JP3554809B2 - Method for analyzing fine particles using a fine particle component analyzer - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for analyzing fine particles using microwave induced plasma for analyzing the components of fine particles, and more particularly to an analysis method for improving measurement accuracy.
[0002]
[Prior art]
For example, fine particles floating in the atmosphere are sucked together with air, the fine particles are collected on a filter, and the number and size of elements constituting the fine particles are measured using microwave induced plasma.
[0003]
In this measuring method, the element type and the particle size of the element are known in advance using a scanning microscope (SEM) or transmission electron microscopy (TEM), and then the element is subjected to microwave induction. The light is emitted by a plasma analyzer, and the emission intensity is converted into an electric signal by a photoelectric converter and output. FIG. 6 shows the number on the vertical axis and the output voltage on the horizontal axis. The hatched bar graph shows an example of the particle size distribution of a commercially available element having a nominal diameter of 5 μm measured by SEM. It can be seen that although the nominal value is 5 μm, it actually varies.
[0004]
The black bar graph in FIG. 6 shows the distribution of the output when the elements of the bar graph shown by the oblique lines measured by SEM are emitted by the plasma analyzer and the emission intensity is converted into an electric signal by the photoelectric converter. According to the figure, the graph shows a distribution similar to that measured by SEM. This indicates that, for example, the output of the element having a diameter of 5 μm is 5 V, and in this case, the conversion coefficient is (5 V / 5 μm) = 1.
[0005]
Therefore, when the type of the element is known and the particle size is unknown under the same conditions, if the result is as shown in FIG. 6, the one having an output of 1 V is estimated to have a diameter of 1 μm. When the output of another element having a diameter of 5 μm is, for example, 4 V (even if the diameter is the same, the emission intensity varies depending on the type of the element), the conversion factor of the element (4 V / 5 μm) is 0.8. In such a case, the diameter of the element with an output of 1 V is estimated to be 1.25 μm.
[0006]
Not only when using microwave-induced plasma but also when emitting light from an element, the device emits light at a plurality of specific wavelengths with different emission intensities. Is measured in accordance with the wavelength at which the maximum output is obtained.
As an example, calcium (Ca) has the highest emission intensity when the wavelength of 393.37 nm is selected, and the emission intensity is lower when the wavelength of 422.67 nm is selected than in the case of the wavelength of 393.37 nm.
[0007]
[Problems to be solved by the invention]
By the way, when it is difficult to obtain a particle having a small emission diameter and a known element having a high emission intensity, the output is not saturated by adjusting the acceleration voltage of an electron multiplier as a photoelectric converter (for example, When the measurement span is set to 10 V, there is a case where the range exceeds this range.)
[0008]
However, when the particle size is determined at a wavelength where the emission intensity is low, there is a problem in that a particle having a small particle size has low sensitivity and is difficult to measure.
The present invention has been made in order to solve the above-mentioned problem. A sensitivity gradient is obtained based on at least two wavelengths at which the output is saturated and at least two wavelengths at which the output is not saturated. An object of the present invention is to accurately measure a particle having a small particle size by obtaining a conversion coefficient at a wavelength.
[0009]
[Means for Solving the Problems]
The configuration of the present invention for solving the above-mentioned problems, the microparticles are atomized and ionized using microwave induction plasma to excite and emit light, and convert a plurality of emitted lights having different wavelengths into electrical signals, emission wavelength of the fine particles, in the analysis method of the fine particles with a particle component analysis device for identifying ingredient particulates from the number and emission intensity for light-emitting, upon obtaining the conversion factor between the diameter and the electric signal of the fine particles, one element A method for determining a sensitivity ratio using at least two wavelengths emitted by the element, and determining a conversion coefficient based on the sensitivity ratio.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
First, a particle component analyzer using microwave induction plasma used in the present invention will be briefly described with reference to FIG.
In FIG. 3, reference numeral 51 denotes a disperser, in which a filter 52 to which solid fine particles (not shown) to be measured are attached is disposed. Numeral 53 denotes an aspirator arranged in the disperser 1 and sucks solid fine particles attached to the filter 52 and supplies the solid fine particles to the reaction tube 54. The inside of the disperser 51 is maintained at a pressure slightly higher than the atmospheric pressure by introducing He gas after air is exhausted by a suction pump (not shown). 55 is a microwave source, and 56 is a cavity into which the microwave from the microwave source 55 is introduced.
[0011]
Reference numeral 57 denotes a detection window provided at the other end of the reaction tube 54. Reference numeral 60 denotes a signal processing unit in which four spectrometers 59 that receive light via four optical fibers 58, respectively, and a CPU to which outputs of these spectrometers are input are arranged.
[0012]
In the above configuration, when a microwave having a frequency of 2.45 GHz is guided from the microwave source 55 into the cavity 56, a plasma of about 4000 ° K is generated in the reaction tube 54. On the other hand, the solid fine particles guided into the reaction tube 54 from the disperser 51 are atomized and ionized in the plasma, and further emit light when excited and fall to the ground state.
[0013]
This emission spectrum is taken out of the reaction tube 54 in the axial direction, collected through the optical window 57, then separated by the spectroscope 59, processed by the CPU of the signal processing 60, and measured and displayed in the sample. . Here, the sample is not necessarily spherical, but the emission intensity of a spherical sample of the same element and a known size is measured in advance, and the equivalent particle size is calculated based on the measured value of the known sample. It is output.
