JP2015152522A - Concentration measurement method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a concentration measurement method that can measure concentration of a substance even when attenuation of excitation light occurs.SOLUTION: A method of irradiating a fluid having a substance of a measurement object contained with excitation light to measure concentration of the substance on the basis of intensity of fluorescence emitted from the substance by the excitation light includes: a measurement process of irradiating a measurement object fluid having the substance contained at unknown concentration with the excitation light to respectively measure intensity of the excitation light and the fluorescence intensity; a reference process of referring to reference information indicative of a corresponding relation between the excitation light of arbitrary intensity with which a reference fluid having the substance contained at known fixed concentration is irradiated and the fluorescence intensity emitted by the excitation light and serving as a reference value to acquire the reference value of the fluorescence intensity corresponding to a measurement value of the excitation light intensity acquired in the measurement process; and a concentration acquisition process of acquiring concentration of a substance in a measurement object fluid on the basis of a ratio of the actual measurement value of the fluorescence intensity acquired in the measurement process to the reference value of the fluorescence intensity acquired in the reference process and the known substance concentration in the reference fluid.

Description

  The present invention relates to a method and apparatus for measuring the concentration of a substance contained in a fluid such as liquid or gas.

Laser-induced fluorescence (LIF) is known as a method for measuring the concentration of a substance contained in a measurement field composed of a fluid such as liquid or gas. In this laser-induced fluorescence method, a substance to be measured is irradiated with laser light, the intensity of fluorescence emitted from the substance excited by the laser light is measured, and the concentration of the substance is obtained based on the intensity of the fluorescence. Is the method.
Patent Document 1 below discloses a concentration measuring apparatus using the laser-induced fluorescence method as described above. This concentration measurement device irradiates a measurement field containing a substance to be measured with laser light, captures fluorescence emitted from molecules of the substance to be measured with a CCD camera, obtains the fluorescence intensity from the captured image, and obtains the substance concentration. ing.

JP-A-7-43303

In the laser-induced fluorescence method as described above, the concentration of a substance is obtained using the relationship that the intensity of fluorescence emitted from a substance excited by laser light having a constant intensity is proportional to the concentration of the substance.
However, since a laser beam is attenuated in a measurement field having a wide area with respect to the direction of laser light irradiation, the intensity of the laser light changes depending on the distance from the light source, and the intensity of the fluorescence emitted from the substance also changes. Therefore, when the laser-excited fluorescence method is applied to a wide measurement field, even if the fluorescence intensities are different from each other at multiple points in the irradiation direction, the change is due to the attenuation of the laser light or the concentration of the substance is different. Therefore, it is difficult to accurately determine the concentration.

  In view of the above problems, an object of the present invention is to provide a concentration measuring method and apparatus capable of measuring even when excitation light is attenuated.

(1) In the concentration measuring method according to the first aspect of the present invention, the substance containing the substance to be measured is irradiated with excitation light, and the substance is based on the intensity of fluorescence emitted from the substance by the excitation light. A method for measuring the concentration of
A measurement step of irradiating a measurement target fluid containing the substance at an unknown concentration with excitation light, and actually measuring the excitation light intensity and fluorescence intensity,
Referring to the reference information showing the correspondence between the excitation light of arbitrary intensity irradiated to the reference fluid containing the substance at a known constant concentration and the fluorescence intensity serving as the reference value emitted thereby, the measurement A reference step for obtaining a standard value of fluorescence intensity corresponding to the actual measurement value of the excitation light intensity obtained in the step;
Based on the ratio between the actual value of the fluorescence intensity acquired in the measurement step and the standard value of the fluorescence intensity acquired in the reference step, and the known substance concentration in the reference fluid, the concentration of the substance in the measurement target fluid And a concentration acquisition step of acquiring.

