JP2882402B2 - Method and apparatus for mass spectrometry - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for mass spectrometry, and more particularly to a method and an apparatus for mass spectrometry for generating ions under atmospheric pressure and performing mass spectrometry.

[0002]

2. Description of the Related Art Atmospheric pressure ionization (API) is frequently used for mass spectrometry of a fluid containing a sample component and a solvent component flowing out of a liquid chromatograph (LC). According to this atmospheric pressure ionization, soft ionization that does not give excessive energy to the sample molecules is performed, so that the sample is less decomposed at the time of ionization and molecular ions are easily observed. Further, due to ionization under a high pressure (atmospheric pressure), even a substance having a low ionization potential is ionized at a high ionization rate, and thus high sensitivity mass spectrometry can be expected. Regarding atmospheric pressure ionization, Analytical Chemistry
al Chemistry), 1990 Vol. 62, No. 13, No. 713
Details are given on pages A to 725A.

[0003] In order to perform mass spectrometry on ions generated under atmospheric pressure, the ions must be introduced into a vacuum. Immediately introducing ions generated under atmospheric pressure into a high vacuum chamber and performing mass spectrometry have problems such as contamination of the high vacuum chamber. Provide a low vacuum chamber and an intermediate vacuum chamber between atmospheric pressure and high vacuum,
The chambers are often independently evacuated using separate evacuation pumps.

[0004]

However, when the low vacuum chamber and the intermediate vacuum chamber are differentially evacuated using separate and independent exhaust systems, the exhaust system becomes complicated and expensive. Further, the pulsation of the exhaust pump is directly transmitted to the low vacuum chamber (intermediate vacuum chamber), and the pressure in these chambers becomes unstable.

A first object of the present invention is to provide a mass spectrometry method and apparatus capable of simplifying an exhaust system. It is a second object of the present invention to provide a method and apparatus for mass spectrometry capable of performing analysis while maintaining a stable chamber.

[0006]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
The feature of the present invention is that the sample is ionized under atmospheric pressure,
The vacant chamber is set at a pressure lower than the atmospheric pressure, and the intermediate vacuum chamber is
The pressure is set lower than the low vacuum chamber, and the high vacuum chamber is
Between the low vacuum chamber and the middle
Providing an opening member having an opening between the vacuum chambers,
The sample ions are transferred to the low vacuum chamber, the opening, and the middle.
Introduced to the high vacuum chamber through a vacuum chamber and analyzed for mass,
The low vacuum chamber and the intermediate portion through a ventilation part different from the opening
Connect a vacuum chamber and at least when analyzing the sample ions
The low vacuum chamber is evacuated through the ventilation section
That is. Furthermore, the sample is ionized under atmospheric pressure.
Then, the high-pressure side vacuum chamber is maintained at the atmospheric pressure by the first exhaust means.
Lower pressure, and the low pressure side vacuum chamber as the second exhaust means
The pressure is set lower than that of the high-pressure side vacuum chamber,
The sample ions ionized under the atmospheric pressure are transferred to the low-pressure side
In a mass spectrometry method for conducting mass spectrometry by leading to an empty room,
The high-pressure side vacuum chamber is provided for the sample ionized under the atmospheric pressure.
The first chamber for introducing the ON and the first exhaust means are connected
A second chamber having an exhaust passage, and a first chamber in front of the first chamber.
Having a vent connecting between the second chambers, at least
When analyzing the sample ions, the first exhaust means
The first chamber is evacuated through the ventilation section.
That is.

In the present invention , since the low vacuum chamber and the intermediate vacuum chamber are evacuated by a common exhaust system, the exhaust system can be simplified, and the cost can be reduced. Still further, the above configuration
It makes it possible to have the role of the dampers,
The pressure fluctuation in the chamber is suppressed.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments of the present invention, the background and the basis of the present invention will be described first.

In order to perform mass spectrometry on ions generated under atmospheric pressure, the ions must first be introduced into a vacuum. For higher sensitivity measurement, it is necessary to guide the loss of ions generated under atmospheric pressure to a high vacuum mass spectrometer (MS) as little (efficiently) as possible. Therefore, the first item that must be considered in the interface of a mass spectrometer or LC / MS directly connected to a liquid chromatograph (LC) is evacuation. There are two major exhaust systems. As shown in FIG. 2, the first method is a method in which the atmospheric pressure part 2 and the vacuum part 8 are separated by a partition having one pore 3, and the ions generated through the pore 3 are sampled. The second method is shown in FIG. 3 or FIG.
In this method, ions are introduced into the MS section 8 through several stages of differential evacuation systems using a plurality of partitions having pores 3, skimmers 5, 7, and the like as shown in FIG. In the first scheme, MS
In order to obtain the required vacuum, the pore diameter d (m) and the pumping speed S (m ³ / s) of the vacuum pump are determined as follows. Here, the operating vacuum degree of MS is 10 ⁻³ to 10 ⁻⁴ Pa
And The conductance C ₁ of the gas in the viscous flow region having the pore diameter d (m) is obtained by the following equation (1).

