JP7590637B2 - Absorbance measuring device - Google Patents

Description

The present invention relates to an absorbance measuring device. More specifically, the present invention relates to an absorbance measuring device suitable for cases where it is difficult to block external light from entering the cell space.

The absorbance measuring device performs measurement by introducing a sample liquid between a pair of cell windows and detecting measurement light transmitted between the pair of cell windows.
In order to prevent light other than the measurement light from entering the light receiving element, in the case of an absorbance measuring device used in a laboratory, the measurement is performed with the cell housed in a light-shielding housing.

When measuring absorbance continuously or intermittently at a factory or in an environment, it is relatively easy to block light from areas other than the cell window by using a flow cell.
However, when using a flow cell, a pump or the like is required to introduce the sample liquid into the cell, which inevitably makes the device large. For this reason, absorbance measurement devices of a type that measures absorbance simply by immersing a detector in the sample liquid, such as a pH electrode, are also used.

The device in Non-Patent Document 1 uses a detector in which a light source unit, which houses multiple light sources with different wavelengths at the tip of a rod-shaped body, and a light receiving unit, which houses multiple light receiving elements that receive light from each light source, are arranged horizontally facing each other. In this device, when the tip of the detector is immersed in a sample liquid, the cell space formed between the cell window of the light source unit and the cell window of the light receiving unit is filled with the sample liquid, making it possible to measure the absorbance of the sample liquid.
In addition, the opening of the cell space of this detector is located below on the opposite side to the rod-shaped body, and the upper part, where mainly external light enters, is connected to the rod-shaped body side, so that external light from above can be blocked by the rod-shaped body etc. to a degree that does not affect the measurement.

SPECIFICATION SHEET "Organic Pollution Monitor UV Meter OPM-1610 Type", DKK-TOA Corporation, November 29, 2019, p1-12

For detectors used in factories or on-site for measuring environmental water, the protective tube method, in which a rod-shaped detector is installed through a guide pipe, is widely adopted because it is strong enough to be installed and can be easily pulled up for maintenance and inspection.
However, in a structure in which a horizontally long member is attached to the tip of a rod-shaped body, such as the device in Non-Patent Document 1, the protective tube method cannot be adopted.

In order to adopt the protective tube method in an absorbance measuring device, it is necessary to arrange the light source unit and the light receiving unit facing each other vertically to form a rod-shaped detector. However, when the light source unit and the light receiving unit are arranged facing each other vertically, external light from above is more likely to enter the cell space than when they are arranged facing each other horizontally.
In particular, when the optical path length in the cell space is increased in order to perform more precise measurements, the influence of external light entering the cell space tends to become large.

Furthermore, when using multiple light sources and multiple light receiving elements as in the device of Non-Patent Document 1, it is necessary to secure an optical path between each light source and light receiving element, and it is difficult to accommodate it in a thin rod-shaped detector. Therefore, it is conceivable to achieve miniaturization by passing light from multiple light sources through a single optical path and detecting it with a single light receiving element.
However, when using a single light receiving element, it is necessary to use a light receiving element with a wide light receiving range, which means that the element will detect light other than the measurement light emitted from the light source, making it particularly susceptible to the effects of external light.

It is possible to arrange a light-shielding member around the cell space to block external light, but in that case, there is a risk that dirt will accumulate in the gaps between the light-shielding member and the light source and light-receiving unit, and that corrosion will occur.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an absorbance measuring device that is capable of performing accurate measurements even when intrusion of external light into a cell space is unavoidable.

