JPH10282059A - Atmospheric pressure ion source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably ionize many samples without requiring an auxiliary atomization gas. SOLUTION: A moving phase flowing to an atomization part 3 is screwed by a liquid column generation means 7 and a large charge is applied by a voltage application means 8 for generation of a large, a small particle size areas. Since the moving phase is screwed, a pressure of the moving phase before the liquid column generation means 7 is raised and the moving phase is jetted out at high speed from the generation means 7. As a result, a liquid column of the jetted moving phase is formed from the generation means 7. When the liquid column becomes a predetermined length, the moving phase is atomized because of the reaction of positively charged particles and spreads like a trumpet. Large liquid drops are present at a central part and fine liquid drops are at the outer periphery. The fine liquid drops are easy to dry and therefore a large amount of naked ions with a solvent removed is produced stably. The naked ions of an area of the fine liquid drops are introduced to an MS analysis part 5 through an orifice 4 and analyzed. In this case, the large amount of naked ions is analyzed, whereby analysis sensitivity at the MS analysis part 5 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of an ion source used for, for example, a mass spectrometer (hereinafter, also referred to as MS), and particularly, to a sample under atmospheric pressure or a pressure close to atmospheric pressure. It belongs to the technical field of an atmospheric pressure ion source which is ionized by.

[0002]

2. Description of the Related Art Liquid chromatograph mass spectrometer (LC)
/ MS), a mobile phase of a sample flowing out of a liquid chromatograph (hereinafter also referred to as LC) is introduced into an ion source to be ionized, and the generated ions are passed through an orifice under a high vacuum mass spectrometer (MS). (Analysis section).

[0003] By the way, as a method of ionizing the mobile phase from the LC, as described above, atmospheric pressure ionization (atmospheric pressure ionization) in which the mobile phase is ionized under atmospheric pressure is used.
(hereinafter, also referred to as API) is widely used. In addition, one of the APIs is an electrospray ionization (ESP) method.
This ESI is a method of generating ions by electrostatic field spray using a high voltage under atmospheric pressure. Further, another one is an ion spray method (Ion Spra
y; hereinafter, also referred to as IS). This IS is a method using an auxiliary spray gas for the above-mentioned ESI, and assists the mobile phase spraying by the ESI with the auxiliary spray gas to form the mobile phase into a spray. It is a method of spraying.

FIG. 5 is a diagram schematically showing an example of a conventional atmospheric pressure ion source based on ESI. In the figure, 1 is LC, 2
Is a liquid sending tube having an inner diameter of 50 μm to 200 μm in which a mobile phase as a mixture of a sample and a solvent from LC1 flows, 3 is a spraying section for spraying the mobile phase under atmospheric pressure, 4 is concentric with the spraying section 3 Orifices 5 are held under high vacuum pressure,
An MS analyzer that detects ions introduced through the orifice 4 and analyzes the mass.

In such a conventional atmospheric pressure ion source based on ESI, a predetermined voltage of 1 to 5 kV is applied between the spray portion 3 of the liquid sending pipe 2 and the counter electrode having the orifice 4 formed thereon. , The mobile phase from the LC 1 is sprayed from the spraying section 3 under atmospheric pressure, and the solvent containing the sample becomes atomized charged droplets.
Positive (+) ions of the sample that can be analyzed by the S analyzer 5 are generated. The generated (+) ions are introduced into the MS analyzer 5 under high vacuum through the orifice 4 and subjected to mass analysis by the MS analyzer 5.

[0006]

By the way, this ESI
In order to reliably and stably ionize the mobile phase when the mobile phase is sprayed under atmospheric pressure from the spray unit 3, the LC1
Is set to a small flow rate (flow rate of less than 20 μL / min) such that the mobile phase flows out of the spray unit 3. However, under such a small flow rate condition, the amount of the sample introduced into the ion source is small, and the amount of ions introduced into the MS analysis unit 5 is also small, and the analysis sensitivity of the sample is not so high.
In order to increase the amount of the sample introduced into the ion source, the flow rate of the mobile phase may be simply set to 20 μL / min or more. In this ESI, when the flow rate of the mobile phase is set to 20 μL / min or more, FIG. As shown in (2), the mobile phase sprayed from the spray unit 3 becomes a droplet having a relatively large particle size. In such a large droplet, the solvent added to the ions is difficult to evaporate, and the ions are not sufficiently dried, so that the analysis sensitivity in the MS analysis unit 5 is reduced and measurement becomes impossible.

