JP2000057991A - Ion source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce positive or negative ions with high efficiency, by installing an electrode near a spray capillary and by applying an electric field on liquid and by spraying the liquid, in a sonic spray ionization method. SOLUTION: This ion source is equipped with a capillary 2 for spraying liquid into the atmospheric air, and an orifice 3 installed by inserting a part near the head of the capillary 2 and formed so that gas will flow up to the head of the capillary 2 along the circumferential wall surface of the capillary 2. A gas flow velocity near the head of the capillary 2 is about a sound velocity, and a voltage is applied between the liquid in the capillary 2 and the orifice 3 or an electrode installed near the capillary 2. Hereby, the electric potential of the liquid can be set equally to the earth potential, and combination of a solution separation means with a liquid introduction part is easily realized. Also, the polarity of produced ions can be controlled according to the polarity of the voltage applied on the electrode. Besides, multi-charged ions of material having a large mass, such as a protein or the like, or the like can be produced with high efficiency and excellent repeatability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion source and a mass spectrometer using the same, and more particularly, to an ion source suitable for ionizing a sample existing in a liquid and introducing it into a mass spectrometer, and a mass using the same. The present invention relates to an analyzer, a liquid chromatograph / mass spectrometer coupling device, and a capillary electrophoresis / mass spectrometer coupling device.

[0002]

2. Description of the Related Art Analytical Chemistry 66
(1994) pp. 4557-4455 (Ana)
Lytical Chemistry, 66 (199
4) pp 4557-4559) describes a sonic spray ionization method. By flowing gas coaxially from the outside of the capillary and spraying the liquid at the end of the capillary, ions and charged droplets are stably generated. When the gas flow velocity at the tip of the capillary is a sonic velocity, the amount of positive and negative ions generated by spraying becomes maximum.

In this case, no electric field or voltage is applied to the liquid. The spray gas produced is totally neutral,
The amount of positive ions and the amount of negative ions are equal.

Further, Journal of Physical Chemistry 88 (1984), p.
459 (Journal of Physical)
Chemistry, 88 (1984) pp 4451-4449) or U.S. Pat. No. 5,130,538 describes electrospray ionization. A high voltage of at least 2.5 kV is applied between the metal capillary into which the liquid is introduced and the counter electrode (ion inlet of the mass spectrometer). That is, a high voltage is applied to the liquid. As a result, the charged droplets are sprayed from the liquid toward the counter electrode into the space where the electric field is applied (electrostatic spraying phenomenon), and ions are generated from the charged droplets. The polarity of the charged droplet or ion matches the polarity of the applied voltage. In the electrospray ionization method, ions having a large charge number can be generated, and are often used for analysis of proteins and the like. The liquid flow rate is usually used in the range of 0.001 to 0.01 ml / min.

Further, Analytical Chemistry 5
9 (1987) pp. 2642 to 2646 (An
alkaline Chemistry, 59 (198
7) pp 2642-2646) or US Pat.
988 describes an ion spray ionization method. As in the case of the electrospray ionization method, a high voltage of 2.5 kV or more is applied between the liquid at the end of the spray capillary and the counter electrode (the ion inlet of the mass spectrometer). As a result, ions and charged droplets are sprayed from the liquid toward the counter electrode into the space where the electric field is applied.
(Electrostatic Spray Phenomenon) In the ion spray ionization method, unlike the electrospray ionization method, a gas flows outside the spray capillary in order to promote the vaporization of the charged droplets. Therefore, since ions are generated using the same electrostatic spray phenomenon, the generated ion species are exactly the same as in the case of electrospray ionization. The polarity of the charged droplet or ion matches the polarity of the applied voltage. But,
The liquid flow rate is used in the range of 0.01 to 1 ml / min, which is higher than the electrospray ionization method.

[0006] The gas flow velocity is set to a maximum of 216 m / s.

[0007] The Journal of Chemical Physics describes that an electrode is provided in the vicinity of a spray portion when a liquid gas is sprayed and a high voltage of 3.5 kV is applied thereto to generate charged droplets and ions. 71 (1979) 4th
451 to 4463 (Journal of C
chemical Physics, 71 (1979) pp
4451-4463) or U.S. Pat.
In the issue. In this example, both liquid and gas are discharged from the injection needle having an inner diameter of 0.3 mm. However, unlike the above-described sonic spray ionization method or ion spray ionization method, the direction in which the liquid is discharged and the direction of the gas flow are orthogonal to each other. The gas flow velocity is unknown.

When a mixed solution containing a large number of substances is introduced into a mass spectrometer, the mass spectrum obtained is too complicated to identify the substance in some cases. Therefore, in the analysis of the mixed solution, a method is used in which the mixed solution is first separated using a means such as a liquid chromatograph or a capillary electrophoresis apparatus, and the extract is introduced into a mass spectrometer. That is, there are a liquid chromatograph / mass spectrometer coupling device and a capillary electrophoresis / mass spectrometer coupling device that realize online separation and analysis of a mixed solution. In a liquid chromatograph, a solution is separated by flowing a solution at a constant flow rate through a column filled with a filler by a pump. Therefore, the potential of the extract is the ground potential. On the other hand, in a capillary electrophoresis apparatus, a high voltage of about 20 to 30 kV is applied to both ends of the capillary with respect to the solution introduced into the capillary, and the solution is separated by electrophoresis. Usually, the potential on the outlet side of the capillary is set to the ground potential, and the potential of the extract is set to the ground potential.

[0009]

In a mass spectrometer, ions are analyzed based on m / z, which is a value obtained by dividing the mass m of an ion by the number of charges z. A mass spectrometer having a very large upper limit of the mass spectrometry range is not practical because the whole device is large and expensive. Therefore, in a general mass spectrometer, the upper limit of the mass analysis range is about m / z = 1000 to 2000.

