JPH0351052B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a secondary ion mass spectrometer that can also analyze organic substances separated by liquid chromatography, and particularly to a secondary ion generator thereof.

Conventionally, the ion microanalyzer (IMA) used to analyze metals and semiconductors can be said to be a type of secondary ion mass spectrometer (hereinafter referred to as SIMS), and the technology in this field is well known. . SIMS that are already in practical use are large and have a large distance between the primary ion source and the sample holder, and in order to accurately collide the primary ions with the sample, a deflection means is required to adjust the direction of movement of the primary ions. Furthermore, a beam focusing means is required to prevent the primary ion beam from spreading, and as a result, the configuration of the device becomes complicated and large.

FIG. 1 is a cross-sectional view of a conventional ion source, in which ions are created by introducing sample gas separated and flowing out by a gas chromatograph (hereinafter referred to as GC) into the ionization chamber 6 from the sample gas introduction pipe 17. It passes through an electrostatic lens 8 and a ground slit 20 and is introduced into a mass spectrometer (hereinafter referred to as MS).
In other words, in this case, MS of sample components separated by GC
liquid chromatograph (hereinafter referred to as LC)
Analysis of non-volatile organic samples such as Ions are created in the ionization chamber 6 by introducing thermionic electrons generated by heating the tip of the filament 7 into the ionization chamber 6 through the electron inlet 23 and colliding with the sample gas to form the ion beam 13. is causing it.

FIG. 2 is a sectional view taken along line A-B in FIG. 1, in which the filament 7 is installed close to the electron inlet 23 provided on the upper side of the ionization chamber 6, and the S pole 21a of the ion source magnetic pole 21 is installed above it. , an N pole 21b is installed below the ionization chamber 6. These ion source magnetic poles 21 provide convergence to the ion beam 13 ejected from the ionization chamber 6.

As described above, conventional ion sources were only capable of using gas, but recently, with the development of LC, SIMS analysis of non-volatile organic samples has become strongly required.

The present invention provides a small, highly sensitive secondary ion mass spectrometer that can analyze both gaseous and liquid organic samples, and in particular, a secondary ion mass spectrometer that can simultaneously perform secondary ion mass spectrometry and electron impact ionization. Its features include a sample holder whose surface is coated with an organic sample, an ionization chamber that accommodates the gas sample, and a primary ion source that generates primary ions to irradiate the sample holder in the ionization chamber. , a means for generating electrons that impact and ionize the molecules of the gas sample, generates ions from the organic sample or gas sample in the sample holder, pulls them out of the ionization chamber, and introduces them into a mass spectrometer for analysis. In a secondary ion mass spectrometer configured as shown in FIG. .

FIG. 3 is a sectional view of a secondary ion generator for SIMS, which is an embodiment of the present invention. In FIG. 3, the same parts as in FIG.
3 shows the electron entrance in the electron impact ionization method (hereinafter referred to as EI). The primary ion source 3 is installed obliquely above the exit of the ionization chamber 6, and irradiates the sample holder 4 with a primary ion beam 14 through the notch of the electrostatic lens 8 and the enlarged opening of the extraction electrode 19 at the exit of the ionization chamber 6. are doing. The secondary ion beam 13 emitted from the organic sample on the surface of the sample holder 4 is transmitted to the extraction electrode 19 and the electrostatic lens 8.
and is introduced into the MS through the earth slit 20.

The slit provided in the extraction electrode 19 is 1×10
mm, and the sample holder 4 has a structure that allows it to be inserted separately from outside the vacuum. In this case, it is convenient to use a solid-state probe such as an emitter insertion device for electric field desorption that is used in ordinary MS analysis. In this case, the primary ion source 3 is attached to a support member apart from the slit mechanism.

