JP2009068884A - Rotation angle measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable measurement of the angle of rotation by a simple signal processing, using the configuration of a device which is devised as a small-sized and compact circular dichroism detector for HPLC. <P>SOLUTION: A rotation angle measuring instrument is equipped with a circular dichroism detecting mechanism which is configured by disposing a light source 10, a polarizer 25, PEM 13, a flow cell 15 and a photodetector 19 so that light is transmitted in this sequence and by disposing a diffraction grating G between the polarizer and the PEM. In this mechanism, an analyzer is disposed between the flow cell and the photodetector so that an included angle formed by the direction of oscillation of the PEM and the direction of a transmission easiness axis of the polarizer be made smaller than π/4 enabling attainment of a maximum phase modulation width. Thereby the phase modulation width δ is set to be smaller than π/4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical rotation measuring device, and more specifically to an apparatus capable of measuring a circular dichroism signal in addition to the optical rotation.

  A conventional circular dichroism detector for HPLC that is suitable for HPLC, has no influence of stray light, and can extract a circular dichroism signal with high sensitivity is disclosed in Patent Document 1. This circular dichroism detector for HPLC uses, for example, a light source whose radiation intensity in the ultraviolet region is relatively large compared to other regions, such as an HgXe lamp. Then, a polarizer that linearly polarizes the light emitted from the light source, one diffraction grating that wavelength-disperses the linearly polarized light emitted from the polarizer, and the linearly polarized light dispersed by the diffraction grating is modulated. A modulation means capable of alternately generating left circularly polarized light and right circularly polarized light, a flow cell disposed on an optical path of light modulated by the modulation means, and a photodiode for receiving light transmitted through the flow cell. Configured. The circular dichroism detector for HPLC disclosed in Patent Document 1 realizes a compact configuration as compared with a general circular dichroism detector by appropriately devising the arrangement of parts. Yes.

  This device can only measure circular dichroism and cannot measure optical rotation (OR). Therefore, in order to measure the optical rotation, it is usually necessary to prepare a separate HPLC polarimeter or the like.

In addition, in a large-sized apparatus generally used as a circular dichroism detector, an optical rotation measurement can be performed by attaching an analyzer and a signal capturing amplifier as an option.
JP-A-11-201959

  However, the above-described conventional apparatus capable of measuring both circular dichroism and optical rotation has the following problems. In other words, if a large-sized device generally used as a circular dichroism detector is equipped with an analyzer and a signal acquisition amplifier as an option, the optical rotation can be measured. Since the frequency is 100 kHz, not only the signal extraction is difficult, but also the apparatus becomes very expensive. These devices are not practical because they are not only very large and expensive, but also difficult to adjust.

  The present invention provides an optical rotation measuring device capable of measuring optical rotation by simple signal processing while utilizing the configuration of a device devised as a small and compact circular dichroism detector for HPLC. With the goal.

  In order to achieve the above-described object, the optical rotation measuring device according to the present invention includes: (1) a light transmission sequence including a light source, a polarizer, phase modulation means, a sample cell (“flow cell” in the embodiment), and light detection; And a circular dichroism detection mechanism configured by disposing any one of a dispersion element such as a diffraction grating or a prism, or a monochromator between the polarizer and the phase modulation means. In this mechanism, an analyzer is arranged between the sample cell and the light detection means, and the phase modulation width δ is set smaller than π / 4.

  (2) Rotating means for rotating the polarizer is provided, and the rotating means rotates the polarizer around the optical axis to rotate the polarization direction. The vibration direction of the phase modulation means, and the polarizer By making the narrow angle with respect to the easy transmission axis direction smaller than π / 4 at which the maximum phase modulation width is obtained, the phase modulation width δ can be set smaller than π / 4. The maximum phase modulation width δ can be obtained when the narrow angle between the vibration direction of the phase modulation means and the easy transmission axis direction of the polarizer is π / 4. By utilizing this, a smaller phase modulation width δ can be obtained by reducing the narrow angle. This is to change the narrow angle between the easy transmission axis direction of the polarizer and the vibration direction axis of the PEM around the transmission optical axis for the purpose of changing the phase modulation width δ of the PEM.

  (3) The phase modulation width δ of the phase modulation means is set to π / 2, and the quarter wavelength plate is installed in front of the sample cell or in front of the phase modulation means on the optical axis closer to the light source side. Thus, the phase modulation width MAX point ± δ can be set to move on the S1 axis.

  (4) The phase modulation means is a PEM, and can be configured to set the phase modulation width δ smaller than π / 4 by reducing the applied voltage.

  (5) In the above (1) to (4), the relative positional relationship may be such that the polarization plane of the analyzer is inclined by 45 ° with respect to the polarization plane of the polarizer.

