JP2004325336A - Circular dichroism measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circular dichroism measuring apparatus which can measure circular dichroism in a powdery sample. <P>SOLUTION: The circular dichroism measuring apparatus 10 is provided with a polarization modulation means 14 which periodically modulates the polarization state of light irradiated by a light irradiation means 12, an integrating sphere 16 arranged at the front of a sample 20, and a detection means 18 which detects light through the integrating sphere 16. By irradiating the sample 20 with modulated polarized light, receiving diffuse reflected light from the sample 20 by the integrating sphere 16, and detecting by the detection means 18, the circular dichroism of the sample 20 is measured. By arranging the integrating sphere in the front of the sample, the circular dichroism measurement using diffuse reflected light is made possible. By arranging the integrating sphere in the rear of the sample, in the circular dichroism measuring apparatus, the circular dichroism measurement using diffuse transmitted light is made possible. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement in a circular dichroism measuring device.
[0002]
[Prior art]
For measurement of circular dichroism (CD) when the sample is a powder, the Nujol method, the KBr tablet method and the like are usually used. The Nujol method uses a suspension of a powder sample in a solvent that does not dissolve the powder sample, and measures circular dichroism by measuring transmitted light. Here, a solvent having substantially the same refractive index as the powder sample is used. In the KBr tablet method, a powder sample was mixed with a transparent material such as KBr and processed into a disc shape to measure the transmission of the sample.
As other methods, Patent Documents 1 and 2 describe that CD is directly measured in a solid phase based on the arrangement information of a sample that does not show a CD in a solution but shows a CD due to the arrangement in a crystal.
[0003]
[Patent Document 1]
JP 2001-31684 A [Patent Document 2]
JP-A-2002-122577
[Problems to be solved by the invention]
However, in the Nujol method, a part of the sample may be dissolved, and there is a problem that the circular dichroism of the powder sample itself cannot be measured. The KBr tablet method has problems such as complicated preparation of a sample. Further, the methods described in Patent Documents 1 and 2 require the use of a sample that is sufficiently thin in order to sufficiently transmit light, and it is difficult to measure the sample particularly when the sample can be obtained only as microcrystals. .
Further, when the sample is cloudy, since the straight transmitted light is not sufficiently strong, it is necessary to arrange a PMT (photomultiplier tube) as a detector as close as possible to the sample. Furthermore, in the case of circular dichroism, a biopolymer is important as an object to be measured, and light scattering by a sample cannot be ignored particularly in the ultraviolet region. For this reason, there has been a demand for an apparatus that can accurately measure circular dichroism even for a sample involving light scattering.
[0005]
The present invention has been made in view of the above problems, and a first object of the present invention is to provide a circular dichroism measuring device capable of measuring circular dichroism even in a powder sample. Another object of the present invention is to provide a circular dichroism measuring device capable of measuring circular dichroism with sufficient accuracy even in a liquid sample involving light scattering.
[0006]
[Means for Solving the Problems]
In order to achieve the first object, the circular dichroism measuring device of the present invention is provided with a polarization modulating means for periodically modulating the polarization state of the light emitted from the light irradiating means, and is arranged in front of the sample. An integrating sphere, and detecting means for detecting light via the integrating sphere, irradiating the sample with the modulated light in the polarized state, and receiving diffusely reflected light from the sample by the integrating sphere. It is characterized in that the circular dichroism of the sample is measured by detecting with the detecting means.
[0007]
In order to achieve the second object, the circular dichroism measuring apparatus according to the present invention further includes a polarization modulating unit that periodically modulates a polarization state of light irradiated from the light irradiating unit, and a polarization modulating unit that is disposed downstream of the sample. Integrated sphere, and detection means for detecting light via the integrating sphere, irradiating the sample with the modulated light in the polarized state, and transmitting linearly transmitted light and diffusely transmitted light from the sample. The circular dichroism of the sample is measured by being received by the integrating sphere and detected by the detecting means.
In the above-mentioned circular dichroism measuring apparatus, it is preferable that the apparatus further includes an optical path changing unit for changing the course of light traveling in the horizontal direction in the vertical direction, and irradiates the sample with light from the vertical direction by the optical path changing unit. It is.
[0008]
In the above-mentioned circular dichroism measuring device, it is preferable that the optical path changing means is constituted by a total reflection prism, and the light in the horizontal direction is bent in the vertical direction by total reflection.
Further, in the above-mentioned circular dichroism measuring device, it is preferable that after the light path changing means changes the course of the light in the vertical direction, the polarization modulation means performs the polarization modulation of the light.
[0009]
In these circular dichroism measuring devices, it is preferable that the polarization modulator is configured using a photoelastic modulator.