In order to achieve the above object, the present invention employs the following configuration.
[1] An absorbance measurement device comprising a light source that emits measurement light, a light source side window through which the measurement light from the light source exits, a light receiving side window into which the light emitted from the light source side window enters, and a measurement light receiving element that detects the measurement light that has entered the light receiving side window, the device measuring the absorbance of a sample liquid introduced between the light source side window and the light receiving side window,
one or more light-shielding plates are provided in an optical path between the light-receiving side window and the measurement light-receiving element;
11. An absorbance measuring device, comprising: a light shielding plate disposed along a plane including an optical axis of the measurement light extending from the light-receiving side window to the measurement light-receiving element;
[2] The absorbance measuring device described in [1], comprising a first light-shielding plate along a first surface including the optical axis of the measurement light, and a second light-shielding plate along a second surface including the optical axis of the measurement light, wherein the first surface and the second surface intersect at the optical axis of the measurement light.
[3] The absorbance measuring device according to [1] or [2], wherein the reflectance of light of the wavelength to be measured with respect to the light-shielding plate is 10% or less.
[4] The absorbance measuring device according to any one of [1] to [3], wherein the light shielding plate has a thickness of 150 to 300 μm.
[5] An absorbance measuring device described in any one of [1] to [4], in which part or all of the optical path between the light-receiving side window and the measurement light-receiving element is surrounded by a peripheral wall having a convex portion that reflects light obliquely incident from the light-receiving side window in the direction of the light-receiving side window.
[6] The absorbance measuring device according to [5], wherein the reflectance of light having a wavelength to be measured on the convex portion is 10% or less.
[7] Further comprising a reference light receiving element and a beam splitter;
The absorbance measuring device according to any one of [1] to [6], wherein the beam splitter splits the light from the light source into the measurement light that passes through the light source side window and heads toward the light receiving side window, and a reference light that heads toward the reference light receiving element.
[8] The light source includes a first light source and a second light source,
the first light source is disposed at a position where the light of the first light source transmitted through the beam splitter can be emitted as the measurement light from the light source side window;
the second light source is disposed at a position where light is incident on a surface of the beam splitter opposite to a surface on which the light from the first light source is incident, and the light from the second light source reflected by the beam splitter can be emitted as the measurement light from the light source side window;
The absorbance measuring device according to [7], wherein the reference light receiving element is positioned so as to be capable of receiving the light of the first light source reflected by the beam splitter as the reference light, and to be capable of receiving the light of the second light source transmitted through the beam splitter as the reference light.

The absorbance measuring device of the present invention allows accurate measurements even when the intrusion of external light into the cell space is unavoidable.

1A and 1B are overall views of an absorbance measuring device according to an embodiment of the present invention, in which (a) is a top view and (b) is a side view. FIG. 2 is a partial longitudinal sectional view of the device of FIG. 1; FIG. 5A and 5B are schematic diagrams illustrating the function of a light blocking plate. 13A and 13B are diagrams for explaining the effect when an optical path is surrounded by a peripheral wall on which a female thread is formed.

As shown in FIG. 1, the absorbance measuring device 1 of this embodiment is roughly composed of a light source unit 10, a light receiving unit 30, and a cell section 50.
The light source unit 10 and the light receiving unit 30 are connected by a connection portion 51 in the cell portion 50 , and a cell space 57 is formed between the light source unit 10 and the light receiving unit 30 .

In the following description, the upper side of the drawing is the vertical upper side and the lower side of the drawing is the vertical lower side, that is, the light source unit 10 and the light receiving unit 30 are arranged opposite each other in the vertical direction (hereinafter, sometimes referred to as the "vertical use mode"). However, the use mode of the absorbance measuring device 1 is not limited to the vertical use mode.

A lead wire connection section 36 is provided on the top of the light receiving unit 30, and the signal obtained by the absorbance measuring device 1 is transmitted to an external indication conversion device or the like via a lead wire connected to the lead wire connection section 36.

2, in the light source unit 10, a light source side optical path space 12 is formed by a light source side optical path forming member 11. Note that the light source side optical path forming member 11 is composed of a plurality of members, and in addition to the light source side optical path space 12, a space for wiring and the like is formed, but detailed illustration is omitted.
A light source side window 13 is provided on the cell portion 50 side of the light source side optical path space 12, and together with an O-ring 14 and an O-ring 15, closes the light source side optical path space 12 liquid-tightly.

The light-source-side optical path forming member 11 accommodates a first light source 21 and a second light source 22 which emit measurement light and face the light-source-side optical path space 12, and a reference light-receiving element 23. A beam splitter 24 is also disposed within the light-source-side optical path space 12.
In addition, a temperature sensor 25 is provided on the upper surface of the light source side optical path forming member 11 .

The first light source 21 is disposed on the lower end side of the light-source-side optical path space 12 so as to face the light-source-side window 13 such that the optical axis of the light emitted from the first light source 21 is in the vertical direction.
In this specification and claims, the optical axis refers to the central axis of the optical path, and the optical path refers to the entire range through which light passes.
The second light source 22 is arranged on the side of the light source side optical path space 12 so that the optical axis of the light emitted from the second light source 22 is horizontal, i.e., so that the angle between the optical axis of the light emitted from the second light source 22 and the optical axis of the light emitted from the first light source 21 is 90 degrees.