[0010]

C ₁ １157 d ₁ ² (Equation ₁ ) Assuming that the evacuation speed of the vacuum pump in the MS section is S ₁ (m ³ / s), the vacuum P _{1 in the} MS section can be obtained by the equation (2). The atmospheric pressure P ₀ is about 10 ⁵ Pa.

[0011]

P ₁ = C ₁ (P ₀ −P ₁ ) / S ₁ (Equation 2) Equation (2) can be approximated to (Equation 2 ′) since P ₀ ≫P ₁ .

[0012]

[Expression 3] P ₁ ≒ C ₁ · P ₀ / S ₁ = C ₁ × 10 ⁵ / S ₁ (Equation 3) The vacuum pump in the MS section is now evacuated at a rate of 1000 liter / s.
= 1m ³ / s oil diffusion pump, the degree of vacuum in the MS section is 1
In order to obtain 0 ^-4 Pa, the diameter d of the pore is determined as follows. From equations (1) and (3)

[0013]

(Equation 4)

That is, the pores have a diameter of about 2.5 μm. Even if a cryopump with a pumping speed of 10,000 liters / s is used, the diameter of the pores is only 7.9 μm. When trying to sample ions from the atmosphere through such small pores, clogging of the pores due to dust in the air frequently occurs. In addition, since the diameter of the pore is small, a large amount of ions cannot be introduced, making high-sensitivity measurement difficult. Another problem is that the cryopump is extremely expensive. FIG. 2 shows a schematic diagram of this method. The ions generated by spraying from the spray nozzle 1 under the atmospheric pressure and high electric field 2 enter the MS section 8 through the pores 3. Neutral molecules are trapped in the cooling fins 16 of the cryopump. On the other hand, the ions travel straight, undergo mass dispersion in the quadrupole MS 9, and arrive at the detector 10.

Rather than sampling ions directly with one pore, two or more pores are arranged in series and coaxially, and the space between the partitions having each pore is evacuated by an independent pump (FIG. 3). In this case, the vacuum of the MS unit 8 is obtained as follows. The atmospheric pressure is P ₀ , and the degree of vacuum of the MS unit 8 is P ₂ . The pumping speeds of the vacuum pumps of the differential pumping section and the MS section are S ₁ and S ₂ , respectively. The conductance of the gas in the first pore 3 and the second pore 5 is C ₁ and C ₂ , respectively. The first and second
The diameters of the pores are d ₁ and d ₂ .

The pressure P _{1 in the} differential exhaust chamber 4 is obtained by the following equation.

[0017]

P ₁ = C ₁ (P ₀ −P ₁ ) / S ₁ ≒ C ₁ P ₀ / S ₁ (Equation 5) Further, the pressure P _{2 of the} MS section is also obtained by the following equation.

[0018]

P ₂ = C ₂ (P ₁ −P ₂ ) / S ₂ ≒ C ₂ · P ₁ / S ₂ (Equation 6) Because P ₀ ≫P ₁ ≫P ₂ .

From equations (5) and (6),

[0020]

P ₂ = C ₁ · C ₂ · P ₀ / (S ₁ · S ₂ ) (Equation 7) is obtained.

Further, C ₁ is obtained by the following equation (1).

[0022]

C ₁ = 157d ₁ ² (Equation 8) The conductance C _{2 in the} molecular flow region is obtained by the following equation.

[0023]

C ₂ = 116 × A (Equation 9) where A is a pore area. This is more

[0024]

Equation 10] _{C 2 = 116 × π (d} 2/2) 2 ... ( number 10) Therefore Equation 7 Equation

[0025]

Equation 11] becomes ^{_{P 2 = 157d 1 2 × 116}} × π (d 2/2) 2 P 0 / (S 1 × S 2) ... ( Equation 11).

The MS section 8 is now evacuated at a pumping speed of 1000 liters /
s and the differential evacuation system 4 is evacuated by a 16.7 liter / s mechanical booster pump. The diameter of the first pore 3 is 200 μm, and the diameter of the second pore 5 is 400 μm. The vacuums P ₁ and P _{2 of} the differential pumping system section 4 and the MS section 8 are calculated from equations (5) and (11), respectively.

[0027]

P ₁ = 37.6 (Pa) P ₂ = 5.6 × 10 ⁻⁴ (Pa) (Equation 12) is obtained. The vacuum in the MS section 8 is sufficient for mass spectrometry. Compared to the first method using a single small pore and a large displacement vacuum pump, the second method using a plurality of pores and a differential pumping system allows a large pore to be used and an inexpensive vacuum pump. It has the advantage of being usable. Therefore, it is widely used in many vacuum devices. Further, as shown in FIG. 4, a differential exhaust three-stage system is similarly used. This differential pumping method is an excellent method in that ions generated under atmospheric pressure are efficiently guided to the MS section. Generally 2
A three-stage and three-stage differential pumping system is used for LC / MS.

