JP2004205266A - Element analysis method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To analyze an element of a substance that is not solid in a normal state or a substance in a powder shape with improved reproducibility by a laser beam breakdown spectrochemical analysis. <P>SOLUTION: An element analysis apparatus comprises an analysis cell 1 for retaining a sample 1a, where a substance to be subjected to an element analysis is cooled and solidified; a laser oscillator 2 for generating a pulse laser beam 15; a total reflection mirror 18 and a laser beam condensation lens 20a for condensing and applying the pulse laser beams 15 to the sample 1a; a spectrograph 3 for detecting fluorescence 17 being discharged from plasma 21 that is generated by the sample 1a by receiving the pulse laser beams 15, and obtaining elements for composing the substance and the content according to the wavelength and intensity of the detected fluorescence 17; a fluorescence detector 4; and a boxcar integrator 16. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for irradiating a sample with laser light, measuring fluorescence emitted from plasma generated at that time, and detecting and quantifying elements contained in the sample.
[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 controlling impurity elements contained in cooling water and components of exhaust gas generated from a prime mover.
[0003]
These elemental analysis techniques include X-ray fluorescence analysis and inductively coupled plasma emission analysis, and a new technique using laser light includes laser-induced breakdown (LIB) spectroscopy (Patent Documents 1 and 2 below). reference). This analysis method is for spectrally analyzing light generated from plasma generated by converging and irradiating a pulsed laser beam onto an analysis sample, and has the advantage that it can be easily applied to various types of elemental analysis.
[0004]
[Patent Document 1]
JP-A-11-31606 [Patent Document 2]
Japanese Patent Application Laid-Open No. 2000-121558
[Problems to be solved by the invention]
In the conventional laser beam breakdown analysis, fluorescence emitted from an element is measured. Although this method is simple, the intensity of occurrence of laser beam breakdown varies greatly depending on the form of the sample, and the intensity of the generated fluorescent light varies greatly, causing problems in measurement accuracy and reproducibility. In particular, it is not possible to directly measure a substance having a powder form, a fluid form, or a clay form such as liquid or soil.
[0006]
The present invention has been made in view of such problems, and an elemental analysis method capable of stably and reproducibly performing elemental analysis of a substance that is not a solid or a powdery substance in a normal state by laser beam breakdown spectroscopy. And an apparatus.
[0007]
[Means for Solving the Problems]
The invention according to claim 1 is an elemental analyzer, comprising: an analysis cell for holding a sample formed by cooling and solidifying a substance to be subjected to elemental analysis; a laser oscillator for generating pulsed laser light; and collecting the pulsed laser light on the sample. An optical system for irradiating light, the sample detects fluorescence emitted from plasma generated by receiving the pulsed laser beam, and obtains an element constituting the substance and its content from the wavelength and intensity of the detected fluorescence. And a fluorescence spectrometer.
[0008]
According to a second aspect of the present invention, the fluorescence spectrometer is configured to gate the detected fluorescence signal at a time unique to each target element in synchronization with the irradiation time of the pulsed laser light.
[0009]
The invention according to claim 3 is configured to include a cell moving mechanism for moving the analysis cell to move a laser beam 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 such that the plurality of samples are alternately irradiated with laser light.
[0010]
The invention according to claim 5 is configured to include a cooling device for cooling the sample and an exhaust device for evacuating the inside of the analysis cell.
The invention according to claim 6 is an elemental analysis method in which a sample obtained by cooling and solidifying a substance to be subjected to elemental analysis is irradiated with pulsed laser light, and the wavelength and intensity of fluorescence emitted from plasma generated by the irradiation are measured. In this manner, the elements constituting the substance and the content thereof are determined.
[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.
The invention according to claim 8 is configured such that the substance is a powder having a non-uniform particle size, and the sample is formed by pulverizing the substance into fine powder, pressing, and cooling and solidifying.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an elemental analyzer according to the present invention will be described with reference to the drawings. As shown in FIG. 1, the elemental analyzer of the present embodiment includes, as main components, 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, A timing controller 7 is provided.
