JP7349632B2 - Cells and analyzers for laser ablation - Google Patents

Description

The present invention relates to a cell that accommodates a sample to be ablated with a laser, and an inductively coupled plasma analyzer having the cell, and particularly relates to a cell and an analyzer suitable for when the sample is a solid.

Inductively coupled plasma (ICP: Inductively coupled plasma) analysis technology is known. Regarding the ICP analysis method, the technique described in the following non-patent document 1 is known.

Non-Patent Document 1 (Fernandez et al.) describes a technique that uses mass spectrometry (MS) using an inductively coupled plasma method to identify multiple elements such as copper, zinc, tin, and lead contained in soil. is listed. In Non-Patent Document 1, when a solid sample is ablated to form an aerosol, a femtosecond laser is used to shorten the time required for the entire analysis.

Beatriz Fernandez, and 4 others, “Direct Determination of Trace Elements in Powdered Samples by In-Cell Isotope Dilution Femtosecond Lase Ablation ICPMS”, Anal.Chem., 2008, 80, 6981-6994

(Problems with conventional technology)
In the technique described in Non-Patent Document 1, a sample ablated in a cell is transported toward a mass spectrometer using helium (He) gas as a carrier gas.
Generally, the smaller the particle size (atomic weight, molecular weight) of the carrier gas, the better the thermal conductivity and the lower the viscosity. The particles in the ablated sample are at a high temperature immediately after ablation, but if the carrier gas has a large molecular weight and poor thermal conductivity, the high-temperature particles may bond with each other before being transported by the carrier gas. , the particle size of the aerosol sample increases. When the particle size of a sample becomes large, there is a problem in that a noise-like signal is observed in a mass spectrometer. Therefore, as the carrier gas, a gas having a small atomic weight and a small molecular weight is preferable. Hydrogen (H ₂ ) gas can also be used, but if oxygen is present in the cell, there is a risk of explosion due to the heat during ablation, so He, which is an inert gas, is preferably used.

However, since He gas has a low viscosity, if the fine particles scattered during laser ablation are at high speed when the scattering direction intersects the flow direction of He gas, before being transported by He gas, It tends to adhere to the window of the cell through which the laser passes (a member through which the laser can pass). As fine particles adhere to and accumulate on the window, laser light is absorbed by the deposited fine particles, making it impossible for the laser light to pass through the window.

The technical objective of the present invention is to suppress contamination of the window due to the ablated sample compared to the conventional method.

In order to solve the technical problem, the laser ablation cell of the invention according to claim 1 has the following features:
a storage section in which the sample is stored;
a window portion through which the laser irradiated to the sample in the storage portion is transmitted;
a first introduction part into which a first gas is introduced that flows parallel to the surface of the sample to which the laser is irradiated and the surface of the window part from one end side of the housing part toward the other end side;
a second introduction part into which a second gas flowing in parallel with the first gas is introduced on a side closer to the window than the first gas and farther from the sample;
a derivation section from which the first gas and the second gas are derived together with the ablated sample;
It is characterized by having the following.

The invention according to claim 2 provides the laser ablation cell according to claim 1,
the first gas having a lower viscosity than the second gas;
It is characterized by having the following.

The invention according to claim 3 is the laser ablation cell according to claim 1 or 2, comprising:
the first gas having a different flow rate than the second gas;
It is characterized by having the following.

The invention according to claim 4 is a cell for laser ablation according to any one of claims 1 to 3, comprising:
the second introduction part that can adjust the position where the second gas flows with respect to the window part;
It is characterized by having the following.

In order to solve the technical problem, an analysis device according to the invention according to claim 5,
A cell for laser ablation according to any one of claims 1 to 4, which accommodates a sample;
a laser ablation device that ablates the sample;
an inductively coupled plasma mass spectrometer into which an ablated sample sent out from the cell is introduced and which performs mass spectrometry on the introduced sample using an inductively coupled plasma method;
It is characterized by having the following.

