JP2924703B2 - 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 a mass spectrometer, and more particularly to an important non-volatile compound (amine, amino acid,
Steroids, antibiotics, sugars, peptides, vitamins, etc.)
And a device combining a liquid chromatograph and a mass spectrometer suitable for separation and analysis, that is, a liquid chromatograph / mass spectrometer.

[0002]

2. Description of the Related Art At present, in the field of analysis, the development of techniques for separating and analyzing substances related to living organisms is one of the important issues. For this purpose, devices that combine a liquid chromatograph with an excellent separation ability and a mass spectrometer with an excellent identification ability have been actively developed. For reference, FIG. 11 shows the entire configuration of a liquid chromatograph / mass spectrometer using a double focusing mass spectrometer comprising an electric field 4 and a magnetic field 5 as a mass spectrometer. The sample in the solution which is separated by the liquid chromatograph 1 and eluted from the liquid chromatograph 1 is introduced into the ion source 3 through the pipe 2. The ions related to the sample molecules generated by the ion source 3 are introduced into the vacuum from the pores. Further, it is introduced into a mass spectrometer comprising an electric field 4 and a magnetic field 5 and subjected to mass analysis. The ions subjected to mass analysis are detected by the ion detector 6 and sent to the data processing unit 7. At this time, the mass analysis unit including the electric field 4 and the magnetic field 5 is evacuated by an appropriate evacuation system 9. Although the principle is simple in this way, liquid chromatography handles samples in solution, whereas mass spectrometers handle samples in gas, which makes it very difficult to develop this device. It has become something.

[0003] Several methods have been proposed to solve this difficult problem. A typical one is disclosed in Japanese Patent Application Laid-Open No. Sho 60-127453 (Japanese Patent Application No. 58-233668).
Atmospheric Pressure Ionization Method, Analytical Chemistry 19
1983, Vol. 55, pp. 750-754, and the like. As shown in FIG. 12, in the atmospheric pressure ionization method, an eluate from a liquid chromatograph is sprayed with a heated capillary 11 or an ultrasonic wave, and further heated and vaporized by a heated metal block 12, and then vaporized. The sample molecules obtained are ionized by corona discharge using the needle electrode 13 and a series of subsequent ion-molecule reactions, and the generated ions are introduced into the vacuum through the first pores 14 and the second pores 15 to obtain a mass. It is a method of analysis. This method has a feature that it is highly sensitive and easy to combine with a liquid chromatograph because the ion source exists at atmospheric pressure. However, among the above-mentioned important non-volatile compounds in the living body, amines, steroids, antibiotics, etc., which are not very polar, have strong molecular ions and can be analyzed, but very polar. Sugars and peptides have the disadvantage that molecular ions are difficult to obtain and analysis is difficult. On the other hand, as shown in FIG. 13, in the thermospray method, the sample is a capillary 1 heated simultaneously with a solution containing an electrolyte such as ammonium acetate.
According to 1 ', the method is a method of spraying in a vacuum of several Torr or less and introducing ions generated when the generated droplets are vaporized into the mass spectrometer through the second pores 15 to detect the ions. In contrast to the above-mentioned atmospheric pressure ionization method, this method can analyze strongly polar substances such as sugars and peptides.
It has the drawback that analysis of less polar amines, steroids, antibiotics, etc. is difficult.

[0004]

Therefore, if an apparatus provided with the above two ion sources is developed, it is considered that important substances related to living organisms can be analyzed widely. An ion source provided with the above two ionization methods may be configured as shown in FIG. However, the following problems arise from the difference that the atmospheric pressure ionization method operates at atmospheric pressure and the thermospray method operates at a pressure of several Torr. First, when using the atmospheric pressure ionization method, a valve must be provided so that the liquid does not leak from the capillary for the thermospray method, and when using the thermospray method, the gas is generated by the atmospheric pressure ionization method. A valve must be provided so that gas does not leak from the fine holes 14 for introducing the ions, and the structure of the ion source becomes complicated. Second, the atmospheric pressure ionization method does not require a liquid nitrogen trap or the like to prevent the eluent from the liquid chromatograph from contaminating the exhaust system, but the thermospray method requires the provision of this trap. During operation, the measurement must be stopped to clean the trap every few hours. Third, in the case of the thermospray method, since the inside of the ion source is constantly exposed to a large amount of gas, the inside of the ion source is easily contaminated.

