Spectrophotometer for chromatography and reference position detection method

Abstract

A diffraction lattice in this chromatographic spectrophotometer disperses light that has been generated by a light source into light having a plurality of different wavelengths. A sample cell receives light of any one of the wavelengths among the plurality of wavelengths of the light dispersed by the diffraction lattice. A photodetector detects light transmitting through the sample cell. A reference position detection unit: causes a motor to rotate in a first direction by a first angle until the amount of light received by the photodetector reaches or exceeds a predetermined threshold value, and then causes the motor to rotate by a second angle that is smaller than the first angle after the amount of light received by the photodetector has reached or exceeded the threshold value, and thereby detects a rotation angle of the motor at which a peak amount of light received by the photodetector appears; and detects a reference position corresponding to a reference angle of the diffraction lattice on the basis of the detected rotation angle.

Description

[Technical field]

[0001] The present invention relates to a spectrophotometer for chromatography and a method for detecting a reference position. [Background technology]

[0002] 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.

[0003] In such a spectrophotometer, for example, light generated by a light source is dispersed by a diffraction grating into a plurality of lights having different wavelengths. Among the dispersed plurality of lights, light having a specific wavelength is guided to a flow cell. The light transmitted through the flow cell is 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 of a wavelength appropriate for analyzing the sample is incident on 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 incident on the flow cell is also known. Therefore, light of a desired wavelength can be guided to the flow cell by adjusting the rotation angle of the diffraction grating from the reference position.

[0004] On the other hand, when the power supply to the spectrophotometer is turned off, the rotation shaft of the motor stops at an arbitrary angle, so the diffraction grating does not necessarily stop at the reference position.

[0005] 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 spectrophotometer is powered 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 spectrophotometer is powered on, the motor rotates the diffraction grating by one pulse until the home position sensor detects that the diffraction grating is in the home position. [Patent Document 1] JP 2018-13412 A Summary of the Invention [Problem to be solved by the invention]

[0006] 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 of the diffraction grating, and a photointerrupter that detects the protrusion may be used as the home position sensor. In these cases, the home position sensor requires parts costs, and manufacturing costs are required to mount the home position sensor.

[0007] An object of the present invention is to provide a spectrophotometer and a reference position detection method that enable a reduction in the cost for detecting the reference position of a diffraction grating. [Means for solving the problem]

[0008] A chromatographic spectrophotometer 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 a plurality of different wavelengths, a motor that changes the angle of the diffraction grating, a sample cell that receives light of any one of the plurality of wavelengths dispersed by the diffraction grating, a photodetector that detects light that passes through the sample cell, and a reference position detection unit that rotates 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 after the amount of light received by the photodetector becomes equal to or greater than the threshold, rotates the motor by a second angle smaller than the first angle to detect a rotation angle of the motor at which a peak in the amount of light received by the photodetector appears, and detects a reference position corresponding to a reference angle of the diffraction grating based on the detected rotation angle.

[0009] 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, the reference position detection method including the steps of generating light from a light source in the spectrophotometer; dispersing the light generated by the light source into light of a plurality of different wavelengths by a diffraction grating and guiding light of any one of the dispersed light of the plurality of wavelengths through a sample cell to a photodetector; 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; after the amount of light received by the photodetector becomes equal to or greater than the threshold, rotating the diffraction grating by a second angle smaller than the first angle to detect a rotation angle of the diffraction grating at which a peak of the amount of light received by the photodetector appears; and detecting the reference position based on the detected rotation angle. Effect of the Invention

[0010] According to the present invention, it is possible to reduce the cost for detecting the reference position of a diffraction grating in a spectrophotometer. [Brief description of the drawings]

[0011] [Figure 1]FIG. 1 is a block diagram showing the configuration of a chromatographic spectrophotometer according to one embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing the structure of a diffraction grating. [Diagram 3] FIG. 3 is a block diagram showing a functional configuration of the detector control unit in FIG. [Figure 4] FIG. 4 is a flowchart showing a reference position detection method according to the embodiment. [Diagram 5] 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. [Figure 6] FIG. 6 is an enlarged view of part A in FIG. [Figure 7] FIG. 7 is a block diagram showing the configuration of a liquid chromatograph including the spectrophotometer of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A spectrophotometer for chromatography and a reference position detection method according to embodiments will be described in detail below with reference to the drawings.