  (6) In the above (1) to (5), the light source uses an HgXe lamp, an Hg lamp, a deuterium lamp, or the like that has a relatively large radiation intensity in the ultraviolet region compared to other regions. Good.

  Assuming that the frequency of the phase modulation means is fHz, when the signal is captured at the phase modulation Max point of ± δ, since ± δ is separated from the S1 axis by π / 2 on the S3 axis, the optical rotation signal (OR signal) ) Appears at 2f, and the circular dichroism signal (CD signal) appears as 1f on the S3 axis. Therefore, when detecting circular dichroism, generally, the phase modulation width δ of the phase modulation means such as PEM is set to approximately π / 2 of the measurement wavelength, and based on the signal of 1f received by the light detection means. Color can be obtained.

  On the other hand, when ± δ is close to the S1 axis, the optical rotation signal (OR signal) is 1f and the circular dichroism signal (CD signal) is 2f. Therefore, if the phase modulation vector is captured on or near the S1 axis, the OR signal is 1f and the CD signal is 2f. Therefore, in the optical rotation measurement mode, the optical rotation signal (OR signal) appears at 1f by adopting each of the above-described configurations, and can be easily obtained based on the signal received by the light detection means.

  The present invention can measure the optical rotation with simple signal processing while utilizing the configuration of a device designed as a compact and compact circular dichroism detector for HPLC.

  FIG. 1 shows a first embodiment of an optical rotation detection device according to the present invention. As shown in the figure, an HgXe lamp, an Hg lamp, or a deuterium lamp having a strong radiation intensity in the ultraviolet region is used as the light source 10. Then, the light emitted from the light source 10 is condensed into parallel light by the lens L1 and applied to the diffraction grating G. Note that the present invention is not limited to the diffraction grating, and instead of the diffraction grating, a dispersion element such as a prism or a monochromator can be used.

  A diffraction grating G with a quartz plate as a protective plate was used. That is, a quartz plate having a thickness of 0.5 mm is placed on the grating surface of the diffraction grating G, and the periphery is hermetically sealed with an adhesive. As a result, a sealed space closed with the adhesive and the quartz plate is formed around the lattice surface. Preferably, this sealed space is evacuated or filled with an inert gas such as nitrogen gas so that oxygen does not exist around the lattice plane. When an HgXe lamp having a strong Hg emission line in the ultraviolet region is used, when the diffraction grating is irradiated with light for a long time, the grating surface of the diffraction grating becomes cloudy and deteriorates, but the problem is solved by providing a protective plate. .

  In the middle of the optical path from the light source 10 to the diffraction grating G, the polarizer 25 is disposed so as to be rotatable around the optical axis. Specifically, the mounting plate 30 is disposed in the middle of the optical path from the light source 10 to the diffraction grating G so as to block the optical path. The mounting plate 30 is provided with a through hole 30 a in its optical path to constitute a bearing 31. Then, the polarizer 25 is mounted on a cylindrical holder 32 having both ends opened, and the holder 32 is rotatably mounted on the bearing 31. A first gear 33 is attached to the upper end of the holder 32. Of course, the center of the first gear 33 is also provided with a through hole so that light from the light source 10 can pass therethrough.

  On the other hand, the mounting plate 30 is provided with a through hole 30b at a position away from the optical path, and a bearing 35 is mounted in the through hole 30b. A rotating shaft 36 is inserted into the bearing 35, and the vicinity of one end (upper side in FIG. 1) of the rotating shaft 36 is rotatably held by the bearing 35. A second gear 37 is attached to one end of the rotating shaft 36, and the second gear 37 and the first gear 33 are connected.

  Further, the other end (downward in FIG. 1) of the rotating shaft 36 passes through a bearing 39 provided in the base plate 38, and a first pulley 40 is attached to the end thereof. The first pulley 40 is linked to a second pulley 43 attached to the output shaft of the motor 42 via a belt 41. As a result, when the motor 42 rotates, the rotational force is transmitted to the rotating shaft 36 via the belt 41, so that the second gear 37 and further the first gear 33 rotate accordingly. Thereby, the polarizer 25 also rotates around the optical axis. Therefore, if the motor 42 can control the rotation angle of a stepping motor or the like and can stop at an arbitrary angle, the polarizer 25 can be rotated to easily adjust the direction of the polarization plane. The rotation range when rotating the polarizer 25 is about ± 45 °, and the accuracy can be sufficiently adjusted with about ± 1 °.

  The polarizer 25 used here may be, for example, a Grand Taylor prism (a wavelength of 220 nm or more can be measured) or a quartz lotion prism (a wavelength shorter than 220 nm can be measured).