There are other considerations for the LC / MS interface other than vacuum. When ions generated under atmospheric pressure are introduced into a vacuum, rapid adiabatic expansion occurs, and the introduced ions and molecules are rapidly cooled. Therefore, molecules such as water and alcohol introduced into the vacuum together with the ions are added to the generated ions to generate cluster ions. In particular, when the sample ion has a large number of charges or an ion having many highly polar functional groups, cluster ions to which many water molecules or alcohol molecules are added are generated. For example, when water is added, it is expressed by the following equation.

[0029]

MH ⁺ + n · (H ₂ O) → (cooling) → {MH · n (H ₂ O)} ^{+ +} (Formula 13) Cluster ions are ions obtained by adding many polar molecules to ions. However, the type and number of molecules to be added are not constant. Therefore, information on the molecular weight of the sample molecule cannot be directly obtained by MS from the cluster ions. Further, since one ion is widely distributed as many cluster ions, the detected ion current value is also small. Therefore, the desolvation (desolvat) that removes the added molecule from the cluster ion
ion) is required. The following methods and their combination methods have been proposed as such methods. In each of the methods, external energy is applied to the cluster ions in excess of the added energy of the polar molecules, and the polar molecules are eliminated from the ions. If an externally applied energy is excessive, the cluster ions are decomposed and do not give molecular weight information.
On the other hand, if it is too low, the elimination of the added molecule becomes insufficient, and the molecular weight information is not given. For this reason, it is necessary to control the energy given to the cluster ions to a value that exceeds the energy required for desorption of the added molecule, and to repeatedly inject the energy into the ions.

(1) Collision with counter gas (2) Adiabatic compression on Mach disk surface (3) Heating (4) Ion acceleration and collision (1) Collision with counter gas FIG. 5 shows a schematic diagram of this method. . Cluster ions are passed through a heated (-70 ° C.) inert gas, for example, dry nitrogen, so that the nitrogen molecules collide with the cluster ions, and the heat is constantly transferred from the nitrogen molecules to the cluster ions to desorb additional molecules from the ions. Let it. Dry nitrogen flows around the ion sampling pores 3 in the direction 24 opposite to the flow of ions. Therefore, the neutral solvent molecules (such as water) flowing along with the ions are pushed back in the direction 23 opposite to the ion sampling pores 3 by the dry nitrogen. On the other hand, the ions 22 are accelerated by the potential applied between the pore 3 and the spray nozzle 1 and collide with dry nitrogen molecules,
The solvent is removed and the light enters the pores 3. This also prevents extra polar molecules from entering the vacuum chamber and reduces the possibility of collision recombination in the vacuum chamber. Although complete desolvation cannot be achieved only by collision with the counter gas, this method is a good method that can limit the incidence of neutral polar molecules into the vacuum chamber. Therefore, desolvation can be more efficiently achieved in combination with the following method than when used alone.

(2) Adiabatic compression on the Mach disk surface Gas molecules incident from the atmospheric pressure through the pores become supersonic molecular flows. Therefore, a shock wave 17 and a Mach disk 18 depending on the pressure in the vacuum chamber are generated as shown in FIG. When the pressure of the outside 2 of the pore 3 is P ₀ , the pressure of the vacuum chamber 4 is P ₁ , and the diameter of the pore is d, a Mach disk is generated at a distance X _M from the pore 4.

[0032]

[Equation 14]

For example, assuming that the pressure before and after a pore having a diameter of 0.3 mm is 10 ⁵ Pa (atmospheric pressure) and 100 Pa, the Mach disk becomes

[0034]

(Equation 15)

That is, from the pores toward the high vacuum section.
A Mach disk is created at 3mm. Since adiabatic compression is performed on the Mach disk surface, cluster ions are also rapidly heated, and as a result, desolvation is performed. First pore 3
When the second pores 5 are arranged so as to be located at a position 7 mm or more behind the cluster ions, the cluster ions always pass through the Mach disk surface, and desolvation is promoted by heating by adiabatic compression. This method is a good method in which desolvation can be achieved without supplying special energy from the outside. However, after the Mach disk, the flow of molecules is completely irregular, and the flow of ions incident on the second pores 5 is not constant, so that there is a disadvantage that the ion sampling yield does not increase.
Generally, in order to improve the ion sampling yield, a fixed molecular flow region in front of the Mach disk (Silent
Zone) 27 is well sampled. However, if sampling is performed in the molecular flow region 27, adiabatic compression and desolvation by a Mach disk are not performed. It simply samples a large amount of aligned molecular flows.