When a reference fluid containing a substance at a known concentration and a measurement target fluid containing a substance at an unknown concentration are irradiated with laser light of the same intensity, the reference value of the fluorescence intensity acquired for the reference fluid The ratio of the fluorescence intensity obtained for the measurement target fluid to the measured value coincides with the ratio of the known concentration to the unknown concentration (see formula (7) described later). Therefore, this unknown concentration can be obtained if the three values of the reference value and the actual measurement value of the fluorescence intensity and the known concentration become clear.
Of the three values, the actual value of fluorescence intensity is measured in the measurement process, and the known concentration is known in advance. Therefore, if the reference value of the remaining fluorescence intensity is obtained, an unknown concentration can be obtained. It becomes. In the present invention, the reference value of the fluorescence intensity is obtained from the reference information corresponding to the actually measured value of the excitation light intensity measured in the measurement target fluid. Since this reference information is obtained from a reference fluid containing the substance at a known constant concentration, the reference value of the fluorescence intensity indicated in the reference information is excited without being affected by changes in the concentration of the substance. The data takes into account only the change (attenuation) of light. Therefore, by using this reference information, the concentration can be measured even in a fluid in which excitation light is attenuated.

(2) The concentration measurement method of the present invention may further include a step of generating the reference information.

(3) Further, the reference information irradiates a reference fluid containing the substance at a known constant concentration with excitation light, measures excitation light intensity and fluorescence intensity at a plurality of points in the irradiation direction, and It may be information in which excitation light intensity and fluorescence intensity are associated with each other.

(4) The reference information may be configured by an arithmetic expression representing a correspondence relationship between excitation light intensity and fluorescence intensity.

(5) Further, the reference information may be configured from a database in which excitation light intensity and fluorescence intensity are recorded in association with each other.

(6) In the above method, the measurement step preferably measures the intensity of excitation light scattered by a tracer mixed in the fluid.
Thereby, even if excitation light is light with high straightness like laser light, the intensity of the excitation light can be easily measured from a direction (for example, a side) intersecting the irradiation direction.

(7) The concentration measuring device according to the second aspect of the present invention is:
An irradiation unit that irradiates a fluid containing a substance to be measured with excitation light;
A measurement unit for measuring the intensity of the excitation light and the intensity of the fluorescence emitted from the substance by the excitation light;
Referring to the reference information showing the correspondence between the excitation light of arbitrary intensity irradiated to the reference fluid containing the substance at a known constant concentration and the fluorescence intensity serving as the reference value emitted thereby, the measurement A standard value of the fluorescence intensity corresponding to the actual value of the excitation light intensity acquired in the process is acquired, and the actual value of the fluorescence intensity measured by the measurement unit and the standard value of the fluorescence intensity obtained from the reference information And a concentration acquisition unit that acquires the concentration of the substance in the measurement target fluid based on the ratio and the known concentration in the reference fluid.
With such a configuration, the same function and effect as those of the above-described concentration measurement method can be achieved.

  According to the concentration measuring method and apparatus of the present invention, measurement is possible even when excitation light is attenuated.

It is the schematic of the density | concentration measuring apparatus which concerns on embodiment of this invention. It is a flowchart which shows the procedure which produces | generates a reference tool. It is a flowchart which shows the procedure which measures the said density | concentration in the measurement field where the substance of unknown density | concentration was contained. It is a graph which shows the relationship between a laser beam intensity | strength and fluorescence intensity | strength, and the distance from a light source. It is a figure which shows a reference tool.

Hereinafter, embodiments of the present invention will be described.
[Overall configuration of concentration measuring device]
FIG. 1 is a schematic diagram of a concentration measuring apparatus according to an embodiment of the present invention.
The concentration measurement apparatus 10 according to the present embodiment includes a light source (irradiation unit) 11 that irradiates a measurement field S made of a fluid such as liquid or gas with a laser beam L, an imaging unit 12 that images the measurement field S, and an imaging unit 12. And a processing device 13 for obtaining the concentration of the substance to be measured contained in the fluid of the measurement field S from the image obtained by the above. In the present embodiment, a liquid such as water is used as the measurement field S, and the concentration of a substance contained in the liquid is detected.

