JP5355269B2 - Measuring method of particle size of dispersed particles in solid materials by micro Raman spectroscopy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring method using a microscopic Raman spectroscopy, capable of quantitatively measuring a particle size of a particle in a solid material. <P>SOLUTION: The method for measuring the particle size of the particle includes the first step of acquiring a specific Raman shift in the particle dispersed in the solid material, the second step of conducting the microscopic Raman spectroscopy for the solid material and performing a binarizing Raman chemical imaging on the basis of a prescribed Raman intensity threshold at the specific Raman shift for the particle, and the third step of calculating the particle size of the particle from a Raman chemical image obtained by the second step. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for measuring the particle size of dispersed particles in a solid material by microscopic Raman spectroscopy. More specifically, the present invention relates to a method for measuring the particle size of dispersed particles in a solid material by setting a threshold value of peak intensity at a peak specific to the Raman spectrum of particles in micro Raman spectroscopy.

  As a method for measuring the particle diameter of particles in a gas or liquid material, for example, a light scattering method, a laser diffraction method, a centrifugal sedimentation method and the like are widely known. However, the measurement of the particle size of micron-order particles in a solid material is performed by imaging the particles to be measured by ordinary image capturing or the like, and therefore cannot be performed when it cannot be apparently distinguished from other components. Further, in order to measure the particle size based on the physicochemical properties, the solid material is pulverized or dissolved in a liquid to obtain a gas or liquid material. The possibility that the particle size has changed during the dissolution process is strongly suspected. Therefore, there is a need for a method for measuring the particle size of micron-order particles in a solid material nondestructively, that is, as the solid material itself, based on the physicochemical properties of the particles.

  As one of such measurement methods, by performing microscopic Raman spectroscopic measurement, based on the specific Raman shift region of the spectrum obtained or the peak intensity and area in the Raman shift, There is a method for obtaining a Raman chemical image and determining the particle size from the image.

  Microscopic Raman spectroscopic measurement uses the Raman effect to measure a weak scattering spectrum caused by a change in polarizability due to vibration between atoms in a molecule, and can measure a spectrum of a substance on the micron order. This measurement can be applied to any state, for example, a gas (liquid) or solid material (sample), and is used for composition or impurity analysis of the material, or identification of a chemical substance in the material. In particular, in the case of a solid material, component analysis of the solid material surface and inside can be performed by microscopic Raman spectroscopic measurement, and the chemical bonding state can be analyzed from the Raman shift, and thus the molecular structure can be analyzed.

  For example, as a particle size measurement method using micro-Raman spectroscopy, a method for detecting the presence or absence of particles by a mathematical algorithm (multivariate analysis) of a peak pattern has been proposed (Non-Patent Document 1).

"Drug Characterization in Low Dosage Pharmaceutical Tablets Using Raman Microscopic Mapping", Applied Spectroscopy, Vol.60, No.11. 2006, p1247-1255

  However, since the above proposal is an analytical solution in which the peak intensity of the spectrum of each component is corrected for sensitivity, it does not necessarily reflect the true value. In addition, since the result is obtained qualitatively, for example, a particle diameter of 10 μm or less cannot be accurately measured.

  Thus, there is not yet a sufficiently specific and useful technique for measuring the particle size of micron-order particles in solid materials based on the physicochemical properties of the particles. Accordingly, an object of the present invention is to provide a measurement method capable of accurately and quantitatively measuring the particle size of particles in a solid material using micro Raman spectroscopy.

  The present inventor pays attention to the fact that it directly affects the spot diameter on the laser sample surface and the peak intensity of the Raman spectrum that can be submerged, and as a result of earnest research, surprisingly, the threshold value of the peak intensity is set. As a result, the inventors have found that the particle size of the particles in the solid material can be quantitatively measured, and have reached the present invention.

  That is, in the first aspect, the present invention is a method for measuring the particle size of particles dispersed in a solid material by microscopic Raman spectroscopy, the first step of obtaining a Raman shift specific to the particles, and the solid A second step of subjecting the material to microscopic Raman spectroscopic measurement and performing binarized Raman chemical imaging based on a predetermined Raman intensity threshold at a Raman shift specific to the particles; and the Raman chemical obtained in the second step There is provided a particle size measuring method including a third step of calculating the particle size of the particle from an image.