An object of the present invention is to solve the above problems,
An object of the present invention is to provide a liquid chromatograph / mass spectrometer having a new ion source in which the atmospheric pressure ionization method and the thermospray method are combined into one ion source.

[0006]

The above objects are achieved by making a thermospray ion source operable under atmospheric pressure and integrating it with an atmospheric pressure ionizing ion source.

However, as shown in FIG. 15, if the operating pressure of the conventional thermospray ion source is increased from a few Torr to atmospheric pressure, ions are hardly taken out and the operation does not work well. This is because with the configuration as shown in FIG. 15, the amount of ions flowing into the vacuum from the fine holes is extremely reduced. In the method of obtaining ions by spraying a solution under atmospheric pressure, the processes of atomization and vaporization by heating and the process of ionization occur in parallel, and at this time, ions are generated at the tip of the capillary as much as possible. This is convenient because neutralization of ions on the inner wall of the capillary does not occur. Further, the radial distribution of the ion current obtained by spraying the solution under the atmospheric pressure is large near the center as shown in FIG. 16, but very small around the periphery, and in the configuration of the conventional thermospray ion source, I cannot extract ions to the analyzer. Therefore, from the above considerations, the tip of the capillary was heated and temperature controlled independently of its inner part, and the center axis of the capillary was arranged so as to pass through the center of the pore leading to the decompression chamber. . The spray thus obtained is sufficiently vaporized and can be used as it is in the atmospheric ionization method.

[0008]

The polar components in the eluate from the liquid chromatograph are ionized when sprayed with a metal capillary, and the generated ions are sampled from the pores and subjected to mass analysis. The weakly polar component is ionized by corona discharge with a discharge electrode such as a needle and a series of subsequent ion-molecule reactions, and mass analyzed. In this way, components with various chemical properties are ionized in parallel,
Can be analyzed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. Here, the system will be described using a double focusing mass spectrometer including an electric field 4 and a magnetic field 5, but other types of mass spectrometers such as a quadrupole mass spectrometer may be used.

FIG. 1 shows a configuration diagram of an ion source according to an embodiment of the present invention. The sample in the solution, which is separated by the liquid chromatograph and eluted from the liquid chromatograph, passes through the pipe 2 and is introduced into the metal capillary 11 with the connector. This metal capillary 11 can be heated and controlled in temperature. The metal capillary 11 is built in the metal block 12 and is heated by a cartridge heater 17. To further heat the distal end portion, an appropriate power supply 16 as shown in FIG.
Was used to directly heat the metal capillary 11. An increase in the amount of ions observed by this tip heating was confirmed. In this example, indirect heating and direct heating are combined, but both may be indirect or both may be direct. In addition, as a method of sufficiently heating the metal capillary 11, as shown in FIG. 2B, the metal capillary 11 can be divided into a plurality of portions and heated. Further, although the amount of ions generated when spraying is reduced as compared with the above two methods, as shown in FIG. 3, only one portion from the tip is directly heated by heating (FIG. 3 (a)). It is also possible to use indirect heating (FIG. 3 (b)), and in order to suppress the pressure rise inside the capillary to some extent due to the vaporization of a part of the liquid by heating, the inside diameter of only the tip of the capillary is reduced. It is possible to heat it by slightly expanding it (FIGS. 3 (c) and 3 (d)) or to connect a capillary 28 having a slightly larger diameter to the capillary to heat them (FIG. 3).
(E)). In any of these cases, a thermocouple 18 is provided on the metal capillary 11 or the metal block 12 to monitor and control the temperature thereof.

The liquid chromatograph 1 which has passed through the metal capillary 11 heated by the heating method described above.
Is heated and vaporized, but a part is released as ions.

