JPH03274427A - Spectroscope - Google Patents

Abstract

PURPOSE:To measure at the high S/N even when the luminance of an exciting light to be monitored or an illuminating light is high by providing an extinction element with variable extinction rate at an optical path of an incident light entering a monitoring photomultiplier and, monitoring the impressed negative high pressure. CONSTITUTION:An exciting light 5 from an exciting spectroscope 6 is incident upon a flow cell 14 to which a liquid from a column for liquid chromatograph is guided. A fluorescent light 15 generated when a sample flowing in the flow cell 14 is excited by the exciting light 5 is incident upon a fluorescent spectroscope 16. The fluorescent light coming out from an exit slit 21 is detected by a measuring photomultiplier 22. In order to monitor the change of the luminance of a light source, a beam splitter 24 is provided at the optical axis of the exciting light 5 of the the exciting spectroscope 6. A part 5a of the separated exciting light 5 enters and is detected by a monitoring photomultiplier 28 through an extinction element 26 having variable extinction rate. If the element 26 is manually adjusted or is made automatically adjustable while the negative high pressure impressed to the photomultipliers 22, 28 is monitored, the impressed negative pressure can be raised nearly to a normal value.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is applicable to fluorescence monitors for liquid chromatographs, etc., which monitor fluorescence intensity fluctuations due to excitation light of a set wavelength while correcting changes in light source brightness, and for electrophoresis gels. Regarding spectroscopic devices such as fluorescence measuring instruments, in particular, in addition to a photomultiplier tube for sample measurement, a photomultiplier tube for monitoring is equipped as a photodetector to monitor the light source intensity, and the device responds to the detection signal of the photomultiplier tube for monitoring. This invention relates to a dinote feedback type spectrometer that controls the negative high pressure of a photomultiplier tube.

(Prior art) In spectroscopic instruments such as spectrofluorometers, in addition to measurement photomultiplier tubes that detect fluorescence, transmitted light, or reflected light from a sample, there are also photomultiplier tubes used for monitoring purposes to monitor changes in the light intensity of a light source. A dynode feedback system is used in which a photomultiplier tube is provided and the negative high voltage of the photomultiplier tube is controlled by a detection signal from a monitoring photomultiplier tube to correct changes in light source intensity.

(Problems to be Solved by the Invention) In a photomultiplier tube, the higher the negative high voltage, the better the ratio (S/N ratio) between the photocurrent, which is a signal component, and the dark current, which is a noise component. On the other hand, in the dynode feedback method, it is necessary to set the negative high voltage applied to the photomultiplier tube to be below the specified value (maximum allowable value) even in the lowest brightness region within the settable wavelength range of the excitation light used. Therefore, as shown in Figure 7, if the reference light incident on the monitor photomultiplier tube has a wavelength with low brightness, the negative high voltage is set high, but if the wavelength has high brightness, the negative high voltage is set high. The high pressure is set low, and dynode feedback is applied at a low level of negative high pressure. This indicates that, from the perspective of the detector, the conditions are not such that measurements can be made with the highest S/N ratio.

SUMMARY OF THE INVENTION An object of the present invention is to provide a spectroscopic device that can perform measurements with a high S/N ratio even when the excitation light or irradiation light to be monitored has high brightness.

(Means for Solving the Problems) The present invention provides a dynode feedback type spectrometer in which a light attenuation element with a variable attenuation rate is provided in the optical path of incidence to a monitoring photomultiplier tube, and the photomultiplier tube is provided with a light attenuation element having a variable attenuation rate. A monitor device is provided to monitor the applied negative high pressure, and the light attenuation rate of the light attenuation element is adjusted so that the negative high pressure increases within a range that does not exceed a permissible value.

(Function) When a monitoring photomultiplier tube is installed to monitor the excitation light separated by an excitation spectrometer, the applied negative high voltage is set to a level close to the specified value at a wavelength with low brightness. Assuming this, when the wavelength becomes high in brightness, the amount of light incident on the monitoring photomultiplier tube increases and the negative high voltage decreases. Therefore, the light attenuation rate of the light attenuation element is increased to raise the negative high pressure to near the specified value.

