JP7616054B2 - Spectrophotometer for chromatography and reference position detection method - Google Patents

Description

The present invention relates to a spectrophotometer for chromatography and a method for detecting a reference position.

Spectrophotometers are used, for example, in liquid chromatography to detect components of a sample separated in an analytical column. A spectrophotometer comprises a light source, a diffraction grating, a flow cell, and a light detector.

In such a spectrophotometer, for example, light generated by a light source is dispersed by a diffraction grating into multiple light beams having different wavelengths. Among the multiple dispersed light beams, light beams having a specific wavelength are guided to a flow cell. The light beams that pass through the flow cell are detected by a photodetector. In this case, the appropriate wavelength differs depending on the sample to be analyzed. Therefore, the angle of the diffraction grating is adjusted by a motor, so that light beams having an appropriate wavelength for analyzing the sample enter the flow cell. Here, the wavelength of light guided by the diffraction grating to the flow cell when the diffraction grating is at a predetermined reference angle (hereinafter referred to as the reference position) is known. In addition, the relationship between the rotation angle of the diffraction grating from the reference position and the wavelength of light entering the flow cell is also known. Therefore, by adjusting the rotation angle of the diffraction grating from the reference position, light beams of the desired wavelength can be guided to the flow cell.

On the other hand, when the power to the spectrophotometer is turned off, the motor shaft stops at an arbitrary angle. Therefore, the diffraction grating does not necessarily stop at the reference position.

In the spectrophotometer described in Patent Document 1, a home position sensor is provided near the diffraction grating to detect that the diffraction grating is in the home position. The home position sensor is, for example, a microswitch. When the power supply to the spectrophotometer is turned off, the motor rotates the diffraction grating by a fixed number of pulses until the home position sensor detects that the diffraction grating is in the home position. After that, the motor rotates the diffraction grating in the opposite direction by a predetermined number of pulses. When the power supply to the spectrophotometer is turned on, the motor rotates the diffraction grating by one pulse at a time until the home position sensor detects that the diffraction grating is in the home position.
JP 2018-13412 A

The spectrophotometer described in Patent Document 1 requires a home position sensor to position the diffraction grating at the home position. A protrusion is provided on the mounting member for the diffraction grating, and a photointerrupter that detects the protrusion is sometimes used as the home position sensor. In these cases, the home position sensor requires parts costs, as well as manufacturing costs for mounting the home position sensor.

The object of the present invention is to provide a spectrophotometer and a reference position detection method that enable reduction in the cost of detecting the reference position of a diffraction grating.

A spectrophotometer for chromatography according to one aspect of the present invention includes a light source, a diffraction grating that disperses light generated by the light source into light of multiple different wavelengths, a motor that changes the angle of the diffraction grating, a sample cell that receives light of one of the multiple wavelengths dispersed by the diffraction grating, a photodetector that detects light passing through the sample cell, and a reference position detection unit that detects the rotation angle of the motor at which the peak of the amount of light received by the photodetector appears by rotating the motor in a first direction by a first angle until the amount of light received by the photodetector becomes equal to or greater than a predetermined threshold value, and then detects the rotation angle of the motor at which the peak of the amount of light received by the photodetector appears based on the detected rotation angle.

A reference position detection method according to another aspect of the present invention is a reference position detection method for detecting a reference position corresponding to a reference angle of a diffraction grating in a spectrophotometer, and includes the steps of generating light from a light source in the spectrophotometer, dispersing the light generated by the light source into light of multiple different wavelengths by a diffraction grating, and guiding light of any one of the dispersed light of the multiple wavelengths through a sample cell to a photodetector, rotating the diffraction grating in a first direction by a first angle until the amount of light received by the photodetector becomes equal to or greater than a predetermined threshold value, detecting the rotation angle of the diffraction grating at which a peak in the amount of light received by the photodetector appears by rotating the diffraction grating by a second angle smaller than the first angle after the amount of light received by the photodetector becomes equal to or greater than the threshold value, and detecting the reference position based on the detected rotation angle.

The present invention makes it possible to reduce the cost of detecting the reference position of a diffraction grating in a spectrophotometer.