  The light source 11 outputs laser light (excitation light) L having a wavelength corresponding to the substance to be measured. More specifically, the light source 11 outputs a laser beam L having a wavelength capable of emitting fluorescence when the substance to be measured absorbs the laser beam L and returns from the excited state to the ground state. . The laser light L output from the light source 11 is shaped into a predetermined shape by the optical system 14 configured by a lens or the like. For example, the laser beam L is applied to the measurement field S in a state where the laser beam L is formed into a belt shape by the optical system 14.

  The imaging unit 12 includes, for example, a CCD camera, and includes a first camera 21 that images the laser light L irradiated to the measurement field S and a second camera 22 that images fluorescence emitted from the substance. Each of the cameras 21 and 22 is provided with a filter that transmits light of a wavelength to be imaged and does not transmit light of other wavelengths.

  In the present embodiment, the tracer is uniformly mixed in the measurement field S in order to perform imaging of the laser light L from the side. This tracer is made of a granular material having the property of scattering the laser beam L. Since the laser light L goes straight in the irradiation direction X, it cannot be imaged from the side as it is. Therefore, by mixing the tracer, the laser beam L is scattered by the tracer, and the scattered laser beam L can be imaged by the first camera 21 arranged on the side. In addition, as a tracer, a fine bubble-like thing (microbubble) etc. can also be used. Further, when the measurement field S originally contains a substance that scatters laser light, the tracer may not be mixed.

  The processing device 13 is composed of, for example, a personal computer, and includes a CPU, a storage unit such as a RAM, a ROM, and an HDD, an input unit such as a keyboard, an output unit such as a liquid crystal panel, and an input / output interface. The CPU executes the application program stored in the storage unit so that various types of image processing can be performed.

The processing device 13 includes an image processing unit 31, a reference tool generation unit 32, and a density acquisition unit 33 as functional configurations.
The image processing unit 31 performs processing for acquiring the laser light L and the fluorescence intensity by reading the information of the images while the images captured by the first and second cameras 21 and 22 are input. Specifically, the image processing unit 31 obtains the laser beam intensity by obtaining the brightness (luminance) of the image obtained by imaging the laser beam L with the first camera 21, and the image obtained by imaging the fluorescence with the second camera 22. The fluorescence intensity is obtained by determining the brightness (luminance) of the. Here, the imaging unit 12 and the image processing unit 31 constitute a measuring unit 15 of the present invention that measures laser light intensity and fluorescence intensity.

  The reference tool generation unit 32 is a functional unit that generates a reference tool (see FIG. 5) in which laser light intensity and fluorescence intensity are associated with each other. The measurement field S of the present embodiment has a certain area with respect to the irradiation direction X of the laser light L. Therefore, when the measurement field S is irradiated with the laser light L, attenuation occurs as the distance from the light source 11 increases, and the intensity of the laser light L decreases. Therefore, in the present embodiment, a reference tool is used in order to consider the influence of the attenuation of the laser light L. Details of this reference tool will be described later.

  The concentration acquisition unit 33 is a functional unit that calculates the concentration of the substance in the measurement field S using the laser light intensity and the fluorescence intensity acquired by the image processing unit 31 and the reference tool. Details of the density acquisition unit 33 will be described later together with the reference tool.

[Principle of concentration measurement]
Next, the principle of concentration measurement using the concentration measuring apparatus 10 will be described.
As shown in FIG. 1, when the fluid of the measurement field S is irradiated with the laser light L, fluorescence is emitted from the excited measurement target substance. The irradiated laser beam L and fluorescence are in a proportional relationship, and the energy of the fluorescence increases as the energy of the laser beam L increases. Further, the energy of the fluorescence emitted from the measurement target substance is proportional to the concentration of the measurement target substance, and the higher the concentration of the measurement target substance, the greater the fluorescence energy emitted. These relationships are expressed by the following equations.