  The light that has passed through the polarizer 25 is wavelength-dispersed by the diffraction grating G, and the dispersed light is incident on the PEM 13 and is phase-modulated by passing through the PEM 13 so that it is alternately right-polarized light and left-circularly polarized light. become. Then, the circularly polarized light emitted from the PEM 13 is collected by the lens L2 and irradiated to the flow cell 15.

  The flow cell 15 is configured to close the sample chamber 16 penetrating in the axial direction, the piping 17 for supplying a sample to the sample chamber 16 and discharging the sample chamber 16, and the opening of the sample chamber 16. And an optically transparent window plate 18 attached to the. The internal shape of the sample chamber 16 is a conical shape that becomes wider along the light traveling direction.

  The light collected by the lens L2 passes through the sample chamber 16 and is then irradiated on the photodetector 19 made of a photodiode. During the measurement, the sample flows in the sample chamber 16 via the pipe line 17, so that the right circularly polarized light and the left circularly polarized light are emitted after being absorbed by a predetermined amount according to the circular dichroism of the sample. The photodiode 19 converts the received light into an electrical signal corresponding to the light intensity of the received light, sends it to a CPU (not shown), and performs arithmetic processing there to extract it as a circular dichroic signal. Note that conventional processing can be used for the arithmetic processing in the CPU, and detailed description thereof is omitted here.

  In the present embodiment, an analyzer 46 is disposed between the flow cell 15 and the photodetector 19. The analyzer 46 can take a state of being located on the optical path from the flow cell 15 to the photodetector 19 and two positions of being separated from the optical path. In the circular dichroism measurement mode, the analyzer 46 is removed from the optical path. In the optical rotation measurement mode, the analyzer 46 is positioned on the optical path. The movement of the analyzer 46 between the two positions may be performed automatically or mechanically, or an attachment member for attaching the analyzer 46 is provided, and the user simply attaches the analyzer 46 to the attachment position. It may be set on a member or removed from an attachment member.

  Further, in this embodiment, a shutter 45 that is opened and closed by a solenoid 44 is provided between the lens L1 and the polarizer 25. The shutter 45 can block light from the light source 10.

Measurement of circular dichroism using the apparatus of this embodiment is performed as follows. When measuring circular dichroism, the analyzer 46 is detached as follows. First, the polarizer 42 is rotated by operating the motor 42 in a state where a solution having no circular dichroism such as H ₂ O is allowed to flow through the flow cell 15. At this time, the output of the photodetector 19 made of a photodiode is monitored, and the rotation of the motor 42 is stopped at a position where the circular dichroism becomes zero. That is, it stops when the output of the left circularly polarized light and the right circularly polarized light becomes equal. When this is stopped, the detection result for the sample having no circular dichroism is “no circular dichroism”, so that there is no polarization characteristic in the optical system and the initial setting is completed.

  In other words, even if measurement is performed using a sample having no circular dichroism due to reflection on the inner wall of the flow cell 15 or polarization characteristics of a window plate or the like, a measurement result indicating that there is circular dichroism is obtained. There is. That is, the right circularly polarized light and the left circularly polarized light are out of phase, resulting in a difference in output. Therefore, if there is such a false circular dichroic output signal (output difference) based on the polarization characteristics of the optical system, the measurement accuracy is lowered, and there is a demand for correction as close to zero as possible. Therefore, correction is performed by rotating the polarizer 25 installed on the light source 10 side of the diffraction grating G as described above. This actively utilizes the polarization characteristics of the diffraction grating G, and when the linearly polarized light that has passed through the polarizer 25 is wavelength-dispersed by the diffraction grating G, the symmetry of the linearly polarized light is lost. That is, the phases of right circularly polarized light and left circularly polarized light are shifted. The amount of phase shift differs depending on the angular position when the linearly polarized light is irradiated onto the diffraction grating G. Therefore, the amount of phase shift that occurs when the polarization direction of linearly polarized light is rotated and wavelength-dispersed by the diffraction grating G is reversed from the phase difference between right circularly polarized light and left circularly polarized light that arises from the polarization characteristics of the optical system. Therefore, the correction can be made as described above.

  In other words, the light transmitted through the polarizer 25 is light in which the phases of the right circularly polarized light and the left circularly polarized light coincide with each other (the deviation is zero). When this light passes through a diffraction grating G having a slight polarization characteristic, a phase shift appears. Since the phase between the left and right circularly polarized light is shifted before passing through the PEM 13, the PEM modulation angle becomes “shift angle of the first phase ± PEM modulation angle”. As a result, left and right elliptically polarized light having different modulation phase angles are obtained. The effect of reflection and polarization generated in the flow cell 15 is to return the elliptically polarized light having different modulation phases to the elliptically polarized light or the circularly polarized light having the same modulation phase angle, thereby completely removing the false circular dichroism. Conceivable.