FIG. 1 is a block diagram showing the configuration of a chromatographic spectrophotometer according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing the structure of a diffraction grating. FIG. 3 is a block diagram showing the functional configuration of the detector control unit in FIG. FIG. 4 is a flowchart showing a reference position detection method according to the embodiment. FIG. 5 is a diagram showing an example of a change in the amount of light received by a photodetector depending on the number of control pulses given to a motor. FIG. 6 is an enlarged view of part A in FIG. FIG. 7 is a block diagram showing the configuration of a liquid chromatograph including the spectrophotometer of FIG.

Below, the spectrophotometer for chromatography and the reference position detection method relating to the embodiments are described in detail with reference to the drawings.

(1) Configuration of the Spectrophotometer Fig. 1 is a block diagram showing the configuration of a spectrophotometer for a chromatography according to one embodiment of the present invention. The spectrophotometer according to the present embodiment is used in, for example, a liquid chromatograph.

The spectrophotometer 10 in FIG. 1 includes a light source 11, a neutral density filter 12, a diffraction grating 13, a flow cell 14, a photodetector 15, a motor 16, and a detector control unit 30. In this embodiment, the light source 11 is, for example, a deuterium lamp. The motor 16 rotates the diffraction grating 13. In this embodiment, the spectrophotometer 10 performs a reference position detection operation and a normal operation. Here, the reference position refers to the angle of the diffraction grating 13 at which light of a predetermined wavelength is guided to the photodetector 15 through the flow cell 14. In this embodiment, the reference position of the diffraction grating 13 is defined as the angle of the diffraction grating 13 when the zero-order light reflected by the diffraction grating 13 is incident on the photodetector 15 through the flow cell 14.

During the reference position detection operation, the light generated by the light source 11 is attenuated by passing through the neutral density filter 12. The attenuated light is guided to the diffraction grating 13 by an optical system (not shown) such as a mirror. The mechanism for attenuating the light is not limited to the neutral density filter 12, and other members or devices may be used. When the amount of light from the light source 11 is small, the neutral density filter 12 may not be provided. On the other hand, during normal operation, the light generated by the light source 11 is guided to the diffraction grating 13 by the optical system without passing through the neutral density filter 12. The diffraction grating 13 reflects the incident light so as to disperse it into light of multiple wavelengths. In this case, the light of multiple wavelengths reflected by the diffraction grating 13 is reflected at different angles. The zero-order light from the diffraction grating 13 contains light of multiple wavelengths. Therefore, the intensity of the zero-order light is higher than the intensity of the light of any wavelength.

Light having any of the wavelengths of the light dispersed by the diffraction grating 13 is guided to the flow cell 14 by an optical system (not shown) such as a mirror. The flow cell 14 is an example of a sample cell. The wavelength of the light guided to the flow cell 14 changes depending on the angle of the diffraction grating 13. The mobile phase and sample supplied from, for example, an analytical column (separation column) of a liquid chromatograph flow through the flow cell 14. The light transmitted through the flow cell 14 is guided to the photodetector 15. The photodetector 15 includes, for example, a photodiode, and detects the intensity of the incident light. The intensity of the light detected by the photodetector 15 is equivalent to the amount of light received by the photodetector 15.

The wavelength of light suitable for analysis varies depending on the type of sample. Therefore, it is necessary to adjust the angle of the diffraction grating 13 so that light of a wavelength suitable for sample analysis passes through the flow cell 14 and enters the photodetector 15.

The detector control unit 30 includes an input/output I/F (interface) 31, a CPU (central processing unit) 32, a RAM (random access memory) 33, a ROM (read-only memory) 34, and a storage device 35. The input/output I/F 31, the CPU 32, the RAM 33, the ROM 34, and the storage device 35 are connected to a bus 38.

