JPH10142155A - Icp mass spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the effects of interference molecular ions and to enable the highly accurate analysis of elements by irradiating any part of an ion path with a light beam and detecting fluorescent radiated from excited plasma ions. SOLUTION: Plasma ions generated from a sample by the passage of a high frequency current through the induction coil 2 of a plasma torch 1 are passed through the openings 6a and 7a of a plasma ion introducing part 3, derived to the side of an ion detecting part 15 by an ion deriving electrode 11, and mass-separated by a mass separator 14, and its specific ions are detected by the ion detector 15. At this time, laser light L emitted form a laser light source 16 and guided along an axis O for passing ions by a reflecting mirror 17A is brought to irradiate a flow of ions in the track K of ions. By this, interfering molecule ions are selectively excited to produce fluorescence and collected by a collectiven lens 18, and then the intensity of fluorescence, i.e., the ion amount of interference ions, is detected by a fluorescence detecting part 20. In addition, an ion mass calculating part 21 subtracts the amount of interference molecular ions from the mass-analyzed value of element ions and detects the mass number of element ions with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ICP mass spectrometer for mass spectrometry by ionizing a sample by ICP.

[0002]

2. Description of the Related Art Generally, an ICP mass spectrometer performs mass spectrometry as follows. That is, first, a sample is turned into plasma by a high-frequency induction electromagnetic field generated by flowing a high-frequency current through an induction coil of a plasma torch, and the plasma ions generated thereby are introduced into a plasma ion introduction unit. The ions that have passed through the plasma ion introducing section are guided to an ion focusing section, where the ions are focused by an ion lens or the like toward a rear ion detecting section, and the ion detecting section focuses the ions by a mass separator. After mass separation, specific ions are detected by an ion detector such as an electron multiplier.

[0003]

By the way, when performing elemental analysis with the ICP mass spectrometer configured as described above,
Depending on the element to be detected, a molecular ion having a mass close to that of the detected ion may be generated and mixed in the detected ion. Such interfering molecular ions are mainly generated as follows. That is, when the sample plasma is introduced through the plasma ion introduction unit, the ion introduction hole of the plasma ion introduction unit (corresponding to the opening of the sampling cone).
The sample plasma in contact with the edge of the sample is cooled by the edge, various recombination reactions are promoted, and the amount of interfering molecular ions is increased.

[0004] As an interfering molecular ion, for example, when argon plasma is used, it is an element to be detected.
There is ³⁸ ArH for ³⁹ K and ¹² C ¹⁶ for ⁴⁴ Ca
There is O ¹⁶ O and there is ⁴⁰ Ar ¹⁶ O for ⁵⁶ Fe. When such interfering molecular ions are mixed, the detection of ions of a specific element is obstructed by the interfering molecular ions, and the detection sensitivity of the element is reduced. Therefore, in elemental analysis, it is necessary to prevent the generation of molecular ions having a mass similar to that of the ions of the element to be detected.

[0005] On the other hand, in the ICP mass spectrometer, generation of interfering molecular ions is intended to be suppressed by forming the plasma ion introduction section with a differential exhaust chamber. That is, by arranging a plurality of differential exhaust chambers having different degrees of vacuum in the plasma ion introducing section in a stepwise manner, the degree of vacuum of the exhaust chamber having an ion introduction hole (located at the plasma introduction end) is reduced. . This increases the diameter of the ion introduction hole, making it difficult for most of the introduced sample ions to come into contact with the edge of the ion introduction hole, suppressing the cooling of the sample plasma, and suppressing the generation of interfering molecular ions. doing.

However, although the generation of the interfering molecular ions can be prevented to some extent by forming the plasma ion introducing portion with the differential exhaust chamber structure, it is necessary to improve the analysis accuracy to the level required for the analysis of trace elements. However, it has been desired to further suppress the influence of interfering molecular ions.

The present invention has been made in view of the above-mentioned conventional problems, and has been made to reduce the influence of interfering molecular ions.
The task is to improve the accuracy of the analysis.

