JP2854761B2 - ESI mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ESI (electrospray ionization) mass spectrometer.

[0002]

2. Description of the Related Art Atmospheric Presso
A liquid chromatograph direct-coupled mass spectrometer (LC / ESI mass spectrometer) using an electrospray ionization method (hereinafter abbreviated as ESI), which is one of re ionization, is a conventional electron impact ionization (EI). Compared to a gas chromatograph direct-coupled mass spectrometer that uses a gas chromatograph, the ionization mechanism uses gentle ionization means with less impact, so it does not decompose when ionizing a sample, especially in the measurement of peptides, etc. Multicharged ions have characteristics that are easy to observe, and have many findings that cannot be obtained with a GC mass spectrometer.

FIG. 2 shows a conventional LC / ESI mass spectrometer.

In FIG. 2, a sample and a mobile phase eluted from a liquid chromatograph 1 (hereinafter abbreviated as LC1) are sent to an ESI probe (electrospray probe) 3 through a sample pipe 2, where a nebulizer gas is sent. 4 (for example, N ₂ gas) and is sprayed from the tip of the ESI probe 3 into the atmospheric pressure region (the internal space of the cover 10) while being atomized.

[0005] The atomized sample is initially a droplet wrapped in a mobile phase, and the ESI probe 3 is fully charged because a high voltage (approximately 3 to 8 kV) is applied. It has become. The mobile phase continues to evaporate until the atomized sample and mobile phase droplets reach the first pore electrode 6, and the droplets become smaller. Then, since the droplet is sufficiently charged, it ruptures due to the repulsion of Coulomb force, and becomes a smaller droplet. The evaporation and rupture of the mobile phase are repeated. The sample obtains protons from the mobile phase in the mobile phase solution and exists as an ion. Therefore, when the droplet becomes sufficiently small and the Coulomb repulsion due to the charge of the sample ion and the mobile phase becomes larger than the surface tension of the mobile phase, the sample ion jumps out of the mobile phase (this is called ion evaporation = Ion Evaporation).
It becomes a sample molecular ion.

[0006] The sample molecular ion is the ESI probe 3
Jumps along the line of electric force formed between the tip of the first pore electrode 6 and the tip of the first pore electrode 6, reaches the second pore electrode 7 via the first pore electrode 6, via the intermediate pressure region 5, and Further, the second pore electrode 7
Is sent to the mass spectrometry unit 8 and mass analyzed.

Therefore, according to the LC / ESI mass spectrometer, highly polar samples having NH, OH, CO, etc., for example, peptides and proteins can be measured with high sensitivity. In addition, these samples are easily broken by heat, and thus cannot be measured at all by a GC mass spectrometer.

The sample atomized from the tip of the ESI probe 3 becomes a sufficiently charged liquid droplet and is sprayed toward the first fine electrode 6 together with the nebulizer gas 4 and flies away. Ion Evap
It depends on how efficient oration is performed.
In order for this Ion Evaporation to be performed efficiently, E
The purpose is to evaporate the mobile phase surrounding the sample efficiently before the droplet atomized from the tip of the SI probe 3 reaches the first pore electrode 6.

However, the size of the droplet generated from the tip of the ESI probe 3 is not constant but varies, and the size ranges from several μm to several tens μm. Therefore, in the conventional method, Ion evaporation occurs before a droplet of several μm reaches the first pore electrode 6, and it is possible to introduce the sample into the analysis unit 8 as ions. In um droplets, Ion Evaporation does not occur because the size of the droplet does not become sufficiently small,
The liquid droplets collided with the first fine electrode 6 or the plate 9 on which the first fine electrode 6 was fixed. Therefore, ions could not be generated from droplets of several tens of μm. For this reason,
To improve this, the nebulizer gas 4 is heated from 60 ° C to 70 ° C. This is because the droplet repeatedly collides with the nebulizer gas 4 in the process before reaching the first pore electrode 6, whereby the evaporation of the droplet is promoted and Ion Evap
oration is more likely to occur.

[0010] This type of prior art is disclosed in, for example, Japanese Patent Application Laid-Open No. 3-179252.
A cylindrical body (atmospheric pressure ionization chamber) with a sample ion passing orifice is provided so as to surround the I probe, and a gas supply pipe for supplying a high-temperature dry gas is introduced into the atmospheric pressure ionization chamber, and is ejected from the gas supply pipe. There is a technique for drying a minute droplet of a sample by flowing a drying gas (counter gas) in a direction opposite to the flow of sample ions. In addition, there is a technique in which a sample gas is directed from the first and second pore electrodes to the ESI probe side. (Counter flow of sample ions) to flow counter gas
A technique has been proposed in which the droplets are collided with the flow of droplets ejected from the SI probe to enhance the atomization of the droplet sample and thereby enhance the ion evaporation.

