JP5454492B2 - Spectrophotometer - Google Patents

Description

  The present invention relates to a spectrophotometer, and more particularly to a double beam type spectrophotometer that distributes measurement light in two directions by a rotating sector mirror or the like.

  The spectrophotometer has a double beam method and a single beam method depending on the configuration of the optical path. The double beam method is more advantageous than the single beam method in terms of analysis accuracy because it is possible in principle to cancel the influence of the light amount fluctuation of the light source in the process of calculating the absorbance.

  In a double beam spectrophotometer, a method of distributing monochromatic light extracted by a spectroscope (monochromator) into a sample side beam and a reference side beam using a rotating sector mirror is well known. For example, in the spectrophotometer disclosed in Patent Document 1, monochromatic light is alternately distributed into a sample-side light beam and a reference-side light beam by a sector mirror that is rotationally driven at a constant speed, and the sample-side light beam is irradiated onto a sample to be measured. The reference-side light beam is irradiated to a reference sample containing only the solvent, for example, which does not contain the component to be measured. Next, the light transmitted through the sample to be measured and the light transmitted through the reference sample are alternately introduced into one detector, and a signal corresponding to each transmitted light is detected. In addition, in order to measure a dark signal due to a dark current or the like in a state where light does not enter the detector, a light-shielding portion that shields light is provided integrally with the sector mirror.

  FIG. 3 is a block diagram of a conventional double beam spectrophotometer. In FIG. 3, light emitted from a light source 41 is introduced into a spectroscope 46 including an entrance slit 42, a diffraction grating 43, an exit slit 44, and a stepping motor 45, and monochromatic light having a predetermined wavelength is extracted from the spectroscope 46. . The stepping motor 45 changes the wavelength of the monochromatic light extracted through the exit slit 44 by changing the angle of the diffraction grating 43 with respect to the incident light that has passed through the entrance slit 42. The extracted monochromatic light, that is, measurement light, is alternately sent in the direction of the two reflecting mirrors 50 and 51 by the sector mirror 48 that is rotationally driven by a motor 49 at a constant speed.

  When the opening 93 arrives at the irradiation position of the monochromatic light from the spectroscope 46 along with the rotation of the sector mirror 48, the monochromatic light passes through the opening 93 and is irradiated onto the reflecting mirror 51 to become the sample-side light beam Ls. The sample 53 to be measured is irradiated. On the other hand, when the reflecting mirror 92 arrives at the irradiation position of the monochromatic light, the monochromatic light is reflected by the reflecting mirror 92 and then irradiated to the reflecting mirror 50 to be irradiated on the reference sample 52 as a reference side light beam Lr. . Further, when the light-shielding portions 94 and 95 arrive at the monochromatic light irradiation position, neither the sample-side light beam Ls nor the reference-side light beam Lr is irradiated.

  For example, the measured sample 53 is a sample cell filled with a measured sample solution, and the reference sample 52 is the same sample cell filled with only a solvent. In the sector mirror 48, an opening 93, a reflecting mirror 92, and light-shielding portions 94 and 95 are provided at intervals of 45 ° around the axis, and a similar portion is provided at a point-symmetrical position of the axis. Therefore, in one cycle (1/2 rotation period), the period during which the sample 53 to be measured and the reference sample 52 are irradiated with light is equal, and the period during which light is shielded is also equal.

  The reference-side light beam Lr that has passed through the reference sample 52 is reflected by the reflecting mirror 54, and the sample-side light beam Ls that has passed through the sample 53 to be measured is reflected by the reflecting mirrors 55 and 56, and both enter the detector 75. By the way, since the spectrophotometer performs spectral analysis in a wide wavelength range from the ultraviolet region to the infrared region, it becomes difficult to detect all wavelengths with one detector when the wavelength range becomes wide, and a plurality of detectors are installed. It will be necessary.

  FIG. 3 shows a case where a photomultiplier tube is used for the non-operating detector 57 and a photodiode is used for the operating detector 75 as an example. The detector 57 having the negative high voltage circuit 74 is connected to the control unit 40 through the current-voltage converter 72 and the AD converter 58, and the detector 75 is connected to the control unit 40 through the current-voltage converter 71 and the AD converter 58. Has been. By the way, when the measurement wavelength changes, the photomultiplier tube of the non-operating detector 57 is switched from the photodiode of the active detector 75 immediately, and a high voltage is constantly applied so that measurement can be started. Is desirable. However, if the photomultiplier tube of the non-operating detector 57 is input with abnormally large light such as external light, an excessive signal is output and deteriorates, so that it is applied to the photomultiplier tube of the non-operating detector 57. Negative high voltage is almost zero.

