Patent Publication Number: US-2022228981-A1

Title: Sample measurement device and sample measurement method

Description:
TECHNICAL FIELD 
     The present invention relates to a sample measurement device and a sample measurement method for measuring an absorbance or a concentration of a sample. 
     BACKGROUND ART 
     One of methods for measuring the concentration of a component in a sample (sample solution) is absorptiometry. The absorptiometry is a method of applying light to a sample to measure the amount of transmitted light and quantifying the concentration from the attenuation amount (absorbance) of the light amount using the Lambert-Beer law. 
     The Lambert-Beer law is a law in which an absorbance of a solution is proportional to the concentration of the solution and the thickness of the solution (an optical path length of a cell containing the solution). A law in which the absorbance is proportional to the optical path length when the concentration is constant is called Lambert&#39;s law. A law in which the absorbance is proportional to the concentration of the solution when the optical path length is constant is called Beer&#39;s law. It is required that a wide concentration range (dynamic range) can be measured with a simpler configuration in measurement of the concentration of a component in a sample by the absorptiometry. Examples of a sample measurement device capable of widening a dynamic range by making a cell optical path length variable are known as, for example, PTLs 1 to 3. 
     In such measurement by the absorptiometry for measuring the amount of transmitted light, however, there is a problem that a variation in the amount of light from a light source is directly reflected in a variation in a measurement result of the concentration. The variation in the amount of light is caused by, for example, a change in the amount of emitted light from the light source due to a temperature change. For example, when an LED light source is used, the amount of emitted light tends to vary depending on the temperature. As described above, when a simple configuration, such as an LED and a camera, is used, the variation in the amount of light is large, so that there are problems that it is difficult to accurately measure the concentration at the time of measuring the sample and the dynamic range is narrowed. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: JP 2004-340804 A 
         PTL 2: JP 2006-194775 A 
         PTL 3: Japanese Patent No. 4220879 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The present invention has been made in view of the above problems. An object of the present invention is to provide a sample measurement device and a sample measurement method capable of accurately measuring an absorbance or a concentration of a sample and obtaining a high dynamic range even when the amount of light of a light source is not stable. 
     Solution to Problem 
     A sample measurement device according to the present invention includes: a sample container that stores a sample solution; a light source that irradiates the sample container with irradiation light from a first direction; an imaging part that captures an image of the sample solution based on light scattered by the sample solution from a second direction intersecting the first direction; and a calculator that calculates an absorbance or a concentration of the sample solution based on the image. The calculator calculates a degree of attenuation of a light amount of the image at a constant optical path length along the first direction based on the image, and calculates the absorbance or concentration of the sample solution according to the degree of attenuation. 
     A sample measurement method according to the present invention includes: storing a sample solution in a sample container; irradiating the sample container with irradiation light from a first direction; capturing an image of the sample solution based on light scattered by the sample solution from a second direction intersecting the first direction; and calculating a degree of attenuation of a light amount of the image at a constant optical path length along the first direction based on the image and calculating an absorbance or a concentration of the sample solution according to the degree of attenuation. 
     Advantageous Effects of Invention 
     According to the present invention, when the sample container is irradiated with the irradiation light emitted by the light source from the first direction of the sample container, the irradiation light is scattered in the sample solution. Based on the scattered light, the image of the sample solution is captured by the imaging part from the second direction intersecting the first direction. The calculator calculates the absorbance or concentration of the sample solution based on the image. At this time, the calculator calculates the degree of attenuation of the light amount of the image along the first direction, and calculates the concentration of the sample solution according to the degree of attenuation. In the present invention, the light irradiated from the first direction and scattered at a plurality of different points in the sample solution is captured as the image by the imaging part from the second direction, and the absorbance or concentration of the sample solution is calculated from the degree of attenuation. The degree of attenuation does not greatly vary in the constant optical path length even if the light amount of the irradiation light irradiated from the light source varies. In the sample solution in the sample container, the irradiation light is scattered at a plurality of positions in the first direction, and the plurality of positions have different optical path lengths. Thus, it is possible to perform measurement with different optical path lengths without adding a complicated configuration. Therefore, it is possible to provide the sample measurement device and the sample measurement method capable of accurately measuring the concentration and obtaining the high dynamic range even when the amount of light of the light source is not stable according to the present invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram for describing a schematic configuration of a sample measurement device according to a first embodiment. 
