JPS6041824B2 - Gas chromatograph mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas chromatograph mass spectrometer, and more particularly to a gas chromatograph mass spectrometer capable of detecting a solvent peak of a sample containing a solvent.

Generally, a gas chromatograph mass spectrometer has a configuration as shown in FIG.

That is, a pre-cut valve 4 is connected to the column 3 which is connected to the injection 2. The injection 2 and column 3 constitute a gas chromatograph 1. In addition, on the outlet side of the pre-cut valve 4, ion tubes L and ι are connected via a molecular separator 7.
, 1, ゜, j ''L ゛jl6,゛ An exhaust device 5 is connected to the other outlet of the tube 4, and only the solvent of the sample containing the solvent discharged from the column 3 is removed from the exhaust device 5.
It is discharged from the pre-cut valve by
Further, a rotary pump 6 is connected to the molecular separator 7. This molecular separator 7 is used to discharge the carrier gas from the gas chromatograph 1, and allows only the sample to be sent to the ion source 8. The ion source 8 has an ion ejection port, and ionizes the sample and outputs it from the ejection port. Ions converted into an ion beam by the ion source 8 are sent into a magnetic field 9 . This magnetic field 9 is a place where a magnetic field is applied to the ions, and the ions are separated by mass and sent to the detector 10.
It is sent to Measurement of a sample using the chromatograph mass spectrometer configured as described above is performed as follows.

That is, when a sample to be measured (including a solvent) is injected 1 into the injection port 2 of the gas chromatograph 1, the injected sample is separated through the column 3 of the gas chromatograph 1 and sent to the pre-cut valve 4. In this pre-cut valve 4, when the valve on the exhaust device 5 side is open, the valve on the molecular separator 7 side is closed, and conversely, when the valve on the molecular separator 7 side is open, the valve on the exhaust device 5 side is closed. It is closed. If the pre-cut valve 4 is currently closed, that is, if the valve on the molecular separator 7 side is closed, all the sample is exhausted by the exhaust device 5, and if the pre-cut valve 4 is open, that is, the valve on the molecular separator 7 side is closed. If it is open, the sample is sent to the molecular separator 7 without being evacuated. In this molecular separator 7, helium gas used as a carrier gas for the gas chromatograph 1 is evacuated by a rotary pump 6, and only the sample is allowed to reach the ion source 8. The sample that has entered the ion source 8 in this manner is ionized and further emitted from the ion source 8 as an ion beam. The mass of this ion beam is dispersed by the magnetic field 9, and depending on the magnetic field strength, it is detected whether only ions satisfy the following formula: M: mass number e: electric charge (electronic charge) K: constant B: magnetic field strength V: ion acceleration voltage Captured by vessel 10,
A mass spectrum is obtained.

It is well known that in normal measurements, the ion accelerating voltage V is kept constant and the magnetic field strength B is varied to obtain a mass spectrum.

As mentioned above, if the solvent in the sample is evacuated by the exhaust device 5, the amount of solvent is extremely larger than the amount of the sample to be measured, so if the solvent is put into the ion source 8 without being evacuated, the ions will This is because it causes contamination of the source 8, which leads to a decrease in resolution and sensitivity of the mass spectrometer.

In this method of separating the solvent using the pre-cut valve 4, the solvent is usually separated by the column 3 of the chromatograph 1 faster than the sample and reaches the pre-cut valve 4. Therefore, the pre-cut valve 4 is initially closed (the molecular separator 7 side is closed), and after the solvent has been exhausted through the exhaust device 5, it is opened (the exhaust device 5 side is closed and the molecular separator 7 side is opened). into the ion source 8. Such solvent evacuation is performed by detecting the degree of vacuum at the pre-cut valve exhaust part of the chromatograph mass spectrometer and driving the pre-cut valve and exhaust device. The detection of the degree of vacuum and the operation of the pre-cut valve are shown in Figure 2. This is done by a circuit as shown.