  The particle diameter measuring method by micro Raman spectroscopy of the present invention has the following effects. (1) The particle size of the particles in the solid material can be quantitatively measured. (2) The particle size can be measured quantitatively by a simple method of setting a peak intensity threshold specific to the Raman spectrum of the particles. (3) The particle size can be measured by microscopic Raman spectroscopy at a level of 1 to 5 μm, for example, with a spatial resolution substantially the same as that of a stereomicroscope. (4) Even if the maximum peak intensity in the observation region is small, the measurement can be performed by appropriately correcting the threshold value.

It is a Raman spectrum of a polystyrene particle. Fig. 2 is a CCD image (left) and Raman chemical image (right) of an optical microscope of drug substance particles before formulation. 2 is a Raman chemical image of 5, 10, and 15 μm polystyrene particles in tablets in Example 1. FIG. Aggregated parts are seen in the Raman chemical image of 5 μm particles. It is a Raman spectrum of main compounding ingredients other than the main ingredient ingredient in Example 2, and the main ingredient ingredient in a tablet. It is a Raman spectrum of magnesium stearate, lactose, D-mannitol, hydroxypropyl cellulose, and ebastine in order from the top.

  Embodiments of the present invention will be described below. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

In the present invention, the solid material may be solid at the time of measurement, and is not limited to an inorganic material or an organic material. This is preferably an organic material from the viewpoint of ease of sample preparation. Examples of the solid material include tablets such as pharmaceuticals and foods that can obtain a smooth surface by cutting or polishing.
In the present invention, the particles are applied to solid particles and are not limited to inorganic or organic substances. Preferably this is a solid organic particle. As an example of particle | grains, the main ingredient component in tablets, such as a pharmaceutical, etc. are mentioned, for example.

  In the present invention, the particle diameter includes, for example, a minor axis diameter, a major axis diameter, a biaxial average diameter, a circular area equivalent diameter, a constant direction diameter, or a constant direction area divided diameter, and which one is measured is measured. Those skilled in the art can appropriately determine the purpose and software used for particle size calculation. Typically, a circular area equivalent diameter, a constant direction diameter, or a constant direction area equal diameter, particularly preferably a circular area equivalent diameter is measured as a particle diameter.

  The particle size range that can be measured in the method of the present invention is determined in consideration of the resolution of both the microscope and the microscopic Raman spectroscope to be used, and is, for example, about 0.1 μm or more, typically about 0.5 to 1000 μm. The thickness is preferably about 1 to 100 μm, more preferably about 1 to 50 μm, but is not limited to such a range. When the stereomicroscope provided in the microscopic Raman spectroscopic apparatus has a spatial resolution of, for example, 0.5 to 5 μm, and the microscopic Raman spectroscopy has a spatial resolution of about 0.5 to 1 μm, It is possible to measure a particle size of 0.5 μm or more, for example 1 μm or more. Further, by using a microscope and a microscopic Raman spectroscopic device with higher spatial resolution, the method of the present invention can measure the particle size of particles having a particle size smaller than the measurable particle size range. .

When obtaining the average particle diameter such as the number average particle diameter (D ₅₀ ), the number of measurement is preferably 100 or more, more preferably 200 or 300, more statistically. When determining the average particle diameter, the average particle diameter closer to the true value can be obtained by measuring a large number of particles at different measurement locations. The average particle diameter calculated primarily by the method of the present invention is the number average particle diameter. However, mathematical processing is performed using, for example, a calculation software program, and other averages such as volume average, Harmonic averages can also be obtained.

In the first step of the process according to the invention, a Raman shift specific for the particles is obtained. As used herein, “particle-specific Raman shift” means that other components other than particles in the solid material have no or substantially no intensity peak, but the particle component has an intensity peak. (Raman shift, unit: cm ⁻¹ ) or a range thereof from a Rayleigh line having The absence of an intensity peak means that the peak intensity at a certain Raman shift is approximately equal to or less than the background value of the peak intensity, typically 105% or less of the background value. Also, having substantially no intensity peak means, for example, that when a Raman spectrum of a solid material containing particles and a solid material containing all components other than particles in the same content ratio is measured, the particles at a certain Raman shift are included. Means that the peak intensity of the solid material that is not present is 50% or less, preferably 30% or less, more preferably 20% or less, and most preferably 10% or less of the peak intensity of the solid material containing particles in the Raman shift. .

