JPS5838911B2 - ion generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion generating device suitable for use in a mass spectrometer, an ionization detection device, or the like.

The present inventor previously proposed a new ion generation method in which an uncharged excited species created from a carrier gas is applied to a sample to ionize the sample.

This proposed method is published in Japanese Unexamined Patent Publication No. 55-9107 (Japanese Patent Publication No. 582
616), it can be implemented using the device configuration roughly illustrated in FIG.

In the figure, reference numeral 1 denotes a glass tube through which a carrier gas, such as argon, is introduced into the interior through an inlet 2. The end of the glass tube 1 is sealed with an insulator 3. A needle electrode 4 is inserted into the glass tube.

At the other end of the glass tube is a counter electrode 5 facing the needle electrode 4.
are attached, followed by the counter electrode 5, a mesh electrode 6, repeller electrodes 7, 8, and rings 9, 10, .
11 and are arranged in this order.

12 is a sample.

Then, a corona discharge is caused between the needle electrode 4 and the counter electrode 5 to create argon ions Ar+, electrons e-, and excited argon atoms Ar (excited species). The feature of this proposed method is that only Ar is extracted, and the sample is ionized by the excitation (internal) energy of the Ar.
(a) liquid samples can be directly ionized under atmospheric pressure; (b)
) If argon is used for %, most organic compounds can be ionized, and water, air, etc. are not ionized at first, so the sample can be handled freely in the air. (c) Since ionization is performed at atmospheric pressure, strict It has many advantages, such as eliminating the need for airtightness and simplifying the device configuration.

The purpose of the present invention is to further improve the proposed method, which has such excellent features, and in particular, involves attaching and holding a sample to a holding member having a large number of protrusions, and applying a high voltage to the holding member. This provides an ion generating device that can dramatically increase the amount of sample ions produced and improve sensitivity by an order of magnitude compared to the first embodiment.

The present invention will be explained in detail below based on the drawings.

FIG. 2 is a cross-sectional view showing an example in which the ion generator according to the present invention is used as an ion source of a quadrupole mass spectrometer;
FIG. 3 is a sectional view taken along the line I-■', and the same components as in FIG. 1 are designated by the same numbers.

In this embodiment, in order to ensure the removal of argon ions (Ar) and electrons (e), there is another layer between the mesh electrode 6 and the liberator electrode 7.
Two mesh electrodes 13 are arranged to apply an appropriate potential, and a ring 14 is also added.

Further, the ring 11 is provided with an exhaust port 15, and a sample holder 16 having a member having a large number of protrusions is inserted therein.

The holder 16 has a glass base 17 and a 2
It consists of a book support electrode 18, 19 and a tungsten wire 20 stretched between the electrodes, and the sample liquid is applied to the tungsten wire 20.
It is attached and held by needle-like protrusions (whiskers: for example, needle-like crystals of silicon or carbon) 21 that are grown in large numbers on the surface of 0.

A high voltage of several hundred volts to several hundred volts is applied to the tungsten wire 20 by a power source 22, and the tungsten wire 20 can be electrically heated by a power source 23 if necessary.

A quadrupole mass spectrometer 29 equipped with lens electrodes 24° 25, a quadrupole electrode 26, an ion detector 27, and a vacuum pump 28 is connected to the latter stage of the ring 11, and a high vacuum is placed between them. An electrode 31 having a pinhole 30 with a conductance that can maintain a pressure difference with the mass spectrometer is installed.

The electrode 31 is insulated from the surroundings by a ring 32 and connected to a power source 3.
3, an appropriate voltage can be applied.

With the above configuration, a steady flow of argon gas of about 1 atm is formed inside the ion generator, passing from the inlet 2 to the exhaust port 15 via the glass tube 1 and the rings 9, 10°14.11. Some of it flows into the mass spectrometer through the pinhole 30.

When a negative high voltage of, for example, about 34 is applied to the needle electrode 4, a corona discharge occurs between the needle electrode 4 and the argon gas in the glass tube.
+, electron e-, and excited state argon atom Ar'' are generated.

The reaction is shown by the following equation. Ar generated in the reaction of equation (2) is in a metastable state (excitation energy 11.5
5 eV and 11.72 eV).

This state of Ar has a long life (10-3 seconds or more), and even if it collides with an Ar atom, only resonance energy transfer occurs as shown in the following equation, and the total number of Ar does not change.

Ar+, e- generated in this way by corona discharge
and Ar move toward the sample holder on a steady flow, or the charged Ar and e cannot pass through the mesh electrodes 6 and 13, which are given an appropriate potential, and are removed. Only uncharged Ar reaches inside the ring 11.

When this Ar'' comes into contact with the sample, all compounds M having ionization energy lower than the excitation energy (11,556 V or 11.72 eV) possessed by Ar'' are ionized according to the following formula.

