JP3300602B2 - Atmospheric pressure ionization ion trap mass spectrometry method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an atmospheric pressure ionization ion trap mass spectrometer and a mass spectrometer, and more particularly to an atmospheric pressure ionization ion trap mass spectrometry and a mass spectrometer suitable for providing molecular weight information and structural information in one spectrum.

[0002]

2. Description of the Related Art Liquid chromatograph (LC) direct mass spectrometers (MS) have been used in the analysis of trace organic compounds in liquids as a combination of the outstanding separation ability of LC and the qualitative and quantitative capabilities of MS. Analysts have drawn attention. However, it is not easy to combine liquid handling LC and MS operating under high vacuum. Recently, ionization under atmospheric pressure (atmospheric ionization = Atmospheric Ionization =
API) and generated ions have been made practical by the development of a differential evacuation system and an ion acceleration / introduction system that lead to high vacuum MS.

[0003] LC / MS technology is disclosed in USP 3,997,29.
8 is described. Here, the amount of liquid introduced into the MS is limited to μl / min in order to maintain the degree of vacuum of the MS.
For this reason, very thin capillaries must be used or USP
As shown in US Pat. No. 4,746,068, an attempt was made to limit the amount of liquid introduced into the MS by a fine orifice or the like.
However, these attempts were not practical due to instability due to clogged capillaries and orifices.

[0004] Atmospheric pressure ionization (API) has attracted attention as an ionization method for LC / MS. Electrospray ionization (Electrospray Ionizaion =) is one of the APIs.
ESI). U.S. Pat. No. 4,209,696 discloses an ion source for ESI. Also shown therein is an ion introducing section provided with a differential pumping system for guiding generated ions to a high vacuum MS section. Ions generated under atmospheric pressure are introduced into the intermediate pressure chamber evacuated from the pores by a vacuum pump. Furthermore, it is accelerated and converged by the electric field created by the electrode installed in the intermediate pressure chamber, and is introduced into the high vacuum chamber where the mass spectrometer MS is placed. The ions are mass analyzed by a mass spectrometer to give a mass spectrum. Here, a constant voltage is applied to the electrode placed in the intermediate pressure chamber during the analysis, so that ions are efficiently guided to the MS.

In US Pat. No. 4,144,451, it is shown that cluster ions can be efficiently broken down to small ions by adjusting the voltage applied to an electrode for accelerating and converging ions installed in an intermediate pressure chamber. That is, when ions are accelerated in a pressure range of about 100 to 1 Pa, the accelerated ions repeatedly collide with neutral molecules. Part of the energy of the collision was taken into the internal energy, indicating that only the ions could be heated. It has been shown that polar molecules such as water added to the ions can be removed (declustered) by the ion heating.

When the ion acceleration voltage is set higher and the collision energy is further increased, the internal energy converted and given to the ions is higher than the covalent bond energy of the ions. Eventually, the covalent bond of the ion is broken. An ion (molecular ion) in which a molecule is intact or becomes an ion by adding a proton or the like is dissociated into smaller ions (fragment ions) by this collision. Molecular ions undergo specific cleavage depending on the structure of the molecule. Therefore, the structural information of the molecule can be obtained by analyzing the fragment ions. This technique is known as Collision Induced Desociation (CID).

[0007] Atmospheric Chemical Ionizat (API) is used in addition to ESI.
ion = APCI) is known. USP 4,023
The APCI is shown at 398. First, a large amount of LC solvent molecules are ionized at atmospheric pressure by corona discharge or the like. The ions of the solvent repeatedly collide with solvent molecules and sample molecules under atmospheric pressure, and finally ionize the sample molecules.

