JPH11108894A - Lc/ms interface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To expand the tolerance range of a skimmer arranging position. SOLUTION: The inner diameter D2 on the internal side of a desolvating pipe 23 is made larger than the inner diameter D0 on the side of the inlet end thereof and the inner diameter D1 on the side of the outlet end thereof. By this constitution, the pressure P2 inside the outlet end of the desolvating pipe 23 becomes for lower than atmospheric pressure P0 and the pressure difference between the inside and outside of the outlet end becomes small. Therefore, a Mach disk is not generated by ejected gas molecules and, even if a skimmer 36 is arranged in the vicinity of the outlet of the desolvating pipe 23, the plunging of gas molecules can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a liquid chromatograph mass spectrometer which is disposed between a liquid chromatograph (LC) section and a mass spectrometry (MS) section to ionize a liquid sample supplied from the LC section. To an LC / MS interface to be introduced into the MS section.

[0002]

2. Description of the Related Art FIG. 2 is a schematic diagram showing an example of a liquid chromatograph mass spectrometer (LC / MS). LC
The liquid sample which is temporally separated and eluted from the column 11 of the section 10 is introduced into the interface section 20 and the needle 2
It is sprayed into the atomization chamber 21 from the nozzle at the two ends and is ionized. The generated ions are transmitted to the interface unit 20 and M
It is sent to the MS unit 30 through a desolvation pipe 23 such as a heated capillary provided between the S unit 30.

The MS section 30 comprises a first intermediate chamber 31, a second intermediate chamber 32, and an analysis chamber 33. The desolvation pipe 23 and the second intermediate chamber 31 are provided between the atomizing chamber 21 and the first intermediate chamber 31. A skimmer 36 having a very small diameter passage hole (orifice) is provided between the first intermediate chamber 31 and the second intermediate chamber 32. The first intermediate chamber 31 is evacuated to about 1 Torr by a rotary pump, the second intermediate chamber 32 is evacuated to about 10 ^-3 to 10 ^-4 Torr by a turbo molecular pump, and the analysis chamber 33 is exhausted to about 10 Torr by a turbo molecular pump. 10 ^-5 to 10 ^-6 To
It is exhausted to about rr.

The ions that have passed through the desolvation pipe 23 are introduced from the first intermediate chamber 31 into the second intermediate chamber 32 through the passage holes of the skimmer 36, converged and accelerated by the ion lens 37, and sent to the analysis chamber 33. . Then, only the target ions having a specific mass number (mass m / charge z) are supplied to the analysis chamber 3
It passes through a quadrupole filter 34 arranged in 3 and reaches a detector 35. The detector 35 extracts a current corresponding to the number of ions.

The interface section 20 generates gas ions by atomizing a liquid sample by heating, high-speed gas flow, high electric field, and the like. The interface section 20 includes an electrospray ionization method (ESI) and an atmospheric pressure chemical ionization method. (APC
Atmospheric pressure ionization methods such as I) are most widely used.

FIG. 3 is a detailed configuration diagram around the interface section in the case of ionization by ESI. At the tip of the needle 22 from which the liquid sample flows, several k
A high voltage of V is applied. Thereby, the needle 22
The liquid sample that has reached the tip is strongly charged, and is sprayed as charged droplets with the aid of an auxiliary gas (mainly nitrogen gas) ejected from the nebulizing tube 24 surrounding the periphery.
The droplet collides with the surrounding atmospheric components and is miniaturized, and the solvent in the droplet evaporates to generate gas ions. The generated ions and fine droplets jump into a desolvation pipe 23 disposed in front of the needle 22. This desolvation pipe 23
Is applied with a voltage of about several tens of volts by a voltage source V2, and is heated to a temperature of about 200 ° C. by a heater (not shown). For this reason, the fine droplets that have jumped into the desolvation pipe 23 evaporate the solvent while passing through the pipe 23, generate more ions and are discharged from the outlet of the desolvation pipe 23. .