(3) Heating The gas diffused from the atmospheric pressure into a vacuum is rapidly cooled by adiabatic expansion. If the gas to be introduced is heated in advance and the interface including the pores is further heated, adiabatic cooling can be covered to some extent, and addition of water or the like can be prevented.
However, it is difficult to achieve complete desolvation only by heating. This is because most organic compound ions generally passing through this interface are easily susceptible to thermal decomposition by heating. Therefore, high-temperature heating for the purpose of removing the solvent is impossible. (4) Ion Acceleration Collision When the pressure becomes 100 Pa to 10 Pa, the mean free path of gas molecules also becomes about 0.06 mm to about 0.6 mm. When an electric field is applied under such a pressure, ions existing in the gas are accelerated in the direction of the electric field and collide with neutral molecules. The ions repeatedly accelerate and collide while flying in the electric field. When the mean free path is 0.1 mm (up to 66 Pa), ions are accelerated by about 1 eV in an electric field of 100 V / cm. Here, e is the valence of the ion. Due to the collision, part of this kinetic energy is converted into internal energy (thermal energy). The value of this internal energy is the additional energy of water molecules or the like (several kJ / mol to several tens kJ / mol = 0.01 e).
V-0.1 eV), water molecules and the like can be eliminated. Important factors in this desolvation method are the degree of vacuum and the electric field strength in the case of accelerated collision. In general, as shown in FIG. 8, a potential is applied between the first pore 3 and the second pore 5 or between the second pore 5 and the third pore 7 and between them to accelerate ions and convert them into neutral molecules. Make them collide. The degree of desolvation can be changed by controlling the applied voltages V ₁ and V ₂ . This method is a very effective method for desolvation.
However, a disadvantage is that the pressure is directly affected by the pressures of the ion acceleration collision sections 4 and 6. In addition, there is a risk that some kinetic energy is not consumed by the collision due to the acceleration of the ions, but is directly imparted to the ions. Therefore, the velocity of ions entering the high vacuum MS unit 8 is spread. This causes a decrease in resolution and sensitivity in direct mass spectrometry. If the velocity spread exceeds 1 eV, in the case of quadrupole MS, it becomes difficult to achieve a resolution of one sample unit or more, and the ion transmittance also decreases. In the case of a double focusing mass spectrometer, energy is greatly dispersed in an electric field, which causes a decrease in sensitivity and a decrease in resolution.

The mean free path of nitrogen molecules from atmospheric pressure (〜１０10 ⁵ Pa) to 10 ³ Pa is about 5 × 10 ^-5 mm to ⁵
It is about × 10 ⁻³ mm. Under these pressures, 100V / mm
The kinetic energy received by the ions is 5 even when an electric field of
It is significantly lower than 1 eV from × 10 ⁻³ eV to 5 × 10 ⁻¹ eV. In this pressure region, collisions occur frequently, so that the moving direction of ions can be changed by applying an electric field, but the ions cannot be accelerated. That is, even if the ions are accelerated under this pressure, the spread of the kinetic energy can be suppressed to 1 eV or less. On the other hand, from 10 ³ Pa to 1 Pa, the mean free path of the nitrogen molecule is about 5 × 10 ⁻³ mm to 5 mm.
Becomes When an electric field of 100 V / mm is applied under this pressure, the kinetic energy received by the ions in the mean free path is 5 ×
From 10 ⁻¹ eV to 5 × 10 ² eV, which causes a large spread of kinetic energy (velocity). On the other hand, 0.1P
When a vacuum of 10 ^-4 Pa is reached from a, the mean free path is 50 m
From 50 m to 50 m, the accelerated ions are less likely to collide with neutral molecules in the acceleration field, and the spread of kinetic energy is reduced. When accelerating ions and performing collisional dissociation, it is necessary to consider the spread of kinetic energy. If the acceleration of the ions is performed in a low vacuum (10 ³ Pa or more) or a high vacuum (10 ^-1 Pa or less), the spread of the ion velocity can be ignored. The advantages of vacuum pumping using a differential pumping system to take in ions generated under atmospheric pressure into a high vacuum MS have been described above. By applying a potential between the pores of the differential evacuation system, ions can be converged and MS can be efficiently introduced. At the same time, desolvation by accelerated collision dissociation can be achieved. However, creating an ion velocity spread in the process of desolvation is counterproductive.

MS ions are directly generated from the atmospheric pressure as shown in FIG.
In the case of the method of taking into the part, the vacuum is temporarily improved from the ion sampling pore 3 toward the ion flight direction of the MS part 8. If there is sufficient space between the ion sampling pore 3 and the ion extraction electrode 20, the ions are accelerated between the two and always pass through the intermediate pressure region (10 ³ Pa to 1 Pa). In the high pressure part (10 ⁵ to 10 ³ Pa), the ions do not show energy spread. On the other hand, pressure is 10 ² to 1P
In the region a, the ions are accelerated to give an energy spread. To suppress the spread of energy (velocity) as low as possible, the ion extraction electrode 20 is brought close to the ion sampling pore 3, and the high pressure part (10 ⁵ to 10 ³ P
a) Accelerating the ions within. However, in this region, the cluster ions cannot be sufficiently accelerated and the energy required for desolvation cannot be given to the cluster ions. Therefore, desolvation in this region cannot be expected. Similarly, in the case of the differential pumping system shown in FIG. 3, the acceleration of ions in the differential pumping system is accelerated in the intermediate pressure region (10 ^{3 to 1} Pa), thereby giving an energy spread. To avoid this energy spread, the following measures are necessary. The pressure differential is controlled stepwise and precisely using multiple differential pumping systems. Further suppressed to as low a level as possible the ion acceleration under 10 ² Pa or less the intermediate pressure of 10 ² to 1 Pa was vacuum perform acceleration desolvation and once accelerated in a high vacuum. This requires difficulty in pressure control and a complicated and expensive differential exhaust system as shown in FIG. In FIG. 8, the pressure in the first vacuum chamber 4 is maintained at 10 ³ to 10 ² Pa, and the ion acceleration voltage V ₁ is maintained at 100 to 200 V. The second vacuum chamber is 10 ~
The ion acceleration voltage V2 is kept at 1 Pa and the ion acceleration voltage V2 is kept at 10 to ₂₀ V. In this way, in a low vacuum region that does not affect the velocity of ions, the ion acceleration voltage is increased to promote collision dissociation,
In the region that affects the ion velocity, the ion acceleration voltage may be kept low. However, it is not easy to constantly control the pressure and the ion acceleration voltage. Further, if a high voltage is applied under an intermediate pressure (10 ^{3 to 1} Pa) in order to promote the desolvation, glow discharge starts easily.
Once the discharge starts, the ions introduced into the interface disappear. Therefore, no discharge occurs and the pressure at which desolvation can be achieved is limited. Generally 5 × 10 ³ Pa to 5
0 Pa is a pressure suitable for desolvation.

