JPH03226955A - Mass spectrometer - Google Patents

Abstract

PURPOSE:To halve the number of devices and parts of an exhaust system so as to reduce both the cost for maintenance of a mass spectrometer and the probability of trouble by attaching the suction opening of a main pump in such a manner as extending over spaces on both sides of a partition between an ion source and a mass spectrometry space. CONSTITUTION:A high vacuum pump 1 forms a pressure gradient in which pressure is heightened toward an exhaust opening 12 from a suction opening 11, while the pump has the action of preventing diffusion of exhaust gases in the direction perpendicular to the direction extending from the suction opening 1 to the exhaust opening 12 i.e., in the direction of the arrow A; when one main pump 1 is connected across an ion source 2 and a mass spectrometry space 3 diffusion of gases from the ion source 2 to the mass spectrometry space 3 through the main pump will not therefore occur even with different pressures on the ion source side and mass spectrometry space side of the suction opening 11 and each space is held at a pressure corresponding to the amount of gases supplied to the space. Therefore one set of exhaust device is enough and the number of parts of the pipe system is reduced so the cost of the exhaust system is reduced and also the probability of trouble is reduced together with the cost for maintenance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a mass spectrometer equipped with a chemical ionization source.

(Prior Art) Chemical ionization (CI) is often used because it provides information on the molecular weight of a sample. In the CI method, it is necessary to introduce a reactive gas into the ionization chamber of the ion source and maintain the interior of the ionization chamber at a relatively low degree of vacuum. Mass spectrometry spaces, on the other hand, require high vacuum. The ion source and mass analysis space are partitioned, and both spaces are connected by a small opening through which ions pass.

Since the ion source and the mass analysis space have different degrees of vacuum in this way, in conventional mass spectrometers using the Ct method, the ion source and the mass analysis space are connected to separate exhaust systems. For this reason, a main pump and an auxiliary pump are required for each of the ion source and the mass spectrometry space, which is expensive and requires a large number of devices and parts, such as pumps in the exhaust system (this makes maintenance troublesome and failures). There was a problem that the probability of

(Problems to be Solved by the Invention) The present invention aims to simplify the exhaust system of a mass spectrometer using the CI method and reduce the number of two parts of the exhaust system by half.

(Means for Solving the Problem) As shown in Fig. 1, the inlet port 11 of the main pump 1 is installed so as to span the ion source 2 and the mass spectrometry space 3, with the partition wall 4 as the boundary. Ta.

(Function) The main pump used in the mass spectrometer is a high vacuum pump, and the high vacuum pump uses some method to move the pump from the intake port to the exhaust port, from 11 to the exhaust port 12 in Fig. 1. It has the ability to form and maintain a pressure gradient that gradually increases.When the pressure at the exhaust port is constant,
The pressure at the intake port is the sum of the gas supplied from the outside to the space to which the exhaust port is connected, that is, the leak gas, and the reactant gas supplied in the case of a CI ion source. The inlet pressure of the main pump is higher in the C■ ion source than in the mass spectrometry space where there is only leakage.However, in a high vacuum pump, the pressure increases from the inlet to the exhaust port. On the other hand, as will be described in detail in the examples below, it has the effect of hindering the diffusion of exhaust gas in the direction perpendicular to the direction from the intake port to the exhaust port, that is, in the direction of arrow A in FIG. Therefore, when one main pump is connected across the ion source and mass analysis space as shown in Figure 1, even if the pressure is different between the ion source side and the mass analysis space side of the inlet, Gas does not diffuse from the ion source to the mass analysis space through the main pump, and each space is maintained at a pressure corresponding to the amount of gas supplied to each space.

(Example) FIG. 2 shows an example of the present invention. In the figure, 1 is the main pump, and a turbo molecular pump is used. Reference numeral 11 indicates an intake port of the main pump, and reference numeral 13 indicates a mounting flange provided around the intake port 11 of the main pump gauging. 12
is connected to an auxiliary rotary pump (not shown) at the exhaust port. 2 is an ion source space, 3 is a mass analysis space, and 4 is a partition wall that separates the rain space. There is a small hole 41 in the center of the partition wall 4.
The ions generated by the ion source 2 enter the mass spectrometry space through this small hole. The lower edge of the partition wall 4 extends to a point where it almost touches the end surface of the rotor 14 of the turbo-molecular pump 1, and the ion source space 2 and the mass analysis space 3 are connected to the small hole 4.
1 and a gap between the lower edge of the partition wall 4 and the upper end surface of the rotor 14 of the main pump, but since these small holes and gaps are small, gas does not flow from the ion source space 2 to the mass spectrometry space. The flow rate is extremely low, and the mass spectrometry space is kept at a high vacuum.