According to the invention described in claims 1 and 5, it is possible to suppress staining of the window portion due to the ablated sample compared to the conventional method.
According to the second aspect of the present invention, the second gas having a high viscosity can trap particles heading toward the window, thereby suppressing staining of the window, compared to a case where the second gas has a low viscosity.
According to the third aspect of the invention, by providing two gas flows with different flow rates, it is possible to transport fine particles on one side and capture fine particles heading toward the window on the other side.
According to the invention set forth in claim 4, the position through which the second gas flows can be adjusted.

FIG. 1 is an overall explanatory diagram of an analyzer according to Example 1 of the present invention. FIG. 2 is an explanatory diagram of main parts of the laser ablation apparatus of Example 1. FIG. 3 is an explanatory diagram of the cell of Example 1. FIG. 4 is an explanatory diagram of the assumed mechanism of Example 1, FIG. 4A is an explanatory diagram when Ar is used as the first gas, and FIG. 4B is an explanatory diagram when He is used as the first gas. . FIG. 5 is an explanatory diagram of an example of a modification of the cell introduction section.

Next, examples that are specific examples of embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples.
In addition, in the following explanation using the drawings, illustrations of members other than those necessary for the explanation are appropriately omitted for easy understanding.

FIG. 1 is an overall explanatory diagram of an analyzer according to Example 1 of the present invention.
In FIG. 1, an analyzer 1 of Example 1 includes a mass spectrometer 2 as an example of an analyzer. The mass spectrometer 2 of Example 1 is constituted by an inductively coupled plasma mass spectrometer (ICP-MS). Note that the analyzer is not limited to ICP-MS, and for example, it is also possible to use an inductively coupled plasma optical emission spectrometer (ICP-OES). Note that ICP-MS and ICP-OES that are conventionally known can be used, and are described in, for example, Japanese Patent Laid-Open No. 2013-130492, and are well known, so detailed explanations will be omitted.

The mass spectrometer 2 is connected to the downstream end of a connecting tube 3, which is an example of a connecting portion. A merging joint 4 is connected to the upstream end of the connecting tube 3. A downstream end of an additional gas tube 6, which is an example of an additional gas supply section, is connected to the merging joint 4. In the first embodiment, the additional gas tube 6 is supplied with argon (Ar) gas as an example of additional gas (make-up gas). In Example 1, the argon gas is supplied at a flow rate of about 0.5 to 1.2 L/min, for example.

A downstream end of a cell connection tube 7 is connected to the merging joint 4 as an example of a cell connection portion. A cell 11 is connected to the upstream end of the cell connection tube 7. The cell 11 is configured to be able to accommodate the sample S therein. A carrier gas tube 12 as an example of a carrier gas supply unit is connected to the cell 11 . In the first embodiment, the carrier gas tube 12 is supplied with helium (He) gas as an example of carrier gas. Note that in Example 1, the carrier gas is supplied at a flow rate of about 0.2 to 1.0 L/min, for example.

Further, above the cell 11, a laser ablation device 21 is arranged. The laser ablation device 21 irradiates the sample S in the cell 11 with laser light to ablate the sample S.
The analysis device 1 of the first embodiment includes a computer device 31 as an example of an information processing device. The computer device 31 includes a computer main body 32, a display 33 as an example of a display section, and a keyboard 34 and a mouse 35 as examples of an input section. The computer main body 32 outputs a signal for controlling the driving of the laser ablation device 21, and can receive detection results from the mass spectrometer 2 and display them on the display 33.

