JPH11108897A - Spraying device and analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an analyzer in which ions are generated stably by using an ion source used to form very small liquid drops and by which a sample can be analyzed with high sensitivity and with good reproducibility by a method wherein a gas is ejected by a gas-flow formation means to the tip outer circumferential part of a capillary into which a sample solution is introduced and the sample solution is ionized. SOLUTION: A sample solution is introduced, from a sample-solution supply part, into a capillary 5 at a flow rate of 100 μl/min. Since the capillary 5 is weak in terms of strength, it is held and fixed by a capillary holding tube 6, and about 4 mm of its tip part is exposed from the capillary holding tube 6. On the other hand, a gas which is introduced from a gas supply part is introduced into an ion source while its flow rate is being regulated, it is made to flow along the outer circumferential part of the capillary 5, and it is ejected to the air from the tip of the capillary 5 at a gas speed of about 200 m/sec or higher. The sample solution generates gaseous psedo molecular ions by sample molecules in addition to very small liquid drops by the ejected gas. The generated ions are introduced into a mass spectrometer by using a gas so as to be analyzed.

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. It relates to an analyzer.

[0002]

2. Description of the Related Art Capillary electrophoresis (CE) or liquid chromatography (LC) can separate a sample present in a solution, but it is difficult to identify the type of the separated sample. On the other hand, a mass spectrometer (MS) can identify a sample with high sensitivity, but cannot separate a sample in a solution. For this reason, when separating and analyzing a plurality of biological substances dissolved in a solvent such as water, a capillary electrophoresis / mass spectrometer (CE / MS) in which capillary electrophoresis or liquid chromatography is connected to a mass spectrometer or A liquid chromatograph / mass spectrometer (LC / MS) is commonly used.

In order to analyze a sample separated by capillary electrophoresis or liquid chromatography with a mass spectrometer, it is necessary to convert sample molecules in a solution into gaseous ions. Conventional techniques for obtaining such ions include ion spraying (Analytical Chemistry),
Vol. 59 (1987) Paragraphs 2642 to 2646
Section) and the like are known. In this ion spray method, gas flows along the outer periphery of the capillary, and a high voltage (3) is applied between a capillary into which a sample solution is introduced and a pore (sampling orifice) for taking ions into a mass spectrometer. -6 kV) is applied, and a strong electric field is generated at the tip of the capillary. Due to the electrostatic spray phenomenon generated under such a configuration, small charged droplets are generated, and the above-mentioned gas vaporizes the solution in the charged droplets, thereby generating gaseous ions. The ions thus generated are introduced into a mass spectrometer via a sampling orifice and subjected to mass analysis. The above gas not only promotes the vaporization of the charged droplets but also suppresses the occurrence of discharge at the tip of the capillary.

When the flow rate of the solution supplied to the capillary is 1
An electrospray method (Journal of Physical Chemistry (Joun), which is a method of ionizing gas at a flow rate of 0 μL (microliter) / min or less without flowing gas.
al of Physical Chemistry), 8th
8 (1984) pp. 4451-4459)
Is distinguished from the ion spray method, but the principle of ion generation is the same as the ion spray method. Atmospheric pressure chemical ionization (analytical chemistry (An)
(Analytical Chemistry), Vol. 54 (1982), pp. 143 to 146), a method is provided in which an electrode for discharging is provided near the tip of a capillary, and a droplet sprayed under atmospheric pressure is ionized by discharging. Has been taken. In these various conventional spray ionization methods, in order to obtain high ion generation efficiency, a diameter of about 1 mm is required.
It is considered necessary to generate fine charged droplets of 0 nm or less.

[0005]

In the above prior art, a high voltage is applied between the capillary and the sampling orifice. Therefore, there is a problem that an electric shock prevention measure is required, and the structure of the device becomes complicated. In a capillary electrophoresis / mass spectrometer, since a high voltage is applied to the tip of the capillary, it is necessary to apply a higher voltage to cause a sample to migrate in a capillary electrophoresis apparatus.

[0006] The electrostatic spraying phenomenon is greatly affected by dirt on the tip of the capillary and the surface of the sampling orifice. In the electrospray method and the ion spray method, once the spraying of the sample solution is stopped, the spraying is restarted under the same conditions. However, the detected ion intensity is different, and the reproducibility is low.
Therefore, to maximize the detected ionic strength,
A complicated operation such as fine adjustment of the capillary position or cleaning of the tip of the capillary or the surface of the sampling orifice is required every time spraying is restarted. For this reason, the structure of the device is complicated to prevent electric shock, resulting in an operational obstacle.

Further, in the above-mentioned prior art, it is necessary to mix a volatile substance such as alcohol or ammonia as a solvent with the sample solution. When a solvent having a low electric conductivity is used, the electrostatic spraying phenomenon does not occur, and in order to cause the electrostatic spraying phenomenon, the electric conductivity of the sample solution is 10 13 to 10
It is empirically known that it is necessary to be in the range of {5Ω} 1cm} 1. Unless these conditions are met,
There is a problem in that the electrostatic spraying phenomenon does not occur stably and the selection of the solvent is restricted.

Further, since a high voltage is applied between the capillary and the sampling orifice, a discharge may occur around the ion source, and it is difficult to use a flammable solvent. When the kind of the solvent that can be used is limited as described above, there is a case where a substance to be measured cannot be separated by capillary electrophoresis or liquid chromatography.
It is an object of the present invention to provide for making very fine droplets. Also, using the ion source by this fine droplet,
An object of the present invention is to provide an analyzer capable of stably generating ions and analyzing a sample with high sensitivity and high reproducibility.