Normally, the pre-cut valve 4 is closed (the molecular separator 7 side is closed and the exhaust device 5 side is open), and the configuration is such that all the effluent from the column 3 of the chromatograph 1 is exhausted by the exhaust device 5. . Therefore, when a sample 3 containing a solvent is injected into the gas chromatograph 1, it passes through the column 3 of the chromatograph 1, is separated from the sample components, and becomes the solvent that flows out from the column 3 of the gas chromatograph 1 first. Therefore, the degree of vacuum in the exhaust pipe between the pre-cut valve 4 and the exhaust device 5, which was initially under vacuum, decreases. A vacuum measuring element 11 for detecting the degree of vacuum is installed in the exhaust pipe between the pre-cut valve 4 and the exhaust device 5 shown in FIG. This vacuum measuring element 11 has a vacuum measuring circuit 12.
The negative input terminal of a differential amplifier 14 is connected to the output terminal of the vacuum measurement circuit 12 via a resistor R1. Further, the positive input terminal of this differential amplifier 14 is grounded, and the threshold value setting variable resistor 13 is connected to the negative input terminal via a resistor R4. Further, the negative input terminal of a differential amplifier 15 is connected to the output terminal of the differential amplifier 14 via a resistor R3. A negative feedback loop is formed in this differential amplifier 14 via a resistor R2. Further, the positive input terminal of the differential amplifier 15 is grounded, and the output terminal is connected to the negative input terminal of the differential amplifier 15 via a resistor R5. Also, a resistor R is connected to the output terminal of this differential amplifier 15.
The input terminal of the timer 16 is connected through the terminal 5. Further, the anode of the diode D1 and the cathode of the diode D2 are connected to the connection point between the resistor R6 and the input terminal of the timer 16, and the cathode of the diode D1 is connected to the (+
)5■ is always applied, and the anode of diode D2 is grounded. Further, the output terminal of the timer 16 is connected to the base of a transistor 1'r1 via an inverter 17, and the emitter of this transistor Trl is grounded. Further, a pre-cut valve 4 which is an electromagnetically driven valve is connected to the collector of this transistor Trl, and a voltage of (+) 24 V is always applied to this pre-cut valve 4. The input terminal and output terminal of this pre-cut valve 4 are bridged by a diode D3. With this configuration, the degree of vacuum is detected by the vacuum measurement element 11, amplified by the vacuum measurement circuit 12, and input to the differential amplifier 14.

The output of this differential amplifier 14 is normally a positive value, but when the output of the vacuum measuring circuit 12 as shown in FIG. 3A exceeds a certain threshold value Vref, it is reversed to a negative output. The threshold value at which this output is inverted is set by a threshold setting variable resistor 13. When the output of the differential amplifier 14 is now inverted from positive to negative, the output of the differential amplifier 15 is a signal inverted from negative to positive, and the diode Dl,
D2 causes a signal as shown in FIG. 3B, and timer 1
6 is input. The timer 16 is driven by the signal applied to the timer 16. This timer 16 always outputs a high level signal, and when this timer 16 is activated, it has a function of lowering the output that was at high level to low level after a predetermined period of time has elapsed as shown in FIG. 3C. It is something that you have. When the output of the timer 16 becomes low level, the inverter 17 supplies a high level signal to the base of the transistor Trl, turning on the transistor Trl. By turning on this Trl, the pre-cut valve 4 is driven, and the pre-cut valve 4 is opened as shown in FIG. 3D. Further, after a certain period of time has elapsed as shown in FIG. 3C, the low level output signal from the timer 16 becomes high level again, and the pre-cut valve 4 is closed as shown in FIG. 3D. Here Tl,
The time T2 is arbitrarily set by the timer 16, and the time T1 indicates the time during which the solvent is flowing out from the column 3 of the chromatograph 1, and the time T2 is the time during which the sample is flowing out. are shown respectively. In such conventional chromatograph mass spectrometers, changing the column temperature of the gas chromatograph or changing the carrier gas flow rate changes the degree of vacuum in the exhaust pipe between the pre-cut valve and the exhaust device. , the threshold value must be changed each time by operating a threshold setting variable resistor, and especially since measurements are often made by changing the column temperature of a gas chromatograph, it is necessary to change the threshold value each time. This has the disadvantage that it requires setting.