  Furthermore, in order to accurately measure an output signal based on the false circular dichroism to be corrected and call it into the CPU, in this embodiment, the shutter 45 is inserted between the lens L1 and the polarizer 25 to block the light. Read the output signal and determine the baseline of the output signal. Next, measurement is performed with the shutter 45 opened, and the polarizer is rotated so that the phase difference between the right circularly polarized light and the left circularly polarized light becomes zero from the output signal.

  Although the polarizer 25 is rotated by the motor 42, it may be rotated manually. In addition, since it is sufficient that the polarization direction of the linearly polarized light and the relative angle between the diffraction grating G can be changed, the polarizer G is not rotated as in the present embodiment, but the diffraction grating G is rotated around its normal direction. Also good. However, it is preferable to rotate the polarizer because the mechanism and control are simple.

  In the apparatus that has been initially set (corrected) in this way, the sample to be measured is supplied to the flow cell 15, the sample is irradiated with light subjected to phase modulation by the PEM 13, and the sample is transmitted through the flow cell 15. The light emitted from the light is detected by a photodetector 19 made of a photodiode. In the photodetector 19, it is converted into an electrical signal corresponding to the light intensity of the received light, sent to a CPU (not shown), where it is processed and extracted as a circular dichroic signal. In addition, since the conventional calculation process for obtaining circular dichroism in the CPU can be used, detailed description thereof is omitted here.

  Next, the principle of optical rotation measurement using the apparatus of this embodiment will be described. In the optical rotation measurement mode, the analyzer 46 is disposed between the flow cell 15 and the photodetector 19. Then, the phase modulation width δ is set as small as δ <π / 4, and the optical rotation signal is extracted by a method of extracting the circular birefringence signal.

  Thus, as a specific method for reducing the phase modulation width δ, for example, the polarization plane of the analyzer 46 is set to the polarization plane tilted to + 45 ° or −45 ° by the rotation of the polarizer 25. This can be realized by setting the relative positional relationship to be inclined by 45 °. As a result, the phase modulation width by the PEM 13 becomes zero. Since this light is elliptically polarized, the modulation width δ is near zero. Thus, a signal received by the photodetector (photodiode) 19 becomes an optical rotation (OR) signal.

  When the state in which the optical signal is extracted as an optical rotation signal (OR signal) is displayed in the Mueller matrix and considered, it is as follows.

但し、
Ｓ_０＝Ａｘ^２＋Ａｙ^２ ：光のエネルギー
Ｓ_１＝Ａｘ^２−Ａｙ^２ ：水平または垂直偏光
Ｓ_２＝２ＡｘＡｙcos Φ ：４５度傾いた平面偏光
Ｓ_３＝２ＡｘＡｙsin Φ ：右または左円偏光
Ａ：平行平面波の光を進行方向から見た光の電界振幅
ｘ：光を進行方向から見た光波面の電界の水平方向表示の添字
ｙ：光を進行方向から見た光波面の電界の垂直方向表示の添字
Φ：この光の右円偏光と左円偏光間の位相のずれ
（以下に示す各式中のΦは、回折格子の偏光特性により生じる左右円偏光間の位相ずれを意味する）

は、下記式に示すように、Ｓ_０＝１，Ｓ_１＝１，Ｓ_２＝０，Ｓ_３＝０となる。

Stokes vector intensity of light with a horizontal axis through the polarizer

However,
S ₀ = Ax ² + Ay ² : Light energy S ₁ = Ax ² −Ay ² : Horizontal or vertical polarization S ₂ = 2AxAycos Φ: Plane polarized at 45 degrees S ₃ = 2AxAysin Φ: Right or left circular polarization A: Parallel Electric field amplitude of light when plane wave light is viewed from traveling direction x: Subscript of horizontal display of electric field of light wavefront when light is viewed from traveling direction y: Vertical display of electric field of light wavefront when light is viewed from traveling direction Subscript Φ: Phase shift between right circular polarization and left circular polarization of this light (Φ in the following equations means phase shift between left and right circularly polarized light caused by the polarization characteristics of the diffraction grating)

As shown in the following equation, S ₀ = 1, S ₁ = 1, S ₂ = 0, and S ₃ = 0.

If the phase modulation angle of the PEM is ± δ and the modulation frequency is fHz from the formula of orthogonal series expansion (Fourier-Bessel expansion), the retardation γ of the PEM is γ = δsin (2πft). Therefore,
cos γ = J ₀ (δ) + 2J ₂ (δ) cos (4πft)
+ 2J ₄ (δ) cos (8πft)
sin γ = 2J ₁ (δ) sin (2πft)
+ 2J ₃ (δ) sin (6πft)
+ 2J ₅ (δ) sin (10πft)
So if you take the second order and ignore the third and higher,
cos γ = J ₀ (δ) + 2J ₂ (δ) cos (4πft) → corresponds to 2f component
sin γ = 2J ₁ (δ) sin (2πft) → corresponds to 1f component

Here, J _n (δ) represents an nth-order first-type Bessel function, δ is a phase modulation angle generated by vibration of PEM, and γ is retardation by PEM modulation.