6 to 10 KV is applied to the primary ion source 3, 3 KV is applied to the sample holder 4, and 2.5 KV is applied to the electrostatic lens 8.
The earth slit 20 is at ground voltage. In addition, a repeller electrode 18 is installed in the ionization chamber 6, and a sample gas introduction pipe 17 is connected to the wall behind it, and an ion source magnetic pole 21 is connected to the front side of the ionization chamber 6 in the same manner as shown in FIG. It is sandwiched between.

FIG. 4 is a sectional view of a SIMS secondary ion generator according to another embodiment of the present invention, in which the same parts as in FIG. 3 are given the same reference numerals. In this case, the sample holder 4 of the primary ion beam 14 is
The incidence angle is set to be larger than 45° to increase the generation of secondary ions. The sensitivity of SIMS improves in proportion to the magnitude of this incident angle.

When the incident angle of the primary ion beam 14 into the ionization chamber 6 is increased, the EI filament 7 and the ion source magnet 21 that focuses the electrons generated from the filament 7 become obstacles, making it difficult to combine with SIMS. However, since the electron emission in the case of electron impact is performed in front of the sample holder 4, the EI
It can also be easily performed in the case of GC/MS using the method. That is, since SIMS for GC and LC using EI can be performed without moving the sample holder 4, the operation becomes easy. Also,
Since the angle of incidence of the sample holder 4 coated with the LC sample is large, the sensitivity of SIMS is further increased.

In addition, the sample gas introduction pipe 17 of the ionization chamber 6
The gas outlet of the GC22 is connected to the GC22 so that the components flowing out can be directly analyzed. That is, with this device, sample gases separated by GC can be analyzed continuously, and samples separated by LC can be analyzed in batches. Note that the repeller electrode 18 and the filament 7 are positively charged with several tens of volts with respect to the ionization chamber 6.

In the secondary ion generator of this example, the primary ion balm is introduced into the ionization chamber from the diagonal upper part of the ionization chamber and the hole, and the electrons of the filament are also incident from this hole, so the GC-separated sample gas is processed by the EI method. Even when analyzing LC-separated organic substances by irradiating the primary ion beam at a large angle of incidence, it can be used as is without moving the sample holder. Therefore, analytical operations become easier. Furthermore, since the angle of incidence of the primary ion beam on the sample holder is large, effects such as improved sensitivity of SIMS can be obtained.

As described above, in the present invention, an electron beam path is provided in the front part of the sample holder, and ionization by fast ions or particles and electron impact ionization can be performed simultaneously in the ionization chamber, so that secondary ion mass spectrometry is possible. Electron impact ionization can be performed simultaneously.

For example, the argon ions Ar ⁺ generated by the primary ion source 3 are approximately 10
It is accelerated to [kV] and emitted toward the sample on the sample holder 4. This primary ion beam 14 has exactly the same effect on high-speed neutral particles that have lost their charge after being accelerated. The sample is in the form of a glycerol matrix, which is sputtered by irradiation with the primary ion beam 14, of which some molecules are ionized. The ionized molecules are accelerated to about 3 [kV] by a secondary ion accelerating power source and sent to a mass spectrometry section for analysis. In this case, the SIMS sample (unknown sample) can be handled in the same way as a normal measurement without considering the reference material.

On the other hand, a standard substance such as perfluorokerocene (PFK) is introduced from the sample gas introduction pipe 17.
It is ionized by electrons of approximately 80 electron volts emitted from filament 7, and sent to mass spectrometry for analysis. In this case, the height of the spectrum of the standard substance can be easily changed by changing the electron current or the flow rate from the introduction system. Therefore, it can be adjusted according to the intensity of the SIMS spectrum. In addition, the spectrum of PFK ranges in mass from less than a few hundred to more than 800, continuously existing at equal intervals. This improves accuracy during accurate mass number interpolation. In this case, ions caused by sputtering and ions caused by electron impact are simultaneously ejected from the ionization chamber at the same potential, so there is no difference in energy, trajectory, or time. Therefore, accurate mass measurement is possible using these two types of ions.