         FIG. 2  is a schematic diagram for describing an operation of the sample measurement device according to the first embodiment. 
         FIG. 3  is a schematic diagram for describing a schematic configuration of a sample measurement device according to a second embodiment. 
         FIG. 4  is a flowchart for describing an operation of the sample measurement device according to the second embodiment. 
         FIG. 5  is a graph illustrating a relationship between a distance L and a light amount value (after normalization) obtained by imaging calibration solutions Sc 1  to Sc 5  with a camera  14 . 
         FIG. 6  illustrates an example of a calibration curve obtained based on measurement results of the calibration solutions Sc 1  to Sc 5 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. In the accompanying drawings, functionally identical elements are sometimes denoted by the same number. Incidentally, the embodiments and implementation examples according to the principle of the present disclosure are illustrated the accompanying drawings. These are given for the understanding of the present disclosure, and are not used to limit the present disclosure by no means. The description in the present specification is merely illustrative and is not intended to limit the scope of the claims or the application of the present disclosure by no means. 
     The present embodiments are described in sufficient detail for those skilled in the art to carry out the present disclosure. However, other types of implementation and forms can be applied, and it is necessary to understand that changes in configurations and the structures can be made and elements can be variously replaced without departing from the scope and the gist of the technical idea of the present disclosure. Therefore, the following description shall not be interpreted in a manner of being limited thereto. 
     First Embodiment 
     A sample measurement device according to a first embodiment will be described with reference to  FIGS. 1 and 2 . As an example, the sample measurement device  1  includes a sample container  11 , a light source  12 , a condenser lens  13 , a camera  14  (imaging part), an A/D converter  15 , a calculation and control unit  16  (calculator), and a display  18 . The sample measurement device  1  is configured to be capable of measuring an absorbance or a concentration of a sample solution Sm in the sample container  11 . 
     The sample container  11  is, for example, a container that has a rectangular shape. The sample container  11  is at least partially made of a transparent material. The sample container  11  is configured to be capable of storing the sample solution Sm (sample) to be measured therein. Here, the sample container  11  includes a first surface S 1  that is at least partially transparent and a second surface S 2  that intersects with the first surface S 1  and is at least partially transparent. The shape of the sample container  11  is not limited to the rectangular shape, and containers having various shapes can be adopted as long as a measurement method to be described later can be executed. In  FIG. 1 , a direction substantially orthogonal to the first surface S 1  is defined as an X direction (first direction). A direction substantially orthogonal to the second surface S 2  is defined as a Y direction (second direction). The first surface S 1  and the second surface S 2  do not need to be substantially orthogonal to each other, and may have a positional relationship in which scattered light can be observed as will be described later. 
     The light source  12  is arranged on the first surface S 1  with the condenser lens  13  interposed therebetween. The light source  12  is, for example, a light emitting diode (LED). For example, a monochromatic LED having an emission wavelength of 660 nm can be suitably used. Note that, the emission wavelength is not limited thereto, and the emission wavelength is not necessarily a single wavelength. It is also possible to adopt a light source that emits light of a plurality of wavelength bands. Irradiation light L 1  emitted from the light source  12  is condensed by the condenser lens and applied to the sample solution Sm via the first surface S 1 . The sample solution Sm contains particles. Examples of the particles include, but are not limited to, latex particles. The irradiation light L 1  incident on the sample solution Sm along the X direction from the first surface S 1  is scattered by the particles, and a part thereof is scattered in the Y direction. 