I = I ₀ Cφε (1)
However, I: Fluorescence flux (W / m ³ ) (corresponding to the energy of fluorescence), I ₀ : Excitation light beam (W / m ² ) (corresponding to the energy of excitation light), C: Concentration of substance (g / m ³ ), Φ: quantum yield, ε: extinction coefficient (m ² / g).

The laser beam L irradiated to the measurement field S and the fluorescence emitted from the substance are imaged by the first and second cameras 21 and 22, respectively. Images captured by the first and second cameras 21 and 22 are brighter (higher brightness) in the portions where the laser light L and the fluorescence energy I ₀ and I are large, and darker in the portions where the energy I ₀ and I are small. (The luminance is small), both of which are proportional. Therefore, the relationship between the laser light L and the fluorescence energy I ₀ , I and the luminance in the captured image can be expressed as in equations (2) and (3) by using the coefficients α and β.

I ₀ = αV ₀ (2)
I = βV (3)
Where V _{0 is} the brightness of the laser beam, and V is the brightness of the fluorescence. Hereinafter, the luminances V ₀ and V may be referred to as “intensity”.

Then, by using the relationship of the expressions (2) and (3), the expression (1) can be rewritten as the following expression (4).
βV = αV ₀ Cφε (4)

When the measurement field S is a small region, it can be assumed that the laser light L irradiated to the measurement field S is hardly attenuated in the measurement field S and its intensity V ₀ is constant. For this reason, when the measurement field S is irradiated with laser light having a predetermined intensity V ₀ , the value of the fluorescence intensity V is affected only by the concentration C and changes. Therefore, the concentration C of the substance can be obtained from the equation (4) by measuring the fluorescence intensity V by the imaging unit 12 and the image processing unit 31 (however, the coefficients α, β, φ, ε are known). And).

On the other hand, when the measurement field S has a wide area with respect to the irradiation direction X of the laser light L, the laser light L is gradually attenuated by passing through the measurement field S. In this case, the intensity V ₀ of the laser beam L is not constant and changes depending on the position in the irradiation direction X of the laser beam L. Further, the fluorescence intensity V also changes with this change. Therefore, the fluorescence intensity V changes not only by the substance concentration but also by the attenuation of the laser light L, and an accurate concentration cannot be obtained only by the above equation (4). For example, when there is uneven density in the measurement field S, the concentration of the substance is low at a position close to the light source, and the concentration of the substance is high at a position away from the light source, the laser light L is positioned away from the light source, Even though the substance concentration is attenuated at a high position, the fluorescence has a high intensity V due to the high substance concentration even at a position away from the light source, and has a proportional relationship with the laser light intensity V ₀ . Disappear.

  The concentration measuring apparatus 10 of the present embodiment enables measurement of the concentration of a substance even in a measurement field S having a wide area with respect to the irradiation direction X of the laser light L. Therefore, measurement taking into account only the attenuation of the laser light L The laser light intensity and the fluorescence intensity are measured in the field S, and a “reference tool (reference information)” in which these are associated with each other is generated in advance. The accurate density is obtained by referring to the reference tool.

The laser light intensity and the fluorescence intensity in the reference tool are measured at a measurement site S (hereinafter, also referred to as “measurement site S with a known concentration”) containing a substance at a constant concentration known in advance. In this case, the laser light intensity V _0K , the fluorescence intensity (reference value) V _ref, and the known concentration C _ref have the relationship of the following expression (5) according to the expression (4).

βV _ref = αV _0K C _ref φε (5)

[Specific contents of reference tool and generation procedure]
FIG. 2 is a flowchart showing a procedure for generating a reference tool.
First, in order to generate a reference tool, a standard measurement field S, that is, a measurement field S containing a substance at a known constant concentration is formed.
And the laser beam which the light source 11 outputs is irradiated to the measurement place S used as a reference | standard (step S1). At this time, the laser light scattered from the measurement field S and the fluorescence emitted from the substance are imaged by the first and second cameras 21 and 22, respectively (step S2).