The beam splitter 24 is disposed at a position where the optical axis of the light emitted from the first light source 21 and the optical axis of the light emitted from the second light source 22 intersect.
The beam splitter 24 is positioned at a 45 degree angle with respect to the optical axes of both light sources, so that the light emitted from the first light source 21 is incident on the bottom side of the beam splitter 24 and the light emitted from the second light source 22 is incident on the top side (the side opposite the bottom) of the beam splitter 24.

The light emitted from the first light source 21 and transmitted from the lower surface side to the upper surface side of the beam splitter 24 travels toward the light source side window 13 and can be emitted from the light source side window 13 to the cell space 57 as measurement light.
The light emitted from the second light source 22 and reflected on the upper surface side of the beam splitter 24 travels toward the light source side window 13 and can be emitted from the light source side window 13 to the cell space 57 as measurement light.

The light emitted from the first light source 21 and reflected by the lower surface side of the beam splitter 24 is directed to the reference light receiving element 23 as reference light.
The light emitted from the second light source 22 and transmitted from the upper surface side to the lower surface side of the beam splitter 24 is directed to the reference light receiving element 23 as reference light.
The reference light receiving element 23 is disposed on the side of the light source side optical path space 12 at a position where it can receive the reference light from both light sources.

In the light-receiving unit 30, a light-receiving side optical path space 32 is formed by a light-receiving side optical path forming member 31. Note that the light-receiving side optical path forming member 31 is composed of a plurality of members, and in addition to the light-receiving side optical path space 32, a space for wiring and the like is formed, but detailed illustration is omitted.
A light-receiving-side window 33 is provided on the cell portion 50 side of the light-receiving-side optical path space 32, and together with an O-ring 34 and an O-ring 35, closes the light-receiving-side optical path space 32 liquid-tightly.

The light-receiving side optical path forming member 31 houses a measurement light-receiving element 41 that detects measurement light at the upper end of the light-receiving side optical path space 32. A light-shielding plate 42 is also disposed within the light-receiving side optical path space 32. The light-shielding plate 42 is fixed to the light-receiving side optical path forming member 31 by a light-shielding plate mounting screw 45.
In addition, the lower side of the light-shielding plate 42 in the light-receiving side optical path space 32 is surrounded by a first peripheral wall 46 having a female thread 46a formed therein, and the upper side of the light-shielding plate 42 in the light-receiving side optical path space 32 is surrounded by a second peripheral wall 47 having a female thread 47a formed therein.

2 and 3, the cell section 50 has a cell space 57 into which a sample liquid is introduced between the light source units 10 and 30 connected by a connection part 51. The lower end of the cell space 57 faces the light source side window 13 of the light source unit 10, and the upper end faces the light receiving side window 33 of the light receiving unit 30, and the light source side window 13, the light receiving side window 33, and the cell space 57 between these windows form a measurement cell.
It should be noted that a space for wiring and the like is formed within the connecting portion 51, but detailed illustration is omitted.

In the cell section 50, a wiper support 52 that can be rotated by a motor (not shown) is erected between the light source unit 10 and the light receiving unit 30, and a wiper support 53 is attached to this wiper support 52. In addition, a wiper 54 and a pair of wiper pressing plates 55 that sandwich the wiper 54 are attached to the wiper support 53 with two mounting screws 56.
When the wiper support 52 is rotated, the wiper 54 rotates, and the top and bottom of the wiper 54 rub against the surfaces of the light source side window 13 and the light receiving side window 33, thereby cleaning both windows.

In addition, an inclined surface 10a is formed on the upper surface of the light source unit 10, which slopes down from the light source side window 13 along the tangent direction of the rotation of the wiper 54, making it easier to discharge dirt scraped off by the wiper 54 outside the cell section 50.
In addition, an inclined surface 30a is formed on the underside of the light-receiving unit 30, which rises along the tangent direction of the rotation of the wiper 54, making it easier to expel air bubbles adhering to the underside of the light-receiving unit 30 outside the cell portion 50.