     The camera  14  opposes the second surface S 2 . The camera  14  images the sample container  11  and the sample solution Sm from the Y direction substantially orthogonal to the second surface S 2 , thereby acquiring an image signal. The camera  14  is arranged independently of the sample container  11  in  FIG. 1 . Alternatively, the sample container  11  and the camera  14  may have an integrated structure. The image signal acquired by the camera  14  is converted into image data as a digital signal by the A/D converter  15  and then input to the calculation and control unit  16 . The calculation and control unit  16  calculates the degree of attenuation (absorbance) of the light amount between at least two points (known optical path lengths) in the image using the digital image data. The calculation and control unit  16  calculates a concentration (particle concentration) of the particles in the sample solution Sm according to the calculation result. The calculated concentration is displayed on the display  18 . 
     The calculation and control unit  16  can be configured using, for example, a general-purpose computer. The calculation and control unit  16  generates data of the concentration of the sample solution Sm or the like by performing certain arithmetic processing on the image data as digital data input from the camera  14 . When the general-purpose computer is used, necessary arithmetic processing can be performed by executing a program by a built-in processor (for example, a CPU or a GPU) and performing processing defined by the program while using a storage resource (for example, a memory), an interface device (for example, a communication port), and the like. The processor may include a dedicated circuit that performs specific processing. Here, examples of the dedicated circuit include a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), a complex programmable logic device (CPLD), and the like. 
     The program may be installed from a program source onto a computer. The program source may be, for example, a program distribution server or a computer-readable storage medium. When the program source is the program distribution server, the program distribution server may include a processor and a storage resource storing a distribution target program. The processor of the program distribution server may distribute the distribution target program to another computer. Further, in examples, two or more programs may be realized as one program, or one program may be realized as two or more programs. 
     Next, a method for calculating the concentration of the sample solution Sm in the first embodiment will be described with reference to  FIG. 2 . 
     When the sample container is irradiated with the irradiation light L 1  from the first surface S 1 , the irradiation light L 1  is scattered by the particles in the sample solution Sm to gradually attenuate as proceeding from the left direction to the right direction in  FIG. 2 . The sample solution Sm irradiated with the irradiation light L 1  in this manner is imaged by the camera  14  from the Y direction, whereby image data thereof is acquired. The image data is stored in a storage (not illustrated) in the calculation and control unit  16 . 
     The graph illustrated at lower position of  FIG. 2  illustrates an example of a relationship between a distance L from the first surface S 1  at a position of the sample solution Sm irradiated with the irradiation light L 1  in the image data and a light amount value (after normalization) at the position. 
     Due to the relationship with scattered light, the light amount value is maximized in the vicinity of a position P 1  slightly away from the first surface S 1  (distance L from the first surface S 1 =L 1 ), and thereafter, decreases as the distance from the first surface S 1  increases. For example, in a case where there are measurement points P 1 , P 2 , P 3 , and P 4  in descending order of distance from the first surface S 1  and a light amount of an image at each of the measurement points P 1  to P 4  is measured, the light amount of the image decreases as the distance from the first surface S 1  increases due to scattering or the like of the particles. 
     The degree of attenuation (slope) in this graph increases as the concentration of the sample solution Sm increases. Then, the calculation and control unit  16  specifies arbitrary two points with the known optical path lengths, for example, the measurement point P 2  (first measurement point: distance L=L 2 ) and the measurement point P 3  (second measurement point: distance L=L 3 *L 2 ). The calculation and control unit  16  measures light amount values Q 2  and Q 3  at these specified two measurement points P 2  and P 3 . Then, the degree of attenuation of the light amount value between the two points (hereinafter, referred to as an attenuation amount Da) is calculated, that is, Da=(Q 3 −Q 2 )/(L 3 −L 2 ) is calculated. Although not illustrated, the calculation and control unit  16  includes a lookup table indicating a relationship between the attenuation amount Da and the concentration of the sample solution Sm. The calculation and control unit  16  refers to the lookup table to identify the concentration of the sample solution Sm. Incidentally, positions of the measurement points P 2  and P 3  to be measured can be appropriately changed. When the positions of the measurement points P 2  and P 3  are changed, the lookup table is also changed according to the positions. 