[0011]

By the way, in this type of apparatus, this ESI is usually used to prevent the atomized mobile phase and nebulizer gas from being released into the atmosphere such as indoors.
The interface portion (atmospheric pressure region for ionizing the atomized sample injected from the ESI probe by Ion Evaporation) is covered with a cover 10, and the cover 10 is usually provided with an exhaust fan 12 to perform the above atomized movement. Exhaust phase and nebulizer gas.

The cover 10 is hermetically closed except that the air intake 14 is provided in a part. For this reason, an air flow is generated in the ESI interface by the exhaust fan 12, and this air flow makes the conditions of Ion Evaporation unstable. Because ES
Droplets atomized together with the nebulizer gas 4 from the tip of the I-probe 3 will mix with the flow of air,
This is because the temperature of the nebulizer gas 4 decreases. For this reason, the droplet cannot be sufficiently small and Io
n Evaporation does not occur efficiently.

Further, the flow of the air lowers the temperature of the first pore electrode 6, which makes it difficult to accelerate the desolvation, leading to a decrease in sensitivity.

Further, in a system as disclosed in Japanese Patent Application Laid-Open No. 3-179252, in which a high-temperature drying gas or a counter gas (hereinafter collectively referred to as a counter gas) flows in a direction opposite to the direction of sample ions, the entire apparatus becomes complicated. If the flow of the counter gas is too strong, it adversely affects the flow of the sample ions, making it difficult to adjust the flow. Also, in order to guide the sample ions to the mass part against the flow of the counter gas, the ESI probe must be used accordingly. In this case, the voltage between the first electrode and the first fine electrode has to be increased, so that there is a problem that the cost is increased.

The present invention has been made in view of the above points, and an object of the present invention is to provide an ESI mass spectrometer with a simple structure, which allows a sample to be atomized from the tip of an ESI probe or an atomized sample. An object of the present invention is to promote the ion evaporation by maintaining the conditions until the electrode reaches the pore electrode, and to improve the sensitivity of the ion peak of the sample molecule to be detected.

[0016]

In order to achieve the above object, the present invention basically proposes the following means for solving the problems. The reference numerals given to the components described below refer to the reference numerals of the embodiment of FIG. 1 for convenience.

That is, a liquid sample is ejected from the ESI probe 3 into a space at or near atmospheric pressure (hereinafter, this space is referred to as an atmospheric pressure region) to perform ion evaporation.
Comprising a ionization unit causing emission (Ion Evaporation) phenomenon, in ESI mass spectrometer for introducing a sample ions generated in the ionization part in the analysis unit 8 through the intermediate pressure region 5 by using a differential pumping, ESI Probe 3 and sample I
Opposite to pore electrode 6 for guiding ON to intermediate pressure region 5
The intermediate pressure region is arranged based on the position of the pore electrode 6.
Space for installing ESI probe 3 is located on the opposite side of 5
It has a first cover 20 covering including Tokoro, a second cover 21 which covers the space between the ESI probe 3 and pore electrode 6 located on the first cover 20, the first cover Reference numeral 20 denotes an air inlet 14 and an exhaust function 12. The second cover 21 has a cylindrical shape and one end thereof is connected to the surface of the pore electrode 6 or the plate surface 9 supporting the same. 21
An end plate 21a having a hole 21b for introducing at least the tip of the ESI probe 3 is provided at the other end of the second cover 21. The inside of the second cover 21 is set to the same atmospheric pressure region as the inside of the first cover 20 , and the second cover 21 is the ionization space I
There is.

[0018]

By covering the space between the ESI probe 3 and the pore electrode 6 with the second cover 21, Ion
A space I of the ionization part that causes evaporation is formed. Second cover 2 forming this ionization section space I
1 is surrounded by a first cover 20, and the inside of the covers 20 , 21 is in an atmospheric pressure region.

When the exhaust function added to the first cover 20 is operated, an air flow is generated in the first cover 20.
The ionization unit space I inside the second cover 21 is not affected by the air flow due to the presence of the cover 21,
The sample and mobile phase atomized together with the nebulizer gas 4 are:
When passing through the inside of the second cover 21, it does not mix with air.

