JPH0748371B2 - Ionization method and apparatus for high pressure mass spectrometry - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ionization method and apparatus for ionizing a sample for mass spectrometry, and particularly to ionizing a gasified sample under atmospheric pressure. The present invention relates to an ionization method and apparatus for high-pressure mass spectrometry that mass-analyzes the same.

(Prior Art) Mass spectrometry is often used to detect trace components. Mass spectrometry is a method in which a sample is ionized and passed through an analysis field consisting of a magnetic field or an electric field to separate each ion according to its mass, and this is detected and measured. Therefore, it is possible to perform analysis on a molecular or atomic basis, and it is particularly useful for detection of trace biometabolites, analysis of pollutant components or ultratrace impurities contained in semiconductor manufacturing process gas.

By the way, in order to perform such mass spectrometry, it is necessary to ionize the sample. Conventionally, an electron bombardment method in which high-speed electrons are applied to a gasified sample has been generally used for ionizing such a sample.

However, in order to ionize the sample by electron impact, it is necessary to accelerate the electrons at a sufficiently high speed, and therefore it is necessary to maintain a high vacuum in the ionization chamber that ionizes the sample. Therefore, the whole mass spectrometer becomes large-scale. Further, when electrons are applied at a high speed, the sample may be destroyed and a low molecular weight substance may be generated. When such a substance is produced, it becomes difficult to interpret the analysis result.

Under these circumstances, an ionization method capable of ionizing a sample even under atmospheric pressure has been demanded, the method has been found, and a high-pressure mass spectrometry method using the method has been developed. In this method, in the ionization chamber maintained at atmospheric pressure or slightly lower than atmospheric pressure, the radiation source ⁶³ Ni or corona discharge is used to generate chemically easily reactive ions. The sample is introduced into the ionization chamber in a gasified state, and is ionized by reacting with ions in the ionization chamber, that is, primary ions.

According to such a high-pressure mass spectrometry method, it is not necessary to maintain a vacuum in the ionization chamber, so that the entire apparatus can be simplified. Moreover, since the sample is not destroyed, more accurate analysis is possible.

(Problems to be Solved by the Invention) By the way, in order to efficiently perform such high-pressure mass spectrometry, it is necessary to increase the concentration of primary ions in the ionization chamber. However, in a conventional ion generator that generates primary ions by radiation or corona discharge, the same number of electrons as the primary ions are generated when the primary ions are generated. Then, the electron recombines with the primary ion. Therefore, there is a problem that the concentration of primary ions in the ionization chamber cannot be increased to a level that can be sufficiently satisfied.

Further, when the sample is a certain kind of organic substance, there is a problem that a chemical reaction with the primary ion is hard to occur.

The present invention has been made in view of such circumstances, and an object thereof is to obtain a method and an apparatus capable of efficiently ionizing a sample even under atmospheric pressure.

(Means for Solving the Problem) In order to achieve this object, in the present invention, the ionized chamber of the high-pressure mass spectrometer, that is, the atmospheric pressure, or a gasified sample which is held at a pressure slightly lower than the atmospheric pressure. A primary ion generator containing an alkali metal salt such as lithium oxide is placed in the ionization chamber into which is introduced, and the ion generator is heated.

The alkali metal salt is mixed with, for example, alumina silicate, and is attached to the electrically heated metal wire in a bead shape.

(Operation) As described above, when the primary ion generator containing the alkali metal salt is heated, the alkali metal ions are ionized from the surface thereof. Alkali metals are most likely to undergo such surface ionization. Moreover, when surface ionization is used, the electrons are retained inside the ion generator. Therefore, the alkali metal ions in the ionization chamber become rich.

Then, the alkali metal ion also undergoes an addition reaction with various organic substances. Lithium ions are particularly susceptible to addition reactions. Therefore, the alkali metal ions in the ionization chamber are efficiently added to the sample to form additional ions of the sample.

Although the alkali metal salt is in powder form, it becomes viscous when mixed with alumina silicate. Therefore, it becomes possible to attach this to a thin metal wire, and it is heated by electrically heating the metal wire.

(Examples) Examples of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a high pressure mass spectrometer to which the present invention is applied. FIG. 1 is an overall configuration diagram thereof, and FIG. 2 is a detailed view of its ion source portion.

As is clear from FIG. 1, the high-pressure mass spectrometer 1 includes an ion source section 2 for ionizing a sample and accelerating it, an analysis field 3 for separating and analyzing an ion beam extracted from the ion source section 2, and a separation field. Detector 4 for detecting and measuring the generated ions
It consists of The analysis field 3 is configured as a lens having a uniform magnetic field, and the ions are separated by their masses and reach the detection unit 4. Ion current is detected in the detector 4.