     It is also possible to execute measurement according to measurement values at a plurality of other measurement points, instead of using the measurement values at the measurement points P 2  and P 3 . For example, in a case where the concentration of the sample solution Sm to be measured is extremely high, the light amount value Q 3  at the measurement point P 3  far from the first surface S 1  is an extremely small value, and thus, is hardly measured. In this case, instead of the measurement at the measurement points P 2  and P 3 , the measurement at the measurement points P 1  and P 2 , which are points closer to the first surface S 1 , can be performed, and the concentration can be calculated according to the measurement result. 
     According to the structure and the measurement method of the first embodiment, even if the light amount of the irradiation light L 1  from the light source  12  varies due to a certain factor (a temperature variation, a variation in power source, or the like), the concentration of the sample solution Sm can be accurately measured, and the measurement can be performed in a high dynamic range. In the first embodiment, the concentration of the sample solution Sm is measured according to the attenuation amount Da of the light amount of the image between at least two points in the sample solution Sm. 
     When the light amount of the irradiation light L 1  varies, the light amount of the image at each measurement point varies accordingly. However, a ratio of a variation in light amount at each measurement point relative to a change in certain light amount of the irradiation light L 1  is substantially the same among a plurality of measurement points. Therefore, the attenuation amount Da does not greatly vary regardless of the variation in the light amount of the irradiation light L 1 . Therefore, the concentration of the sample solution Sm can be accurately measured even if the light amount of the irradiation light L 1  varies according to the first embodiment. Further, the positions of the measurement points P 1  to P 4  can be easily changed in the calculation and control unit  16  without requiring a complicated additional structure. Thus, measurement with an appropriately changed optical path length is also possible. Therefore, the measurement can be performed in a high dynamic range. 
     Meanwhile, the case where the concentration of particles is measured by using scattering of light in the particles in the sample solution Sm (sample) has been mainly described in the first embodiment described above. Instead of measuring the concentration of the particles in the sample solution Sm, it is also possible to measure the concentration of a light-absorbing substance in the sample solution Sm while keeping the concentration of the particles in the sample solution Sm constant. In this case, a component based on scattered light is constant, while a light amount value increases as the light-absorbing substance increases in a light amount value in image data measured by the camera  14  and the calculation and control unit  16 . 
     Second Embodiment 
     Next, a sample measurement device according to a second embodiment will be described with reference to  FIGS. 3 to 6 .  FIG. 3  is a schematic diagram for describing an overall structure of the sample measurement device according to the second embodiment. In  FIG. 3 , the same components as those of the first embodiment ( FIG. 1 ) are denoted by the same reference signs in  FIG. 3 , and redundant descriptions thereof will be omitted hereinafter. The second embodiment is different from the first embodiment in that a calibration data storage  19  that stores calibration data is provided, and a concentration of a sample solution Da to be measured can be measured according to the calibration data. 
     The calibration data storage  19  is a storage that stores calibration data acquired by measuring a calibration solution having a known concentration. The calibration data is obtained by measuring a plurality of types of calibration solutions having known concentrations in advance, and indicates a relationship between the attenuation amount Da and an absorbance Ab. When the attenuation amount Da of the sample solution Sm to be measured is obtained by the same method as that in the first embodiment, the absorbance or concentration of the sample solution Sm can be accurately measured by referring to the calibration data. Since the measurement is performed by referring to the calibration data obtained according to the measurement results of the calibration solutions having known concentrations, a more reliable measurement result can be obtained. 
     Next, an execution procedure of a concentration measurement method in the second embodiment will be described with reference to  FIGS. 4 to 6 .  FIG. 4  is a flowchart illustrating the execution procedure of the measurement method. Graphs of  FIGS. 5 and 6  illustrate a method for generating calibration data in the second embodiment. 
     In this method, prior to measurement of the sample solution Sm to be measured, calibration solutions Sc (here, five types of calibration solutions Sc 1  to Sc 5 ) are sequentially injected into the sample solution  11 . Then, a light amount value is measured by the same method ( FIG. 2 ) as the measurement of the sample solution Sm in the first embodiment. That is, the sample container  11  into which the calibration solutions Sc 1  to Sc 5  have been injected is irradiated with the irradiation light L 1  from the X direction. Then, an image based on scattered light is captured by the camera  14  from the Y direction, and image data obtained as a result is stored in the calibration data storage  19  (step S 11 ). 