Next, the image picked up by the first and second cameras 21 and 22 is processed by the image processing unit 31 to acquire the laser light intensity V _0K and the fluorescence intensity V _ref (step S3).
Then, a reference tool is generated using the acquired laser light intensity V _0K and fluorescence intensity V _ref (step S4).

FIG. 4 shows the relationship between the laser light intensity V _0K and the fluorescence intensity V _ref acquired in step S 3 and the distance from the light source 11. It can be seen that the laser light intensity V _0K and the fluorescence intensity V _ref both decrease as the distance from the light source 11 increases. Since the concentration of the measurement field S is constant, the decrease in the laser light intensity V _0K and the fluorescence intensity V _ref is caused only by the attenuation of the laser light by passing through the measurement field S.

In order to generate the reference tool in step S4, as shown in FIG. 5, the distance from the light source 11 is plotted on the graph with the laser light intensity V _0K as the horizontal axis and the fluorescence intensity V _ref as the vertical axis. The laser light intensity V _0K and the fluorescence intensity V _ref are plotted in correspondence with each other at the same point. At this time, it is possible to obtain a relationship of only the light intensities V _0K and V _{ref excluding} the distance element. Then, a function approximating a plurality of points P plotted on the graph is obtained and used as a reference tool. In this embodiment, as an example, a plurality of points P plotted on a graph are approximated by a straight line A expressed by a linear function, and this is used as a reference tool. Therefore, the reference tool shows a correspondence relationship between a laser beam having an arbitrary intensity V _0K irradiated to the measurement field S as a standard and a fluorescence intensity V _ref as a standard value emitted thereby. This reference tool is stored in the storage unit of the processing device 13.

[Concentration measurement procedure for substances of unknown concentration]
Next, a procedure for measuring the concentration in a measurement site S containing the substance to be measured at an unknown concentration (hereinafter also referred to as “measurement site S of unknown concentration”) will be described with reference to FIG.
First, the laser beam output from the light source 11 is irradiated to the measurement site S containing the substance at an unknown concentration (step S11). At this time, the laser light scattered from the measurement field S and the fluorescence emitted from the substance are imaged by the first and second cameras 21 and 22, respectively (step S12).

Then, the image captured by the first and second cameras 21 and 22 and processed by the image processing unit 31, a laser beam intensity _{V 0,} respectively to obtain a fluorescence intensity V (step S13).
As described above, at the measurement site S of unknown concentration, the measured laser beam intensity V ₀ , fluorescence intensity V, and unknown concentration C are in the relationship represented by the equation (4).

By the way, using the above formulas (4) and (5), when the ratio of the fluorescence intensity V _{ref serving} as a reference in the measurement field S with a known concentration and the fluorescence intensity V in the measurement field S with an unknown density is taken, The following equation (6) is obtained.

Then, when the equation (6) is arranged by deleting the coefficients α, β, φ, ε, V ₀ , V _0K and the like, the fluorescence intensities V, V _ref and the concentrations C, C _ref are expressed by the equation (7). (Note that the laser light intensity V ₀ and the laser light intensity V _0K are the same).

From this equation (7), the ratio of the fluorescence intensity V _ref at the measurement site S with the known concentration and the fluorescence intensity V at the measurement site S with the unknown concentration agrees with the ratio between the known concentration C _ref and the unknown concentration C. I understand that. Therefore, the unknown concentration C has three values of the fluorescence intensity V, the fluorescence intensity (reference value) V _ref, and the known concentration C _ref without considering each coefficient α, β, φ, ε, V ₀ , V _0K. If it becomes clear, it can be obtained.