In the above prior art, ions are mainly generated from fine charged droplets. In the prior art related to the electrospray ionization method and the ion spray ionization method, a charged droplet having a high charge density is generated,
A multiply-charged ion having a charge number z of 3 or more can be generated. Therefore, even a substance having a large mass such as a protein having a mass m of about tens of thousands can be analyzed because the value of m / z falls within the mass analysis range. However, in the prior art relating to the sonic spray ionization method and the fourth prior art, there is a tendency that charged droplets having a low charge density are generated and ions having a small charge number z are generated. That is,
Generation of monovalent and divalent ions such as peptides and mass spectrometry are possible. However, in the analysis of a protein or the like having a very large mass number m, it is not possible to generate a multivalent ion having a charge number z of 3 or more. It has the disadvantage that it cannot be analyzed.

In the prior arts relating to the electrospray ionization method and the ion spray ionization method, a high voltage is applied to a liquid, and ions and charged droplets are generated by an electrostatic spray phenomenon. The droplets generated by this phenomenon include fine charged droplets with high charge density, but also large charged droplets of micron order with low charge density. The large charged droplet has a mass that is too large compared to the charge amount, and it is difficult to control its movement by an electric field or a magnetic field. Therefore, when performing mass analysis using a quadrupole mass spectrometer or a quadrupole ion trap mass spectrometer, large charged droplets reach the detection unit without being separated by mass and are detected as random noise. Particularly, in the prior art relating to the ion spray ionization method, the generation of large charged droplets is remarkable because the liquid flow rate is high. A similar problem exists in the fourth prior art. In the fourth prior art, the liquid is sprayed by a gas flow. However, the spray section has a configuration in which the direction in which the liquid is discharged and the direction of the gas flow are orthogonal to each other. Therefore, at the end of the injection needle from which the liquid is discharged, there is a difference in the gas flow velocity between the upstream side and the downstream side of the gas flow, and the size of the droplet generated on the downstream side is larger, so that the droplet size is larger. There's a problem. Also, electrodes (US Pat. No. 430)
The electrode 27) in FIG. 2 of No. 0044 is a single rod. For this reason, the charge density of the droplets generated in a region closer to the electrode and in a region farther from the electrode in the liquid spray portion is different. Therefore, many large droplets having a low charge density are generated. In the fourth prior art, a counter gas flow is generated at the ion inlet of the mass spectrometer to promote the vaporization of the droplet, but sufficient vaporization is not possible. As described above, ions are mainly generated from fine charged droplets, and it is known that the ion generation efficiency is higher as the droplet size is smaller. The efficiency of generating ions from large charged droplets is so low as to be ignored. Therefore, there is a problem that the ion detection sensitivity is significantly reduced due to the reduction of the signal intensity and the increase of the noise level due to the generation of large charged droplets.

Further, in the prior arts relating to the electrospray ionization method and the ion spray ionization method, it is necessary to optimize the ion intensity by adjusting the position of the ion source every time the spraying is started, and the operation is complicated. There are inherent problems with the electrostatic spray phenomenon. this is
This is because the electrostatic spray phenomenon has a characteristic that the shape of the generated spray gas is significantly different due to dirt or wetness of the spray capillary or the counter electrode (mass spectrometer ion intake port).
Therefore, the conventional techniques relating to the electrospray ionization method and the ion spray ionization method require skill and have a problem of extremely low operability.

Further, in the prior art relating to the above-mentioned electrospray ionization method and ion spray ionization method, a liquid chromatograph / mass spectrometer coupling device in which a solution separation means such as a liquid chromatograph or a capillary electrophoresis device is connected to the upstream side, When employed in a capillary electrophoresis / mass spectrometer combination device, a high voltage is applied to the entire solution separation means, and there is a risk of electric shock during handling. In some cases, the potential of the entire solution separating means is set to the ground potential, but in this case, since a kind of electrophoresis is realized in the capillary, the reproducibility of ion generation and ion analysis is significantly reduced. Therefore, the liquid chromatograph / mass spectrometer coupling device and the capillary electrophoresis / mass spectrometer coupling device have a problem that they do not exhibit sufficient operation and function.

[0014]

In order to achieve the above object, there is provided a flow passage for flowing a liquid to a predetermined position, and at least a part of the flow passage for passing the liquid is an insulator. An ion source is provided, comprising: an electric field applying means for applying an electric field to the liquid; and a spray means disposed downstream of the liquid to which the electric field is applied, for spraying the liquid to generate a charged gas.

In order to achieve the above object, a flow path for flowing a liquid to a predetermined position, and at least a part of the flow path for the liquid, is an insulator, and an electric field is applied through the insulator. Spraying means which is a room comprising: an electric field applying means for supplying gas; a gas supply unit for supplying gas; a supply port for supplying gas from the gas supply unit; an injection port for discharging gas; and a holding unit for holding the flow passage. Is provided.

In order to achieve the above object, a separation means for separating a sample liquid containing a mixture, a flow path for flowing the separated sample liquid to a predetermined position, and At least a part of the path is an insulator, an electric field applying means for applying an electric field through the insulator, a gas supply unit for supplying gas, a supply port for supplying gas from the gas supply unit, and discharging gas. There is provided a mass spectrometer including a spray unit as a room including an injection port and a holding unit for holding the flow passage, and an analysis unit for performing mass analysis and analysis of the sprayed gas.