As shown in FIG. 2, the ion source section 2 is provided with an ionization chamber 5 which is opened under atmospheric pressure. A sample introduction port 6 is provided in the ionization chamber 5, and the gasified sample is introduced into the ionization chamber 5 through the introduction port 6 together with a carrier gas composed of an inert gas such as nitrogen gas. . Also, on the front end face of the ionization chamber 5,
An ion source slit 7 is provided for introducing the ionized sample into the analysis field 3.

A heating wire 8 made of platinum is arranged in the ionization chamber 5. The heating wire 8 is connected to an external power source via a pair of lead wires 9 and is electrically heated. Attached to the heating wire 8 is a primary ion generator 10 made of a mixture of lithium oxide, which is an alkali metal salt, mixed with alumina silicate. The ion generator 10 is formed in a bead shape.

Next, the operation of the high-pressure mass spectrometer configured as described above will be described.

When the heating wire 8 is electrically heated, the primary ion generator 10 attached thereto is heated, and the lithium ion Li ⁺ is ionized from the surface thereof. The ionization is sufficiently performed even under atmospheric pressure. Then, the electrons generated by the ionization are retained inside the ion generator 10. Therefore, the ionization chamber 5 is rich in lithium ions.

Then, since the gasified sample is introduced together with the carrier gas into the ionization chamber 5 in that state, lithium ions stick to the sample. That is, when the sample molecule is M, an addition reaction of Li ⁺ + M → MLi ⁺ occurs. In this way, the sample M becomes the additional ions MLi ⁺ and is ionized.

The additional ions are accelerated into an ion beam, which is guided from the ion source slit 7 through the analysis field 3 to the detection unit 4. Therefore, although the mass of the additional ion is detected in the detection unit 4, since the mass of the lithium ion is known, the mass of the sample can be obtained from the mass of the additional ion.

In this way, by utilizing the surface ionization of alkali metal and the addition reaction of alkali metal ion, it becomes possible to efficiently ionize the sample even under atmospheric pressure. Surface ionization due to heating occurs with any alkali metal, but cesium is most easily ionized. However, lithium is most likely to cause an addition reaction with an organic substance. Therefore, although the lithium salt is used in this embodiment, a sodium salt, a potassium salt or the like may be used.

In addition, by mixing the alkali metal salt and the alumina silicate, the mixture becomes viscous and can be easily fixed to the thin heating wire 8. However, the powdery alkali metal salt is fixed to the surface of a flat plate or the like made of a stable material by an appropriate method,
It is also possible to heat it.

In addition, in the above-mentioned embodiment, the example in which the present invention is applied to the high-pressure mass spectrometer has been described, but it is clear that the present invention is not limited to this and can be applied to the high-pressure mass analyzer.

(Effect of the invention) As is apparent from the above description, according to the present invention, an alkali metal ion is generated by heating an alkali metal salt in an ionization chamber, and a sample is formed by an addition reaction between the alkali metal ion and the sample. Is ionized, the ionization can be efficiently performed even under atmospheric pressure, and various organic substances can be ionized. Since the sample is not destroyed, mass spectrometry with high accuracy can be performed.

Further, according to the present invention, the alkali metal salt and the alumina silicate are mixed, and the mixture is used to form the primary ion generator. Therefore, it is possible to easily and surely fix even a thin metal wire. it can. When the metal wire is electrically heated, the primary ion generator fixed to the metal wire is heated, so that an extremely simple ionization device can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an example of a high-pressure mass spectrometer to which the present invention is applied, and FIG. 2 is an enlarged vertical sectional view showing an ion source part of the high-pressure mass spectrometer. 1 ... High-pressure mass spectrometer, 2 ... Ion source section 5 ... Ionization chamber, 6 ... Sample inlet 8 ... Heating wire (metal wire) 10 ... Primary ion generator

Claims (3)

[Claims] 1. A high-pressure mass spectrometric method for mass-analyzing a gasified sample by introducing it into an ionization chamber maintained at atmospheric pressure or a pressure slightly lower than atmospheric pressure and ionizing the sample ion. An ionization method, wherein a primary ion generator containing an alkali metal salt is placed in the ionization chamber, an alkali metal ion is generated by heating the ion generator, and the sample is produced by an addition reaction between the alkali metal ion and the sample. Ionization method for high pressure mass spectrometry, which is adapted to form adduct ions of. 2. The ionization method according to claim 1, wherein a lithium salt is used as the alkali metal salt. 3. A high-pressure mass spectrometric method in which a gasified sample is introduced into an ionization chamber maintained at atmospheric pressure or slightly lower than atmospheric pressure to be ionized, and the sample ions are subjected to mass spectrometry. An ionization device, wherein a metal wire to be electrically heated is arranged in the ionization chamber, and a mixture of an alkali metal salt and alumina silicate is attached to the metal wire in a bead shape. And an ionizer for high pressure mass spectrometry.