JPS625550A - Quadrupole type mass spectrometer - Google Patents

Abstract

PURPOSE:To obtain high accuracy lineariyty to make mass scanning over the whole region of mass number possible by generating d.c. voltage applied to quadrupoles by superimposing it on high frequency voltage by detecting the partial voltage of the high frequency voltage. CONSTITUTION:The high frequency voltage from a high frequency oscillator 7 is applied to quadrupoles 1-4 of a quadrupole type mass spectrometer through a resonance circuit of inductance and synthetic equivalent capacities 9 and 10. the high frequency voltage is converted into d.c. voltage by a detection circuit Q and the d.c. voltage is applied to the quadrupoles by superimposing it on the high frequency voltage through a choke CH2. The detection circuit Q finds the difference between partial voltage of the high frequency produced by capacitors C1 and C2 and detection output voltage with a comparator A and amplifies it, then outputs the voltage obtained to a peak hold capacitor C3 through a diode D1 to obtain a detection output. The d.c. voltage having good linearity can be obtained to perform mass scanning in spite of small high frequency signal.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to improvements in quadrupole mass spectrometers.

(Prior art and its problems) A quadrupole mass spectrometer is a quadrupole mass spectrometer, as shown in FIG. A voltage of +U+Vc-O5ωt is applied to 1 and 3, and -U -V cos is applied to the other opposing electrode pair 2 and 4.
By applying a voltage ωt, among the ions that are ionized by an ion source (not shown) and incident on this quadrupole section, the mass pair determined by the DC voltage U, high-frequency voltage peak value V, and angular frequency ω is determined. Only ions having a charge ratio m/z are made to draw a stable trajectory and pass through the quadrupole analysis section, and are detected by an ion collector at the exit of the quadrupole analysis section.

Here, the mass scanning of the ions to be detected is carried out while keeping the ratio U/V of the DC voltage U and the high-frequency voltage peak value (■) constant. Alternatively, this can be done by changing the angular frequency ω.

Figure 2 shows a conventional quadruple transverse electric field power supply in a quadruple model mass spectrometer that performs the above-mentioned mass scan by varying U (and therefore V) while keeping U/V and ω constant. This is an example electric circuit.

To explain FIG. 2, when a reference voltage Vref (generally a sweep voltage) corresponding to the scanning mass number is outputted from the reference signal generator 5, the angular frequency ω
The high frequency generator 7 is controlled, and its output high frequency voltage is input to the primary winding of the high frequency transformer 8. A resonant circuit is formed by the inductance of the secondary winding of the high-frequency transformer 8, and the capacitors 9 and 10, which are synthetic equivalent capacitances such as the tuning capacitor, the balance capacitor, and the capacitance between the quadrupole 1, 2, and 3.4. is formed in the secondary winding of the high frequency transformer 8, and the high frequency voltage +Vcosωt (the negative side is -Vco
sωt (hereinafter, the negative side is shown in parentheses) is induced and applied to the quadrupole electrode 1.3 (2, 4) via the DC blocking capacitors C, (C4').

On the other hand, the high frequency divided voltage divided from the voltage dividing point P (P') of the secondary winding of the high frequency transformer 8 is transferred to the rectifying element D- (D2'
), resistor R3 (R3') and capacitor C3 (C,
' ) and a rectifier circuit consisting of DC voltage +U (-
U), and this DC voltage is passed through the high frequency blocking choke C.
Quadrupole electrode 1.3 (2,
4) and the high frequency voltage +Vcosωt(-V
cosωt) and quadrupole electrode 1.3(2,4)
A superimposed voltage of +U+Vcosωt (-U −Vcosωt) is applied to. Here, the DC voltage U is applied to the error amplifier 6 and compared with the reference voltage Vref to control the high frequency generator 7, thereby maintaining the above-mentioned U/V in a constant relationship.

However, due to the power supply circuit as described above, the high frequency voltage V
Even when trying to accurately detect cosωt, a diode generally has a curved part with a large bend in its forward characteristics, and the characteristics are greatly affected by temperature, so the linearity of detection is poor and unstable. be. Even if a DC detector for general communications with relatively good linearity is used, there is also a curved portion of the forward characteristic according to the 3/2 law, and the linearity of detection is still poor.

Therefore, in the circuit shown in Fig. 2, it is not possible to keep the U/V constant and to keep the resolution and transmittance constant over a wide scanning range, and it is not possible to maintain a constant resolution and transmittance over a wide scanning range. Accuracy cannot be expected.

In order to eliminate this drawback, various methods have been devised and tried over the past ten years, including those in the following publications.

Special Publication No. 45-26679 (quadruple model mass spectrometer) uses the synchronous rectification method.

Special Publication No. 47-4588 (Power supply for quadruple seed mass spectrometer)
Here is a method that keeps the operating point of the rectifier constant.