The storage device 35 includes a storage medium such as a semiconductor memory or a memory card, and stores a detector control program. The RAM 33 is used as a working area for the CPU 32. The ROM 34 stores a system program. The CPU 32 executes the detector control program stored in the storage device 35 on the RAM 33 to control the light source 11, the neutral density filter 12, and the motor 16 through the input/output I/F 31, and receives the output signal of the photodetector 15 through the input/output I/F 31. The detector control program also includes a reference position detection program. The CPU 32 executes the reference position detection program stored in the storage device 35 on the RAM 33 to implement a reference position detection method, which will be described later. The input/output I/F 31 is connected to, for example, the analysis control unit 50 (FIG. 7) of the liquid chromatograph.

(2) Configuration and Operation of the Diffraction Grating FIG. 2 is a schematic diagram showing the configuration of the diffraction grating. As shown in FIG. 2, the diffraction grating 13 has a diffraction grating reflecting surface 13a. The diffraction grating 13 is attached to the rotating shaft 16a of the motor 16 by a mounting member 13b. In this embodiment, the motor 16 is a stepping motor. The detector control unit 30 in FIG. 1 provides the motor 16 with a pulse signal including a control pulse and a rotation direction indication signal indicating the rotation direction. Each time a control pulse is provided to the motor 16, the rotating shaft 16a rotates by a fixed angle in the direction indicated by the rotation direction indication signal. As a result, the diffraction grating 13 rotates by a fixed angle in the forward or reverse direction as indicated by the arrow R. In this case, one control pulse corresponds to a fixed rotation angle of the motor 16. For example, when the motor 16 rotates once by providing 40,000 control pulses, the rotation angle of the motor 16 per one control pulse is 0.009 degrees.

When the power supply of the spectrophotometer 10 is turned off after the analysis of the sample, the angle of the diffraction grating 13 usually does not coincide with the reference position. In this case, it is necessary to detect the angle of the diffraction grating 13 relative to the reference position when the power supply of the spectrophotometer 10 is turned off. To do this, it is necessary to detect the reference position relative to the initial state of the diffraction grating 13 when the power supply is turned on. The relationship between the angle of the diffraction grating 13 relative to the reference position and the wavelength of the light incident on the photodetector 15 is known. Therefore, when the reference position is detected, the angle of the diffraction grating 13 can be set so that light of the desired wavelength is guided to the photodetector 15 through the flow cell 14 according to the sample. In this embodiment, the reference position of the diffraction grating 13 is detected by the reference position detection operation before normal operation.

(3) Functional Configuration of Detector Control Unit Fig. 3 is a block diagram showing the functional configuration of the detector control unit in Fig. 1. As shown in Fig. 3, the detector control unit 30 includes a light source driving unit 301, a motor driving unit 302, a light receiving amount acquiring unit 303, a storage unit 304, a reference position detecting unit 305, an operation switching unit 306, and a normal operation control unit 307. The functions of the above components (301 to 307) are realized by the CPU 32 in Fig. 1 executing a detector control program, which is a computer program stored in a storage medium (recording medium) such as a storage device. Note that some or all of the components of the detector control unit 30 may be realized by hardware such as an electronic circuit.

The light source driving unit 301 turns the light source 11 on and off. The motor driving unit 302 gives the motor 16 a pulse signal including a control pulse to rotate the motor 16 in the forward or reverse direction and a direction indication signal indicating the direction of rotation. The light reception amount acquisition unit 303 acquires the amount of light received by the light detector 15 based on the output signal of the light detector 15, and also acquires a pulse signal and a direction indication signal from the motor driving unit 302. The light reception amount acquisition unit 303 also integrates the number of control pulses included in the pulse signal. In this case, when the rotation direction indicated by the direction indication signal is the forward direction, the light reception amount acquisition unit 303 adds the number of control pulses included in the pulse signal. Also, when the rotation direction indicated by the direction indication signal is the reverse direction, the light reception amount acquisition unit 303 subtracts the number of control pulses included in the pulse signal. This allows the relationship between the number of control pulses and the amount of light received to be obtained. The change in the amount of light received according to the change in the number of control pulses is sequentially stored in the memory unit 304.

