Spectroscopic detector

1. A spectroscopic detector comprising:

a light source;

a flow cell having an internal space through which a sample flows;

a diffraction grating configured to disperse light from the light source so that intensity of one of plus side diffracted light and minus side diffracted light is higher than intensity of the other thereof;

a diffraction grating drive unit configured to adjust a rotation position of the diffraction grating within a range that light of a specified wavelength region of the plus side diffracted light and light of the specified wavelength region of the minus side diffracted light among diffracted light caused by the diffraction grating is selectively guided to the flow cell;

an optical sensor configured to detect light emitted from the flow cell due to light guided to the flow cell from the diffraction grating; and

a diffraction grating position adjustment unit configured to adjust the rotation position of the diffraction grating by controlling an operation of the diffraction grating drive unit in order to selectively guide one of the light of the specified wavelength region of the plus side diffracted light and the light of the specified wavelength region of the minus side diffracted light among the diffracted light caused by the diffraction grating.

2. The spectroscopic detector as recited in claim 1 , further comprising a measurement condition setting unit configured to set a level of intensity of light guided to the flow cell as a measurement condition along with a measurement wavelength,

wherein the diffraction grating position adjustment unit is configured to control the operation of the diffraction grating drive unit so as to adjust the rotation position of the diffraction grating in which diffracted light higher in intensity between the plus side diffracted light and the minus side diffracted light is guided to the flow cell when the intensity of light is set to high in the measurement condition setting unit, and

wherein the diffraction grating position adjustment unit is configured to control the operation of the diffraction grating drive unit so as to adjust the rotation position of the diffraction grating in which diffracted light lower in intensity between the plus side diffracted light and the minus side diffracted light is guided to the flow cell when the intensity of light is set to low in the measurement condition setting unit.

3. The spectroscopic detector as recited in claim 1 , further comprising a calibration information holding unit configured to hold information on a correlation between the rotation position of the diffraction grating and a wavelength of the light guided to the flow cell as calibration information for both a plus side region of the diffracted light and a minus side region of the diffracted light caused by the diffraction grating.

4. The spectroscopic detector as recited in claim 1 , further comprising an alteration characteristic measurement unit configured to guide the light of the specified wavelength region of the plus side diffracted light and the light of the specified wavelength region of the minus side diffracted light of the diffracted light caused by the diffraction grating to the flow cell at different timings in order to measure alteration characteristics of the sample in a state in which a measurement target sample flows through the flow cell, and obtain a detection signal of the optical sensor when the light of the specified wavelength region of the plus side diffracted light is being guided to the flow cell and a detection signal of the optical sensor when the light of the specified wavelength region of the minus side diffracted light is being guided to the flow cell.

5. The spectrophotometer as recited in claim 4 ,

wherein the alteration characteristic measurement unit is configured to judge whether or not a difference between the detection signal of the optical sensor when the light of the specified wavelength region of the plus side diffracted light is being guided to the flow cell and the detection signal of the optical sensor when the light of the specified wavelength region of the minus side diffracted light is being guided to the flow cell, determine that the sample is likely to be decomposed or altered by light when the difference is equal to or greater than a predetermined value, and determine that the sample is unlikely to be decomposed or altered by light when the difference is less than the predetermined value,

wherein, when it is determined that the sample is unlikely to be decomposed or altered by light, the diffraction grating position adjustment unit controls the operation of the diffraction grating drive unit so as to adjust the rotation position of the diffraction grating to a position in which the diffracted light higher in intensity between the positive side diffracted light and the minus side diffracted light is guided to the flow cell, and

wherein, when it is determined that the sample is likely to be decomposed or altered by light, the diffraction grating position adjustment unit controls the operation of the diffraction grating drive unit so as to adjust the rotation position of the diffraction grating to a position in which the diffracted light lower in intensity between the positive side diffracted light and the minus side diffracted light is guided to the flow cell.