JP3920211B2 - Elemental analysis method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an element analysis method and apparatus for detecting and quantifying an element contained in a sample by irradiating a sample with laser light and measuring fluorescence emitted from plasma generated at that time.
[0002]
[Prior art]
In general, techniques for detecting and quantifying various elements contained in a sample are applied in many fields. For example, detecting and quantifying elements contained in soil and wastewater is important for preventing environmental pollution. In the field of thermal nuclear power plants, this elemental analysis technique is extremely important for the management of impurity elements contained in cooling water and the components of exhaust gas generated from prime movers.
[0003]
These elemental analysis techniques include fluorescent X-ray analysis and inductively coupled plasma emission analysis. As a new technique using laser light, there is laser light breakdown (LIB) spectroscopic analysis (Patent Documents 1 and 2 below). reference). This analysis method is a technique for spectrally analyzing light generated from plasma generated by condensing and irradiating an analysis sample with pulsed laser light, and has a feature that it can be easily applied to various elemental analysis.
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 11-311606 [Patent Document 2]
Japanese Patent Laid-Open No. 2000-121558
[Problems to be solved by the invention]
In the conventional laser light breakdown analysis, fluorescence emitted from an element is a measurement object. Although this method is simple, there is a large variation in the intensity of laser light breakdown depending on the form of the sample, resulting in large variations in the fluorescence intensity generated, and there is a problem in measurement accuracy and reproducibility. In particular, it is not possible to directly measure a substance having a powder form such as liquid or soil, a fluid form, or a clay form.
[0006]
The present invention has been made in response to such problems, and an elemental analysis method capable of performing elemental analysis with good reproducibility by laser beam breakdown spectroscopy for substances that are not solid or powdery in the normal state. And an object to provide an apparatus.
[0007]
[Means for Solving the Problems]
The invention of claim 1 is an elemental analyzer, an analysis cell for holding a sample obtained by cooling and solidifying a substance to be elementally analyzed, an exhaust device for evacuating the analysis cell to a low vacuum of about 1 Pa, A laser oscillator that generates a pulsed laser beam; an optical system that focuses and irradiates the sample with the pulsed laser beam; and a fluorescence that is emitted from plasma generated by the sample upon receiving the pulsed laser beam. And a fluorescence spectroscopic measuring means for obtaining the element constituting the substance and its content from the wavelength and intensity of the fluorescence.
[0008]
According to a second aspect of the present invention, the fluorescence spectroscopic measurement means is configured to perform gate processing of the detected fluorescence signal at a time unique to each target element in synchronization with the irradiation time of the pulse laser beam.
[0009]
According to a third aspect of the present invention, there is provided a cell moving mechanism that moves the analysis cell to move the laser light irradiation position of the sample.
According to a fourth aspect of the present invention, the analysis cell holds a plurality of samples, and the cell moving mechanism operates so that the plurality of samples are alternately irradiated with laser light.
[0010]
The invention of claim 5 has a structure in which a cooling equipment for cooling the sample.
The invention of claim 6 is an elemental analysis method, wherein a sample obtained by cooling and solidifying a substance to be analyzed is irradiated with a pulsed laser beam in an atmosphere evacuated to a low vacuum level of about 1 Pa , and By measuring the wavelength and intensity of the fluorescence emitted from the plasma generated by irradiation, the element constituting the substance and the content thereof are obtained.
[0011]
The invention according to claim 7 is configured to correct the content of the element to be analyzed based on the emission intensity of the plasma or the emission line intensity of the specific element.
According to an eighth aspect of the present invention, the substance is a powder having a non-constant particle size, and the sample is formed by pulverizing the substance into a fine powder, pressing, and cooling and solidifying.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the elemental analysis apparatus of the present invention will be described with reference to the drawings. As shown in FIG. 1, the elemental analysis apparatus of the present embodiment includes an analysis cell 1, a laser oscillator 2, a spectroscope 3, a fluorescence detector 4, an internal observation camera 5, a data recording device 6 and a main constituent device. A timing controller 7 is provided.