The reference position detection unit 305 controls the motor drive unit 302 and detects the reference position of the diffraction grating 13 based on the change in the amount of received light stored in the memory unit 304. The details of the reference position detection method will be described later. The operation switching unit 306 switches between the reference position detection operation and the normal operation. In addition, the operation switching unit 306 inserts the neutral density filter 12 into the optical path between the light source 11 and the diffraction grating 13 during the reference position detection operation, and removes the neutral density filter 12 from the optical path between the light source 11 and the diffraction grating 13 during the normal operation. Note that, when the amount of light from the light source 11 is small, the neutral density filter 12 does not need to be provided. The normal operation control unit 307 adjusts the angle of the diffraction grating 13 from the reference position by controlling the motor 16 based on the reference position stored in the memory unit 304. In this case, the normal operation control unit 307 adjusts the angle of the diffraction grating 13 so that light of a wavelength corresponding to the sample is guided to the photodetector 15 through the flow cell 14.

(4) Reference Position Detection Method FIG. 4 is a flow chart showing a reference position detection method according to an embodiment. FIG. 5 is a diagram showing an example of a change in the amount of light received by the photodetector 15 depending on the number of control pulses given to the motor 16. FIG. 6 is an enlarged view of part A in FIG. 5. The vertical axis in FIG. 5 and FIG. 6 indicates the amount of light received by the photodetector 15, and the horizontal axis indicates the number of control pulses given to the motor 16. The number of control pulses in FIG. 5 and FIG. 6 is added when the motor 16 rotates in the forward direction, and is subtracted when the motor 16 rotates in the reverse direction. As shown in FIG. 5 and FIG. 6, a threshold value Th for detecting the peak of the zeroth order light is set in advance. In this embodiment, the threshold value Th is set to be smaller than the peak value (maximum value) of the amount of light received of the zeroth order light guided from the diffraction grating 13 to the photodetector 15 through the flow cell 14 and larger than the amount of light received other than the zeroth order light. The reference position detection method in FIG. 4 is implemented by executing a reference position detection program.

The operation switching unit 306 determines whether the power of the spectrophotometer 10 is turned on (step S1). If the power is turned on, the light source driving unit 301 turns on the light source 11 (step S2). In this state, the operation switching unit 306 instructs the reference position detection unit 305 to perform a reference position detection operation, and inserts the neutral density filter 12 into the optical path between the light source 11 and the diffraction grating 13 (step S3). The motor driving unit 302 rotates the diffraction grating 13 in the positive direction by a first angle by giving M control pulses to the motor 16 (step S4). M is, for example, 20. In this embodiment, the number of control pulses M is set so that the first angle is smaller than the width of the peak of the zeroth order light at the intersection point between the peak of the zeroth order light and the threshold value Th.

The light-receiving amount acquisition unit 303 acquires the amount of light received by the light detector 15 based on the output signal of the light detector 15 (step S5). The amount of light received acquired by the light-receiving amount acquisition unit 303 is stored in the memory unit 304. The reference position detection unit 305 determines whether the amount of light received stored in the memory unit 304 is equal to or greater than a preset threshold value Th (step S6). If the amount of light received is lower than the threshold value Th, the motor drive unit 302 returns to step S4 and further rotates the diffraction grating 13 by a first angle in the positive direction by providing M control pulses to the motor 16. The processing of steps S4 to S6 is repeated until the amount of light received becomes equal to or greater than the threshold value Th. The processing of steps S4 to S6 performs rough adjustment of the diffraction grating 13 so that the angle of the diffraction grating 13 approaches the reference position.

If the amount of received light is equal to or greater than the threshold value Th in step S6, the motor drive unit 302 rotates the diffraction grating 13 in the reverse direction by a third angle by applying K control pulses to the motor 16 (step S7). K is, for example, half M, and is 10 in this example.

In the example of Figure 5, the amount of light received when the diffraction grating 13 rotates in the forward direction from the initial state by an angle corresponding to the control pulse number P1 is equal to or greater than the threshold value Th. At this time, the rotation angle of the diffraction grating 13 exceeds the angle at which the amount of light received is at its peak. Also, as shown in Figure 6, the diffraction grating 13 returns in the reverse direction from the angle corresponding to the control pulse number P1 by an angle corresponding to the control pulse number K. As a result, the angle of the diffraction grating 13 becomes an angle corresponding to the control pulse number P2 from the initial state. At this time, the rotation angle of the diffraction grating 13 is smaller than the angle at which the amount of light received is at its peak.