Another object of the present invention is to provide an ion source which can use a wide range of solvents used in capillary electrophoresis or liquid chromatography, and a mass spectrometer using the same.

[0010]

According to the present invention, there is provided a member having a hollow portion which is a flow path of a sample solution, a gas flow path for flowing a gas so as to flow out from the periphery of the member, and an end portion of the member. This is achieved by a spraying device provided with gas supply means for giving a substantially sonic flow velocity to the gas so that the sample solution is sprayed to produce a gaseous substance. A gas flow forming means for forming a gas flow is formed at the outer periphery of the end of the thin tube into which the sample solution is introduced, and the gas is ejected toward the atmospheric pressure at the outer periphery of the end to ionize the sample solution. There is a characteristic in the ion source to be used. Further, the Mach number determined from the flow velocity of the gas and the velocity of the sound wave transmitted through the gas is in the range of 0.75 to 1.25, and the Mach number is 0.8 to 1.2.
And the Mach number is in the range of 0.95 to 1.2. The gas flow forming means has a gas inlet through which gas is introduced, a thin tube and an opening formed in a direction in which the gas of the gas flow forming means is ejected, and an outer peripheral portion and an inner peripheral surface of the opening. It has a configuration having a minute space formed therebetween. The present invention is characterized by an analyzer using an ion source having the above characteristics.

The features of the present invention will be described in more detail below. A capillary for spraying a sample solution into the atmosphere and a gas guide tube inserted and installed near the tip of the capillary are provided from the gas inlet. A gas guide tube configured so that the introduced gas flows along the outer peripheral wall surface of the capillary to the tip of the capillary, wherein the flow velocity of the gas near the tip of the capillary reduces the sound velocity in the gas. When C (m / s), (C
It is characterized in that the sample is ionized in the range of -85) m / s to (C + 75) m / s. In order to efficiently ionize the sample, the gas flow rate at the tip of the capillary is more preferably in the range of (C-60) m / s to (C + 60) m / s, and more preferably in the range of (C-30) m / s. (C + 30)
The best effect can be obtained in the range of m / s.

The distal end of the capillary is arranged at the opening having the smallest inner diameter at the distal end of the gas guide tube so that the central axis of the capillary coincides with the central axis of the opening. The above gas is ejected from the formed minute space by the outer peripheral surface of the capillary. Means for changing the distance between the tip of the gas guide tube (the surface of the opening on the atmospheric pressure side) and the tip of the capillary along the central axis of the capillary adjusts the ionization efficiency of the sample. It is also possible to provide a heating means in a part of the gas guide tube to heat the gas to increase the ionization efficiency of the sample.

When the ions generated by the ion source are introduced into the mass spectrometer through the sampling orifice,
A cover having a hole through which ions pass is provided between the ion source and the sampling orifice. By this cover, the gas blown out of the gas guide tube and the droplet of the sample solution are prevented from hitting the sampling orifice,
Prevents the temperature of the sampling orifice from dropping.

In order to efficiently introduce ions into the mass spectrometer, the distance between the tip of the capillary and the sampling orifice is adjusted. In addition, the relative relationship between the center axis position of the tip of the capillary and the center axis position of the sampling orifice is adjusted so that both center axes coincide. Further, a voltage may be applied between the capillary and the sampling orifice.

The size of the droplet generated at the tip of the capillary is determined by the gas flow velocity, and if there is no outward pressure gradient around the tip of the capillary, no charged droplet is generated. In order for such a pressure gradient to occur,
The distance at which the tip of the capillary is exposed from the tip of the portion where the inner diameter of the gas guide tube is the smallest is -0.25 mm to 1.0 m
A capillary is provided so as to be m. In order to increase the generation efficiency of charged droplets, the thickness of the capillary is 10
Use a thin one in the range of μm to 150 μm. Further, the flow rate of the sample solution supplied to the capillary is 60 μm.
L (microliter) / min or less. If the gas flow rate at the capillary tip becomes uneven, the flow of the gas containing the charged droplets is not formed axisymmetrically, and the reproducibility of ion generation is also reduced. And that of the gas guide tube.

A sample solution is supplied from a capillary electrophoresis apparatus or a liquid chromatography apparatus to the capillary. By using a capillary electrophoresis apparatus or a liquid chromatography apparatus, a sample solution containing a plurality of sample components is separated, and then supplied to a capillary in an ion source, and a plurality of samples are successively temporally separated. The components are subjected to mass spectrometry to identify the sample components.

Dry nitrogen containing little water vapor is used as the gas, and the gas flow rate in the vicinity of the tip of the capillary (the above minute space) is set to (250 to 400) m / s (Mach number at 0 ° C. is 0.75 to 1). The sample is set to the range of 2) to efficiently ionize the sample. Further, the flow velocity of the gas at the tip of the capillary (the above-mentioned minute space) is set to (2
75 to 400) m / s (Mach number at 0 ° C. is 0.
In the range of 8 to 1.2), the sample is more efficiently ionized.

[0018]

The gas ejected from the minute space at the tip of the capillary generates fine charged droplets of the sample solution at the tip of the capillary. As the gas flow rate approaches the speed of sound, smaller charged droplets are created. The solvent is vaporized from the generated charged droplets by the ejected gas, and gaseous ions are generated. The generated ions can be introduced into a mass spectrometer and analyzed.

When the flow rate of the spray gas at the tip of the capillary exceeds a certain level, the sample solution introduced into the capillary is fragmented at the tip of the capillary, and charged droplets of various sizes are generated. Then, the very fine charged droplets are easily desolvated (dried). In solution
Neutral sample molecules may combine with protons and sodium ions in extremely fine liquid droplets to realize pseudo-molecular ionization, and it is considered that ions that can be analyzed by a mass spectrometer are obtained.