Therefore, if the phase modulation angle of the PEM is ± δ and the modulation frequency is fHz, the retardation γ of the PEM is γ = δsin (2πft).

Therefore, when the PEM is transmitted, the following PEM modulated wave is obtained.

となるので、先のＰＥＭ変調波がこのフローセルを透過した信号は、下記のようになる。

Furthermore, when the flow cell 15 into which a sample having a circular birefringence (projection onto the S ₁ S ₂ plane becomes an optical rotation) Δ and a sample having a circular dichroism ψ is represented by a Mueller matrix,

Therefore, a signal obtained by transmitting the previous PEM modulated wave through the flow cell is as follows.

And since the light after passing through the flow cell 15 passes through the analyzer by rotating the transmission axis by 45 degrees, the light intensity after passing is expressed by the following equation.

By performing matrix operation on the right side of this equation, circular dichroism Ψ and circular birefringence Δ in the flow cell are obtained. Specifically, it is as follows.

As is apparent from the above equation, the signal S ₀ component is
1-sin γcos 2Ψ − cos γsin 2Ψ sin △
It is represented by Here, sin γ corresponds to the odd order of the Fourier expansion term, and cos γ corresponds to the even order, so if it is up to the second order, sin γ corresponds to the 1f component, and cos γ corresponds to the 2f component and the DC component. Since S ₀ is an expression that holds when γ is on the S ₃ axis, that is, −π / 2 ≦ γ ≦ π / 2, the following replacement can be made. When δ is small, “γ” is “π / 2-γ ", then
sin γ → sin (π / 2−γ) → cos γ
cos γ → cos (π / 2−γ) → sin γ
It becomes.

Therefore, when the analyzer is passed with the phase modulation angle reduced as in this embodiment, the signal received by the photodetector 19 from the above replacement is
1-2J (δ) sin (2πft) sin (Δ) sin (2Ψ) −J ₀ (δ) cos (2Ψ)
-2J ₂ (δ) cos (4πft) cos (2Ψ)
Thus, the optical rotation Δ appears in the 1f component, and the circular dichroism appears in the 2f component very small.

  Thus, the circular dichroism signal measured by removing the analyzer 46 and the optical rotation signal measured by arranging the analyzer 46 are both 1f components (50 Hz), and the optical rotation can be obtained by a simple signal processing circuit. Can be sought.

Figure 2 is a diagram of the Poincare sphere in the case of phase modulation angle δ is small viewed from S ₂ axially. For simplicity, let us consider a case where the phase rotation Φ is negligible. In the figure, arrows and dotted lines indicate the range of phase modulation, and indicate a state in which phase modulation is performed on the Poincare sphere with B-A and B-C around the point B. A thick arrow indicates a phase modulation vector. The circularly polarized birefringence at the point + δ appears as a rotation of the thick arrow vector | OA> on the circumference perpendicular to the paper surface with OA as the radius. The shadow of this vector is projected onto the S1S2 plane. Observing this vector from the S2 axis orientation will observe the signal with a polarizer (analyzer) tilted 45 °. That is, the projection of the thick arrow vector onto the S2 axis is observed as a signal. The circularly polarized birefringence at the point −δ appears as a rotation of a thick arrow vector | OC> on a circumference perpendicular to the paper surface with O-C as a radius. The projection of this vector onto the S2 axis is observed as a signal.

  In this case, the projection component due to the circular birefringence of the vectors | O−A> and | O−C> to the S2 axis is distributed as + − and appears as a 1f component. Here, when the phase rotation Φ is added, as the vectors | OC> and | OA> approach the S1 axis, the projected component of the circular birefringence signal onto the S2 axis increases, and therefore the symmetry of the optical rotation signal is increased. Collapse.