[0013]
The analysis cell 1 has a laser beam introduction window 8 and an internal observation window 9, to which a vacuum pump 10 is connected and is placed on a cell moving mechanism 11. A sample cooling stage 12 is provided in the analysis cell 1, and a chiller 13 is connected to the sample cooling stage 12.
[0014]
From the timing controller 7, a laser control signal 7 a that defines the timing for oscillating the pulse laser beam 15 for laser beam breakdown is output from the laser oscillator 2. Further, a detection control signal 7b for defining a fluorescence measurement gate is output to the fluorescence detector 4 with a certain delay, and only the fluorescence 17 generated in a predetermined time zone is measured.
[0015]
The sample 1 a is placed on the sample cooling stage 12 in the sealable analysis cell 1. The analysis cell 1 is evacuated by a vacuum pump 10. The entire analysis cell 1 is provided on a cell moving mechanism 11 so that the laser irradiation position on the sample 1a can be moved to a place not always receiving laser irradiation. As the cell moving mechanism 11, a normal XY stage can be applied. In this case, a plurality of samples can be arranged in parallel, and a plurality of samples can be measured simultaneously. Of course, for example, a rotary stage may be applied in addition to the XY stage.
[0016]
As an optical system, a total reflection mirror 18, a scraper mirror 19 with holes, and condenser lenses 20a and 20b are installed. The pulse laser beam 15 for laser beam breakdown passes through the hole of the scraper mirror 19 and then is irradiated to the sample 1a in the analysis cell 1 by the condenser lens 20a.
[0017]
The fluorescence 17 generated from the plasma 21 generated by this laser irradiation is converted into a parallel beam by the laser beam condensing lens 20a, then reflected by the scraper mirror 19 and condensed by the fluorescence condensing lens 20b to the spectroscope 3. Led. The fluorescence dispersed by the spectroscope 3 is further guided to the fluorescence detector 4 and converted into an electrical signal. The electrical signal is integrated by the boxcar integrator 16 and recorded by the data recording device 6. Further, the state of occurrence of laser breakdown in the analysis cell 1 is monitored by the internal observation camera 5 through the internal observation window 9.
[0018]
In the present embodiment, when an analysis target is a liquid or a viscous substance, this is cooled and solidified below the freezing point to obtain a sample 1a, and laser irradiation is performed in a solid state to convert the sample 1a into plasma. In order to generate the stable plasma 21, it is necessary to make the sample surface not move. However, when the analysis target is a liquid or a viscous substance, the surface of the laser light irradiation surface changes, so the solid of the analysis target substance Is effective.
[0019]
As the chiller 13 for cooling and solidifying the sample 1a, there are apparatuses such as refrigerant cooling using dry ice or liquid nitrogen and electronic cooling using a Peltier cooling element. For a liquid having a melting point of about minus 20 degrees C or more, the use of a Peltier cooling element is the simplest.
[0020]
In the present embodiment, the generation of the plasma 21 due to the irradiation of the laser beam 15 can be stabilized by evacuating the analysis cell 1 with the vacuum pump 10. A vacuum level of about 1 Pa that can be evacuated by a rotary pump is sufficient. As a result of this evacuation, it is possible to measure a sample that requires the determination of the nitrogen content, which cannot be measured due to the influence of nitrogen in the air. Furthermore, by setting the atmosphere to a vacuum, the temperature of the plasma 21 can be lowered, and the background light intensity due to the plasma 21 can be reduced to measure a low background.
[0021]
As described above, the present embodiment includes the cell moving mechanism 11 that externally drives the analysis cell 1 that holds the sample 1a. When the sample 1a is irradiated with the laser beam 15, the elements present on the surface are instantaneously vaporized and a part thereof is turned into plasma. If this laser beam brazing phenomenon is continued, the sample surface is slightly removed. As a result, when the surface irregularity changes, the generation state of the generated plasma 21 also changes. For this reason, it is necessary to sequentially change the laser beam irradiation point in order to averagely measure the elements constituting the sample.
