JP7136209B2 - chromatography detector - Google Patents

Description

The present invention relates to a chromatographic detector such as a differential refractive index detector and an absorbance detector.

A differential refractive index detector is known as a detector for liquid chromatography. The differential refractive index detector irradiates a flow cell having a sample cell and a reference cell partitioned by a partition wall with measurement light through a slit, and forms a slit image of the measurement light passing through the flow cell on a light receiving element. By measuring the amount of displacement of the slit image, the change in refractive index difference between the sample solution flowing through the sample cell and the reference solution flowing through the reference cell is detected (see Patent Document 1).

In recent years, solid state light emitting devices such as light emitting diodes (LEDs) and laser diodes (LDs) are often used as light sources for detectors. As described above, the differential refractive index detector detects changes in the refractive index based on the amount of displacement of the slit image formed on the light receiving element. Even if the actual position remains unchanged, variations in the amount of light from the light source are erroneously detected as displacement of the slit image, and are output as variations in the refractive index. Therefore, in a differential refractive index detector, in order to prevent erroneous detection of refractive index changes due to changes in elements other than those that should be recognized as refractive index changes, temperature control of the optical system and high-precision (low noise) light sources are required. Measures such as adoption of a drive power supply are taken.

JP 2017-223507 A

It has been found that problems such as erroneous detection of refractive index change, increase in noise, and deterioration in sensitivity occur in spite of the measures taken as described above. When examining the cause, while the light intensity is stable in the central region of the light emitting surface of a solid light emitting device such as an LED, the light intensity in the peripheral region of the light emitting surface fluctuates more than in the central region. is the cause of erroneous detection of refractive index change. This is due to variations in chip mounting of solid-state light emitting devices such as soldering, CAN packaging, and resin sealing, differences in stress accumulated in chips when chips are cut from wafers, and changes in processes (whether or not cleaning is performed, etc.). ) and the change in the base material.

Such variations in the amount of light within the light-emitting surface of the solid-state light-emitting device occur not only when the solid-state light-emitting device is used as a light source for a differential refractive index detector, but also when it is used as a light source for a detector such as an absorbance detector. adversely affect.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to enable a solid-state light-emitting device to be used as a light source for a detector with a stable amount of light.

The detector for chromatography according to the present invention comprises a solid-state light-emitting device that emits measurement light, a flow cell arranged on the optical path of the measurement light, a detection unit for detecting the measurement light that has passed through the flow cell, and the a light amount fluctuation reduction element provided between the solid light emitting element and the detection unit, and for reducing the influence of light amount fluctuation in a peripheral area of the light flux of the measurement light emitted from the solid light emitting element.

As the light amount fluctuation reduction element, an aperture light shielding plate that guides only the central region of the light flux of the measurement light emitted from the solid-state light emitting element to the flow cell can be used.

The aperture light shielding plate may shield 50% or more of light on the peripheral edge side of the light flux of the measurement light emitted from the solid-state light emitting device, and extract only the central region.

In a preferred embodiment, a first lens collects the measurement light from the solid-state light emitting device and irradiates it onto the opening light shielding plate, and collects the measurement light passing through the opening light shielding plate and irradiates it onto the flow cell. and a second lens.

Further, as the light amount fluctuation reduction element, a mask that covers the peripheral area of the light emitting surface of the solid light emitting element to block the light emitted from the peripheral area can be used.

Further, as the light amount fluctuation reduction element, a light diffusion plate can be used that mixes the central area and the peripheral area of the luminous flux of the measurement light emitted from the solid-state light-emitting element and guides them to the flow cell.

Since the detector for chromatography according to the present invention is provided with the light intensity fluctuation reduction element that reduces the influence of light intensity fluctuations in the peripheral area of the luminous flux of the measurement light emitted from the solid state light emitting element, the peripheral edge of the light emitting surface of the solid light emitting element The influence of fluctuations in the amount of light emitted from the region is reduced. As a result, the solid-state light-emitting device can be used as a light source for a detector with a stable amount of light.

1 is a schematic configuration diagram showing an example of a chromatographic detector; FIG. FIG. 4 is a conceptual diagram for explaining a peripheral area of measurement light that is blocked by a light amount fluctuation reducing element in the same embodiment; It is a figure which shows the modification of a light amount fluctuation|variation reduction element. FIG. 10 is a diagram showing a further modified example of the light intensity fluctuation reducing element; It is data showing the verification result of the relationship between the presence or absence of arrangement of the light intensity fluctuation reduction element and the stability of the detection signal of the light receiving element.

An embodiment of a differential refractive index detector, which is one of detectors for chromatography, will be described below with reference to the drawings.

As shown in FIG. 1, the differential refractive index detector includes a flow cell 2, a solid state light emitting element 4, a lens 5, an aperture shielding plate 8, a lens 10, a mirror 12, a zero glass 14, a light receiving element 16, and an arithmetic control unit 20. It has The solid light emitting device 4 is an LED or LD. The flow cell 2 is arranged on the optical axis of the measurement light 6 emitted from the solid state light emitting device 4 . The flow cell 2 has a sample cell 2a and a reference cell 2b, and these cells 2a and 2b are separated by a transparent partition.