FIG. 3 is a view of the Poincare sphere viewed from the S2 axis direction when the phase rotation Φ is considered. Also in this figure, arrows and dotted lines are diagrams showing the range of phase modulation. That is, it shows a state where the phase of the Poincare sphere is phase-modulated with ABC. Precisely, the vector tip fixed around O is phase-modulated on the Poincare sphere as B-C and B-A around B. That is, it shows a state of being modulated to + δ and −δ. A thick arrow indicates a phase modulation vector. The circularly polarized birefringence at the point + δ appears as a rotation of the thick arrow vector | OA> tip on the circumference perpendicular to the paper surface with OA as the radius. This vector is projected onto the S ₁ S ₂ plane. Observing the vector from S ₂ axis orientation is to observe the signal at the polarizer is tilted 45 ° (analyzer). That projection of the S ₂ axis bold arrow vector is observed as a signal. The circularly polarized birefringence at the −δ point appears as a rotation of the thick arrow vector | OC> on the circumference perpendicular to the paper surface with OC as the radius. Projection of S ₂ axis of the vector is observed as a signal. In this case the vector of the _{S 2} axis | O-A>, | projection component by circular birefringence of the O-C> is + - sorted to appear as 1f component.

Here, if the rotation of the phase Φ is applied vector | O-C>, | because O-A> is the projection component to the S ₂ axis by the circular birefringence signal person approaching the S ₁ axis is greater optical rotation signal magnitude It affects. However, it can be seen that the symmetry of the optical rotation is not affected. In the case of circular dichroism measurement (CD measurement), since the projection of the S ₃ axis of the phase modulation vector Φ it is directly affects the symmetry. However, since it becomes the 2f component, it does not affect the 1f component.

  In addition to the fact that the optical rotation (OR) appears in the 1f component because the phase modulation width δ becomes small, the phase rotation of Φ that appears due to the effect of the polarization characteristics of the diffraction grating arranged next to the polarizer is 1 / It is considered that an effect similar to that obtained by inserting a four-wavelength plate is exerted, and the OR signal appears in the 1f component.

  When this is examined using the Mueller matrix, it is as follows. As shown in FIG. 6A, when plane polarized light parallel to the diffraction grating engraving is incident, both S-polarized light and P-polarized light form π / 4 with respect to the diffraction grating surface. It remains polarized. On the other hand, as shown in FIG. 6B, when the axis of the diffraction grating engraving line and the polarization axis is tilted, the angle between the S-polarization and P-polarization diffraction grating planes changes, so that a phase difference occurs, resulting in elliptical polarization. Become. In the case of measuring the optical rotation, the polarizer 25 is rotated, and as shown in FIG. 6B, elliptically polarized light is given to the PEM 13.

Considering such matters, the situation of taking out as an optical rotation signal when the phase rotation in the diffraction grating is taken into consideration is displayed as a Mueller matrix and considered as follows. When the retardation plate is displayed in the Mueller matrix, it is as follows. Here, Φ represents retardation associated with reflection at the diffraction grating (phase rotation due to polarization characteristics of the diffraction grating).

If the rotation angle of the polarizer (rotation angle from the horizontal direction in the direction of the easy axis of transmission of the polarizer) is α, and the phase change at that time is Φ, then Φ = f (α). Here, f (α) is a function indicating the phase rotation Φ generated when the polarizer is rotated by α around the optical axis. Assuming that Φ is a phase rotation in the PEM modulation direction, the signal of plane polarized light reflected by the diffraction grating is expressed as follows.

When the modulation angle of PEM is ± δ and the modulation frequency is fHz, the retardation γ of PEM is
γ = δsin (2πft)
It becomes. Therefore, when the plane polarized light passes through the PEM, the PEM modulated wave specified below is obtained. In the case of plane polarized light incidence, Φ is 0, and in the case of elliptically polarized light incidence, Φ is other than 0.

となる。よって、先の変調波がこの試料が供給されるフローセルを透過した信号は、

となる。 Furthermore, when the flow cell 15 into which a sample having a circular birefringence Δ and a circular dichroism Ψ is introduced is represented by a Mueller matrix,

It becomes. Therefore, the signal that the previous modulated wave has passed through the flow cell supplied with this sample is

It becomes.

This is because the Fourier expansion formula of the signal output is as follows using the first type Bessel function formula.

1-cos (2Ψ) (sin (γ) cos (Φ) + cos (γ) sin (Φ))
= 1−J ₀ (δ) cos (2Ψ) sin (Φ)
-2J ₁ (δ) cos (2Ψ) sin (2πft) cos (Φ)
-2J ₂ (δ) cos (2Ψ) cos (4πft) sin (Φ)
-2J ₃ (δ) cos (2Ψ) sin (6πft) cos (Φ)
-2J ₄ (δ) cos (2Ψ) cos (8πft) sin (Φ)
-2J ₅ (δ) cos (2Ψ) sin (10πft) cos (Φ)
≒ 1-2J ₁ (δ) sin (2πft) cos (2Ψ + Φ)
-2J ₃ (δ) sin (6πft) cos (2Ψ + Φ)
-2J ₅ (δ) sin (10πft) cos (2Ψ + Φ)

Can be approximated. This equation is the same as the one in which cos (2ψ + Φ) in the Fourier expansion equation of the signal output of a general CD measuring device is replaced with cos (2ψ + Φ). This is a phase shift Φ caused by rotating the polarizer shown in FIG. 1 about the optical axis. Using this Φ, it becomes possible to cancel the artifact signal included in 2Ψ directly related to the actual CD measurement.