  Therefore, in the method of the present invention, it is preferable that each component in the solid material is understood to such an extent that a Raman shift specific to particles can be obtained. Typically, the first step includes measuring a Raman spectrum of each component contained in the solid material, and obtaining a Raman shift specific to the particle by comparing the spectra. Alternatively, when a specific Raman shift is foreseeable, for example, when a specific Raman shift is obtained from known information, for example, a database, the present invention is used by using the Raman shift without measuring the Raman spectrum of each component. You may perform the method of.

  Alternatively, when it is unclear what components the solid material contains, the components of the solid material can be analyzed according to conventional methods. Such methods include any method available to those skilled in the art. Those skilled in the art can appropriately select an optimal method for analyzing the components based on the properties of the solid material. Alternatively, when it is known that the unknown component in the solid material is a trace amount, for example, less than about 10% by weight, compared to the particle, the unknown component can be ignored to obtain a specific Raman shift for the particle. Good.

For example, when the solid material is a tablet and the particles are the active ingredient, the tablet usually contains a compound having no benzene ring, such as an excipient, a binder, a lubricant, a disintegrant, and the active ingredient. Since a compound having a benzene ring is usually contained, the 1607 cm ⁻¹ Raman shift derived from the C═C stretching vibration of the benzene ring does not overlap with the Raman shift of the excipient etc. It becomes a shift.

  The second step of the method of the present invention includes subjecting the solid material to microscopic Raman spectroscopic measurement, and the observation position of the solid material may be on the surface or inside of the material. In order to measure the material without breaking it, the surface of the material can be measured. In addition, since it is easy to focus in microscopic Raman spectroscopic measurement, it is desirable that the observation location is a smooth surface. The smooth surface is created by cutting a solid material, for example. For the cutting, a conventionally known cutting technique can be used. Cutting can be performed on any surface of the material, such as a vertical surface, a horizontal surface, and the like. When the solid material is broken by cutting, the solid material can be embedded and fixed with a resin or the like. When the embedding material infiltrates into the solid material, the solid material can be coated with a metal or the like in advance and embedded with a resin or the like. In particular, when the solid material is a tablet, since the tablet is fragile at the time of cutting, for example, after applying a surface metal coat and resin embedding and fixing, it can be cut using a technique such as microtome cutting to obtain a smooth cross section. it can.

  Usable resins include, but are not limited to, a visible light curable resin, an ultraviolet curable resin, or a thermal effect resin. Particularly preferably, the solid material is fixed using a visible light curable resin (for example, trade name: D-800 (Toagosei)) or an ultraviolet curable resin (for example, trade name: A-1864 (Tesque Corporation)). Can do. Also, metals that can be used for coating include, but are not limited to, gold, platinum, silver, aluminum and the like. Particularly preferably, gold can be used to coat the solid material.

  Further, the predetermined Raman intensity threshold in the second step of the present invention directly affects the spot diameter on the sample surface of the laser and the peak intensity of the Raman spectrum that can be submerged in the microscopic Raman spectroscopic measurement. , To reflect the true value. If the set threshold value is too low, more peak intensities in the observation region are captured, so the particle size is larger than the true value. Conversely, if the threshold value set is too high, a smaller peak intensity in the observation region is captured, so the particle size is smaller than the true value. In order to obtain the same particle size as the actual particle size, it is necessary to set an appropriate threshold value.

  Preferably, a predetermined Raman intensity threshold at a particle-specific Raman shift is applied to the particle position and size in a stereomicroscopic image for the particle prior to dispersion in the solid material and to the particle of the microscopic Raman spectrometer. The position and size of the particles in a Raman chemical image with a specific Raman spectrum can be set to overlap (fitting threshold).

  The threshold of the peak intensity when the size of the particle by the stereomicroscope of the particle before the dispersion in the solid material and the size of the particle by the stereomicroscope and the size of the particle at the same position overlap in the Raman chemical image of microscopic Raman spectroscopy. Since the threshold when measuring particles dispersed in the solid material is used, the particle size of the particles dispersed in the solid material measured by microscopic Raman spectroscopy using the threshold is the same as the particle size observed with the stereomicroscope. It is equivalent. When determining the threshold value, it is preferable that fitting is performed on particles before dispersion, for example, 100 to 1000 particles, and an average of the obtained threshold values can be adopted. Usually, a microscopic Raman spectroscopic apparatus is usually provided with a stereomicroscope, so that microscopic observation and Raman chemical imaging can be performed in the same apparatus. Although fitting can be performed visually, it can also be performed using image analysis software or the like.