[0022]
When the target element for detection is present in a sample in a non-uniform manner, the sample can be moved and averaged for detection as it is moved as in the present embodiment. In addition, although the magnitude | size of the condensing point of a laser beam is several micrometers-several tens of micrometers, the recessed part of an order of 100 micrometers is formed by laser irradiation depending on a sample. Therefore, the moving speed of the sample needs to be 100 μ / pulse or more.
[0023]
Now, for example, considering a YAG laser beam having a pulse energy of about 10 mJ and a pulse width of 5 ns, the output is a pulse output of 2 MW. When such a pulsed laser beam 15 is focused and irradiated onto the sample 1a, so-called breakdown occurs, and the sample in the irradiated region is ionized to become plasma 21.
[0024]
The recombination of the plasma 21 resulting from this laser light irradiation begins with the end of irradiation with the pulsed laser light 15, and the constituent elements of the irradiated sample become excited atoms for several μs to several tens of μs. When the atom in the state transitions to the lower level, it emits fluorescence 17 proportional to the number of atoms. When the target element is quantified from the sample 1a, high analysis accuracy can be obtained by capturing a predetermined component of the fluorescence 17 emitted from the plasma 21.
[0025]
Signal processing in the elemental analysis apparatus of the present embodiment is performed as follows. That is, as shown in FIG. 2, a laser oscillation signal 27 is output in the laser control signal 7a with a certain delay time Δt1 with respect to the master clock signal 26 from the timing controller 7 that oscillates at a certain frequency.
[0026]
Fluorescence 17 in the detection control signal 7b has a delay time Δt2 appropriately set in its time function with respect to the signal 28 of the fluorescence 17 that changes with time caused by irradiation of the pulsed laser light 15 emitted by the laser oscillation signal 27. A signal measurement gate signal 29 is output, and the fluorescence signal 28 is measured by the lock-in amplifier and the boxcar integrator 16 during this time period.
[0027]
The time delay Δt2 from the laser irradiation of the fluorescence signal measurement gate signal 29 and the gate width 30 need to be optimized for the element to be analyzed. In general, for an element having a short excitation lifetime of fluorescence generation, measurement with a high S / N ratio can be performed by reducing the time delay Δt2 and reducing the gate width 30. Conversely, for atoms having a long excitation lifetime, measurement with a high S / N ratio can be performed by increasing the time delay Δt2 and increasing the gate width 30.
[0028]
As described above, in the present embodiment, the fluorescence signal 28 detected by the fluorescence detector 4 is processed in synchronism with the irradiation time of the laser light 15 and with a unique time gate for each target element. Thereby, it is possible to measure a high S / N ratio for elements having different fluorescence lifetimes.
[0029]
A spectroscope is generally used for fluorescence measurement. However, if measurement of only a specific element is sufficient, measurement using a photomultiplier tube provided with an interference filter is also possible. The content of the element to be detected in the sample is analyzed with the intensity ratio of the wavelength by measurement in parallel with the standard sample. As the laser oscillator, a YAG laser is taken as an example here, but a laser such as an excimer laser can also be applied as long as it is a pulsed laser beam capable of laser beam breakdown.
[0030]
In the present embodiment, the content of the element to be analyzed is corrected based on the emission intensity of the plasma 21 generated by the breakdown laser beam 15 or the emission line intensity of the specific element. The size and temperature characteristics of the plasma 21 when the sample 1a generates the plasma 21 by the laser light 15 are caused by fluctuations in the output of the laser light 15, the amount of elements emitted from the surface of the sample 1a, fine irregularities on the surface of the sample 1a, and the like. Affected.
[0031]
In general, the size and temperature of the plasma 21 generated by the laser beam 15 are in proportion to the intensity of the white light generated by the black body radiation generated from the plasma 21 or the emission line intensity of the specific element. For this reason, in order to reduce the variation in measurement, the fluorescence or ion signal from the element to be analyzed is corrected by the variation in the plasma generation amount for each laser light pulse. When quantified pure water is used for freezing and fixing the sample 1a, hydrogen Hα (656.2 nm), Hβ (486.1 nm), Hγ (434.0 nm), Hδ (410.2) are used as standard lines for plasma generation. nm).