The final signal that passes through the 45 ° polarizer and is received by the photodetector 19 is as follows.

When Fourier expansion of the signal component is performed, the result is as follows.
1-cos 2Ψ (sin (γ) cos (Φ) + cos (γ) sin (Φ))
−sin 2Ψsin △ (cos (γ) cos (Φ) −sin (γ) sin (Φ))
≒ 1-2J1 (δ) sin (2πft) cos (2Ψ + Φ)
-2J3 (δ) sin (6πft) cos (2Ψ + Φ)
-2J5 (δ) sin (10πft) cos (2Ψ + Φ)
-J0 (δ) sin (△) sin (2Ψ + Φ)
-2J2 (δ) cos (4πft) sin (△) sin (2Ψ + Φ)
-2J4 (δ) cos (8πft) sin (△) sin (2Ψ + Φ)

  In the above calculation, the effect of reducing the phase modulation angle due to the angle α obtained by rotating the polarizer of FIG. 1 is ignored. However, the phase modulation angle actually changes as δ = (π / 2) −2α. When α approaches π / 4, sin (δ−π / 2) and cos (δ−π / 2) become −cos (δ) and sin (δ), so that the 1f component and the 2f component are switched. . That is, the CD signal disappears and the optical rotation signal appears.

Furthermore, when the rotation angle α of the polarizer in FIG. 1 approaches π / 4, the above signal can be approximated by the following equation.

1-2J1 (δ) sin (2πft) sin (Δ) sin (2Ψ + Φ)
-2J3 (δ) sin (6πft) sin (Δ) sin (2Ψ + Φ)
-2J5 (δ) sin (10πft) sin (Δ) sin (2Ψ + Φ)
-J0 (δ) cos (2Ψ + φ)
-2J2 (δ) cos (4πft) cos (2Ψ + Φ)
-2J4 (δ) cos (8πft) cos (2Ψ + Φ)

  In this case, as will be described later, even if a quarter-wave plate is not inserted, Δ is detected as a 1f component if the rotation angle α of the polarizer is increased. In this signal, an alternating current component of 2f appears on the base.

  Further, as in this embodiment, the method of reducing δ is the same as the method of reducing the phase modulation width δ by directly controlling the modulation voltage of the PEM 13, and in this case, the analyzer 46 is used for CD measurement. The adjustment knob 42b is set to a rotation angle of 0 °, the voltage applied to the PEM 13 is increased, the phase modulation width is set to π / 2, and CD (circular dichroism) measurement is performed. Next, in the case of measuring the optical rotation, the polarization plane of the analyzer 46 is attached at an angle of 45 ° with respect to the polarization plane of the polarizer 25. Further, the optical rotation can be measured by reducing the voltage applied to the PEM 13 and setting the phase modulation width to about π / 9. As a result, it is possible to easily extract the CD signal and the OR signal from the output signal without changing any signal processing. The above method can obtain the same result even if the applied voltage of PEM is increased and the phase modulation width δ is π.

  FIG. 4 shows a second embodiment of the present invention. In the present embodiment, the quarter wavelength plate 50 is inserted between the PEM 13 and the lens L2 based on the apparatus of the first embodiment described above. Note that the insertion position of the quarter-wave plate 50 is not limited to the illustrated one, and may be provided between the lens L2 and the flow cell 15. Further, it can be provided in any one of the optical paths from the polarizer 25 to the PEM 13.

As described above, the signal S ₀ component (1-sin γcos 2Ψ−cos γsin 2Ψ sin Δ) shown in the equation (8) corresponds to sin γ corresponding to the odd order of the Fourier expansion term and cos γ corresponding to the even order. If up to the second order, sin γ corresponds to the 1f component, and cos γ corresponds to the 2f component and the DC component. Since S ₀ is an equation that holds when γ is on the S ₃ axis, that is, −π / 2 ≦ γ ≦ π / 2, when ¼ wavelength plate 50 is inserted, γ is γ−π. / 2.

Along with this,
sin γ → sin (γ−π / 2) → −cos γ
cos γ → cos (γ−π / 2) → sin γ
Can be replaced.

Therefore, when a quarter-wave plate is inserted, from the above replacement, the equation of the S ₀ component that is a signal received by the photodetector 19 is
1-2J ₁ (δ) sin (2πft) sin (Δ) sin (2Ψ) + J ₀ (Δ) cos (2Ψ)
+ 2J ₂ (δ) cos (2Ψ) cos (4πft)
Thus, the optical rotation Δ appears in the 1f component, and 2Ψ of the circular dichroic CD signal appears small in the 2f component.