A lens 10 is arranged in front of the flow cell 2, and a mirror 12 for reflecting the measuring light 6 transmitted through the flow cell 2 is arranged in the rear. A light receiving element 16 such as a photodiode is provided on the optical path of the measuring light 6a reflected by the mirror 12, and the measuring light 6a reflected by the mirror 12 and transmitted through the flow cell 2 forms an image on the light receiving element 16. . A zero glass 14 is arranged between the lens 10 and the light receiving element 16 on the optical path of the reflected measuring light 6a to translate the image of the measuring light 6a formed on the light receiving element 16 . An arithmetic processing unit 20 is connected to the light receiving element 16 .

The measurement light 6 emitted from the solid-state light-emitting element 4 is condensed by the lens 5, passes through the aperture light shielding plate 8, passes through the lens 10, is irradiated onto the flow cell 2, passes through the flow cell 2, and is reflected by the mirror 12. be done. The measurement light 6a reflected by the mirror 12 passes through the flow cell 2 again and is imaged on the light receiving element 16 by the lens 10. FIG. The light-receiving element 16 has two light-receiving regions 16A and 16B, and a detection signal based on the amount of light incident on each light-receiving region is fetched into the processing unit 20. FIG.

When the refractive index difference between the sample cell 2a and the reference cell 2b changes, the optical path of the measurement light 6 passing through the flow cell 2 changes, and the image of the measurement light 6a formed on the light receiving surface of the light receiving element 16 is oriented in a certain direction. to The light receiving areas 16A and 16B of the light receiving element 16 are arranged side by side in the displacement direction of the image of the measurement light 6a.

When the refractive index difference between the sample cell 2a and the reference cell 2b is 0, an image of the measurement light 6a is formed on the light receiving surface of the light receiving element 16 so as to straddle the boundary between the light receiving regions 16A and 16B. adjusted to When the sample component is introduced into the sample cell 2a and the refractive index in the sample cell 2a changes, the difference in refractive index between the sample cell 2a and the reference cell 2b changes and an image is formed on the light receiving surface of the light receiving element 16. The image of light 6a is displaced. The displacement is detected by taking the difference between the detection signal values of the light receiving regions 16A and 16B, and the refractive index difference between the sample cell 2a and the reference cell 2b is obtained.

The arithmetic processing unit 20 is implemented by a computer provided in this differential refractive index detector or a dedicated or general-purpose computer connected to this differential refractive index detector. The arithmetic processing unit 20 has a function of obtaining the refractive index difference between the sample cell 2a and the reference cell 2b in the flow cell 2 based on the detection signal values of the respective light receiving areas 16A and 16B of the light receiving element 16. FIG.

In this embodiment, an opening light shielding plate 8 is provided between the flow cell 2 and the solid state light emitting device 4 . The aperture light shielding plate 8, as shown in FIG. 2, shields the peripheral area of the light flux of the measurement light 6 emitted from the solid state light emitting element 4 and passed through the lens 5, and extracts only the central area. is. In other words, the aperture light shielding plate 8 constitutes a light amount fluctuation reducing element that reduces the influence of light amount fluctuations by shielding the peripheral region where the light amount fluctuations are large among the luminous flux emitted from the solid state light emitting element 4 .

The aperture light shielding plate 8 shields 50% or more of light on the peripheral edge side of the light flux of the measurement light 6 emitted from the solid-state light emitting device 4, and extracts only the central region. Originally, a slit is provided between the light source of the differential refractive index detector and the flow cell, but this slit is for extracting parallel light, and only the central region of the light flux where the light amount is stable is extracted. It's not for

The inventor of the present invention was the first to find out that the amount of light emitted from the peripheral region of the light emitting surface of the solid light emitting element 4 is unstable. Furthermore, in a detector such as a differential refractive index detector, if the amount of light that passes through the flow cell and reaches the light receiving part is small, there are problems such as a decrease in detection sensitivity and an increase in S/N. Blocking out most of the light is hitherto inconceivable.

From the viewpoint of shielding the light emitted from the peripheral region of the light emitting surface of the solid state light emitting device 4, as shown in FIG. A mask 8' made of metal, oxide, dielectric, or the like may be arranged as the light amount variation reduction element. The mask 8 ′ makes it possible to extract only the central region of the flux of the measurement light 6 emitted by the solid-state light emitters 4 .

Further, as shown in FIG. 4, the light in the central area and the light in the peripheral area of the measurement light 6 are mixed on the optical axis of the measurement light 6 emitted from the solid-state light-emitting device 4. A light diffuser 9 may be arranged to even out instabilities within the beam. As the light diffusing plate 9, a microlens array (for example, LSD (lens diffusing plate: a product of Optical Solutions Co., Ltd.)) having a light diffusing function can be used. With such a light diffusion plate 9, the light is mixed within the light flux of the measurement light 6 emitted from the solid-state light emitting element 4, the instability of the light intensity is uniformed within the light flux, and the influence of light intensity fluctuations in the peripheral region of the light flux is reduced. be done.