Although there is no particular limitation on the type of the first light source 21 and the second light source 22, it is preferable to use a semiconductor light-emitting element such as a light-emitting diode (LED). A semiconductor light-emitting element has the advantages of easily obtaining light with a narrow wavelength half-width and having a clear optical axis. In addition, intermittent lighting is also possible.
The first light source 21 and the second light source 22 are not limited to semiconductor light emitting elements, and a low pressure mercury lamp, a laser light, or the like may be used.
Furthermore, a combination of a light source that emits light in a wide range of wavelengths, such as a deuterium lamp or a xenon lamp, and a bandpass filter or the like may be used as the first light source 21 or the second light source 22 .

The wavelength regions of the light emitted by the first light source 21 and the second light source 22 may be the same or different. If the two wavelength regions are the same, the measurement accuracy can be improved by double measurement. If the two wavelength regions are different, optical information in different wavelength regions can be obtained.
In addition, the two wavelength regions being different means that the two wavelength regions do not completely overlap. When the two wavelength regions are different, it is preferable that the wavelength range of the half width of the light emitted by the first light source 21 and the wavelength range of the half width of the light emitted by the second light source 22 are completely different regions and do not overlap.

There is no particular limitation on the specific range of the wavelength region of the light emitted by the first light source 21 and the light emitted by the second light source 22, but it is particularly suitable for application when one of the wavelength regions is in the ultraviolet light region.
According to this embodiment, the first light source 21 and the second light source 22 can be sufficiently separated from each other, and the light between them can be sufficiently shielded by the light-source-side optical path forming member 11. Therefore, even if one of the wavelength regions is an ultraviolet light region, there is no risk of the light source emitting light of the other wavelength region being deteriorated by ultraviolet light.

The beam splitter 24 is preferably a half mirror that splits the light so that the amount of light heading toward the light source side window 13 and the amount of light heading toward the reference light receiving element 23 are approximately equal, but is not limited to this.
Incidentally, since the refractive index of the beam splitter 24 is different from that of air, there is a slight deviation between the optical axis of the light incident on the beam splitter 24 and the optical axis of the light that passes through the beam splitter 24 and is emitted.

The measurement light receiving element 41 and the reference light receiving element 23 are each sensitive to at least a part of the wavelength range of the light emitted by the first light source 21 and at least a part of the wavelength range of the light emitted by the second light source 22.
This allows the measurement light receiving element 41 and the reference light receiving element 23 to be used as a common light receiving element even if the wavelength regions of the first light source 21 and the second light source 22 are different.
Photodiodes, phototransistors, etc. may be used as the measurement light receiving element 41 and the reference light receiving element 23. Photodiodes are preferred because they are inexpensive and easy to use.

As shown in Fig. 4, the light shielding plate 42 is provided along a plane including the optical axis X of the measurement light L from the light receiving side window 33 to the measurement light receiving element 41 in the optical path between the light receiving side window 33 and the measurement light receiving element 41. There is no limitation on the number of light shielding plates 42, but Fig. 4 shows an embodiment including a first light shielding plate 43 along a first plane including the optical axis X of the measurement light L and a second light shielding plate 44 along a second plane including the optical axis X of the measurement light L.
The first and second surfaces preferably intersect at the optical axis X of the measurement light, and more preferably at a right angle, so that the light blocking plate 42 can be disposed evenly in the optical path.
As shown in FIG. 4, it is preferable that the first light-shielding plate 43 and the second light-shielding plate 44 intersect on the optical axis X of the measurement light.

In addition, the light-shielding plate 42 only needs to be arranged along a plane including the optical axis X of the measurement light L in the optical path between the light-receiving side window 33 and the measurement light-receiving element 41, so the light-shielding plate 42 itself does not need to be a plane including the optical axis X of the measurement light L.
For example, in the embodiment of FIG. 4, only the intersection portion of the first light shielding plate 43 and the second light shielding plate 44 on the optical axis X may be removed in a pinhole manner.
That is, when the light blocking plate 42 is made up of multiple plates, the multiple plates may be arranged radially around the optical axis X, rather than intersecting each other. In this case, there is no limitation on the number of plates, and the number may be an odd number, such as three or five, or may be two. The light blocking plate 42 may be a single plate.

The thickness of the light shielding plate 42 is preferably 150 to 300 μm, more preferably 170 to 230 μm, and even more preferably 190 to 210 μm.
When the thickness of the light-shielding plate 42 is equal to or less than the preferable upper limit, it becomes difficult to reflect the measurement light L. When the thickness of the light-shielding plate 42 is equal to or more than the preferable lower limit, it becomes easier to maintain the necessary strength.

