JPH1040857A - Inductively coupled plasma mass analyzing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the detection limit for an object element to be measured, by reducing the size of an ion beam passing hole which divides an ion lens part and a mass selecting part, and lowering a vacuum degree, between a skimmer cone and an opening plate, by a gas introduced from a sampling cone. SOLUTION: The downstream side of the skimmer cone 34 of an ion lens part, and a mass selecting part on which a mass filter 52 is provided, are divided by an opening plate 104. A vacuum degree, between the skimmer cone 34 and the opening plate 104, is lowered by about 1×10<-3> Torr, by reducing the size of the ion beam passing hole 106 of the opening plate 104, and by gas (e.g. Ar) introduced from a sampling cone 32. Consequently, the number of ions related to argon such as ArCl, ArO, and Ar2 , infiltrating into the mass filter 52 side by the lowering of the vacuum degree, can be reduced, for lowering the detection limit of a object element to be measured such as Fe, As, and Se.

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, and more particularly to an inductively coupled plasma mass spectrometer which has a simple structure and reduces the influence of molecular ions harmful to measurement, thereby lowering the detection limit of an element to be measured. It relates to a possible inductively coupled plasma mass spectrometer.

[0002]

2. Description of the Related Art In recent years, an inductively coupled plasma mass spectrometer has been proposed in which an inductively coupled plasma used as a light source for emission analysis is used as an ion source of a mass spectrometer to perform elemental analysis in a solution by ions. (For example,
2-26757).

This inductively coupled plasma mass spectrometer, as shown in FIG. 1, for example, constantly sends a sample 8 for atomizing a solution sample 8 and introducing it into an ionization section 20, and sends the sample 8 from a spray chamber 16. A peristaltic pump 12 for discharging waste liquid, a nebulizer 14 for atomizing the solution sample 8 sampled by the peristaltic pump 12, and only fine particles among the particles atomized by the nebulizer 14 are selected. A sample introduction unit 10 including a spray chamber 16, a gas control unit 18 for injecting a carrier gas (for example, Ar gas) into the nebulizer 14, and an element in a sample carried together with the carrier gas from the sample introduction unit 10. The torch 22 and the induction coil 24 wound outside the torch 22 for ionizing An ionization section 20, an RF power supply 26 for supplying high-frequency power to the induction coil 24 to generate plasma, and sampling an element ionized by the ionization section 20 under atmospheric pressure, under high vacuum. A sampling cone 32 for aligning the direction of kinetic energy of ions generated in the torch 22 for introduction into the ion lens section 40, and a skimmer for passing a part of ions passing through the sampling cone 32 An interface section 30 including a cone 34, an extraction electrode 42 using an electrostatic ion lens, a converging lens 44, and an ion lens 46 for converging ions passing through the interface section 30 and leading the ions to a mass spectrometer.
, A mass selection unit 50 including a quadrupole mass filter 52 composed of, for example, four electrode rods 54, and a mass filter driving circuit 56 for driving the quadrupole mass filter 52 And the mass selection unit 50
For counting ions of the measured mass number that has passed through the
For example, a detection unit 60 including a secondary electron multiplier 62 is provided.

In FIG. 1, reference numeral 70 denotes a rotary pump 72 for evacuating the inside of an interface chamber 38 formed by the sampling cone 32 and the skimmer cone 34, and a high vacuum inside the ion lens chamber 48 of the ion lens section 40. Turbo-molecular pump 74 for evacuating the analyzer, a turbo-molecular pump 76 for evacuating the analyzer chamber 58 containing the quadrupole mass filter 52 and the secondary electron multiplier 62 to a high vacuum, and the turbo-molecular pump 76 The evacuation system 80 including a rotary pump 78 for evacuating the molecular pumps 74 and 76 to a low vacuum is provided by the sample introduction unit 10, the gas control unit 18,
F power supply 26, mass filter drive circuit 56, detection unit 60,
A system controller 82 for controlling the evacuation system 70 and the like is a personal computer for giving instructions to the system controller 80 and for collecting data and analyzing analysis data.