Further, in order to achieve the above object, a separating means for separating a sample liquid containing a mixture, a flow path for flowing the separated sample liquid to a predetermined position, and At least a part of the path is an insulator, an electric field applying means for applying an electric field through the insulator, a gas supply unit for supplying gas, a supply port for supplying gas from the gas supply unit, and discharging gas. There is provided a mass spectrometer including a spraying unit, which is a room including an injection port and a holding unit for holding the flow passage, and a quadrupole mass spectrometer for mass-analyzing and analyzing the sprayed gas.

Further, in order to achieve the above object, a separating means for separating a sample liquid containing a mixture, a flow passage for flowing the separated sample liquid to a predetermined position, and At least a part of the path is an insulator, an electric field applying means for applying an electric field through the insulator, a gas supply unit for supplying gas, a supply port for supplying gas from the gas supply unit, and discharging gas. There is provided a mass spectrometer including a spraying unit, which is a room including an injection port and a holding unit that holds the flow passage, and a quadrupole trap mass spectrometer that performs mass analysis and analysis of the sprayed gas.

Further, in order to achieve the above object, a separating means for separating a sample liquid containing a mixture, a detecting means for detecting characteristics of the separated sample liquid, and A flow path for flowing the sample liquid to a position, an electric field applying means for applying an electric field through the insulator, at least a part of the flow path being an insulator, a gas supply unit for supplying a gas, and the gas Spraying means, which is a room comprising a supply port for supplying gas from the supply section, an injection port for discharging gas, and a holding section for holding the flow passage, and an analysis means for mass-analyzing and analyzing the sprayed gas, A mass spectrometer having a control unit for controlling an electric field applying unit and an analyzing unit based on a signal from the detecting unit is provided.

Further, in order to achieve the above object, an injection port, which is formed by spraying a liquid to generate polyvalent ions having at least three charges, is partially or entirely made of an insulating material. There is provided a mass spectrometer having a first electrode disposed around and a second electrode disposed to face the first electrode and generating a uniform electric field between the first electrode and the first electrode. You.

In order to achieve the above object, a liquid separating means for separating a liquid, a metal for determining a potential of the liquid separated by the liquid separating means, a flow passage through which the liquid is supplied, An electric field applying means electrically insulated from the flow passage for applying an electric field to the liquid flowing in the passage,
A part that is arranged downstream of the liquid to which the electric field is applied and has an ion source that has a spraying unit that sprays the liquid to generate charged droplets, and that generates a multiply-charged ion having at least three charges by spraying the ion source; Or, an injection port entirely composed of an insulator, a first electrode disposed around the injection port, and disposed opposite to the first electrode, uniformly between the first electrode. There is provided a mass spectrometer to which a liquid separating means including a mass spectrometer having a second electrode for generating a strong electric field is coupled.

According to another aspect of the present invention, there is provided a fuel cell system comprising: a first electrode disposed around a nozzle for spraying a liquid; and a second electrode disposed opposite to the first electrode. In the uniform electric field generated by the above method, multiply-charged ions having at least three charges are generated, and a mass spectrometry for analyzing the ions by a mass spectrometer is provided.

Further, in order to achieve the above object, a separation step of separating the liquid, a step of applying an electric field to the separated liquid having a predetermined potential, and a step of applying an electric field to the liquid, Mass in which a multiply-charged ion having at least trivalent charge passes through a uniform electric field generated between the electrode and a second electrode disposed opposite to the first electrode to perform mass analysis. Supplying the mass spectrometer to the mass spectrometer for analysis by mass spectrometry.

According to another aspect of the present invention, there is provided a fuel cell system comprising: a first electrode disposed around an injection port for spraying a liquid; and a second electrode disposed opposite to the first electrode. Charge generated in a uniform electric field generated by at least 3
An electric field applying step of changing the polarity of an electric field applied to the liquid in accordance with the polarity of the multiply-charged ions having a valence.

In order to achieve the above object, an electric field applying step for changing the polarity of an electric field applied to the liquid, a first electrode disposed around an injection port for spraying the liquid, Generating a multiply-charged ion having a polarity corresponding to the polarity of the electric field in which the electric charge is at least trivalent in a uniform electric field generated between the second electrode disposed opposite to the electrode; There is provided a mass spectrometry comprising:

An object of the present invention is to provide a high-efficiency ion source, a high-sensitivity mass spectrometer or a high-sensitivity mass spectrometer capable of realizing the generation and analysis of polyvalent ions having a charge number z of 3 or more in order to analyze a substance having a large mass number. An object of the present invention is to provide an efficient ionization method and a high-sensitivity mass spectrometry.

It is another object of the present invention to provide a high-sensitivity mass spectrometer and a high-sensitivity mass spectrometry method in which large charged droplets which cause a reduction in ion detection sensitivity are not generated.

Yet another object of the present invention is to provide a highly efficient ion source, a highly sensitive mass spectrometer, a highly efficient ionization method, and a highly sensitive mass spectrometry with high operability.

Still another object of the present invention is to enable the potential of the liquid to be set to the ground potential, to be safe, to have high reproducibility of ion generation and ion analysis, to obtain a highly efficient ion source, and to have a high sensitivity mass spectrometer. Another object is to provide a high-efficiency ionization method and a high-sensitivity mass spectrometry.

In the conventional sonic spray ionization method,
The atomization initially produces electrically neutral droplets. The droplets contain the same number of positive and negative ions, but the density distribution of the positive and negative ions is significantly different near the surface than at the center due to the surface potential determined by the combination of the droplet and the surrounding gas. Further, fine droplets are separated from the droplet surface by the sonic gas flow. Since the number of positive and negative ions is different in these fine droplets, the droplets are charged as a whole although the charge density is low. The ions are generated from the finely charged droplets by the ion evaporation process or the vaporization of the completely charged droplets.