(Description of laser ablation device)
FIG. 2 is an explanatory diagram of main parts of the laser ablation apparatus of Example 1.
In FIG. 2, a laser ablation device 21 of Example 1 includes a femtosecond laser 22 as an example of a laser light source. The femtosecond laser 22 outputs, as an example of laser light, femtosecond laser light 22a having a pulse width on the order of femtoseconds. The femtosecond laser 22 of Example 1 outputs the femtosecond laser beam 22a with a pulse width of 230 fs, as an example, but the pulse width is not limited to the illustrated numerical value and can be changed.
The femtosecond laser 22 of Example 1 has a shutter (not shown) disposed inside, and is configured to be able to control the frequency at which the femtosecond laser beam 22a is output (the reciprocal of the interval at which the laser beam 22a is output). . In the first embodiment, as an example, the frequency can be controlled between 100 Hz and 1000 Hz. That is, the femtosecond laser 22 outputs the laser beam 22a at 1000Hz, and when the frequency is 1000Hz, the shutter is kept open at all times, and when the frequency is 100Hz, 9 out of 10 femtosecond laser beams 22a are output with the shutter open. It is possible to obtain an output of 100 Hz by blocking the signal.

The femtosecond laser beam 22a is introduced into a galvano optical system 23, which is an example of an optical system. The galvano optical system 23 of the first embodiment includes a first galvano mirror 24 as an example of a first mirror, and a second galvano mirror 25 as an example of a second mirror. The first galvano mirror 24 reflects the laser beam 22a from the femtosecond laser 22 toward the second galvano mirror 25, and the second galvano mirror 25 reflects the laser beam 22a from the first galvano mirror 24 toward the sample S. reflect.
The first galvanometer mirror 24 is rotatably supported around a first mirror axis 24a. Drive is transmitted to the first mirror shaft 24a from a first galvano motor 24b, which is an example of a first drive source. Therefore, in response to the drive from the first galvano motor 24b, the first galvano mirror 24 rotates and tilts around the first mirror axis 24a, changing the direction of reflection of the laser beam 22a.

Like the first galvano mirror 24, the second galvano mirror 25 also has a second mirror axis 25a and a second galvano motor 25b as an example of a second drive source, and changes the direction of reflection of the laser beam 22a. . In Example 1, as an example, the first galvanometer mirror 24 mainly controls the irradiation position in the X direction along the gas flow direction on the surface of the sample S, and the second galvano mirror 25 mainly controls the irradiation position in the gas flow direction. Controls the irradiation position in the Y direction intersecting the . Therefore, by controlling the two galvano mirrors 24 and 25, it is possible to scan the laser beam 22a two-dimensionally. In the first embodiment, as an example, the laser beam 22a is configured to be able to irradiate a range of 20 cm x 20 cm.
A lens 26, which is an example of an optical member, is arranged between the second galvano mirror 25 and the cell 11. The lens 26 focuses the passing laser beam 22a so that the focal point of the laser beam 22a is on the surface of the sample S.

(Cell description)
FIG. 3 is an explanatory diagram of the cell of Example 1.
In FIG. 3, the cell 11 of Example 1 has a storage section 41 in which the sample S is stored.
A window portion 42 through which the laser beam 22a can pass is arranged on the upper surface of the accommodating portion 41.
A first gas introduction section 51 as an example of a first introduction section is formed at one end side (upstream section) of the accommodating section 41 . A first gas introduction hose 52 is connected to the first gas introduction section 51 . Therefore, the first gas 53 is introduced from the first gas introduction section 51 into the storage section 41 through the first gas introduction hose 52 .

A second gas introduction section 56 is arranged inside the first gas introduction section 51 . The second gas introduction section 56 of the first embodiment is constituted by a cylindrical body extending in the left-right direction. A second gas introduction hose 57 is connected to the inside of the cylindrical body of the second gas introduction section 56 . Therefore, the second gas 58 is introduced from the second gas introduction section 56 into the housing section 41 through the second gas introduction hose 57. The second gas introduction hose 57 is arranged to penetrate inside the first gas introduction hose 52. Therefore, the two gas introduction hoses 52+57 constitute the carrier gas tube 12.
The second gas introduction section 56 is configured to be rotatable about the central axis 56a of the cylinder. Further, the second gas introduction portion 56 is formed with a slit-shaped gas ejection port 56b extending in the axial direction. The second gas introduction part 56 is rotatably supported by the side wall of the cell 11 at both ends in the axial direction. By operating a handle, which is an example of an operating unit disposed outside the cell 11, the position of the gas ejection port 56b can be adjusted, and the direction in which the second gas is ejected can be adjusted. In the first embodiment, the second gas 58 is set to flow closer to the window 42 than the first gas 53 and farther from the sample S.

