GB2143673A

GB2143673A - Ionizing samples for secondary ion mass spectrometry

Info

Publication number: GB2143673A
Application number: GB08415193A
Authority: GB
Inventors: Minoru Sakairi; Hideki Kanbara
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1983-06-16
Filing date: 1984-06-14
Publication date: 1985-02-13
Also published as: JPH0556619B2; GB2143673B; JPS6044A; GB8415193D0

Abstract

An interface for coupling a secondary ion mass spectrometer to a liquid chromatograph for separating an organic sample in solution, comprises a particle beam generation section 38 for generating a primary particle beam 36, and a sample ionization chamber 20 having a target 42 for depositing the sample inside the chamber, the target being subject to bombardment by the primary particle beam 36 in an inclined direction, wherein a molecular beam-like sample inlet section 14 is so structured as to introduce a solution of the organic sample in a molecular beam-like state 16 into the ionization chamber and to allow the solution to hit the position to be bombarded by the primary particle beam on the surface of the target, whereby a secondary ion beam 40 is generated from the organic sample. The target may be a movable belt or a plate. The inlet section 14 includes a differential pumping system for reaching the vacuum of the ionization chamber in stages. <IMAGE>

Description

SPECIFICATION "Secondary ion mass spectrometer" Background of the invention This invention relates to a secondary ion mass spectrometer, and particularly to a secondary ion mass spectrometer provided with a sample inlet suitable for ionizing nonvolatile compounds in a solution.

Recently, life science has been remarkably progressed, and separation and analysis of nonvolatile and thermolabile compounds relating to living bodies are necessary and indispensable as a basic technique in this field. Liquid chronatograph (LC) has been widely employed as an apparatus for separating such compounds, but has not satisfied needs with respect to detection sensitivity and identification. Thus, direct coupling of LC with a mass spectrometer having a high detection sensitivity and high identification has been studied in the world for these ten years, but has not been successful yet, because there still remain various technical problems to be solved as regards ionization of samples in a solution.

For ionization in the direct coupling of the liquid chromatograph with the mass spectrometer (hereinafter referred to merely as "LC/MS"), many procedures such as atmospheric pressure ionization, chemical ionization, etc. have been proposed, one of which is a secondary ion mass spectrometry (SIMS procedure) comprising bombarding a sample coated on a metallic plate with primary ions, and analyzing secondary ions generated thereby.At the part that couples LS with MS according to the conventional SIMS procedure, that is, the interface, a sample coated on a silver belt by spraying is introduced by revolving the belt into an ionization chamber kept under a pressure ranging from the atmospheric pressure to a high vacuum such as 10 5 Torr - 10e Torr by means of differential gas pumping-out at a plurality of stages, the sample is bombarded with primary ions in the ionization chamber, and the generated secondary ions are mass-analyzed by a mass spectrometer [for example, Org. Mass Spectrum., 15459 (1980)]. However, the prior art procedure still has the following problems.

(a) A sample cannot be coated onto the silver belt satisfactorily.

(b) Slits for the differential pumping system, through which the silver belt must be passed, have as narrow clearance as about 300 pHm, so that the sample coated on the silver belt can foul the slits and can contaminate another successive sample.

(c) It is difficult to completely remove the sample from the silver belt after the mass-analyzing, and thus there is a memory effect. That is, the preceding sample stays remained even if a fresh sample is coated onto the silver belt for successive measurement, and consequently new measurement of mass spectra is contaminated with the signal of the preceding remaining sample, so that no correct spectra can be obtained.

(d) When a sample is coated onto the silver belt by spraying the coating area can be broadened.

(e) Some substances relating to living bodies are stable only in a solvent, and may be decomposed when the solvent is removed therefrom and when the substances are left standing as they are. In analyzing samples of such substances according to the prior art SIMS procedure, the samples may be decomposed when coated onto a metallic plate, so that there is a difficulty in measurement.