In the ionization method and ion source of the present invention, an electric field is applied to the liquid introduced into the capillary in the sonic spray ionization method from an electrode provided outside. For example, when a negative voltage is applied, the positive ion density becomes significantly higher than the negative ion density near the liquid surface. Therefore, when the liquid is sprayed by the gas flow, positively charged droplets are preferentially generated, and the sprayed gas is positively charged. Positive ions are concentrated near the surface of the droplet due to Coulomb repulsion. The charge density of these charged droplets is higher than the charge density of the charged droplets generated in the usual sonic spray ionization method. Further, when fine droplets are separated from the droplet surface by the sonic gas flow, fine droplets having extremely high charge density are generated. It is known that ions are generated from the fine droplets by the ion evaporation process or the evaporation of completely charged droplets. In the former case, the ion generation efficiency of multiply charged ions is generally much lower than that of monovalent ions and is negligible, but when the charge density of the droplet is high, the Coulomb repulsion in the droplet is significantly large Therefore, the ion generation efficiency of the multiply-charged ions also increases. Therefore, multiply-charged ions can also be generated. With the ionization method of the present invention, the density of positive or negative ions near the liquid surface can be very high before being sprayed. Therefore, it is meaningless to apply an electric field to the droplet generated by spraying. It is necessary to apply an electric field to the liquid before being sprayed.

Further, in the mass spectrometer and mass spectrometry of the present invention, since the electrostatic spraying phenomenon is not used for ion generation, contamination of the ion inlet of the mass spectrometer and the spray capillary is reduced.
Ion formation is not affected by wetting. Therefore, handling of the apparatus is easy, and reproducibility of ion generation is high.

In the mass spectrometer and mass spectrometry of the present invention, the potential of the liquid introduced into the ion source can be set to the ground potential. This makes it easy to connect a capillary electrophoresis device, a liquid chromatograph, or the like upstream of the ion source. Further, the reproducibility of ion generation is not impaired by the bonding.

The method of applying an external electric field to a liquid includes:
There is a method in which an insulator such as quartz or resin is used as the material of the capillary, and a voltage is applied to a metal orifice into which the end of the capillary is inserted. As yet another alternative,
There is a method in which an insulator is used as the material of the capillary, and the outer surface near the end of the capillary is coated with a metal, and a voltage is applied to the outer surface of the capillary. Further, there is a method of inserting an insulator capillary into a metal tube to which a voltage is applied. In any method, it is necessary to keep the distance from the liquid surface to the electrode constant for high-efficiency ion generation. When a conductor such as a metal is used as the material of the capillary, it is necessary to apply a high voltage to the electrode because the metal capillary has an electrical shielding effect.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a configuration diagram of an ion source according to one embodiment of the present invention. The liquid is introduced into the capillary 2 through the flow passage 1. The tip of the capillary 2 is inserted coaxially into the orifice 3. The gas supplied from the gas supply unit 4 is introduced into the ion source main body 6 from the gas introduction pipe 5 and is discharged from the orifice 3 to the outside. The orifice 3 is made of metal, and a voltage is applied between the orifice 3 and the metal tube 8 by a power supply 7. Since there is no conduction between the orifice 3 and the liquid, no current flows, but an electric field is applied to the liquid. The liquid that has reached the end of the capillary 2 is sprayed with gas. Ions and fine charged droplets are generated in the spray gas.

FIG. 2 is a sectional view of an ion source according to an embodiment of the present invention. At a flow rate of 5 to 100 microliters per minute, the liquid is introduced into the metal tube 8 whose potential is set to the ground potential, and then into the quartz capillary 2 (inner diameter 0.1 mm, outer diameter 0.2 mm). An orifice plate 9 having an orifice 3 (inner diameter 0.4 mm, thickness 1 mm) is made of duralumin, and a voltage is applied from a power supply 7. The capillary 2 is inserted into the Teflon tube 10 and the stainless steel tube 11, and is fixed to the stainless steel tube 11 with an adhesive. The liquid and the ion source body 6 are electrically insulated by the space between the two stainless steel tubes 11. Capillary 2 and orifice 3
Are aligned, and the end of the capillary 2 is exposed from the orifice plate 9 by about 0.2 mm. Stainless steel pipe 11
Is also used for fixing the capillary 2 to the ion source body 6. When the orifice plate 9 is cooled by the adiabatic expansion of the gas, the generated droplets may condense and do not become fine. In this case, large charged droplets are generated as a result, and the amount of ions is reduced. This problem can be avoided by installing a heater on the orifice plate 9 or the ion source main body 6 or by heating the gas introduced into the ion source with a heater in advance. The gas is introduced into the gas introduction pipe 5 by a gas cylinder or a gas compressor. On the way, a gas flow controller such as a mass flow controller or a purge meter is installed to adjust the flow rate of gas used for spraying. When the gas flow rate is just 3 liters per minute, the gas flow velocity near the end of the capillary 2 becomes sonic.

It is known that ions are generated from fine charged droplets having a diameter of 10 nanometers or less. In this embodiment, fine charged droplets are generated by gas spraying as in the sonic spray ionization method. The average droplet size generated by gas spraying decreases with increasing gas flow velocity, but the average droplet size increases with increasing gas flow velocity. This is because a shock wave is generated. (See FIG. 9) Therefore, when the gas flow velocity is the sonic velocity, the average droplet size is minimized, and ion generation is performed most efficiently. The smaller the wall pressure of the capillary 2, the higher the efficiency of generating fine droplets and consequently the higher the efficiency of ion generation.

