JPH0620642A - Inductive coupling plasma mass spectrometer - Google Patents

Abstract

PURPOSE:To prevent divergence caused by space charge due to the effect of ion density by carrying out rough separation based on the mass of ions by a mass separation means of a mass spectrometer, by letting ions of predetermined masses pass, and by inhibiting passing of the ions other through the separation means. CONSTITUTION:A high frequency magnetic field is formed around a high frequency induction coil 6 by the coil 6, which the inside of a fore chamber main body 11 sandwiched between a sampling cone 8 and a skimmer cone 9 is evacuated, and the vacuum degree of a rear chamber 17 in which a mass fillter 16 is stored, is further increased. A Wien filter 30 having mass separation effect is provided on the front step of an ion optical system 14. Ions in the high frequency induction plasma 7 are guided to the filter 30 through the cones 8, 9, and a extracting electrode 10. The filter 30 is provide with the function of carrying out rough separation of ions based on the ion mass, and only ions of predetermined masses can pass through the filter 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inductively coupled plasma mass spectrometer capable of preventing a decrease in measurement sensitivity due to various factors.

[0002]

2. Description of the Related Art An inductively coupled plasma mass spectrometer uses a high frequency inductively coupled plasma to excite a sample, and guides the generated ions to a mass spectrometer through an interface consisting of a sampling cone and a skimmer cone for electrical detection. The element to be measured in the sample is analyzed with high accuracy by measuring the amount of this ion precisely.

Regarding such an inductively coupled plasma mass spectrometer, JP-A-2-122258 and JP-A-2
-216048 and JP-A-2-227653.

FIG. 3 is a configuration diagram showing a conventional configuration of such an inductively coupled plasma mass spectrometer. In this figure, argon gas is supplied from an argon gas supply source 3 to the outer chamber 1b and the outermost chamber 1c of the plasma torch 1 via a gas regulator 2, and the sample in the sample tank 4 is nebulized in the inner chamber 1a. After being vaporized by 5, it is carried in by argon gas.

A high-frequency current is applied to the high-frequency induction coil 6 wound around the plasma torch 1 by a high-frequency power source 6b, and a high-frequency magnetic field is formed around the high-frequency induction coil 6.

On the other hand, the inside of the fore chamber main body 11 sandwiched between the sampling cone 8 and the skimmer cone 9 is sucked by a vacuum pump 12 to, for example, 10 ^-4 Torr and accommodates a mass filter (quadrupole mass filter etc.) 16. The inside of the rear chamber 17 is sucked by the second oil diffusion pump 18 to, for example, 10 ⁻⁵ Torr.

In this state, when electrons or ions are implanted in the argon gas in the vicinity of the above-mentioned high frequency magnetic field, the high frequency magnetic field causes the high frequency induction plasma 7 to instantly operate.
Occurs.

Ions in the high frequency induction plasma 7 are
It converges through the sampling cone 8 and the skimmer cone 9 between the ion lenses 14a and 14b (or the doublet quadrupole lens), and then the mass filter 1
It is guided to the secondary electron multiplier 19 through 6 and detected. The detection signal is sent to the signal processing unit 20 and is subjected to arithmetic processing, whereby the measured elemental analysis value in the sample is obtained.

[0009]

In the inductively coupled plasma mass spectrometer having the above structure, a beam having a high ion density is handled at a low speed, so that it is affected by space charge. Due to the influence of this space charge, ultimate high sensitivity cannot be obtained.

Further, due to the non-spectral matrix effect,
The problem of desensitization in a dense matrix concentration sample is also described in "ANALYTICAL CHEMISTRY", June 15, 1988, pp. 1472-1474.

That is, due to the high ion density,
This is because the space charge causes ion divergence. The present invention has been made in view of the above-mentioned problems of the conventional art, and an object thereof is to prevent ion divergence due to space charge and realize a highly sensitive inductively coupled plasma mass spectrometer.

[0012]

The first means for solving the above-mentioned problems is to excite a sample by using high-frequency inductively coupled plasma, extract the generated ions from a skimmer cone, and make them converge by an ion optical system, In an inductively coupled plasma mass spectrometer that analyzes the element to be measured in a gas sample by guiding it to an electron multiplier, the ion mass is extracted before the ions extracted from the skimmer cone enter the ion optical system. The method is characterized in that a mass separation means for roughly separating ions is provided to roughly separate ions other than the mass to be measured.

[0013]

In the above-mentioned means, the mass separation means performs the rough separation according to the mass of the ions, so that only the ions having the preset predetermined mass can pass and the ions having the other masses cannot pass through the mass separation means. Therefore, unnecessary ions are not introduced into the optical system, and the ion density is reduced. This prevents the diffusion of ions due to the space charge due to the influence of the ion density.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention. In this figure, the same parts as those in FIG. 3 are designated by the same reference numerals.