Using this method, for example, the molecular formula of the protonated molecular ion of Kanamycin B (Kanamycin-B), which is a refractory substance, can be determined as C18H38N5O10, m/
I was able to hit the ball with a Z484.2569 error of -4.9 mm.

On the other hand, as an application other than accurate mass measurement, it is also possible to simultaneously measure fragment ions in which the molecular ions of the sample are destroyed by electron bombardment, thereby providing information on the structure of the molecules. Since the amount and energy of electrons can be well controlled, the ratio of molecular ions to fragments can also be adjusted by adjusting these values.

Since the SIMS method and electron impact ionization can be performed simultaneously in this way, the following effects are achieved.

(1) For low-volatile, highly polar compounds measured by SIMS, it is possible to select the weld and matrix that best suit the sample, without considering the standard sample. Handling many substances that are difficult to measure even under normal circumstances
This is the most important thing in the SIMS method.

(2) Since the standard sample uses the electron impact method, most compounds can now be used. For example, non-polar compounds such as hydrocarbons cannot be used as standard samples because ions are not generated by the SIMS method, but the present invention has made it possible. Furthermore, the electron impact spectrum has a larger number of peaks even for the same sample. Therefore, the probability that the standard peak for calculating the accurate mass number will appear closer to the unknown peak increases, improving accuracy.

(3) Since the ionization of the standard substance uses the electron impact method, the height of the peak can be changed independently from the peak of the unknown substance by changing the electron current, gas pressure, etc. It is possible to make the height the same. As a result, the center of gravity of each peak could be measured with high accuracy, and the accuracy of accurate mass measurement was improved.

(4) SIMS spectra and electron impact ionization spectra can be obtained simultaneously, which not only improves the accuracy of accurate mass measurements, but also allows the information obtained from these spectra to include more molecular structural information. This is important for mass spectrum analysis.

FIG. 5 shows SIMSN which is another embodiment of the present invention.
FIG. 2 is a cross-sectional view of a secondary ion generator. 1 is an object point slit, 2 is a fine movement device for adjusting the position and spacing of the object point slit 1, and 3 is a primary ion source attached to the slit mechanism. When the primary ion beam 14 emitted from the primary ion source 3 is irradiated onto the sample holder 4 in the ionization chamber 6, the sample holder 4
Secondary ions are generated from the organic sample applied to the surface of the electrostatic lens 8 and become a secondary ion beam 13.
MS passes between slit blade 5 of object point slit 1 and
15 will be introduced.

Further, during EI, electrons generated by the filament 7 are introduced into the ionization chamber 6 to ionize the sample gas, thereby generating the secondary ion beam 13. Note that the stand 9 supports the ionization chamber 6, and the terminal 10 is a connection adjustment terminal for supplying a current to excite the primary ion source 3, and the ion source box 1
Reference numeral 1 denotes a container to which these members are attached and contains a secondary ion generator, and its lower opening is connected to an exhaust system 12 for high vacuum.

The operation of the secondary ion source configured in this way is similar to that of the embodiments shown in FIGS. 3 and 4, and a gas such as argon or xenon is introduced into the primary ion source 3 from the gas introduction system 16. However, since a voltage of 5 to 6 KV is applied between the electrodes of the primary ion source 3, the ionized argon is accelerated and collides with the organic sample on the sample holder 4, causing spatter and ionization. The ionized sample ions pass between the electrostatic lens 8 and the slit blade 5 of the object point slit 1, and become a secondary ion beam 13.
Introduced in MS15.

To obtain high resolution with MS, object point slit 1
It is necessary to adjust the gap and position of the slit blade 5, but in this embodiment, when the object point slit 1 is moved, the primary ion source 3 is also moved, so the difference between the primary ion beam 14 and the secondary ion beam 13 is The relative position does not change. That is, since the object point slit 1 and the primary ion source 3 are attached to the same slit mechanism, the structure is suitable for obtaining high resolution. Therefore, the secondary ion beam 13 can be extracted efficiently. In addition, the primary ion source 3
Since the primary ion beam 14 is placed as close as possible to the sample holder 4, the spread of the primary ion beam 14 is small and no converging lens is required, and the organic sample coated on the surface of the sample holder 4 can be analyzed with high sensitivity.