The generation of the sonic flow requires a gas pressure of about 2 atm upstream of the orifice 3, assuming that the pressure around the ion source is 1 atm and the thickness of the orifice 3 is ignored. However, depending on the thickness of the orifice plate 9, the pressure reduction in the orifice 3 may not be ignored. It is convenient to provide a pressure gauge in the ion source body 6 and adjust the gas pressure to generate a sonic gas flow. In this case, orifice 3
It is safe to adjust the pressure so that a gas pressure of about 0.5 to 5 atm can be applied upstream of the pressure. It is also realistic to generate a sonic flow by a gas flow rate adjusting means such as a purge meter or a mass flow meter. If the thickness of the orifice 3 is too large, the pressure in the orifice 3 increases, and it becomes necessary to pressurize unnecessarily. Ion source body 6
It is not necessary to be thicker than the wall thickness. Conversely, orifice 3
Is too thin, it cannot withstand the pressure difference between the inside and outside of the ion source body 6 in terms of strength. Therefore, it is realistic that the diameter is about 0.5 to 1 mm, which is thicker than the diameter of the capillary 2. Ion source body 6 upstream of orifice 3
In order to prevent the gas pressure from being reduced, a space that serves as a gas reservoir is required. The size of the space needs to be at least five times the diameter of the capillary 2.

FIG. 3 shows a sketch of the ion source according to the embodiment of the present invention shown in FIG.

The spray gas is released in the forward direction. The cross section of the ion source main body 6 in a direction perpendicular to the central axis of the capillary 2 is quadrangular, but may be circular. The orifice plate 9 has four holes in addition to the orifice 3,
Four screws are used to fix the orifice plate 9 to the ion source body 6. Under the microscope, the center of the orifice 3 and the center of the capillary 2 are adjusted so as to coincide with each other, and the orifice plate 9 is fixed by screws. In this way, a uniform gas flow is formed at the end of the capillary 2.

The dimensions in the figure indicate that the ion source of the present invention is extremely compact.

FIG. 4 shows the dependence of the total ion current generated by the spraying on the voltage applied to the orifice 3. This is an experimental result when a solution containing 47.5% methanol / 47.5% water / 5% acetic acid was used as a liquid. It is shown that when a positive voltage is applied, negative ions and charged droplets are generated, and when a negative voltage is applied, the opposite is true. In other words, it is shown that if a voltage having a polarity opposite to the polarity of the ion to be generated is applied, ions having a desired polarity are generated. When the absolute value of the applied voltage is 1 kV or less, the ion current decreases with an increase in the applied voltage, but when the absolute value of the applied voltage is about 1 kV or more, the ion current does not change much and saturates. Is shown. This indicates that the ion density of the same sign near the liquid surface just before spraying reached the limit. Therefore, it is practical to set the absolute value of the applied voltage in the range of 1 kV to 2 kV based on the experimental results.

Assuming that the electric conductivity of the liquid is sufficiently high, the potential of the central axis of the capillary 2 can be regarded as 0 V, and the electric field strength is 5000 kV / m (= 1000 V / 0.2 m).
m). Therefore, when the inner diameter of the orifice 3 is larger or when the electrode is installed at a more distant position, it is necessary to apply a higher voltage.

FIG. 5 shows the results of mass analysis of ions generated when the applied voltage is set to -1 kV. This is a 1 micromol / liter (mmol / L) cytoc
rome-C (a kind of protein, molecular weight about 1250
0) A solution (solvent: 48% methanol water to which 5% acetic acid was added) was introduced into the capillary at a flow rate of 30 microliter / minute, and ions generated by spraying using a sonic gas flow were analyzed by a quadrupole mass spectrometer. It is an analysis result (mass spectrum). A series of multiply-charged ions from 13 valences to 20 valences centered on 16-valent ions (m / z = 766) in which 16 protons are added to the cytochrome-C molecule are clearly shown in the region of m / z = 1000 or less. Is detected.

Heretofore, ion-spray ionization and electrospray ionization (the principle of ion generation is almost the same) have been used for the production of multiply charged ions. Therefore, ions were generated from the same cytochrome-C solution using the ion spray ion method, and ions were detected by the same quadrupole mass spectrometer. FIG. 6 shows the result.
The vertical axis is the same as in FIG. As for the multiply-charged ions, the same spectrum turn in the mass spectrum was obtained, but the ion intensity was 2.6 compared with the result of FIG.
About twice as low. This corresponds to the ion detection sensitivity obtained by setting the applied voltage to about 700 V in the ion source of the present invention. In FIG. 6, the noise level is
It is shown to be significantly higher than This noise is
This is because a large amount of large charged droplets are generated in the ion spray ion method as compared with the ionization method of the present invention, and they are detected as random noise. The S / N ratio is about 9 times smaller than that of FIG. Therefore, it is shown that more highly sensitive ion detection can be performed by using the ionization method of the present invention shown in FIG. In FIG. 6,
Many ions derived from the solvent are detected in the region where m / z is 300 or less. Analysis of such complex mass spectra requires skill.

FIGS. 7 and 8 show myoglobin solution (concentration: 1 micromol / liter, solvent: 48% methanol water to which 5% acetic acid was added) and hemoglobin solution (concentration: 1 micromol / liter, solvent: 5% acetic acid added) 48% methanol water). myoglobin has a molecular weight of 17
The value is 200, and a series of multiply-charged ions from 18 valences to 26 valences centering on 22-valent ions (m / z = 772) to which 22 protons are added is detected. hemoglob
“in” is a protein having a molecular weight of 64,500 in which two types of subunits are bonded two by two. In FIG. 8, the mass spectrum of the subunit is observed.

