JP2001291487A - Ion source and mass spectrometer using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ion source of a high ionization efficiency and a mass spectrometer using the same, without applying voltage to a capillary. SOLUTION: A solution sample is introduced from a sample solution supplying part 1 to a capillary in an ion source 2. The rate of the flow of the gas that is supplied from a gas supplying part 3 is regulated by a flowmeter 4, then the gas flows along the perimeter of the capillary, and it is introduced to a gas guiding tube, which has been configured to jet the gas at the tip of the capillary. The sample solution is ionized at the tip of the capillary by an effect of the jetted gas action, and analyzed by a mass spectrometer 11. Thereby, an ion's intensity, which is 10 times as large or more than that is obtained from a conventional ionization method, can be obtained, and an operation can be performed safely.

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 mixed sample. For this reason, when separating and analyzing a plurality of biological substances dissolved in a solvent such as water, capillary electrophoresis or liquid electrophoresis coupled to a mass spectrometer.
A mass spectrometer (CE / MS) 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. As a conventional technique for obtaining such ions, ion spraying (Analytical Chemistry), No. 5
9 (1987), paragraphs 2642 to 2646) 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. Used. In these various conventional spray ionization methods, it is considered that fine charged droplets having a diameter of about 10 nm or less need to be generated in order to obtain high ion generation efficiency.

[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.

[0007] Further, in the above conventional technique, 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 10-5.
It is empirically known that it is necessary to be in the range of Ω-1cm-1. Unless these conditions are satisfied, there is a problem in that the electrostatic spray 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 type 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.

An object of the present invention is to provide a safe and highly operable ion source, and a mass spectrometer capable of stably generating ions and analyzing a sample with high sensitivity and reproducibility using the ion source. To provide.

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.

[0011]

According to the present invention, there is provided a gas flow forming means for forming a gas flow at an outer peripheral portion of an end portion of a thin tube into which a sample solution is introduced. It is characterized by an ion source that is ejected into the sample to ionize the sample solution. Further, it is characterized in that the Mach number determined from the flow velocity of the gas and the velocity of the sound wave transmitted through the gas is at least in the range of 1 to 2. Further, the gas flow forming means has a gas inlet through which gas is introduced, and an opening through which gas is ejected, and an end of a thin tube is inserted and arranged in the opening. The gas is ejected from a minute space formed between the gasket and the peripheral surface. Further, the present invention is characterized by a mass spectrometer using an ion source having the above characteristics.

Hereinafter, the features of the present invention will be described in more detail. A capillary for sending a sample solution into the atmosphere and the above-mentioned tip for forming a gas flow along the outer peripheral surface of the capillary to the tip of the capillary. And a gas guide tube into which the gas is inserted, and a standard state of gas (20 ° C., 1 atm)
A characteristic value relating to a gas flow determined from a flow rate F converted into a gas flow rate and a minimum area S of a cross section of the space between the outer peripheral surface of the distal end portion and the gas guide tube orthogonal to the central axis of the capillary near the distal end portion. The F / S is within a predetermined range, and the sample solution delivered to the atmosphere is characterized by being ionized in the vicinity of the tip by the gas flow. The predetermined range of the characteristic value F / S is 200 m / s to 200 m / s. Desirably, it is 1000 m / s. From the viewpoint of efficiently ionizing the sample, it is preferably 350 m / s to 700 m / s, more preferably 5 m / s to 700 m / s.
The characteristic value F / S is set in the range of 00 m / s to 600 m / s. Here, the dimension of F / S is the same as the velocity, but is different from the actual flow velocity of the ejected gas. The flow rate F is a value obtained by converting the flow rate of the ejected gas into a standard state. The actual effluent gas is at a pressure higher than 1 atm.

The flow rate of the sample solution is 1 μL (microliter) / minute to 200 μL (microliter) / minute.

The fine gas droplets of the sample solution are generated at the tip of the capillary by the gas ejected from the minute space at the tip of the capillary. Mach number of gas flow is 1
, Smaller charged droplets are generated. The solvent is vaporized from the generated charged droplets by the ejected gas,
Gaseous ions are produced. The generated ions can be introduced into a mass spectrometer and analyzed.

When the characteristic value F / S of the jet gas flow at the tip of the capillary exceeds a certain value, the sample solution introduced into the capillary is fragmented at the tip of the capillary, and charged droplets of various sizes are generated. I do. And extremely fine charged droplets of at least 100 nm or less can be easily formed,
The solvent is removed (dried). In a solution, a neutral sample molecule may combine with a proton or a sodium ion in an extremely fine droplet to generate a pseudo-molecular ion, and when an ion that can be analyzed by a mass spectrometer is obtained, Conceivable.