[0013]
The analysis cell 1 has a laser light introduction window 8 and an internal observation window 9, is connected to a vacuum pump 10, and is mounted 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]
The timing controller 7 outputs a laser control signal 7 a that defines the timing at which the laser oscillator 2 oscillates the pulsed laser beam 15 for laser beam breakdown. Further, a detection control signal 7b 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 1a is placed on the sample cooling stage 12 in the sealable analysis cell 1. The inside of the analysis cell 1 is evacuated by a vacuum pump 10. The whole analysis cell 1 is provided on a cell moving mechanism 11 so that the laser irradiation position on the sample 1a can always move to a place where the laser irradiation is not performed. As the cell moving mechanism 11, a normal XY stage can be applied. In this case, a plurality of samples are arranged in parallel, and a plurality of samples can be measured at the same time. Of course, for example, a rotary stage or the like may be applied other than the XY stage.
[0016]
As the optical system, a total reflection mirror 18, a scraper mirror 19 with holes, and condenser lenses 20a and 20b are provided. After passing through the hole of the scraper mirror 19, the pulse laser beam 15 for laser beam breakdown is applied to the sample 1a in the analysis cell 1 by the condenser lens 20a.
[0017]
The fluorescent light 17 generated from the plasma 21 generated by the laser irradiation is converted into a parallel beam by a laser light collecting lens 20a, reflected by a scraper mirror 19, collected by a fluorescent light collecting lens 20b, and condensed by a spectroscope 3. Be guided. The fluorescence separated by the spectroscope 3 is further guided to the fluorescence detector 4 and converted into an electric signal. The electric 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 the analysis target is a liquid or a viscous substance, it is cooled and solidified to a temperature below the freezing point to obtain a sample 1a, and the sample 1a is turned into a plasma by irradiating a laser beam in a solid state. In order to generate stable plasma 21, it is necessary to keep the sample surface stationary. However, when the analysis target is a liquid or a viscous substance, the surface of the laser light irradiation surface fluctuates, so that the solid Is effective.
[0019]
As the chiller 13 for cooling and solidifying the sample 1a, there are devices such as refrigerant cooling using dry ice or liquid nitrogen or electronic cooling using a Peltier cooling element. For liquids having a melting point of about minus 20 degrees C or higher, the use of a Peltier cooling element is the simplest.
[0020]
Further, in the present embodiment, by evacuating the inside of the analysis cell 1 by the vacuum pump 10, the generation of the plasma 21 by the irradiation of the laser beam 15 can be stabilized. As for the degree of vacuum, a low degree of vacuum of about 1 Pa that can be evacuated by a rotary pump is sufficient. With this evacuation, it is possible to measure a sample that needs to be quantified for nitrogen even if it cannot be measured in the atmosphere 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 reduced, and the background light intensity can be reduced by the plasma 21 to measure a low background.
[0021]
As described above, in the present embodiment, the cell moving mechanism 11 for externally driving the analysis cell 1 holding the sample 1a is provided. When the sample 1a is irradiated with the laser beam 15, the elements existing on the surface are instantaneously vaporized, and a part thereof is turned into plasma. If this laser beam brazing phenomenon is continued, the surface of the sample is slightly scraped. As a result, when the surface unevenness changes, the state of generation of the generated plasma 21 also changes. For this reason, it is necessary to sequentially change the laser beam irradiation point in order to measure the elements constituting the sample on average.
[0022]
When the element to be detected is non-uniformly present in the sample, the average can be detected by moving the sample and performing continuous measurement as in the present embodiment. The size of the focal point of the laser beam is several μm to several tens μm, but depending on the sample, a concave portion of the order of 100 μm is formed by laser irradiation. Therefore, the moving speed of the sample needs to be 100 μ / pulse or more.
[0023]
Now, for example, when a YAG laser beam having a pulse energy of about 10 mJ and a pulse width of 5 ns is considered, the output is a 2 MW pulse output. When the pulsed laser beam 15 is condensed and irradiated on the sample 1a, a so-called breakdown occurs, and the sample in the irradiated area is ionized to become plasma 21.