In the above-mentioned circular dichroism measuring device, in order to perform wavelength scanning, it is preferable that the light irradiation unit includes a light source and a spectroscope, and the light from the light source is converted into monochromatic light by the spectroscope. .
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a circular dichroism measuring device according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a first embodiment of a circular dichroism measuring device of the present invention. The circular dichroism measuring device 10 shown in FIG. 1 includes a light irradiating unit 12 (light source 22 and a spectroscope 24) and a polarization modulating unit 14 (for periodically modulating the polarization state of light from the light irradiating unit 12). It comprises a polarizer 26, a photoelastic modulator (PEM) 28), an integrating sphere 16 arranged in front of the sample 20, and a detecting means 18 for detecting light via the integrating sphere 16.
[0011]
Here, the light irradiation unit 12 includes a light source 22 and a spectroscope 24 in order to perform wavelength scanning in a predetermined range, and the light emitted from the light source 22 is converted into monochromatic light by the spectroscope 24.
The polarization modulator 14 includes a polarizer 26 and a photoelastic modulator 28. The monochromatic light emitted from the spectroscope 24 is linearly polarized by the polarizer 26. The azimuth angle of the polarizer 26 is inclined at a predetermined angle (for example, 45 °) with respect to the azimuth angle of the PEM 28, and the linearly polarized light passes through the photoelastic modulator 28 to be converted into a polarization component in an independent direction. Given a phase difference, the polarization state is periodically modulated. That is, the light alternately and continuously changes from right circularly polarized light to left circularly polarized light and from left circularly polarized light to right circularly polarized light. A drive voltage of a predetermined frequency (for example, 50 kHz) is applied to the photoelastic modulator 28, and the polarization state is periodically modulated according to the frequency.
[0012]
The light emitted from the polarization modulator 14 passes through the integrating sphere 16 and irradiates the sample 20. The irradiated light is diffusely reflected by the sample 20, and the diffusely reflected light is received by the integrating sphere 16 and detected by the detecting means 18. Here, a photomultiplier tube (PMT) or the like may be used as the detecting means.
The circular dichroism of the sample is measured from the detection signal of the diffuse reflection light detected in this way. The method of calculating the circular dichroism from the detection signal may be performed in the same manner as in the related art. That is, the circular dichroism is obtained using the same frequency component as the modulation frequency of the PEM 28 in the detection signal. By performing this measurement while changing the wavelength of light, a CD spectrum can be obtained.
[0013]
As described above, by detecting the diffuse reflection light from the sample using the integrating sphere, it was possible to measure the circular dichroism even if the sample was a powder. That is, by using the diffuse reflection light, unlike the conventional one, the measurement of circular dichroism can be performed while the sample is in a powder state.
Further, by detecting light through the integrating sphere, the polarization characteristics of the light receiving surface of the detector can be reduced. That is, the light receiving surface of the detector generally has sensitivity unevenness. For example, a photomultiplier tube has a difference of 10 times or more depending on the location. Therefore, by performing the detection through the integrating sphere, the light is scrambled, and the light can be uniformly received on the light receiving surface.
[0014]
Next, a second embodiment of the circular dichroism measuring device of the present invention will be described. Here, the circular dichroism measuring apparatus utilizes both the straight transmitted light and the diffuse transmitted light from the sample. FIG. 2 is a schematic configuration diagram of the embodiment. The parts corresponding to those in FIG.
The circular dichroism measuring device 110 shown in FIG. 2 includes a light irradiating unit 112 (a light source 122 and a spectroscope 124) and a polarization modulating unit 114 (a polarization unit) that periodically modulates the polarization state of the light irradiated from the light irradiating unit 112. Element 126, a photoelastic modulator 128), an integrating sphere 116 disposed downstream of the sample 120, and a detecting means 118 for detecting light via the integrating sphere 116.
[0015]
As in the embodiment shown in FIG. 1, the light emitted from the light source 122 passes through the spectroscope 124 to become monochromatic light, and the polarization state is further modulated by the polarizer 126 and the photoelastic modulator 128. The light whose polarization state has been modulated is irradiated onto the sample 120, and the transmitted light from the sample 120 is detected by the detection means 118 including a photomultiplier tube or the like. The transmitted light from the sample includes not only straight transmitted light but also diffuse transmitted light for light scattering by the sample. In order to detect the diffused transmitted light at the same time, an integrating sphere 116 is installed in the vicinity of the subsequent stage of the sample 120.
[0016]
As shown in FIG. 2, a standard diffuse reflection plate 130 is provided on the integrating sphere 116 on the opposite side of the installation position of the sample 120. Therefore, the straight transmitted light and the diffuse transmitted light are captured by the integrating sphere 116 and detected by the detecting means 118. As a result, the measurement can be performed without losing important information regarding the measurement of circular dichroism.