The condition for determining the size of the droplet generated at the tip of the capillary is determined by the characteristic value F /
While S or Mach number plays an essential role, there are other factors to consider in the production efficiency of very fine droplets. That is, it is necessary that the pressure difference between the solution surface and the periphery at the tip of the capillary is larger than a certain level. By making the thickness of the capillary 100 μm or less, the efficiency of generating extremely fine droplets can be increased.

Furthermore, the central axis of the capillary is made to coincide with the central axis of the gas guide tube to make the flow velocity of the gas at the tip of the capillary uniform, thereby forming an axially symmetric flow of the jetting gas containing the droplets of the sample solution. In addition, reproducibility of ionization conditions can be improved.

If the characteristic value F / S of the gas flow is constant, the size of the droplet of the sample solution is substantially constant, and has little relation to the gas flow rate F and the area S of the minute space from which the gas is ejected. Empirically, it is sufficient if the gas flow rate F is 0.5 L / min or more. The material of the capillary and the potential applied to the capillary hardly affect the size of the droplet generated from the solution.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below 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.
The gas is introduced into the ion source 2 and flows along the outer periphery of the capillary, and the characteristic value F /
S is ejected as a gas flow having a value of about 200 m / s 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, a spray ionization method.
y) method)). The generated ions are introduced from the tip of the capillary into the mass spectrometer 11 by the above gas,
It is 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 connecting pipe (not shown), 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 an ion source used in this embodiment. The sample solution was supplied at a flow rate of 100 μL (microliter) / min.
The sample solution is supplied from the sample solution supply unit 1 arranged on the left side of FIG. 2 to an inner diameter of 100 μm and an outer diameter of 300 μm). 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. Gas flows along the outer periphery of the capillary 5,
A gas guide tube for ejecting a gas having a predetermined gas flow rate into the atmosphere at the tip of the capillary includes a gas guide tube tip 7 and a gas guide tube tip holder 10.

The 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 (the smallest inside diameter of the inside diameter of the gas guide tube is Part with inner diameter of 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. The gas is ejected through a minute space formed by the inner peripheral surface of the opening and the outer peripheral surface of the capillary 5. The characteristic value F / S of the gas flow in the micro space is obtained from the cross-sectional area S of the micro space in the plane orthogonal to the central axis of the capillary 5 or the opening and the flow rate F flowing in the gas guide tube. When the shape of the opening is a circle (inner diameter D) and the outer shape of the cross section in a plane orthogonal to the longitudinal direction of the capillary 5 is a circle (outer diameter d), the cross-sectional area S is obtained by (Equation 1). .

[0025]

S = π (D 2 −d 2) / 4 (Equation 1) The gas flow rate F can be determined using a mass flow meter or a flow meter such as a purge meter. In the embodiment of the present invention, the maximum flow rate of the N2 gas is 10 L (liter) / min (standard condition, 20 ° C., 1 atm), the pressure on the upstream side of the meter is 7 atm, and the gas flow rate is in the standard condition (20 ° C, 1
A mass flow meter (5850E, manufactured by Brooks Corporation) obtained by calibrating to the value of (atmospheric pressure) with an accuracy of 1% was used.

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.

When the length of the tip of the capillary 5 exposed from the gas guide tube tip portion 7 (exposed length L) is 2 mm or more, the pressure gradient of the gas at the tip of the capillary 5 is reduced, and the ion generation efficiency is reduced. 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.
A rare gas such as argon or carbon dioxide may be ejected. Further, it is preferable to use nitrogen, air or carbon dioxide from the viewpoint of cost for purchasing gas. More preferably, use of dry nitrogen containing less water vapor is preferred.

In this embodiment, the axial thickness of the portion having the smallest inner diameter at the tip of the gas guide tube tip 7 is set to 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 supplied to the sample solution supply unit 1 via a connecting pipe (not shown), or the capillary, which is a separation tube of the capillary electrophoresis apparatus, is used as the sample solution. Supply unit 1
It is directly connected to.

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 into 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 the 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.

The sampling orifice 17 of the 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 moved 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.