Next, the motor drive unit 302 rotates the diffraction grating 13 in the positive direction by a second angle by applying N control pulses to the motor 16 (step S8). N is smaller than M and K, for example, 1.

The light-receiving amount acquisition unit 303 acquires the amount of light received by the light detector 15 based on the output signal of the light detector 15 (step S9). The amount of light received acquired by the light-receiving amount acquisition unit 303 is stored in the memory unit 304. The reference position detection unit 305 determines whether or not the peak value of the amount of light received stored in the memory unit 304 has been detected (step S10). If the peak value of the amount of light received is not detected, the motor drive unit 302 returns to step S8 and further rotates the diffraction grating 13 a second angle in the positive direction by providing N control pulses to the motor 16. The processes of steps S8 to S10 are repeated until the peak value of the amount of light received is detected.

6, control pulses are given to the motor 16 one by one from a state in which the angle of the diffraction grating 13 is an angle corresponding to the control pulse number P2, and the diffraction grating 13 rotates by the third angle. As a result, the amount of received light gradually increases, and when the angle of the diffraction grating 13 is an angle corresponding to the control pulse number P3, the amount of received light reaches a peak value (maximum value) Pe. In this case, the amount of received light decreases when the angle of the diffraction grating 13 rotates to an angle corresponding to the control pulse number P4. As a result, it can be determined that the amount of received light reaches the peak value Pe at an angle corresponding to the control pulse number P3 before the angle corresponding to the control pulse number P4. The method of determining whether the peak value Pe of the amount of received light is detected is not limited to the above method, and other methods may be used.

When a peak value of the amount of received light is detected in step S10, the reference position detection unit 305 stores the number of control pulses corresponding to the peak value of the amount of received light as the reference position in the memory unit 304 (step S11). In the example of Figure 6, the number of control pulses P3 is stored in the memory unit 304 as the reference position. The control pulse corresponding to the reference position is accurately detected by the processing of steps S8 to S10.

Then, the operation switching unit 306 instructs the normal operation control unit 307 to perform normal operation. The relationship between the rotation angle of the diffraction grating 13 from the reference position and the wavelength is stored in advance in the memory unit 304. The number of control pulses given to the motor 16 after the power of the spectrophotometer is turned on is given to the normal operation control unit 307. The normal operation control unit 307, for example, calculates the difference between the number of control pulses given to the motor 16 and the number of control pulses corresponding to the reference position, and rotates the motor 16 by the motor drive unit 302 so that the difference in the number of control pulses corresponds to the wavelength specified according to the sample. As a result, the light of the specified wavelength among the light generated by the light source 11 is guided to the photodetector 15 through the flow cell 14.

(5) Liquid Chromatograph FIG. 7 is a block diagram showing the configuration of a liquid chromatograph including the spectrophotometer 10 of FIG.

7 includes a pump 110 for the mobile phase, a sample introduction section 120, an introduction port 130, an analytical column 140, a column oven 150, and a spectrophotometer 10. The analytical column 140 is provided in the column oven 150. The column oven 150 maintains the analytical column 140 at a set temperature.

The pump 110 draws in the mobile phase (eluent) in the mobile phase container 111 and supplies it to the analytical column 140. The sample introduction section 120 includes, for example, an autosampler or injector, and introduces the sample to be analyzed into the mobile phase at the introduction port 130. The mobile phase and sample that have passed through the analytical column 140 flow through the flow cell 14 (see FIG. 1) of the spectrophotometer 10 and are discharged into the waste liquid container 112.

The liquid chromatograph 100 includes an analysis control unit 50, an operation unit 51, and a display unit 52. The operation unit 51 is used by a user to give various commands to the analysis control unit 50. The analysis control unit 50 controls the pump 110, the sample introduction unit 120, the column oven 150, and the spectrophotometer 10. The analysis control unit 50 also generates a chromatogram based on the output signal of the spectrophotometer 10. The generated chromatogram is displayed on the display unit 52.