[0008]

According to the present invention, there is provided an ICP mass spectrometer which introduces plasma ions generated in an ICP from a plasma ion introduction section and detects the plasma ions in an ion detection section. Irradiation means for irradiating any part of the ion path from the plasma ion introduction part to the ion detection part with a light beam, and fluorescence detection means for detecting fluorescence emitted from plasma ions excited by irradiation of the light beam It is characterized by having

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below based on the illustrated embodiments. FIG. 1 is a schematic configuration diagram of an ICP mass spectrometer according to one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a plasma torch,
Reference numeral 2 denotes an induction coil, 3 denotes a plasma ion introducing unit that samples and introduces ions from the plasma torch 1, and 4 denotes an ion converging unit that converges ions passing through the plasma ion introducing unit 3. Reference numerals 5 and 5 denote ion detectors for detecting the ions converged by the ion converging unit 4 by mass separation.

The plasma ion introducing section 3 includes a sampling cone 6 and a skimmer cone 7 disposed in front and rear along the direction of the ion passage axis O.
A first differential exhaust chamber 8 is formed therebetween. And
The sampling cone 6 and the skimmer cone 7 have openings 6a, 7a formed coaxially with the ion passage axis O, respectively. A vacuum pump (not shown) is connected to the first differential exhaust chamber 8 between the cones 6 and 7 through an exhaust pipe 9.

The ion focusing section 4 has a second differential pumping chamber 10 which is evacuated by a pumping means such as a diffusion pump. The second differential pumping chamber 10 has passed through the plasma ion introducing section 3. An ion extraction electrode 11 for extracting ions, and a polarized ion lens system 12 for converging the ion trajectory K extracted by the ion extraction electrode 11 toward the ion detector 5
Is provided. The polarized ion lens system 12 is
In order that the light generated by the plasma torch 1 becomes noise and does not directly enter the ion detection unit 15, the ion passage axis O in the ion converging unit 4 is different from the ion passage axis O in the plasma ion introduction unit 3. The ion trajectory K is guided so as to be slightly shifted.

The ion detector 5 has a vacuum chamber 13 which is evacuated by a diffusion pump or the like. In the vacuum chamber 13, a quadrupole mass separator for mass-separating ions from the ion focusing section 4 is provided. And an ion detector 15 such as an electron multiplier for detecting specific ions mass-separated by the mass separator 14.

Further, in this ICP mass spectrometer, a laser light source 16 as irradiation means for irradiating the ion trajectory K in the second differential exhaust chamber 10 with a light beam, and a laser light irradiated from the laser light source 16 A reflecting mirror 17A for guiding the laser beam L along the ion passing axis O, a reflecting mirror 17B for reflecting the laser beam L guided along the ion passing axis O again in a direction away from the ion passing axis O, and a laser beam L Lens 18 for collecting fluorescence generated from ions excited by the
An optical fiber 19 for guiding the fluorescence collected by the condenser lens 18 to the outside of the apparatus; a fluorescence detection unit 20 for detecting the fluorescence guided by the optical fiber 19; and an ion mass detection detected by the ion detector 15. A mass calculating unit 21 that calculates a final mass detection value from the value and the amount of fluorescence (ion mass detection value) detected by the fluorescence detection unit 20. Reference numerals 22 and 23 denote transmission windows for transmitting the laser light L emitted from the laser light source 16 into and out of the second differential exhaust chamber 10.

The laser light L of the laser light source 16 is set to a wavelength that can excite specific interfering molecular ions. Here, the specific interfering molecular ion is a molecular ion which may be included in the ion flow introduced from the plasma ion introducing unit 3 and has a mass close to the element to be detected. This is a factor that hinders sensitivity elemental analysis. Interfering molecular ions having such characteristics can be estimated in advance from the element to be detected and other analysis conditions.
The wavelength of the laser beam that can excite a specific interfering molecular ion depends on the molecular structure of the molecule, and can be determined by experiments or calculations.

Next, the main operation of the ICP mass spectrometer having the above configuration will be described. The sample is turned into plasma by flowing a high-frequency current through the induction coil 2 of the plasma torch 1, and the plasma ions generated by this pass through the opening 6 a of the sampling cone 6 constituting the plasma ion introduction unit 3 and the first difference It is introduced into the dynamic exhaust chamber 8, passes through the opening 7 a of the skimmer cone 7, and is extracted by the ion extraction electrode 11 toward the ion detector 5. Then, the ions are converged toward the rear ion detector 5 by the polarized ion lens system 12 and then mass-separated by the mass separator 14 in the ion detector 5. Is detected by the detector 15.