[0013] (1) Spectrophotometer configuration 1 is a block diagram showing the configuration of a spectrophotometer for a chromatography according to an embodiment of the present invention, which is used in, for example, a liquid chromatograph.

[0014] 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 an 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 enters the photodetector 15 through the flow cell 14.

[0015] 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 zeroth order light from the diffraction grating 13 includes light of multiple wavelengths. Therefore, the intensity of the zeroth order light is higher than the intensity of the light of any of the wavelengths.

[0016] Light having any wavelength among the light dispersed by the diffraction grating 13 is guided to a 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. A mobile phase and a 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 a 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.

[0017] 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.

[0018] 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.

[0019] 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 an output signal from 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, an analysis control unit 50 (FIG. 7) of a liquid chromatograph.

[0020] (2) Structure and operation of diffraction grating FIG. 2 is a schematic diagram showing the configuration of a 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.

[0021] When the power supply of the spectrophotometer 10 is turned off after the analysis of the sample, the angle of the diffraction grating 13 does not usually coincide with the reference position. In this case, when the power supply of the spectrophotometer 10 is turned off, it is necessary to detect the angle of the diffraction grating 13 with respect to the reference position. For this purpose, it is necessary to detect the reference position with respect 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 with respect 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 a 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 the normal operation.

[0022] (3) Functional configuration of the 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 reception 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.

[0023] 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 received light amount acquiring unit 303 acquires the amount of light received by the photodetector 15 based on the output signal of the photodetector 15, and also acquires the pulse signal and the direction indication signal from the motor driving unit 302. The received light amount acquiring 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 received light amount acquiring unit 303 adds the number of control pulses included in the pulse signal. When the rotation direction indicated by the direction indication signal is the reverse direction, the received light amount acquiring unit 303 subtracts the number of control pulses included in the pulse signal. In this way, the relationship between the number of control pulses and the amount of received light is obtained. The change in the amount of received light according to the change in the number of control pulses is sequentially stored in the storage unit 304.

[0024] 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.

[0025] (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 through the flow cell 14 to the photodetector 15, 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.

[0026] The operation switching unit 306 judges whether the power supply of the spectrophotometer 10 is turned on (step S1). If the power supply 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 by a first angle in the positive direction by applying 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.

[0027] The received light amount acquiring unit 303 acquires the amount of received light of the photodetector 15 based on the output signal of the photodetector 15 (step S5). The amount of received light acquired by the received light amount acquiring unit 303 is stored in the memory unit 304. The reference position detecting unit 305 judges whether the amount of received light stored in the memory unit 304 is equal to or greater than a preset threshold value Th (step S6). If the amount of received light is lower than the threshold value Th, the motor driving unit 302 returns to step S4 and applies M control pulses to the motor 16 to further rotate the diffraction grating 13 by a first angle in the positive direction. The processes of steps S4 to S6 are repeated until the amount of received light becomes equal to or greater than the threshold value Th. The processes of steps S4 to S6 perform rough adjustment of the diffraction grating 13 so that the angle of the diffraction grating 13 approaches the reference position.

[0028] If the amount of received light is equal to or greater than the threshold value Th in step S6, the motor driver 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 of M, and is 10 in this example.

[0029] In the example of FIG. 5, the amount of received light is equal to or greater than threshold value Th when diffraction grating 13 rotates in the forward direction from the initial state by an angle corresponding to control pulse number P1. At this time, the rotation angle of diffraction grating 13 exceeds the angle at which the amount of received light is at its peak. Also, as shown in FIG. 6, diffraction grating 13 returns in the reverse direction from the angle corresponding to control pulse number P1 by an angle corresponding to control pulse number K. As a result, the angle of diffraction grating 13 becomes an angle corresponding to control pulse number P2 from the initial state. At this time, the rotation angle of diffraction grating 13 is smaller than the angle at which the amount of received light is at its peak.