In this inductively coupled plasma mass spectrometer, a mist-like sample 8 is introduced into plasma generated by flowing a carrier (Ar) gas through a torch 22 and applying high frequency power to an induction coil 24. Then, the elements in the sample are ionized. This ion is supplied to the sampling cone 32
Introduced to the ion lens section 40 via the interface section 30 composed of the and the skimmer cone 34, and further, the elements are detected by mass with the quadrupole mass filter 52, so that the detection lower limit of most elements is sub-ng / L
Ultra-sensitive elemental analysis that can measure up to (ppt) level becomes possible.

[0006]

However, conventionally, since a large amount of molecular ions originating from components in a carrier gas, for example, argon, are generated, the background in measurement of an element which interferes with the molecular ions is high. And it is difficult to lower the detection limit.

In order to solve such a problem, argon gas or hydrogen gas is injected immediately after the skimmer cone,
It is also conceivable to relatively reduce the influence of molecular ions such as Ar ₂ and ArO which are harmful to the measurement. However,
It is necessary to add a pipe or provide a gas injection port immediately after the skimmer cone, which causes a problem that the configuration becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and it is an object of the present invention to reduce the influence of molecular ions harmful to measurement by a simple structure and to lower the detection limit of an element to be measured. And

[0009]

According to a first aspect of the present invention, in an inductively coupled plasma mass spectrometer, a sample is atomized,
A sample introduction section for introducing into the ionization section, an ionization section including a torch for ionizing elements in the sample carried together with the carrier gas from the sample introduction section, and ionization at the ion section under atmospheric pressure. An interface unit including a sampling cone and a skimmer cone for sampling the introduced element into the ion lens unit under vacuum; an ion lens unit for converging ions passing through the interface unit; Ions introduced from the lens unit, for dividing by mass number of measurement, a mass selection unit including a mass filter, and a detection unit that counts ions of the measurement mass number that has passed through the mass selection unit,
The size of the ion beam passage hole of the aperture plate separating the ion lens unit and the mass selection unit is reduced so that the degree of vacuum between the skimmer cone and the aperture plate is reduced by gas introduced from the sampling cone. Thus, the above problem has been solved.

That is, as described in the above-mentioned literature, if argon gas or hydrogen gas is injected from the outside immediately after the skimmer cone, it is necessary to add a pipe for this or to provide a gas injection port. The configuration becomes complicated. Therefore, in the first invention, instead of introducing gas immediately after the skimmer cone, the size of the ion beam passage hole of the aperture plate separating the ion lens portion and the mass selection portion is reduced, and the conductance is reduced. The gas introduced from the sampling cone reduces the degree of vacuum between the skimmer cone and the aperture plate so that the same result as when gas is introduced immediately after the skimmer cone is obtained.

According to a second aspect of the present invention, there is provided an inductively coupled plasma mass spectrometer similar to the first aspect, wherein at least a part of the ion beam passage hole of the skimmer cone has a cross section substantially the same as the ion beam traveling direction. But for example 0.5m
This problem has been solved by forming the shape of a cylinder having a length of m or more.

That is, as shown in detail in FIG. 2, the cross-sectional shape of the conventional skimmer cone 34 around the ion beam passage hole 35 is a knife-edge shape, and molecular ions caused by argon in plasma are reduced to molecular mass side. It was easy to invade.
Therefore, in the second invention, as shown in FIG. 3, the cross-sectional shape of the skimmer cone 34 is changed from a knife edge shape to a plate shape, and the ion beam passage hole 35 has a substantially same cross section in the ion beam traveling direction, for example, a long cross section. L = 0.5 mm or more in a cylindrical shape, and molecular ions caused by, for example, argon in the plasma existing on the plasma side (left side in the figure) of the skimmer cone 35 are reduced in the cylindrical portion. Things.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

The first embodiment to which the first invention is applied is a mass selection apparatus in which a mass filter 52 and a downstream side of a skimmer cone 34 are provided as shown in FIG. The size of the ion beam passage hole 106 of the aperture plate 104 which separates the portion 50 is reduced, so that the conductance of the aperture plate 104 is reduced.