As shown in FIG. 3, the turbo-molecular pump has rotors R and stators S arranged alternately, each having a large number of radially cut slits G. The slit G is inclined with respect to the axial direction, and the direction of the inclination is opposite between the rotor and the stator. When the rotor rotates in the direction of arrow r, molecules traveling from the left side of the rotor at a speed in the direction of arrow m will hit the slit G of the rotor 1iIJ, but molecules in other directions and speeds will hit the wall of the slit. , cannot pass through the slit. Molecules coming from the right side of the rotor cannot pass through the slit because all molecules with any direction velocity hit the slit wall. Thus, molecules can pass through the rotor from left to right, but the resistance to passage from right to left is very high. The inclination of the slits in the stator is opposite to that of the rotor, and the molecules that have passed through the rotor are moving in the direction of arrow m, so they pass through the slits in the stator. Therefore, in the molecular pump as a whole, gas molecules move from left to right, creating a pressure gradient that gradually increases from left to right. Molecules in the slits of the rotor or stator are obstructed by the walls of the slits, and the gas molecules move from left to right. It cannot be diffused in the circumferential direction.

Also, since the gap between the rotor and stator is small, diffusion through this gap can be ignored. Therefore, even if the pressure on the ion source side is higher than the pressure on the mass spectrometry space in Figure 2, very few gas molecules diffuse from the ion source side to the mass spectrometry space through the turbo molecular pump. Even if the turbomolecular pump inlet is installed across the ion source and mass analysis spaces, each rain space can maintain its own pressure.

Since turbomolecular pumps do not use oil, they are often used in mass spectrometry bags, racks, etc. because they can keep the inside of a vacuum device clean, but the present invention can also be applied to cases where a diffusion pump is used.

FIG. 4 shows an example using a diffusion pump. Components corresponding to those in FIG. 2 are given the same reference numerals. 1 is an oil diffusion pump, and H is a cap attached to the upper end of the oil vapor riser pipe.
A step downward nozzle N is formed. The lower edge of the partition wall 4 extends until it comes into contact with the upper surface of the shade H, and preferably, as shown in FIG. It is best to extend it slightly downward. In the exhaust action space on the outer periphery of the oil vapor riser pipe of the diffusion pump, the partial pressure of the oil vapor decreases as the temperature decreases downward from the nozzle N, but on the contrary, the partial pressure of the exhaust gas gradually increases. , the sum of both partial pressures is the pressure at the exhaust port, that is, the pressure at the suction port of the auxiliary pump. The vapor pressure of oil is high near the nozzle N, and the mean free path of gas molecules therein is significantly smaller than in the ion source and mass analysis space. Therefore, the diffusion rate of the exhausted gas near the nozzle N is much smaller than when the pressure is in the ion source or mass analysis space, and the diffusion of gas from the ion source to the mass analysis space can be ignored. It is. Also, for this reason, the exhaust gas molecules that have entered the oil vapor are carried away by the downward flow of the oil vapor.

As shown in Figure 2, the intake port of the main pump is installed so that the partition wall 4 is closer to the mass analysis space than the center, and the exhaust port area is smaller in the mass analysis space; This is because the analysis space is completely sealed and there is almost no air leakage from the outside, whereas the ion source side supplies the reaction gas, so the amount of exhaust gas is larger on the ion source side.

(Effects of the Invention) According to the present invention, since both the ion source and the mass analysis space, which have different pressures, can be commonly evacuated using one exhaust system, only one set of exhaust equipment is required, and the number of piping system parts is reduced. As a result, the exhaust system becomes less expensive, the probability of failure decreases, and maintenance costs can also be reduced.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the outline of the present invention, Fig. 2 is a longitudinal cross-sectional side view of essential parts of an embodiment of the invention, Fig. 3 is an explanatory diagram of a turbo molecular pump, and Fig. 4 is another embodiment of the invention. FIG. 5 is a cross-sectional view of the main part of the same embodiment. DESCRIPTION OF SYMBOLS 1... Main pump, 2... Ion source space, 3... Mass analysis space, 4... Partition wall, 11... Inlet port, 12...
...Exhaust port, 13...7 lunge, 41...Ion passage small hole, 14...Rotor.

Claims (1)

[Claims] A mass spectrometer characterized in that an inlet port of a main pump is installed so as to span an ion source and a mass spectrometry space with a partition between the two spaces as a boundary.