As described above, in ESI, 20 μL / m
Since the mobile phase having a flow rate of in or more cannot be stably ionized, the flow rate of the mobile phase is limited, and the flow rate of the mobile phase cannot be simply increased.

Further, in order to introduce more ions into the MS analyzer 5 and increase the analysis sensitivity of the MS analyzer 5, the (+) ions generated under atmospheric pressure are efficiently directed to the orifice 4. It is conceivable that the spraying unit 3
It is conceivable to increase the voltage between the electrode and the counter electrode to a high voltage. However, if the voltage is simply increased, the distance between the spraying part 3 and the counter electrode is relatively short, so that a discharge occurs between them. In order to prevent this discharge, if the distance between the spray unit 3 and the counter electrode is increased and the voltage is increased, the discharge is prevented. However, this time, the sprayed and atomized mobile phase droplets have a large diameter. It becomes particles and causes the same problem as described above.

Therefore, in this ESI, 20 μL / m
In order to stably ionize even a mobile phase having a flow rate of in or more, the above-described ionization method using IS is used. In this IS, by spraying the mobile phase in the form of atomized spray with the auxiliary spray gas, the mobile phase becomes finer in the form of a mist, so that it is possible to stably ionize the mobile phase even at a flow rate of 20 μL / min or more. Become.

However, the ionization of the mobile phase by the IS has a problem that a large amount of auxiliary spray gas is required.

The present invention has been made in view of such circumstances, and has as its object to provide an atmospheric pressure ion source capable of stably ionizing a large amount of a sample without requiring an auxiliary spray gas. It is to provide.

[0012]

In order to solve the above-mentioned problems, the invention of claim 1 sprays a mobile phase comprising a sample and a solvent, which flows through a liquid sending pipe, from a spraying section under atmospheric pressure. At the same time, the atomized mobile phase is ionized under this atmospheric pressure, and the ions of the generated sample are introduced from the atmospheric pressure through the orifice into the analysis unit under a pressure lower than the atmospheric pressure. Liquid column generating means for ejecting the mobile phase so that the mobile phase ejected from the spray unit forms a liquid column of a predetermined length is provided, and the spray unit and the orifice are formed. After the liquid column having the predetermined length is formed between the counter electrode and the counter electrode, a phase in which a mist-like droplet having a large particle size is located at the center and fine mist-like particles are formed around the center. Two phases are formed with the phase where the droplets of the particle size are located Large and small particle size region generating voltage applying means for applying a voltage for applying a large charge to the mobile phase, and further, the orifice is located at the fine particle size droplet. It is characterized in that it is arranged in the region of the phase or close to the outer periphery of this region.

Further, the invention of claim 2 is characterized in that the liquid column generating means is constituted by a fine hole having an inner diameter smaller than the inner diameter of the liquid sending pipe. Further, the invention according to claim 3 is characterized in that a heating means for heating the mobile phase of the liquid column is provided in a region where the liquid column of the mobile phase is formed.

Further, the invention of claim 4 is characterized in that the direction in which the mobile phase is ejected from the spray section and the direction of the orifice hole of the orifice are set to intersect each other. Further, the invention according to claim 5 is characterized in that the direction in which the mobile phase is ejected from the spray unit and the direction of the orifice hole of the orifice are set to be orthogonal to each other.

[0015]

In the atmospheric pressure ion source of the present invention having such a configuration, a large amount of mobile phase is ejected from the atomizing section at a high speed under the atmospheric pressure by the liquid column generating means without the need for an auxiliary atomizing gas. At the same time, the ejected mobile phase forms a liquid column of a predetermined length. In addition, when the mobile phase is ejected from the spray unit, a large charge is applied to the mobile phase by a large voltage applied between the spray unit and the counter electrode by the large and small particle size region generating voltage applying means. . As a result, the flow velocity decreases around the end of the liquid column having a predetermined length, and the mobile phase is atomized by the repulsion of the (+)-charged droplet particles. And expands like a trumpet. In this case, in the spreading region of the mobile phase, a phase in which a mist-like droplet having a large particle diameter is located at the center and a phase in which a mist-like droplet having a fine particle diameter is located at the outer periphery of the central portion are provided. Two phases are formed.