In the present invention, the sample is attached and held by a member having a large number of needle-like protrusions, and a high voltage is applied to this, so an extremely strong electric field exists in the needle-like protrusions, and the sample surface is exposed to this electric field. has been done.

Therefore, sample molecules that receive the energy of Ar (11.55 eV or 11.72 eV) upon contact with Ar are immediately ionized and quickly desorbed from the surface by this strong electric field, so a high voltage is applied. Even if the same amount of Ar is applied, the amount of sample ions desorbed can be dramatically increased compared to when no Ar is applied.

Furthermore, in the present invention, since the sample is attached and held by a large number of needle-like protrusions, the surface area of the sample (ie, the contact area with Ar'') becomes large, and the amount of sample ions generated also increases on this surface.

In experiments conducted by the inventor, it was confirmed that the amount of sample ions detected increased by 102 to 103 times compared to when no high voltage was applied, and therefore the sensitivity improved by 102 to 103 times.
It was also confirmed that even non-volatile samples can be effectively ionized.

It was confirmed that the amount of sample ions produced could be increased as the applied voltage was increased; however, if the voltage exceeds about 1500 V, not only the sample molecules but also the surrounding argon excited species will be ionized due to the strong electric field, causing the sample ions to ionize. Since it gives an overwhelmingly large background current compared to , it is not suitable, and in reality, the range of 100V to 1500V is optimal as the applied voltage.

Furthermore, conventional attempts have been made to increase the amount of sample ions generated by heating the sample, but in the present invention, which can dramatically increase the amount of ions by applying a high voltage, heating is not necessarily necessary. Therefore, even a thermally unstable sample can be ionized without destroying the sample.

However, in the present invention, it is also possible to further increase the amount of generated ions by using electrical heating from the power source 23, and even in that case, there is no need to raise the temperature to such a high temperature.

A large amount of sample ions generated in this manner are introduced into the mass spectrometer by the force of the voltage applied to the repeller electrode 7 and the argon gas flow flowing from near the sample toward the pinhole 30, and are subjected to mass analysis. Therefore, the sensitivity of mass spectrometry will also be significantly improved.

In this example, positive ions are introduced into the mass spectrometer, but if negative ions are to be analyzed, the tungsten wire 2
0. The polarity of the voltage applied to the repeller electrode 7 and pinhole electrode 31 may be reversed.

The present invention is not limited to the embodiments described above and can be modified in many ways.

For example, if the present invention is applied to an ionization detector, an ion collector electrode may be placed close to the sample, and the generated sample ions may be collected on the collector electrode and detected.

In addition, in the above-mentioned example, the sample was attached to a tungsten wire with many needle-like protrusions grown thereon, but the shape of any member having a large number of protrusions can be chosen arbitrarily, such as a plate or a coil. .

In addition, by inserting a pipe connected to the separation column of the liquid chromatograph into the ring 11 and letting the flowing sample solution drip or continuously adhere to the needle-like protrusion, the liquid chromatograph and the mass spectrometer can be connected online. It becomes possible to do so.

Further, in the above-described embodiment, discharge was used to generate the excited species Ar, but it is also possible to use light or other radiation, and the carrier gas is not limited to argon, but other gases can also be used.

Furthermore, in the embodiment described above, the charged particles (
It is possible to use an electrode in which Ar+, e) is removed but with a hole in the center, or an electric field or a magnetic field in a direction perpendicular to the gas flow may be applied to remove charged particles.

Furthermore, there is also a method in which the excited species is applied to the sample from a direction perpendicular to the plane of the paper.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the equipment configuration for explaining the proposed method;
FIG. 2 is a sectional view showing the configuration of an embodiment of the present invention, and FIG. 3 is an IP sectional view thereof. 4: needle electrode, 5: counter electrode, 6. γ: mesh electrode, 16: sample holder, 20: tungsten wire, 21: needle-like projection, 2
2: power supply, 29: mass spectrometer, 30: pinhole.

Claims (1)

[Scope of Claims] 1. An excitation means for exciting a carrier gas, a charged particle removal means disposed in a passage through which charged particles and excited species generated by the excitation are guided, and a passage through which the excited species that have passed through the removal means pass. A member having a large number of protrusions arranged at positions and means for applying a high voltage to the member, a sample is attached to the member having a large number of protrusions, and the excited species is applied to the sample. An ion generating device characterized by ionizing. 2. The device according to claim 1, wherein sample ions ionized by the excited species are introduced into the mass spectrometer. 3. The apparatus according to claim 1, wherein sample ions ionized by the excited species are guided to an ion collector. 4. The device according to claim 1, wherein the excitation means excites the carrier gas by corona discharge.