The length of the light shielding plate 42 is not particularly limited since it depends on the performance of the light source and the light receiving element, but is preferably 4 to 10 mm, more preferably 5 to 8 mm, and even more preferably 6 to 7 mm.
When the length of the light shielding plate 42 is equal to or greater than the preferable lower limit, it becomes easier to sufficiently exclude external light N. When the length of the light shielding plate 42 is equal to or less than the preferable upper limit, it becomes harder to weaken the intensity of the measurement light L. In addition, it is possible to avoid an increase in the size of the entire device.

The reflectance of the light having the wavelength to be measured on the light shielding plate 42 is preferably 10% or less, and more preferably 5% or less. The lower the reflectance, the more the intensity of the measurement light L reaching the measurement light receiving element 41 can be secured.
In order to reduce the reflectance, it is preferable to form the light shielding plate 42 from a material that does not easily reflect light of the wavelength to be measured, to change the color of the light shielding plate 42 to a color that does not easily reflect light of the wavelength to be measured, or to apply an anti-reflection treatment to the surface of the light shielding plate 42. Examples of the anti-reflection treatment include applying an anti-reflection paint, forming an anti-reflection film, roughening the surface, etc.
It is also preferable to form the light blocking plate 42 from a material that is difficult for the external light N to transmit, or to form the light blocking plate 42 from a material that is easy to absorb the external light N.
For example, when it is desired to measure light having wavelengths of 255 nm and 660 nm, a thin plate made of SUS and having been subjected to an alumite treatment can be used as the light blocking plate 42 .

When the light-shielding plate 42 is provided along a plane including the optical axis X of the measurement light L extending from the light-receiving side window 33 to the measurement light-receiving element 41, the measurement light L, although having some spread, travels straight at an angle close to the vertical direction at a point close to the optical axis X, and can reach the measurement light-receiving element 41 as shown in FIG. 4.
In contrast, even if external light N is reflected by the upper surface of the light source unit 10 and then enters the light-receiving side window 33, it is at an oblique angle to the vertical direction, so it hits the light-shielding plate 42 and cannot reach the measurement light-receiving element 41.

The first peripheral wall 46 has the female thread 46a formed thereon, and thus has the effect of reflecting the external light N in the direction of the light-receiving side window 33 to prevent the external light N from reaching the measurement light-receiving element 41. In other words, the female thread 46a corresponds to a convex portion that reflects light that is obliquely incident from the light-receiving side window in the direction of the light-receiving side window.
Here, "obliquely incident from the light-receiving side window" means that the optical axis of the light obliquely incident from the light-receiving side window is tilted from the optical axis X of the measurement light L to such an extent that it hits the convex portion of the peripheral wall.
The measurement light L travels straight at an angle close to the vertical direction in a location close to the optical axis X and does not substantially hit the first peripheral wall 46, so that it can pass through an optical path surrounded by the first peripheral wall 46 as shown in FIG. 5.
In contrast, even if external light N enters the light-receiving side window 33 , it is at an oblique angle to the vertical direction, so it hits the female threads 46 a of the first peripheral wall 46 and cannot pass through the optical path surrounded by the first peripheral wall 46 .

The second peripheral wall 47 also has a female thread 47a formed thereon, which acts to reflect the external light N in the direction of the light-receiving side window 33 and prevent the external light N from reaching the measurement light-receiving element 41. In other words, the female thread 47a corresponds to a convex portion that reflects the incident light in the direction of the light-receiving side window 33.
The convex portion that reflects the obliquely incident light to the light-receiving side window is not limited to a female thread, and may be, for example, an annular convex portion. However, a female thread is preferable because it allows the convex portion to be formed continuously around the entire circumference of the optical path and along the length direction, and is easy to process.
The peripheral wall on which the convex portion that reflects obliquely incident light is formed may be provided so as to surround the entire optical path between the light-receiving side window 33 and the measurement light-receiving element 41 .

The reflectance of the light having the wavelength to be measured on the convex portion that reflects the obliquely incident light to the light receiving side window is preferably 10% or less, and more preferably 5% or less. The lower the reflectance, the more the intensity of the measurement light L that reaches the measurement light receiving element 41 can be secured.
As a method for reducing the reflectance, the same method as the method for reducing the reflectance of the light blocking plate 42 can be used.