More preferably, (a) the maximum value of the peak intensity of Raman shift specific to the particle is expressed by the formula (1)
Peak intensity = fitting threshold × 2 / A ² (1)
If the peak intensity value is equal to or greater than the peak intensity value calculated from (1), the fitting threshold is used, or (b) the peak intensity value calculated from the above equation (1) is the peak intensity value in the observation region. If less than, formula (2)
Threshold = maximum peak intensity × (1/2) × A ² (2)
(Here, in the above formulas (1) and (2), A is the spatial resolution in the xy direction of the objective lens used in the microscopic Raman spectroscopic device / the mapping size of the microscopic Raman spectroscopic device)
The threshold value obtained by (Expression (2) threshold value) can be used.

  In the above formula, the maximum peak intensity is the maximum value of the peak intensity of Raman shift specific to particles in the observation region. Further, the peak intensity of the Raman spectrum changes even when the focus in the z direction in the measurement is slightly shifted, so that it is within the focus range up to about (1/2) of the maximum peak intensity. (1/2) in the above formula (2) means this. When performing high-resolution measurement in the z direction, it is desirable to use a high-magnification objective lens.

  A shows the ratio between the mapping size of the microscopic Raman spectroscope and the spatial resolution of the xy plane of the objective lens used. For example, in a typical example, since the spatial resolution in the xy direction of the objective lens used in the optical microscope used is about 0.5 μm and the mapping size of the Raman spectrometer is 1 μm, the ratio A is (1/2). It is. A 0.5 μm square corresponds to ¼ pixel. Here, the mapping is an operation of irradiating a laser at a fixed interval in the xy direction of the observation region and acquiring a Raman spectrum of the irradiated portion in the microscopic Raman spectroscopic device. A pixel is a unit of a CCD detector of a microscopic Raman spectroscopic device, and spectral information of one irradiation location in a mapping operation is accumulated in one pixel.

  Binarized Raman chemical imaging is performed in the second step of the method of the present invention using the threshold value thus obtained. Binarized Raman chemical imaging is a process (binarization) in which particles are present at an irradiation site showing a peak intensity equal to or higher than a predetermined threshold, and particles are not present at an irradiation site showing a peak intensity lower than a predetermined threshold. ) Means to obtain the shape and distribution of particles in the observation region as an image. The image thus obtained is referred to as a Raman chemical image. The binarization process and the imaging process can be performed by using image processing software, typically image processing software attached to the micro Raman spectroscopic apparatus to be used. Therefore, Raman chemical imaging can be performed by inputting a threshold value into data output from the microscopic Raman spectroscopic device, or a Raman chemical image can be output by inputting the threshold value into the microscopic Raman spectroscopic device in advance.

  In the third step of the method of the present invention, the particle size of the particles is calculated from the Raman chemical image thus obtained. The calculation of the particle diameter can be performed by a method known to those skilled in the art, and typically can be performed using image processing software.

  As described above, in the second aspect, the present invention compares the images obtained by the stereomicroscope and the microscopic Raman spectroscopic apparatus with respect to the particles before the predetermined Raman intensity threshold value is dispersed in the solid material. The particle size measurement method of the present invention, wherein the position and size of the particles in the Raman chemical image of the Raman spectrum specific to the particles of the microscopic Raman spectroscopic device is a threshold value for overlapping.

According to the third aspect of the present invention, in the third aspect, the predetermined Raman intensity threshold is (a) the maximum peak intensity of the Raman shift specific to the particle is represented by the formula (1)
Peak intensity = fitting threshold × 2 / A ² (1)
When the peak intensity value is equal to or greater than the peak intensity value calculated from (1), it is the fitting threshold value, or (b) the peak intensity value calculated from the above equation (1) is the peak intensity value within the observation region. If less than, formula (2)
Threshold = maximum peak intensity × (1/2) × A ² (2)
(Here, in the above formulas (1) and (2), A is the spatial resolution in the xy direction of the objective lens used in the microscopic Raman spectroscopic device / the mapping size of the microscopic Raman spectroscopic device)
It is related with the measuring method of the particle size of the said invention which is the threshold value obtained by this.