The present invention is embodied by the following technology.

High pressure region (atmospheric pressure of 10 ⁵ Pa to 10 ³
In Pa), the movement of ions is significantly restricted even in an electric field. Therefore, the control of the movement direction of the ions can be achieved by the electric field, and the velocity of the ions does not spread. In the range of 10 ² Pa to ¹ Pa, ions are accelerated and repeatedly collide with neutral molecules. The result is a large spread in ion velocity. In a high vacuum of 1 Pa or less, the probability of collision between accelerated ions and residual molecules is reduced, and consequently the spread of velocity is reduced. That is, an intermediate region (1) between a case where the pressure is high and a case where the vacuum is high.
When the ions are accelerated at a pressure of 0 ^{2 to 1} Pa), the velocity spreads. Therefore, the middle area of the vacuum and the high-pressure, high-vacuum area are physically separated by a partition with an orifice.
In each vacuum chamber, a voltage required for ion acceleration is applied. The interface section is provided with a chamber to reduce the pressure in order from atmospheric pressure.The chamber adjacent to atmospheric pressure is evacuated from the bypass hole opened to the next high vacuum section without using an independent pump. The pressure can be easily set by the conductance of this hole. This simplifies the vacuum pump, exhaust duct, control power supply, and the like.

It is easy to maintain different pressures for different chambers with a single or common exhaust system. 200 to 1 in a chamber maintained at a pressure of 10 ³ to 10 ² Pa
The ions are accelerated by an electric field of 00 V / 5 mm. Thereby, the energy required for desolvation and the number of collisions can be given while suppressing the spread of energy to 1 eV or less. In a chamber of 10 ² to 1 Pa, a potential (10 to 20 V / 5 mm) sufficient to converge ions is applied. As a result, the energy spread in this region is reduced by 1e.
V or less.

An embodiment of the present invention will be described with reference to FIG . The ESI (ionization by liquid spray in a high electric field, ie, electrospray ionization) interface includes a spray nozzle 1 to which a high voltage V ₀ is applied, a counter gas introduction chamber 25, a first pore (ion sampling pore) 3,
First vacuum chamber 4, second pore 5, second vacuum chamber 6, third pore 7
And an ion acceleration power supply 21, a heater 14, a heating power supply 15, and the like.

The eluent sent from the LC reaches the spray nozzle 1 and is sprayed into the atmosphere 2. Many electric charges are accumulated on the surface of the sprayed droplet. The droplets become smaller by evaporating the solvent from the droplet surface while flying in the atmosphere 2. When the repulsion of charges of the same polarity on the surface exceeds the surface tension, the droplet is subdivided at once. Eventually, the ions have moved from the liquid phase to the atmosphere 2 (gas phase). In order to assist the fragmentation of the droplets and to prevent neutral polar molecules (such as water) from entering the interface, a counter gas is supplied from the gas cylinder 13 through the needle valve 12 through the vicinity of the first pore 3 to the atmosphere. I'm going to flow in the opposite direction to the flight direction of the ions. Counter gas is generally 6
Heat to 0-70 ° C. to promote evaporation of the solvent from the droplets. The ions travel against the flow of the counter gas with the help of the electric field and enter the first vacuum chamber 4 through the first pores 3. The ions are then passed through the first pore 3 and the second pore 5 of the first vacuum chamber.
Is accelerated by the voltage V ₁ applied to the partition wall having the above, and collides with the neutral gas molecules to undergo desolvation. The ions further enter the second vacuum chamber 6 via the second pore 5. Where the ions are at voltage V ₂
, And enters the third pore 7. The ions entering the MS section 8 via the third pore 7 are accelerated by the third pore 7 and the acceleration voltage applied to the ion accelerating electrode 20, undergo mass dispersion in the quadrupole MS 9, and are detected by the detector 10. A mass spectrum is given through the DC amplifier 11. The first, second, and third pores generally have a skimmer structure to prevent diffused neutral molecules from entering the next vacuum chamber. The first vacuum chamber 4 does not have an independent vacuum pump, and is configured to be evacuated by the vacuum pump 1 through the second vacuum chamber 6 from a bypass hole 26 provided below the second pore 5. The MS section is evacuated by an independent vacuum pump 2. In addition, 9 is a quadrupole and 21 is an ion acceleration power supply.