The conditions that determine the size of the droplet generated at the tip of the capillary are essentially determined by the gas flow velocity of the gas to be sprayed. Element also exists. That is, unless the pressure difference between the solution surface and the periphery at the tip of the capillary is greater than a certain level, extremely fine droplets are not generated. Therefore, using a thin capillary having a thickness of 100 μm or less enhances the efficiency of generating extremely fine droplets. Further, it is desirable that the central axis of the capillary coincides with the central axis of the gas guide tube. Otherwise, the flow velocity of the gas at the tip of the capillary becomes non-uniform, so that the atomized gas containing the generated solution is not formed axially symmetrically, and the reproducibility is reduced.

The gas flow rate has little to do with the subdivision of the solution. Empirically, a gas flow rate of 0.5 liter / min or more is sufficient. The material of the capillary and the potential applied to the capillary hardly affect the fragmentation of the solution.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an apparatus configuration of the present invention. The solution sample is supplied to the sample solution supply unit 1, and the solution sample is introduced into a capillary (capillary tube) (not shown) provided inside the ion source 2. The gas flow rate of the gas supplied from the gas supply unit 3 is adjusted by the flow controller 4.
It is introduced into the ion source 2 and flows along the outer periphery of the capillary. At the tip of the capillary, about 200 m /
s (Mach number at 0 ° C. is about 0.6) or more. In the sample solution introduced into the capillary, gas ejected at the tip of the capillary generates gaseous pseudo-molecular ions of sample molecules in addition to microdroplets from the sample solution. Sonic spray (Sonic spray)
Spray) method). The generated ions are introduced into the mass spectrometer 11 from the tip of the capillary by the above gas, and analyzed by the mass spectrometer 11. Hereinafter, features of the ion source according to the present invention will be described based on the configuration of the ion source according to the present invention and an analysis example using the ion source.

First Embodiment In this embodiment, an ion source is connected to a liquid chromatograph to constitute a liquid chromatograph / mass spectrometer (LC / MS). The sample solution separated by liquid chromatography is shown in FIG.
The liquid is supplied to the sample solution supply unit 1 via a connection tube, or a separation tube of a liquid chromatograph is directly connected to the sample solution supply unit 1. FIG. 2 is a sectional view showing the ion source used in the present embodiment. The sample solution is introduced into the capillary 5 (made of stainless steel, inner diameter 100 μm, outer diameter 300 μm) at a flow rate of 100 μL (microliter) / min from the sample solution supply unit 1 arranged on the left side of FIG. When the capillary 5 has a small thickness, the capillary 5 is weak in strength and easily bent, so the capillary 5 is held and fixed by a capillary holding tube (made of stainless steel) 6. About 4 mm of the tip of the capillary 5 is exposed from the capillary holding tube 6. The gas flows along the outer periphery of the capillary 5, and a gas guide pipe for ejecting a gas having a predetermined gas flow rate into the atmosphere at the tip of the capillary includes a gas guide pipe tip 7 and a gas guide pipe tip. And a unit holding unit 10. A central axis of the capillary at the tip of the capillary 5 and an opening formed at the gas guide tube tip 7 to form an outlet from which gas is blown out (a portion having the smallest inside diameter among the inside diameters of the gas guide tube). Yes, inner diameter is 4
The capillary 5 is fixed to the gas guide tube tip holding portion 10 via the capillary holding tube 6 so that the central axis of the gas guide tube coincides with the central axis of the gas guide tube. It is fixed to the unit 10. The outside of the gas guide tube is the atmosphere. As shown in FIG. 2, the tip of the capillary 5 projects by a dimension L to the surface of the opening on the atmosphere side.

Into the gas guide tube, nitrogen gas or air is introduced from a gas cylinder or a compressor through a flow controller 4 (FIG. 1) and a gas introduction tube 8. Through a small space formed by the inner peripheral surface of the opening and the outer peripheral surface of the capillary 5,
The gas gushes. From the cross-sectional area S of the micro space in a plane orthogonal to the central axis of the capillary 5 or the opening and the flow rate F flowing in the gas guide tube, the gas flow velocity v in the micro space is obtained by v = F / S. . When the shape of the opening is a circle (inner diameter D) and the outer shape of the cross section in a plane perpendicular to the longitudinal direction of the capillary 5 is a circle (outer diameter d), the gas guide is calculated from the flow rate F flowing in the gas guide tube. Pipe tip 7
From the inner diameter D of the tip having the smallest inner diameter, the outer diameter d of the capillary 5, and the measured gas flow rate F (measured with an error of about 3%), the gas flow velocity v at the outlet of the above minute space Is obtained by (Equation 1).

[0026]

V = 4F / (π (D2-d2)) (Formula 1) The gas flow velocity v is determined directly or indirectly by means for measuring the flow velocity without using a flow meter. Is also good. For example, the flow velocity may be measured using a hot wire anemometer, a laser Doppler anemometer, or an anemometer by a tracking method or a spark tracking method.

At the gas outlet of the gas guide tube tip 7, the gas undergoes adiabatic expansion, and the gas guide tube tip 7 and the capillary 5 are cooled. Therefore, in order to maintain the temperature of the ejected gas at room temperature or higher and to promote the vaporization of the generated droplets, a heater 9 is provided at the gas guide tube tip 7, and the introduced gas is heated from 50 ° C. to about 90 ° C. It is desirable to heat at a temperature between.