A quadrupole mass spectrometer is used as the mass spectrometer, and even when a voltage of several hundred volts is applied to the sampling orifice 17 at a 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, an intermediate voltage (for example, 1-2 kV) between the ground potential and the acceleration potential is applied to the cover 19.
And the capillary 5 and the sampling orifice 1
7 is about 1 cm, and O
By using a gas having a high electron affinity, such as 2 or SF6, discharge can be avoided and the potential at the periphery of the tip of the capillary 5 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 difference of about 200 V is applied to the inside of the vicinity of the tip of the capillary 5 so that the portion close to the surface of the sample solution coming out from the tip of the capillary 5
Separation of positive and negative ions is caused, so that a portion close to the surface of the sample solution is rich in either positive or negative ions. 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 features 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 measurement conditions, the potentials of the capillary tip, the sampling orifice, and the cover 19 were set to the same potential. N2 gas was used as the ejected gas, and the characteristic value F / S of the ejected gas was set to 550 m / s. The flow rate of the sample solution (Gramicidin-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 by using the present ion source (FIG. 4).

FIG. 4 shows that one kind of peptide, Grami
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 ions having m / z = 140 are considered to be derived from impurities mixed in the sample solution or from the atmosphere.
CH3OH2 positive ion derived from methanol (m / z =
Although 33) is slightly observed, no H3O positive ion or a cluster formed by adding a water molecule to the H3O positive ion is observed, and a simple spectrum is obtained, which facilitates spectrum analysis. In conventional methods such as an electrospray method and an ion spray method, when a mass spectrum is measured using a dilute sample solution, ions derived from a solvent are strongly observed. In the present invention, the positive ion intensity of CH3OH2 derived from the solvent hardly changes even when the sample solution concentration is changed by 10 times, and the mass spectrum of the sample to be measured can be measured without being affected by the sample solution concentration. it can.

(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) The 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 ionic strength.

Even if the gas flow velocity and the outer diameter of the capillary are 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 changed from 0.4 mm to 0.5 mm. The detected ionic strength did not change. On the other hand, when the gas flow rate is constant and the inner diameter of the opening, which is the gas outlet at the end of the gas guide tube tip 7, is 0.5 mm, the ionic strength is significantly higher than when the inner 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 tip 7 is fixed to 0.5 mm, and a quartz capillary (0.1 mm in inner diameter, 0.2 mm in outer diameter) having a thickness of 50 μm and a thickness of about 3 mm are used. This was compared with a quartz capillary (0.1 mm in inner diameter and 0.375 mm in outer diameter) with a thickness of 137.5 μm, which is twice as large.
Even if the gas flow rate is the same, the detected ion intensity is 5
The quartz capillary of 0 μm is about one digit higher, and the thinner the capillary, the higher the ion generation efficiency and the more preferable.
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 is used as the capillary, a stainless steel capillary may be used. If the capillary has a thickness in the range of 10 to 150 μm, there is a margin in strength and the sample can be ionized efficiently.

(4) Relationship between characteristic value F / S of ejected gas and ion intensity, measurement of Mach number M (FIG. 6).

In FIG. 6, a sample solution of an aqueous methanol solution having a methanol concentration of 50% (sample concentration: 1 μM) was prepared using Gramicidin-S as a sample. Next, the sample solution was added in an amount of 40 μL (microliter) /
At a flow rate of 1 min. Ejected gas includes
N2 and Ar were used. Gramicidin-S
Is a divalent positive ion (m
/ Z = 571).

The measurement diagram in FIG. 6 is obtained by plotting the ion intensity of the above-mentioned divalent ion (m / z = 571) of Gramicidin-S against the characteristic value F / S of the gas flow. In FIG. 6, .largecircle. Indicates the relative ion intensity observed when N2 gas and Ar gas were used (the maximum value of relative ion intensity was set to 10 in each case).

Under the conditions indicated by the arrow C in FIG. 6, the gas pressure on the upstream side of the gas flow flowing through the gas guide tube of the ion source is 7 atm (P0 = 7 atm). The pressure outside the ion source is 1 atm (P = 1 atm). Therefore, the Mach number M can be obtained by using the following relational expression for the isentropic flow.

[0055]

P0 / P = {1 + 0.5 (γ−1) M2} ** α (Expression 2) In Expression 2, α = {γ / (γ−1)}, and **
Is a power, and γ is a specific heat ratio of gas, which is 1.4 in the case of N 2 gas (references: Takefumi Ikui, Kazuyasu Matsuo;
Mechanics of compressible fluids (Rigaku Kogyo, 1977); W. L
iepmann, A .; Roshko; Elements
of Gasdynamics (John Wile
y & Sons Inc. NY, 1960). When the Mach number M is obtained by using the relational expression of (Equation 2), the characteristic value F / S at point C indicated by an arrow in FIG.
/ S, it is estimated that M = 1.93. From this, it is concluded that the experimental results of FIG. 6 were obtained under the condition that the Mach number M was 2 or less.