However, in order for Equation (7) to hold, it is necessary that the laser light intensity V _0K in the measurement field S with a known concentration matches the laser light intensity V ₀ in the measurement field S with an unknown density. Therefore, by referring to the reference tool (straight line A shown in FIG. 5) stored in the storage unit of the processing device 13 and applying the laser light intensity V ₀ measured at the measurement field S of unknown concentration, the laser The fluorescence intensity (reference value) V _ref in the measurement field S having a known concentration corresponding to the light intensity V ₀ is extracted (step S14). That is, assuming that the laser beam having the intensity V ₀ measured at the measurement site S of unknown density is irradiated to the measurement site S of known density, the fluorescence intensity V _ref that will be obtained at that time is _expressed as Obtain from the reference tool. As a result, the laser beam intensities V ₀ and V _0K can be matched between the measurement field S of unknown density and the measurement field S of known density.

Then, the unknown concentration C is obtained by substituting the fluorescence intensity V measured at the measurement site S of unknown concentration, the fluorescence intensity V _ref extracted from the reference tool, and the known concentration C _ref into the equation (7). (Step S15). The obtained unknown concentration C can be output from an output unit such as a monitor in the processing device 13.
As described above, even in the measurement field S where the attenuation of the laser beam L occurs, it is possible to accurately measure the substance concentration in consideration of the attenuation by using the reference tool. In addition, the substance concentration can be acquired by a simple calculation as shown in Expression (7).

Further, by using the reference tool, even if the concentration of the substance in the measurement field S is uneven, the fluorescence intensity V _ref is obtained from the laser light intensity V ₀ at a plurality of points in the measurement field S and unknown. The concentration C can be accurately obtained, and the concentration distribution in the entire measurement field S can be accurately obtained.

[Other Embodiments]
The present invention is not limited to the above-described embodiment, and can be modified within the scope of the invention described in the claims. For example, the present invention can be implemented in the following forms.
(1) When the substance to be measured is a substance that does not emit fluorescence when irradiated with laser light, the concentration of the substance can be measured using the concentration measuring apparatus 10 by the following method.
For example, when the concentration of a substance that does not emit fluorescence mixed in the liquid in the measurement field S is to be measured, a dye that emits fluorescence is first mixed in the liquid. As this pigment, for example, rhodamine can be used. This rhodamine is a substance that emits orange fluorescence (wavelength of about 580 nm) when irradiated with green light (wavelength of about 520 nm). And the density | concentration of the pigment | dye is calculated | required with the density | concentration measuring apparatus 10 about the liquid which mixed the pigment | dye. The substance whose concentration is actually desired can be obtained by subtracting the pigment concentration (%) from 100%.

(2) In the above embodiment, the case where the fluid in the measurement field is a liquid has been described, but the present invention can also be applied to a case where the fluid is a gas. In this case, by using a micro soap bubble or a smoke-like thing as a tracer, the laser beam in gas can be scattered and the image can be acquired by an imaging part.

(3) A plurality of types of reference tools can be provided according to the temperature of the measurement field. In this case, a temperature measurement unit that measures the temperature of the measurement site S may be further provided, and the type of reference tool to be used may be selected according to the temperature measured by the temperature measurement unit. In this way, even if the laser light intensity or the fluorescence intensity varies depending on the temperature of the measurement field S, the concentration measuring device 10 can measure the concentration of the substance. As the temperature measurement unit, a thermometer that directly measures the temperature of the measurement field may be used, or the temperature may be obtained from an image captured by the imaging unit.

(4) The concentration measuring apparatus 10 of the above embodiment can be used in combination with a method for measuring the moving speed of a fluid. As described above, the concentration measuring apparatus 10 captures the image of the laser beam L and the fluorescence of the substance. Therefore, by capturing a plurality of images in a continuous frame, the movement of the particles reflected in the image is tracked. It becomes possible to do. Then, the flow velocity of the substance can be obtained from the imaging interval of the frame and the moving distance of the particles therebetween. Such a method for measuring the flow velocity is also referred to as PIV (Particle Image Velocity).