[0030] Next, the motor driver 302 applies N control pulses to the motor 16 to rotate the diffraction grating 13 in the positive direction by a second angle (step S8). N is smaller than M and K, and is, for example, 1.

[0031] The received light amount acquiring unit 303 acquires the amount of received light of the photodetector 15 based on the output signal of the photodetector 15 (step S9). The amount of received light acquired by the received light amount acquiring unit 303 is stored in the memory unit 304. The reference position detecting unit 305 judges whether or not the peak value of the amount of received light stored in the memory unit 304 has been detected (step S10). If the peak value of the amount of received light has not been detected, the motor driving unit 302 returns to step S8 and provides N control pulses to the motor 16 to further rotate the diffraction grating 13 by a second angle in the positive direction. The processes of steps S8 to S10 are repeated until the peak value of the amount of received light is detected.

[0032] In the example of FIG. 6, control pulses are provided to motor 16 one by one from a state in which the angle of diffraction grating 13 is an angle corresponding to control pulse number P2, and diffraction grating 13 rotates by a third angle. As a result, the amount of received light gradually increases, and the amount of received light reaches a peak value (maximum value) Pe when the angle of diffraction grating 13 is an angle corresponding to control pulse number P3. In this case, the amount of received light decreases when the angle of diffraction grating 13 rotates to an angle corresponding to control pulse number P4. As a result, it can be determined that the amount of received light reaches peak value Pe at an angle corresponding to control pulse number P3, which is before the angle corresponding to control pulse number P4. The method of determining whether or not peak value Pe of the amount of received light is detected is not limited to the above method, and other methods may be used.

[0033] When the 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 storage unit 304 (step S11). In the example of Fig. 6, the number of control pulses P3 is stored as the reference position in the storage unit 304. The control pulse corresponding to the reference position is accurately detected by the processing of steps S8 to S10.

[0034] Thereafter, 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 storage unit 304. The number of control pulses given to the motor 16 after the power supply of the spectrophotometer is turned on is given to the normal operation control unit 307. The normal operation control unit 307 calculates, for example, 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 having the specified wavelength among the light generated by the light source 11 is guided to the photodetector 15 through the flow cell 14.

[0035] (5) Liquid chromatograph FIG. 7 is a block diagram showing the configuration of a liquid chromatograph including the spectrophotometer 10 of FIG.

[0036] 7 includes a pump 110 for a 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 disposed within the column oven 150. The column oven 150 maintains the analytical column 140 at a set temperature.

[0037] Pump 110 draws in the mobile phase (eluent) in mobile phase container 111 and supplies it to analytical column 140. Sample introduction section 120 includes, for example, an autosampler or an injector, and introduces a sample to be analyzed into the mobile phase at introduction port 130. The mobile phase and sample that have passed through analytical column 140 flow through flow cell 14 (see FIG. 1) of spectrophotometer 10 and are discharged into waste liquid container 112.

[0038] 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.

[0039] (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 to be 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 allows the cost of detecting the reference position of the diffraction grating 13 in the spectrophotometer 10 to be reduced.

[0040] In this embodiment, when the amount of light received by photodetector 15 becomes equal to or greater than threshold value Th, motor 16 is rotated in the reverse direction by the third angle. Therefore, even if the first angle is set to a relatively large value, it is possible to detect the rotation angle of motor 16 at which the peak value of the amount of light received by photodetector 15 appears. This makes it possible to detect the reference position of diffraction grating 13 in a short time.

[0041] 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 having the highest intensity.