In a compressible fluid such as a gas, a change in refractive index due to a change in density exists in the fluid. Using this property, the flow can be visualized. So, N2
The sample solution was not introduced using gas, and the arrow A in FIG.
Characteristic values F / S indicated by B and C = 345, 691, 1040
A Schlieren photograph was taken under the condition of m / s, and the Mach number M was obtained based on (Equation 2). FIG. 7 schematically shows a schlieren photograph of the obtained ejected gas. FIG.
(A) is a schematic diagram of a schlieren photograph of the ejected gas obtained at the characteristic value F / S = 345 m / s at the point A in FIG.
The left side in FIG. 7A is a side view schematically showing a gas flow state at the tip of the ion source, and the tip of the capillary is exposed from the ion source by about 0.3 mm. The ejected gas flows rightward from around the tip of the capillary shown in FIG. In this Schlieren photograph, only the outline of the gas flow is obtained. Characteristic value F at points B and C in FIG.
FIG. 7B schematically shows a schlieren photograph obtained at / S = 691, 1040 m / s. Compared to FIG. 7A, a stripe pattern corresponding to a large change in density appears significantly in the gas flow. This is determined to be an expansion wave generated in a supersonic flow. At point B, it is concluded that a supersonic flow occurs near the tip of the capillary and the Mach number M is 1 or more. On the other hand, at the characteristic value F / S = 345 m / s at the point A,
No Mach number M is 1 or less without a stripe pattern. Accordingly, M = M in the region between the point A and the point B indicated by the arrow in FIG. 6, that is, the region including the characteristic value F / S at which the ionic strength is maximized.
The condition that becomes 1 exists.

In FIG. 6, when the Mach number M of the flow rate of the ejected gas is a supersonic speed of 1 or more, a shock wave or an expansion 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 likely to be generated, and fine charged droplets required for ion generation are unlikely to be generated, and the observed ion intensity is considered to decrease. In addition, in the supersonic region, the jet gas is insulated. It is considered that the droplets are significantly cooled by expansion (the gas guide tube is not heated in order to prevent the cooling in the experiment for obtaining FIG. 6), so that the vaporization of the charged droplets is suppressed. It is assumed that a point between the point A and the point B, that is, about 550 m / s which gives the characteristic value F / S at which the ionic strength is maximum is a point where the Mach number M = 1.

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 ion intensity detected when the characteristic value F / S of the ejected gas is about 550 m / s 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. In the spray ionization method, the voltage applied to the capillary tip,
No heating effect is required. 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. The generation of charged droplets having a diameter of 10 nm or less is realized only by ejecting the sample solution into the atmosphere.

On the other hand, the characteristic value F / S of the gas flow is set to 5 m / s where the amount of ions generated by gas ejection can be ignored, and a high voltage of about 3 kV is applied between the capillary and the sampling orifice. The ion intensity detected in the case of the ion spray method of generating ions by the electrostatic spraying phenomenon is about 1/1 of the maximum value of the ion intensity shown in FIG.
It is a low value of 0 or less.

The characteristic value F / S of the ejected gas is set to 350 to 700.
By setting the value in the range of m / s, it is possible to obtain an ionic strength of about three times or more the ionic strength by the conventional ion spray method. The characteristic value F / S of the ejected gas is 400 to 800 m / s
Is preferably set in the range, and an ion intensity of about 6 times or more of the ion intensity obtained by the conventional ion spray method can be obtained. Further, the characteristic value F / S of the ejected gas is set to 500 to 60.
If it is set in the range of 0 m / s, it is possible to obtain an ion intensity 10 times or more that of the conventional ion spray method, and it is possible to obtain the most preferable result.

(5) Relationship between the displacement of the sampling orifice with respect to the capillary tip position and the ion intensity (FIG. 8).