Since the droplets in the region of the fine droplets are easy to dry, the ions in this region are more effectively removed from the solvent, and a large amount of bare ions from which the solvent has been removed is generated stably. Become so. Then, since a large amount of naked ions in this region are introduced into the MS analyzer through the orifice and analyzed, the analysis sensitivity is improved.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an example of an embodiment of an atmospheric pressure ion source according to the present invention, and FIG. 2 is a partially enlarged view of FIG. The same components as those of the ion source shown in FIGS. 5 and 6 are denoted by the same reference numerals, and a detailed description thereof will be omitted.

As shown in FIGS. 1 and 2, in the ion source of the present embodiment, the distance between the spray unit 3 and the counter electrode 6 is set longer than in the conventional ion source. Further, the ion source of the present example is configured to generate a liquid column of a mobile phase having a predetermined length at the open end of the conventional ESI spraying unit 3 shown in FIG. Means 7 are provided. The liquid column generating means 7 is composed of pores having an inner diameter φ1 of 20 μm, and the inner diameter φ1 has an inner diameter of 50 μm or less.
The value is set to a value considerably smaller than the inner diameter φ2 of the liquid sending pipe 2 which is 1 mm. That is, the opening diameter of the spray section 3 of the ion source of this example is set to be considerably smaller than the opening diameter of the spray section 3 of the conventional ion source shown in FIGS. 5 and 6 by the liquid column generating means 7.

The tip of the spraying part 3 of the liquid feed pipe 2 is formed of a conductive material, and a conventional material is provided between the conductive part of the spraying part 3 and the counter electrode 6 provided with the orifice 4. 8 to 15 kV, which is much larger than the applied voltage of 1 to 5 kV
The large and small particle size region generating voltage applying means 8 for applying the large voltage of the above is provided. The large and small particle size region generating voltage applying means 8 applies a large charge to the mobile phase flowing through the spraying section 3, and as a result, FIG.
As shown in (a), the mobile phase ejected from the spray unit 3 is:
After a liquid column of a predetermined length is formed until the flow velocity decreases to a predetermined speed, the particles charged in (+) of the mobile phase are repelled by the repulsion between the liquid column and become a mist and spread in a trumpet shape. . In this case, as shown in FIGS. 2 (b) and 2 (c), in this expanded region, the mobile phase is composed of the phase of the mist-like large droplet located at the center thereof and It is in a two-phase state with a mist-like small annular droplet phase having a small particle diameter and located around the outer periphery of the phase.

In the ion source of the present embodiment, the orifice 4 for introducing (+) ions of the sample into the MS analyzer 5
Are arranged in the area of the fine droplets. That is, the orifice 4 is eccentric from the spray unit 3. Other configurations of the ion source of this example are the same as those of the conventional ion source shown in FIGS.

In the thus configured ion source of the present embodiment, the conventional ion source is applied between the spray portion 3 and the counter electrode 6 having the orifice 4 by the voltage applying means 8 for generating large and small particle size regions. Much higher than the applied voltage of the source, 8
With a large voltage of １５15 kV applied, a mobile phase, which is a mixture of a sample and a solvent, flows from the LC 1 to the spray unit 3 through the liquid sending pipe 2 at a flow rate of 20 μL / min or more, which cannot be measured by the conventional ESI. Let it. The mobile phase flowing into the spraying section 3 has the hole diameter φ1 of the liquid column generating means 7 set to be much smaller than the inner diameter φ2 of the liquid sending pipe 2, so that the flow is restricted by the liquid column generating means 7 Since a large voltage is applied to the spray unit 3 by the large and small particle size region generating voltage applying means 8, a large charge is applied to the mobile phase. Since the pressure of the mobile phase in front of the liquid column generating means 7 is increased by narrowing down the mobile phase, the mobile phase is ejected from the liquid column generating means 7 to the atmospheric pressure at a high speed, and the ejected mobile phase is used as the liquid column. A liquid column is formed from the generating means 7. In that case, since the mobile phase is fast even if it is throttled, a much larger amount is ejected than in the past. The flow rate of the mobile phase in which this liquid column is formed is 100 μL / min to 1000 μL
/ Min.