In the first embodiment, in order to suppress mixing of the first gas 53 and the second gas 58, a gas outlet is provided diagonally upward (on the window 42) below the gas outlet 56b (on the side far from the window 42). A gas separator 61 as an example of a separation member is supported toward the approaching side). The gas separator 61 can be formed by bending a plastic film.
Further, in the first embodiment, He gas is used as an example of the first gas 53, and Ar gas is used as an example of the second gas 58. He gas has a lower viscosity than Ar gas.
A lead-out portion 66 is formed at the other end (downstream portion) of the accommodating portion 41 and is connected to the cell connection tube 7 .

Note that the control of the femtosecond laser 22 and the galvano optical system 23, the flow rate control of the gases 53 and 58, the measurement with the ICP-MS 2, etc. are controlled by the computer device 31. The computer device 31 has an input/output interface I/O for inputting and outputting signals to and from the outside. Further, the computer device 31 has a read-only memory (ROM) in which programs, information, etc. for performing necessary processing are stored. Further, the computer device 31 has a RAM (random access memory) for temporarily storing necessary data. Further, the computer device 31 has a central processing unit (CPU) that performs processing according to a program stored in a ROM or the like. Therefore, the computer device 31 can realize various functions by executing programs stored in the ROM or the like.

(Effect of Example 1)
In the analyzer 1 of Example 1 having the above configuration, the position of the target analysis position on the sample S is adjusted using the galvanometer mirrors 24 and 25, and the laser beam 22a is irradiated thereon. Here, in the galvano optical system 23 of the first embodiment, two galvano mirrors 24 and 25 are independently controlled by galvano motors 24b and 25b (two-axis control). Therefore, it is possible to ablate any two-dimensional position in the sample S and perform measurement and analysis.
Here, as the sample is ablated, fine particles of the sample S scatter and separate from the sample S, and float in the storage chamber 41. When the frequency of the laser beam 22a is low (for example, on the order of 1000 times/second), there are few suspended particles that adhere to the window 42, and even if they do, the amount is small enough that cleaning only once every six months is enough to cause no problem. Met. However, with the femtosecond laser 22 (on the order of 10,000 times/second), the scattering speed of fine particles increases, and the number of times the fine particles scatter increases, resulting in noticeable adhesion, and the laser beam There is a possibility that 22a may be absorbed and have an adverse effect on ablation.

On the other hand, in Example 1, the ablated particles are transported by He gas, which is the first gas 53, and measured by the mass spectrometer 2, and the particles scattered at high speed during ablation are It is captured by a highly viscous second gas 58 (Ar gas) flowing near the section 42 . Therefore, it is possible to maintain a state in which it is difficult for fine particles to adhere and accumulate on the window portion 42. Therefore, dirt on the window portion 42 can be suppressed.
FIG. 4 is an explanatory diagram of the assumed mechanism of Example 1, FIG. 4A is an explanatory diagram when Ar is used as the first gas, and FIG. 4B is an explanatory diagram when He is used as the first gas. .
In FIG. 4A, it is possible to use only Ar gas without using He gas, but if Ar gas is also used near the sample S, the scattered particles of the sample S will fall into the crater irradiated with the laser beam 22a. There is a problem in that the sample S tends to adhere to the outer periphery of the irradiated area of the shaped sample S. This is thought to be because the thermal conductivity of Ar gas is low with respect to the fine particles that become hot and scatter due to laser irradiation, so the area where the temperature remains high is narrow (only in the vicinity of the crater). Therefore, it is thought that at the time when the scattered particles cool down and begin to aggregate, there are not many particles scattered from the crater, and the density of the scattered particles is high (density decreases in proportion to the cube of the radius). It will be done. Therefore, there is a problem that the diameter of the particles after aggregation is large, and the measurement accuracy in the mass spectrometer 2 is also reduced.
On the other hand, if only He gas is used, since the viscosity of He gas is low, the viscosity of He will not be able to capture the fine particles that fly into the vicinity of the window 42, causing the problem that the fine particles will easily adhere to and accumulate on the window 42. Occur. Note that when He gas is present near the sample S, the high temperature region is considered to be wide because the thermal conductivity is high. Therefore, it is considered that when the high-temperature fine particles cool down and begin to aggregate, the density of the fine particles decreases, there is less aggregation, the particle diameter becomes smaller, and the measurement accuracy improves.

