winding of the high-frequency transformer. A high-frequency transformer driving circuit, a driving circuit having a DC power source for superimposing positive and negative DC voltages on each of two secondary windings of the high-frequency transformer connected to the multipole, and supplying power to the high-frequency transformer driving circuit A multipole type mass spectrometer having a stabilizing voltage source , wherein the high-frequency transformer , the high-frequency transformer driving circuit, and an internal part are provided in a metal shield having an air-cooling fan for cooling the inside. a heater which is heating means for heating the, placing a heater driving circuit, and is supplied to the high frequency transformer drive circuit from the regulated voltage source A current detector for detecting the flow I, comprising a power regulator, the heater is turned coulometric P _H calculated based on the detected current from the I (2) wherein the heater of the stabilized voltage source as a power source throw into
P _H = V · (1−η) · (Imax−I) (2)

P _H: heater input power

V: Stabilized voltage source voltage

η: Conversion efficiency
Imax: detection current corresponding to the maximum mass number to be measured

I: Detection current

It is characterized by having a configuration.
Here, the heating means, with respect to the air flow formed by the fan, it is preferable to make disposed upstream of the high-frequency transformer.

  That is, by disposing the heat generating means in the metal shield and changing the amount of current supplied to the heat generating means in accordance with the number of ions, the temperature change inside the metal shield can be suppressed. As a result, even if the mass number is changed, the tuning condition is always maintained, so that highly accurate mass analysis can be continued stably.

  The heat generating means is preferably arranged on the upstream side of the high-frequency transformer, and the heat generated by the heat generating means can be efficiently transmitted to the high-frequency transformer to further suppress the temperature change.

According to the present invention, that is, the amount of heat generated in the metal shield containing the multipole drive circuit is kept constant regardless of the mass number, the tuning condition is maintained with high accuracy, and mass spectrometry is improved. It becomes possible to carry out with accuracy and stability. Therefore, for example, even when the mass number is greatly changed, the ion concentration can be measured with high accuracy, and it is possible to perform highly reliable measurement without changing with time.
Further, since it is only necessary to add the heat generating means and its control means to the conventional circuit, a low-cost and highly reliable mass spectrometer can be realized.

  One configuration example of the multipole mass spectrometer of the present invention is shown in FIG. FIG. 1 is a conceptual diagram showing an analysis unit of a quadrupole mass spectrometer. The analysis unit of the quadrupole mass spectrometer according to the present embodiment has a quadrupole 7 in which four metal electrode rods are arranged in parallel and two sets of opposing electrode rods (U + Vcosωt) and − (U + Vcosωt). The overall configuration of the mass spectrometer is as shown in FIG.

  The drive circuit includes an oscillation circuit 1 that oscillates a high-frequency signal having a predetermined frequency, a high-frequency transformer 3, a high-frequency transformer drive circuit 2 that amplifies the high-frequency signal and supplies a high-frequency current to the primary winding of the high-frequency transformer 3. DC power supplies 5 and 6 for superimposing positive and negative DC voltages connected to each of two secondary windings connected to the multipole 7, and a stabilized voltage source 9 serving as a power supply source for the high-frequency transformer drive circuit 2. And consist of A variable capacitor 8 for impedance matching is disposed between the two secondary windings. Note that. Reference numeral 4 denotes a virtual grounding capacitor.

  Among these, the high-frequency transformer drive circuit 2 and the high-frequency transformer 3 are disposed inside the metal shield box 10 so that the generated high frequency does not affect other control circuits, measuring instruments, and the like. An air cooling fan 11 is attached to the metal shield 10 to suppress a temperature rise of a high frequency transformer or the like. Furthermore, a heater 12 (for example, a ceramic heater or a resistance heater) is disposed in the upstream side of the high-frequency transformer 3 in the metal shield. By arranging in this way, the heat generated by the heater 12 is efficiently transmitted to the downstream high-frequency transformer 3 and the like. For example, the heater is mounted on a straight line connecting the high-frequency transformer 3 and the air cooling fan 11 using a spacer such as steatite.

In the present embodiment, the current output from the stabilized voltage source 9 that supplies power to the high-frequency transformer drive circuit 2 is detected by the current detector 13, and the operation is performed so that the amount of heat generated in the metal shield is constant. .
That is, when measuring a large mass number, the power supplied to the high-frequency transformer drive circuit 2 (further, the quadrupole 7) is maximized, so the power input to the heater 12 disposed inside the metal shield 10 is minimized (or Zero). On the other hand, when measuring a small mass number, the power supplied to the quadrupole 7 is small, so that the power loss at this time and the power loss that occurs when the power supply to the quadrupole 7 is maximum. Electric power corresponding to the difference from the minute is input to the heater 12.