Summary of the invention An object of the present invention is to provide an LC/MS interface of novel type according to SIMS procedure and also to provide an apparatus capable of mass-analyzing a substance that is stable only in a solvent.

The present invention proposes a method of nebulizing a sample dissolved in a solution by a nebulizer, etc., injecting the nebulized sample through a nozzle under pressure, thereby making a molecular beam of the nebulized sample, introducing the molecular beam into a high vacuum chamber through an aperture, allowing the molecular beam to hit a metallic plate in the chamber, thereby depositing the sample on the metallic plate, simultaneously bombarding the sample-deposited area with a particle beam of inert gas ions, neutral particles, etc., thereby generating secondary ions from the sample, leading the generated secondary ions to a massanalyzing section and mass-analyzing the secondary ions.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic view showing the entirety of a secondary ion mass spectrometer embodying the present invention.

Figure 2 is a cross-sectional view of sample ionization chamber, primary particle beam generation section, and molecular beam-like sample inlet section, when the target is in a plate form, in a first embodiment of the invention.

Figure 3 is a cross-sectional view of sample ionization chamber, primary particle beam generation section and molecular beam-like sample inlet section when the target is in a belt form, in a second embodiment of the invention.

An entire structure of a secondary ion mass spectrometer according to the present invention will be described below, referring to Figure 1,which particularly shows a magnetic sector type mass spectrometer, wherein the secondary ion mass spectrometer comprises a liquid chromatograph 2, an interface 14, an ion source 4, an electric field 6 and a magnetic field 8 for separating secondary ions generated in the ion source 4 by mass differences, a detection system 10 for detecting the separated secondary ions, and a gas pumping system 12. The mass spectrometer (MS) is constituted from the ion source 4, the electric field 6, the magnetic field 8, the detection system 10 and the gas pumping system 12, where the electric field 6, the magnetic field 8and the detection system 10 are called "analyzer".The interface 14 couples LC 2 with MS, and serves to lead a sample from LC 2 to the ion source 4 of MS. The interface 14 is the subject of the present invention.

The gas pumping system 12 is constituted from oil diffusion pumps 12a ans 12d, and rotary pumps 12b and 12c.

The present invention will be described in detail according to embodiments.

Figure 2 is a schematic view of part of the secondary ion mass spectrometer according to the present invention.

Sample solutions, which are successively separated in the liquid chromatograph 2 are passed through a nebulizer 14 having a nozzle, for example, 10 wLm in diameter, as an interface and injected as molecular beam-like samples 16. The nebulizer 14 can be of any type, for example, a type of spraying a sample solution through a nozzle by means of an ultrasonic vibrator, a type of spraying a sample solution through a nozzle under high pressure, etc.

The molecular beam-like samples 16from the nebulizer 14 pass through one or a plurality of heated apertures 18a and 18b and are led into an ionization chamber 20 kept in a high vacuum in the order of 10-5 Torr - 10-6 Torr, and allowed to hit a metallic target 22, for example, silver plate, provided in the ionization chamber 20.The spaces between the nebulizer 14, the apertures 18a and 18b (two apertures in the drawing) and the ionization chamber 20 are subjected to differential pumping system at two stages in the direction of arrows 34 by rotary pumps 24a and 24b with a gas pumping rate of 25 liters/ second, an oil diffusion pump 26 with a gas pumping speed of 100 litres/second, and a rotary pump 28 with a gas pumping speed of 25 liters/second and an oil diffusion pump 30with a gas pumping speed of 600 litersisecond through liquid nitrogen traps 32a and 32b.

Most of the samples introduced into the ionization chamber2O and hit onto the metallic target 22 in the state of molecular beam-like sample 16 are deposited on the surface of target 22. The sampledeposited area on the target 22 is bombarded with primary ion beam 36 of inert gas such as xenon gas, etc. with a current density of 10.6 A/cm2 or higher at an inclination of about 20 to the surface of target 22 from the opposite side to the molecular beam-like sample 16. Numeral 38 is a generating source of the ion beam 36. Why the bombardment inclination of the primary beam 36 to the target 22 is selected to be about 20 is to efficiently withdraw an organic sample as secondary ion beam 40.A fast neutral particle beam can be used in place ofthe ion beam as the primary ion beam.

