JPH09152421A - Icp mass spectrograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To analyze a plurality of elements in a trace sample accurately by providing a plurality of ion lead-out parts for a pressure reducing chamber and providing a detecting section individually for each ion lead-out part. SOLUTION: A sample atomized through an atomizer 5 is ionized by means of a plasma torch 6 through action of an induction coil 6a. Ionized sample is introduced, in the form of a bundle having diameter of about 1mm, through the ion introduction hole 7a of a sampling cone 7 into a pressure reducing chamber 3 and reaches a skimmer cone 8 while being diffused. The ionized sample is led out through a plurality of ion lead-out holes 8a to each detecting part 4 by means of a lead-out electrode 9a at each ion converging part 9. At each detecting part 4, the ionized sample is converged through an ion lens 9b and and mass-analyzed individually by the mass spectrometer 10a at each detecting part 10. Furthermore, specified elements in mass-analyzed ionized sample are detected by an ion detector 10b, e.g. an electron multiplier.

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 that ionizes a sample with an ion source and then performs mass spectrometry.

[0002]

2. Description of the Related Art As an ICP mass spectrometer,
There is one shown in FIG.

This ICP mass spectrometer 50 comprises an atomizer 5
1 and a plasma torch 52 are provided, and the sample is atomized by the atomizer 51 and then converted into plasma by the induction coil 52a of the plasma torch 52. Then, the ionized sample generated thereby is led to the detection unit 55 via the decompression chamber 54. The detection unit 55 includes an ion focusing unit 56 and a detection unit main body 57. First, the ionized sample is extracted from the decompression chamber 54 to the ion focusing unit 56 by the extraction electrode 56a, and then the ion lens 56 is used.
It is converged at b and sent to the detection unit main body 57. In the detector main body 57, mass separation is performed by the mass spectrometer 57a.
Further, an ion detector 57 such as an electron multiplier is used to detect a specific element in the ionized sample subjected to the mass separation.
Detect at b.

Further, in this ICP mass spectrometer 50,
A decompression chamber 54 and an ion converging unit 56, each having a different degree of vacuum, are provided in order to connect the detection unit main body 57 that requires a high vacuum state and the ion source 53 side that is in a normal pressure state. Is provided, the normal pressure ion source 53 side and the high vacuum state detection unit main body 57 are connected. Furthermore, since the ion source 53 side and the decompression chamber 54, which have a large degree of vacuum gap, and the decompression chamber 54 and the ion converging section 56 are connected without difficulty, the decompression chamber 54 has an ion introduction side of φ1 mm. Sampling cones 58 each having an ion introduction hole 58a are provided, and a skimmer cone 59 having an ion extraction hole 59a having a diameter of about 1 mm is provided on the ion extraction side of the decompression chamber 54.

Further, in the ICP mass spectrometer 50 having the above-mentioned structure, the atomizer 51 is used as a nebulizer for atomizing the sample with a piezoelectric element, or the sample is dripped into a coil in an energized state and atomized. There is a flash atomizer (hereinafter abbreviated as FA) for atomizing, and a graphite furnace atomizer (hereinafter abbreviated as GFA) for dropping and atomizing a sample into a heated graphite container. Although the nebulizer can always maintain a constant atomization amount, it is difficult to atomize with a very small amount of sample. On the other hand, although FA and GFA can atomize even a very small amount of sample, the amount of atomization varies with time, and it is not possible to maintain a constant amount of atomization.

Therefore, when analyzing a very small amount of sample, FA or GFA was used as the atomizer 51. However, in these atomizers 51, since the atomization amount does not become uniform over time, when analyzing a plurality of elements from a very small amount of sample (in this case, quantitative analysis), the analysis operation will be described below. It is time-shared so that

That is, the elemental analysis operation is time-divided for each time-division unit interval, and then the analysis element is periodically assigned for each time-division unit interval. Then, the analysis operation thus time-divided is periodically repeated. In the analysis data thus obtained, the analysis data of each analysis element is obtained for each repeating cycle of each analysis operation (= time division unit interval × number of analysis elements). Therefore, each element is quantitatively analyzed by integrating the analysis data of the analysis element for each repeating cycle.