The interface section is heated by a heating power supply 15 and a heater 14 to prevent cooling due to adiabatic expansion.

Now, assume that the diameters of the first, second and third pores are 200 μm, 400 μm and 500 μm, respectively, and the diameter of the bypass hole below the second pore is 5 mm. Vacuum pumps 1 and 2
Pumping speed is 16.7 L / S and 1000 L / S. At this time, the degree of vacuum in the first and second vacuum chambers and the MS section is defined as P ₁ , P ₂ , and P ₃ . Assuming that the exhaust conductance of the first fine hole 3 is C1, it is obtained by the following equation (1) and therefore as follows.

[0046]

## EQU16 ## C ₁ = 157d ² = 157 × (0.2 × 10 ⁻³ ) ^{2 = 6.3 × 10 -6 (m 3} / s) ... ( Equation 16) the exhaust conductance of the second pores 5 C ₂ ', .C ₂ of the exhaust conductance of the lower bypass hole 26 and C ₂ "'
Since {C ₂ ″, the total exhaust conductance C ₂ from the first vacuum chamber 4 to the second vacuum chamber 6 is

[0047]

C ₂ = C ₂ ′ + C ₂ ″ ≒ C ₂ ″ (Expression 17)

The conductance C _{2 in the} molecular flow region is obtained as follows.

[0049]

C ₂ = 116 × 0.834 × A = 116 × 0.834 × 3.14 × (2.5 × 10 ^-3 ) ² = 1.9 × 10 ⁻³ (m ³ / s) (Equation 18) Here, the coefficient 0.834 is a conductance correction term of a thick pore.

When the flow rate of the gas flowing through the first pores 3 is Q ₁ and the flow rate of the gas flowing from the first vacuum chamber 4 to the second vacuum chamber 6 is Q ₂ , both are equal.

[0051]

Q ₁ = C ₁ (P ₀ −P ₁ ) ≒ C ₁ P ₀ = 6.3 × 10 ⁻⁶ × 10 ⁵ = 0.63 (Pa · m ³ / s) (Equation 19)

[0052]

(Equation 20) Q ₂ = 1.9 × 10 ⁻³ P ₁ (Equation 20) Since Q ₁ = Q ₂ , the pressure P ₁ of the first vacuum chamber is

[0053]

P ₁ = 0.63 / (1.9 × 10 ⁻³ ) = 0.33 × 10 ³ = 0.33 (Pa) ... (Equation 21) the pressure P ₂ of the second vacuum chamber 6

[0054]

P ₂ = C ₂ P ₁ / S ₁ = 1.9 × 10 ⁻³ × 330 / (16.7 × 10 ⁻³ ) = 37.5 (Pa) (Equation 22)

The second vacuum chamber provides a vacuum approximately one order better than the first vacuum chamber. The vacuum P _{3 in the} MS section is further obtained as follows.

[0056]

P ₃ = C ₃ P ₂ / S ₂ = 116 × π × (200 × 10 ⁻⁶ ) ² × 38 / (10 ³ × 10 ⁻³ ) = 5.5 × 10 ⁻⁴ (Pa) (Equation 23) This vacuum is sufficient for mass spectrometry. is there.

The following is a summary of the parameters of each section under these conditions.

First pore diameter: 200 μm Second pore diameter: 400 μm Third pore diameter: 500 μm Bypass pore diameter: 5 mm Pumping speed of pump 1 (for example, mechanical booster pump): 16.7 liter / s Pump 2 (for example, oil diffusion pump) ) Pumping speed
: 1000 liter / s First vacuum chamber pressure: 330 Pa Second vacuum chamber pressure: 38 Pa MS section vacuum chamber pressure: 5.5 × 10 ^-4 Pa When the bypass hole diameter is changed from 5 mm to 2.5 mm, the pressure of the first vacuum chamber P ₁ is 330 × (5 / 2.5) ² = 1320 Pa,
Conversely, if it is 8 mm, 330 × (5/8) ² = 129P
a.