FIG. 5 shows data showing the results of verification of the relationship between the presence or absence of arrangement of the light amount fluctuation reducing element such as the aperture light shielding plate and the light diffusion plate and the stability of the detection signal of the light receiving element 16 .

In the verification of FIG. 5, under the condition that the refractive index difference between the sample cell 2a and the reference cell 2b does not change, the aperture light shielding plate 8 was placed on the optical axis of the measurement light 6 from the solid state light emitting device 4 (LED). In the case where the light diffusion plate 9 (LSD) was arranged, and in the case where the light amount fluctuation reduction element was not arranged, the variation of the detection signal was monitored. The aperture light shielding plate 8 used in this verification is designed to shield the peripheral side of the luminous flux of the measuring light 6 by about 70%.

If the refractive index difference between the sample cell 2a and the reference cell 2b does not change, theoretically, the signal intensity of the light receiving element 16 should be constant. However, as shown in FIG. 5, when the light amount fluctuation reduction element is not arranged, the signal intensity includes large noise and fluctuates between approximately 100 and 1100. FIG. When the signal intensity fluctuates in this way, it is erroneously detected as a displacement of the image of the measurement light 6a formed on the light receiving element 16, and is erroneously detected as a change in the refractive index difference between the sample cell 2a and the reference cell 2b. On the other hand, when the aperture light shielding plate 8 and the light diffusing plate 9 are arranged on the optical axis of the measurement light 6, the noise included in the signal intensity is small and the signal intensity of the light receiving element 16 is stable. Therefore, the change in refractive index difference between the sample cell 2a and the reference cell 2b is not erroneously detected.

In this way, by extracting only the central region of the light flux of the measurement light 6 or by mixing the central region and the peripheral region of the light flux using the light intensity fluctuation reduction element, the peripheral region of the light emitting surface of the solid state light emitting device 4 It is possible to reduce the influence of fluctuations in the amount of light emitted from the solid-state light-emitting element 4 on the detection signal, and to use the solid-state light-emitting element 4 as a light source for a detector with a stable amount of light.

The inventor also verified the relationship between the width dimension of the aperture of the aperture light shielding plate 8 and the signal intensity of the light receiving element 16 . The verification results are as follows.
Aperture width dimension (mm) Noise amount (ASTM)
1.92 67.42
1.37 59.84
0.70 43.53
0.50 22.21
0.42 18.64

From the above verification results, it can be seen that the smaller the aperture width dimension of the aperture light shielding plate 8, the smaller the noise amount. This indicates that the closer to the center of the measuring light beam 6, the more stable the light intensity, and conversely, the closer to the peripheral side of the measuring beam 6, the greater the light intensity fluctuation.

In the embodiment described above, the light amount fluctuation reducing elements such as the aperture light shielding plate 8 and the light diffusing plate 9 are arranged on the optical axis of the measurement light 6 between the solid light emitting device 4 and the flow cell 2. is not limited to this, and a light quantity fluctuation reducing element may be arranged on the optical axis of the measurement light 6a between the flow cell 2 and the light receiving element 16. FIG.

Further, in the above embodiments, a differential refractive index detector was described as an example of a detector for chromatography, but the present invention can also be applied to a detector such as an absorbance detector that uses a solid light emitting device as a light source. can be applied.

2 flow cell 2a sample cell 2b reference cell 4 solid state light emitting element 5, 10 lens 6, 6a measurement light 12 mirror 14 zero glass 16 light receiving element 20 arithmetic processing unit

Claims (5)

A solid-state light-emitting element that emits measurement light, wherein the light intensity is stable in a central region of the luminous flux of the measurement light, while the light intensity in the peripheral region of the luminous flux of the measurement light fluctuates more than in the central region. an element;
a flow cell arranged on the optical path of the measurement light;
a detection unit for detecting the measurement light that has passed through the flow cell;
a light amount fluctuation reduction element provided on the optical path of the measurement light between the solid state light emitting element and the detection unit, the element reducing the influence of light amount fluctuation in a peripheral area of the luminous flux of the measurement light emitted from the solid state light emitting element; , and
The light amount fluctuation reduction element guides only a central region of the luminous flux of the measurement light emitted from the solid-state light emitting device to the flow cell, and blocks a peripheral region of the luminous flux of the measurement light that fluctuates more than the central region.
Chromatographic detector. 2. The detector for chromatography according to claim 1, wherein said light amount fluctuation reduction element is an aperture light shielding plate. 3. The light shielding plate for chromatography according to claim 2, wherein the aperture light shielding plate shields 50% or more of light on the peripheral side of the light flux of the measurement light emitted from the solid-state light emitting device, and extracts only the central region. Detector. a first lens that collects measurement light from the solid-state light-emitting element and irradiates it onto the aperture light shielding plate;
4. The detector for chromatography according to claim 2, further comprising a second lens that condenses the measurement light that has passed through said opening light shielding plate and irradiates said flow cell. 2. The detector for chromatography according to claim 1, wherein said light amount fluctuation reduction element is a mask that covers a peripheral area of a light emitting surface of said solid light emitting element to block light emitted from said peripheral area.

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