(6) Effects of the embodiment In the chromatographic spectrophotometer 10 and the liquid chromatograph 100 according to the present embodiment, the motor 16 is rotated in the forward direction by a first angle until the amount of light received by the photodetector 15 becomes equal to or greater than a predetermined threshold value Th. This allows the diffraction grating 13 to be roughly adjusted close to the reference position in a short time. Thereafter, the motor 16 is rotated by a second angle smaller than the first angle, thereby detecting the number of control pulses corresponding to the rotation angle of the motor 16 at which the peak value of the amount of light received by the photodetector 15 appears. This allows the reference position of the diffraction grating 13 to be accurately detected. In this case, no additional member or element such as a home position sensor is required to detect the reference position of the diffraction grating 13. This makes it possible to reduce the cost of detecting the reference position of the diffraction grating 13 in the spectrophotometer 10.

In addition, in this embodiment, when the amount of light received by the photodetector 15 becomes equal to or greater than the threshold value Th, the motor 16 is rotated in the reverse direction by the third angle. Therefore, even if the first angle is set relatively large, it is possible to detect the rotation angle of the motor 16 at which the peak value of the amount of light received by the photodetector 15 appears. This makes it possible to detect the reference position of the diffraction grating 13 in a short time.

Furthermore, in this embodiment, the reference position of the diffraction grating 13 can be detected more accurately based on the amount of received zero-order light, which has the highest intensity.

The first angle is set smaller than the angle corresponding to the peak width at the intersection of the peak of the zero-order light guided from the diffraction grating 13 through the flow cell 14 to the photodetector 15 and the threshold value Th. This prevents a situation in which the amount of received light exceeds the threshold value Th between the time before the diffraction grating 13 is rotated by the first angle and the time after the diffraction grating 13 is rotated by the first angle. Therefore, the angle at which the amount of received light is equal to or greater than the threshold value Th can be reliably detected. Therefore, when an angle at which the amount of received light is equal to or greater than the threshold value Th is not detected, there is no need to perform a process such as resetting the first angle to a smaller value. As a result, the reference position of the diffraction grating 13 can be reliably detected in a short time.

(7) Other Embodiments In the above embodiment, the angle of the diffraction grating 13 corresponding to the control pulse number at which the peak of the zero-order light from the diffraction grating 13 appears is detected as the reference position, but the reference position is not limited to this. For example, the angle of the diffraction grating 13 at which the peak of a specific wavelength appears when the diffraction grating 13 is rotated may be detected as the reference position.

In the above embodiment, when the amount of light received by the photodetector 15 becomes equal to or greater than the threshold value Th due to the rotation of the motor 16 in the forward direction by the first angle, the motor 16 is rotated in the reverse direction by the third angle. However, it is not necessarily necessary for the motor 16 to be rotated in the reverse direction by the third angle. For example, there are cases where the angle of the diffraction grating 13 does not exceed the angle corresponding to the peak value due to the rotation of the motor 16 in the forward direction by the first angle. In this case, when the amount of light received by the photodetector 15 becomes equal to or greater than the threshold value Th, the motor 16 may not be rotated in the reverse direction and the diffraction grating 13 may be fine-tuned.

In the above embodiment, the threshold value Th is set to be smaller than the maximum amount of received zero-order light and larger than the amount of received zero-order light, but the threshold value Th is not limited to this. For example, when the reference position is detected based on the peak of the amount of received light having a specific wavelength other than zero-order light, the threshold value Th may be set to be smaller than the peak value of the amount of received light having a specific wavelength and larger than the amount of received light having other wavelengths.

In the above embodiment, the control pulse number M corresponding to the first angle is set to be smaller than the control pulse number corresponding to the peak width at the intersection of the peak of the amount of received zero-order light and the threshold value Th, but the control pulse number M is not limited to this. For example, the control pulse number M may be initially set to be large, and when the diffraction grating 13 is rotating within a certain angle range, a process may be performed in which the control pulse number M is reduced if the amount of received light does not become equal to or greater than the threshold value Th.

During the reference position detection operation, the motor 16 may rotate once or within a predetermined angle range. Also, a mechanism using a motor, a belt, and a pulley may be used to rotate the diffraction grating 13.