In the embodiment shown in FIGS. 4 and 5, the ions obtained as described above are efficiently extracted, and the vaporized sample molecules are ionized by corona discharge under atmospheric pressure. . The radial distribution of the ions sprayed from the capillary 11 is as shown in FIG.
That is, the vicinity of the central axis is large and the ends are small. Therefore, in order to efficiently introduce ions, the pores 14 need to be formed on the axis of the capillary 11. When the distance between the tip of the capillary 11 and the pore 14 is changed, the amount of ion current obtained changes as shown in FIG. That is,
If it is 1 cm or less, it does not change much, but if it is 3 cm away, it is reduced to 1/10 or less, and it becomes impractical. On the other hand, it is efficient to place the discharge portion of the corona discharge electrode at a position 3 to 5 mm away from the pore. That is, the discharge electrode was inserted into the ion source in a form inserted between the capillary 11 and the first pore 14, and the capillary potential was set to the same potential as or higher than the discharge electrode. As a corona discharge electrode, as shown in FIG. 4, when a wire 19 is used (FIG. 4B) in addition to a normal needle 13 (FIG. 4A), a wire or a mesh 20 is put on. (FIG. 4 (c)), a case where the wire 19 is directly attached to the capillary (FIG. 4 (d)), etc. When it is desired to obtain only a mass spectrum by corona discharge, the capillary portion is connected to the discharge electrode. Of course, ions can be generated and observed in the thermospray mode without applying a voltage to this electrode, and a voltage can be applied to the discharge electrode at a certain frequency as shown in FIG. Pressing or cutting the
The thermospray mode (in the case of A) and the atmospheric pressure ionization mode (in the case of B) may be alternately generated.

In order to simultaneously detect the ions by the atmospheric pressure ionization method and the ions by the thermospray method, as shown in FIG. 5, the potential at the tip of the capillary 11 is increased, and the auxiliary electrode 23 is provided. It is necessary to devise such that the ions to be emitted are not deflected by the discharge electrode potential and reach the first pores 14. FIG.
In the case of (a) and FIG. 5 (b), discharge is caused by the edge 21 or the large number of needles 22 of the metal capillary 11, and ions are generated by the atmospheric pressure ionization method together with ions generated from the capillary. In this case, a mass spectrum combining the two is obtained. In the case of FIG. 5C and FIG. 5D, FIG.
5B, an auxiliary electrode 23 is provided so that a discharge electrode such as a wire 19 is located at the center and an electric field is concentrated in the direction of the first pore 14 instead. is there. Also, as shown in FIG. 5C, when the wire 19 and the like are positioned at the center, the potential of the wire 19 is raised with respect to the first pore 14, and the capillary temperature is controlled,
The field emission effect of ions can be provided at the tip of the wire.

As described above, the generated ions are supplied to the pores of the first electrode 14 held by the electrode support block 24 and the second ions held by the electrode support block 25 with the exhaust port.
It is introduced into the vacuum through the pores of the electrode 15. Electrode support block 24 and electrode support block 25 with exhaust port
Electrically insulated by an insulating plate 26 made of ceramic or the like,
A voltage is applied between both blocks so that exhaust can be performed at the same time. This voltage is used to accelerate cluster ions generated by adiabatic expansion when ions are introduced from the pores of the first electrode 14 and collide with neutral molecules to cleave cluster ions that are not convenient for analysis. is there. As described above, the ions that have passed through the pores of the first electrode 14 and the second electrode 15 are further subjected to mass analysis by the double focusing mass spectrometer including the electric field 4 and the magnetic field 5, and detected by the ion detector 6. Will be.

For reference, FIG. 8 shows sucrose (molecular weight: 342), which is one of the easily decomposable substances, for the atmospheric pressure ionization method (a), the thermospray method (b), and the method of the present invention. The mass spectrum measured by (c) is shown. At this time, water was used at a flow rate of 1 ml (milliliter) / min as a mobile phase of the liquid chromatograph. Further, the discharge current at the time of discharging was 5 μA. In the mass spectrum by atmospheric pressure ionization, the molecular ion species to which protons are added ((M + H) having a mass number of 343)
, A fragment ion (mass number 163) formed by breaking the molecule, and a cluster ion of a solvent molecule are observed. In the mass spectrum in the thermospray mode, in addition to sodium ions (mass number 23) and potassium ions (mass number 39), alkali metals such as sodium and potassium contained in water used for the mobile phase of the liquid chromatograph were added. Molecular ion species (cation of (M + Na) with molecular weight 365, (M
+ K) only) and fragment ions are hardly observed. When the ions by the atmospheric pressure ionization method and the ions by the thermospray method are simultaneously detected, the mass spectrum of the atmospheric pressure ionization and the thermospray becomes a combined mass spectrum, and the (M + H) positive Ions, (M + Na) cations, and (M + K) cations are observed.

