JPS617556A - Mass spectrometer for secondary ions - Google Patents

Abstract

PURPOSE:To simplify the structure of the ion source and save the labor of adding an alkali metal salt prior to subjecting a highly polar substance to mass spectrometry by using alkali metal ions produced by surface ionization as primary ions. CONSTITUTION:A surface ionization source 6 is prepared, for example, by applying an alkali salt to a tungsten ribbon. It is set in a primary-ion-producing part 2. When the tungsten ribbon is heated by a power supply 9 to ionize the alkali salt in the surface of the tungsten ribbon, alkali metal ions are discharged from the tungsten ribbon. These alkali metal ions are then drawn by electrodes 7 before striking the sample applied to a belt 1 to eliminate ions from the surface of the sample. Secondary ions discharged from the belt 1 pass through electrodes 4 before being introduced into a mass spectrometric part 3.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to liquid Ch
romato-graph; hereinafter abbreviated as LC. ) and a mass spectrometer (hereinafter abbreviated as MS).
C/MS and secondary ion mass spectrometer (5econdar
y Ion Mass Spectrometer; hereinafter abbreviated as SIMS. ) regarding the ion source.

[Background of the invention]

For example, the analysis of substances extracted from living organisms begins with the separation of each component using LC, but LC currently lacks a versatile and highly sensitive detector. Therefore, various attempts have been made to combine MS and LC [for example, P., J., Arpino a.
nd G, Guiochon, Anal, Che
m, 51°683 A (1979)].

Two important technical issues in such an LC/MS apparatus are how to efficiently remove the solvent and how to ionize a hardly volatile and thermally unstable substance. In particular, removing the solvent is important from the viewpoint of protecting the ion source from contamination and maintaining its long life. The best method for solvent removal is the use of a moving belt [for example, U.S. Pat.
No. 55987], and commercial products are also available from several companies. In other words, in this method (belt introduction method), the LC eluate is applied onto a belt (or wire) made of metal or polymer, the solvent is removed by drying, and the less volatile components are transferred onto the belt (or wire). Hold. This belt is introduced into the MS by differential pumping from the atmospheric pressure section through a narrow gap, and can continuously transport substances attached to the surface from the atmospheric pressure to the ionization chamber under high vacuum. A sample introduced into the ionization chamber is vaporized by heating, then ionized by electron bombardment, chemical ionization, or ion bombardment, and subjected to mass spectrometry.

Among the above ionization methods, ionization method by ion bombardment [
For example, A. Benninghoven et al.
, , ApplPhys, , 11.35 (i97
6), -An,al,Chem,,50.1180
(1978)] is suitable for the analysis of poorly volatile or thermally unstable substances. Many of the samples handled by LC are difficult to volatile and often thermally unstable, and with other ionization methods that require heating, thermal decomposition of the sample occurs prior to ionization, making it difficult to obtain sufficient information. This is because there are many things.

When analyzing organic matter attached to a solid surface by SIMS9, the energy of the primary ion is set to 1 to 5 keV.
This method is used to obtain information near the solid surface, but it is inconvenient if, in addition to the sample, oil diffusion pump oil or other hydrocarbons adhere to the solid surface, which will appear as background in the spectrum. Therefore, when performing the above analysis, a high vacuum of 10-8 to 10-9 TOrr was used.

L using SIMS and moving belt targeting this organic matter
Even when the C/MS interface is connected, it is desirable to maintain a high degree of vacuum in the ion irradiation chamber or mass spectrometer. The causes of the decrease in vacuum level include the inflow of gas when the moving belt is introduced by differential pumping, and the inflow of gas (mainly Ar) into the ion irradiation chamber to be introduced into the primary ion source to generate primary ions (mainly Ar+). There is. Normally, the primary ion source is evacuated by a pump separate from the ion irradiation chamber, but this is often insufficient.

Thus, one important point in LC/SIMS is how to maintain a high degree of vacuum.

Further, when a large amount of organic sample is applied to the surface of the metal (moving belt), if Ar+ is used as the primary ion, secondary ions may not be observed due to charge-up or the like.

When trying to ionize fragile compounds (such as sugars) with Sl or MS4, even if a molecular ion or an H+-added molecular ion is generated, it may break down immediately and give many fragment ions. Even in such cases, alkali metal ions and organic compounds are stable and often generate raster [for example, U, G
iessmann and F.

W, ROllgen, Org, Mass Spec
trom, 11.1094 (1976)]. Conventionally, therefore, an alkali metal or its salt was added to the sample or onto the belt.