In this manner, by providing the integrating sphere at the subsequent stage of the sample, it is possible to detect not only normal linearly transmitted light but also diffusely transmitted light. As a result, the detected light amount of transmitted light increases, so that it is possible to measure circular dichroism with sufficient accuracy, especially for a sample involving light scattering. Further, for the same reason as in the embodiment in FIG. 1, by detecting light through the integrating sphere, the polarization characteristics of the light receiving surface of the detector can be reduced.
[0017]
Next, a preferred embodiment of the circular dichroism measuring device according to the present invention will be described.
FIG. 3 is a schematic configuration diagram, FIG. 3 (a) is a configuration for measuring circular dichroism by diffuse reflection, and FIG. 3 (b) is measurement of circular dichroism by straight transmitted light and diffuse transmitted light. FIG. The parts corresponding to those in FIG.
3A and 3B, the circular dichroism measuring device 210 includes a light irradiation unit 212 (a light source 222 and a spectroscope 224) and a polarization modulation unit 214 that periodically modulates the polarization state of light. (Polarizer 226, photoelastic modulator 228), integrating sphere 216, and detecting means 218 for detecting light via integrating sphere 216. Further, an optical path changing means (total reflection prism 232) is provided in front of the sample 220 and the integrating sphere 216.
[0018]
In the case of FIG. 3A in which measurement is performed by diffuse reflection, the sample 220 is placed downstream of the integrating sphere 216 with respect to the path of irradiation light, similarly to the configuration shown in FIG. Also, in the case of FIG. 3B where transmission measurement is performed, a sample is placed in front of the integrating sphere 216 with respect to the path of the irradiation light, and the sample is further provided in the subsequent stage of the integrating sphere 216 as in the configuration of FIG. A standard diffusion plate 230 is provided on the window side.
[0019]
The light emitted from the light irradiation means 212 travels in the horizontal direction, is totally reflected by the total reflection prism 232, and is bent in the vertical direction. The polarization state of the light traveling in the vertical direction is periodically modulated by the polarization modulator 214. In FIG. 3A, the light traveling in the vertical direction passes through the integrating sphere 216 and irradiates the sample 220. Then, the diffuse reflected light from the sample 220 is picked up by the integrating sphere 220 and detected by the detecting means 218. Similarly, in FIG. 3B, light traveling in the vertical direction first enters the sample 220. Then, the linearly transmitted light and the diffused transmitted light that have passed through the sample 220 are detected by the detection means 218 via the integrating sphere 216.
[0020]
The feature of the present embodiment is that light can be irradiated to the sample from the vertical direction by using the optical path changing means (total reflection prism 232). Therefore, the sample can be measured in a horizontal state. That is, conventionally, light was generally irradiated in the horizontal direction due to the limitation of the device configuration, and the sample had to be installed in a vertical state.
Therefore, when the sample is installed vertically, especially in the case of a powder sample or a liquid sample, it is necessary to store the sample in a container for holding the sample. At this time, it is necessary to provide a window plate in the sample container in order to transmit the measurement light. When the window plate is fitted into the container, the window plate is distorted by the stress applied thereto. Due to this distortion, the optical properties of the window plate itself changed, which had an adverse effect on the measurement.
[0021]
Therefore, if the sample can be set horizontally as in the present embodiment, there is no need to seal the sample container. That is, there is no need to provide a window plate, and it is possible to eliminate measurement errors due to the window plate.
Further, the optical path changing means in the present embodiment is not limited to the total reflection prism, but may be an optical fiber, a mirror, or the like.
[0022]
Further, the arrangement relationship between the optical path changing means and the polarization modulation means will be described. FIG. 4 is an explanatory diagram of an arrangement relationship between the optical path changing unit and the polarization modulation unit. FIG. 4A shows an example in which the polarizer 326 and the PEM 328 are placed after the optical path changing unit 332 (on the detector side), similarly to the embodiment of FIG. In this case, since the polarization state of the light is modulated after the light path is changed by the light path changing means 332, the light path changing means 332 is not limited to the total reflection prism but may be an optical fiber, a mirror, or the like. .
[0023]
However, as shown in FIG. 4B, when the polarizer 326 and the PEM 328 are placed in front of the optical path changing unit 332 (on the light source side), the polarization state of light is affected by the optical element used as the optical path changing unit 332. I will. For this reason, if the PEM 328 is installed in front of the optical path changing unit as shown in FIG. 4B, the polarization characteristics of the optical elements constituting the optical path changing unit appear in the measurement results, and good measurement data cannot be obtained.