[0008]

By the way, the ICP mass spectrometer 50 constructed as described above has a problem that it is not possible to accurately analyze a plurality of elements from a very small amount of sample. That is, in the conventional ICP mass spectrometer 50, as described above, when performing analysis of a plurality of elements from an extremely small amount of sample, the FA as the atomizer 51 is used.
And GFA are used and the analysis operation is time-shared. However, the analysis accuracy in the case of performing time-division analysis operation is closely related to the repetition cycle of each analysis operation, and if the repetition cycle is shortened, the integration accuracy increases and the analysis accuracy of each element increases. If the length is increased, the integration accuracy will decrease and the analysis accuracy of each element will decrease.

The repetition period is determined by the time-division unit interval and the number of analysis elements as described above, and it is necessary to narrow the time-division unit interval in order to shorten the repetition period under the condition that a plurality of analyzes are performed. is there. However, a certain amount of time is required for the mass spectrometer 57a to stabilize each time the analysis element changes in the detection unit 55, and there is a structural limit to narrowing the time division unit interval.
Therefore, as the number of elements to be analyzed increases, the repetition cycle becomes longer and the analysis accuracy must be lowered.

Therefore, it is an object of the present invention to enable accurate analysis of a plurality of elements from a very small amount of sample.

[0011]

In order to achieve such a subject, in the present invention, an ion source for atomizing a sample and then ionizing it, and a decompression chamber into which an ionized sample formed by the ion source is introduced. An ICP mass spectrometer, comprising: an ionization sample drawn from an ion derivation part of a decompression chamber; and a detection part that converges the extracted ionization sample and detects a specific element in the ionization sample. It is characterized in that a plurality of ion derivation parts of the chamber are provided and the detection part is individually provided for each ion derivation part.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of an ICP mass spectrometer 1 which is an embodiment of the present invention.

This ICP mass spectrometer 1 ionizes the sample and then ionizes it, a decompression chamber 3 for introducing the ionized sample formed by the ion source 2, and an ionized sample drawn from the decompression chamber 3. It is provided with a detection unit 4 for detecting a specific element in the ionized sample after converging.
Although such a configuration is basically the same as that of the conventional example, in this ICP mass spectrometer 1, the ionized sample extracted from the decompression chamber 3 is branched into a plurality of (4 in this example), and each branched ionization is performed. A feature is that a plurality of (four in this example) detection units 4 are provided to analyze each sample. Note that, in FIG. 1, only two detection units 4 are shown for convenience of drawing. The features of the ICP mass spectrometer 1 will be described below according to the configuration thereof.

The ion source 2 has an atomizer 5 for atomizing the sample and a plasma torch 6 for ionizing the sample by atomizing the sample atomized by the atomizer 5 into a plasma using an induction coil 6a. There is.

The decompression chamber 3 plays a role of guiding the ionized sample ejected from the plasma torch 6 to the detection unit 4 which is set in a high vacuum state. A sampling cone 7 is provided on the ion introduction side of the decompression chamber 3, and a skimmer cone 8 is provided on the ion derivation side of the decompression chamber 3.
The sampling cone 7 is formed with a conical ion introduction hole 7a having an opening on the plasma torch 2 side of about φ1 mm, and the skimmer cone 8 has a conical shape with an opening on the decompression chamber 3 side of about φ1 mm. The ion lead-out hole 8a is formed. While the sampling cone 7 is provided with a single ion introduction hole 7a, the skimmer cone 8 is provided with a plurality of ion extraction holes 8a (four in this example) as shown in FIG. There is.

A plurality of detectors 4 (four in this example) are provided corresponding to a plurality of ion derivation holes 8a, so that ionized samples derived from the respective ion derivation holes 8a can be individually analyzed. ing. Each detection unit 4 communicates with the decompression chamber 3 via each ion derivation hole 8a.
And a detector main body 10 that is provided next to the ion converging unit 9 in communication therewith. In the ion focusing unit 9, the skimmer cone 8 is provided with the ionized sample introduced to the decompression chamber 3.
An extraction electrode 9a drawn from the ion extraction hole 8a of
Ion lens 9b for converging the extracted ionized sample
And The detection unit main body 10 includes a quadrupole mass spectrometer 10a, and the mass spectrometer 10a performs mass separation of the ionized sample focused by the ion focusing unit 9.