[0008]

Since both ESI and APCI are mildly ionized, ions (pseudo-molecular ions) in which a proton is added to a molecule are generated, and fragment ions in which the molecular ion is cleaved are not easily generated. for that reason,
While the information on the molecular weight of the sample component can be obtained, the information on the molecular structure is small, which has been regarded as a drawback of the API. In many cases, the obtained mass spectrum becomes a simple one as shown in the upper part (A) of FIG. In general, the API / MS is provided with an intermediate pressure chamber for guiding ions generated under atmospheric pressure to a high vacuum mass spectrometer. This room is evacuated by a vacuum pump,
The pressure is maintained at about 100 Pa. The role of this intermediate pressure chamber is to force ions generated under atmospheric pressure into a high vacuum mass spectrometer without difficulty. The ions are accelerated and converged by the voltage applied to the electrodes placed in this chamber, so that the ions are less lost and are sent to the next mass spectrometer. Neutral molecules other than ions diffuse without being accelerated and converged, and are exhausted by a vacuum pump. The ions are accelerated,
At a vacuum of about 100 Pa, it immediately collides with many neutral molecules existing in the intermediate pressure chamber. When this ion acceleration voltage is set high, the ions are broken into many fragment ions by collision dissociation (CID). If the number of fragment ions is increased by CID, structural information can be obtained. However, as shown in the lower part (B) of FIG. 3, if the CID is sufficiently performed, the pseudo molecular ion indicating the information of the molecular weight disappears, and the molecular weight becomes unknown. Therefore, when it is desired to obtain molecular weight information and structural information, LC / MS analysis is generally performed twice. That is, once, the ion acceleration voltage is set low to emphasize molecular ions, and a mass spectrum as shown in the upper part (A) of FIG. 3 is obtained. The second time, a mass spectrum as shown in the lower part (B) of FIG. 3 in which the ion acceleration voltage is set high and the fragment ions are emphasized has been obtained. However, this requires more than twice the analysis time and consumes valuable samples.

An object of the present invention is to provide an atmospheric pressure ionization ion trap mass spectrometry method and apparatus suitable for rapidly obtaining a mass spectrum containing molecular weight information and structural information and reducing consumption of a valuable sample. is there.

Another object of the present invention is to provide an atmospheric pressure ionization ion trap mass spectrometry method and apparatus suitable for obtaining constant ion accumulation efficiency and obtaining excellent reproducibility of analysis results. .

Another object of the present invention is to provide an atmospheric pressure ionization ion trap mass spectrometry method and apparatus suitable for preventing detection of stray ions and improving sensitivity by reducing noise. .

[0012]

According to the present invention, a sample is ionized under atmospheric pressure or a pressure close to the atmospheric pressure, ions are accelerated in a evacuated space, and a three-dimensional quadrupole field under high vacuum is formed. Atmospheric pressure ionization mass spectrometry for introducing and accumulating and sweeping the three-dimensional quadrupole field to obtain a mass spectrum, wherein, when the ions are accelerated, atmospheric pressure ionization is performed by collision dissociation under a plurality of collision dissociation conditions. Provided is an ion trap mass spectrometry method.

The present invention also provides a method of ionizing a sample under atmospheric pressure or a pressure close to the atmospheric pressure, accelerating ions in a space provided with an accelerating electrode, and introducing the ions into a three-dimensional quadrupole field under a high vacuum. In the atmospheric pressure ionization ion trap mass spectrometric method for obtaining a mass spectrum by sweeping the three-dimensional quadruple horse, the atmospheric pressure ionization ion changing a voltage value applied to the acceleration electrode during acceleration of the ions. A method for trap mass spectrometry is provided.

[0014] The present invention also changes the further the applied voltage value, the second step of applying a first step of applying a level of a voltage that does not break the molecular ion, the level of the voltage for generating the fragment ions Atmospheric pressure ionization ion trap mass spectrometry comprising:

Further, the present invention further to the end gap electrodes and the ring electrode to form the three-dimensional quadrupole field, providing atmospheric pressure ionization ion trap mass spectrometry method of adding a DC bias.

Further , the present invention comprises an atmospheric pressure ionizing ion source, an ion introducing section, and a mass spectrometer having a three-dimensional quadrupole field, wherein the atmospheric pressure ionizing ion source has a pressure at or near atmospheric pressure. The sample is ionized below to generate ions of the sample, and the generated ions are introduced into the three-dimensional quadrupole field of the mass spectrometry unit by the ion introduction unit and accumulated, and the three-dimensional quadrupole is accumulated. In an atmospheric pressure ionization ion trap mass spectrometer that obtains a mass spectrum by sweeping a field, when ions pass through the ion introduction unit,
The present invention provides an atmospheric pressure ionization ion trap mass spectrometer comprising means for causing the generated ions to collide and dissociate in the ion introducing section under a plurality of collision dissociation conditions.

