JPH03248045A - Sample pan for spectroscopic analysis and spectroscopic analysis method - Google Patents

Abstract

PURPOSE:To make it possible to perform measurement characterized by high S/N and high accuracy by using a sample pan comprising a rotary parabolic surface wherein the inner wall is constituted of a light reflecting material. CONSTITUTION:In a sample pan 1, a recess part is provided at the approximately central part of a metal stage so that the wall surface forms a rotary parabolic surface 2. The parabolic surface 2 is finished so as to have the mirror surface, and gold is plated. Therefore, light is excellently reflected from the surface 2. Light 20 from a light source is made to be the monochromatic parallel light through a spectroscopic system using a monochromator or an interference filter. The light 20 is reflected from a mirror 13 and inputted into the sample pan 1 in parallel with the rotary axis of the parabolic surface 2. Then, the light which is inputted in the sample pan 1 directly impinges a sample 5. Or the light is reflected from the parabolic surface 2 and directed to a focal point F. Then, the light impinges the sample 5. When the sample 5 is illuminated, light 21 emitted from the sample 5 is inputted into an integrating sphere 11 directly or after the reflection from the parabolic surface 2. The light is reflected from the inner wall of the integrating sphere 11 and finally inputted into a detector 12. Thus the sample 5 is analyzed.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a sample dish used in spectroscopic analysis performed by detecting light emitted from a sample when the sample is irradiated with light, and a spectroscopic analysis method. [Prior Art] Conventionally, as a sample dish used for this type of spectroscopic analysis, there is a type in which a flat plate is provided with a concave portion having a constant depth. Figure 3 shows
It is a sectional view of essential parts of a spectrometer using this conventional sample dish and integrating sphere. The integrating sphere 11 has an inner wall made of a material that reflects light, and has openings at the top and bottom, respectively. The light detector 12 is fixed to the inner wall of the integrating sphere 11. A mirror 13 is provided directly above the opening at the top of the integrating sphere 11,
A sample dish 30 is attached in contact with the lower opening. The sample dish 30 has a flat plate with a concave portion having a constant depth, and a powder or liquid sample 3 is placed in the concave portion.
1 is fulfilled. The light from the light source is monochromated by an interference filter or a monochromator to become parallel light 20, which is reflected by a mirror 13 and irradiated onto a sample 31. The light 21 emitted from the sample 31 upon being irradiated with the light 20 hits the inner wall of the integrating sphere 11, is reflected, and finally enters the detector 12. The light emitted from the sample here refers to irradiation light that is diffusely reflected on the sample surface, irradiation light that passes through the sample and is reflected at the interface between the sample and sample plate, and fluorescence that is emitted when the sample is excited by the irradiation light. This refers to all the light that comes out of a sample as a result of irradiating the sample with light. The ratio of the intensity of the light irradiated to the sample and the light emitted from the sample changes depending on the wavelength of the irradiated light, and the change in the ratio of light intensity depending on the wavelength is due to the chemical substances that make up the sample.