The ions analyzed in this way include, in addition to the ions of the element to be detected, molecular ions which have little difference in mass from this element and inhibit high-sensitivity detection of this element. there is a possibility. When such an interfering molecule is contained, it becomes difficult for the ion detector 15 to separate and detect the element ion to be detected and the interfering molecular ion.

In the ICP mass spectrometer, the influence of such interfering molecular ions is eliminated by using a laser-induced fluorescence analysis system as follows. That is, the laser light L is emitted from the laser light source 16 to the ion flow introduced into the second differential exhaust chamber 10. The laser light L emitted from the laser light source 16 is guided along the ion passage axis O by the reflecting mirror 17A, and is irradiated on the ion flow in the ion trajectory K here. The wavelength of the laser light L is set in advance to a wavelength that selectively resonates and excites the interfering molecular ions that may be included in the ion stream. It emits fluorescence when selectively excited. This fluorescence is condensed by a condenser lens 18 and then input to a fluorescence detector 20 via an optical fiber 19, where the fluorescence intensity, that is, the amount of ions of a specific interfering molecule is selectively detected. . Since the laser beam L applied to the ion stream is reflected by the reflecting mirror 17B in a direction away from the ion passage axis O and is drawn out of the apparatus, it may not enter the ion detector 15 as noise. Absent.

In the fluorescence detector 20, since the measurement system is different from that of the ion detector 15, a specific interfering molecular ion is individually detected by selecting the wavelength of the laser beam L to be irradiated. Thus, the ion mass calculation unit 21 subtracts the ion amount of a specific interfering molecule detected by the fluorescence detection unit 20 from the mass analysis value of the element ion to be detected detected by the ion detector 15 to perform detection. The mass number of the element ion to be detected is accurately detected.

Further, since this ICP mass spectrometer is provided with two measurement systems, the ion detector 15 and the fluorescence detection unit 20, one measurement operation (operation for introducing plasma ions from the plasma torch 1) is performed. Thus, two types of analysis can be performed simultaneously. Therefore, this IC
By using the P mass spectrometer in this way, the analysis time can be reduced.

Further, the variation in the amount of fluorescence detected by the fluorescence detecting section 20 is measured, and the mass analysis value obtained by the ion detector 15 is subjected to an internal standard correction based on the variation in the amount of fluorescence, thereby enabling ion detection. The detection accuracy of the detector 15 can also be improved.

Next, a modified example will be described with reference to FIG.

The ICP mass spectrometer includes a sample cone 31 for sampling and introducing ions from the plasma torch 30, an ion converging unit 32 for converging ions introduced from the sample torch 31, and an ion converging unit 32. And an ion detector 33 for mass-separating and detecting the ions converged by the above.

This ICP mass spectrometer has only the sampling cone 31 along the direction of the ion passing axis O, and does not have a skimmer cone.
The first differential exhaust chamber in the embodiment described above does not exist.

The ion converging section 32 has a differential pumping chamber 34 evacuated by a pumping means such as a diffusion pump, and the differential pumping chamber 34 has an ion extraction port for extracting ions passing through the sampling cone 31. An electrode 35 and an ion lens system 36 for converging the ion trajectory K extracted by the ion extraction electrode 35 toward the ion detector 33 are provided.

The ion detector 33 has a vacuum chamber 37 evacuated by a diffusion pump or the like.
A quadrupole mass separator 38 for mass-separating the ions from the ion converging unit 32 and an ion detector 39 such as an electron multiplier for detecting specific ions mass-separated by the mass separator 38 are provided. Are located.

Further, in this ICP mass spectrometer, the opening 31 a of the sampling cone 31 is located behind the plasma torch 30 with respect to the ion trajectory K in the differential exhaust chamber 34.
A laser light source 40 as an irradiating means for irradiating a light beam along an ion passing axis O through an (ion introduction hole); and a laser beam L irradiated from the laser light source 40 is reflected in a direction away from the ion passing axis O. And a reflecting mirror 41 for blocking incidence on the ion detector 39. Reference numeral 42 denotes a transmission window for transmitting the laser light L emitted from the laser light source 40 to the outside of the differential exhaust chamber 34.