[0024]
FIG. 4C shows a case where the polarizer 326 is placed before the light path changing means 332 (on the light source side) and the PEM 328 is placed after the light path changing means 332 (on the detector side). In the arrangement of FIG. 4C, after the light is linearly polarized by the polarizer 326, the light path is changed by the light path changing means. In this case, since the polarization state of the light is periodically modulated by the PEM 328 after changing the light path, unlike the case of FIG. 4B, the measurement data is not adversely affected. Therefore, in the case of FIG. 4C, a mirror (mirror) or a polarization-maintaining optical fiber can be used as the optical path changing means in addition to the total reflection prism. However, an optical element with little change in the polarization state is desirable.
[0025]
FIG. 5 shows a graph of a measurement result obtained by performing a baseline measurement using the circular dichroism measuring apparatus of the present invention. As a device configuration, a device similar to that shown in FIG. 3B was used, and transmission measurement was performed without setting a sample. However, the measurement was performed when the PEM was installed after the total reflection prism (see FIG. 4A) and when the PEM was installed before the total reflection prism (see FIG. 4B).
[0026]
The solid line 400 in FIG. 5 is the baseline of the measurement result when the PEM is installed after the total reflection prism, and the long broken line 410 is the baseline when the PEM is installed before the total reflection prism. The short dotted line indicates the 0 position (x-axis of the graph). As can be seen from this graph, when a PEM is installed at a stage prior to the optical path changing unit, the polarization characteristics of the optical element itself constituting the optical path changing unit appear in the measurement data, and the baseline is disturbed.
[0027]
However, when the PEM is installed after the optical path changing unit, as shown in FIG. 5, the PEM is almost flat and is on the x-axis of the graph, and the baseline is greatly improved.
Therefore, it is understood that it is best to arrange the PEM after the optical path changing unit. That is, it has been found that this arrangement avoids the deterioration of the polarization characteristics due to the optical elements constituting the optical path changing means, and prevents the generation of false signals.
[0028]
【The invention's effect】
According to the circular dichroism measuring device of the present invention, the circular dichroism measurement using the diffuse reflection light becomes possible by installing the integrating sphere before the sample.
Further, according to the circular dichroism measuring device of the present invention, the circular dichroism measurement using diffuse transmitted light can be performed by installing the integrating sphere at the subsequent stage of the sample.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram (diffuse reflection measurement type) of a circular dichroism measuring device of the present invention.
FIG. 2 is a schematic configuration diagram (transmission measurement type) of the circular dichroism measuring device of the present invention.
FIG. 3 is a schematic configuration diagram of an embodiment of a circular dichroism measuring device of the present invention.
FIG. 4 is an explanatory diagram of an arrangement relationship between an optical path changing unit and a polarization modulating unit.
FIG. 5 is a graph showing the results of a baseline measurement using the circular dichroism measuring device of the present invention.
[Explanation of symbols]
Reference Signs List 10 circular dichroism measuring device 12 light irradiating means 14 polarization modulating means 16 integrating sphere 18 detecting means 20 sample

Claims (7)

Polarization modulation means for periodically modulating the polarization state of light emitted from the light irradiation means,
An integrating sphere arranged in front of the sample,
Detecting means for detecting light via the integrating sphere,
Irradiating the sample with the modulated light in the polarized state, receiving the diffuse reflection light from the sample by the integrating sphere, and detecting the circular dichroism of the sample by the detection unit. Dichroism measuring device. Polarization modulation means for periodically modulating the polarization state of light emitted from the light irradiation means,
An integrating sphere arranged after the sample,
Detecting means for detecting light via the integrating sphere,
Irradiating the sample with the modulated light in the polarized state, receiving the linearly transmitted light and the diffusely transmitted light from the sample by the integrating sphere, and detecting the circular dichroism of the sample by the detection means; And a circular dichroism measuring device. The circular dichroism measuring device according to claim 1 or 2,
An apparatus for measuring circular dichroism, comprising: an optical path changing means for changing the course of light traveling in a horizontal direction in a vertical direction, and irradiating the sample with light in the vertical direction by the optical path changing means. The circular dichroism measuring device according to claim 3,
The circular dichroism measuring device, wherein the optical path changing means is constituted by a total reflection prism, and bends light in a horizontal direction in a vertical direction by total reflection. The circular dichroism measuring device according to claim 3 or 4,
A circular dichroism measuring device, wherein after the light path changing means changes the course of light in the vertical direction, the polarization modulation means performs light polarization modulation. The circular dichroism measuring device according to any one of claims 1 to 5,
The circular dichroism measuring device, wherein the polarization modulator is configured using a photoelastic modulator. The circular dichroism measuring device according to any one of claims 1 to 6,
In order to perform wavelength scanning, the light irradiating means includes a light source and a spectroscope, and the light from the light source is converted into monochromatic light by the spectroscope.

Images