If the length of the tip of the capillary 5 exposed from the gas guide tube tip 7 (exposed length L) is 2 mm or more, the gas flow rate at the tip of the capillary 5 is reduced, so that the ion generation efficiency is low. . Therefore, in order to adjust the distance between the tip of the capillary 5 and the tip of the gas guide tube tip 7, the gas guide tube tip 7 is screwed into the gas guide tube tip holder 10 and fixed. By adjusting the screwing position of the gas guide tube tip 7,
The generation efficiency of ions or extremely fine charged droplets can be maximized.

In the above description, the case where nitrogen gas or air is ejected from the gas guide tube tip 7 has been described. However, a rare gas such as argon or carbon dioxide may be ejected. Also, due to the cost of purchasing gas, nitrogen,
Preference is given to using air or carbon dioxide. More preferably, dry nitrogen containing less water vapor is used.

In this embodiment, the axial thickness of the portion of the gas guide tube tip 7 having the smallest inner diameter at the tip is 2 mm. The thinner the thickness, the easier the axis alignment of the gas guide tube tip 7 and the capillary 5 becomes.
About m is preferable from an actual work operation.

[Second Embodiment] In this embodiment, an ion source is connected to a capillary electrophoresis apparatus to constitute a capillary electrophoresis / mass spectrometer combined apparatus (CE / MS). In FIG. 1, the sample solution separated by the capillary electrophoresis apparatus is connected to a sample solution supply unit 1 through a connecting pipe.
Or a capillary, which is a separation tube of a capillary electrophoresis apparatus, is directly connected to the sample solution supply unit 1.

FIG. 3 is a sectional view showing an ion source used in this embodiment. Similar to the ion source shown in the first embodiment, as shown in FIG. 3, the gas guide tube includes a gas guide tube tip 7 and a gas guide tube tip holding unit 10. In the capillary electrophoresis apparatus, the flow rate of the sample solution is as low as 0.1 μL (microliter) / min or less, and dilutes the separated sample solution that migrates to the end of the electrophoresis capillary. By diluting this sample solution,
The diluted sample solution can be continuously supplied to the capillary 5 continuously. When adding a diluting solvent, the ion concentration and pH of the sample solution can be optimized to increase the ionization efficiency of the measurement sample.

The solution sample separated by the capillary electrophoresis apparatus is introduced from the electrophoresis capillary 12 to the mixing joint 14 and mixed with the diluting solvent introduced from the pipe 13 at a flow rate of 20 μL (microliter) / min. , Are introduced into the capillary 5. Next, similarly to the first embodiment, the sample is converted into a pseudo molecular ion of a gaseous sample molecule by the gas introduced from the gas introduction tube 8 at the tip of the capillary 5, as in the first embodiment. .

The capillary 5 is fixed to the mixing joint 14 and the gas guide tube tip holding portion 10 via a metal capillary holding tube 6. The capillary holding tube 6 or the mixing joint 14 is used as an electrode for electrophoresis of the capillary electrophoresis apparatus. The position adjusting jig 15 for fixing the gas guide tube tip 7 is fixed to the gas guide tube tip holder 10 using screws 16. The hole through which the screw 16 provided on the position adjusting jig 15 penetrates is made larger than the screw outer shape. For this reason, the position of the gas guide tube tip 7 fixed to the position adjusting jig 15 is adjusted in a plane perpendicular to the center axis of the capillary 5, and the center axis of the capillary 5 and the gas guide tube tip 7 is adjusted. Can be matched. In order to prevent the capillary 5 from being damaged during the operation, a projection forming a circumference is provided at the tip of the gas guide tube tip 7. As in the first embodiment, a heater may be provided at the gas guide tube tip 7 to heat the jet gas.

Sampling orifice 17 of mass spectrometer
Is, for example, 0.3 mm in inner diameter and 15 mm in depth of the orifice. In addition, sampling orifice 1
7 is 100 ° C. to 150 ° C. by the ceramic heater 18.
Heat to ° C. A cover 19 is provided outside the sampling orifice 17 (atmospheric pressure side) to prevent the sampling orifice 17 from being cooled by the ejected gas and the droplet of the sample solution. The center axis of the capillary 5 and the sampling orifice 17 are controlled by the xyz stage 20.
Fine adjustment of the center axis position of
The ions generated at the tip of are efficiently introduced into the mass spectrometer. The solution sample can be efficiently analyzed with high accuracy and high sensitivity using the capillary electrophoresis / mass spectrometer coupling device of this embodiment.

When a quadrupole mass spectrometer is used as the mass spectrometer and the voltage of several hundred volts is applied to the sampling orifice 17 at the maximum, the capillary 5, the capillary holding tube 6, or all of the periphery thereof, that is, The potential of the entire ion source can be grounded. In a capillary electrophoresis apparatus, the electrophoresis potential is given based on this potential with respect to the ground potential. When a magnetic field type mass spectrometer having an acceleration voltage of about 4 kV for mass separation of ions in a magnetic field is used as the mass spectrometer, the same voltage as the acceleration voltage is applied to the sampling orifice 17, so that the capillary 5 There is a possibility that discharge occurs between the tip of the sample and the sampling orifice 17. However, a voltage intermediate between the ground potential and the acceleration potential (for example, 1-2 k
V), the distance between the capillary 5 and the sampling orifice 17 is reduced to about 1 cm, and a gas having a high electron affinity such as O2 or SF6 is used as a gas to be ejected. Can be grounded.

