JP2508171B2 - Inductively coupled plasma mass spectrometer - Google Patents

Description

TECHNICAL FIELD The present invention relates to an inductively coupled plasma mass spectrometer that performs mass spectrometry using inductively coupled plasma as an ion source.

(B) Conventional technology and its problems In general, an inductively coupled plasma mass spectrometer (hereinafter referred to as ICP /
(Referred to as MS) is a plasma torch 1 as shown in FIG.
A high-frequency current is applied to the induction coil 2 to convert the sample into plasma, and the ions generated thereby are extracted by the ion extracting electrode 8 after passing through the orifices 4a and 6a of the sampling cone 4 and the skimmer 6 that form the interface. , After focusing these ions at the entrance of the quadrupole mass spectrometer 12 with the lens system 10, the mass spectrometer
Since mass separation is performed in 12, the detection sensitivity is high, trace amount analysis is possible, and it is also suitable for isotope analysis and the like.

By the way, in this ICP / MS, in order to maintain a high detection sensitivity of ppb or less, it is necessary to reduce the background appearing on the mass spectrum without reducing the signal intensity. The cause of this background is the influence of light that enters the mass spectrometer 12 at the same time as ions from the plasma, and the scattering of ions at the electrodes 10a to 10c that form the lens system 10. Therefore, in the conventional ICP / MS, the disk 14 is arranged on the orbital central axis O of the ion beam at the entrance of the lens system 10 to block light, and the ions passing through the circumference of the disk 14 are passed through the lens system 10. It is configured to converge.

However, with such a conventional configuration, although the influence of light can be eliminated, the influence of ion scattering or the like cannot be sufficiently eliminated. That is, since the plasma ions spread to the ion extraction electrode 8 through the sampling cone 4 and the skimmer 6, the beam diameter of the ion at the position of the ion extraction electrode 8 as seen from the lens system 10 is large. The ions passing through the electrode 8 diverge in a large solid angle range, and the ions may collide with the electrodes 10a to 10c forming the lens system 10 to cause scattering or generate secondary electrons. Since the scattering of these ions and the secondary electrons cause noise, the background could not be sufficiently reduced in the conventional device.

The present invention has been made in view of the above circumstances, in which the invasion of both light and scattered ions, which are the causes of the background, into the mass spectrometer is reduced as much as possible, and high detection sensitivity is obtained. The purpose is to be able to maintain.

(C) Means for Solving the Problems In order to achieve the above-mentioned object, the present invention aims to achieve the above-mentioned object, and an ion extraction electrode for extracting ions generated in a plasma torch toward a mass spectrometer, and an ion extraction electrode for extracting the ions. The following configuration is adopted in the ICP / MS provided with a lens system for converging ions to the entrance of the mass spectrometer.

That is, in the ICP / MS of the present invention, a light blocking wall is provided on the ion extracting electrode, and an orifice is formed at a position deviated from the central axis of the ion extracting electrode of the light blocking wall, while the ion extracting electrode is formed. It is characterized in that a deflector is arranged between the lens system and the lens system to deflect the ions passing through the ion extraction electrode toward the central axis of the lens system.

(D) Action The orifice formed in the ion extracting electrode is deviated from the central axis of the ion extracting electrode, so that the light from the plasma torch is blocked by the light blocking wall and does not pass through the orifice. Then, only the ions pass through the orifice and are extracted. In this case, the beam diameter of the ions at the position of the ion extracting electrode viewed from the lens system is the orifice diameter, and therefore small, so that the divergence of the ions can be suppressed within a small solid angle range. Moreover, since the ions that have passed through the ion extraction electrode are deflected by the deflector with the lens system directed toward the central axis, the frequency with which the ions collide with each electrode that configures the lens system decreases, and ion scattering and secondary Generation of electrons is reduced.

(E) Example FIG. 1 is a block diagram of an inductively coupled plasma mass spectrometer according to the present invention, in which parts corresponding to the conventional example in FIG.