When the number of bypass holes having a hole diameter of 5 mm is increased to two, 330/2 = 165 Pa. Thus, the pressure of the first vacuum chamber can be easily set by changing the diameter of the bypass hole or the number thereof. In this case, the exhaust system is the same as that shown in FIG. That is, it is equivalent to a three-stage differential pumping system including an oil rotary pump (pumping speed: 120 l / min), a mechanical booster pump (pumping speed: 1000 l / min), and an oil diffusion pump (pumping speed: 1000 l / s). Interface shown in FIG. 1,
Oil rotary pump and piping, etc. exhaust sequence is not required, it is possible to greatly simplify the mechanism. 100 V between the first pore 3 and the second pore 5 and 10 V between the second and third pores 7
Is applied. The distance between the first, second and third pores is 5 mm, respectively. The pressure of the first vacuum chamber 4 is 330 Pa,
Since the pressure in the second vacuum chamber 6 is 38 Pa, 0.02 × in the mean free path in the first vacuum chamber 4 20 = 0.4 (e
V), 0.17 × 2 = 0.34 (e) in the second vacuum chamber 6
At an energy of V), the ions are accelerated on average. A maximum of 0.4 + 0.34 = 0.74 (eV) is expected to spread in acceleration energy between the two chambers. This is below 1 eV, which is a range in which sufficient sensitivity and resolution can be obtained in both quadrupole MS and magnetic field type MS. In the first vacuum chamber 4,
5 / 0.02 = 250, that is, 250 collisions of ions with neutral molecules (such as nitrogen) are performed. Due to these numerous collisions, the energy of the collision is converted into internal energy such as vibration (equivalent to heated one) , which is sufficient energy to dissociate the added molecules. This enables highly efficient desolvation. On the other hand , in the case of a one-stage differential evacuation system as shown in FIG. 9, when acceleration is performed at an ion acceleration voltage V _{1 of} 100 V and the pressure in the first vacuum chamber 4 is 38 Pa, the maximum is 0.17 × 100/5 = 3. will be caused the rate of spread of .4 (eV), longer high resolution, such can be obtained sensitivity Kunar.

FIG. 10 shows an example in which the evacuation of the first vacuum chamber 4 is performed exclusively through the second pores 5. The second pore has a diameter of several mm
If the distance is set to about 5 mm, it is equivalent to the embodiment of FIG.

FIG. 11 shows another embodiment of the present invention. The ion sampling depends on the capillary (inner diameter: 0.5 to 0.2 m, length: 100 mm to 200 mm) without depending on the pore. The capillary may be made of quartz or metallic such as stainless steel. However, in the case of quartz, it is necessary to apply silver plating to both ends so that an ion accelerating potential can be applied. It is also possible to heat the capillary to help remove the solvent. However, the first vacuum chamber is evacuated by the pump 1 through the bypass hole 26 in the first embodiment.
Is equivalent to

FIG. 12 shows an insulin (molecular weight: 5734.6) mass spectrum obtained by the conventional method shown in FIG. The sample introduction amount is 1 μg. No significant peak (polyvalent ion) appears on the mass spectrum. For this measurement, a double focusing mass spectrometer was used, and the acceleration voltage was 4 kV.

FIG. 13 is a mass spectrum of bovine insulin obtained according to the embodiment of the present invention (FIG. 1). The sample introduction fee is 10 ng. Despite the aforementioned 1/100 sample introduction, the multiply-charged ions of Insuline (M +
6H) ⁶ +, (M + 5H) ⁵ +, and (M + 4H) ⁴ + clearly appear. This is considered to be due to the incomplete removal of the solvent according to the above-mentioned method, and that the multiply-charged ions appeared irregularly as noise in a wide mass region or were captured by the electric field of the double focusing mass spectrometer. According to the embodiment of the present invention, the desolvation of polyvalent ions is sufficiently performed, and a mass peak is clearly given on a mass spectrum. Also, noise on the mass spectrum due to cluster ions is reduced.

As described above, polyvalent ions and pseudomolecular ions can be sufficiently removed from the solvent, and measurement can be performed with high sensitivity.

Although the description has been made on the electrospray ionization (ESI) as the atmospheric pressure ionization, the same effect can be obtained by the atmospheric pressure chemical ionization (APCI), the fluid assisted ESI, and the like. Further, the present invention is not limited to LC / MS only, but is applied to supercritical chromatography (SFC) / MS,
The present invention is applicable to a method of ionizing under atmospheric pressure such as CZE (Capillary Zone Electrophoresis) / MS.

[0066]

According to configuration of the present invention, a differential pumping system is simplified, it is possible to provide an inexpensive apparatus. Furthermore , the structure of the exhaust system of the present invention plays the role of a damper.
Since it can be provided, the pressure fluctuation of the chamber can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an entire configuration of a liquid chromatograph / mass spectrometer showing one embodiment according to the present invention.

FIG. 2 is a conceptual diagram of an LC / MS device according to the related art.

FIG. 3 is a conceptual diagram of an LC / MS device according to the related art.

FIG. 4 is a conceptual diagram of an LC / MS device according to the related art.

FIG. 5: LC / M by ionization using a counter gas method
It is a conceptual diagram of S apparatus.

FIG. 6 is a schematic diagram of a shock wave caused by a supersonic fluid introduced into a vacuum from under atmospheric pressure.

FIG. 7 is a conceptual diagram of an LC / MS device provided with an ion extraction electrode for suppressing the spread of velocity.

FIG. 8 is a conceptual diagram of LC / MS using three stages of a differential pumping system.

FIG. 9 is a conceptual diagram of a two-stage LC / MS of a differential pumping system.

FIG. 10 is a conceptual diagram of an LC / MS apparatus showing another embodiment of the present invention.

FIG. 11 is a conceptual diagram of an LC / MS apparatus showing another embodiment of the present invention.

FIG. 12 is a diagram showing a mass spectrum of Insuline obtained by a conventional method.