     Next, the calculation and control unit  16  analyzes the image data of the calibration solutions Sc 1  to Sc 5  obtained in step S 11 , calculates a light amount value (after normalization) at each measurement point, and creates a calibration curve (step S 12 ). 
       FIG. 5  is a graph illustrating an example of a relationship between the distance L of each measurement point from the first surface S 1  and the light amount value (after normalization) at each measurement point in the image data of the calibration solutions Sc 1  to Sc 5 . The calibration solutions Sc 1  to Sc 5  have different concentrations and absorbances Ab. The degree of decrease in the light amount value between the same distances increases as the concentration and the absorbance Ab increase. In the example of  FIG. 5 , the calibration solution Sc 1  has the lowest concentration, and the concentration increases in the order of the calibration solutions Sc 2 , Sc 3 , Sc 4 , and Sc 5 . Therefore, an inclination (attenuation amount) of the obtained graph also increases in this order. As an example, the calculation and control unit  16  measures the attenuation amount Da as the degree of decrease in the light amount value (after normalization) between the measurement point P 2  (distance L 2 ) and the measurement point P 3  (distance L 3 ), and generates a calibration curve based on the measurement result. 
       FIG. 6  illustrates an example of the calibration curve for the sample measurement device  1  obtained from the graph of  FIG. 5 . This calibration curve can be formed by acquiring the relationship between the absorbance Ab of the calibration solution Sc stored in the sample container  11  and the above-described attenuation amount Da and connecting obtained plots. The calibration curve in  FIG. 6  is formed by simply connecting a plurality of plots with a straight line, but is not limited thereto. A calibration curve may be obtained by approximate calculation using a least squares method or the like. The obtained calibration curve is stored in the calibration data storage  19  as calibration data. 
     When the calibration curve is obtained and stored in the calibration data storage  19  as the calibration data, the sample solution Sm (sample) to be measured is subsequently injected into the sample container  11 , and measurement similar to that in the first embodiment is executed. That is, the first surface S 1  of the sample container  11  into which the sample solution Sm has been injected is irradiated with the irradiation light L 1  along the X direction. In this state, the sample solution Sm is imaged by the camera  14  from the Y direction (step S 13 ). Image data obtained by the camera  14  is stored in the storage (not illustrated) in the calculation and control unit  16 . The calculation and control unit  16  calculates a light amount value (after normalization) at each point in the image data acquired in Step S 13  and stored in the storage (Step S 14 ). 
     Then, data of the light amount value calculated in step S 14  is compared with the calibration curve generated in step S 12 , and the concentration of the sample solution Sm (sample) to be measured is calculated based on the comparison result (step S 15 ). Specifically, the attenuation amount Da at each of points P 2  and P 3  in the image data of the sample solution Sm is measured, and the absorbance Ab corresponding to the attenuation amount Da is identified according to the calibration curve ( FIG. 6 ). As the absorbance Ab is identified, a corresponding concentration value is calculated by the calculation and control unit  16 . The calculated concentration value is displayed on the display  18 . 
     As described above, according to the second embodiment, the calibration data acquired by measuring the calibration solution having the known concentration is stored in the calibration data storage  19 , and the concentration of the sample solution Sm to be measured can be accurately measured according to the calibration data. 
     The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail in order to describe the present invention in an easily understandable manner, and are not necessarily limited to one including the entire configuration that has been described above. Further, some configurations of a certain embodiment can be substituted by configurations of another embodiment. Further, a configuration of another embodiment can be added to a configuration of a certain embodiment. Moreover, addition, deletion or substitution of other configurations can be made with respect to some configurations of each embodiment. 
     REFERENCE SIGNS LIST 
     
         
           1  sample measurement device 
           11  sample container 
           12  light source 
           13  condenser lens 
           14  camera 
           15  A/D converter 
           16  calculation and control unit 
           18  display 
           19  calibration data storage 
         S 1  first surface 
         S 2  second surface 
         Sc(Sc 1  to  5 ) calibration solution 
         Sm sample solution