In the interface section 20 having the above structure, the inlet side of the desolvation pipe 23 (inside the atomizing chamber 21) has an atmospheric pressure P.
0, the pressure on the outlet side (inside the first intermediate chamber 31) is much lower than the pressure P0. Inner diameter D0 (for example, 0.5m
The nebulizing gas and the atmosphere flow into the desolvation pipe 23 of m) one after another from the atomization chamber 21 side, so that the inside is almost at atmospheric pressure P0. The temperature in the first intermediate chamber 31 is much lower than that in the desolvation pipe 23. For this reason, the first intermediate chamber 3
The gas (including ions) jetted into 1 becomes a substantially conical high-speed jet due to rapid adiabatic expansion, and a so-called Mach disk is generated at a position separated by a predetermined distance. Generally, the predetermined distance (Mach disk distance) XM is obtained by the following equation. XM = 0.67 (P0 / P1) ^1/2 · d where d is the outlet diameter of the desolvation pipe 23,
Here, d = D0.

[0008]

It is considered that ions in the desolvation pipe 23 travel substantially along the central axis, and after exiting the desolvation pipe 23, they travel substantially straight to the Mach disk. Since the gas flow returns to the thermal motion flow due to collision with the residual gas molecules downstream of the Mach disk distance, its traveling direction is disturbed, and the ion flow is also affected by this. For this reason, in order to sample ions efficiently, the passage hole of the skimmer 36 is preferably arranged within the Mach disk distance XM. On the other hand, the passage holes are formed in the
Too close to the outlet, the ions can be efficiently sampled, but the ejected gas molecules also jump into the second intermediate chamber 32 at the same time. For this reason, the second intermediate chamber 32
The degree of vacuum is easily deteriorated, and a vacuum pump having a high evacuation capacity must be used to maintain the degree of vacuum.
Therefore, in order to satisfy both the ion sampling efficiency and the small number of gas molecules, it is optimal to arrange the passage hole of the skimmer 36 at the Mach disk distance XM or slightly inside. As described above, in the conventional configuration, the adjustment of the position of the passage hole of the skimmer is extremely delicate, and if not arranged at an appropriate position, the ion sampling efficiency is extremely reduced, or many gas molecules pass through the passage hole. There is a problem that the load of the vacuum evacuation at the subsequent stage becomes heavy.

In the above configuration, large liquid droplets can be prevented from jumping into the desolvation pipe 23 by displacing the center axis of the needle 22 and the center axis of the desolvation pipe 23 in parallel. In some cases, an electrode plate for ion deflection may be arranged between 23 and the skimmer 36, but in any case, the position adjustment of the skimmer 36 is still delicate.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to increase the permissible range of the position accuracy of an ion sampling unit such as a passage hole of a skimmer and to efficiently convert ions. It is an object of the present invention to provide an LC / MS interface that can sample undesired gas molecules and eliminate undesired gas molecules from jumping to the subsequent stage.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to a method for ionizing a liquid sample supplied from a liquid chromatograph section of a liquid chromatograph mass spectrometer and introducing the ionized liquid sample into the mass spectrometric section. A) an atomizing chamber at atmospheric pressure provided with a spraying means for spraying a liquid sample; b) a vacuum chamber provided downstream of said atomizing chamber; A transport pipe for transporting ions generated in the atomization chamber to the vacuum chamber, wherein a part of the pipe has an inner diameter larger than the inner diameter of the inlet on the atomization chamber side and the inner diameter of the outlet on the vacuum chamber side. A pipe; and d) ion sampling means arranged at a predetermined distance from the outlet of the transport pipe.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an LC / MS interface according to the present invention, when gas and ions ejected from a spraying unit jump into a transport pipe, the ions are generated in the pipe by a voltage applied to the transport pipe. Under the influence of the electric potential, it passes near the central axis of the transport pipe. On the other hand, the gas spreads inside when passing through a portion having a large inner diameter, that is, a cross-sectional area, so that the pressure difference between the inside (upstream side) and the outside (downstream side) of the outlet end of the transport pipe is different from the conventional case. Therefore, the size is smaller than that of a transport pipe having the same inner diameter. For this reason, the velocity of the gas ejected at the outlet of the transport pipe becomes slower than in the conventional case, and a Mach disk hardly occurs. For this reason, ions that exit the transport tube
The gas is collected by the ion collecting means arranged substantially on the extension of the central axis. On the other hand, since the gas spreads immediately after the ejection, the gas is hardly caught by the ion collecting means.