[0042] Moreover, the first angle is set to be smaller than an angle corresponding to a peak width at the intersection of the peak of the zeroth 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 a time point before the diffraction grating 13 is rotated by the first angle and a time point after the diffraction grating 13 is rotated by the first angle. Therefore, it is possible to reliably detect an angle at which the amount of received light is equal to or greater than the threshold value Th. Therefore, when an angle at which the amount of received light is equal to or greater than the threshold value Th is not detected, it is not necessary to perform a process such as resetting the first angle to a smaller value. As a result, it is possible to reliably detect the reference position of the diffraction grating 13 in a short time.

[0043] (7) Other embodiments In the above embodiment, the angle of diffraction grating 13 corresponding to the control pulse number at which the peak of the zero-order light from diffraction grating 13 appears is detected as the reference position, but the reference position is not limited to this. For example, the angle of diffraction grating 13 at which a peak of a specific wavelength appears when diffraction grating 13 is rotated may be detected as the reference position.

[0044] 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 always necessary to rotate the motor 16 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.

[0045] 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 the 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.

[0046] In the above embodiment, the number of control pulses M corresponding to the first angle is set to be smaller than the number of control pulses 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 number of control pulses M is not limited to this. For example, the number of control pulses M may be initially set to be large, and when the amount of received light does not become equal to or greater than the threshold value Th while the diffraction grating 13 is rotating within a certain angle range, a process may be performed in which the number of control pulses M is reduced.

[0047] During the reference position detection operation, the motor 16 may rotate once or within a predetermined angle range. In addition, a mechanism using a motor, a belt, and a pulley may be used to rotate the diffraction grating 13.

[0048] In the above embodiment, the spectrophotometer 10 is used in the liquid chromatograph 100, but the spectrophotometer 10 may be used in other chromatographs such as a supercritical chromatograph.

[0049] 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.

[0050] (8) Description It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0051] (Item 1) A chromatographic spectrophotometer according to one embodiment 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 by a first angle in a first direction 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.

[0052] According to the spectrophotometer for chromatography 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. This allows the diffraction grating to be adjusted close to the reference position in a short time. Thereafter, the motor is 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.

[0053] In this case, no additional member or element is required to detect the reference position of the diffraction grating, which makes it possible to reduce the cost of detecting the reference position of the diffraction grating in the spectrophotometer.

[0054] (2) The chromatographic spectrophotometer according to (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.

[0055] According to the spectrophotometer for chromatography described in paragraph 2, even if the first angle is set to a relatively large value, it is possible to detect the rotation angle of the motor at which the peak of the amount of light received by the photodetector appears, thereby making it possible to detect the reference position in a shorter time.

[0056] (Item 3) In the chromatographic spectrophotometer according to item 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.

[0057] According to the spectrophotometer for chromatography described in the third aspect, the reference position of the diffraction grating can be detected more accurately based on the intensity of the zeroth order light having the highest intensity.

[0058] (Item 4) In the chromatographic spectrophotometer described in Item 1, 2 or 3, the first angle may be smaller than an angle corresponding to a peak width at an intersection point between a peak of the amount of zero-order light received from the diffraction grating through the sample cell to the photodetector and the threshold value.

[0059] According to the spectrophotometer for chromatography described in the fourth aspect, a situation does not occur in which the amount of received light exceeds the threshold value between a time point before the diffraction grating is rotated by the first angle and a time point 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.

[0060] (Item 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, comprising: 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; 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.

[0061] 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 time. Thereafter, the diffraction grating is rotated by a second angle smaller than the first angle, and the rotation angle of the diffraction grating at which the amount of light received by the photodetector appears at a peak is detected. This allows the reference position of the diffraction grating to be accurately detected.

[0062] In this case, no additional member or element is required to detect the reference position of the diffraction grating, which makes it possible to reduce the cost of detecting the reference position of the diffraction grating in the spectrophotometer.

Claims

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.

2. 2. The chromatographic spectrophotometer 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 an 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 in increments.

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

4. 4. The chromatographic spectrophotometer according to claim 1, wherein the first angle is smaller than an angle corresponding to a peak width at an intersection point between a peak of a received light amount of zero-order light guided from the diffraction grating through the sample cell to the photodetector and the threshold value.

5. 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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