The present invention also includes an atmospheric pressure ionizing ion source, an ion accelerating unit to which an accelerating voltage is applied, and a mass spectrometric unit for forming a three-dimensional quadrupole field by an end gap electrode and a ring electrode. In the atmospheric pressure ionization ion source, a sample is ionized under atmospheric pressure or a pressure close to the atmospheric pressure to generate ions of the sample, and the generated ions are accelerated by the acceleration voltage. An atmospheric pressure ionization ion trap mass spectrometer that introduces and accumulates in a quadrupole field and obtains a mass spectrum by sweeping the three-dimensional quadrupole field, comprising means for setting the acceleration voltage to a plurality of values, Provided is an atmospheric pressure ionization ion trap mass spectrometer that accelerates the generated ions by the set acceleration voltages when the generated ions pass through the ion acceleration unit. .

The present invention further provides an atmospheric pressure ionization ion trap mass spectrometer in which the set values are a voltage that does not break molecular ions and a voltage that generates fragment ions.

The present invention further provides an atmospheric pressure ionization ion trap mass spectrometer characterized in that a direct current bias is applied to the end gap electrode and the ring electrode.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. The sample molecules separated for each component by the liquid chromatograph (LC) 1 are supplied from a DC power supply 3.
It is fed into the metal capillary 2 to which a DC voltage of ５5 kV is applied. Many fine droplets 40 having electric charges are sprayed into the atmosphere 4 from the tip of the metal capillary. The fine droplets 40 collide with atmospheric molecules while advancing in the atmosphere 4 according to the electric field, and are miniaturized. Eventually the ions are released into the atmosphere.

The generated ions are taken into the intermediate pressure part 9 of the ion introducing part from the pore 5 provided at the center of the electrode 6. This intermediate pressure section 9 is a vacuum pump 1 such as an oil rotary pump.
It is exhausted at 0 and maintained at a pressure of about 100 Pa. The ions are accelerated by an ion accelerating voltage applied between the electrode 6 and the electrode 8, and are sent to an ion focusing / transporting system section 20 of an ion introducing section through a pore 7 provided at the center of the electrode 8. The ion focusing / transporting system unit 20 including the mass spectrometric unit 24 having a three-dimensional quadrupole field described later is evacuated by, for example, a turbo molecular pump 25 and is maintained at a pressure (vacuum) of about 10 ⁻⁴ Pa. I have. The ions are accelerated by the voltage applied between the electrode 8 and the ion guide 11. The accelerated ions are transferred through the ion guide 11 and converged. As the ion guide 11, one using an electrostatic field, one applying a high frequency to an octupole, or the like is used.

The ions are introduced through an ion gate 17 into an ion trap type mass spectrometer 24 having a three-dimensional quadrupole field. The ions enter the three-dimensional quadrupole field of the mass spectrometry unit 24 from the pore 22 provided at the center of the end cap electrode 13 used to form the three-dimensional quadrupole field. The ions form a stable orbit in the three-dimensional quadrupole field according to the mass of the ions by the high frequency applied to the ring electrode 13,
Stably remain (ie, accumulate) in the quadrupole field. When the high-frequency voltage (high-frequency amplitude) applied to the ring electrode 13 is swept, the ions become unstable in the Z-axis (the axial direction of the two end caps) in order from low mass, and It is released to the outside from the provided pores 23. This ion is detected by the detector 15,
A mass spectrum can be obtained by the data processor 16.

FIG. 2 shows this series of procedures along the time axis. Here, a procedure for acquiring one mass spectrum will be described. The actual measurement will repeat this procedure.
The uppermost curve shows a high-frequency voltage (high-frequency amplitude) applied to the ring electrode 13. Next, the ion acceleration voltage applied between the electrodes 6 and 8 is shown. Next, the ion gate voltage applied to the ion gate 17 will be described. The bottom row shows the current value of the ions detected by the detector 15.