[0014]
Note that the subsequent stage of the spectroscope 59 has a photomultiplier tube and outputting an electrical signal corresponding to the intensity of light of a selected wavelength (not shown), the size of the fine particles amplifier output signal Classified according to size .
[0015]
The filter 52 has a predetermined area, and the aspirator 53 scans the filter 52 a plurality of times as shown in FIG. 4, and is configured to inhale the same amount of fine particles each time.
[0016]
Also, in this apparatus, it is assumed that fine particles composed of a plurality of elements are distributed on the filter at the same ratio. It is assumed that the number of elements sucked by the plurality of scans is always the same ratio, and that a spectrometer is set to one wavelength for each scan and analyzes one element.
[0017]
FIG. 5 shows the emission timing when analyzing the fine particles with the measurement wavelengths of the four spectrometers set to the wavelengths of Ni, Cu, Fe, and A1, where Ni and Fe emit light simultaneously. This indicates that two elements exist in one fine particle.
The present invention relates to a conversion coefficient for determining the relationship between the emission intensity and output of each element prior to analyzing the type and size of such an element.
[0018]
FIG. 1 shows a method for obtaining a conversion coefficient of calcium (Ca) using the apparatus shown in FIG. 3, for example, where calcium (Ca) fine particles (for example, 5 μm) adhere to a filter of the above-mentioned fine particle analyzer. Let it. Then, the measurement wavelength of one of the two spectroscopes is set to 393.37 nm, which is the wavelength of the maximum emission intensity of Ca, and the other measurement wavelength is set to 422, 67 nm, which is the emission length of low intensity.
[0019]
As schematically shown in FIG . 1, No. Wavelength set at 2 spectrometer (λ1, λ2) output is detected at the same time at a set wavelength into two spectrometers. Here, λ1 is set to a wavelength having a high emission intensity, and λ2 is set to a wavelength having a low emission intensity. It should be noted that the figure shows a part of a typical output, and a large number of signals having different levels are actually output.
[0020]
As can be seen, the two spectrometers output signals at a fixed ratio. Here, the portion surrounded by A indicates that the signal is saturated. FIG. 2 is a plot of the signal shown in FIG. 1, and it can be seen here that the wavelength of λ1 emits light with twice the emission intensity as the wavelength of λ2. From this, the sensitivity ratio between λ1 and λ2 can be obtained.
[0021]
Then, in the actual measurement, the set wavelength of Ca is set to λ1, and the conversion coefficient set based on the wavelength of λ2 is multiplied by 2 to set the conversion coefficient. it can.
[0022]
It should be noted that the foregoing description of the invention merely illustrates certain preferred embodiments for purposes of explanation and illustration. Thus, it will be apparent to one skilled in the art that the present invention may be modified or modified in many ways without departing from its essentials. For example, the element to be measured is not limited to Ca, but may be applied to any element having a strong luminescence intensity, the peak portion of which is over-ranged, and an output having a low luminescence intensity at a lower wavelength.
[0023]
【The invention's effect】
According to the present invention as described in detail above, microparticles are atomized and ionized using microwave induction plasma to excite and emit light, a plurality of emitted lights having different wavelengths are converted into electric signals, and a plurality of using particulate component analyzer performs a particular element, the emission wavelength of the fine particles, in the analysis method of the fine particles with a particle component analysis device for identifying ingredient particulates from the number and emission intensity for light emission, and the diameter of the fine particles When obtaining the conversion coefficient with respect to an electric signal, the conversion coefficient is obtained using at least two wavelengths emitted by one element for one element, so that a particle having a small particle size can be measured with high accuracy.
[Brief description of the drawings]
FIG. 1 is a diagram showing a difference in output level when two spectroscopes receive light of the same element at different wavelengths.
FIG. 2 is a diagram for obtaining a sensitivity ratio between a strong wavelength and a weak wavelength of light emission intensity.
FIG. 3 is a configuration explanatory view of a particle analyzer used for describing the present invention.
FIG. 4 is a diagram showing a state in which an aspirator scans on a filter.
FIG. 5 is a diagram illustrating an example of emission timing of an element having a set wavelength when four spectroscopes are used.
FIG. 6 is a diagram comparing the particle size measured using an SEM, a TEM, or the like with the output of an analyzer.
[Explanation of symbols]
51 Disperser 52 Filter 53 Aspirator 54 Reaction tube 55 Microwave source 56 Cavity 57 Optical window 59 Spectroscope 60 Signal processing unit

Claims (2)

The microparticles are atomized and ionized using microwave induction plasma to excite and emit light, a plurality of lights having different emitted wavelengths are converted into electric signals, and the emission wavelength of the particles, the number of times of light emission and the intensity of light emission are determined. in the analysis method of the fine particles with a particle component analysis device for identifying ingredient particulate, upon obtaining the conversion factor between the diameter and the electric signal of the fine particles, using at least two wavelengths the element emitted for one element A method for analyzing fine particles, wherein a sensitivity ratio is determined, and a conversion coefficient is determined based on the sensitivity ratio. 2. The method for analyzing fine particles according to claim 1, wherein two wavelengths for obtaining the conversion coefficient are a wavelength that emits the strongest light with the same particle diameter and a wavelength that emits the light with the second largest light intensity.

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