  The stereomicroscope and the microscopic Raman spectroscope used in the present invention are not particularly limited, but commercially available ones can be used. Since the lower limit value of the particles that can be measured by the method of the present invention depends on the spatial resolution of the microscopic Raman spectroscopic apparatus, in order to measure smaller particles, an apparatus having a high spatial resolution, for example, an objective lens having a large numerical aperture It is preferable to use one provided with

  Hereinafter, embodiments of the present invention will be specifically described with reference to examples. However, it is not intended that the scope of the present invention be limited to the examples by the examples.

The particle size of the particles in the tablet was measured by micro Raman spectroscopy. The particles used were polystyrene particles (Duke Scientific, “DRI-CAL” Praticle Standards) used as calibration standard particles for particle size distribution measurement, and three types of 5, 10, and 15 μm were used. After producing each uncoated tablet according to a conventional method using lactic acid hydrate, crystalline cellulose, hydroxypropyl cellulose, carmellose calcium, magnesium stearate and light anhydrous silicic acid for polystyrene particles of each particle size, hypromellose Each film tablet was manufactured using Macrogol 6000, titanium oxide and talc.
First, the tablets were coated with gold, fixed with D-800 (Toagosei Co., Ltd.), cut with a microtome, set in a microscopic laser Raman spectrometer, and the tablet cross section was observed under the following measurement conditions.

Device name: LabRAM ARAMIS (manufactured by Horiba, Ltd., laser Raman spectrometer)
Laser wavelength: 633 nm
Laser intensity: 6mW
Slit size: 100 μm
Pinhole size: 200μm
Step size (stage): 1 μm
Objective lens: 100 times (numerical aperture 0.9)
Irradiation time: 0.5 seconds Integration count: 1 time

As the measurement peak, a specific Raman shift of 1607 cm ⁻¹ derived from the C═C stretching vibration of the benzene ring that does not overlap with the peaks of the ingredients other than the main ingredient was selected. FIG. 1 shows the Raman spectrum of polystyrene particles. A broad mapping of the surface of the cross section of the tablet was performed for this peak, the place where polystyrene particles were present was searched visually, and the local mapping was performed for that location. Local mapping was performed on several regions of 100 μm × 100 μm using a 100 × objective lens.

On the other hand, the polystyrene particles before formulation are observed with an optical microscope of a microscopic Raman spectroscope, and a Raman chemical image is formed by laser Raman spectroscopy for the same observation area, and the two screens are compared, and both particles are compared. 200 was determined as the threshold value of the peak intensity when the position and size overlap (FIG. 2).
Since the spatial resolution in the xy direction of the objective lens used in the optical microscope used is about 0.5 μm and the mapping size of the Raman spectroscopic device is 1 μm, the ratio A is (½). A 0.5 μm square corresponds to ¼ pixel. When this value and the above-determined threshold value 200 are put into the above equation (1), the peak intensity is 1600. When the maximum peak intensity at 1607 cm ⁻¹ in the measurement area in the tablet was 1600 or more, the threshold was set to 200, and when the maximum peak intensity was less than 1600, Raman chemical imaging was performed using the threshold calculated according to the above formula (2). . And the particle size was measured based on this Raman chemical image. Table 1 shows the average particle diameter D ₅₀ (number average particle diameter; equivalent circle diameter) calculated based on this result together with other results. In the case of 10 and 15 μm particles, values close to the values obtained by the microscopic method are shown, but in the case of 5 μm particles, the values are slightly different. This is because, as shown in FIG. 3, an aggregated portion of 5 μm particles was seen in the Raman chemical image, and that portion was evaluated as one coarse particle. Good results were obtained by measuring an observation region with good dispersion. Is expected to have been obtained.

Although the standard deviation value is slightly large when measured by the method of the present invention, the average particle diameter shows the same value as the displayed value, so that the particle diameter of the particles in the solid material can be measured quantitatively and accurately. I understand.