  Thus, the circular dichroism signal measured by removing the analyzer 46 and the optical rotation signal measured by arranging the analyzer 46 are both 1f components (50 Hz), and the optical rotation can be obtained by a simple signal processing circuit. Can be sought.

The actual CD value is represented by 2Ψ = CD− (π / 2). Therefore,
cos (2Ψ) = cos (CD− (π / 2)) = sin (CD)
Since sin (CD) is substantially equivalent to CD, a CD signal is extracted.

Figure 5 is a view when 1/4 Poincare sphere when inserting a wavelength plate 50 from S ₂ axially. As in FIGS. 2 and 3, the arrows and dotted lines indicate the phase modulation range. That is, it is a diagram showing a state where the phase of the Poincare sphere is phase-modulated with ABC. The phase is modulated with B-A and B-C around the point B. A thick arrow indicates a phase modulation vector. The circularly polarized birefringence at the point + δ appears as a rotation of the thick arrow vector | OA> on the circumference perpendicular to the paper surface with OA as the radius. The shadow of this vector is projected onto the S1S2 plane. Observing this vector from the S2 axis orientation will observe the signal with a polarizer (analyzer) tilted 45 °. That is, the projection of the thick arrow vector onto the S2 axis is observed as a signal. The circularly polarized birefringence at the point −δ appears as a rotation of a thick arrow vector | OC> on a circumference perpendicular to the paper surface with O-C as a radius. The projection of this vector onto the S2 axis is observed as a signal. In this case, the projections of the vectors | O-A> and | O-C> due to circularly polarized birefringence onto the S2 axis are distributed as +-and appear as 1f components. In this embodiment, the rotation of the vector due to circular birefringence and the optical rotation plane completely coincide with each other, so that the optical rotation measurement is the best condition.

  In each of the above-described embodiments and modifications, the measurement was performed by making a measurement using a circular dichroism detector for HPLC and having an analyzer 46 attached to the incident light side. For this reason, the applied voltage of the PEM 13 is fixed and used in the product specifications, but it does not prevent the applied voltage from fluctuating. Furthermore, the system of the present invention can be applied to all the optical systems shown in the description of JP-A-11-201959.

It is a figure which shows 1st Embodiment of the optical rotation measuring apparatus which concerns on this invention. It is a figure explaining an operation principle. It is a figure explaining an operation principle. It is a figure which shows 2nd Embodiment of the optical rotation measuring apparatus which concerns on this invention. It is a figure explaining an operation principle. It is a figure explaining an effect | action.

Explanation of symbols

10 Light source 13 PEM
15 Flow cell 18 Quartz plate 19 Photo detector 25 Polarizer 46 Analyzer 50 1/4 wavelength plate G Diffraction grating

Claims (6)

The light transmission sequence is a light source, a polarizer, a phase modulation unit, a sample cell, and a light detection unit, and a dispersive element such as a diffraction grating or a prism, or between the polarizer and the phase modulation unit, Provided with a circular dichroism detection mechanism configured by arranging any of the monochromators,
In this mechanism, an analyzer is arranged between the sample cell and the light detection means,
An optical rotation measuring device characterized in that the phase modulation width δ is set smaller than π / 4. Rotating means for rotating the polarizer is provided, and the rotating means rotates the polarizer around the optical axis to rotate the polarization direction.
By making the narrow angle between the vibration direction of the phase modulation means and the easy transmission axis direction of the polarizer smaller than π / 4 that provides the maximum phase modulation width, the phase modulation width δ is less than π / 4. 2. The optical rotation measuring device according to claim 1, wherein the optical rotation measuring device is set to be small.   The phase modulation width δ of the phase modulation means is set to π / 2, and a quarter wave plate is installed in front of the sample cell or in front of the phase modulation means on the optical axis closer to the light source side, 2. The optical rotation measuring apparatus according to claim 1, wherein the phase modulation width Max point ± δ is set to move on the S1 axis.   2. The phase modulation means according to claim 1, wherein the phase modulation means is a PEM, and the phase modulation width δ is set smaller than π / 4 by reducing an applied voltage applied to the PEM. Optical rotation measuring device.   5. The optical rotation measuring apparatus according to claim 1, wherein a relative positional relationship is made such that a polarization plane of the analyzer is inclined by 45 ° with respect to a polarization plane of the polarizer. 6.   6. The light source according to claim 1, wherein the radiation intensity of the ultraviolet region, such as an HgXe lamp, an Hg lamp, or a deuterium lamp, is relatively large compared to other regions. The optical rotation measuring device according to item.

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