(Embodiment) FIG. 1 shows an embodiment in which the present invention is applied to a fluorescence monitor.

2 is a xenon lamp as a light source, 4 is a concave mirror for condensing light,
Light from the xenon lamp 2 enters an excitation spectrometer 6.

10 is an entrance slit of the excitation spectrometer 6, 12 is an exit slit, and 8 is a concave diffraction grating as a dispersion element.

Reference numeral 14 denotes a flow cell into which the column effluent of the liquid chromatograph is guided, and the excitation light 5 from the excitation spectrometer 6 is incident on the flow cell 14 . Fluorescence 15 generated when the sample flowing through the flow cell 14 is excited by the excitation light 5 is detected by the fluorescence spectrometer 1.
6. 20 is an entrance slit of the fluorescence spectrometer 16;
18 is a concave diffraction grating which is a dispersion element, and 21 is an exit slit. Fluorescence passing through the exit slit 21 is detected by a photomultiplier tube 22 for measurement.

In order to monitor variations in light source brightness, a beam splitter 24 is provided on the optical axis of the excitation light 5 of the excitation spectrometer 6. A portion 5a of the excitation light 5 separated by the beam splitter 24 passes through a light attenuation element 26 whose light attenuation rate is variable, enters a monitoring photomultiplier tube 28, and is detected. The light attenuation element 26 is capable of spatially changing the amount of light passing through.
For example, a mechanism that changes the cross-sectional area of a hole through which light can pass, such as a camera's aperture mechanism, can be used.

The negative high pressure of the photomultiplier tube 22 and the photomultiplier tube 28 is adjusted in accordance with the detection signal of the monitoring photomultiplier tube 28 using a die note feedback method.

FIG. 2 shows the dynode feedback type measurement system in FIG. 1.

The detection signal from the measurement photomultiplier tube 22 is amplified by a preamplifier 3o, and then passed through an overcurrent protection circuit 32 and recorded on a recorder 34. The detection signal of the monitor photomultiplier tube 28 is amplified by the preamplifier 36 and compared with the reference voltage Vr by the comparator 38, and the output signal of the comparator 38 is DC/
It is input to the negative high voltage generator 4o of the DC converter. A negative high voltage -Vd is applied from the negative high voltage generator 40 to the photomultiplier tubes 22 and 28.
is applied, and feedback is applied so that the amplified detection signal of the monitoring photomultiplier tube 28 in the comparator 38 becomes equal to the reference voltage Vr.

A level monitor 42 is provided in the negative high voltage generator 4o to monitor the negative high voltage -Vd. Level monitor 42
The circuit has a function of notifying that the negative high voltage has reached a set value (a value slightly lower than the specified value), and can be configured as a circuit as shown in FIG. 3, for example.

In FIG. 3, 44 is a comparison section, and the negative high pressure generator 4
A negative high voltage -Vd from 0 is divided by a resistor circuit and applied. The comparison unit 44 includes, for example, an amplifier 46 and a comparator 48.
A negative high voltage setting value -vo is applied to the non-inverting input terminal of the comparator 48. A monitor lamp 50 is connected to the output terminal of the comparator 48.

In the level monitor shown in FIG. 3, the monitor lamp 50 lights up when the negative high pressure reaches the set value.

The operation of the embodiment shown in FIGS. 1 to 3 will be explained.

It is assumed that among the excitation wavelengths of the excitation spectrometer 6, the negative high voltage applied to the photomultiplier tubes 22 and 28 is set to a set value close to the specified value at the wavelength with the lowest brightness.

When the excitation wavelength of the excitation spectrometer 6 is set to a certain wavelength, when the monitor brightness of the excitation light 5 increases and the negative high pressure decreases,
The lighting of the level monitor 42 goes out.

