JP2000036280A - Ionization device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily execute adjustment of a reaction gas introduction quantity of a small flow rate. SOLUTION: A split passage 28 is formed by branching on the upper stream of a resistor tube 22, and flow control valves 27, 29 are installed on the upstream and the split passage 28 respectively. The second flow control valve 29 controls a split flow rate so that a detected gas pressure of a pressure gauge 24 will agree with a target pressure P1 calculated corresponding to a reaction gas introduction quantity into an ionization chamber 11. On the other hand, the first flow control valve 27 sends the reaction gas of a flow rate determined by adding a sufficient split flow rate with the reaction gas introduction quantity. As a result, the reaction gas of a desired introduction quantity f1 flows in the resistor tube 22 and the reaction gas of a most residual flow rate f2 flows in the split passage 28, and as soon as the target pressure P1 is modified, the introduction quantity is changed followingly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ionization apparatus used in a mass spectrometer and the like, and more particularly, to a reaction gas introduction section for introducing a reaction gas into an ionization chamber during chemical ionization.

[0002]

2. Description of the Related Art In a mass spectrometer, gaseous sample molecules are ionized by an ion source, and the ions are converted into a mass number (mass m / m).
It has a configuration in which detection is performed separately according to the number of charges z). Various methods, such as an electron impact method and a surface ionization method, are used for ionizing a sample molecule.

FIG. 2 shows a chemical ionization method (hereinafter referred to as “CI = Chemical Ionization”) which is one method of ionization.
FIG. 1 is a configuration diagram of a mass spectrometer using a conventional ionization device according to the present invention. The ionization chamber 11, the ion lens 12, the quadrupole filter 13, the detector 14, and the like are arranged in a vacuum housing 10, and the vacuum housing 10 is maintained in a high vacuum state by a vacuum pump 15. A sample gas flow path 20 for introducing a sample gas and a reaction gas flow path 21 for introducing a reaction gas such as methane and isobutane are introduced into the ionization chamber 11.
And are connected.

[0004] In the above-mentioned mass spectrometer, a sample containing sample molecules is used.
The source gas passes through the sample gas flow path 20 and the reaction gas
The gas is introduced into the ionization chamber 11 through the reaction gas channel 21.
The reaction gas molecules contained in the reaction gas in the ionization chamber 11
Collision with the electron flow (indicated by e in FIG. 2) causes the electrons to
When a specific ion (eg, CH₅ ⁺, (CH ₃)
₃C⁺Etc.) occur. These reaction ions are sample molecules
And the sample molecules are ionized as a result.
The sample ions generated in the ionization chamber 11 are
1 and the ion voltage to which an appropriate voltage is applied
Quadrupole filter after being converged and accelerated by lens 12
13 is introduced. DC voltage is applied to the quadrupole filter 13.
A voltage superimposed on the AC voltage is applied, and the voltage
Only ions with a specific mass number depending on the
The light passes through the filter 13 and reaches the detector 14.

[0005] In such CI, the generated sample ions do not have excessive internal energy, and thus are less likely to be cleaved. Therefore, an ion very close to the mass of the original sample molecule can be detected by the detector 14, which is extremely useful for estimating the molecular weight of the sample molecule.

Generally, the flow rate of the reaction gas introduced into the ionization chamber 11 is as small as 1 cc / min or less. For this reason, as shown in FIG. 2, the conventional reaction gas flow path 21 has a resistance pipe 22 having a large flow resistance in order from the downstream side.
(For example, a thin tube having a diameter of several tens μm and a length of several meters), a solenoid valve 23,
The pressure gauge 24 and the pressure regulating valve 25 are provided. When the reaction gas flows through the resistance tube 22 by opening the solenoid valve 23, the flow rate of the reaction gas depends on the pressure P on the inlet side of the resistance tube 22.
1, the outlet side pressure P2, the flow path resistance of the resistance tube 22, the viscosity coefficient of the reaction gas, and the like. Of these parameters, other parameters except the inlet pressure P1 are determined values.
By adjusting the (detected gas pressure at the pressure gauge 24), the flow rate of the reaction gas introduced into the ionization chamber 11 can be controlled.