[0032]
Another example of the arrangement of the sample and the laser irradiation method in this embodiment will be described with reference to FIGS. That is, as shown in FIG. 3, a standard sample 22 and an analytical sample 23 are placed side by side as samples in the analysis cell 1, and these are placed on a coolable sample cooling stage 12.
[0033]
When performing the elemental analysis, the analysis cell 1 is evacuated by the vacuum pump 10, the entire analysis cell 1 is moved by the cell moving mechanism 11, and the laser irradiation positions on the samples 22 and 23 are always irradiated with laser. Measure while moving to a place where you have not yet received. FIG. 4 shows an example thereof. In this case, a lot of data is obtained with a small sample by moving the laser irradiation path 32 on the samples 22 and 23 continuously like a single stroke during analysis. be able to.
[0034]
When measuring the ratio of the specific element, as shown in FIG. 5, the accurate ratio can be obtained by tracing the measurement of the standard sample 22 and the analysis sample 23 alternately.
[0035]
Thus, by loading a plurality of samples into the analysis cell 1 and measuring the analysis sample 23 of them simultaneously or alternately with the standard sample 22 whose content of the element to be measured is known, The content of the contained elements can be quickly quantified.
[0036]
If the substance to be analyzed is a powder, it is also effective to mix a solidified adhering material and solidify the sample. In this case, the frozen solidification method can be frozen as long as there is moisture in the analyte, and if the moisture is insufficient for solidification, a simple method of solidifying by adding quantified pure water is easy. is there.
[0037]
An example of a method for preparing such a sample will be described with reference to FIG. That is, for the powdery substance to be analyzed, in order to make the particle size uniform, the particle size is set to about 10 μm to 100 μm or less by the crushing mill 33 (step (2)). As for the clay-like substance, there is no problem if the particle size is about the above, but when particles having a particle size of 100 μm or more are present, it is necessary to pulverize them with a mill or the like.
[0038]
Next, a substance to be analyzed is packed in a press frame 35 that matches the size of the sample frame 31 and pressed at a pressure of 10 MPa to 100 MPa. For normal soils, good solidification can be achieved with pressures in this range.
[0039]
Depending on the state of solidification of the substance to be analyzed by the press, water can be added as a particle binder (step (3)), so that solidification is accelerated during cooling and a sample with less variation in plasma generation due to laser irradiation can be created. . In addition, if the substance to be analyzed contains a large amount of moisture, it is preferable to dry it to the extent that it can be pressed. Etc., and is placed on the sample cooling stage 12.
[0040]
In this way, when the analysis target substance is a powder such as soil and the particle size is not constant, the analysis target substance is pulverized in advance with a mill, pressed, and measured to obtain a laser-generated plasma. Can be generated stably, and the measurement variation can be reduced to obtain a highly reliable measurement result.
[0041]
Still another example of the arrangement of the sample and the laser irradiation method in this embodiment will be described with reference to FIGS. That is, as shown in FIG. 7, the standard sample 22 and the analysis sample 23 are placed side by side as samples in the analysis cell 1, and these are placed on a rotating stage 36 that can be cooled.
[0042]
When performing the elemental analysis, the analysis cell 1 is evacuated by the vacuum pump 10, and the laser irradiation position is switched between the sample 22 and the sample 23 by the rotation of the rotary stage 36. FIG. 8 shows an example thereof. In this case, the laser irradiation path on the samples 22 and 23 moves in a circle in the analysis. Further, by moving the entire analysis cell 1 with the cell moving mechanism 11, the irradiation position of the laser light can be appropriately moved from the rotation center of the rotary stage 36. Therefore, data at an arbitrary position on the surface of each sample 22 and 23 can be obtained.
[0043]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the elemental analysis method and apparatus which can carry out elemental analysis of the substance which is not solid in a normal state or a powdery substance with a laser beam breakdown spectroscopy analysis stably with sufficient reproducibility can be provided.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an elemental analyzer according to an embodiment of the present invention.