FIG. 9 shows the spray gas flow rate F dependence on the relative intensity of the 16-valent ions in FIG. The ion source used was that of the embodiment shown in FIG. The gas flow velocity is in a relationship that increases with an increase in the gas flow rate. In this experiment, it is already known that when the gas flow rate is about 3 liters / minute, the gas flow rate corresponds to the speed of sound (Mach 1), and when the gas flow rate is about 7 liters / minute, the gas flow rate is less than or equal to Mach 2. (Analytical Chemistry 66 (1994) 45th
Item 57 to Item 4559 (Analytical Ch
chemistry, 66 (1994) pp 4557-45
59)) From the figure, when the gas flow rate is 1.4 liters / min or less, no ions are generated, and when the gas flow rate is 1.4 liters / min or more, the ion intensity increases with the gas flow rate. The intensity is maximum at about 3 liters / min, and at higher flow rates (supersonic range), it is shown that the ionic strength decreases due to the generation of shock waves. Thus, the ion intensity dependence on the gas flow rate is similar to that of the conventional sonic spray ionization method, but the spray gas generated from the ion source of the present invention is characterized by being positively or negatively charged as a whole. .

As described above, it is also possible to control the gas flow rate by adjusting the gas flow rate F using the flow rate adjusting means. In the example of the ion source shown in FIG.
The area S of the cross section perpendicular to the capillary between the orifice and the capillary is calculated to be 9.4 × 10−8 m 2. When F is in a standard state (20 ° C., 1 atm), F
/ S is estimated to be 250 m / s when F is 1.4 liters / minute, and about 1200 m / s when F is 7 liters / minute. Here, it should be noted that the unit of F / S is a velocity, but is different from a gas flow velocity.

The gas flow rate can be controlled by the gas pressure in the ion source. In FIG. 9, ion generation starts at about 1.2 atm. Assuming isentropic flow, if the orifice thickness is sufficiently thin, a Mach of about 0.5 at a gas pressure of 1.2 atm and a Mach 1 of about 2 atm are achieved. To achieve Mach 2 requires 7.8 atmospheres. Incidentally, Mach 3 requires about 40 atm, which is problematic in practical use.

In order to control the gas flow rate by the gas pressure, it is practical to adjust the gas pressure in the range of 0.5 to 5 atmospheres.

In this ion source, the orifice diameter is 0.4.
mm, and the outer diameter of the quartz capillary is 0.2 mm. Therefore, the sectional area S between the gap between the orifice and the capillary is calculated to be 9.4 × 10 −8 m 3. Therefore, when the parameter F / S is used, when F is 1.4 liter / min, the speed is 250 m / s, and the state of the sound velocity is 53 m / s.
0 m / s. (It should be noted that the unit of the parameter F / S is velocity, but it is not related to the actual gas flow velocity.) Even if F is increased to 7 (F / S = 1200 m / s) or more, The ion production efficiency does not increase only by increasing the consumption.

Therefore, the F / S is actually 250 to 12
Used within the range of 00 m / s. Since S is determined by the structure of the ion source, it is convenient to adjust the gas flow rate F using a flow controller such as a mass flow meter or a purge meter.

The gas is used for atomizing the liquid. Therefore, the type of gas hardly contributes to ion generation. Actually, it is convenient to use nitrogen gas. This is because it is inexpensive and is effective in vaporizing droplets because it is dry. Similar effects can be obtained by using air, oxygen, carbon dioxide, a rare gas, or the like in addition to nitrogen gas.

FIG. 10 is a sectional view of an ion source according to another embodiment of the present invention. Aluminum is deposited on the outer surface of a 5 mm end portion of the quartz capillary 2 (inner diameter 0.01 mm, outer diameter 0.05 mm), and a voltage is applied from a power supply 7. As described in the description of FIG. 4, in order to efficiently generate ions, it is necessary to generate a certain or more electric field intensity. In this embodiment, the voltage applied to the electrodes can be set to a lower voltage than in the embodiment of FIG. In this embodiment, since the ion source body 6 can be set to the ground potential, the safety during operation is extremely high.

FIG. 11 is a sectional view of an ion source according to still another embodiment of the present invention.

The resin capillary 2 is inserted into the tubular electrode 12, and a voltage is applied to the electrode 12 from the power supply 7. The resin capillary 2 and the electrode 12 are fixed with an insulating adhesive. If a sufficiently high voltage is applied, the tubular electrode 12 does not necessarily need to be installed coaxially with the capillary 2. However, in the case of a coaxial shape, ion generation is performed at a low applied voltage. Similarly, the electrode 12
The electrode 12 does not necessarily need to be tubular if a sufficiently high voltage is applied. The applied voltage can be much lower when the electrode 12 is installed before the end of the capillary 2 than when it is not.

FIG. 12 is a sectional view of an ion source according to still another embodiment of the present invention.

The quartz capillary 2 is heated by a heating block 14 heated by a heater 13. Therefore, the liquid introduced into the capillary 2 is sprayed by heating. Due to the electric field generated by the electrodes 12, the droplets generated by spraying in the capillary 2 are charged, and charged droplets and ions are generated. An infrared laser or a lamp can be used for heating the liquid.

FIG. 13 is a sectional view of an ion source according to still another embodiment of the present invention.

The liquid introduced into the quartz capillary 2 is sprayed from the lateral direction at the end thereof by a gas flow generated by the gas injection unit 15. In this case, a relatively large charged droplet is generated, but the position of the capillary 2 can be adjusted extremely easily. In particular, when it is not necessary to generate ions and only the generation of charged droplets is sufficient, the present embodiment is a very simple charged droplet generation device.