[0007]

However, this conventional configuration has the following problems. First, since there is a large flow resistance between the pressure regulating valve 25 and the outlet of the resistance pipe 22, the gas pressure does not immediately decrease even if an attempt is made to decrease the flow rate by lowering the inlet pressure P1. It takes a comparatively long time for the constant to stabilize. Secondly, as described above, since the amount of introduced reactant gas is extremely small, an electric open / close control type valve which can perform only relatively rough control is used as the pressure regulating valve 2.
5 is difficult to use. Third, since the flow rate of the reaction gas is small, the influence of contamination in the pipe of the reaction gas flow path 21 becomes relatively large, and the pipe is always kept clean for high-precision analysis. I have to keep it. The present invention has been made for the purpose of solving such various problems.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to an ionization apparatus for introducing a reaction gas into an ionization chamber to perform ionization, wherein: a) an outlet end is connected to the ionization chamber; A resistance pipe; b) a split flow path at an inlet end side of the resistance pipe for branching a reaction gas flowing from the upstream thereof; and c) a split flow path provided upstream of a branch point between the split flow path and the resistance pipe. Pressure detecting means; d) first flow rate adjusting means provided upstream of the pressure detecting means and adjusting the total flow rate of the reaction gas flowing through both the resistance tube and the split flow path to a predetermined flow rate; e) the split And a second flow rate adjusting means provided on the flow path and adjusting the split flow rate so that the value detected by the pressure detecting means becomes a predetermined value.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The amount of a reaction gas introduced into an ionization chamber through a resistance tube depends on the gas pressure in the ionization chamber on the outlet side of the resistance tube, the size of the resistance tube, the viscosity coefficient of the reaction gas, and the like. If known, it depends on the gas pressure at the resistance tube inlet side, that is, at the position where the pressure detecting means is provided. Therefore, when the desired reaction gas introduction amount is determined, the target pressure value on the resistance tube inlet side can be obtained by calculation. Therefore,
When this target pressure value is given to the second flow rate adjusting means, the second flow rate adjusting means adjusts the split flow rate so that the value detected by the pressure detecting means matches the target pressure value. On the other hand, the first flow rate adjusting means adjusts the passing flow rate so that the total flow rate is at least equal to the sum of at least the desired reaction gas introduction amount and a certain split flow rate that can be controlled by the second flow rate adjusting means. As a result, of the reaction gas that has passed through the first flow rate adjusting means, the desired reaction gas introduction amount flows toward the resistance tube side, and the remainder is discharged through the split flow path.

[0010]

In the ionization apparatus according to the present invention, when it is desired to reduce the reaction gas introduction amount, if the target pressure value is corrected downward, the degree of opening of the second flow rate adjusting means is increased and the split is increased. The flow rate increases. As a result, the flow rate of the reaction gas flowing to the resistance tube side quickly decreases. Therefore, unlike the conventional configuration, the response to the change in the flow rate of the reaction gas is extremely good.

In addition, even if the amount of the reaction gas introduced is very small, the flow rate of the reaction gas passing through the first and second flow rate adjusting means can be made much larger than the amount of the reaction gas introduced. Electrically controlled valves that can perform only rough control can be used for the first and second flow rate adjusting means. Furthermore, the flow rate of the reactant gas is large upstream from the branch point of the split flow path, and a part of the reactant gas flow is introduced into the ionization chamber. This contributes to improving the accuracy of the analysis.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the ionization apparatus according to the present invention will be described below with reference to FIG. FIG. 1 is a configuration diagram of the reaction gas flow path 21 in the ionization apparatus of the present embodiment. A pressure regulating valve 25, a flow meter 26, a first flow control valve 27, and a pressure gauge 24 are arranged from the upstream side of the reaction gas flow path 21. The flow path is a split flow path 28 and a resistance pipe at a branch point downstream of the pressure gauge 24. 22
And it is forked. A second flow control valve 29 is provided on the split flow path 28, and the end of the flow path is
1 connected. On the other hand, the outlet end of the resistance tube 22 is connected to the ionization chamber 11 via a three-way valve (3 port 2 position valve) 30.

The first flow control valve 27 is configured to automatically adjust the opening of the first flow control valve 27 so that the detection value of the flow meter 26 coincides with a target flow value given from the outside. On the other hand, the second flow control valve 29 is configured to automatically adjust the opening degree of the valve so that the detection value of the pressure gauge 24 matches a target pressure value given from outside. The control unit 32 includes a microcomputer and the like, and sends a target flow value to the first flow control valve 27 and a target pressure value to the second flow control valve 29.

First, the operation when introducing a reaction gas into the ionization chamber 11 in the above configuration will be described. In this case, the control unit 32 switches the three-way valve 30 to the connection state indicated by the dotted line in FIG. 1 to make the outlet end of the resistance tube 22 communicate with the ionization chamber 11.