Therefore, it is possible to prevent the temperatures of the nebulizer gas 4 and the liquid drops from being lowered. Further, the temperature of the pore electrode 6 can be prevented from lowering.

Since the end plate 21a having the probe insertion hole 21b is provided on the side of the second cover 21 on which the ESI probe 3 is introduced, a large droplet of the atomized sample is supplied to the second cover 21. It is possible to circulate in the cover 21 (the end plate 21a acts to guide the flow of this circulating flow),
The droplet is confined in the second cover 21 for a long time, so that it is possible to cause Ion evaporation even from a large droplet.

The nebulizer gas and the atomized mobile phase in the cover 21 gradually pass through the first cover 2 through the holes 21b.
It flows out to the 0 side and is discharged through the exhaust mechanism 12. Further, the sample ions (sample molecular ions) ionized by Ion Evaporation fly along the lines of electric force formed between the tip of the ESI probe 3 and the tip of the pore electrode 6, and the pore electrodes 6, intermediate It is guided to the mass spectrometry unit 8 through a pressure region and the like.

Next, when a heater function is added to the second cover 21, it is possible to accelerate the evaporation of the mobile phase forming the droplet by the radiant heat generated from the inner wall of the cover 21 and to make the droplet smaller faster. it can. Furthermore, it is possible to immediately evaporate the droplets (charged droplets) attached to the inner wall of the second cover 21, to stably maintain the electric field formed by the ESI probe 3 and the pore electrode 6, and to use the nebulizer gas. And the flow of the droplets can be kept stable.

Next, when the second cover 21 is made of a conductive material, the ESI probe 3 and the pore electrode 6 are electrically shielded from the outside. The electric field formed between the electrodes 6 is not disturbed by external influence.

[0025]

An embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a block diagram showing an ESI mass spectrometer according to one embodiment of the present invention. In the figure, the same reference numerals as those in the conventional example shown in FIG. 2 indicate the same or common elements.

Here, the point different from the conventional one is that the atmospheric pressure region is constituted by the first cover 20 and the second cover 21.

Intermediate pressure between ESI probe 3 and sample ions
The first pore electrode 6 for leading to the region 5 is disposed so as to face the first pore electrode 6.
The first cover 20 is located at the position of the first pore electrode 6.
The space located on the opposite side of the intermediate pressure area 5 with respect to
An exhaust fan 12 and an air intake 14 are provided so as to cover the installation location of the ESI probe 3 . The support base 15 of the ESI probe 3 is on the first cover 20.

The second cover 21 is located inside the first cover 20 and covers between the ESI probe 3 and the first fine electrode 6. The second cover 21 has a cylindrical shape, one end of which is connected and fixed to the first pore electrode 6 or the plate surface 9 supporting the same, and the other end of the second cover 21 has a hole 21b. An end plate 21a is provided. This hole 21b is
It is located at the center of one end of the cover 21 and is connected to the ES through the hole 21b.
The tip of the I probe 3 is introduced into the cover 21. Through the holes 21b, the inside of the second cover 21 is also in the same atmospheric pressure region as in the first cover 20, and the inside of the cover 21 is the ionization section space I.

In this embodiment, the second cover 21 is a cylindrical member having a diameter of 50 mm and a length of 40 mm, and is formed of a conductive member. Since one end of the second cover 21 is connected and fixed to the first pore electrode mounting plate 9, there is no gap between the first pore electrode mounting plate 9 and the second cover 21. Further, the second cover 21 is provided with a heater (not shown) capable of variably adjusting the temperature of the cover 21.

End plate 21a of second cover 21
The hole 21b for introducing an ESI probe provided in
The round hole of 0 mm has a diameter smaller than the diameter of the cylinder constituting the second cover 21.

The ESI probe 3 has a mechanism capable of moving and adjusting in a direction perpendicular and parallel to the center axis of the second cover 21. The tip of the probe 3 is located substantially at the center of the hole 21a by the moving adjusting mechanism. The distance between the probe 3 and the tip of the first fine electrode 6 is set to an optimum distance (normally about 15 mm).

In the ESI interface thus configured, the liquid sample and the mobile phase from the LC 1 are injected into the second cover 21 together with the nebulizer gas 4 from the tip of the ESI probe 3. The atomized sample (mobile phase,
The nebulizer gas (including the nebulizer gas) is not mixed with the flow of air generated by the exhaust fan 12 by being covered with the cover 21.