Laser light L emitted from laser light source 40
Is set to a value capable of decomposing a specific interfering molecular ion that is approximately similar in mass to the element to be detected. Here, the specific interfering molecular ion is a molecular ion which may be included in the ion flow from the plasma torch 30 and has a mass close to that of the element to be detected. This is a factor that can be estimated in advance from the element to be detected and other analysis conditions. The wavelength at which a specific interfering molecular ion can be decomposed depends on the molecular structure of the molecule, and can be determined by experiments or calculations.

The wavelength of the laser beam L is not specified, and a high-power laser beam is used so as to keep the opening (ion introduction hole) of the sampling cone 31 at a high temperature and suppress the generation of interfering molecules as a whole. It may be configured.

In the above configuration, the plasma torch 30
The ions generated at the opening 3 of the sampling cone 31
After passing through 1a, it is introduced into the differential exhaust chamber 34, and is extracted by the ion extraction electrode 35 to the ion detection unit 33 side.

The ions thus extracted include, in addition to the atomic ions of the element to be detected, molecular ions which have no difference in mass from the atomic ions and inhibit high-sensitivity detection of the element. Could be.

When the laser beam L is applied to the ion stream between the differential exhaust chambers 34, the molecular ions absorb the energy of the laser beam L and become molecular ions or atomic ions having a smaller mass. Decompose.

Then, the ions are converged by the ion lens system 36 toward the rear ion detector 33,
Mass separation is performed by a mass separator 38 in the ion detection unit 33,
The specific ions separated by mass are detected by the ion detector 39.

In this ICP mass spectrometer, since most of the specific interfering molecular ions contained in the ion stream are decomposed and reduced by the irradiation of the laser beam L, the mass separation and detection are performed together with the atomic ions of the element to be detected. The number of molecular ions to be detected is small, and element detection is performed with high sensitivity.

Further, since the interfering molecular ions are decomposed by the irradiation of the laser beam L to eliminate the influence of the interfering molecular ions, the structure has the following features. That is, conventionally, in order to suppress the generation of interfering molecular ions, the sample corn 3
Inevitably, the diameter of one opening 31a must be increased, and accordingly, a plurality of differential exhaust chambers such as a first and a second are provided, and a skimmer cone is provided between the differential exhaust chambers. To maintain a high vacuum.

However, this IC, which is capable of decomposing interfering molecular ions by irradiating the laser beam L,
In the P mass spectrometer, the opening 3
It is no longer necessary to suppress the generation of interfering molecules by increasing the diameter of 1a. Therefore, it is possible to maintain a high vacuum by reducing the diameter of the opening 31a, and accordingly, there is no need to provide a plurality of differential exhaust chambers and a skimmer cone provided between the plurality of differential exhaust chambers, Accordingly, the configuration of the ICP mass spectrometer is simplified.

[0037]

According to the present invention, the following effects can be obtained.

The analysis value of the preventive molecular ion, which is similar in mass to the ion of the element to be detected, is detected by the fluorescence detection means, and is subtracted from the analysis value of the element to be detected detected by the ion detection section. The influence of molecular ions can be eliminated, and element analysis with high precision can be performed accordingly.

Further, since two measurement systems, ie, an ion detection unit and a fluorescence detection unit, are provided, two types of analysis can be performed simultaneously by one measurement operation, thereby shortening the analysis time. Can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an ICP mass spectrometer according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an ICP mass spectrometer according to a modification.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Plasma torch 3 Plasma ion introduction part 4 Ion convergence part 5 Ion detection part 16 Laser light source (irradiation means) 20 Fluorescence detection part 21 Mass calculation part L Laser light (light beam)

Claims (1)

[Claims] 1. An ICP mass spectrometer for introducing plasma ions generated in an ICP from a plasma ion introduction unit and detecting the plasma ions in an ion detection unit, comprising: an ion path from the plasma ion introduction unit to the ion detection unit. An ICP mass spectrometer comprising: an irradiating unit that irradiates a light beam to a portion of the ICP; and a fluorescence detecting unit that detects fluorescence emitted from plasma ions excited by the irradiation of the light beam.