Further, in the ICP mass spectrometer 1, the detection unit body 10 is maintained in a high vacuum (about 10 ^{-5 to -6} Torr), and the ion focusing unit 9 has a medium vacuum (10 ^{-3 to-). 4} Torr
The vacuum chamber 3 is maintained at a low vacuum (10 _Torr
The ion source 2 is in a substantially normal pressure state. By changing the degree of vacuum stepwise in this way, the ionized sample is allowed to pass therethrough, and the normal pressure ion source 2 and the high vacuum detector main body 10 are made to communicate with each other.

Next, the operation of analyzing a sample by the ICP mass spectrometer 1 thus constructed will be described. In addition, here, description will be made on the premise that a plurality of elements are analyzed from an extremely small amount of sample. Further, the atomizer 5 has an FA (flash atomizer) so that it is suitable for atomizing a very small amount of sample.
Or GFA (graphite furnace atomizer) is used.

First, the sample is supplied to the atomizer 5 and atomized. At this time, the amount of the sample supplied is extremely small, and when atomized by the atomizer 5 made of FA or GFA, the atomized amount changes with time as shown in FIG. Note that in FIG. 3, the horizontal axis represents the passage of time and the vertical axis represents the atomization amount.

The sample atomized by the atomizer 5 is introduced into the plasma torch 6, where it is ionized by the action of the induction coil 6a. The sample ionized by the plasma torch 6 is introduced into the decompression chamber 3 through the ion introduction hole 7a of the sampling cone 7 as a bundle having a diameter of about 1 mm. At this time, since the decompression chamber is decompressed (about 10 Torr), the ionized sample introduced into the decompression chamber 3 reaches the skimmer cone 8 while diffusing. The ionized sample reaching the skimmer cone 8 is led out to the ion focusing section 9 of each detecting section 4 from each of the plurality of ion leading holes 8a provided by the action of the extraction electrode 9a provided in each ion focusing section 9.

The ionized sample led to each ion converging unit 9 is individually analyzed in each detecting unit 4. That is, the ionized sample led to each detection unit 4 is individually focused by the ion lens 9b provided in the ion focusing unit 9, and then individually mass-separated by the mass spectrometer 10a in each detection unit main body 10, Further, the specific element in the ionized sample subjected to the mass separation is detected by an ion detector 10b such as an electron multiplier.

As described above, in the ICP mass spectrometer 1, since the skimmer cone 8 is provided with a plurality of ion derivation holes 8a, when the number of elements to be analyzed is equal to or smaller than the number of ion derivation holes 8a. Eliminates the need for time-sharing elemental analysis operations. The fact that the analysis accuracy deteriorates due to the time-sharing operation of elemental analysis is as described in the “Problem to be solved by the invention” of the present application. Therefore, if the element analysis does not need to be time-divided, the factors that deteriorate the analysis accuracy are reduced accordingly, and the analysis accuracy is improved.

On the other hand, the number of elements to be analyzed depends on the ion introduction hole 8a.
If the number is larger than the number, the analysis operation is time-shared in at least one detection unit 4 as follows. That is, the elemental analysis operation is time-divided for each time division unit interval T _B (see FIG. 3), and then the analysis elements G _{1 to} G _n (n ≧ 2) are periodically assigned for each time division unit interval T _B. . Then, the time-division analysis operation is repeated according to the number of analysis elements n (n ≧ 2) S (= time-division unit interval T _B × number of analysis elements n:
(See FIG. 3). In the analytical data obtained in this way, analytical data of each analytical element G _{1 to} G _n is obtained for each repeating cycle S of each analytical operation. Therefore, quantitative analysis of each element G _{1 to} G _n is performed by integrating the analysis data of the analysis elements G _{1 to} G _n for each repeating cycle S.

In such an analysis operation, the analysis accuracy is closely related to the repetition cycle S of each analysis operation. If the repetition cycle S is shortened, the integration accuracy is increased and the analysis of each element G 2 to _n is performed. While the accuracy increases, the integration accuracy decreases when the repetition cycle S is lengthened, and the analysis accuracy of each element G 2 to _n decreases.