It is possible to increase the total amount of ions and the efficiency of generating multiply charged ions without using the electrostatic spraying phenomenon. In order to generate multiply charged ions by the electrostatic spraying phenomenon, it is necessary to apply a voltage of 2.5 kV or more to the tip of the capillary.
In the present invention, the total ion amount and the generation efficiency of multiply charged ions can be increased by using a low voltage of 2.5 kV or less.

In this apparatus, a voltage of about 1 kV is applied between the capillary 5 and the sampling orifice 17 to separate positive and negative ions at a portion near the surface of the sample solution coming out from the tip of the capillary 5. And a portion close to the surface of the sample solution can be in a state where either positive or negative ions are large. Therefore, in the sonic spraying method of the present invention, the charge density of the charged droplets generated by the ejection of gas is increased, and the total ion amount and the generation efficiency of multiply charged ions are increased without using the electrostatic spray phenomenon. Can be.

[Third Embodiment] The first and second embodiments described above.
In an embodiment of the present invention, a sample solution separated by a liquid chromatograph, a capillary electrophoresis apparatus, or another analyzer is supplied to a sample solution supply unit 1 shown in FIG. 1 by a syringe or a syringe pump, and the sample solution is ionized. Needless to say, mass spectrometry can be performed by ionizing with the source 2.

[Fourth Embodiment] The characteristics of the present ion source will be described below based on a measurement example using the ion source according to the present invention. In this example, all mass spectrometry described below was performed under the following apparatus configuration and measurement conditions, unless otherwise specified.

As an apparatus configuration, the cover 19 shown in FIG. 3 was installed on the capillary side of the sampling orifice using the ion source shown in FIG. The cover 19 has a diameter of 2
A stainless steel plate having a thickness of 1 mm and a hole of mm was used, and a sampling orifice having an inner diameter of 0.3 mm was used. A capillary made of quartz (inner diameter 0.1 mm, outer diameter 0.2 mm) was used as the capillary 5. The inner diameter of the opening at the tip of the gas guide tube was 400 μm. The distal end position of the capillary 5 was protruded by 0.65 mm from the surface on the atmospheric pressure side of the opening (400 μm) at the distal end of the gas guide tube. As the mass spectrometer, a double focusing mass spectrometer (Hitachi, M-80) was used. Opening (400μ
m), the central axes of the capillary 5 and the sampling orifice were set coaxially so that the detected ion intensity was maximized.

As the measurement conditions, the potentials of the tip of the capillary, the sampling orifice, and the cover 19 were set to the same potential. N2 gas was used as the ejected gas, and the flow rate of the ejected gas was 337 m / s (corresponding to the sound speed at 0 ° C. in N2 gas). Sample solution (Gramicid
The flow rate of (in (gramidine) -S) was 40 μL (microliter) / min. The gas guide tube was kept at room temperature, and the ionic strength was measured without heating the gas guide tube tip 7 by the heater 9.

(1) Mass spectrum obtained using the present ion source (FIG. 4).

FIG. 4 shows a graph of Grami which is a kind of peptide.
3 shows a mass spectrum obtained by using a solution of cidin-S (concentration: 1 μM, solvent: 50% aqueous methanol solution) as a sample solution. The ion at m / z = 140 is considered to be derived from impurities mixed in the sample solution or from the atmosphere. CH3OH2 plus ion derived from methanol (m
/ Z = 33) is slightly observed, but no H3O positive ion or a cluster formed by adding a water molecule to the H3O positive ion is observed, a simple spectrum is obtained, and spectrum analysis is easy. become. In conventional methods such as electrospray and ion spray,
When a mass spectrum is measured using a dilute sample solution, ions derived from the solvent are strongly observed. In the present invention, the positive ionic strength of CH3OH2 derived from the solvent hardly changes even if the sample solution concentration is changed by a factor of 10,
The mass spectrum of the sample to be measured can be measured without being affected by the concentration of the sample solution.

(2) Relationship between flow rate of sample solution and ionic strength (FIG. 5).

FIG. 5 shows the intensity of the divalent ion of Gramicidin-S detected when the flow rate of the sample solution was changed. At flow rates of 40 μL (microliter) / min or less, the ionic strength increases linearly as the flow rate increases. However, as the flow rate increases, droplets having a diameter larger than fine charged droplets (diameter of about 10 nm) are preferentially generated, and the temperature of the sampling orifice decreases, so that 40 μL (microliter) / min or more With the flow rate of, the increase in ionic strength is small even if the flow rate is increased. If the flow rate of the sample solution is in the range of 10 to 60 μL (microliter) / min, the sample can be efficiently ionized.

Even when the flow rate of the sample solution is zero, a decompression space having a pressure lower than the atmospheric pressure generated by the gas ejected from the tip of the gas guide tube is generated. Therefore, in the spray ionization method, the sample is ionized to zero. Is not obtained (not shown in FIG. 5).

(3) Relationship between the size of the opening at the tip of the gas guide tube from which gas is ejected, the size of the capillary, and the ion intensity.

With the gas flow velocity and the outer diameter of the capillary kept constant, the inner diameter at the point where the cross-sectional area of the gas outlet at the tip of the gas guide tube tip 7 is smallest is 0.4 mm to 0.5 mm.
The ion intensity to be detected did not change even if it was changed to.
On the other hand, when the gas flow rate is constant and the inside diameter of the opening is 0.5 mm, which is the gas outlet at the end of the gas guide tube tip 7, the ion intensity is significantly higher than when the inside diameter of the opening is 0.4 mm. Low and virtually no ions were detected. Therefore, the generation of ions depends not on the gas flow rate but on the gas flow rate.