Special Publication No. 47-18191 (quadruple horizontal power supply for mass spectrometry) uses a DC feedback method.

Special Publication No. 47-32783 (quadruple model mass spectrometry) uses a separate rectifier for correction.

However, none of the systems disclosed in the above-mentioned publications are currently commercially available, and the circuit shown in FIG. 3 is currently commonly used.

To explain FIG. 3, the reference signal generator 5 generates the reference voltage V.
ref is output, the high frequency generator 7 is controlled via the error amplifier 6, and the high frequency voltage generated at 2\ is input to the primary winding of the high frequency transformer 8'. High frequency transformer 8
A high frequency voltage Vcosωt (-Vcosωt) is induced by the resonant circuit of the inductance of the secondary winding 1 and the capacitors 9 and 10, which are the combined equivalent capacitance of various capacitances. On the other hand, voltage dividing capacitor C, c2 (c1', c2')
, DC detector D3 (D3') and resistor R4 (R4')
The peak value V dat of the high frequency voltage detected by the detection circuit consisting of is inputted to the error amplifier 6 on the one hand and compared with the reference voltage Vref to control the high frequency generator 7, and on the other hand the DC amplifier 11 ( 12) and generates a DC voltage U (-U), which is applied to the high frequency blocking choke CH.
2(CH,'), and a voltage element U+Vcosωt is applied to the quadrupole electrode 1.3 (2,4).
(−U−Vcosωt) is applied. However, even with this circuit, the detection characteristics of the rectifier need to be corrected, and when trying to accurately measure a wide area including low mass areas, it is necessary to add a nonlinear circuit somewhere in the system to correct it. There is.

FIG. 4, FIG. 5, and FIG. 6 are all examples of currently used correction circuits.

FIG. 4 shows a correction circuit inserted in the section 21 of FIG. 3, which utilizes the reference voltage Vref. VRI is a variable resistor for high mass range correction. Variable resistor VR2 and transistor Q
1 forms a low quality range correction circuit.

FIG. 5 shows a correction circuit inserted in the section 22 of FIG. 3, which also uses the reference voltage Vref. VRl is a variable resistance for high mass range correction. Al, A2, A3. A low quality range correction circuit is carefully constructed using an A4 operational amplifier.

In FIG. 6, a low-quality voltage range correction circuit is inserted into the output section P3 of the DC voltage ±U generator.

As is clear from the above examples and descriptions, in the quadruple species mass spectrometer, especially when performing mass spectrometry on ions with low mass numbers,
Although a well-adjusted, low-value superimposed voltage is required, the nonlinearity of high-frequency voltage detection that inevitably exists in the low-voltage region poses a major obstacle when analyzing this low mass number. arise.

Furthermore, the fact that this nonlinear characteristic changes unstably depending on the ambient temperature and filament temperature makes the analysis error extremely large. Therefore, a solution to this problem has been strongly desired.

(Objective of the Invention) The present invention is a long-life semiconductor device that is stable against temperature, has good detection characteristics even for small high-frequency signals, and can detect high-frequency waves with good linearity over a wide operating range. The objective is to provide a quadruple seed mass spectrometer equipped with a quadruple transverse electric field power source with high frequency detection capability.

(Structure of the Invention) The present invention provides quadruple species mass spectrometry in which mass spectrometry is performed by applying a superimposed voltage of a high frequency voltage and a direct current voltage to a quadrupole, and causing ions to enter an electric field constituted by the quadrupole. In total,
The DC voltage is generated by detecting a divided voltage of the high frequency voltage, and the generating device includes a voltage obtained by amplifying the difference between the divided voltage and the detected output voltage. The above object is achieved by a quadruple seed mass spectrometer equipped with a high frequency detection means that applies the detected output voltage via a diode to a circuit connected in parallel with a capacitor and a resistor.

(Example) The present invention will be explained in detail below based on the drawings.

FIG. 1a is a diagram showing only the high frequency detection circuit constituting the main part of an embodiment of the quadruple seed mass spectrometer of the present invention. The voltage is divided by 1 voltage dividing capacitors C, , C,. R□ is resistance. The high frequency voltage obtained by voltage division is input to the non-inverting input terminal of comparator A, that is, the (+) terminal in the figure. The output terminal of comparator A is connected to peak value hold capacitor C1 via diode D□,
The capacitor C1 is first charged with the peak value of the divided voltage and outputted as the detected output voltage Vdet. However, the detected output voltage V dat is input to the inverting input terminal of the comparator A, that is, the (-) terminal in the figure, so that the difference from the above-mentioned divided voltage value is amplified by the comparator A. The charge charged in the capacitor C1 is discharged in such a way that the discharge time constant is sufficiently long with respect to the period of the input high-frequency voltage and sufficiently short with respect to the ion mass number sweep speed. A resistor R2 is connected in parallel to the capacitor C3. When the high frequency detection circuit of the quadruple seed mass spectrometer is formed as described above, detection with good linearity can be performed even for a small input high frequency voltage. Experiments have revealed that linearity is better when the amplification factor of amplifier A is higher and when the high frequency characteristics are better. This is theoretically possible.