Thus, the mass spectrum obtained by the present invention has a different mass spectrum characteristic from the thermospray method already reported.

(1) In the ordinary thermospray method, an electrolyte such as ammonium acetate is required to obtain molecular ions. However, in the ion source of the present invention, the molecular ion strength does not depend on the amount of ammonium acetate. Observation is possible even with simple mixtures of water and methanol. FIG. 9 shows that, using the ion source of the present invention, 100% water, water / methanol (50/50), water /
Methanol (10/90), 0.01 M ammonium acetate aqueous solution, and 0.1 M ammonium acetate aqueous solution used pseudo-molecular ions of sucrose ((M + N
The ionic strength of (a) cation) was compared. As can be seen from the results, in the ion source according to the present invention, the ionic strength does not depend much on the type of the mobile phase, so that it is convenient to determine the analysis conditions of the liquid chromatograph.

(2) By adding an alkali metal or the like, an ion having an alkali metal added to a molecule can be stably obtained.

(3) In the thermospray method, multivalent ions such as divalent and trivalent ions which are inconvenient for analysis are easily generated. However, the method according to the present invention has few polyvalent ions and has a simple mass spectrum. Is easy to interpret.

(4) As in the present invention, when the ion source is a common ion source for the atmospheric pressure ionization method and the thermospray method, the conventional thermospray method can mainly measure only those having a strong polarity. , While only less polar ones could be measured, with the new ion source,
Measurement can be performed regardless of the polarity. FIG. 10 shows a graph of 1 according to the present invention, atmospheric pressure ionization method and thermospray method.
Comparison of molecular ionic strength of 7 alpha progesterone (one kind of steroid, which is not very strong), arginine (one kind of amino acid, which is slightly strong), and stachyose (one kind of sugar, which is particularly strong) Was.
As can be seen from the results, it is difficult to measure particularly polar sugars by the atmospheric pressure ionization method, and it is difficult to measure steroids that are not very polar by the thermospray method, whereas in the method of the present invention, In each case, the molecular ionic strength can be measured strongly.

[0021]

According to the present invention, the two ion sources for the atmospheric pressure ionization method and the thermospray method can be made into one ion source operating under the atmospheric pressure. With the analyzer, (1) the range of application for important non-volatile substances related to living organisms is greatly expanded, and (2) continuous long-time operation without the need to provide a trap in the exhaust system as in the ordinary thermospray method. (3) It is no longer necessary to introduce a large amount of gas into a vacuum, and contamination inside the ion source is reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an ion source of a mass spectrometer showing one embodiment of the present invention.

FIG. 2 is a diagram showing a method for heating a metallic capillary.

FIG. 3 is a diagram showing a method for heating a metallic capillary.

FIG. 4 is a diagram showing an example of a corona discharge electrode.

FIG. 5 is a diagram showing an example of a corona discharge electrode.

FIG. 6 is a diagram showing a change in ionic strength of a molecular ion (a (M + Na) cation having a molecular weight of 365) of sucrose according to the distance between the tip of the metallic capillary and the first pore in the thermospray mode.

FIG. 7 is a diagram showing a voltage and a current value applied to a discharge electrode.

FIG. 8 shows a mass spectrum of sucrose.

FIG. 9 is a diagram showing a change in molecular ion intensity depending on a mobile phase of a liquid chromatograph.

FIG. 10 is a comparison diagram of the molecular ion intensities of 17alpha progesterone, arginine, and stachyose by the atmospheric pressure ionization method, the thermospray method, and the method according to the present invention.

FIG. 11 is a configuration diagram of a general liquid chromatograph / mass spectrometer.

FIG. 12 is a configuration diagram of an ion source of the atmospheric pressure ionization method.

FIG. 13 is a configuration diagram of an ion source of a thermospray method.

FIG. 14 is a configuration diagram showing an example of an ion source obtained by combining an atmospheric pressure ionization method and a thermospray method.

FIG. 15 is a configuration diagram showing an example of an ion source obtained by combining an atmospheric pressure ionization method and a thermospray method.

FIG. 16 is a diagram showing a change in a current value depending on a distance from a central axis when ions generated in a thermospray mode are detected at a position 10 mm from a capillary tip at atmospheric pressure by an electrode having a width of 1 mm.