The distance between the capillary 5 and the sampling orifice 17 is maintained at 5 mm, and the opening of the gas guide tube, the capillary 5, and the sampling orifice 17 of the ion source are explained as described in the fourth embodiment. 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))
FIG. 8 shows the result of detection of. The sharp peak having a relative ion intensity of about 2.8 in the center of FIG. 8 disappears when the characteristic value F / S (550 m / s) of the gas flow at the time when the sharp peak is obtained is further increased. Instead, it results in a broad, dull peak with a relative ionic strength of about 1.6. The travel distance of the ion source is -1 mm and 0.5
Small peaks appear in the vicinity of mm, and it is considered that these peaks are caused by turbulence of the jet gas flow due to a hole (2 mm in diameter) of the cover 19 in front of the sampling orifice 17. The results shown in FIG. 8 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 arranging the center position of the sampling orifice inside the circumference of the bottom surface of the right cone, preferably having the apex angle of 22.5 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 above-mentioned apex angle of 4.5 degrees, the ion intensity obtained by the conventional ion spraying method is about 6 times or more. An ionic strength is obtained.

Further, the characteristic value F / S of the ejected gas is set to 550.
Even in the case of supersonic velocities which are further increased from m / s, an ionic strength of about 6 times or more the ionic strength obtained by the conventional ion spray method can be obtained.

(6) The relationship between the length of the tip of the capillary exposed from the tip of the gas guide tube and the ionic strength (FIG. 9).

FIG. 9 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. 10).

FIG. 10 shows the ion intensity detected when the concentration of Gramicidin-S was changed. In the low concentration region of about 1 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. In the high concentration region of about 2 μM or more, the reason that the increase in ionic strength does not change much even when the sample concentration is changed is that the pH of the solution is about 5,
In the high concentration region, most of the protons in the sample solution are G
ramicidin-S, which is thought to be due to the depletion of protons in the sample solution.

(Fifth Embodiment) Next, a simple manufacturing method of a gas guide tube will be described with reference to FIG. FIG. 11 is a cross-sectional view showing a modification of the gas guide tube tip holding portion shown in FIG.

In FIG. 11, the details of the components 7, 15, and 16 shown in FIG. 3 are the same as those in FIG. As is clear from the cross-sectional view of FIG. 11, 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 materials described in each of the above embodiments, and various kinds of metal materials, glass materials, ceramic materials, and high filler filling. It may be formed using a molecular resin material.

[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 diagram showing a relationship between a characteristic value F / S of ejected gas and ion intensity.

FIG. 7 is a diagram schematically showing a schlieren photograph of ejected gas.

FIG. 8 is a diagram showing a relationship between a positional deviation between a capillary tip position and a sampling orifice position and ion intensity.

FIG. 9 is a diagram showing a relationship between an exposure length at a capillary tip position and an ion intensity.

FIG. 10 is a diagram showing a relationship between a sample solution concentration and an ionic strength.

FIG. 11 is a cross-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.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuaki Takada 1-280 Higashi Koikekubo, Kokubunji City, Tokyo Inside the Central Research Laboratory of Hitachi, Ltd. (72) Inventor Hideaki Koizumi 1-280 Higashi Koikekubo Kokubunji City, Tokyo Hitachi, Ltd. (72) Inventor Kaoru Umemura 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo In-house Central Research Laboratory, Hitachi, Ltd.

Claims (5)

[Claims] 1. A gas flow is formed at the tip of a capillary using an ion source having a capillary for delivering a sample solution and a gas guide tube having an opening for flowing gas at the tip of the capillary. In the ionization method for ionizing the sample solution, the flow rate of the gas stream is converted to a standard state (20 degrees Celsius, 1 atm).
And a characteristic value F / S determined from a gas ejection area S at the opening is 350 m / s or more and 700 m / s or less. 2. A capillary having an outer dimension d and a gas guide tube having an opening having an inner diameter D, wherein a central axis of the capillary and a central axis of the gas guide tube are coaxially arranged. In the ionization method in which the sample solution is ionized by forming a gas flow at the tip of the capillary by using the obtained ion source, the flow rate of the gas flow was converted to a standard state (20 degrees Celsius, 1 atmosphere). Flow rate F
And a characteristic value F / S defined by an area S defined by S = π (D2−d2) / 4 using d and D is 350.
An ionization method characterized by being at least m / s and at most 700 m / s. 3. The range of the characteristic value F / S is further 500 m /
3. The ionization method according to claim 1, wherein the ionization method is not less than s and not more than 600 m / s. 4. The ionization method according to claim 1, wherein the gas guide tube is provided when the case where the tip of the capillary coincides with the opening of the gas guide tube is set to zero. An ionization method, wherein the distance between the opening and the tip of the capillary is -0.25 mm or more and +1.0 mm or less. 5. The ionization method according to claim 1, wherein the temperature of the gas flow formed at the tip of the capillary is equal to or higher than room temperature.