The inner diameter of the opening at the tip of the gas guide tube 7 is fixed to 0.5 mm, and a quartz capillary (inner diameter 0.1 mm, outer diameter 0.2 mm) with a thickness of 50 μm and a thickness of about 3 mm are used. A comparison was made with a 137.5 μm thick quartz capillary (inner diameter 0.1 mm, outer diameter 0.375 mm), which was twice as thick. Even if the gas flow velocity is the same, the detected ion intensity is about one order of magnitude higher for a quartz capillary with a thickness of 50 μm, and the thinner the capillary, the higher the ion generation efficiency. This is because when the thickness of the capillary is increased, the gas flowing through the outer periphery of the capillary does not effectively act on the sample solution flowing out of the capillary, so that the ionization efficiency is reduced.

Although a quartz capillary was used as the capillary, a stainless steel capillary may be used. If the thickness of the capillary is in the range of 10 to 150 μm, there is a margin in strength and the sample can be ionized efficiently.

(4) Relationship between jet gas velocity, solvent concentration and ionic strength (FIG. 6).

FIG. 6 shows a sample of Gramicidin-S having a methanol concentration of 20%, 50%,
And three types of solutions of the samples (both sample concentrations of 1 μM) were prepared using a methanol aqueous solution of 80%.
Next, the three kinds of sample solutions were individually introduced into the capillary 5 at a flow rate of 40 μL (microliter) / min. Gr
Amicidin-S is a 2 to which two protons are added.
It was detected as a positive ion (m / z = 571).

The measurement diagram of FIG. 6 shows the above Gramicidi for the gas flow rate (error of about ± 3%) at the tip of the capillary calculated from the gas flow rate according to (Equation 1).
The ionic strength of the divalent ion of nS (m / z = 571) is also plotted. In FIG. 6, □ is 20%, ○ is 5
0% and ● show the relative ionic strengths observed for a sample solution using an 80% aqueous methanol solution as a solvent. The surface tension of the sample solution at the tip of the capillary 5 governs the size and generation efficiency of the charged droplet. The surface tensions of water and methanol are 0.073 and 0.022, respectively.
This is significantly different from 5 N / m, and the surface tensions of the three types of aqueous methanol solutions used as solvents are also different. As is clear from FIG. 6, the flow rate of the ejected gas is about 220 m / s (0 ° C.).
When the Mach number in is more than about 0.65), ions are detected, and the ion intensity increases as the gas flow rate increases. The ionic strength reaches a maximum when the gas flow velocity is around 337 m / s (corresponding to the sound velocity at 0 ° C. in N2 gas).
In the supersonic range, the ionic strength tends to decrease somewhat with increasing gas velocity. However, in a 50% methanol aqueous solution, even when the gas flow rate exceeds the sound speed (337 m / s) in N2 gas, the ionic strength is almost constant up to about 400 m / s (Mach number at 0 ° C. is about 1.2). Has been detected. Similarly, in a 20% methanol aqueous solution, even if the gas flow rate exceeds the sound velocity in N2 gas, about 3
An almost constant ionic strength is detected up to 70 m / s (Mach number at 0 ° C. is about 1.1).

In FIG. 6, as is apparent from the extrapolated line shown by the dotted line, the lower limit of the gas flow rate at which ions are detected is about 220 m / s (the Mach number at 0 ° C. is about 0.65). When the flow velocity of the ejected gas is supersonic, a shock wave is generated near the tip of the capillary, and the pressure near the tip of the capillary fluctuates. For this reason, large droplets are easily generated, and it is difficult to generate fine charged droplets necessary for ion generation, and the observed ion intensity decreases. Further, in the supersonic region, the jet gas is significantly cooled by adiabatic expansion, and when the gas guide tube is not sufficiently heated to prevent cooling, the vaporization of the charged droplets is suppressed.

When the measurement results shown in FIG. 6 were obtained,
The apparatus conditions are such that the potential of the capillary tip and the potential of the sampling orifice are set to the same potential, and the temperature of the gas guide tube and the capillary is room temperature without heating. Further, the flow rate of the ejected gas is about 330 m / s (the Mach number at 0 ° C. is about 1.
The ion intensity detected in the case of 0) does not change even when a high voltage of 3 kV is applied between the tip of the capillary and the sampling orifice. Therefore, the ion intensity shown in FIG. 6 is not based on the heating of the capillary and the ions generated by the voltage applied to the capillary, but the observed ion generation is due to the effect of only the ejected gas, The spray ionization method of the present invention does not require the voltage applied to the tip of the capillary or the effect of heating. Further, even when the capillary is not heated as shown in FIG. 6, sufficient ionic strength is obtained as compared with the conventional method, as described below. That is, in the conventional ionization method, generation of charged droplets having a diameter of 10 nm or less was considered to have no means other than using a strong electric field or heating. However, in the sonic spray method of the present invention, gas was used. The generation of charged droplets having a diameter of 10 nm or less is realized only by spraying the sample solution.

On the other hand, the gas flow velocity was set to 5 m / s where the amount of ions generated by gas ejection was neglected, and a high voltage of about 3 kV was applied between the capillary and the sampling orifice to perform electrostatic spraying. The ion intensity detected in the case of the ion spray method that generates ions by the phenomenon,
This is a low value of 1/10 or less of the ionic strength detected in the 50% aqueous methanol solution shown in FIG. 6, and is almost equal to the ionic strength detected in the 80% aqueous methanol solution shown in FIG.