Therefore, when the light attenuation rate is increased by adjusting the light attenuation element 26, the amount of light incident on the monitoring photomultiplier tube 28 decreases, and the negative high pressure increases. When the negative high pressure reaches the set value, the lamp 50 of the level monitor 42 lights up, so the dimming element 26 is set in that state.

The above embodiment shows an example in which the measurer manually adjusts the light attenuation element 26 while monitoring the negative high pressure with the level monitor 42, but if the light attenuation element 26 is a mechanism that can be automatically adjusted, The dimming element 26 can be automatically and optimally set using the negative high pressure monitor value.

FIG. 4 shows an example of automating the adjustment of the dimming element.

A comparator 60 is provided, which compares the negative high voltage -Vd from the negative high pressure generator 4o with a set value -vo, and automatically operates the dimming element 26 until the negative high voltage -Vd becomes equal to the set value.

An example of an automatically adjustable light attenuation element is an ND filter 5 that does not have wavelength dependence, as shown in FIG. 5, for example.
2 attached to the rotating shaft of the motor 54 can be used. The motor 54 is, for example, a stepping motor, and by rotating the motor 54, the ND filter 5
The amount of reference light 5a that passes through 2 can be changed.

As the light attenuation element 26, for example, as shown in FIG. 6, a filter plate 56 in which a large number of light transmission holes are formed in a thick plate in a direction perpendicular to the plane of the plate may be used. The filter plate 56 may be attached to the motor 58 so that the rotation axis of the motor 58 is aligned in the in-plane direction of the plate 56. The reference light 5a is made incident on the filter plate 56 and transmitted, and the motor 58 separates the reference light 5a from the surface of the filter plate 56.
By changing the angle between the reference beam 5a and the incident direction of the reference beam 5a, the amount of the reference beam 5a that passes through the filter plate 56 can be changed.

Even a diaphragm mechanism, such as the one commonly used in cameras, can automatically change the amount of transmitted light.

(Effects of the Invention) In the present invention, in a dynode feedback type spectrometer, the negative high pressure is set to be close to the maximum allowable value when the brightness of the reference light incident on the monitoring photomultiplier tube is low. In addition, when the intensity of the reference target incident on the monitor photomultiplier tube becomes high, such as at a wavelength with high light source brightness, the attenuation rate of the attenuation element is increased to maintain the negative high pressure at a high level. Even if the amount of light incident on the monitoring photomultiplier tube changes, the S/N ratio can be maintained at a high level.

[Brief explanation of drawings]

Fig. 1 is a perspective view of the main parts of an embodiment in which the present invention is applied to a fluorescence monitor, Fig. 2 is a circuit diagram showing a measurement system in the same embodiment, and Fig. 3 is an example of the level monitor in Fig. 2. FIG. 4 is a block diagram showing the control section of an embodiment that automatically adjusts the dimming element, and FIGS.
Each figure is a configuration diagram showing an example of an automatically adjustable dimming element. FIG. 7 is a diagram showing the light source brightness and negative high voltage setting in the conventional dynode feed bank system. 2...Xenon lamp, 6...Excitation spectrometer, 8°18...Concave diffraction grating, 14...Flow cell, 16...Fluorescence spectrometer, 22... ... photomultiplier tube for measurement, 26 ... attenuation element, 28.
...Photomultiplier tube for monitor, 42...Level monitor. Figure 2, Figure 3, Figure 4-V.

Claims (1)

[Claims] (1) A dynode that is equipped with a photomultiplier tube for monitoring to monitor the light source intensity in addition to the photomultiplier tube for sample measurement, and that controls the negative high pressure of the photomultiplier tube according to the detection signal of the photomultiplier tube for monitoring. In a feedback type spectrometer, a light attenuation element with a variable attenuation rate is provided in the optical path of incidence to the monitoring photomultiplier tube, and a monitor device for monitoring the negative high pressure is provided so that the negative high pressure does not exceed a permissible value. A spectroscopic device characterized in that the light attenuation rate of the light attenuation element is adjusted so that it becomes high within a range.