In FIG. 1, 1 is a plasma torch, 2 is an induction coil, and 4 and 6 are a sampling cone and a skimmer that respectively constitute an interface. The sampling cone 4 and the skimmer 6 have orifices 4a and 6a formed on a common central axis O. Then, a differential pumping is performed between the sampling cone 4 and the skimmer 6 by a rotary pump or the like. Reference numeral 8 is an ion extraction electrode for extracting ions that have passed through the orifices 4a and 6a of the sampling cone 4 and skimmer 6 toward a mass spectrometer 12 described later.
A light blocking wall 8a is provided on the end face of the ion extracting electrode 8, and an orifice 8b is formed in the light blocking wall 8a at a position displaced from the central axis O by a predetermined distance. Reference numeral 10 is a lens system for converging the ions extracted by the ion extraction electrode 8 to the entrance of the mass spectrometer 12. Reference numeral 11 denotes the central axis O of the lens system 10 for the ions passing through the ion extraction electrode 8.
It is a deflector for deflecting toward, and is arranged between the ion extracting electrode 8 and the lens system 10. The ion extracting electrode 8, the lens system 10 and the deflector 11 are arranged in a differential exhaust chamber 9 which is evacuated by a diffusion pump or the like. A quadrupole mass spectrometer 12 is arranged in a vacuum chamber 13 that is evacuated by a diffusion pump or the like.

Next, the operation of the ICP / MS having the above configuration will be described.

When a high-frequency current is passed through the induction coil 2 of the plasma torch 1 to turn the sample into plasma, ions and light are generated thereby. Light and ions pass through the orifices 4a, 6a of the sampling cone 4 and the skimmer 6, respectively, and then head toward the ion extraction electrode 8.

In this case, the orifice 8b formed in the ion extracting electrode 8
Is deviated from the central axis O by a predetermined distance, the light from the plasma torch 1 is blocked by the light blocking wall 8a and does not pass through the orifice 8b. On the other hand, the ions pass through the orifice 8b guided by the electric field formed by the voltage applied to the ion extracting electrode 8. In this case, the ion beam diameter at the ion extraction electrode 8 as viewed from the lens system 10 is narrowed because it becomes the diameter of the orifice 8b, and therefore the divergence of the ions passing through the orifice 8b is in the range of a small solid angle. It can be suppressed. Then, the ions that have passed through the ion extracting electrode 8 are reflected by the deflector 11 into a lens system.
It is deflected toward the central axis O of 10. Therefore, as in the conventional case, the frequency of collision of the ions with each of the electrodes 10a to 10c forming the lens system 10 is reduced, and the scattering of ions and the generation of secondary electrons are reduced. As a result, the background is reduced.

If an orifice 8b is provided in the ion extracting electrode 8,
It seems that the amount of ions passing through this area decreases and the signal intensity seems to drop at first glance, but if both ends of the ion extraction electrode are open ends as in the conventional case, the ion beam diameter here becomes extremely large. Therefore, the ions cannot be sufficiently focused at the entrance of the mass spectrometer 12, and the detection efficiency deteriorates. Therefore, even when the ions are extracted through the orifice 8b, the signal intensity does not change much from the conventional case.

In the above embodiment, the light blocking wall 8a of the ion extracting electrode 8 is used.
Are arranged orthogonally to the central axis O, but they may be inclined by a predetermined angle θ as shown in FIG. By doing so, the ions emitted from the skimmer 6 can easily pass through the orifice 8b due to the electric field formed between the ions and the ion extraction electrode 8. In this case, it is necessary to increase the deflecting action of the deflector 11.

(F) Effect As described above, according to the present invention, it is possible to reduce as much as possible the invasion of both light and scattered ions, which cause the background, into the mass spectrometer. Only the background can be reduced without any reduction. Therefore, excellent effects such as high detection sensitivity can be maintained are exhibited.

[Brief description of drawings]

FIG. 1 is a block diagram of an inductively coupled plasma mass spectrometer of the present invention, FIG. 2 is a sectional view showing another modification of the ion extraction electrode, and FIG. 3 is a block diagram of a conventional inductively coupled plasma mass spectrometer. is there. DESCRIPTION OF SYMBOLS 1 ... Plasma torch, 8 ... Ion extraction electrode, 8a ... Light blocking wall, 8b ... Orifice, 10 ... Lens system, 11 ... Deflector, 12 ... Mass spectrometer.

Claims (1)

(57) [Claims] 1. An inductive coupling comprising an ion extraction electrode for extracting ions generated by a plasma torch toward a mass spectrometer, and a lens system for converging the ions extracted by the ion extraction electrode to the entrance of the mass spectrometer. In the plasma mass spectrometer, a light blocking wall is provided on the ion extracting electrode, and an orifice is formed at a position deviated from the central axis of the ion extracting electrode of the light blocking wall, while the ion extracting electrode and the lens are formed. An inductively coupled plasma mass spectrometer, characterized in that a deflector for deflecting ions passing through an ion extraction electrode toward the central axis of the lens system is arranged between the system and the system.