The flow rate of the jet gas is 250 to 410 m / s
By setting the Mach number at 0 ° C. in the range of 0.75 to 1.2, it is possible to obtain an ion intensity that is about three times or more the ion intensity obtained by the conventional ion spray method. It is preferable to set the flow rate of the ejected gas in the range of 275 to 400 m / s (the Mach number at 0 ° C. is 0.8 to 1.2),
An ionic strength that is about six times or more the ionic strength obtained by the conventional ion spray method can be obtained. Further, the flow rate of the ejected gas is set to 3
20 to 400 m / s (Mach number at 0 ° C. is 0.95
-1.2), it is possible to obtain an ion intensity 10 times or more that of the conventional ion spray method, and to obtain the most preferable result.

As shown in FIG. 6, 20% or 5%
The ionic strength obtained when using a 0% aqueous methanol solution is about 10 or more than the ionic strength obtained when using an 80% aqueous methanol solution. Therefore, the present invention is very effective for high-sensitivity analysis of a sample solution separated by liquid chromatography suitable for analyzing a sample solution containing a high concentration of water.

(5) Relationship between the displacement of the sampling orifice with respect to the capillary tip position and the ion intensity (FIG. 7).

The distance between the capillary 5 and the sampling orifice 17 is maintained at 5 mm, and as described in the fourth embodiment, the opening of the gas guide tube, the capillary 5, and the sampling orifice 17 of the ion source. Each central axis is adjusted and set coaxially so that the detected ion intensity is maximized (this position is set as a reference position (= 0) of the following movement change), and ions from the sample solution are set. Measure strength. Next, the position of the entire ion source is moved and changed in the horizontal direction, and the ionic strength of the divalent ion of Gramicidin-S (the sample solution is the G
ramicidin-S solution (concentration 10 μM))
Is shown in FIG. The sharp peak at a relative ion intensity of about 2.8 in the center of FIG.
m / s (corresponding to the sound velocity at 0 ° C. in N 2 gas), it disappears when the supersonic velocity is increased to 400 m / s, and the relative ionic strength is about 1.6 instead. It becomes a broad dull peak. Small peaks appear near the movement distance of the ion source of -1 mm and 0.5 mm. These peaks are caused by the turbulence of the spray gas flow due to the hole (2 mm in diameter) of the cover 19 in front of the sampling orifice 17. It is thought that it was. The results shown in FIG. 7 are the same even when the position of the entire ion source is moved and changed in the vertical direction.

The above-mentioned moving distance of 1 mm corresponds to the circumference of the bottom surface of a straight cone having an apex angle of about 22.5 degrees with the center at the tip of the capillary 5 as the apex and the center axis of the capillary as the axis. It's above. That is, the sampling orifice 1
The center position (1 mm) of 7 is on this circumference. Similarly, the position of the moving distance of 0.2 mm is set to the capillary 5.
Is on the circumference of the bottom surface of a right cone with an apex angle of about 4.5 degrees, with the center of the tip of the apex as the apex and the center axis of the capillary as the axis. That is, the center position (0.2 mm) of the sampling orifice 17 is on this circumference. By disposing the center position of the sampling orifice inside the circumference of the bottom surface of the right cone, preferably having the apex angle of 4.5 degrees, about 2.5 times or more the ion intensity obtained by the conventional ion spray method. Is obtained. More preferably, by arranging the center position of the sampling orifice inside the circumference of the bottom surface of the right cone having the apex angle of 22.5 degrees, the ion intensity obtained by the conventional ion spray method is about 6 times or more. An ionic strength is obtained.

Further, the gas flow velocity was set to a sonic velocity of 337 m / s (N
(Corresponding to the sound velocity at 0 ° C. in two gases), even at a supersonic velocity further increased, an ion strength of about 6 times or more the ion strength obtained by the conventional ion spray method can be obtained.

(6) Relationship between the length of the tip of the capillary exposed from the tip of the gas guide tube and the ionic strength (FIG. 8).

FIG. 8 shows the capillary 5 from the atmospheric pressure surface of the opening having the minimum inner diameter at the tip of the gas guide tube tip 7.
5 shows the ion intensity detected when the exposure length (L shown in FIGS. 2 and 3) at which the front end of the sample is exposed is changed. When the exposure length L is 1.2 mm or more, the ionic strength decreases.
As the exposure length L increases, the gas flow velocity at the tip of the capillary substantially decreases, and the detected ion intensity decreases. Therefore, the above exposure length L is -0.25 to
Preferably, it is set to 1.0 mm.

(7) Relationship between sample solution concentration and ionic strength (FIG. 9).

FIG. 9 shows the ion intensity detected when the concentration of Gramicidin-S was changed. About 1
In a low concentration region of μM or less, the ionic strength increases linearly with respect to the sample concentration. The ionization method of the present invention is particularly suitable for a sample solution concentration of about 1 μM or less. At a sample concentration of about 2 μM or more, the detected ionic strength shows a linear change different from a linear change in a low concentration region of about 1 μM or less. The reason that the increase in ionic strength does not change so much even when the sample concentration is changed in a high concentration region of about 2 μM or more is that the pH of the solution is about 5, and most protons in the sample solution are Gr in the high concentration region.
amicidin-S, which is thought to be due to the depletion of protons in the sample solution.

[Fifth Embodiment] Next, a simple method for manufacturing a gas guide tube will be described with reference to FIG. FIG. 10 is a cross-sectional view showing a modified example of the gas guide tube tip end holding portion shown in FIG.

In FIG. 10, the details of parts 7, 15, and 16 shown in FIG. 3 are the same as in FIG. As is clear from the cross-sectional view of FIG. 10, the gas guide tube tip end holding portion can be obtained by a simple manufacturing method using a cylindrical material and only a simple boring process.