An object of the present invention is to provide a gas chromatograph mass spectrometer that can accurately exhaust and separate a solvent even if the degree of vacuum changes by changing the column temperature of the gas chromatograph, changing the carrier gas flow rate, etc. be.

Examples of the present invention will be described below.

FIG. 4 shows a drive circuit for a pre-cut valve showing an embodiment of the gas chromatograph mass spectrometer according to the present invention.

In the drawings, the same reference numerals as in the conventional example shown in FIG. 2 indicate the same parts and have the same functions.

This embodiment differs from the conventional example shown in FIG. 2 in that a differentiating circuit 20 and an integrating circuit 30 are used in place of the differential amplifiers 14 and 15 of the conventional example shown in FIG. That is, in FIG. 4, a capacitor C1 is connected to the output end of the vacuum measuring circuit 12 via a resistor R1, and the negative input terminal of an operational amplifier 18 is connected to the other end of the capacitor C1. The positive input terminal of this operational amplifier 18 is grounded, and the negative input terminal is connected to the output terminal via a resistor R2.
A differentiating circuit 20 is constituted by a capacitor C1, a resistor R2, and an operational amplifier 18. Furthermore, this operational amplifier 1
8 is connected to the negative input terminal of an operational amplifier 19 via a resistor R3, and the positive input terminal of this operational amplifier 19 is grounded. This resistance RlOl capacitor C
2. The operational amplifier 19 constitutes an integrating circuit 30. Further, at the output terminal of this operational amplifier 19, there is a capacitor C2 and a resistor. is connected and this capacitor C2
and the operational amplifier 19 of the integrating circuit 30 at the other end of the resistor RlO.
The negative input terminal of is connected. Also, this integration circuit 30
The input terminal of the timer 16 is connected to the output terminal of the operational amplifier 19 via a resistor R6, and the anode of the diode D1 and the cathode of the diode D2 are connected to the connection between the resistor R6 and the input terminal of the timer 16. The cathode of the diode D1 is always supplied with a voltage of (+)5cm, and the anode of the diode D2 is grounded. In addition, the inverter 17 is connected to the output terminal of the timer 16.
The base of the transistor Trl is grounded via. The terminal of this transistor Trl is grounded, and the pre-cut valve 4 is connected to the collector.
This pre-cut valve 4 is bridged by a diode D3. Also, this pre-cut valve 4 always has (+
)24■ voltage is applied. The output VOd of the differential circuit 20 configured in this way is Vi: vacuum measurement circuit 12
If it is an ideal differentiator circuit expressed by the output voltage of , the frequency gain characteristic of this circuit will be as shown in FIG.

In addition, when the signal from the vacuum measurement circuit 12 indicating the change in vacuum level due to the solvent changes as shown in Figure 6, the height from the baseline to the peak top is very small, and the sample injection into the gas chromatograph 1 is 1 μ' to 2 μl, which is several times. Millivolt (approx. 1
7T1. v~2rn. ■), the peak width on the baseline is about 0.5 to 1. @ (this varies depending on the temperature of the gas chromatograph column). This solvent peak is shown in the frequency and gain characteristics of the differential circuit shown in Figure 5, so that the capacitor C is somewhat higher than the frequency of FHd.
1. Resistor R2 is set. Figure 6 shows the change in the degree of vacuum that occurs when the temperature of column 3 of gas chromatograph 1 is changed, and the frequency of this change is F
Since it is sufficiently lower than Hd, it does not appear as output ■0d. Next is the output ■ of the integrating circuit 30.

, and the frequency gain characteristics of the integrating circuit in this case are shown in FIG.