Particles of active ingredient [4-diphenylmethoxy-1- [3- (4-ter-butylbenzoyl) propyl] piperidine, commonly called ebastine) particles in a tablet “Ebastel Tablet” (trade name, manufactured by Dainippon Sumitomo Pharma Co., Ltd.) The diameter was measured by microscopic Raman spectroscopy.
First, the tablets were coated with gold, fixed with D-800 (Toagosei Co., Ltd.), cut with a microtome, set in a microscopic laser Raman spectrometer, and the tablet cross section was observed under the following measurement conditions.

Device name: LabRAM ARAMIS (manufactured by Horiba, Ltd., laser Raman spectrometer)
Laser wavelength: 633 nm
Laser intensity: 6mW
Slit size: 100 μm
Pinhole size: 200μm
Step size (stage): 1 μm
Objective lens: 100 times (numerical aperture 0.9)
Irradiation time: 0.5 seconds Integration count: 1 time

As a measurement peak, a specific peak at 1607 cm ⁻¹ derived from the C═C stretching vibration of the benzene ring that does not overlap with the peaks of the ingredients other than the main ingredient was selected. FIG. 4 shows the Raman spectrum of the main ingredient component and ingredients other than the main ingredient. FIG. 4 shows that the peak at 1607 cm ⁻¹ does not exist in the Raman spectrum of other components in the tablet.

On the other hand, the drug substance particles, which are the main drug components prior to formulation, as in Example 1, were observed with an optical microscope of a microscopic Raman spectroscopic device, and the threshold value was 200.
In the same manner as in Example 1, the peak intensity of (1) was 1600. When the maximum peak intensity at 1607 cm ⁻¹ in the measurement region was 1600 or more, the threshold was set to 200, and when the maximum peak intensity was less than 1600, Raman chemical imaging was performed using the threshold calculated according to (2) above. And the particle size was measured based on this Raman chemical image. When the number of measurement areas of the sample was measured, the total number of particles was 733. The average particle diameter D ₅₀ (number average particle diameter; equivalent circle diameter) calculated based on this measurement value was 2.96 μm.

Table 2 shows the results of other particle size distribution measurement methods and the measurement results in tablets for the drug substance particles of the main ingredient. The average particle size in the tablet is slightly smaller than the drug substance particles. This is presumably because the maximum particle size of the particles is not always visible in the results of the tablet cross section, but a value almost similar to the drug substance particles was obtained. The same tablet was further evaluated three times by this method. The method using a conventional mathematical algorithm cannot be measured quantitatively with good reproducibility. Moreover, it is the standard deviation of the same level as the standard deviation measured by ordinary powder particles before being dispersed in the solid material. Therefore, it can be seen that the method of the present invention has the same accuracy as the conventional measurement method with good accuracy for measuring ordinary powder particles. Therefore, it can be seen that the particle size of the particles in the solid material can be accurately and quantitatively measured by using the method of the present invention.

Claims (4)

  A method of measuring the particle size of particles dispersed in a solid material by microscopic Raman spectroscopy, the first step of obtaining a Raman shift specific to the particles, and subjecting the solid material to microscopic Raman spectroscopy, A second step of performing binarized Raman chemical imaging based on a predetermined Raman intensity threshold at a Raman shift specific to the particle, and calculating the particle size of the particle from the Raman chemical image obtained in the second step A method for measuring a particle size, comprising a third step.   A predetermined Raman intensity threshold for the particles in the Raman chemical image of the Raman spectrum specific for the particle position and size in a stereomicroscopic image and in the microscopic Raman spectrometer for the particles before being dispersed in the solid material. The particle size measuring method according to claim 1, wherein the position and size are threshold values (fitting threshold values) that overlap. The predetermined Raman intensity threshold is (a) the maximum value of the peak intensity of the Raman shift specific to the particle is the formula (1)
Peak intensity = fitting threshold × 2 / A ² (1)
If it is equal to or greater than the peak intensity value calculated from (2), it is the threshold defined in claim 2, or (b) the maximum peak intensity value in the observation region is calculated from the above equation (1). If the peak intensity is less than
Threshold = maximum peak intensity × (1/2) × A ² (2)
(Here, in the above formulas (1) and (2), A is the spatial resolution in the xy direction of the objective lens used in the microscopic Raman spectroscopic device / the mapping size of the microscopic Raman spectroscopic device)
The particle size measurement method according to claim 2, wherein the threshold value is obtained by the following equation.   The particle size measuring method according to any one of claims 1 to 3, wherein the solid material is a tablet.

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