  Therefore, first, when the mass is large, after the temperature stabilizes, the variable capacitor 8 is adjusted to obtain the resonance condition and tuned. After that, the high-frequency transformer and the like are maintained at substantially the same temperature even if the mass is changed. Therefore, the peak intensity can be accurately and stably measured without deviating from the resonance condition. That is, by this operation, the amount of heat generated in the metal shield 10 is always constant, and the temperature inside the metal shield 10 is constant regardless of the mass number to be measured. Accordingly, the temperature of the high-frequency transformer is also kept constant, and no synchronization deviation occurs.

More specifically, for example, a current detector 13 for detecting the current I supplied to the high frequency transformer driving circuit 2 calculates the power P _H corresponding the measured current value (2) power regulator 14 When attaching a driving circuit 15 of the heater may be configured to adjust the power P _H is supplied to the heater in accordance with the mass number.
P _H = V · (1−η) · (I _max −I) (2)
P _H : Heater input power V: Stabilized voltage source voltage η: Conversion efficiency I _max : Detection current corresponding to the maximum mass number to be measured I: Detection current

As described above, the conventional quadrupole mass spectrometer can be improved to a more accurate and stable analyzer simply by adding a heater and its control system.
In this embodiment, the heater is arranged upstream of the high-frequency transformer with respect to the air flow formed by the fan. However, the present invention is not limited to this. For example, the heater is also arranged beside the high-frequency transformer. It may be arranged such that the peak fluctuation at each mass number is minimized. Further, as the heat generating means of the present invention, in addition to the heater described above, it is also possible to use, for example, an electrical component that generates heat due to a current such as a power resistor, a power transistor, or a power MOSFET.

In the above embodiment, the stabilized power source 9 is also used as the heater power source. However, a heater power source may be provided separately, and when a predetermined power is supplied to the heater in advance, the measurement is started. Thus, stable mass spectrometry measurement can be performed for a desired mass number.
Moreover, although the mass spectrometer using a quadrupole has been described in the above embodiments, the present invention similarly uses a mass electrode using multiple electrodes such as a hexapole, an octupole, and a 16-pole. It can be applied to analyzers.

In addition, it cannot be overemphasized that this invention can be applied suitably also when sweeping and using a mass number continuously, In this case, higher measurement accuracy can be obtained.
Furthermore, the present invention provides, for example, a quadrupole mass spectrometer (QMS), a gas chromatograph mass spectrometer (GC / MS), a liquid chromatograph mass spectrometer (LC / MS), and a secondary ion mass spectrometer (SIMS). ) And an ion attachment mass spectrometer (IAMS).

It is a conceptual diagram which shows one structural example of the analysis part of the quadrupole type | mold mass spectrometer of this invention. It is a conceptual diagram which shows the conventional quadrupole-type mass spectrometer. It is a conceptual diagram which shows an example of the analysis part of the conventional quadrupole-type mass spectrometer.

Explanation of symbols

1 source oscillator,
2 High frequency transformer drive circuit,
3 High frequency transformer,
4 Virtual grounding capacitor,
5 negative U voltage source,
6 Positive U voltage source,
7 Quadrupole,
8 Variable capacitors,
9 Stabilized voltage source,
10 Metal shield,
11 fans,
12 Heating means (heater),
13 Current detector,
14 Power regulator,
15 heater drive circuit,
21 quadrupole mass spectrometer,
22 Vacuum chamber,
23 ion source,
24 Analysis Department,
25 detector,
26 Exhaust device.

Claims (3)

A multipole, an oscillation circuit that oscillates a high-frequency signal having 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 the multipole A multipole type having a drive circuit having a DC power source for superimposing positive and negative DC voltages on each of the two secondary windings of the high frequency transformer, and a stabilized voltage source for supplying power to the high frequency transformer drive circuit a mass spectrometer, in a metallic shield the air-cooling fan mounted on one end face for cooling the interior, and the high-frequency transformer, and the high frequency transformer drive circuit, a heater and a heating means for heating the interior , a current detector is disposed a heater driving circuit, and for detecting the current I supplied to the high frequency transformer drive circuit from the regulated voltage source, ; And a power regulator, the heater is turned coulometric P _H calculated based on the detected current from the I (2) equation, multipole, characterized in that it put into the heater to the stabilized voltage source as a power source Mass spectrometer.
P _H = V · (1−η) · (Imax−I) (2)

P _H: heater input power

V: Stabilized voltage source voltage

η: Conversion efficiency
Imax: detection current corresponding to the maximum mass number to be measured

I: Detection current
2. The multipole mass spectrometer according to claim 1, wherein the heat generating unit is disposed upstream of the high-frequency transformer with respect to an air flow formed by the air-cooling fan . The multipole mass spectrometer according to claim 2 , wherein the heater is mounted on a straight line connecting the high-frequency transformer and the air-cooling fan .

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