FIG. 13 is a diagram showing a mass spectrum of Insuline obtained according to an example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Spray nozzle, 2 ... Atmospheric pressure area, 3 ... Ion sampling pore (first pore), 4 ... First vacuum chamber, 5 ... Second pore, 6 ... Second vacuum chamber, 7 ... Third fine Hole, 8 ... MS part, 9 ...
Quadrupole, 10 detector, 11 DC amplifier, 12 needle valve, 13 gas cylinder, 14 heater, 15
... heater power supply, 16 ... cryopump cooling fan, 17
... Shock wave, 18 ... Mach disk, 19 ... Skimmer, 2
0: ion accelerating electrode, 21: ion accelerating power supply, 22: ion beam, 23: neutral molecule flow, 24: counter gas flow, 25: counter gas chamber, 26: bypass hole.

Claims (11)

(57) [Claims] A sample is ionized under atmospheric pressure, a low vacuum chamber is set at a pressure lower than the atmospheric pressure, an intermediate vacuum chamber is set at a pressure lower than the low vacuum chamber, and a high vacuum chamber is set at the intermediate vacuum. The pressure is set lower than the chamber, an opening member having an opening is provided between the low vacuum chamber and the intermediate vacuum chamber, and the generated sample ions are passed through the low vacuum chamber, the opening and the intermediate vacuum chamber. Introduced to a high vacuum chamber for mass spectrometry, and connected the low vacuum chamber and the intermediate vacuum chamber through a ventilation section different from the opening, and at least when analyzing the sample ions, the low vacuum chamber through the ventilation section. A mass spectrometric method characterized by evacuating a chamber. 2. The mass spectrometry method according to claim 1, wherein said ventilation portion is provided in a partition wall between said low vacuum chamber and said intermediate vacuum chamber. 3. A sample is ionized under atmospheric pressure, and a high pressure side vacuum is applied.
The chamber is set to a pressure lower than the atmospheric pressure by a first exhaust means , and the low pressure side vacuum chamber is set to a high pressure side by a second exhaust means.
Set to a lower pressure than the vacuum chamber, b under the atmospheric pressure
The ionized sample ions are led to the low-pressure side vacuum chamber to
In the mass spectrometric method for mass spectrometry, the high-pressure side vacuum chamber
Introduces the sample ions ionized under the atmospheric pressure.
A first chamber and an exhaust path to which the first exhaust unit is connected
And a second chamber having the first chamber and the second chamber.
A vent that connects between them, and at least at the time of analysis of the sample ions, the vent is provided by the first exhaust unit.
Exhausting the first chamber through the mass spectrometer. 4. An ion generating means for ionizing a sample under atmospheric pressure, a low vacuum chamber set at a pressure lower than atmospheric pressure,
An intermediate vacuum chamber set at a lower pressure than the low vacuum chamber,
A high vacuum chamber set at a lower pressure than the intermediate vacuum chamber,
An opening member provided between the low vacuum chamber and the intermediate vacuum chamber and having an opening; and guiding the sample ions to the high vacuum chamber through the low vacuum chamber, the opening and the intermediate vacuum chamber. In the mass spectrometer for mass spectrometry, the low vacuum chamber and the intermediate vacuum chamber are connected via a ventilation part different from the opening, and at least at the time of analyzing the sample ions, the low vacuum chamber is connected through the ventilation part. A mass spectrometer characterized by evacuating. 5. The method of claim 4, an exhaust port for exhausting the high vacuum chamber, said exhaust port mass spectrometer, characterized by being larger than said opening. 6. The method of claim 4, a mass spectrometer, wherein the spread of the ion kinetic energy in the low vacuum chamber is less than 1 eV. 7. The method according to claim 4 , wherein a first electrode and a second electrode are provided so as to sandwich at least a part of the low vacuum chamber, and a voltage is applied to the first electrode and the second electrode. A mass spectrometer characterized in that: 8. The method of claim 4, comprising a capillary for guiding the sample ions in said low vacuum chamber, the mass spectrometer, which comprises heating the capillary. 9. The mass spectrometer according to claim 8 , wherein said capillary is made of metal. 10. The mass spectrometer according to claim 4 , wherein the opening is smaller than a cross-sectional area of the exhaust path. 11. An ion generating means for ionizing a sample under atmospheric pressure, a high-pressure side vacuum chamber set to a pressure lower than the atmospheric pressure, and a low-pressure side vacuum chamber set to a pressure lower than the high- pressure side vacuum chamber. And a first exhausting the high-pressure side vacuum chamber.
Exhaust means and a second exhaust means for exhausting the low-pressure side vacuum chamber
A mass spectrometer that mass-analyzes the sample ions generated by the ion generating means to the low-pressure side vacuum chamber, the high-pressure side vacuum chamber being generated by the ion generating means. Sa
A first chamber for introducing the extracted sample ions, and the first exhaust
A second chamber having an exhaust passage to which the means is connected , wherein the first chamber is provided between the first chamber and the second chamber.
Having a ventilation part for exhausting by the first exhaust means.
Mass spectrometer, characterized by.