An example of the operation of the device of this embodiment will be described below using an apparatus for measuring chemical oxygen demand as an example, using an LED having a peak wavelength at 255 nm, which is in the ultraviolet light range, as the first light source 21 and an LED having a peak wavelength at 660 nm, which is in the visible light range, as the second light source 22.
In this example, the first light source 21 and the second light source 22 are turned on alternately.

When the first light source 21 is turned on with the second light source 22 turned off, the amount of light transmitted through the beam splitter 24, the light source side window 13, the cell space 57, and the light receiving side window 33 is measured by the measurement light receiving element 41, thereby enabling the absorbance at 255 nm to be measured.
The first light source 21 is feedback-controlled so that the amount of light is constant, based on the result of measuring the amount of light reflected by the beam splitter 24 by the reference light-receiving element 23 .
Moreover, instead of or in addition to the feedback control, the absorbance at 255 nm measured by the measurement light-receiving element 41 may be corrected by the amount of light measured by the reference light-receiving element 23 .

When the second light source 22 is turned on with the first light source 21 turned off, the amount of light reflected by the beam splitter 24 and transmitted through the light source side window 13, the cell space 57, and the light receiving side window 33 is measured by the measurement light receiving element 41, thereby making it possible to measure the absorbance at 660 nm.
The second light source 22 is feedback-controlled so that the amount of light is constant, based on the result of measurement of the amount of light transmitted through the beam splitter 24 by a reference light-receiving element 23 .
Moreover, instead of or in addition to the feedback control, the absorbance at 660 nm measured by the measurement light-receiving element 41 may be corrected by the amount of light measured by the reference light-receiving element 23 .

The absorbance at 255 nm is multiplied by a correction coefficient and the resulting value is subtracted from the absorbance at 660 nm. The result is converted into chemical oxygen demand (COD) based on a previously determined calibration curve, making it possible to determine the amount of organic pollution in the sample solution while eliminating the influence of turbidity.
The correction coefficient is appropriately set depending on the properties of the sample liquid.
Furthermore, by periodically rotating the wiper support 52 and using the wiper 54 to clean the light source side window 13 and the light receiving side window 33, stable absorbance measurements can be continued.

In the above example, an LED that emits light in the ultraviolet region is used as the first light source 21, and an LED that emits light in the visible region is used as the second light source 22. However, an LED that emits light in the ultraviolet region may be used as the second light source 22, and an LED that emits light in the visible region may be used as the first light source 21. There are also no particular limitations on the specific wavelengths of light emitted by each light source.

Although the first light source 21 and the second light source 22 are alternately turned on in the embodiment, the device of the present invention may be configured to turn on one light source continuously and the other intermittently. In this case, the absorbance of the light emitted from the intermittently turned on light source is calculated from the difference between the amount of light received when both light sources are turned on and the amount of light received when only the continuously turned on light source is turned on.
Furthermore, as a light source having a peak wavelength in the ultraviolet region, for example, a low pressure mercury lamp (peak wavelength: 254 nm) may be used.

In the present invention, the number of light sources may be one.
Furthermore, various optical elements, such as a condenser lens, an optical filter, a slit, a diaphragm, a shutter, etc., may be arranged in the optical path as long as they do not impair the spirit of the present invention.

Although the absorbance measuring device 1 has been described in accordance with a vertical use mode, the absorbance measuring device 1 may be used with its length direction oblique to the vertical direction. It may also be used with its length direction horizontal. Furthermore, as in Non-Patent Document 1, the present invention may be applied to a measuring device in which a light source unit and a light receiving unit are horizontally arranged opposite each other at the tip of a rod-shaped body.
Furthermore, even in the case of an apparatus that uses a flow cell, the effect of external light can be further reduced by applying the present invention.

[Example 1]
When the absorbance measuring device 1 was immersed in tap water in the upright usage mode, the measurement signal, base signal, and ratio of the measurement signal to the base signal detected by the measurement light receiving element 41 were obtained for each of 255 nm and 660 nm.
A deep ultraviolet LED was used as the first light source 21, a red LED was used as the second light source 22, and a silicon photodiode was used as the measurement light receiving element 41.

4, a first light-shielding plate 43 and a second light-shielding plate 44 were used, which intersected at a right angle with each other. Each of the first light-shielding plate 43 and the second light-shielding plate 44 was a thin plate made of SUS and having a thickness of 200 μm and a length of 6.5 mm, which was anodized.
The results are shown in Table 1.