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Therefore, since it is unique, the sample can be analyzed by detecting the light emitted from the sample. The above-mentioned spectrometer uses light of several specific wavelengths of near-infrared light with a wavelength of about 800 nm to 2500 nm, for example, to analyze water contained in samples such as grains, dairy products, oils and fats, pharmaceuticals, and fibers. There are commercially available devices for quantifying oil content, protein content, sugar content, alcohol content, etc. [Problems to be Solved by the Invention] As described below, the conventional sample dish described above has the disadvantage that it is not suitable for measuring granular samples such as plant seeds in their original form without being crushed. There is. For example, when performing spectroscopic analysis to select seeds suitable for germination, seeds must be analyzed one by one without being crushed, and granular samples must be crushed into powder. Analysis shows that water and volatile matter are lost during grinding;
Accurate quantification may not be possible. Therefore, attempts have been made to analyze granular samples in their original shape, but when measurements are carried out by placing granular samples one by one on a conventional sample dish, the beam diameter of the irradiated light is generally smaller than that of the sample. Since the diameter of the sample plate is larger than the diameter of the sample plate, a considerable portion of the irradiated light does not hit the sample, but instead hits the sample plate and is reflected and enters the detector, deteriorating the S/N ratio of the measurement. Measurement S/N
It is also clear that the worse the ratio, the worse the accuracy of the measurements. If you narrow down the irradiation light beam to reduce the amount of light that hits the sample plate directly, the amount of light will decrease accordingly, resulting in a worse S/N ratio.Also, narrowing down the irradiation light beam to match the size of the sample is important for analysis. complicate the work. The purpose of the present invention is to provide a sample dish suitable for the analysis of granular samples, which does not deteriorate the S/N ratio and accuracy even when the granular samples are measured one by one in their original shape, and an analysis using this sample dish. The purpose is to provide a method. [Means for Solving the Problems] The present invention capable of achieving the above object is a sample dish used for spectroscopic analysis performed by detecting light emitted from a sample when the sample is irradiated with light, comprising: A sample dish whose inner wall is made of a paraboloid of revolution made of a material that reflects light, and using this sample dish, the sample is placed in the sample dish so that the focal point of the paraboloid of revolution is located inside the sample. The spectroscopic analysis method is characterized in that parallel light is made incident on the sample dish along the rotation axis of the paraboloid of revolution. [Function] Since the inner wall of the sample dish of the present invention is made of a paraboloid of revolution made of a material that reflects light, all light incident on this sample dish parallel to the rotation axis of the paraboloid of revolution is reflected by the rotation. Focus the light on the focal point of the paraboloid. Therefore, if a granular sample is placed on this sample plate so that the focal point is located inside the sample, and light is incident parallel to the rotation axis, all of the incident light will hit the sample. When the sample is irradiated, the light emitted from the sample goes out of the sample dish through the opening of the paraboloid of revolution, either directly or while being reflected by the paraboloid of revolution. Therefore, spectroscopic analysis can be performed by monochromating the light incident on the sample dish and measuring the intensity of the light exiting from the sample dish. In this case, all of the incident light hits the sample without narrowing down the beam diameter of the incident light, making it possible to perform measurements with a high S/N ratio and improving measurement accuracy. In addition, since the focal point is located inside the sample, the sample is irradiated with light from almost all directions, which reduces variations in measurement values due to the orientation of the sample. There is no need to pay attention to the orientation of the sample when loading it, improving work efficiency. This sample dish can also be used for powder or liquid samples, and if the focus is placed inside the sample, all of the incident light will hit the sample, making it possible to use a conventional sample dish. It is possible to perform measurements with a high S/N ratio and high accuracy using a smaller amount of sample than when using a conventional method. [Example] Next, an example of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a sample dish according to an embodiment of the present invention, FIG. 2 is a sectional view of essential parts of an example of a spectrometer using the sample dish 1 illustrated in FIG. FIG. 3 is a diagram showing spectra measured using the dish 1 and the conventional sample dish 30, respectively. The sample dish 1 of this embodiment has a concave portion substantially in the center of a metal pedestal 3 so that the wall surface forms a paraboloid of revolution 2. This paraboloid of revolution 2 has a mirror finish and is plated with gold, so it reflects light well. Here, if the distance from the apex of the paraboloid of rotation 2 to the focal point is set to be less than or equal to the diameter of the granular sample, and the opening 4 of the sample plate is directed upward, the sample can be placed in the sample plate 1. When placed one by one, the sample will be located near the apex of the paraboloid of revolution 2 due to the action of gravity, and the focal point will be located inside the