JPH0582077A - Atmospheric pressure ionization mass spectrometer - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to improve the sensitivity of the sample molecule ion peak to be detected by more completely dissociating the molecules of the mobile phase or solvent added to the sample molecule ion, especially the molecules of water. LC / ESI mass spectrometer. [Structure] The time required for increasing the distance of the pores of the second pore electrode 7 so that the sample molecule ions generated at atmospheric pressure pass through the pores provided in the second pore electrode 7. To be longer.

Description

Detailed Description of the Invention

[0001]

This invention relates to atmospheric pressure ionization (Atmosp
heric Pressore Ionization) or an atmospheric pressure ionization mass spectrometer having an ionization function utilizing a molecular reaction such as chemical ionization, and particularly to improvement of measurement of multiply charged ions.

[0002]

2. Description of the Related Art A liquid chromatograph direct coupled mass spectrometer (hereinafter LC / LC) utilizing an electrospray ionization method (hereinafter abbreviated as ESI) which is one of atmospheric pressure ionization methods (hereinafter abbreviated as API) The ESI mass spectrometer is an ionization compared to a conventional gas chromatograph direct-coupling mass spectrometer (hereinafter, GC mass spectrometer) that uses electron impact ionization (hereinafter, EI). Since the mechanism uses a gentle ionization means with little impact, it does not decompose when the sample is ionized, and it has the characteristic that it is easy to observe quasi-molecular ions and polyvalent ions particularly in the measurement of peptides and the like. It has a lot of knowledge that cannot be obtained from the total.

FIG. 1 shows a schematic of an LC / ESI mass spectrometer. The sample and mobile phase eluted from the liquid chromatograph 1 (hereinafter abbreviated as LC) pass through the sample pipe 2.
It is sent to the ESI probe 3, where it is atomized together with the nebulizer gas 4 from the tip of the ESI probe 3. The atomized sample is initially in the form of droplets surrounded by the mobile phase, and since the ESI probe 3 is applied with a high voltage (about 5 to 8 kv), it is in a sufficiently charged state. There is. The droplets of the atomized sample and the mobile phase continue to evaporate in the mobile phase until they reach the first micropore electrode 6, and the droplets become smaller. Then, since the droplet is sufficiently charged, it bursts due to the repulsion of the Coulomb force, and becomes a smaller droplet. This evaporation and burst of the mobile phase is repeated. The sample exists as an ionic state in the mobile phase solution by obtaining protons from the mobile layer. 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) and becomes a sample molecular ion.

The sample molecular ions pass through the first fine-pore electrode 6, the intermediate pressure portion 5, and reach the second fine-pore electrode 7.
It is sent to the mass spectrometer 8 through the pore electrode 7 and subjected to mass analysis. Therefore, according to the LC / ESI mass spectrometer, N
A highly polar sample having H, OH, CO, etc., such as a peptide, can be measured with high sensitivity. Moreover, since these samples were easily broken by heat, they could not be measured by the GC mass spectrometer at all.

[0005]

In the LC / ESI mass spectrometer, the differential pumping method is used to introduce ions from the atmospheric pressure into the analysis section, so that the pressure difference between the atmospheric pressure section and the intermediate pressure section 5 is maintained. The first micropore electrode 6 and the second micropore electrode 7 that holds the pressure difference between the intermediate pressure portion 5 and the high vacuum portion (analysis portion) are usually formed by ,
Very small pores with a diameter of 0.1 mm to 0.3 mm are used. The sample molecular ions generated under atmospheric pressure are ideally supplied with heat when passing through the first pore electrode 6 and added to the sample molecular ions by collision with neutral particles in the intermediate pressure section 5. Mobile phase or solvent molecules, especially water molecules, are dissociated and introduced into the mass spectrometer 8 through the second pore electrode 7, but the sample molecule ion peak detected due to insufficient action thereof. Was not sensitive enough.

The object of the present invention is to improve the sensitivity of the sample molecular ion peak to be detected by more completely dissociating the molecules of the mobile phase or solvent added to the sample molecular ion, especially the molecules of water. To provide a simple LC / ESI mass spectrometer.