In the above embodiment, the spectrophotometer 10 is used in a liquid chromatograph 100, but the spectrophotometer 10 may also be used in other chromatographs, such as a supercritical chromatograph.

In the above embodiment, the light source 11 is a deuterium lamp, but the light source 11 may be another lamp such as a tungsten lamp, or may be another light-emitting element such as a light-emitting diode.

(8) Aspects It will be understood by those skilled in the art that the exemplary embodiments described above are specific examples of the following aspects.

(Item 1) A chromatographic spectrophotometer according to one aspect comprises:
A light source;
a diffraction grating for dispersing the light generated by the light source into light of a plurality of different wavelengths;
A motor that changes the angle of the diffraction grating;
a sample cell for receiving light of any one of the plurality of wavelengths dispersed by the diffraction grating;
a photodetector that detects light passing through the sample cell;
and a reference position detection unit that detects a rotation angle of the motor at which a peak of the amount of light received by the photodetector appears by rotating the motor in a first direction by a first angle until an amount of light received by the photodetector becomes equal to or greater than a predetermined threshold, and then rotates the motor by a second angle smaller than the first angle after the amount of light received by the photodetector becomes equal to or greater than the threshold, and detects a reference position corresponding to a reference angle of the diffraction grating based on the detected rotation angle.

According to the chromatographic spectrophotometer described in paragraph 1, the motor is rotated in a first direction by a first angle until the amount of light received by the photodetector becomes equal to or greater than a predetermined threshold value. This allows the diffraction grating to be adjusted close to the reference position in a short period of time. The motor is then rotated by a second angle smaller than the first angle, and the motor rotation angle at which the peak of the amount of light received by the photodetector appears is detected. This allows the reference position of the diffraction grating to be accurately detected.

In this case, no additional members or elements are required to detect the reference position of the diffraction grating. Therefore, it is possible to reduce the cost of detecting the reference position of the diffraction grating in the spectrophotometer.

(2) The chromatographic spectrophotometer according to the above (1),
The reference position detection unit may rotate the motor in a second direction opposite to the first direction by a third angle smaller than the first angle and larger than the second angle when the amount of light received by the photodetector becomes equal to or greater than the threshold value, and then rotate the motor by the second angle.

According to the spectrophotometer for chromatography described in paragraph 2, even if the first angle is set relatively large, it is possible to detect the motor rotation angle at which the peak of the amount of light received by the photodetector appears. This makes it possible to detect the reference position in a shorter time.

(3) The chromatographic spectrophotometer according to claim 1,
The threshold value may be set to be smaller than a maximum received amount of zero-order light guided from the diffraction grating through the sample cell to the photodetector and larger than a received amount of light other than the zero-order light.

According to the spectrophotometer for chromatography described in paragraph 3, the reference position of the diffraction grating can be detected more accurately based on the intensity of the zeroth order light, which has the highest intensity.

(Clause 4) In the chromatographic spectrophotometer described in paragraphs 1, 2 or 3, the first angle may be smaller than an angle corresponding to a peak width at the intersection of the peak of the received amount of zero-order light guided from the diffraction grating through the sample cell to the photodetector and the threshold value.

According to the spectrophotometer for chromatography described in paragraph 4, a situation does not occur in which the amount of received light exceeds the threshold value between a point in time before the diffraction grating is rotated by the first angle and a point in time after the diffraction grating is rotated by the first angle. This eliminates the need to perform processing when the peak of the amount of received light of the photodetector is not detected. This makes it possible to reliably detect the reference position of the diffraction grating in a shorter time.

(5) A reference position detection method according to another aspect is a reference position detection method for detecting a reference position corresponding to a reference angle of a diffraction grating in a spectrophotometer, the method comprising the steps of:
generating light in the spectrophotometer with a light source;
dispersing the light generated by the light source into a plurality of light beams having different wavelengths by a diffraction grating, and guiding one of the plurality of light beams having different wavelengths to a photodetector through a sample cell;
rotating the diffraction grating in a first direction by a first angle until an amount of light received by the photodetector becomes equal to or greater than a predetermined threshold;
a step of detecting a rotation angle of the diffraction grating at which a peak of the amount of light received by the photodetector appears by rotating the diffraction grating by a second angle smaller than the first angle after the amount of light received by the photodetector becomes equal to or greater than the threshold value;
and detecting the reference position based on the detected rotation angle.