When the mobile phase ejected at a high speed moves to the MS analyzer 5 by a predetermined amount and the flow rate of the mobile phase decreases by a predetermined amount, that is, when the liquid column is formed to a predetermined length, the mobile phase (+) Due to the repulsion of the charged particles, the mobile phase is atomized and spreads in a trumpet shape. In the spreading region of the mobile phase, a large atomized droplet having a large mass is located at the center, and a small atomized droplet having a small mass is located at the outer periphery of the central portion. Since the mobile phase is finely divided in the region of fine droplets, the entire surface area of the mobile phase in this region becomes large, so that the fine droplets are more easily dried. Since the solvent is more effectively removed from the ions by drying the fine droplets, a large amount of bare ions from which the solvent has been removed is stably generated.

The orifice 4 is formed in a fine droplet area.
Is disposed, a large amount of bare ions from which the solvent has been removed is introduced into the MS analyzer 5 under a high vacuum through the orifice 4 and analyzed as in the conventional case. In this case, since a large amount of naked ions are analyzed, the analysis sensitivity of the MS analyzer 5 is improved.

As described above, according to the ion source of this embodiment, a large amount of mobile phase is finely divided into fine particles and dried reliably, so that the mobile phase can be stably ionized and the conventional IS can be used. A large amount of mobile phase is ejected to atmospheric pressure without the need for auxiliary spray gas as in
Large amounts of ions can be generated.

Further, since a large amount of mobile phase can be made finer and finer, the particle size of the mobile phase does not increase even if the distance between the spray portion 3 and the counter electrode 6 is increased. Can be set larger than before. As a result, even if the voltage applied between the spray unit 3 and the counter electrode 6 is much higher than the conventional voltage, the discharge does not occur because the distance between the spray unit 3 and the counter electrode 6 is large. .

FIG. 3 is a view similar to FIG. 2A showing another example of the embodiment of the present invention. The same components as those of the ion source shown in FIGS. 1, 5 and 6 are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 3, the ion source of this example is
A vaporizer 9 of a metal heating tube, which is a heating means, is provided in the mobile phase liquid column forming region, and the mobile phase liquid column passes through the vaporizer 9. Then, the mobile phase in a liquid column state is dried by the vaporizer 9. By the drying by the vaporizer 9, the mobile phase is more effectively dried. At this time, the vaporizer 9 heats the liquid column-shaped mobile phase moving at a high speed, so that thermal decomposition of the mobile phase is prevented.

It should be noted that a voltage smaller than the large voltage of the large and small particle size region generating voltage applying means 8 may be applied to the metal heating tube. By applying the voltage, the mobile phase can be more stably sprayed. As a heating means, laser, infrared rays, microwaves, hot air or the like can be used in addition to the heating tube. Other configurations and other effects of the ion source of this example are the same as those of the ion source of the example shown in FIGS.

FIG. 4 is a view similar to FIG. 2A, showing still another example of the embodiment of the present invention. The same components as those of the ion source shown in FIGS. 1, 5 and 6 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the ion source of each of the above-described examples, the orifice 4 is arranged so that the direction of the orifice hole is orthogonal to the direction of ejection of the mobile phase from the spray unit 3 and the orifice hole is close to the outer periphery of the fine droplet. It is provided so that
The ions are attracted through the orifice 4 in a direction perpendicular to the direction in which the mobile phase is ejected. On the side opposite to the orifice 4 with respect to the expanded mobile phase, a repeller electrode 10 for applying a (+) voltage to fine droplets is provided. The (+) voltage from the repeller electrode 10 causes the (+) ions in the fine droplet region to be pushed toward the orifice 4, so that the ions pass through the orifice 4 to form the mobile phase. It is easy to order in the direction perpendicular to the jetting direction.

Other configurations and other operational effects of the ion source of this embodiment are the same as those of the ion source of the embodiment shown in FIGS. Note that the direction of the orifice hole and the direction in which the mobile phase is ejected from the spray unit 3 may obliquely intersect.