JP 2010-156655 A

  However, since the negative high voltage applied to the photomultiplier tube of the non-operating detector 57 is almost zero, when switching from the photodiode of the active detector 75 to the photomultiplier tube of the non-operating detector 57, Further, it is necessary to increase the negative high voltage of the non-operating detector 57 again, and it takes time to stabilize, so there is a disadvantage that analysis time becomes long. In addition, there is a drawback in that the accuracy of data deteriorates if data is taken without waiting for the negative high voltage to stabilize.

  In order to solve the above problems, the present invention provides means for alternately distributing measurement light to a sample-side optical path and a reference-side optical path, optical path switching means for shielding measurement light for a certain period in one cycle in the distribution, A double beam comprising a plurality of detectors for detecting a sample side signal passing through a sample to be measured arranged in a sample side optical path and a reference side signal passing through a reference sample arranged in the reference side optical path In the spectrophotometer of the system, the non-operating said photomultiplier tube using a voltage is applied during the stable waiting time of the dark signal when the measurement light is blocked when the measurement light is switched by the optical path switching means. It is provided with a protection means for protecting the detector.

  Further, the present invention provides a means for alternately distributing the measurement light into the sample side optical path and the reference side optical path, an optical path switching means for shielding the measurement light for a certain period in one cycle of the distribution, and the sample side optical path. In a spectrophotometer of a double beam system comprising a plurality of detectors for detecting a sample side signal that has passed through a measured sample and a reference side signal that has passed through a reference sample disposed in the reference side optical path, In order to measure the voltage applied to the detector using a photomultiplier tube during the measurement signal stabilization waiting time of the sample side signal or the reference side signal generated when the measurement light is switched by the optical path switching means The measuring means is provided.

  A new function for improving the performance of the spectrometer is added to the measurement signal stabilization standby time and the dark signal stabilization standby time.

  Without increasing the number of AD converters, it is possible to detect the abnormality of the signal of the photomultiplier tube and immediately perform the self-protection operation, so that reliable protection can be achieved.

It is a block diagram of the principal part of the spectrophotometer by the Example of this invention. It is a timing diagram for demonstrating the data processing in the spectrophotometer of the Example of this invention. FIG. 2A shows a “signal input to the detector”. FIG. 2B shows “measurement signal measurement time”. FIG. 2C shows “stable waiting time”. FIG. 2D shows a “signal input to the control unit from the photo sensor of the sector mirror”. FIG. 2E shows the “sector mirror mode”. It is a block diagram of the principal part of the conventional spectrophotometer.

  FIG. 1 is a configuration diagram of a main part of a double beam type spectrophotometer according to the present invention. In FIG. 1, light emitted from a light source 1 is introduced into a spectroscope 6 including an entrance slit 2, a diffraction grating 3, an exit slit 4, and a stepping motor 5, and monochromatic light having a predetermined wavelength is extracted from the spectroscope 6. . The stepping motor 5 changes the wavelength of the monochromatic light extracted through the exit slit 4 by changing the angle of the diffraction grating 3 with respect to the incident light that has passed through the entrance slit 2. The extracted monochromatic light, that is, measurement light, is alternately sent in the direction of the two reflecting mirrors 10 and 11 by the sector mirror 8 that is rotationally driven by the motor 9 at a constant speed.

  When the opening 83 arrives at the position where the monochromatic light from the spectroscope 6 is irradiated with the rotation of the sector mirror 8, the monochromatic light passes through the opening 83 and is irradiated onto the reflecting mirror 11 to become the sample-side light beam Ls. The sample 13 to be measured is irradiated. On the other hand, when the reflecting mirror 82 arrives at the irradiation position of the monochromatic light, the monochromatic light is reflected by the reflecting mirror 82 and then irradiated to the reflecting mirror 10 to be irradiated to the reference sample 12 as a reference side light beam Lr. Further, when the light shielding portions 84 and 85 arrive at the monochromatic light irradiation position, neither the sample-side light beam Ls nor the reference-side light beam Lr is irradiated.