FIG. 14 is a sectional view of an ion source according to still another embodiment of the present invention. The liquid introduced into the quartz capillary 2 is converted into droplets by the ultrasonic vibrator 16. The droplet is charged by the electric field generated by the electrode 12 when the droplet is generated. The charged atomizing gas diffuses widely in space. In the embodiment shown in FIGS. 12 to 14,
There is an advantage that ions can be generated without using a gas cylinder or a compressor.

FIG. 15 shows a configuration diagram of a mass spectrometer according to one embodiment of the present invention. The liquid is introduced into the capillary 2 through the flow passage 1 at a constant flow rate. The tip of the capillary 2 is inserted coaxially into the orifice 3. The nitrogen gas supplied from the gas supply unit 4 is introduced into the ion source body 6 from the gas introduction pipe 5 and is discharged from the orifice 3 to the outside. A voltage is applied from a power supply 7 to the metal orifice plate 9. As a result, an electric field is applied to the liquid that has reached the end of the capillary 2. The liquid to which the electric field is applied is sprayed under atmospheric pressure according to the gas flow from the orifice 3. Generally, there is a uniform electric field in the space between the orifice plate 9 where the atomized gas is generated and the pore 17 at the entrance of the mass spectrometer. Ions and charged droplets generated in the spray gas are introduced into a vacuum through the pores 17 at the entrance of the mass spectrometer, and mass-separated by an electric field or a magnetic field in a mass analyzer 18 installed in a high vacuum section. The mass-separated ions are detected by the ion detector 19. The output of the ion detector 19 is calculated by the computer 2.
0 and parsed.

The power supply 7 and the mass spectrometer 18 can be controlled by a computer 20. That is, positive and negative ions generated by the intermittent voltage signal generated from the power supply 7 can be mass-separated in synchronization with ion generation and detected. For example, when the potential of the metal tube 8 is set to the installation potential, and the power supply 7 applies a rectangular wave voltage having an amplitude of 1 kV to the orifice plate 9 to generate positive and negative ions, the positive and negative ions are analyzed in synchronization with the generation. Can be. When the capillary 2 or the metal tube 8 and the pores 17 are set at the same potential so that no electric field exists in the space where the spray gas is generated,
Even when a potential difference of about V is generated, there is no problem in ion detection.

When the potential of the metal tube 8 is set to the ground potential, the potential of the liquid flowing in the capillary 2 can be set to the ground potential. Therefore, it is easy to connect to the flow passage 1 a solution separation means such as a capillary electrophoresis device or a liquid chromatograph.

FIG. 16 is a configuration diagram of a capillary electrophoresis / mass spectrometer combination apparatus according to one embodiment of the present invention. The mixed solution is introduced into the capillary electrophoresis device 21 and separated by electrophoresis by a high voltage applied to both ends of the capillary. The separation solution is introduced into the capillary 2 after being detected by the detection unit 22. The tip of the capillary 2 is inserted coaxially into the orifice 3. The nitrogen gas supplied from the gas supply unit 4 is introduced into the ion source body 6 from the gas introduction pipe 5 and is discharged from the orifice 3 to the outside. The orifice plate 9 is made of metal, and a voltage is applied from the power supply 7. The liquid that has reached the end of the capillary 2 is sprayed under atmospheric pressure by gas. Ions and charged droplets generated in the spray gas are introduced into a vacuum through the pores 17 at the entrance of the mass spectrometer, and mass-separated by an electric field or a magnetic field in a mass analyzer 18 installed in a high vacuum section. The mass-separated ions are detected by the ion detector 19. Ion detector 19
Is sent to the computer 20 and analyzed. The power supply 7 and the mass spectrometer 18 can be controlled by a computer 20. That is, positive and negative ions generated by the intermittent voltage signal generated from the power supply 7 can be mass-separated in synchronization with ion generation and detected. For example, a metal tube 8
Is set to the installation potential, and a power supply 7 applies a rectangular wave voltage having an amplitude of 1 kV to the orifice plate 9 to generate positive and negative ions, whereby the positive and negative ions can be analyzed in synchronism therewith. Whether the capillary 2 or the metal tube 8 and the pores 17 are set to the same potential so that no electric field exists in the space where the spray gas is generated, or when a potential difference of about 200 V is generated, Is no problem at all. The mass spectrometer 18 includes any mass spectrometer such as a quadrupole mass spectrometer, a quadrupole trap mass spectrometer, a magnetic field mass spectrometer, a time-of-flight mass spectrometer or a Fourier transform mass spectrometer. Can be used. By setting the potential of the metal tube 8 to the ground potential, the capillary electrophoresis device 2
The potential of the mixed solution 1 can also be set to the ground potential. Therefore, the capillary electrophoresis apparatus 21 can be operated without any trouble in the separation of the mixed solution, and high-sensitivity separation analysis of the mixed solution can be realized online. Even if a solution separation means such as a liquid chromatograph is used in place of the capillary electrophoresis apparatus 21, highly sensitive separation analysis of a mixed solution can be realized in the same manner on-line.

FIG. 17 is a configuration diagram of a capillary electrophoresis / mass spectrometer coupling apparatus according to one embodiment of the present invention. The mixed solution is introduced into the capillary electrophoresis device 21 and separated by electrophoresis by a high voltage applied to both ends of the capillary. The separated solution is introduced into the capillary 2 through the metal tube 8 set to the ground potential after being detected by the detecting unit 22. The tip of the capillary 2 is inserted coaxially into the orifice 3. The nitrogen gas supplied from the gas supply unit 4 is introduced into the ion source body 6 from the gas introduction pipe 5 and is discharged from the orifice 3 to the outside. The orifice plate 9 is made of metal, and a voltage is applied from the power supply 7. The liquid that has reached the end of the capillary 2 is sprayed under atmospheric pressure by gas. Ions and charged droplets generated in the spray gas are introduced into a vacuum through the pores 17 at the entrance of the mass spectrometer, and mass-separated by an electric field or a magnetic field in a mass analyzer 18 installed in a high vacuum section. The mass-separated ions are detected by the ion detector 19. The output of the detection unit 22 is sent to the computer 20. Based on the signal, the computer 20 sends a signal indicating the power source 7 and the mass spectrometer 18. Then, the output of the ion detector 19 is sent to the computer 20 and analyzed.