[0007]

The object of the present invention is to increase the distance between the pores of the second pore electrode 7 so that the sample molecular ions generated at atmospheric pressure are provided in the second pore electrode 7. This is achieved by allowing a longer time to pass through the pores.

[0008]

[Function] The temperature of the first and second pore electrodes 6 and 6 can be set in the range from room temperature to a maximum of 250 ° C, and in the case of normal measurement, it is set to 120 ° C ± 20 ° C. Has been done. It takes time for the sample molecular ions generated at atmospheric pressure to pass through the pores of the first pore electrode 6 because the distance between the first pore electrodes 6 has already been increased. It is possible for the molecular ions to obtain a larger amount of heat by the first pore electrode 6. As a result, the mobile phase or solvent molecules added around the sample molecule ions, especially water molecules, are dissociated or the bond with the sample molecule ions becomes unstable and is introduced into the intermediate pressure section 5. ..

After that, the sample molecule ions in which the bond between the sample molecule ion and the water molecule becomes unstable are easily dissociated from the water molecule by colliding with the neutral molecule in the intermediate pressure section 5. However, the state of the sample molecule ions when they are introduced into the analysis section from the second pore electrode 7 can be an ideal sample molecule ion without addition of solvent molecules, but it is not always sufficient. Has not yet been dissociated. Therefore, by increasing the distance of the pores of the second pore electrode 7, the sample molecule ions obtain a larger amount of heat in the second pore electrode 7 as well as the action of the first pore electrode 6. This makes it possible to dissociate the mobile phase or the solvent molecules from the sample molecule ions in which the mobile phase or the solvent molecules have not dissociated at the intermediate pressure section 5, thereby improving the sensitivity.

[0010]

FIG. 2 shows an embodiment of the present invention. Here, the difference from the conventional one is that the thickness of the second pore electrode 7 is 0.2 mm as compared with the conventional one.
Is, for example, 5 mm.

The sample and mobile phase eluted from LC1 are E
It is atomized together with the nebulizer gas 4 from the tip of the SI probe 3 as in the conventional method. The atomized sample and mobile phase repeatedly evaporate and burst in the mobile phase of droplets until they reach the first micropore electrode 6, becoming smaller and finally by Ion Evaporation. The sample is ionized. This process is also similar to the conventional method. However, although the sample molecule ions ionized by Ion Evaporation are schematically illustrated as being ionized only by the sample molecules, in reality, a considerable number of migrations occur in the sample molecule ions. Ionization is carried out with the addition of phase molecules, especially water molecules. Moreover, when the sample molecule ions pass through the intermediate pressure portion 5, the water molecules cannot be sufficiently dissociated only by collision with neutral molecules,
Therefore, a part of the sample molecular ions will pass through the second pore electrode 7 while the water molecules are still added. The sample molecule ions that have passed through the second pore electrode 7 are dissociated from water molecules by collision with neutral particles in the free space before reaching the entrance of the electric field 10 or in the space of the electric field 10. The number of water molecules dissociated in these two spaces reaches, for example, 20 to 50. This can be confirmed by measuring the width of the kinetic energy of the sample molecular ion passing through the electric field 10. The sample molecule ions dissociated from water molecules in the free space and the electric field space are detected by the detector 1
2 cannot be reached, so that the peak intensity of the sample molecule ions, that is, the so-called sensitivity, is reduced accordingly.

Next, the sample molecule ions that have passed through the electric field 10 reach the magnetic field region 11. Here, the sample molecular ions are mass-dispersed by the magnetic field and are divided by the molecular weight. However, the sample molecule ions that have passed through the electric field region 10 collide with neutral particles even in the space up to the exit of the magnetic field 11, and the water molecules added to the sample molecule ions are dissociated. The sample molecule ions dissociated in the space from the outlet of the electric field 10 to the outlet of the magnetic field 11 reach the detector 12 and can be detected as ions, but they are random ion peaks, and the sensitivity is lowered in this case as well. Becomes