■As can be seen from equation (3). The output of , is the differentiator circuit 2
0 output voltage■. d1 time t1 resistance RlOl capacitor C
Determined by 2. Capacitor C2 and resistor RlO are set so that the solvent peak signal output from the differentiating circuit 20 has a frequency somewhat lower than the frequency of FHi shown in FIG. ×
The resistor RlOl capacitor C2 is set so that the output voltage for driving the timer 16 is determined by 0.5 seconds to 112×1 seconds). By doing this, output signals of higher frequencies than FH, such as signals such as noise, do not appear as the output (2) of this integrating circuit 30, and only signals below FHi are detected. When actually measured in this manner, the only signal lower than FHi is the solvent peak signal. In this way, by connecting the differentiating circuit 20 and the integrating circuit 30 in series and operating the timer 16, fluctuations in the baseline due to column temperature changes and noise can be ignored, and only the solvent peak can be detected without error. The timer 16 can be started.

Therefore, the pre-cut valve 4 can also be opened and closed without malfunction. Another embodiment of the invention is shown in FIG. In this embodiment, the differential circuit and the integral circuit are provided separately, whereas the embodiment shown in FIG. 4 is provided with separate circuits. That is, operational amplifier 40
The raw input terminal of the operational amplifier 20 is grounded, a resistor Rll is connected to the negative input terminal via a capacitor C3, and a parallel circuit of a resistor Rl2 and a capacitor C4 is connected between the output terminal and the negative input terminal of the operational amplifier 20. It is cross-linked. FIG. 9 shows the frequency and gain characteristics of the circuit shown in FIG. 8, which is a combination of such a differentiating circuit and an integrating circuit. At this time, FHD(5fHi) is, and the peak signal due to the solvent is set to fall between this FHD(5fHi).

The width of FHD and FH can be set to the width of FHD-FHi that satisfies the gas chromatograph usage conditions. In addition, in the circuit shown in the illustrated embodiment in FIG. 4 and the illustrated embodiment in FIG. 8, if the fluctuation per unit time of the baseline shown in FIG. If a circuit for setting a threshold value is provided, malfunctions can be prevented here. Further, in this embodiment, although the purpose is to open and close the pre-cut valve 4, the purpose is not limited to this, but it is also effective as a temperature increase start signal for the open temperature of the column 3 of the gas chromatograph 1.

Therefore, by simply injecting the sample, heating, evacuation of the solvent, and introduction of the sample into the ion source 8 can all be automated.
Therefore, according to the embodiment of the present invention, a solvent peak can be detected even if the column temperature setting or the carrier gas flow rate is changed.

Further, according to this embodiment, it is possible to start raising the temperature of the gas chromatograph, exhaust the solvent, and inject the sample into the ion source by simply injecting the sample.

As explained above, according to the present invention, even if the degree of vacuum changes, the solvent can be separated and discarded accurately by changing the column temperature of the gas chromatograph, changing the carrier gas flow rate, etc.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a gas chromatograph mass spectrometer, Figure 2 is a pre-cut valve drive circuit of a conventional chromatograph mass spectrometer, Figure 3 is a time chart of the conventional example shown in Figure 2, and Figure 4 is the invention of the present invention. 5 is a diagram showing the frequency-gain characteristics of the differential circuit shown in FIG. 4, and FIG. 6 is a diagram showing the time characteristics of the voltage corresponding to the amount of carrier gas and sample. 7 is a frequency-gain characteristic diagram of the integrating circuit shown in FIG. 4, FIG. 8 is a circuit diagram showing another embodiment of the present invention, and FIG.
FIG. 3 is a frequency gain characteristic diagram of the illustrated embodiment. 1... Gas chromatograph, 2... Injection, 3... Column, 4...
・Pre-cut valve, 5... Exhaust device, 11.
... Vacuum measurement element, 12 ... Vacuum measurement circuit, 16 ... Timer, 17 ... Inverter, 1
8, 19, 40... operational amplifier, 20...
Differential circuit, 30...Integrator circuit.

Claims (1)

[Claims] 1 In a gas chromatograph/mass spectrometer that performs mass analysis on a sample component in the effluent from a gas chromatograph column after separating the solvent therein using a pre-cut valve and an exhaust device, there is a gap between the outlet of the column and the exhaust device. a first means for detecting the degree of vacuum which changes over time depending on the outflow state of the solvent; and a second means for detecting the amount of change per unit time in the value detected by the first means. A gas chromatograph mass spectrometer characterized in that the precut valve is opened and closed based on the output from the second means.