Accordingly, the degree of vacuum between the skimmer cone 34 and the aperture plate 104 is changed by the carrier gas (for example, Ar).
It is reduced to about 1 × 10 ⁻³ torr, and the same result as when argon gas is introduced immediately after the skimmer cone 34 is obtained.

Accordingly, the intrusion into the mass filter 52 side occurs.
The number of argon-related molecular ions such as ArCl, ArO, and Ar ₂ decreases, and the detection limit of the element to be measured such as Fe, As, and Se decreases.

In the figure, ICP is an inductively coupled plasma,
Reference numeral 100 denotes an octapole ion beam guide provided on the ion lens unit 44, for example, in which eight electrode rods 102 are arranged point-symmetrically with respect to the center line as shown in FIG. This is a gate valve for keeping the ion lens chamber 48 including the octapole ion beam guide 100 and the analyzer chamber 58 including the mass filter 52 in vacuum.

The configuration of the ion beam guide is not limited to the one using an octapole, but the present invention is similarly applied to the one using a Q pole in which four electrode rods are arranged point-symmetrically with respect to the center line. Applicable to

Next, a second embodiment in which the first invention is applied to an inductively coupled plasma mass spectrometer having an octapole ion beam guide divided in the direction of travel of the ion beam will be described with reference to FIG. .

In the second embodiment, an octapole ion beam guide 110 on the skimmer cone 34 side and an outgoing octapole ion beam guide 112 on the mass filter 52 side are provided.
For example, a positive voltage is applied to the entrance octapole ion beam guide 112 and a negative voltage is applied to the exit octapole ion beam guide 112 so that good ion transmission efficiency can be obtained. I have.

In the second embodiment, the ion beam passage hole of the aperture plate 114 closer to the skimmer cone 34 and provided between the entrance octapole ion beam guide 110 and the exit octapole ion beam guide 112 is provided. The size of the inductively coupled plasma (IC
The gas introduced from the direction P) through the sampling cone 32 causes the skimmer cone 34 and the aperture plate 114 to be in contact with each other.
The degree of vacuum during is reduced.

In other respects, the downstream aperture plate 104
Since the size of the ion beam passage hole 106 is the same as that of the first embodiment except that it is the same as the conventional one, the description is omitted.

Also in the second embodiment, one of the entrance octapole ion beam guide 110 and the exit octapole ion beam guide 112, or both may be ion beam guides using a Q pole.

Next, a third embodiment to which the second invention is applied will be described in detail.

In the third embodiment, in the inductively coupled plasma mass spectrometer similar to the conventional one shown in FIG. 1, the skimmer cone 34 has a substantially uniform sectional thickness as shown in FIG. Ion beam passage hole 35
However, it is formed in a cylindrical shape having substantially the same cross section in the direction of travel of the ion beam.

The length L of the cylindrical portion in the traveling direction of the ion beam
Can be, for example, 0.5 mm or more.

The other points are the same as those in the above-mentioned conventional example, and the description is omitted.

In this embodiment, the skimmer cone 3
Since the ion beam passage hole 35 has a cylindrical shape over the entire thickness of No. 4, processing is easy and the effect of reducing molecular ions due to, for example, argon is high. The shape and the length of the cylinder portion are not limited to the above. For example, only a part of the ion beam passage hole 35 may have a cylindrical shape, and the other portion may have a tapered shape.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In an inductively coupled plasma mass spectrometer employing a third embodiment of the present invention, ArO interferes with Fe.
As a result, the results shown in FIG. 7 were obtained. As is clear from the figure, the value of the blank constituting the background is such that the cylindrical portion does not exist in the third embodiment in which the cylindrical portion is formed on the skimmer cone,
Compared to the knife-edge-shaped conventional example, it was confirmed that the value was reduced to about 1/10, and the detection limit (3σ) at which the standard deviation σ indicating the variation of the measured value was tripled could be reduced to about 1/10. .