FIG. 3 shows a mass spectrum of bovine insulin measured under the above conditions. m / z 900 to m / z 18
Ion peak is detected at 00, but it is tetravalent, 5
Peaks that are considered to be random noise are detected between the valent and hexavalent ion peaks. This peak is the peak of the sample molecule ion in which water molecules are dissociated in the space from the outlet of the electric field 10 to the outlet of the magnetic field 11. In the present invention,
Although devised to solve these problems, the mobile phase molecules added to the sample molecular ions before the sample molecular ions pass through the second pore electrode 7, in particular, the water molecules are dissociated to form the sample molecular ions. This problem can be solved by passing it through the second fine hole electrode 7 and accelerating it by the ion acceleration voltage 13 as only. This can be achieved by increasing the distance between the pores of the second pore electrode 7 of the present invention. In the LC / ESI interface, which could not be observed as a mass spectrum at all, it has already been filed (applied that the mass spectrum of multiply charged ions can be obtained by increasing the distance of the pores of the first pore electrode 6). Request reception number: 0119100710), but in the present invention, it is intended to measure with higher sensitivity by increasing the distance of the pores of the second pore electrode 7. In this method, mobile phase molecules, especially water molecules, which are added to all sample molecule ions by the method of the above-mentioned applied patent (application request reception number: 0119100710) are the first pore electrode 6 or the intermediate. Since it cannot be dissociated in the pressure part, it is dissociated by applying an appropriate amount of heat even when passing through the second pore electrode 7. FIG. 4 shows a mass spectrum of beef insulin measured with the second pore electrode 7 having a wall thickness of 5 mm. As is clear from comparison with FIG. 3, although a small amount of random noise is detected between the four, five, and six ion peaks, each of the four, five, and six ion peaks is detected. It can be seen that the intensity of the ion peak is 2-3 times more sensitive. The thickness of the first micropore electrode 6 at this time is 5 mm. However, also in this case, the set temperature of the second pore electrode 7 is 100 ° C. to 1 ° C.
It is necessary to keep between 40 ° C. Although this has also been described in the above-mentioned patent, the sample molecule ions themselves are destroyed by heat by raising the temperature of the second pore electrode 7 too much as in the case of the first pore electrode 6. Because it will be. Therefore, 100 ° C to 140 ° C
The important point is to keep the temperature during the period, not to destroy the sample molecular ions, and to dissociate the water molecules added to the sample molecular ions.

Further, by further increasing the distance between the pores of the second pore electrode 7, the following advantages can be obtained. This makes it possible to maintain the degree of vacuum on the side of the mass spectrometric section 8 at a high degree of vacuum, and the number of collisions with neutral particles until the sample molecular ions that have passed through the second pore electrode 7 reach the detector 12. This can prevent the scattering of the sample molecule ion beam, and also in this respect, the sensitivity can be improved. This is because the conductance becomes about 1/9 times when the distance of the pores of the second pore electrode 7 is changed from 0.2 mm to 5 mm, and the measured value is 1 ×.
This is because 10 ⁻⁶ Torr is improved to 5 to 6 × 10 ⁻⁷ Torr, and the mean free path of molecules at this time is also changed from 50 m to 100 m.

[0015]

According to the present invention, when an ESI interface is attached to a magnetic field type mass spectrometer, it becomes possible to detect multivalent ions such as bovine insulin with high sensitivity.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a conventional LC / ESI mass spectrometer.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing a mass spectrum of bovine insulin measured by a conventional LC / ESI mass spectrometer.

FIG. 4 is a diagram showing a mass spectrum of bovine insulin obtained according to the present invention.

[Explanation of symbols]

1 ... Liquid chromatograph, 2 ... Teflon pipe, 3 ... E
SI probe, 4 ... Nebulizer gas, 5 ... Intermediate pressure part, 6 ... First pore electrode, 7 ... Second pore electrode, 8 ... Mass spectrometer, 9 ... Data processing device, 10 ... Electric field, 11 ... Magnetic field, 12 ... Detector, 13 ... Ion acceleration power supply, 14 ... Drift power supply.

Claims (1)

[Claims] 1. An atmospheric pressure ionization mass spectrometer comprising an ionization section that operates at or near atmospheric pressure, and can use differential evacuation to introduce ions generated in the ionization section into the analysis section through an intermediate pressure region. 2. The atmospheric pressure ionization mass spectrometer, wherein the length of the pores of the electrode for introducing the ions from the intermediate pressure region to the analysis section is 1 mm or more.