[0013]

As described above, according to the LC / MS interface according to the present invention, the allowable range of the position of the ion sampling unit arranged at the outlet is widened, and the generation position of the Mach disk is changed as in the conventional interface. Irrespective of the exact arrangement taken into account, it is possible to efficiently collect the ions that have jumped out of the transport tube, while eliminating unwanted gas molecules, such as auxiliary gases, as far as possible.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of an LC / MS interface according to the present invention will be described below with reference to FIG. FIG. 1 is a configuration diagram of the present embodiment. A feature of the LC / MS interface according to the present invention is that a constant inner diameter D from the inlet to the outlet as in the prior art.
Instead of using a desolvation pipe having 0, as shown in FIG. 1, the inside diameter D2 in the inside is larger than the inlet end inner diameter D0 and the outlet end inner diameter D1. That is, a solvent pipe 23 is used. FIG.
In this example, the inner diameter D0 on the inlet end side and the inner diameter D1 on the outlet end side are the same, but the relation of D0 <D1 <D2 may be satisfied.

The charged droplets forcibly sprayed from the tip of the needle 22 along with the flow of the auxiliary gas collide with the atmospheric components in the atomizing chamber 21 to be divided into fine droplets and the solvent in the droplets. Is evaporated, and jumps into the desolvation pipe 23 in a state where ions generated from the droplets and fine droplets are mixed. A voltage is applied from the voltage source V2 to the desolvation pipe 23, and a uniform potential is generated concentrically from the central axis in the pipe 23, so that ions are substantially distributed along the central axis in the desolvation pipe 23. Go right.

On the other hand, gas molecules that have jumped into the desolvation pipe 23 also travel rightward in the desolvation pipe 23, but have an inner diameter of D.
The direction of travel is disturbed at the point where it spreads, and the speed decreases.
For this reason, in this part, the pressure is P, which is halfway between P0 and P1.
Becomes 2. Further, the pressure inside the outlet end of the desolvation pipe 23 also becomes almost P2. That is, in this embodiment, the inside (upstream side) and the outside (downstream side) of the outlet end of the desolvation pipe 23 are used.
Is much smaller than the conventional one. For this reason, the velocity of gas molecules ejected from the outlet of the desolvation pipe 23 is low, and no Mach disk is generated. That is, the gas molecules largely spread in the first intermediate chamber 31 immediately after jumping out of the outlet of the desolvation pipe 23. Therefore, skimmer 3
Even though the passage hole 6 is disposed near the exit end of the desolvation pipe 23, the number of gas molecules jumping into the passage hole is small.

The ions released from the desolvation pipe 23 are also slightly affected by the turbulence of the gas flow.
As shown in (2), it is sent to the second intermediate chamber 32 through the passage hole of the skimmer 36.

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

[Brief description of the drawings]

FIG. 1 is a configuration diagram of one embodiment of an LC / MS interface of the present invention.

FIG. 2 is a schematic configuration diagram of a general liquid chromatograph mass spectrometer.

FIG. 3 is a configuration diagram of a conventional LC / MS interface.

[Explanation of symbols]

 Reference Signs List 21 atomizing chamber 22 needle 23 desolvation pipe 24 nebulizing pipe 31 first intermediate chamber 36 skimmer V1, V2 voltage source

Claims (1)

[Claims] 1. An LC / MS interface for ionizing a liquid sample provided from a liquid chromatograph unit of a liquid chromatograph mass spectrometer and introducing the ionized sample into a mass spectrometric unit. An atomizing chamber under atmospheric pressure, b) a vacuum chamber provided at a stage subsequent to the atomizing chamber, and c) a transport pipe for transporting ions generated in the atomizing chamber to the vacuum chamber. And a transport pipe in which a part of the pipe has a larger inner diameter than the inner diameter of the inlet on the atomization chamber side and the inner diameter of the outlet on the vacuum chamber side, and d) at a position separated by a predetermined distance from the outlet of the transport pipe. An LC / MS interface, comprising: an arranged ion sampling means.