FIG. 2 is a graph for explaining the operation of the elemental analyzer according to the embodiment of the present invention.
FIG. 3 is a cross-sectional view showing another example of sample placement in the elemental analyzer according to the embodiment of the present invention.
FIG. 4 is a perspective view showing a method for irradiating a sample with a laser according to an embodiment of the present invention.
FIG. 5 is a perspective view showing another example of a laser irradiation method for a sample according to an embodiment of the present invention.
FIG. 6 is a flowchart showing an example of a sample preparation procedure in the embodiment of the present invention.
FIG. 7 is a sectional view showing still another example of sample setting in the elemental analyzer according to the embodiment of the present invention.
FIG. 8 is a perspective view showing still another example of a method for irradiating a sample with a laser according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Analysis cell, 1a ... Sample, 2 ... Laser oscillator, 3 ... Spectroscope, 4 ... Fluorescence detector, 5 ... Internal observation camera, 6 ... Data recording device, 6a ... Timing control signal, 7 ... Timing controller, 7a ... Laser control signal, 7b ... detection control signal, 8 ... laser beam introduction window, 9 ... internal observation window, 10 ... vacuum pump, 11 ... cell moving mechanism, 12 ... sample cooling stage, 13 ... chiller, 14 ... laser power supply, 15 ... Pulse laser light, 16 ... Boxcar integrator, 16a ... Fluorescence signal, 17 ... Fluorescence, 18 ... Total reflection mirror, 19 ... Scraper mirror, 20 ... Analysis cell exhaust system, 20a ... Laser light condensing lens, 20b ... Fluorescence Condensing lens, 21 ... plasma, 22 ... standard sample, 23 ... analytical sample, 26 ... master clock signal, 27 ... laser oscillator timing signal, 28 ... fluorescence signal, 29 ... Optical measurement timing signal, 30 ... fluorescence measurement gate width, 31 ... sample frame, 32 ... laser beam irradiation path, 33 ... grinding mill, 34 ... plastic bag, 35 ... press frame, 36 ... rotary stage.

Claims (8)

An analysis cell for holding a sample obtained by cooling and solidifying a substance to be elementally analyzed, an exhaust device for evacuating the analysis cell to a low vacuum level of about 1 Pa, a laser oscillator for generating pulsed laser light, and the pulse An optical system that condenses and irradiates the sample with laser light, and detects fluorescence emitted from plasma generated by the sample upon receiving the pulsed laser light, and configures the substance from the wavelength and intensity of the detected fluorescence. An elemental analyzer comprising: a fluorescence spectroscopic measuring means for determining an element and its content.   2. The element analysis apparatus according to claim 1, wherein the fluorescence spectroscopic measurement means performs gate processing on the detected fluorescence signal at a time unique to each target element in synchronization with the irradiation time of the pulse laser beam.   The elemental analysis apparatus according to claim 1, further comprising a cell moving mechanism that moves the analysis cell to move a laser light irradiation position of the sample.   The element analysis apparatus according to claim 3, wherein the analysis cell holds a plurality of samples, and the cell moving mechanism operates so that the plurality of samples are alternately irradiated with laser light. Elemental analyzer according to claim 1, characterized in that it comprises a cooling equipment for cooling the sample. A sample obtained by cooling and solidifying a substance to be subjected to elemental analysis is irradiated with pulsed laser light in an atmosphere evacuated to a low vacuum level of about 1 Pa, and the wavelength of fluorescence emitted from the plasma generated by the irradiation is determined. An elemental analysis method characterized in that an element constituting the substance and its content are determined by measuring strength. The elemental analysis method according to claim 6, wherein the content of the element to be analyzed is corrected by the emission intensity of the plasma or the emission line intensity of the specific element. The elemental analysis method according to claim 6, wherein the substance is a powder having a non-constant particle size, and the sample is formed by pulverizing the substance into a fine powder, pressing, and solidifying by cooling.

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