[Example 2]
Except for using only the first light-shielding plate 43 instead of the light-shielding plate 42, the measurement signal detected by the measurement light-receiving element 41, the base signal, and the ratio of the measurement signal to the base signal were obtained for each of 255 nm and 660 nm in the same manner as in Example 1.
The results are shown in Table 1.

[Example 3]
Except for replacing the light-shielding plate 42 with only the second light-shielding plate 44, the measurement signal detected by the measurement light-receiving element 41, the base signal, and the ratio of the measurement signal to the base signal were obtained for each of 255 nm and 660 nm in the same manner as in Example 1.
The results are shown in Table 1.

[Comparative Example 1]
Except for not using the light-shielding plate 42, the measurement signal detected by the measurement light-receiving element 41, the base signal, and the ratio of the measurement signal to the base signal were obtained for each of 255 nm and 660 nm in the same manner as in Example 1.
The results are shown in Table 1.

As shown in Table 1, in the example, the measurement signal was slightly lower than in Comparative Example 1, but the base signal was significantly lower, and therefore an improvement in the ratio of the measurement signal to the base signal was observed. In particular, in Example 1, in which the light shielding plate 42 was formed by a first light shielding plate 43 and a second light shielding plate 44 intersecting at right angles, a significant improvement in the ratio of the measurement signal to the base signal was observed.

Reference Signs List 1 Absorbance measuring device 10 Light source unit 11 Light source side optical path forming member 12 Light source side optical path space 13 Light source side window 21 First light source 22 Second light source 23 Reference light receiving element 24 Beam splitter 25 Temperature sensor 30 Light receiving unit 31 Light receiving side optical path forming member 32 Light receiving side optical path space 33 Light receiving side window 41 Measurement light receiving element 42 Light shielding plate 46 First peripheral wall 47 Second peripheral wall 50 Cell portion 51 Connection portion 54 Wiper 57 Cell space L Measurement light N External light

Claims (8)

1. An absorbance measurement device comprising: a light source that emits measurement light; a light source side window through which the measurement light from the light source is emitted; a light receiving side window through which the light emitted from the light source side window is incident; and a measurement light receiving element that detects the measurement light incident on the light receiving side window, the absorbance measurement device measuring the absorbance of a sample liquid introduced between the light source side window and the light receiving side window,
one or more light-shielding plates are provided in an optical path between the light-receiving side window and the measurement light-receiving element;
11. An absorbance measuring device according to claim 10, wherein the light-shielding plate is provided along a plane including an optical axis of the measurement light extending from the light-receiving side window to the measurement light-receiving element. The absorbance measuring device according to claim 1, comprising a first light-shielding plate along a first surface including the optical axis of the measurement light, and a second light-shielding plate along a second surface including the optical axis of the measurement light, and the first surface and the second surface intersect at the optical axis of the measurement light. The absorbance measuring device according to claim 1 or 2, wherein the reflectance of the light of the wavelength to be measured on the light shielding plate is 10% or less. The absorbance measuring device according to any one of claims 1 to 3, wherein the thickness of the light shielding plate is 150 to 300 μm. The absorbance measuring device according to any one of claims 1 to 4, wherein a part or all of the optical path between the light receiving side window and the measurement light receiving element is surrounded by a peripheral wall having a convex portion formed thereon that reflects the light obliquely incident from the light receiving side window toward the light receiving side window. The absorbance measuring device according to claim 5, wherein the reflectance of the light of the wavelength to be measured on the convex portion is 10% or less. Further, a reference light receiving element and a beam splitter are provided,
The absorbance measuring device according to any one of claims 1 to 6, wherein the beam splitter splits the light from the light source into the measurement light that passes through the light source side window and heads toward the light receiving side window, and a reference light that heads toward the reference light receiving element. The light source includes a first light source and a second light source,
the first light source is disposed at a position where the light of the first light source transmitted through the beam splitter can be emitted as the measurement light from the light source side window;
the second light source is disposed at a position where light is incident on a surface of the beam splitter opposite to a surface on which the light from the first light source is incident, and the light from the second light source reflected by the beam splitter can be emitted as the measurement light from the light source side window;
8. The absorbance measuring device according to claim 7, wherein the reference light receiving element is arranged at a position capable of receiving, as the reference light, the light from the first light source reflected by the beam splitter, and receiving, as the reference light, the light from the second light source transmitted through the beam splitter.

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