FIG. 1 is a circuit diagram of a quadruple transverse electric field power source of a quadruple seed mass spectrometer of the present invention, which is configured to include the high frequency detection circuit Q of FIG. 1a described above. The configuration of each part other than the high frequency detection circuit section is the same as the conventional circuit shown in FIG. 3. The UZV ratio retention characteristic of this quadruple transverse electric field power supply shown in Figure 1 is extremely excellent.
The above-mentioned section 4.5 used in the conventional power supply circuit of FIG.
The correction circuit shown in Figure 6 is no longer necessary, and it is now possible to perform high-precision mass scanning over the entire range from low mass range to high mass range, which was previously impossible, without any correction at all. Ta.

To explain by giving a specific example for comparison, in Figure 3 C□,
When C7 is appropriately selected and a two-pole detector 6AL5 is used, the plate reverse voltage of this detector is 330V, and Vdet and power can be detected and used up to a maximum of 165V. In order to improve linearity, we will detect this maximum voltage, divide it, and use it in the next stage circuit.If we calculate the ratio of the nonlinear part in the maximum voltage, the nonlinear part of the detector tube will be Since it is about 0°7v, 0.7/165=0.0
042, that is, a nonlinear portion occurs in a portion of 0.42% on the smaller side of the detection voltage, and accurate detection becomes impossible in this portion.

On the other hand, according to the circuit shown in FIG. 1 of the present invention, even if C1°C2 is selected appropriately and the maximum value of the detected output is selected to be 2V, which is quite low, the comparator A with a maximum differential input discrimination sensitivity of about 1mV.
If you use , the ratio of non-linear part is 1 x 10-3/2
=0. OOO5, that is, 0.05% of the smaller detection voltage
Only the portion becomes non-linear, and the accuracy can be improved by about one order of magnitude.

In this example, a peak value hold circuit is formed using a comparator, but this does not have any limiting meaning; the difference between the input high-frequency voltage and the detected output voltage is amplified, and the detected output is Many other variations of the circuit for charging the capacitor are possible.

(Effects of the Invention) According to the quadruple model mass spectrometer of the present invention, mass scanning over the entire range of mass numbers is possible with highly accurate linearity.

[Brief explanation of drawings]

FIG. 1a is a diagram of a high frequency detection circuit of an embodiment of the quadruple model mass spectrometer of the present invention. Figure 1 is a circuit diagram of the quadruple transverse electric field power supply. FIG. 2 is a similar diagram of a conventional quadruple model mass spectrometer. FIG. 3 is a similar diagram of another conventional quadruple model mass spectrometer. FIG. 4.5.6 is a diagram of a nonlinearity correction circuit combined with the circuit of FIG. 3. 1 , 2 , 3 , 4-------1------- Quadrupole electrode 5-------------------
1. Reference signal generator 6--
−−−−−−Error amplifier 7−−−−−−−−−−−−−
-----------High frequency generator 8, 8' ---
---------------1~--High frequency transformer 9, 1
0---------------Capacitor 11
, 12--------------One DC amplifier A
−−−−−−−−−−−−−−−−−−−−1 comparator A+A! r A 3 t A 4------
--One operational amplifier C□+ct',c,,c,' +-
＋＋− Voltage dividing capacitor C3−−−−−−−−−−−
-------1--Peak hold capacitor C4, C4' --------1 DC blocking capacitor CH1, CH', CH2, CH2'
-----High frequency blocking choke D l l D 29 D Z '-"----"'-
-----Diode D 3. D,' -----------
--------One DC detector R0, R2, R,, R,'
, R4, R4' --- One resistance VR□, VR, ---
−−−−−−−−−−1 variable resistor Q, −−−−−−−−
-------------Transistor; I-1 diagram
a Figure 1 b Figure 2 Figure O 4. Zukan - 15v

Claims (1)

[Claims] In a quadrupole mass spectrometer that performs mass spectrometry by applying a superimposed voltage of a high frequency voltage and a direct current voltage to a quadrupole and causing ions to enter an electric field constituted by the quadrupole, the direct current voltage is It is generated by detecting a divided voltage of a voltage, and the generating device amplifies the voltage difference between the divided voltage and the detected output voltage, and the amplified voltage is passed through a diode. , a quadrupole mass spectrometer comprising: high frequency detection means for applying the detected output voltage to a parallel connected circuit of a capacitor and a resistor holding the detected output voltage.