For example, when a user inputs and sets a desired reaction gas introduction amount via an input unit (not shown), the control unit 32
Are the preset dimensions (inner diameter and length) of the resistance tube 22, the viscosity coefficient of the reaction gas, the ambient temperature of the resistance tube 22 (this may be an actually measured value or a set value), and the degree of vacuum in the ionization chamber 11. A predetermined calculation is performed using a known parameter such as (ie, gas pressure P2), and the inlet pressure P1 of the resistance tube 22 with respect to the desired reaction gas introduction amount is calculated. Then, it instructs the second flow control valve 29 using the inlet pressure P1 as a target pressure value. The second flow control valve 29 adjusts the flow rate of the reaction gas flowing through the split flow path 28 so that the detection value of the pressure gauge 24 becomes P1.

In general, in a flow control valve capable of electric opening and closing control, accurate control cannot be performed when the flow rate becomes lower than a minimum limit flow rate (for example, 1 cc / min). Therefore, the control unit 32
Instructs the first flow control valve 27 to set a value equal to or more than the flow rate obtained by adding the minimum limit flow rate to the above-described reaction gas introduction rate (for example, several cc / min) as the target flow rate value. The target flow rate value may be calculated by the control unit 32, or may be set by the user through the input unit. The first flow control valve 27 adjusts the opening of the valve so that the flow rate detected by the flow meter 26 becomes the target flow value. In addition, pressure regulating valve 2
Reference numeral 5 denotes an appropriate opening in advance so that a sufficient flow rate of the reaction gas flows through the first flow control valve 27.

When the reactant gas flows at a flow rate near the target flow rate, the inlet pressure of the resistance tube 22 becomes P as described above.
Since the second flow control valve 29 constantly adjusts the split flow rate so as to be 1, the desired introduction amount f1
Of the reaction gas flows, and most of the remaining
Thus, the gas is discharged from the exhaust duct 31 to the outside through the split flow path 28. The reaction gas passing through the resistance tube 22 is introduced into the ionization chamber 11 through the three-way valve 30,
Used for chemical ionization.

When it is not necessary to introduce the reaction gas into the ionization chamber 11, the control unit 32 switches the three-way valve 30 to the connection state indicated by the solid line in FIG. Then, the reactant gas flowing through the resistance tube 22 also merges with the reactant gas flowing through the split flow path 28 and is collectively discharged from the exhaust duct 31 to the outside. In this state, a predetermined flow rate of the reaction gas continues to flow through the resistance tube 22.
As long as the three-way valve 30 is switched to the connection state shown by the dotted line, the reaction gas is immediately introduced into the ionization chamber 11.
Therefore, this configuration also has an effect that the ionization by the electron impact method without introducing the reaction gas into the ionization chamber 11 and the chemical ionization or the negative chemical ionization that requires the reaction gas can be switched in a short time.

When it is not necessary to perform chemical ionization or negative chemical ionization as described above, the first and second flow control valves 27 and 29 are completely closed, and the three-way valve 30 is shown by a solid line in FIG. What is necessary is just to be in a connection state. Thereby, the reaction gas stops.

The above embodiment is merely an example, and it is apparent that modifications and changes can be made within the spirit of the present invention.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a reaction gas flow path in an ionization device of the present invention.

FIG. 2 is a configuration diagram of a conventional chemical ionization apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Ionization chamber 21 ... Reaction gas flow path 22 ... Resistance pipe 24 ... Pressure gauge 26 ... Flow meter 27 ... 1st flow control valve 28 ... Split flow path 29 ... 2nd flow control valve 30 ... Three way valve 32 ... Control part

Claims (1)

[Claims] 1. An ionization apparatus for introducing a reaction gas into an ionization chamber to perform ionization, comprising: a) a resistance tube having an outlet end connected to the ionization chamber; and b) an upstream end of the resistance tube at an inlet end side thereof. A split flow path for branching the flowing reaction gas, c) a pressure detection means provided upstream from a branch point between the split flow path and the resistance tube, and d) a pressure detection means provided upstream from the pressure detection means, First flow rate adjusting means for adjusting the total flow rate of the reaction gas flowing through both the resistance tube and the split flow path to a predetermined flow rate; e) provided on the split flow path, and a value detected by the pressure detecting means becomes a predetermined value. A second flow rate adjusting means for adjusting the split flow rate as described above.