To insert the sample holder 4 into the ionization chamber 6, a direct sample introduction device or an emitter insertion probe for electric field desorption is used.

The SIMS secondary ion generator of this example has a primary ion source installed near the sample holder, so even without a converging lens, a large amount of primary ions collide with the liquid sample on the sample holder to generate a large amount of primary ions. Secondary ions can be obtained. Furthermore, even if the object point slit is moved to adjust the relationship with the MS, since the primary ion source is attached to this slit mechanism, the adjustment is easy without a decrease in sensitivity. Furthermore, since the entire structure is simple, it is easy to assemble.

In addition to the above embodiments, the following is also possible. That is, by sending the LC outflow components into the ionization chamber 6 using a rotating belt system, it is possible to efficiently analyze a large number of organic samples. To do this, for example, it is convenient to insert a rotating belt in place of the sample gas introduction pipe 17 and to connect the sample gas introduction pipe 17 to the ionization chamber 6 in a direction perpendicular to the plane of the paper.

The SIMS of the present invention can also be used by switching between a means for analyzing organic components discharged from LC and a means for analyzing gas sample components discharged from GC using the EI method.

As described above, the SIMS of the present invention is a small, highly sensitive secondary ion mass spectrometer that can analyze both gaseous and liquid organic samples, and in particular can perform secondary ion mass spectrometry and electron impact ionization simultaneously. It has this effect.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a conventional secondary ion source, Fig. 2 is a sectional view taken along line A-B in Fig. 1, and Fig. 3 is a sectional view of a SIMS secondary ion generator, which is an embodiment of the present invention. , FIG. 4 is a cross-sectional view of a secondary ion generator for SIMS, which is another embodiment of the present invention, and FIG. 5 is a cross-sectional view of a secondary ion generator for SIMS, which is still another embodiment of the present invention. be. 1...Object point strip, 2...Fine movement device, 3...
...Primary ion source, 4... Sample holder, 5... Slit blade, 6... Ionization chamber, 7... Filament, 8... Electrostatic lens, 9... Stand, 10... Terminal, 11... Ion source Box, 12...Exhaust system, 13
...Secondary ion beam, 14...Primary ion beam, 15...MS, 16...Gas introduction system, 17...
... Sample gas introduction pipe, 18 ... Repeller electrode, 1
9... Extraction electrode, 20... Earth slit, 2
1...Ion source magnetic pole, 22...GC, 23...electron inlet.

Claims (1)

[Scope of Claims] 1. A sample holder whose surface is coated with an organic sample and an ionization chamber that accommodates a gas sample, a primary ion source that generates primary ions to irradiate the sample holder in the ionization chamber, and means for generating electrons that impact molecules to ionize them, and generate ions from the organic sample or the gas sample in the sample holder, extract them from the ionization chamber, and introduce them into a mass spectrometer for analysis. In the secondary ion mass spectrometer configured as shown in FIG. A secondary ion mass spectrometer characterized by: 2. The secondary ion mass spectrometer according to claim 1, wherein the primary ion source is a device attached to a slit mechanism disposed at the exit of the ionization chamber. 3. The primary ion source is attached to a separate member from the slit mechanism, and the primary ions generated therefrom are passed through the extraction electrode and the notch of the electrostatic lens and obliquely enter the ionization chamber. A secondary ion mass spectrometer according to claim 1. 4 The primary ion source is attached to a member separate from the slit mechanism, and the primary ions generated therefrom are allowed to pass through an electron inlet of the ionization chamber close to the slit mechanism and obliquely enter the ionization chamber. The secondary ion mass spectrometer according to claim 1, which is an apparatus. 5. The secondary ion mass spectrometer according to any one of claims 1 to 4, wherein the means for generating electrons is a filament that generates thermoelectrons.