[0024]
The recombination of the plasma 21 caused by this laser beam irradiation starts when the irradiation of the pulse laser beam 15 is completed, and the constituent elements of the irradiated sample become excited atoms during several μsec to several tens μsec. When the atoms in the state transition to the lower level, they emit fluorescence 17 proportional to the number of atoms. When quantifying the target element from the sample 1a, a high analysis accuracy can be obtained by capturing a predetermined component of the fluorescence 17 emitted from the plasma 21.
[0025]
The signal processing in the element analyzer 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 constant delay time Δt1 with respect to the master clock signal 26 from the timing controller 7 which oscillates at a constant frequency.
[0026]
The signal 28 of the fluorescent light 17 which is generated by irradiation of the pulsed laser light 15 emitted by the laser oscillation signal 27 and changes with time has a delay time Δt2 appropriately set in the time function, and the fluorescent light is included in the detection control signal 7b. The signal measurement gate signal 29 is output, and the fluorescence signal 28 is measured by the lock-in amplifier and the boxcar integrator 16 in this time zone.
[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 life of fluorescence generation, a smaller time delay Δt2 and a smaller gate width 30 can perform a measurement with a higher S / N ratio. Conversely, for atoms having a long excitation lifetime, a larger time delay Δt2 and a larger gate width 30 allow measurement with a higher S / N ratio.
[0028]
As described above, in the present embodiment, the fluorescence signal 28 detected by the fluorescence detector 4 is processed by a time gate unique to each target element in synchronization with the irradiation time of the laser light 15. This makes it possible to measure a high S / N ratio for elements having different fluorescence lifetimes.
[0029]
A spectrometer is generally used for fluorescence measurement, but if only a specific element is to be measured, measurement using a photomultiplier tube provided with an interference filter is also possible. In addition, the content of the element to be detected in the sample is analyzed by the measurement in parallel with the standard sample at the intensity ratio of the wavelength. Here, a YAG laser is taken as an example of the laser oscillator, but a laser such as an excimer laser can also be used as long as it is a pulsed laser light capable of laser light 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 depend on fluctuations in the output of the laser light 15, the amount of elements emitted from the surface of the sample 1a, and fine irregularities on the surface of the sample 1a. Affected.
[0031]
In general, the size and temperature of the plasma 21 generated by the laser light 15 are proportional to the intensity of the white light or the emission line intensity of the specific element due to the black body radiation generated from the plasma 21. Therefore, in order to reduce the variation in the measurement, the fluorescence or ion signal from the element to be analyzed is corrected by the fluctuation of the plasma generation amount for each laser light pulse. When the quantified pure water was used for freezing and fixing of the sample 1a, hydrogen Hα (656.2 nm), Hβ (486.1 nm), Hγ (434.0 nm), and Hδ (410.2 nm) were used as standard lines for plasma generation. It is better to use a line such as nm).
[0032]
Another example of the arrangement of the sample and the laser irradiation method in the present embodiment will be described with reference to FIGS. That is, as shown in FIG. 3, a standard sample 22 and an analysis sample 23 are placed side by side in the analysis cell 1 as samples, and these are set on a sample cooling stage 12 that can be cooled.
[0033]
When performing elemental analysis measurement, the analysis cell 1 is evacuated by the vacuum pump 10 and the entire analysis cell 1 is moved by the cell moving mechanism 11 so that the laser irradiation positions on the samples 22 and 23 always emit laser light. Measure while moving to a place not yet received. FIG. 4 shows an example of such a case. In this case, a large amount of data can be obtained with a small sample by continuously moving the laser irradiation path 32 on the samples 22 and 23 as a single stroke during analysis. be able to.
[0034]
When measuring the ratio of a specific element, an accurate ratio can be obtained by tracing the measurement of the standard sample 22 and the analysis sample 23 alternately as shown in FIG.
[0035]
As described above, a plurality of samples are loaded in the analysis cell 1, and the analysis sample 23 is simultaneously or alternately measured with the standard sample 22 having a known content of the element to be measured. The content of the contained element can be quickly quantified.
[0036]
When the substance to be analyzed is a powder, it is also effective to mix and fix a fixing material to obtain a sample. In this case, as a method of freezing and solidifying, if there is moisture in the substance to be analyzed, it can be frozen as it is, and when the moisture is insufficient for solidification, a method of adding a fixed amount of pure water and solidifying is simple. is there.