(5) Although the reference tool of the above embodiment is in the form of a linear function, a plurality of points shown in FIG. 5 may be approximated by a quadratic or higher function. In addition, the reference tool (reference information) is not limited to being configured by an arithmetic expression (graph) such as a linear function, but may be configured in the form of a database, table, map, or the like in which laser light intensity and fluorescence intensity are associated with each other. it can.

(6) The present invention can be used for various applications related to concentration measurement. For example, it can be used for monitoring a state in which a plurality of liquids are mixed in a food field, a pharmaceutical field, or the like. Alternatively, in the air conditioning field, it can be used to monitor a state where air whose temperature is adjusted is blown out and diffused from an air conditioner. In these applications, it is more effective to combine with the PIV method described in (4) above.

10: Concentration measuring device 11: Light source (irradiation unit)
12: Imaging unit 13: Processing device 15: Measurement unit 31: Image processing unit 32: Reference tool generation unit 33: Density acquisition unit C: Unknown density C _ref : Known density L: Laser light V: Fluorescence intensity (actual measurement value)
V ₀ : Laser beam intensity V _0K : Laser beam intensity irradiated to a measurement field of known concentration V _ref : Fluorescence intensity (reference value)
X: Irradiation direction

Claims (7)

A method of irradiating a fluid containing a substance to be measured with excitation light and measuring the concentration of the substance based on the intensity of fluorescence emitted from the substance by the excitation light,
A measurement step of irradiating a measurement target fluid containing the substance at an unknown concentration with excitation light, and actually measuring the excitation light intensity and fluorescence intensity,
Referring to the reference information showing the correspondence between the excitation light of arbitrary intensity irradiated to the reference fluid containing the substance at a known constant concentration and the fluorescence intensity serving as the reference value emitted thereby, the measurement A reference step for obtaining a standard value of fluorescence intensity corresponding to the actual measurement value of the excitation light intensity obtained in the step;
Based on the ratio between the actual value of the fluorescence intensity acquired in the measurement step and the standard value of the fluorescence intensity acquired in the reference step, and the known substance concentration in the reference fluid, the concentration of the substance in the measurement target fluid A concentration measurement method, comprising: acquiring a concentration.   The concentration measurement method according to claim 1, further comprising a step of generating the reference information.   The reference information is obtained by irradiating a reference fluid containing the substance at a known constant concentration with excitation light, measuring excitation light intensity and fluorescence intensity at a plurality of points in the irradiation direction, and exciting light intensity at each point. The concentration measurement method according to claim 1, wherein the concentration measurement method is information that associates fluorescence intensity with fluorescence intensity.   The concentration measurement method according to claim 1, wherein the reference information is configured by an arithmetic expression representing a correspondence relationship between excitation light intensity and fluorescence intensity.   The concentration measurement method according to claim 1, wherein the reference information includes a database in which excitation light intensity and fluorescence intensity are associated with each other.   The concentration measurement method according to claim 1, wherein the measurement step measures the intensity of excitation light scattered by a tracer mixed in the fluid. An irradiation unit that irradiates a fluid containing a substance to be measured with excitation light;
A measurement unit for measuring the intensity of the excitation light and the intensity of the fluorescence emitted from the substance by the excitation light;
Referring to the reference information showing the correspondence between the excitation light of arbitrary intensity irradiated to the reference fluid containing the substance at a known constant concentration and the fluorescence intensity serving as the reference value emitted thereby, the measurement A standard value of the fluorescence intensity corresponding to the actual value of the excitation light intensity acquired in the process is acquired, and the actual value of the fluorescence intensity measured by the measurement unit and the standard value of the fluorescence intensity obtained from the reference information A concentration measurement device comprising: a concentration acquisition unit configured to acquire a concentration of a substance in the measurement target fluid based on a ratio and a known concentration in the reference fluid.