  For example, the sample 13 to be measured is a sample cell filled with a sample solution to be measured, and the reference sample 12 is a sample cell filled with only a solvent. The sector mirror 8 is provided with an opening 83, a reflecting mirror 82, and light shielding portions 84 and 85 at an interval of 45 ° around the axis, and has a similar portion at a point-symmetrical position of the axis. Therefore, in one cycle (1/2 rotation period), the period during which the sample 13 to be measured and the reference sample 12 are irradiated with light is equal, and the period during which the light is shielded is also equal.

  Next, the movement of the sector mirror 8 will be described in detail. The sector mirror 8 is provided with reflecting mirrors 82, openings 83, and light-shielding portions 84 and 85 alternately around the axis. Now, assuming that the sector mirror 8 is installed at a position where the monochromatic light beam extracted from the spectroscope 6 is incident along the dotted line shown in FIG. Proceeds in the order of the reflecting mirror 82 → the light shielding portion 84 → the opening 83 → the light shielding portion 85 → the reflecting mirror 82 → the light shielding portion 84. FIG. 2 shows a timing chart for explaining data processing in the spectrophotometer of the present invention. As a mode of the sector mirror 8, as shown in FIG. 2 (e), reflection (R) → light shielding (DR ) → passing (S) → shading (DS) → reflection (R) → shading (DR).

  The sample-side light beam is irradiated to the sample to be measured during the passage (S), and the reference-side light beam is irradiated to the reference sample during the reflection (R) period. Note that light does not enter the detector during the period of light shielding (DS, DR). As a result, in the detector, the sample-side signal is time-divisionally transmitted during the passage (S) period, the reference-side signal is transmitted during the reflection (R) period, and the dark signal is transmitted during the light-shielding (DS, DR) period. can get.

  An example of the change in the detection signal is shown in FIG. Usually, when the sector mirror 8 rotates, the signal changes greatly before and after the switching of each sector. However, due to the restriction of the frequency response of the detector and the subsequent electric circuit, the change of the signal is as shown in the figure. Dullness occurs at the rise and fall. For this reason, a stable waiting time in which the signal shown in FIG. This detection signal is sampled at a predetermined sampling period and converted to a digital value in the AD converter. However, as described above, accurate data cannot be obtained in a range where the signal is not settled. Data is collected during the period shown in 2 (b). 2D shows a timing signal indicating when the sector mirror 8 is switched to the opening 83, the reflecting mirror 82, and the light shielding portions 84 and 85 from a photo sensor (not shown) installed in the sector mirror 8. In FIG. Show.

  That is, in FIG. 2B, Ds is the sample-side signal data collection period, Dr is the reference-side signal data collection period, Dds is the sample-side dark signal data collection period, and Ddr is the reference-side dark signal data collection period. It is. In FIG. 2C, Ts is a sample side signal stabilization standby time, Tr is a reference side signal stabilization standby time, Tds is a sample side dark signal stabilization standby time, and Tdr is a reference side dark signal stabilization standby time.

  The reference-side light beam Lr that has passed through the reference sample 12 is reflected by the reflecting mirror 14, and the sample-side light beam Ls that has passed through the sample 13 to be measured is reflected by the reflecting mirrors 15 and 16, and both are introduced into the detector 19. A detection signal from the detector 19 is input to the AD converter 18 via the current-voltage converter 31, sampled at a predetermined sampling period, and converted into a digital value. As a result, data corresponding to the intensity of the light incident on the detector 19 is obtained and input to the controller 20.

  By the way, since the spectrophotometer performs spectral analysis in a wide wavelength range from the ultraviolet region to the infrared region, it becomes difficult to detect all wavelengths with one detector when the wavelength range becomes wide, and a plurality of detectors are installed. It will be necessary. FIG. 1 shows a case where a photomultiplier tube is used for the non-operating detector 17 and a photodiode is used for the operating detector 19 as an example. The detector 17 is connected to the control unit 20 via the current-voltage converter 32 and the AD converter 18, and the detector 19 is connected to the control unit 20 via the AD converter 18. Here, a voltage is constantly applied to the non-operating detector 17, and when the measurement wavelength is changed, the non-operating detector 17 is immediately switched from the active detector 19 and measurement by the immediate detector 17 is started. By the way, if the photomultiplier tube of the non-operating detector 17 is input with abnormally large light such as outside light, an excessive signal is output and deteriorates, so that it is necessary to protect the detector 17.