[0037]
An example of a method for preparing such a sample will be described with reference to FIG. That is, the powdery substance to be analyzed is reduced to a particle size of about 10 μm to 100 μm or less by the pulverizing mill 33 in order to make the particle diameter uniform (step (2)). There is no problem if the particle size of the clay-like substance is as large as above, but if particles having a particle size of 100 μm or more are present, it is also necessary to carry out a pulverizing treatment with a mill or the like.
[0038]
Next, the substance to be analyzed is packed in a press frame 35 corresponding to 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 at pressures in this range.
[0039]
Depending on the state of solidification of the substance to be analyzed by the press, by adding water as a binder for the particles (step (3)), solidification is promoted during cooling, and a sample with less variation in plasma generation by laser irradiation can be prepared. . When the substance to be analyzed contains a large amount of water, it is preferable to dry the substance to the extent that it can be pressed. Then, the sample is flattened and placed on the sample cooling stage 12.
[0040]
As described above, when the substance to be analyzed is a powder like soil and the particle size is not constant, the substance to be analyzed is finely pulverized by a mill in advance, and then pressed and measured. Can be generated stably, and the variation in measurement 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 the present embodiment will be described with reference to FIGS. That is, as shown in FIG. 7, a standard sample 22 and an analysis sample 23 are placed side by side in the analysis cell 1 as samples, and these are set on a rotatable stage 36 that can be cooled.
[0042]
When performing 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 for measurement. FIG. 8 shows an example thereof. In this case, the laser irradiation paths on the samples 22 and 23 move in a circle during the analysis. In addition, by moving the entire analysis cell 1 by the cell moving mechanism 11, the irradiation position of the laser beam can be appropriately moved from the rotation center of the rotary stage 36. Therefore, data at an arbitrary position on the surface of each of the samples 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 stably perform elemental analysis with good reproducibility by laser beam breakdown spectroscopy on a substance which is not a solid in normal state or a powdery substance can be provided.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an element analysis device according to an embodiment of the present invention.
FIG. 2 is a graph illustrating an operation of the elemental analysis device according to the embodiment of the present invention.
FIG. 3 is a cross-sectional view showing another example of sample installation in the element 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 method for irradiating a sample with a laser according to an embodiment of the present invention.
FIG. 6 is a flowchart showing an example of a procedure for preparing a sample in the embodiment of the present invention.
FIG. 7 is a cross-sectional view showing still another example of sample installation in the element 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 light 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 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 formed by cooling and solidifying a substance to be subjected to elemental analysis, a laser oscillator for generating pulsed laser light, an optical system for condensing and irradiating the sample with the pulsed laser light, and A fluorescence spectrometer for detecting the fluorescence emitted from the plasma generated by receiving the laser beam, and determining the elements constituting the substance and the content thereof from the wavelength and intensity of the detected fluorescence. Elemental analyzer that features: 2. The element analyzer according to claim 1, wherein the fluorescence spectrometer measures a gate of the detected fluorescence signal at a specific time for each target element in synchronization with the irradiation time of the pulse laser beam. The element analyzer according to claim 1, further comprising: a cell moving mechanism that moves the analysis cell to move a laser beam irradiation position of the sample. The element analyzer 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 irradiated with laser light alternately. The element analyzer according to claim 1, further comprising a cooling device for cooling the sample, and an exhaust device for evacuating the inside of the analysis cell. By irradiating the sample obtained by cooling and solidifying the substance to be subjected to elemental analysis with pulsed laser light, and measuring the wavelength and intensity of the fluorescence emitted from the plasma generated by the irradiation, the elements constituting the substance and the content thereof An elemental analysis method characterized by determining an amount. The element analysis method according to claim 6, wherein the content of the element to be analyzed is corrected based on the emission intensity of the plasma or the emission line intensity of the specific element. 7. The elemental analysis method according to claim 6, wherein the substance is a powder having a non-uniform particle size, and the sample is formed by pulverizing the substance into fine powder, pressing, and solidifying by cooling.

Images