The repeating period S is determined by the time division unit interval T _B and the number of analysis elements n. To shorten the repetition period S, the number of analysis elements n is decreased or the time division unit interval T _B is shortened. do it. However, if the time division unit interval T _B is shortened, the stabilization time of the detection unit 4 (the time required for the setting of the mass spectrometer 10a and the stabilization of the voltage applied to the ion lens 9b etc.) is also shortened accordingly. However, there is a limit to the reduction of the stabilization time in terms of the structure of the detection unit 4.

However, this ICP mass spectrometer 1
In the above, the ion derivation hole 8 provided in the skimmer cone 8
The detector 4 is also added along with the addition of a, and the number of analysis elements in charge of each detector 4 is also small. Therefore, the number of analysis elements in charge of each detection unit 4 is reduced, so that the repetition cycle S is shortened and the analysis accuracy is improved as much as possible.

Further, according to the invention of the present invention, which is provided with a plurality of detecting portions 4,
The CP mass spectrometer 1 has the conventional I having a single detector.
Analysis sensitivity equivalent to that of a CP mass spectrometer can be obtained. Less than,
The reason will be described. Generally, in the ICP mass spectrometer, the ionized sample introduced into the decompression chamber 3 reaches the skimmer cone 8 in a diffused state. This is a phenomenon caused by the difference in vacuum degree between the ion source 2 and the decompression chamber 3. On the other hand, the diameter of the ion lead-out hole 8a provided in the skimmer cone 8 is set to a relatively small diameter of about 1 mm in order to maintain the degree of vacuum of the ion focusing section 9. Therefore, the amount of the ionized sample led out to the detection unit 4 through the ion lead-out hole 8a is a very small amount in the ratio of about 1% of the entire ionized sample.

Therefore, when only a single outlet 8a is provided, the remaining 99% of the ionized sample cannot be delivered and must be discarded. When a plurality of ion derivation holes 8a are provided, the ionized sample that had to be discarded in the single derivation hole 8a is derivable by the newly provided derivation hole 8a. In other words, it means that the ionized sample, which was previously discarded, is reused. Therefore, when the number of the ion derivation holes 8a is increased to some extent, the amount of the ionized sample derived from each of the ion derivation holes 8a does not decrease, and a plurality of ionized samples are taken out from a single sample for analysis. The analysis sensitivity does not drop when you do.

[0029]

As described above, according to the present invention, it becomes possible to take out a plurality of ionized samples from a single sample and analyze them simultaneously, and in the case of analyzing a plurality of elements from a very small amount of sample. It is possible to almost eliminate the time-sharing processing of the analysis operation that greatly affects the analysis accuracy, and in the case where the time-sharing processing must be performed, the repetition cycle of the time-sharing processing that affects the analysis accuracy is possible. It seems that it can be reduced to. Therefore, it has become possible to accurately analyze a plurality of elements even from a very small amount of sample.

Furthermore, by branching the ionized sample in the ion derivation section of the decompression chamber, the analysis of each detection section can be performed without lowering the detection sensitivity.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of an ICP mass spectrometer according to an embodiment of the present invention.

FIG. 2 is a perspective view of a skimmer cone that constitutes the ICP mass spectrometer of the embodiment.

FIG. 3 is a diagram showing a change in atomization amount of the atomizer.

FIG. 4 is a cross-sectional view showing the configuration of a conventional ICP mass spectrometer.

[Explanation of symbols]

 2 Ion source 3 Decompression chamber 4 Detection part 8 Skimmer cone 8a Ion derivation hole

Claims (1)

[Claims] 1. An ion source that atomizes a sample and then ionizes it, a decompression chamber into which the ionized sample formed by the ion source is introduced, and an ionization sample that is drawn out from the ion derivation unit of the decompression chamber and that is drawn out. An ICP mass spectrometer equipped with a detection part for detecting a specific element in an ionized sample after converging the ionization sample, wherein a plurality of ion derivation parts of the decompression chamber are provided, and the detection parts are provided for each ion derivation part. An ICP mass spectrometer characterized by being provided individually for each.