[Purpose of the invention]

The present invention has been made in order to solve such difficulties in LC/SIMS and to save the labor of adding an alkali metal salt.

[Summary of the Invention/Embodiments] In order to achieve this, the present invention employs alkali metal ions generated by surface ionization as primary ions.

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 is a schematic diagram for explaining the main part configuration of a belt-introduced SIMS according to the present invention. In the figure, 1 is a sample introduction belt, 2 is a primary ion generator (ion source), 3 is a mass spectrometer, 4 is an electrode for extracting secondary ions and introduced into the mass spectrometer 3, and 4' is a The counter electrode, 4" is a lens and deflection electrode, 4"' is a ground slit, 5 is a heater stem, 6 is a surface ionization source, 7 is an electrode for extracting primary ions and performing ion bombardment, and 7' is an ion bombardment. 7# is a lens/deflection electrode, 7' is a ground slit, 8 is a hermetic 7 flange, and 9 is a power source.

The surface ionization source 6 is, for example, a 1i tungsten ribbon (wire).
It has an alkali salt coated on top and is set in the primary ion generator. The tungsten ribbon (
When the alkali salt is surface ionized by heating a
and is released. The ions extracted by the electrode 7 are 1 to 5
The sample coated on the belt l is bombarded with energy of keV, and a portion of it is desorbed from the surface as ions.

Secondary ions emitted from the belt pass through the electrode 4 and are introduced into the mass spectrometer 3.

Note that in order to obtain a certain amount of alkali metal ions by surface ionization, the tungsten ribbon is heated with a constant current power source or a power source with an emission regulator. It is also possible to configure the surface ionization source 6 portion to be detachable in order to supply the alkali salt onto the tungsten ribbon as needed.

That is, the tungsten ribbon for surface ionization (a metal based on rhenium or the like can also be used) is attached to a direct introduction probe that is easy to attach and detach, so that the ribbon can be easily replaced and replenished onto the alkaline earth metal ribbon. Just configure it.

In the present invention, since metal ions are used as primary ions, the above-mentioned trouble due to charge-up is less likely to occur due to their conductivity. In addition, for strongly polar substances such as sugars, the molecular ion (M+Na)+ to which an alkali metal ion such as sodium is attached is more stable as an ion than the molecular ion or protonated molecular ion. If they coexist,
This ion species can be observed with high sensitivity. Like this (M+
Observing Na)+ is important in knowing its molecular weight, and the method of irradiating with alkali metal ions according to the present invention is convenient because the alkali metal is automatically replenished onto the belt.

In addition to the method of using surface ionization as an alkali metal ion source, it is also possible to use a high-temperature metal furnace or the like that can obtain a large current, but this is not preferable because the apparatus becomes large-scale.

The amount of primary ions required for the purpose of the present invention is 10-7~
1O-9A, and the amount of ions obtained by surface ionization is sufficient.

〔Effect of the invention〕

As described above, according to the present invention, no gas is required to generate primary ions, so a system such as differential pumping is not required, and the configuration of the ion source itself is extremely simple. Particularly in SIMS, it is desirable that the ion bombardment section has a good degree of vacuum, so this is a great advantage. Another great advantage is that when measuring highly polar substances, (M+Na)+ can be generated with high efficiency without adding an alkali metal salt in advance, making it convenient for determining molecular weight. .

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining the main part configuration of a belt-introduced SIMS according to the present invention. ■...Sample introduction belt 2...Primary ion generator (ion source) 3...Mass spectrometer 4...Electrodes 5...Heater stem 6...Surface ionization source 7...Electrode Category 8... Hermetic flange 9... Power supply

Claims (1)

[Claims] 1. Secondary ion mass analysis of an organic sample using secondary ions generated when primary ions are irradiated onto an organic sample attached to the surface of a sample carrier made of a metal or an insulator. 1. A secondary ion mass spectrometer, characterized in that the primary ion generation section of the mass spectrometer is equipped with means for generating alkali metal ions through surface ionization. 2. In the secondary ion mass spectrometer according to claim 1, the sample carrier moves from at least a first position away from the primary ion irradiation part of the mass spectrometer to a first position which becomes the primary ion irradiation part. The belt is movable up to a second position, and after the organic sample is supplied to the first position as the organic sample liquid containing the solvent eluted from the chromatograph, the belt moves to the first position, and after the organic sample is supplied to the first position as the organic sample liquid containing the solvent eluted from the chromatograph, the belt moves to the first position. A secondary ion mass spectrometer, characterized in that the secondary ion mass spectrometer is supplied to the second position as an organic sample.