The material of each part constituting the gas guide tube may be other than the material described in each of the above embodiments, and various kinds of metal materials, glass materials, ceramic materials, and high filling of the filler can be used. It may be formed using a molecular resin material.

In the description of the present invention, the Mach number in parentheses described with respect to the gas flow rate is based on the assumption that the temperature near the tip of the gas guide tube is 0 ° C. ± about 10 ° C. , Sound velocity at 0 ° C in N2 gas at 337 m /
s ("Science Chronology", National Astronomical Observatory of Japan (1993), Maruzen Co., Ltd. (Tokyo)).

[0072]

According to the present invention, ions can be efficiently generated from a sample solution by a jet gas while the potential of each part such as a capillary constituting an ion source is grounded. As a result, as compared with the conventional ionization method, the structure of the ion source is simplified, and the operability and safety are improved. In addition, when the ion source of the present invention is applied to a capillary electrophoresis apparatus and a capillary electrophoresis / mass spectrometer is configured, the tip of the capillary can be set to the ground potential as described above.
Capillary electrophoresis equipment can apply potential independently,
The configuration of the entire apparatus is simplified, the operation of the apparatus is simplified, and the safety of the operation is significantly improved.

Further, in the conventional ionization method, the generation of ions is greatly affected by dirt around the capillary and the sampling orifice. However, according to the present invention, ions are generated from the sample solution by the ejected gas. Unlike the conventional method, the sonic spray method is not affected by dirt around the capillary or the sampling orifice.

In the conventional ionization method, the detected ion intensity is greatly affected by contamination around the sampling orifice and in the capillary. However, in the sonic spray method of the present invention, the detected ion intensity is different from the conventional method. The ionic strength of the sample is not affected by the contamination around the capillary, is not much affected by the contamination around the sampling orifice, enables high-sensitivity detection of the sample, and has good reproducibility. That is, by setting the tip of the capillary and the gas guide tube at the optimum positions, ions can be generated and detected from the sample solution with high reproducibility and high efficiency.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an apparatus of the present invention.

FIG. 2 is a sectional view showing a first embodiment of the ion source of the present invention.

FIG. 3 is a sectional view showing a second embodiment of the ion source of the present invention and a sampling orifice.

FIG. 4 is a diagram showing an example of a mass spectrum obtained using the ion source of the present invention.

FIG. 5 is a diagram illustrating a relationship between a sample solution flow rate and detected ionic strength.

FIG. 6 is a view showing a relationship between a jet gas velocity, a solvent concentration, and an ion intensity.

FIG. 7 is a diagram showing a relationship between a positional deviation between a capillary tip position and a sampling orifice position and ion intensity.

FIG. 8 is a diagram showing a relationship between an exposure length at a capillary tip position and an ion intensity.

FIG. 9 is a diagram showing a relationship between a sample solution concentration and an ionic strength.

FIG. 10 is a sectional view for explaining a simple manufacturing method of the gas guide tube.

[Explanation of symbols]

1 ... sample solution supply unit, 2 ... ion source, 3 ... gas supply unit,
4 ... Flow controller, 5 ... Capillary, 6 ... Tube, 7 ... Gas guide tube tip, 8 ... Gas introduction tube, 9 ... Heater, 10
... Gas guide tube tip holder, 11 ... Mass spectrometer, 12
... Capillary for electrophoresis, 13 ... Piping, 14 ... Mixing joint, 15 ... Jig for position adjustment, 16 ... Screw, 17 ...
Sampling orifice, 18 ... ceramic heater,
19 ... cover, 20 ... xyz stage.

Continued on the front page (72) Inventor Hideaki Koizumi 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside Hitachi, Ltd. Central Research Laboratory (72) Inventor Kaoru Umemura 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Hitachi, Ltd. In the laboratory

Claims (6)

[Claims] 1. A flow path for a sample solution, a gas flow path for flowing a gas around the flow path, and a gas that gives a substantially sonic flow velocity to the gas so as to generate a gaseous substance by spraying the sample solution at an end of the member. A spray device comprising a supply unit. 2. A flow path for a sample solution, a gas flow path for guiding a gas to flow out of the periphery of the flow path, and gas supply means for giving a flow rate of 200 m / S or more to the gas at an end of the flow path. A spray device comprising: 3. A flow path for a sample solution, a supply path for supplying gas around the flow path, a jet port for jetting the gas into the atmosphere, and an opening diameter of the jet port through the path. A spraying device which is smaller than an opening diameter of the supply path and which gives the gas a substantially sonic flow velocity at the jet port through the supply path. 4. A member having a partially hollow portion which is a flow path of a sample solution, a gas flow channel for flowing a gas so as to flow out from the periphery of the member having a partially hollow portion, and said partially hollow portion. An analyzer comprising: gas supply means for giving a substantially sonic flow velocity to the gas so as to generate a gaseous substance by spraying a sample solution at a tip of the member; and analysis means for analyzing the gaseous substance. 5. A capillary, which is a flow path of a sample solution,
A gas flow path through which gas flows out of the periphery of the capillary, gas supply means for spraying a sample solution at the tip of the capillary to generate a microdroplet, and a gas supply means for giving the gas a substantially sonic flow velocity; Analyzing means for vaporizing and analyzing the droplets. 6. A capillary, which is a flow path of a sample solution,
A gas flow path for guiding gas flowing out from the periphery of the capillary, a flow rate of the gas in the gas flow path being F, and a cross-sectional area of the gas flow path being S / S where F / S is a predetermined value or more. An analyzer comprising: a gas supply unit configured to ionize a sample solution according to the gas flow rate; and an analyzer configured to analyze a spray gas including ion micro-droplets generated near a tip of the capillary.