According to the reference position detection method described in paragraph 5, the diffraction grating is rotated in a first direction by a first angle until the amount of light received by the photodetector becomes equal to or greater than a predetermined threshold. This allows the diffraction grating to be adjusted close to the reference position in a short period of time. Thereafter, the diffraction grating is rotated by a second angle smaller than the first angle, thereby detecting the rotation angle of the diffraction grating at which the peak of the amount of light received by the photodetector appears. This allows the reference position of the diffraction grating to be accurately detected.

In this case, no additional members or elements are required to detect the reference position of the diffraction grating. Therefore, it is possible to reduce the cost of detecting the reference position of the diffraction grating in the spectrophotometer.

Claims (5)

1. A chromatographic spectrophotometer comprising:
A light source;
A diffraction grating that disperses light generated by the light source into light of a plurality of different wavelengths ,
a diffraction grating having a known relationship between an angle of the diffraction grating with respect to a reference position corresponding to a reference angle of the diffraction grating and a wavelength ;
a motor for changing an angle of the diffraction grating, the angle of the diffraction grating not coinciding with the reference position when the power supply of the chromatographic spectrophotometer is turned off;
a sample cell for receiving light of any one of the plurality of wavelengths dispersed by the diffraction grating;
a photodetector that detects light passing through the sample cell;
a reference position detection unit that detects the reference position when the power supply of the chromatographic spectrophotometer is turned on;
a control unit that controls the motor based on the detected reference position and adjusts the angle of the diffraction grating so as to guide light of a desired wavelength through the sample cell to the photodetector;
the reference position detection unit rotates the motor in a first direction by a first angle until the amount of light received by the photodetector becomes equal to or greater than a threshold value that is smaller than a predetermined peak, and after the amount of light received by the photodetector becomes equal to or greater than the threshold value, rotates the motor by a second angle that is smaller than the first angle to detect a rotation angle of the motor at which the peak of the amount of light received by the photodetector appears, and detects the reference position based on the detected rotation angle. The spectrophotometer for chromatography according to claim 1, wherein the reference position detection unit rotates the motor in a second direction opposite to the first direction by a third angle smaller than the first angle and larger than the second angle when the amount of light received by the photodetector becomes equal to or greater than the threshold value, and then rotates the motor by the second angle. The spectrophotometer for chromatography according to claim 1, wherein the threshold value is set to be smaller than the maximum amount of received zero-order light guided from the diffraction grating through the sample cell to the photodetector and larger than the amount of received light other than the zero-order light. The spectrophotometer for chromatography according to any one of claims 1 to 3, wherein the first angle is smaller than an angle corresponding to a peak width at an intersection point between the peak of the amount of received zero-order light guided from the diffraction grating through the sample cell to the photodetector and the threshold value. A reference position detection method for detecting a reference position corresponding to a reference angle of a diffraction grating in a spectrophotometer, comprising the steps of:
a relationship between an angle of the diffraction grating with respect to the reference position and a wavelength of light is known;
When the spectrophotometer is powered off, the angle of the diffraction grating does not coincide with the reference position,
generating light in the spectrophotometer by a light source when the spectrophotometer is powered on ;
dispersing the light generated by the light source into a plurality of light beams having different wavelengths by the diffraction grating, and guiding one of the plurality of light beams having different wavelengths to a photodetector through a sample cell;
rotating the diffraction grating in a first direction by a first angle until the amount of light received by the photodetector becomes equal to or greater than a threshold value that is smaller than a predetermined peak;
detecting a rotation angle of the diffraction grating at which the peak of the amount of light received by the photodetector appears by rotating the diffraction grating by a second angle smaller than the first angle after the amount of light received by the photodetector becomes equal to or greater than the threshold value;
and detecting the reference position based on the detected rotation angle.

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