As a result, the temperature of the nebulizer gas 4 and the droplets is not lowered and the spraying state is not disturbed, and the nebulizer gas 4 and the nebulizer gas 4 stably fly toward the first pore electrode 6 to form a small liquid. Ion Ev efficiently from drops
Sample ions are generated by aporation. The ions are supplied to the first pore electrode 6, the intermediate pressure section 5, the second pore electrode 7
While passing through the mass spectrometer 8 while being accelerated.

Large droplets of the spray flow ejected from the ESI probe 3 circulate in the second cover 21 without colliding with the first fine electrode mounting plate 9. Because ESI
The sample becomes a droplet from the tip of the probe 3 and is atomized together with the nebulizer gas 4. The nebulizer gas 4 is 2 (l / min; liter per minute).
From the tip of the ESI probe 3 together with the sample and mobile phase at a rate of 3 (l / min). Therefore, the nebulizer gas 4 flies toward the first pore electrode 6 together with the sample and the mobile phase, hits the first pore electrode mounting plate 9 and then moves along the inner wall of the cylindrical second cover 21 along with the ESI probe. It flows toward the third side, and is further guided by the end plate 21a of the second cover 21, and changes the flow again to the first pore electrode 6 side. Large droplets of the atomized sample also circulate in the second cover 21 on the circulating flow of this gas.

The droplets are applied to the second cover 21 for a longer time.
Trapped in the water, and Ion E
Vaporation can occur. For this reason, according to the present invention, the counter gas currently generally used becomes unnecessary. The counter gas is to flow a gas heated from 50 ° C. to 70 ° C. from the first pore electrode 6 side toward the tip of the ESI probe 3, and the purpose thereof is, as described above, from the tip of the ESI probe 3. By colliding the sample to be atomized, the mobile phase with the counter gas, the mobile phase that forms the atomized droplets is evaporated more quickly, the droplets are made smaller and the droplets are used to efficiently cause ion evaporation. It is something that can be done.

According to this embodiment, it is possible to stably cause ion vaporization without using a counter gas, and to improve the sensitivity. Of course,
All of the large droplets circulate through the second cover 21
The ion is not generated by the evaporation, and some droplets adhere to the inner wall of the first pore electrode mounting plate 9 or the second cover 21. A part is discharged into the first cover 20 from the hole 21b of the end plate 21a. However, due to this circulation, Ion Evapo
This makes it possible to generate ions even from droplets in which ration has not occurred, thereby improving sensitivity. Thus, according to the present invention, not only can ions be generated stably, but also the sensitivity can be improved three to five times. FIG. 3A shows the result. This indicates the peak intensity of divalent ions when measured using Tuftsin, which is a kind of peptide, as a sample. FIG. 3B shows the ion peak intensity measured by the conventional method. Obviously, according to the present invention, the sensitivity is improved three times.

In addition, the second cover 21 has a heater function, which has the following advantages (a) and (b). (B) ESI
In order to make droplets atomized from the tip of the probe 3 smaller faster, it is necessary to apply heat to the droplets by some method. For this purpose, the temperature of the nebulizer gas 4 is already increased from 60 ° C to 70 ° C. He said he was warming up. Furthermore, by elevating the temperature of the second cover 21, the evaporation of the mobile phase that forms droplets more quickly by radiant heat generated from the wall surface of the second cover 21 can be promoted, and the droplets can be made smaller. Therefore ESI probe 3
Even if the droplet generated from the tip of the first pore electrode 6 is larger than the conventional one, the droplet can be made smaller before reaching the tip of the first pore electrode 6. If droplets can be made smaller, Ion Evaporation
Ions are generated as described above. The sensitivity can be further improved.

Here, warming the second cover 21 is one of the reasons why the above-mentioned counter gas is not required.

(B) If, for example, the temperature of the second cover 21 is kept at room temperature, when a large droplet circulates in the second It collides with the inner wall of the water and adheres to it, forming water droplets. Then, the electric field in the cover 21 changes due to the influence of the electric charge of the liquid droplets attached to the inner wall of the cover 21, so that ions cannot be stably taken in from the tip of the first fine electrode 6. Therefore, in the present embodiment, the temperature of the second cover 21 is usually 100 ° C. to 1 °.
It is set between 50 ° C.