The substances separated by the capillary electrophoresis apparatus 21 include those that become positive ions and those that become negative ions by spraying. Therefore, for example, even if a substance that becomes a negative ion is separated, the substance cannot be analyzed if only positive ions can be generated by spraying or if only positive ions can be analyzed. Therefore, while the separation substance is sprayed from the capillary 2, the polarity of the voltage applied to the orifice plate 9 is inverted, and both positive ion analysis and negative ion analysis are performed. Since the potential of the metal tube 8 is set to the set potential, performing the positive / negative ion analysis does not affect the capillary electrophoresis apparatus 21. Even if a solution separation means such as a liquid chromatograph is used in place of the capillary electrophoresis apparatus 21, highly sensitive separation analysis of a mixed solution can be realized in the same manner on-line.

[0068]

According to the ion source of the present invention and the mass spectrometer using the same, the stability and reproducibility of ion generation are higher than those of the electrospray ionization method or the ion spray ionization method utilizing the electrostatic spray phenomenon. Even if the spraying is interrupted and then restarted, the ion generation is reproduced, so that the operability of the ion source is extremely high. This is because only gas atomization of the solution is used in ion generation.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an ion source according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an ion source according to one embodiment of the present invention.

FIG. 3 is a sketch of an ion source according to an embodiment of the present invention.

FIG. 4 shows the dependence of the total ion current on the voltage applied to the orifice 3.

FIG. 5 is a mass spectrum obtained from a cytochrome-C solution.

FIG. 6 is a mass spectrum obtained from a cytochrome-C solution by an on-spray ionization method.

FIG. 7 is a mass spectrum obtained from a myoglobin solution.

FIG. 8 is a mass spectrum obtained from a hemoglobin solution.

FIG. 9 shows dependence of ion intensity on spray gas flow rate.

FIG. 10 is a sectional view of an ion source according to another embodiment of the present invention.

FIG. 11 is a sectional view of an ion source according to still another embodiment of the present invention.

FIG. 12 is a sectional view of an ion source according to still another embodiment of the present invention.

FIG. 13 is a sectional view of an ion source according to still another embodiment of the present invention.

FIG. 14 is a sectional view of an ion source according to still another embodiment of the present invention.

FIG. 15 is a configuration diagram of a mass spectrometer according to one embodiment of the present invention.

FIG. 16 shows capillary electrophoresis / example of the present invention.
The block diagram of the mass spectrometer coupling device.

FIG. 17 is a configuration diagram of a capillary electrophoresis / mass spectrometer combination device according to another embodiment of the present invention.

[Explanation of symbols]

1: flow channel, 2: capillary, 3: orifice, 4:
Gas supply unit, 5: gas introduction pipe, 6: ion source body, 7:
Power supply, 8: metal tube, 9: orifice plate, 10: Teflon tube, 11: stainless steel tube, 12: tubular electrode, 13: heater, 14: heating block, 15: gas injection unit, 16:
Supersonic oscillator, 17: pore, 18: mass spectrometer, 19:
Ion detector, 20: computer, 21: capillary electrophoresis apparatus, 22: detector.

Continued on the front page (72) Inventor Minoru Sakairi 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory of Hitachi, Ltd. (72) Inventor Yasuda Takada 1-280 Higashi Koikebo-ku, Kokubunji-shi, Tokyo In-house (72) Inventor Takayuki Nabeshima 1-280 Higashi-Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (9)

[Claims] A flow path for flowing a liquid to a predetermined position;
An electric field applying means for applying an electric field through the insulator, wherein at least a part of the flow passage is an insulator, and the liquid is disposed downstream of the liquid to which the electric field is applied, and the liquid is sprayed and charged. An ion source, comprising: spraying means for generating a compressed gas. 2. The ion source according to claim 1, wherein said flow passage is a capillary. 3. The ion source according to claim 1, wherein a heater for heating the liquid is provided as a means for spraying the liquid. 4. A flow path for a sample solution, a first electrode for determining a potential of the sample solution, a second electrode for applying an electric field to the sample solution, and a voltage applied to the first electrode and the second electrode. A gas flow path that guides the gas so as to flow out along the flow path, and a gas feeder that applies a flow rate to the gas as if spraying a sample solution at the tip of the flow path. An ion source, comprising: means for applying a voltage different from the voltage applied to the first electrode to the second electrode provided on the flow passage side to generate ions. 5. A flow path for flowing a liquid to a predetermined position,
An electric field applying means for applying an electric field through the insulator, at least a part of the flow path being an insulator, a gas supply unit for supplying a gas, and a supply port for supplying a gas from the gas supply unit An ion source, comprising: a spraying means, which is a room including a gas discharge port and a holding section for holding the flow passage. 6. The ion source according to claim 5, wherein said gas supply unit has gas heating means for heating a gas. 7. An ion source according to claim 5, wherein said electric field applying means comprises an electrode and a power supply means for supplying a voltage to said electrode. 8. The ion source according to claim 7, wherein said electrode is provided inside said flow passage and is coaxial with said flow passage. 9. The ion source according to claim 7, wherein said electrode comprises a ring-shaped member or a tubular member.