At t1, a low-frequency high-frequency (low-frequency high-frequency) is applied to the ring electrode 13. This allows ions introduced from the outside to be stably captured and accumulated in the three-dimensional quadrupole field. The ion acceleration voltage is t
It is kept at V1 between 1 and t2. Another voltage V2 is applied between t2 and t3. The high frequency applied to the ring electrode from t1 to t3 is kept at a low potential. A potential for introducing ions (about 10 V for positive ions and about 10 V for negative ions) is applied to the ion gate 17. Between t1 and t3, the ions are supplied to the ion gate 17,
After passing through the end cap electrode 12, it is introduced into a three-dimensional quadrupole field, and is captured and accumulated. At t3, the ring electrode 13
When the high frequency applied to the end cap is swept (the amplitude of the high frequency is gradually increased), the ions are sequentially emitted from the center pore 23 of the end cap electrode 14 to the outside from the low mass, and the ion current is measured by the detector 15. You. The ion current shows a different value for each ion mass. This is the mass spectrum. The ion accumulation time is between t1 and t3.

Now, it is assumed that V1 <V2, and V1 is accelerated so that ions can be sufficiently sent to the three-dimensional quadrupole field, but the acceleration voltage does not break molecular ions. Generally, it is around 100 V depending on the vacuum of the intermediate pressure section 9. The mass spectrum obtained in this state is a mass spectrum of a molecular ion emphasized type as shown in FIG. V2 is raised to a potential at which molecular ions break and become fragment ions (fragment ions). Generally, it is around 150V. The mass spectrum in this state is a mass spectrum of a structure information emphasized type as shown in FIG. In FIG. 3, the horizontal axis represents the mass-to-charge ratio (m / Z).

The molecular ions generated at atmospheric pressure from t1 to t2 are stably sent to the three-dimensional quadrupole field. On the other hand, t2
From t to t3, the molecular ions are destroyed by the CID and fragment ions are sent to the three-dimensional quadrupole field. This t
The ions introduced between 1 and t3 remain in the three-dimensional quadrupole. From time t3 to time t4, ions are emitted to the outside by the high frequency sweep applied to the ring electrode 13 to give a mass spectrum. The obtained mass spectrum is a CID with two ion acceleration voltages V1 and V2 as shown in FIG.
The average spectrum of FIG. 2 shows that two ion acceleration voltages are changed. This voltage can be changed by three or more.

In the case of the method shown in FIG. 2, it is necessary to set a plurality of ion acceleration voltages in advance. This can be omitted by sweeping the ion acceleration voltage. FIG. 5 shows the procedure. Between t1 and t3, a high frequency of a low potential is applied to the ring electrode, so that ions can be captured. In this state, the ion gate is open and allows ions to pass. The ion accelerating voltage is swept to capture and accumulate ions during this time. As a result, during the period from t1 to t3, ions are changed from V1 to V
It is accelerated, collided and dissociated at a voltage of 2. The obtained mass spectrum is an average value of the mass spectrum by CID corresponding to the voltage from V1 to V2.

When the CID is performed at a degree of vacuum of about 100 Pa, fragment ions can be efficiently generated, and the energy of the generated ions becomes uniform. For this reason, it is general to perform the process in the intermediate pressure section 9. CID also occurs due to the acceleration of ions in the low vacuum area near the outlet of the intermediate pressure section 9.
Can be achieved. The ion acceleration voltage applied between the electrode 8 and the ion guide 11 can be changed as shown in FIGS.

The ion acceleration voltage accelerates ions. Therefore, the kinetic energy of the ions changes according to the ion acceleration voltage. This change affects the ion trapping efficiency of the three-dimensional quadrupole field. If the ion acceleration energy is too high, the trapping efficiency will decrease. Most of the ion kinetic energy is converted into the kinetic energy of neutral molecules by elastic collision with neutral molecules. For this reason, the energy of the ions is not directly changed by the ion acceleration, but is imparted to the ions as a spread of kinetic energy. Generally, the end cap electrode and the ring electrode operate at a DC potential close to the ground potential. If a DC voltage is superimposed on the DC voltage from the DC power supply 19, the increase in the kinetic energy of the ions can be offset.