sample, which is advantageous. Next, a spectroscopic analysis method using the sample dish 1 will be explained. This spectroscopic analysis method is carried out using a spectrometer as shown in FIG. 2, for example. This spectrometer is similar to the spectrometer shown in FIG. 3 described above, and the sample dish 1 of this embodiment described above is attached in place of the conventional sample dish 30. The granular sample 5 is placed near the apex of the paraboloid of revolution 2, and the focal point F of the paraboloid of revolution 2 is inside the sample 5. Next, the operation of the above-mentioned spectrometer will be explained. Light 20 from a light source (not shown) passes through a spectroscopic system (not shown) using a monochromator or an interference filter, becomes monochromatic and parallel, and is reflected by a mirror 13 to form a paraboloid of rotation with respect to the sample dish 1. The light is incident parallel to the axis of rotation of surface 2. The light incident on the sample dish 1 either hits the sample 5 directly or hits the sample 5 by being reflected by the paraboloid of revolution 2 and heads toward the focal point F.The light 21 emitted from the sample 5 when the sample 5 is irradiated enters the integrating sphere 11 either directly or by being reflected by the paraboloid of revolution 2, is reflected by the inner wall of the integrating sphere 11, and finally enters the detector 12. If necessary, the granular sample 5 is analyzed by repeating measurements using a plurality of wavelengths. Next, this example will be explained using specific numerical values. Example 1 A sample dish 1 whose opening 4 has a diameter of 24 mm and a depth of 18 mm, an integrating sphere 11 whose inner wall is plated with gold,
Using the above-mentioned spectrometer using the detector 12 using lead sulfide (PBS), place one grain of soybean on the sample plate 1,
Spectra were measured over the wavelength range from 1l100n to 2500nm. Focus F of the paraboloid of revolution 2 of the sample dish 1
is located 2 mm above the apex. The solid line in FIG. 3 is the ratio of the intensity of light emitted from the sample to the intensity of light incident on the sample plate 1, and is expressed as an absorption spectrum of soybean. Comparative Example 1 In the spectrometer of Example 1, instead of the sample dish l,
The spectra of the same sample were measured under the same conditions as in Example 1 using a conventional sample dish 30 with a flat plate having a recess of 24 mm in diameter and 1 mm in depth. The results are shown by dotted lines in FIG. . Comparing the spectrum of Example 1 with the spectrum of Comparative Example 1, Example 1 has clearer absorption maxima and minima, better represents the shape of the absorption spectrum, and the measured S
It can be seen that the /N ratio has improved. Example 2 One soybean was placed on the sample plate 1 of Example 1, and the spectrometer of Example 1 measured 2310 nm, 2230 nm, and 2180 nm.
Fat in soybeans was quantified using near-infrared light of four wavelengths: nm and 1940 nm. As a result of repeating the measurement 10 times, the average measured value was 20.3
g/di, which was consistent with the results of wet analysis. Also, 1
The standard deviation of 0 measurements was 0121 g/dl, and the coefficient of variation was 1.03. Comparative Example 2 One soybean was placed on the sample plate 30 of Comparative Example 1, and the fat content of the same sample was determined under the same conditions as in Example 2. As a result of repeating the measurement 10 times, the average measured value was 13.8
g/di, which was about two-thirds the value of the wet analysis result. Also, the standard deviation of 10 measurements is 3.30
g/di, the coefficient of variation was 23.91. As is clear from a comparison between Example 2 and Comparative Example 2, by using the sample dish 1 according to the present invention, fat in soybeans can be quantified more easily than when using the conventional sample dish 30. Accuracy was significantly improved and agreed with objective values. Furthermore, an improvement of 23 times or more was confirmed in the repeatability of measurement. [Effects of the Invention] As explained above, the present invention uses a sample dish whose inner wall is a paraboloid of revolution made of a material that reflects light, so that each granular sample can be shaped as it is. This method has the effect of making it possible to perform measurements with a high S/N ratio and accuracy, and it also has the effect of making it possible to perform measurements with a small amount of sample even for powder or liquid samples.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a sample dish according to an embodiment of the present invention, FIG. 2 is a sectional view of essential parts of an example of a spectrometer using the sample dish 1 illustrated in FIG. FIG. 4 is a cross-sectional view of a main part of a spectrometer using the conventional sample dish 30. 1. Sample dish, 2. Paraboloid of revolution, 3. 5. 12. 20. 21. 30. F. Pedestal, 4. Opening, Granular sample, 11. Integrating sphere, Detection 13. Mirror, ・Parallel light from the light source, ・Light emitted from the sample, ・Sample dish, 31. Sample, ・Focus.

Claims (1)

[Claims] 1. A sample dish used for spectroscopic analysis performed by detecting light emitted from a sample when the sample is irradiated with light, the inner wall of which is made of a material that reflects light. A sample dish consisting of a paraboloid of revolution. 2. In a spectroscopic analysis method that detects the light emitted from a sample when the sample is irradiated with light, a sample dish whose inner wall is a paraboloid of revolution made of a material that reflects light is used. , the sample is placed on the sample plate so that the focal point of the paraboloid of revolution is located inside the sample, and parallel light is made incident on the sample plate along the axis of rotation of the paraboloid of rotation. Spectroscopic analysis method.