Therefore, in Example 1, by using the two gases 53 and 58, it is possible to suppress staining of the window portion 42 while improving measurement accuracy.
Note that the particulates captured by the second gas 58 are also sent to the mass spectrometer 2 and measured.
In particular, when the first gas 53 is He gas and the second gas 58 is Ar gas as in Example 1, the two gases 53 and 58 have a large difference in viscosity, so they are inherently difficult to mix. Therefore, the two gases are less likely to be mixed and adversely affect the measurement results. In particular, since the second gas is Ar gas and the make-up gas added on the downstream side of the cell is also Ar gas, there is almost no problem if they are mixed together in a small amount. Alternatively, it is also possible to measure the amount of makeup gas to be mixed in advance through experiments or the like, and to increase or decrease the amount of makeup gas depending on the amount of makeup gas to be mixed.
Furthermore, the flow rate of the gases 53 and 58 flowing within the cell 11 may be insufficient compared to the appropriate flow rate in the mass spectrometer 2. That is, the flow rates of the gases 53 and 58 in the cell 11 are not necessarily appropriate flow rates in the mass spectrometer 2. Therefore, with respect to the flow rate flowing out from the cell 11, it is possible to compensate for the insufficient flow rate with the make-up gas to obtain an appropriate flow rate in the mass spectrometer 2. In particular, it is easy to adjust the flow rate of the makeup gas, and it is also possible to freely adjust the flow rate while checking the measurement results and sensitivity of the mass spectrometer 2.

Further, in the first embodiment, the direction of the gas ejection port 56b can be adjusted. Therefore, the gas type of the second gas 58, the combination with the first gas 53 (size of difference in viscosity and thermal conductivity, etc.), the flow rate of the gas, the type of sample S to be measured, and the ease of ablation. The direction in which the second gas 58 is ejected can be adjusted depending on how easily it scatters, how easily it adheres, etc.

(Example of change)
FIG. 5 is an explanatory diagram of an example of a modification of the cell introduction section.
In the embodiment described above, as shown in FIG. 3, a configuration in which the direction of the gas ejection port 56b of the second gas introduction section 56 can be adjusted was illustrated, but the present invention is not limited to this.
As shown in FIG. 5, it is also possible to fixedly support a second gas introduction part 56' in parallel above and parallel to the first gas introduction part 51'.

(Other change examples)
Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various changes can be made within the scope of the gist of the present invention as described in the claims. Is possible. Modifications (H01) to (H09) of the present invention are illustrated below.
(H01) In the above embodiment, one sample was used as the sample S, but it is also possible to use two or more samples.
(H02) In the embodiments described above, the galvano optical system 23 has been illustrated as having a two-axis control configuration, but it is also possible to have a configuration with three or more axes. Note that the irradiation range, region, irradiation method, etc. of the galvano optical system 23 are not limited to the specific ranges illustrated in the examples, and can be arbitrarily changed depending on the experimental purpose, application, measurement object, etc. Therefore, it is possible to use a known optical system without using the galvano optical system 23.