[0030]

According to the present invention, the influence of molecular ions caused by a carrier gas such as argon can be reduced with a simple structure, and the detection limit of the element to be detected which has been interfered by the molecular ions can be reduced. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram including a partial cross-sectional view showing a configuration of an example of a conventional inductively coupled plasma mass spectrometer.

FIG. 2 is a cross-sectional view showing a cross-sectional shape around an ion beam passage hole of a conventional skimmer cone used in the inductively coupled plasma mass spectrometer.

FIG. 3 is a cross-sectional view showing a cross-sectional shape around an ion beam passage hole of a skimmer cone used in a third embodiment of the inductively coupled plasma mass spectrometer according to the present invention.

FIG. 4 is a side view showing a configuration around an ion lens unit according to the first embodiment of the present invention.

FIG. 5 is a transverse sectional view taken along line VV in FIG. 4;

FIG. 6 is a side view showing a configuration around an ion lens unit according to a second embodiment of the present invention.

FIG. 7 is a table showing a detection limit in a third embodiment of the present invention in comparison with a conventional example.

[Explanation of symbols]

Reference Signs List 8 ... sample 10 ... sample introduction part 20 ... ionization part 22 ... torch 30 ... interface part 32 ... sampling cone 34 ... skimmer cone 35 ... ion beam passage hole 40 ... ion lens part 50 ... mass selection part 52 ... quadrupole mass filter Reference numeral 60: detection unit 62: secondary electron multiplier 104, 114: aperture plate 106, 116: ion beam passage hole 100, 110, 112: octapole ion beam guide

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kazuo Yamanaka 1-15-5 Nakamachi, Musashino-shi, Tokyo Mitaka Takagi Building Yokogawa Analytical Systems Co., Ltd.

Claims (3)

[Claims] 1. A sample introduction part for atomizing a sample and introducing it into an ionization part, and an ionization part including a torch for ionizing elements in the sample carried together with a carrier gas from the sample introduction part. And, for sampling an element ionized in the ion part under atmospheric pressure and introducing it into an ion lens part under vacuum,
An interface unit including a sampling cone and a skimmer cone; an ion lens unit for converging ions passing through the interface unit; and a mass filter for separating ions introduced from the ion lens unit for each measured mass number And a detection unit that counts ions of the measured mass number that has passed through the mass selection unit, and the size of the ion beam passage hole of the aperture plate that separates the ion lens unit and the mass selection unit. An inductively coupled plasma mass spectrometer characterized in that the gas is introduced from a sampling cone to reduce the degree of vacuum between the skimmer cone and the aperture plate. 2. A sample introduction part for atomizing a sample and introducing it into an ionization part, and an ionization part including a torch for ionizing elements in the sample carried together with a carrier gas from the sample introduction part. And, for sampling an element ionized in the ion part under atmospheric pressure and introducing it into an ion lens part under vacuum,
An interface unit including a sampling cone and a skimmer cone; an ion lens unit for converging ions passing through the interface unit; and a mass filter for separating ions introduced from the ion lens unit for each measured mass number And a detection unit that counts ions of the measured mass number that has passed through the mass selection unit. At least a part of the ion beam passage hole of the skimmer cone is substantially the same in the ion beam traveling direction. An inductively coupled plasma mass spectrometer characterized by being formed in a cylindrical shape having a continuous cross section. 3. The ion beam according to claim 2, wherein the length of the cylinder in the direction of travel of the ion beam continuing substantially the same cross section is 0.5 m.
m or more.