FIG. 6 shows another embodiment of the present invention. The ions generated under the atmospheric pressure 4 move in the atmosphere by the electric field, and are taken into the intermediate pressure part 9 from the pore 5 provided at the center of the electrode 6. The ions are accelerated by an ion accelerating electric field applied between the electrodes 6 and 8, and are introduced into the ion focusing / transporting unit 20. The ions are further sent to the three-dimensional quadrupole field via the ion guide 11 and the ion gate 17. While the ions are being captured in the three-dimensional quadrupole field, the ion accelerating voltage is also applied. Naturally, the ion gate is also open. The DC bias voltage of each of the electrodes 12, 13, and 14 for forming a three-dimensional quadrupole field is changed according to the ion acceleration voltage. This DC bias voltage is set to a value that offsets the kinetic energy obtained by the ions. It becomes about 10 V from several V. As a result, the ions are decelerated as they pass through the end cap electrode 12, and are captured and accumulated in the three-dimensional quadrupole field. When the accumulation of ions is completed, the sweep of the three-dimensional quadrupole field is started. During this time, no ion acceleration voltage is applied, and no ions are introduced into the ion focusing / transporting unit 20. The ion gate 17 is also closed so that stray ions and the like are not sent to the three-dimensional quadrupole field. FIG. 7 shows a case where the ion acceleration voltage is swept. In this case, the bias voltage may be swept in conjunction with the ion acceleration.

The ion gate 17 serves to introduce ions into the three-dimensional quadrupole field while accumulating ions and to prevent ions from being introduced into the three-dimensional quadrupole field during sweeping. When a voltage having the opposite polarity to the ion polarity is applied to the ion gate 17, the ions pass through the gate. Conversely, when a voltage having the same polarity as the ions is applied, the ions cannot pass through the gate. The gate can be opened and closed by switching the polarity of the voltage applied to the ion gate 17. The voltage applied to the electrodes 6 and 8 is turned on / off in conjunction with the opening and closing of the ion gate. Thereby, during the accumulation of ions (from t1 to t3)
Only), the ions pass through the intermediate pressure section 9 and are sent to the high vacuum chamber, where they are accumulated in the three-dimensional quadrupole field. At other times, no ions are sent from the intermediate pressure section 9 into the high vacuum chamber, and therefore no stray ions are generated.

Although the above is an example of ESI, it goes without saying that the present invention may be applied to atmospheric pressure chemical ionization using a combination of corona discharge and ion molecule reaction.

According to the embodiment of the present invention, it is possible to quickly obtain a mass spectrum containing molecular weight information and structural information and to reduce consumption of a valuable sample. In addition, the ion accumulation efficiency of the ions in the three-dimensional quadrupole field is made constant, so that excellent reproducibility of the analysis results can be obtained.
In addition, the ion acceleration voltage is turned on /
By turning off, noise due to stray ions can be reduced, sensitivity can be improved, and the life of the detector can be prevented from being shortened.

[0034]

According to the present invention, there is provided an atmospheric pressure ionization ion trap mass spectrometry method and apparatus suitable for quickly obtaining a mass spectrum containing molecular weight information and structural information and reducing consumption of a valuable sample. Is done.

According to another aspect of the present invention, there is provided an atmospheric pressure ionization ion trap mass spectrometric method and apparatus suitable for obtaining a constant ion accumulation efficiency and obtaining excellent reproducibility of analysis results. You.

According to another aspect of the present invention, there is provided an atmospheric pressure ionization ion trap mass spectrometry method and apparatus suitable for preventing detection of stray ions and improving sensitivity by reducing noise. You.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an atmospheric pressure ionization ion trap mass spectrometer showing one embodiment of the present invention.

FIG. 2 is a time chart for explaining the operation of the apparatus of FIG. 1;

FIG. 3 is an exploded view of a mass spectrum obtained by the apparatus of FIG. 1, wherein (A) is a mass spectrum chart rich in molecular weight information, and (B) is a mass spectrum chart rich in structural information.

FIG. 4 is a mass spectrum diagram obtained by the apparatus of FIG.