  Therefore, when an abnormality is detected by the photomultiplier tube using the AD converter 18 during the dark signal stabilization standby time when the AD converter 18 is not used by the photodiode, a command from the control unit 20 is used. Thus, the protection operation of turning off the power of the photomultiplier tube is performed. However, abnormal input to the photomultiplier tube is not monitored except for the stable waiting time of the dark signal, but the stable waiting time occurs at intervals of 5 to 6 msec for normal measurement and at intervals of 10 to 12 msec for the slowest measurement. Protection of the photomultiplier tube is possible.

  Further, a voltage is constantly applied to the detector 17, and it is necessary to constantly monitor the voltage in order to ensure measurement accuracy. Therefore, the sample-side signal in which the AD converter 18 is not used by using the AD converter 18 that has been used only for the measurement of the sample-side detection signal and the reference-side detection signal without newly adding an AD converter. Alternatively, the voltage applied to the photomultiplier tube of the detector 17 by the negative high voltage circuit 34 is measured by the monitor circuit 33 during the detection signal stabilization standby time of the reference side signal. The measurement data is input to the control unit 20 via the AD converter 18, and if the reference voltage is deviated, the photomultiplier tube is turned off by the command from the control unit 20 and the measurement of the spectrometer is interrupted.

  The detection signal input to the AD converter 18 is sampled at a predetermined sampling period and converted into a digital value, and data corresponding to the intensity of the light incident on the detector 19 is obtained, which is input to the control unit 20. . Timing signal of change in input light amount when switching from the photosensor (not shown) installed in the sector mirror 8 to the opening 83, the reflecting mirror 82, and the light shielding portions 84 and 85 of the sector mirror 8 (FIG. 2D). The control unit 20 sends a control signal for controlling the stepping motor 5 and the motor 9 and the like. The control unit 20 selects and classifies necessary data, classifies and stores the data, and executes predetermined calculation processing using the data, and calculates the absorbance of the sample to be measured for each wavelength.

DESCRIPTION OF SYMBOLS 1, 41: Light source 2, 42: Entrance slit 3, 43: Diffraction grating 4, 44: Exit slit 5, 45: Stepping motor 6, 46: Spectrometer 8, 48: Sector mirror 9, 49: Motors 10, 11, 14, 15, 16, 50, 51, 54, 55, 56: Reflector 12, 52: Reference sample 13, 53: Sample 17 to be measured 17, 57: Detector (photomultiplier tube)
19, 75: Detector (photodiode)
18, 58: AD converter 20, 40: Control units 31, 32, 71, 72: Current-voltage converter 33: Monitor circuit 34, 74: Negative high voltage circuit 82, 92: Reflector 83, 93: Opening 84, 94: Shading part (R)
85, 95: Shading part (S)

Claims (2)

  Means for alternately distributing the measurement light to the sample-side optical path and the reference-side optical path, optical path switching means for shielding the measurement light for a certain period in one cycle of the distribution, and a sample to be measured disposed in the sample-side optical path A double-beam spectrophotometer comprising a plurality of detectors that detect a sample-side signal that has passed through and a reference-side signal that has passed through a reference sample disposed in the reference-side optical path. Protective means for protecting the non-operating detector using a photomultiplier tube to which a voltage is applied during the stable standby time of the dark signal at the time of shielding the measuring light that occurs when switching is performed by the optical path switching means A spectrophotometer characterized by that.   Means for alternately distributing the measurement light to the sample-side optical path and the reference-side optical path, optical path switching means for shielding the measurement light for a certain period in one cycle of the distribution, and a sample to be measured disposed in the sample-side optical path A double-beam spectrophotometer comprising a plurality of detectors that detect a sample-side signal that has passed through and a reference-side signal that has passed through a reference sample disposed in the reference-side optical path. Measuring means for measuring the voltage applied to the detector using a photomultiplier tube during the measurement signal stabilization waiting time of the sample side signal or the reference side signal that is generated when switching is performed by the optical path switching means. A spectrophotometer characterized by that.

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