Next, the second cover 21 is preferably made of a conductive material. This is because the electric field formed between the tip of the ESI probe 3 and the tip of the first pore electrode 6 must be kept stable. Because Ion Evaporation
Sample ions generated by ESI probe 3
Fly along the line of electric force formed between the tip of the first pore electrode 6 and the tip of the first pore electrode 6. Therefore, usually, the tip of the ESI probe 3 and the tip of the first pore electrode 6 are sharpened so that the electric field is concentrated, and the discharge is not caused between the ESI probe 3 and the first pore electrode 6. A high voltage, usually a voltage of 2.5 kV to 3.5 kV, is applied. Therefore, the lines of electric force formed between the tip of the ESI probe 3 and the first pore electrode 6 must not be disturbed.
To this end, the potential of the second cover 21 is maintained at the same potential as the potential of the first pore electrode mounting plate 9, and the tip of the ESI probe 3 and the tip of the first pore electrode 6 are covered by the second cover 21. It is good to take it.

Further, the second cover 21 is preferably formed in a cylindrical shape. This is because a cylindrical shape can be manufactured at the lowest cost. The shape of the cover 21 does not necessarily have to be particular. Hole 2 provided in end plate 21a
1b is preferably a round hole, but the portion constituting the second cover 21 may be, for example, a square, a pentagon, or a so-called polygonal cylinder. Although the above embodiment has been described with reference to the LC / ESI mass spectrometer, the present invention is also applicable to an ESI mass spectrometer that is not combined with an LC.

[0043]

As described above, according to the present invention, by providing the second cover serving as the ionization section in the first cover having the exhaust function serving as the atmospheric pressure region, the structure is simplified and the cost is reduced. Sample ions can be stably generated without using a conventional counter gas, and measurement can be performed with high sensitivity.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an LC / ESI mass spectrometer according to one embodiment of the present invention.

FIG. 2 is a configuration diagram showing an example of a conventional LC / ESI mass spectrometer.

FIG. 3 (a) shows an example of the effect of the present invention, and shows a divalent ion peak of Tuftsin measured using the apparatus of the above embodiment, and FIG. 3 (b) shows a divalent ion peak of Tfutsin measured using the above conventional apparatus. Measurement data diagram showing each ion peak

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Liquid chromatograph, 3 ... ESI probe, 4 ... Nebulizer gas, 5 ... Intermediate pressure part, 6 ... 1st pore electrode,
7 2nd pore electrode, 8 ... mass spectrometer, 9 ... 1st pore electrode mounting plate, 13 ... exhaust fan, 14 ... air inlet, 20
... 1st cover, 21 ... 2nd cover, 21a ... end plate, 21b ... hole for probe insertion, I ... ionization part space.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01J 49/10 H01J 49/04 H01J 49/26

Claims (5)

(57) [Claims] 1. An ion evaporation phenomenon by ejecting a liquid sample from an electrospray probe (hereinafter abbreviated as an ESI probe) into a space at or near atmospheric pressure (hereinafter, this space is referred to as an atmospheric pressure region) . ESI (electrospray ionization method) in which a sample ion generated by the ionization unit is provided and introduced into the analysis unit through an intermediate pressure region using differential evacuation.
In the mass spectrometer, the ESI probe and the sample ions are placed in the intermediate pressure region.
A fine pore electrode for guiding is arranged to face, and is opposed to the intermediate pressure region with reference to the position of the fine pore electrode.
The space on the opposite side should be
A first cover for covering including, and a second cover which covers the space between the first of the ESI probe located within the cover and the pores electrode, the first cover air intake The second cover has a cylindrical shape, one end of which is connected to the pore electrode surface or a plate surface supporting the same, and the other end of the second cover has the ESI probe. An end plate with a hole for introducing at least the tip is provided, and the inside of the second cover is an atmospheric pressure region similar to the inside of the first cover , and the inside of the second cover is an ionization section space. ESI mass spectrometer. 2. The ESI mass spectrometer according to claim 1, wherein the ESI probe has a mechanism capable of moving and adjusting the ESI probe in a direction perpendicular and parallel to a central axis of the second cover. 3. The ESI mass spectrometer according to claim 1, wherein the second cover has a heater function. 4. The ESI mass spectrometer according to claim 1, wherein the second cover is made of a conductive material. 5. The ESI mass spectrometer according to claim 1, wherein the ESI mass spectrometer is of a type combined with a liquid chromatograph.
The ESI mass spectrometer according to any one of claims 1 to 7.