FIG. 5 is a time chart of another example for explaining the operation of the apparatus of FIG. 1;

FIG. 6 is a time chart of yet another example for explaining the operation of the apparatus of FIG. 1;

FIG. 7 is a time chart of another example for explaining the operation of the apparatus of FIG. 1;

[Explanation of symbols]

1: liquid chromatograph (LC), 2: metal capillary, 3: DC power supply, 4: atmospheric pressure part, 5: pore, 6: electrode, 7: pore, 8: electrode, 9: intermediate pressure part, 10 : Vacuum pump, 11: ion guide, 12: end cap electrode, 13: ring electrode, 14: end cap electrode, 1
5: detector, 16: data processor, 17: ion gate, 18: high-frequency power source, 19: DC power source, 20: ion focusing / transfer system, 22: pore, 23: pore, 24: three-dimensional four An ion trap type mass spectrometer with a quadrupole field.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01J 49/42 G01N 27/62

Claims (8)

(57) [Claims] A sample is ionized under atmospheric pressure or a pressure close to the atmospheric pressure, ions are accelerated in a evacuated space, introduced into a three-dimensional quadrupole field under a high vacuum, and stored therein. An atmospheric pressure ionization ion trap mass spectrometry method for obtaining a mass spectrum by sweeping a source quadrupole field, wherein, during acceleration of the ions, collision dissociation is performed under a plurality of collision dissociation conditions. Analysis method. 2. A sample is ionized under atmospheric pressure or a pressure close to the atmospheric pressure, ions are accelerated in a space provided with an accelerating electrode, introduced into a three-dimensional quadrupole field under a high vacuum, and accumulated. An atmospheric pressure ionization ion trap mass spectrometric method for obtaining a mass spectrum by sweeping the three-dimensional quadrupole field, wherein, when the ions are accelerated, a voltage value applied to the accelerating electrode is changed. Ionization ion trap mass spectrometry. 3. The method according to claim 2, wherein the applied voltage is changed in a first step of applying a voltage that does not break molecular ions and a second step of applying a voltage that generates fragment ions. Atmospheric pressure ionization ion trap mass spectrometry characterized by comprising: 4. An atmospheric pressure ionization ion trap mass spectrometry method according to claim 2, wherein a DC bias is applied to an end gap electrode and a ring electrode for forming said three-dimensional quadrupole field. 5. An atmospheric pressure ionization ion source, an ion introduction unit, and a mass analysis unit having a three-dimensional quadrupole field, wherein a sample is sampled under the atmospheric pressure or a pressure near the atmospheric pressure in the atmospheric pressure ionization ion source. The sample is ionized to generate ions of the sample, and the generated ions are introduced into the three-dimensional quadrupole field of the mass spectrometric unit by the ion introduction unit and accumulated, and the three-dimensional quadrupole field is swept. An atmospheric pressure ionization ion trap mass spectrometer for obtaining a mass spectrum by means of: a means for causing the generated ions to collide and dissociate in the ion introducing section under a plurality of collision dissociation conditions when the ions pass through the ion introducing section. An atmospheric pressure ionization ion trap mass spectrometer characterized by comprising: 6. An atmospheric pressure ionization ion source, comprising: an ion acceleration section to which an accelerating voltage is applied; and a mass analysis section for forming a three-dimensional quadrupole field by an end gap electrode and a ring electrode. In the ion source, the sample is ionized under atmospheric pressure or a pressure near the same to generate ions of the sample, and the generated ions are accelerated by the accelerating voltage, and the ions are applied to the three-dimensional quadrupole field of the mass spectrometer. An atmospheric pressure ionization ion trap mass spectrometer for introducing and accumulating and sweeping the three-dimensional quadrupole field to obtain a mass spectrum, comprising: means for setting the acceleration voltage to a plurality of values; Wherein the gas is accelerated by the set acceleration voltages when passing through the ion accelerating unit. 7. The method according to claim 6, wherein the set value is:
An atmospheric pressure ionization ion trap mass spectrometer characterized by a voltage at a level that does not destroy molecular ions and a voltage at a level that generates fragment ions. 8. An atmospheric pressure ionization ion trap mass spectrometer according to claim 6, wherein a direct current bias is applied to said end gap electrode and ring electrode.