[Explanation of symbols]

1: Liquid chromatograph, 2: Piping, 3: Ion source, 4
... electric field, 5 ... magnetic field, 6 ... ion detector, 7 ... data processing device, 8 ... power supply for ion source, 9 ... exhaust system, 10 ... signal or control line, 11 ... metal capillary, 12 ... metal block, 13 needle electrode, 14 first pore, 15
Second pore, 16: power supply, 17: cartridge heater,
18 thermocouples, 19 wires, 20 wires or mesh, 21 edges, 22 needles, 23 auxiliary electrodes,
24: an electrode support block, 25: an electrode support block with an exhaust port, 26: an insulating plate, 27: a portion having an expanded inner diameter,
28 ... Capillary with large inner diameter.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01J 49/00-49/48 G01N 27/62

Claims (11)

(57) [Claims] A passage for guiding a solution containing a sample into an ionization space; a heating means provided at an end of the passage; a pore; a high vacuum space from which ions to be analyzed are taken; Comprising a discharge electrode provided in the ionization space,
The heating means heats the solution at a temperature at which the solution is sprayed from the passage into the ionization space, and the solution guided through the passage by the spraying of the solution and discharge by the discharge electrode is ionized in the ionization space, and the ions are ionized. An ion source which is guided to the high vacuum space through the pores and is taken out of the high vacuum space. 2. A passage for introducing a solution containing a sample into an ionization space, a heating means provided at an end of the passage, a pore, and a high vacuum space from which ions to be analyzed are taken out. The ion source is configured, wherein the solution guided through the passage is ionized in an ionization space, and the ions are guided to the high vacuum space through the pores and extracted from the high vacuum space, The ion source is characterized in that the heating means comprises a discharge electrode for heating and ionizing the solution at a temperature at which the solution is sprayed from the passage into the ionization space and for ionizing the sprayed sample in the ionization space by discharge. . 3. The ion source according to claim 1, wherein said passage comprises a capillary. 4. The ion source of claim 3, wherein said capillary is made of a metal capillary. As claimed in claim 5, wherein said heating means is provided around the passage, the ion source according to claim 1 or 2, wherein it is a heating means for a heater. 6. The ion source of claim 1 or 2, wherein the pressure in the ionization space is in the range from several Torr of atmospheric pressure. 7. A method according to claim 1, further comprising a passage for introducing a solution containing the sample into the ionization space, a pore, a high vacuum space for extracting ions to be analyzed, and a discharge electrode provided in the ionization space. The passage has a heating function, the solution is heated at a temperature at which the solution is sprayed from the passage into the ionization space, and the solution guided through the passage by the spray of the solution and discharge by the discharge electrode is ionized in the ionization space,
The ion source is characterized in that the ions are guided to the high vacuum space through the pores and are extracted from the high vacuum space. 8. A passage, which leads a solution containing a sample to an ionization space, a pore, and a high vacuum space from which ions to be analyzed are taken out, wherein the solution led through the passage is provided. An ion source that is ionized in an ionization space, the ions are guided to the high vacuum space through the pores, and are extracted from the high vacuum space, wherein the passage is a passage including a heating function, and the passage is A discharge electrode for heating and ionizing the solution at a temperature at which the solution is sprayed into the ionization space, and for ionizing the sprayed sample in the ionization space by discharge. 9. The ion source according to claim 7, wherein said passage has a structure heated by energization. An electrically budge passage 10. The solution that contains the sample into the ionization space, a heating means provided at an end of the passage, a pore, ions to be analyzed are placed on a high vacuum space taken Mass spectrometer, and a discharge electrode provided in the ionization space, wherein the heating means heats the solution at a temperature at which the solution is sprayed from the passage into the ionization space, and discharges the solution by the spray and the discharge electrode. The mass spectrometer is characterized in that the solution guided through the passage is ionized in an ionization space, the ions are guided to the high vacuum space through the pores, and analyzed by the mass spectrometer. 11. A passage for introducing a solution containing a sample into an ionization space, a heating means provided at an end of the passage, a pore, a high vacuum space for extracting ions to be analyzed, And a mass spectrometer for analyzing ions extracted from the pores.The heating means heats and ionizes the solution at a temperature at which the solution is sprayed from the passage into the ionization space, and sprays the solution in the ionization space. A mass spectrometer comprising a discharge electrode for ionizing a sample by discharge, wherein the solution is ionized in an ionization space.