[0032]

As is apparent from the above description, according to the ion source of the first aspect of the present invention, the liquid column generating means allows a large amount of mobile phase to be discharged from the spray section without the need for an auxiliary spray gas. The liquid is ejected at a high speed under atmospheric pressure to form a liquid column of a predetermined length of the mobile phase, and a large voltage is applied to the mobile phase by a large voltage from the large and small particle size region generating voltage applying means to form a liquid column. After the end of the column, the mobile phase is atomized and spreads in a trumpet shape, and in the spreading region of this mobile phase, a phase in which large droplets of mist are located at the center and a mist is formed on the outer periphery of the center. Since two phases are formed with the phase in which the droplet having the fine particle diameter is located, the solvent adhering to the ions in the region of the fine droplet can be more effectively removed. This makes it possible to stably generate a large amount of bare ions from which the solvent has been removed. Then, by introducing a large amount of naked ions in this region through the orifice into the MS analysis unit for analysis, the analysis sensitivity can be improved. In addition, a large amount of mobile phase is ejected at a high speed by the liquid column generating means, so that the conventional auxiliary spray gas is not required.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an embodiment of an atmospheric pressure ion source according to the present invention.

2 (a) is a partially enlarged view showing the atmospheric pressure ion source of the example shown in FIG. 1 in a partially enlarged manner, and FIG. 2 (b) is a partially enlarged view of an IIB portion in FIG. 1 (a) first and second orifices FIG. 2C is a partially enlarged view of a portion, and FIG. 2C is a cross-sectional view taken along line IIC-IIC in FIG.

FIG. 3 shows another example of the embodiment of the present invention.
It is a figure similar to (a).

FIG. 4 is a view similar to FIG. 2A, showing still another example of the embodiment of the present invention.

FIG. 5 is a diagram showing an example of a conventional atmospheric pressure ion source.

6 is a partially enlarged view showing the atmospheric pressure ion source shown in FIG. 5 in a partially enlarged manner.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Liquid chromatograph (LC), 2 ... Liquid sending pipe, 3 ... Spray part, 4 ... Orifice, 5 ... Mass spectrometry part (MS analysis part), 6 ... Counter electrode, 7 ... Liquid column generation means, 8 ... Large , A voltage applying means for generating a small particle size region, 9: a heating tube (vaporizer), 10: a repeller electrode

Claims (5)

[Claims] 1. A mobile phase comprising a sample and a solvent flowing through a liquid sending pipe is sprayed from a spray section under atmospheric pressure, and the sprayed mobile phase is ionized under this atmospheric pressure to produce a sample. In an atmospheric pressure ion source that introduces ions from an atmospheric pressure through an orifice into an analysis unit under a pressure lower than the atmospheric pressure, the mobile phase ejected from the spray unit forms a liquid column of a predetermined length in the spray unit. Liquid column generating means for ejecting the mobile phase is provided, and the liquid column of the predetermined length is formed between the spray portion and the counter electrode in which the orifice is formed. After that, two phases are formed such that a phase in which a mist-like droplet having a large particle diameter is located in the center and a phase in which a mist-like droplet having a small particle diameter is located on the outer periphery of the center. Applying a voltage that gives a large charge to the mobile phase A voltage applying means for generating a small particle size region, and the orifice is arranged in a region of a phase in which the droplet having the fine particle size is located or close to an outer periphery of the region. Atmospheric pressure ion source characterized by the above-mentioned. 2. The atmospheric pressure ion source according to claim 1, wherein said liquid column generating means is constituted by a pore having an inner diameter smaller than the inner diameter of said liquid sending pipe. 3. The atmospheric pressure ion source according to claim 1, wherein heating means for heating the mobile phase of the liquid column is provided in a region where the liquid column of the mobile phase is formed. 4. An ejection direction of a mobile phase from the spray unit,
The atmospheric pressure ion source according to any one of claims 1 to 3, wherein the direction of the orifice hole of the orifice is set so as to cross each other. 5. An ejection direction of a mobile phase from the spray unit,
The atmospheric pressure ion source according to claim 4, wherein directions of the orifices of the orifice are set to be orthogonal to each other.