A high-frequency current is supplied to the high-frequency induction coil 6 by a high-frequency power source, and a high-frequency magnetic field is formed around the high-frequency induction coil 6. On the other hand, the inside of the fore chamber main body 11 sandwiched between the sampling cone 8 and the skimmer cone 9 is, for example, 10 ⁻⁴ To by a vacuum pump (not shown).
The inside of the rear chamber 17 which is sucked by rr and accommodates the mass filter (quadrupole mass filter or the like) 16 is sucked by, for example, 10 ⁻⁵ Torr by a second oil diffusion pump (not shown). In addition, a Wien filter 30 having a mass separation effect is installed in front of the ion optical system 14.

In this state, when electrons or ions are implanted in the argon gas in the vicinity of the above-mentioned high frequency magnetic field, high frequency induction plasma is instantaneously generated by the action of this high frequency magnetic field.

Ions in the high frequency induction plasma 7 are
It is guided to the Wien filter 30 via the sampling cone 8, the skimmer cone 9 and the extraction electrode 10.
The Wien filter 30 has a mass separation effect (ability to roughly separate ions by ion mass), and is configured so that only ions of a predetermined mass pass through.

FIG. 2 is a block diagram showing the structure of the Wien filter 30. The Wien filter 30 has a variable voltage power supply 30a, electrodes 30b to 30c, and magnetic field generating means 30d to.
It is composed of 30e. In this figure, the Wien filter 30 is viewed from the side of the skimmer cone 9, and ions proceed in the vertical direction from the front to the back of the paper. Here, assuming that the electric field generated by the power source 30a is E, the magnetic flux density generated by the magnetic field generating means 30d to 30e is B, and the passing speed of the ions is v, the Lorentz force F acting on the ions to pass can be expressed as follows.

[0019]

[Equation 1]

When the ions are accelerated with a constant voltage, the ion traveling speed v varies depending on the mass of the ions. Therefore, the Lorentz force F varies depending on the mass of the ions. Therefore, the Lorentz force F becomes 0 in an ion having a certain predetermined mass and passes through the Wien filter 30 (straight ahead).
can do. The Lorentz force F acts on the ions having other masses, and thus the ions cannot travel straight in the Wien filter 30. Therefore, the variable voltage power supply is adjusted so that the Lorentz force F acting on the ion having the mass to be measured becomes zero. By doing so, it is possible to roughly separate the ions by the ion mass.

After that, the ions that have passed through the Wien filter 30 (straight or substantially straight) travel to the ion lens 14a,
14b (or a doublet quadrupole lens) to be converged, and then to a secondary electron multiplier 19 through a mass filter 16 to be detected. The detection signal is sent to the signal processing unit 20 and is subjected to arithmetic processing, whereby the measured elemental analysis value in the sample is obtained.

As described above, since the ion density is lowered by performing the rough separation of the ions by the ion mass, the space charge, which has been an obstacle to improving the sensitivity by improving the ion lens. High sensitivity can be realized without being affected by the effect.

Further, the non-spectroscopic matrix effect (the effect of decreasing the sensitivity of the element to be measured when the salt concentration of the sample is high) can be prevented, and high sensitivity can be realized.

In the above embodiment, the case where the Wien filter is used has been described, but the present invention is not limited to this, and the same effect can be obtained by using another filter having a mass separation effect.

[0025]

As described above in detail with reference to the embodiments, in the present invention, the ion density is lowered by performing the rough separation of the ions by the ion mass before the ion focusing is performed by the ion optical system. A high-sensitivity inductively coupled plasma mass spectrometer, which is not affected by the space charge effect and the non-spectroscopic matrix effect, which are obstacles to improving the sensitivity by improving the ion lens. Can be realized.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a configuration of a main part of one embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an overall configuration of a conventional device.

[Explanation of symbols]

 6 High-frequency induction coil 8 Sampling cone 9 Skimmer cone 10 Extraction electrode 11 Forechamber 14 Ion optical system 16 Mass filter 17 Rear chamber 19 Secondary electron multiplier 30 Wien filter 30a Variable voltage power supply 30b, 30c Electrode 30d, 30e Magnetic field generating means

Claims (1)

[Claims] 1. A sample in a gas sample is extracted by exciting a sample using high-frequency inductively coupled plasma, extracting ions from a skimmer cone, converging them by an ion optical system, and guiding them to a secondary electron multiplier to detect them. In an inductively coupled plasma mass spectrometer that analyzes the elements to be measured, a mass separation unit that roughly separates the ions by the ion mass is provided at the stage before the ions extracted from the skimmer cone enter the ion optical system. An inductively coupled plasma mass spectrometer characterized by roughly separating ions other than.