(H03) In the above embodiments, the specific shape can be arbitrarily changed according to the design, specifications, etc. For example, the shape of the accommodating portion 41 of the cell 11 can be changed arbitrarily.
(H04) In the above embodiments, it is preferable to use He gas as the first gas, but the invention is not limited thereto. For example, it can be changed to hydrogen gas, neon gas, etc. depending on the type of sample to be analyzed and the required accuracy.
Furthermore, it is also possible to use Ar gas as the first gas. That is, it is possible to use the same gas type for the first gas and the second gas. At this time, the first gas transports the ablated sample, and the second gas maintains a difference in flow rate between the first gas and the second gas in order to make it difficult for the sample to adhere to the window 42. By allowing the sample to flow in a laminar flow, adhesion of the sample to the window portion 42 can be reduced.
Moreover, although Ar gas was illustrated as the second gas, it is not limited thereto. For example, it is also possible to use Xe gas, Kr gas, Rn gas, etc. At this time, it is preferable that the first gas has a lower viscosity than the second gas. Generally, the smaller the molecular weight (or atomic weight), the lower the viscosity and the higher the thermal conductivity. Therefore, it is preferable to use a gas having a larger molecular weight (or atomic weight) than the first gas as the second gas.

(H05) In the above embodiment, the illustrated cell 11 can be suitably used in the analyzer 1 having the laser ablation device 21 that can scan in two dimensions, but it can also be used in a laser ablation device that can operate in one dimension. It is also possible to use
(H06) In the above embodiment, a configuration using two gases was illustrated, but a configuration using three or more gases, that is, the first gas flowing near the sample S and the first gas flowing near the window 42, It is also possible to have a configuration in which a third gas or a fourth gas flows between the flowing second gas.

(H07) In the above embodiments, a femtosecond laser was exemplified as a laser for ablating the sample, but the present invention is not limited to this. For example, it is applicable to any laser that can ablate a sample, such as a Nd:YAG laser.
(H08) In the first embodiment, it is desirable to have a configuration in which the direction of discharge of the second gas is variable, but it is also possible to have a configuration in which the second gas introduction section 56 is fixed.
(H09) In the first embodiment, the gas separator 61 is made of film-like plastic, but the gas separator 61 is not limited thereto. For example, it can be constructed of a metal plate, metal foil, etc., and any material that does not affect ICP analysis can be used.

1...Analyzer,
2...Inductively coupled plasma mass spectrometer,
11...Cell,
21...Laser ablation device,
22a...Laser light,
41...Accommodation department,
42...window section,
53...first gas,
51...first introduction part,
58...Second gas,
56...Second introduction part,
66... Derivation part,
S...Sample.

Claims (5)

a storage section in which the sample is stored;
a window portion through which the laser irradiated to the sample in the storage portion is transmitted;
a first introduction part into which a first gas is introduced that flows parallel to the surface of the sample to which the laser is irradiated and the surface of the window part from one end side of the housing part toward the other end side;
a second introduction part into which a second gas flowing in parallel with the first gas is introduced on a side closer to the window than the first gas and farther from the sample;
a derivation section from which the first gas and the second gas are derived together with the ablated sample;
A cell for laser ablation characterized by comprising: the first gas having a lower viscosity than the second gas;
The cell for laser ablation according to claim 1, further comprising: the first gas having a different flow rate than the second gas;
The cell for laser ablation according to claim 1 or 2, comprising: the second introduction part that can adjust the position where the second gas flows with respect to the window part;
A cell for laser ablation according to any one of claims 1 to 3, comprising: A cell for laser ablation according to any one of claims 1 to 4, which accommodates a sample;
a laser ablation device that ablates the sample;
an inductively coupled plasma mass spectrometer into which an ablated sample sent out from the cell is introduced and which performs mass spectrometry on the introduced sample using an inductively coupled plasma method;
An analysis device characterized by comprising:

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