When the primary ion beam is impinged into a solid constituting the target 22 at a high speed, a portion of kinetic energy possessed by the impinging ions is given to the atoms constituting the solid.

The atoms as given by the kinetic energy undergo successive hitting, and then the hitting cascade reaches the surface of the target and expels the atoms near the surface outwards. Silver has a good efficiency of this sputtering, that is, a good sputtering effect, and thus is suitable as a material for the target 22 for sample deposition. When the atoms constituting the target 22 are expelled as described above, the expelled atoms hit an organic sample deposited on the surface of target 22 to impart the kinetic energy to the expelled atoms to the organic sample. Thus, the organic sample is ionized and released from the surface of target 22 into the secondary ion beam 40. The secondary ion beam 40 is led to a mass spectrometric section (not shown in Figure 2) connected to the ionization chamber 20 and analyzed.

According to the secondary ion mass spectrometer according to this embodiment of the present invention, organic samples, etc. in a solvent can be separated and analyzed according to the SIMS procedure, and particularly a substance that is stable only in a solvent can be also analyzed satisfactorily.

Furthermore, with more intensified primary ion beams, substantially all of the sample deposited on the target can be completely removed through the sputtering, thereby eliminating the memory effect.

Figure 3 is a schematic view of another embodiment according to the present invention, wherein the plate target 22 provided in the ionization chamber 20 in Figure 2 is replaced with a belt target 42.

Numeral 44 is a heater to the belt target 42. With this structure, the part for ion hitting on the target 42 is moved into the high vacuum ionization chamber 20, and new target surfaces can be successively jetcoated with samples and subjected to ion bombardment, thereby eliminating the memory effect due to fouling on the target surfaces.

According to the present invention, an interface for LC/MS capable of analyzing a sample in a solvent according to the SIMS procedure can be provided, and a subsance that is stable only in a solvent can be analyzed satisfactorily.

Claims

1. A secondary ion mass spectrometer comprising a particle beam generation section for generating a primary particle beam, a liquid chromatograph for separating an organic sample dissolved in a solvent, and a sample ionizatjion chamber having a target for depositing the sample inside the chamber, the target being subject to bombardment of the primary particle beams in an inclined direction, characterized by a molecular beam-like sample inlet section so structured as to introduce a solution of the organic sample dissolved in the solvent in a molecular beam-like stream to a primary particle beambombarded position on the target surface in the sample ionization chamber from the outside of the sample ionization chamber without lowering a vacuum in the chamber, thereby allowing the solution of the organic sample to hit the target surface and deposit thereon, and to generate a secondary ion beam of the organic sample by simultaneous bombardment of the deposited organic sample with the primary particle beam.

2. A secondary ion mass spectrometer according to Claim 1, wherein the target is made of a metal.

3. A secondary ion mass spectrometer according to Claim 2, wherein the target metal is silver.

4. A secondary ion mass spectrometer according to Claim 1, wherein the target is in a plate form.

5. A secondary ion mass spectrometer according to Claim 1, wherein the target is in a belt form.

6. A secondary ion mass spectrometer according to Claim 1, wherein the molecular beam-like sample inlet section has a nubulizer having a sample solution inlet connected to the outlet of the liquid chromatograph and a nozzle for spraying and injecting the sample solution in a molecular beam-like state, and apertures in the passage of the molecular beam-like sample solution, the differential pumping section being gas-evacuated to such a degree as not to lower the vacuum in the sample ionizing chamber.

7. A secondary ion mass analyzer according to Claim 1, wherein the sample ionization chamber has a vacuum of 10-5 Torr - 10-6 Torr.

8. A secondary ion mass spectrometer having an interface section substantially as herein described with reference to and as shown in Figure 2 or Figure 3 of the accompanying drawings.