How to measure the optical spectrum

Abstract

To provide a measurement method and a device therefor with which, even for a liquid that contains air bubbles, it is possible to measure an optical spectrum stably with high sensitivity and high accuracy, without being affected by generation or growth of the air bubbles.SOLUTION: Provided is a device for giving a liquid, with diffuse-reflective particles added, to a cell and measuring the optical spectrum of the liquid, comprising: a rotation mechanism for rotationally stirring around a revolving shaft so as to form a dispersion flow of the diffuse-reflective particles along the optical window of the cell; and an optical system for giving incident light via the optical window and obtaining diffuse-reflectance light arriving by being scattered by the diffuse-reflective particles, then measuring its optical spectrum. In such a device, diffuse-reflective particles are added to a liquid and rotationally stirred around a revolving shaft so as to form a dispersion flow of the diffuse-reflective particles along the optical window of a cell. Incident light is given via this optical window and diffuse-reflectance light arriving by being scattered by the diffuse-reflective particles is obtained, and its optical spectrum is measured.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and an apparatus for measuring the optical spectrum of a solution, and more particularly to a method and an apparatus for measuring the optical spectrum of a solution containing bubbles. [Background technology]

[0002] When formic acid (HCOOH) is decomposed in the presence of a suitable catalyst, hydrogen (H2) and carbon dioxide (CO2) can be selectively obtained without generating much carbon monoxide (CO). For example, Patent Document 1 discloses a method for obtaining high-pressure hydrogen and carbon dioxide by carrying out a reaction in a pressure-resistant vessel using a liquid catalyst made of a metal complex. Here, it is proposed to measure the optical spectrum of the solution in order to observe in-situ the deterioration state of the metal complex catalyst dissolved in the reaction solution. On the other hand, in such a reaction system, light is scattered and / or reflected by bubbles (gas bubbles) generated in the solution, so that whether a transmission type or a reflection type method of measuring the light absorption spectrum is used, sufficient and stable light intensity cannot be obtained in the light receiving system, resulting in a signal with a low signal-to-noise ratio (S / N ratio), making it difficult to perform accurate measurement and difficult to detect minute changes.

[0003] Here, many methods for increasing the S / N ratio in the measurement of optical absorption spectrum have been proposed. For example, Patent Document 2 discloses a method for measuring an optical absorption spectrum by collecting light using an integrating sphere and increasing the optical absorption intensity. In addition, Non-Patent Document 1 describes a method for measuring an optical absorption spectrum by impregnating the surface of a powder with oil, which is a liquid, and drying the powder, and then mirror-finishing the surface to increase the reflected light intensity from the oil using the diffuse reflection method, in a diffuse reflectance method generally used for measuring powders and solid samples. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-124730 A [Patent Document 2] Japanese Patent Application Publication No. 5-118911 [Non-patent literature]

[0005] [Non-Patent Document 1] Takeshi Fujisawa, "Quantitative Analysis of Mineral Oil-Based Lubricants by Solution Sample Drop Diffuse Reflectance Method," Nagano Prefectural Industrial Technology Center Research Report, No. 14, p. M1-M6, 2019 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, in a reaction system that generates gas, such as the decomposition reaction of formic acid, bubbles contained in the solution make it difficult to accurately measure the optical absorption spectrum of the solution. In addition, bubbles (gas bubbles) are generated from the inner surface of the reaction vessel, attach to the surface, grow, and finally detach. That is, the volume, density, and distribution state of the bubbles change over time and space. Therefore, even if the optical sensitivity of the light receiving system is increased, in measurements that require a certain amount of time, such as wavelength sweeping measurements and repeated (interval) measurements that track changes over time, the temporal and spatial changes in the bubbles are reflected in the measurement data, making it difficult to perform stable and accurate measurements.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to propose a new method and apparatus for measuring the optical spectrum of a solution, and to provide a measurement method and apparatus therefor that are capable of performing highly sensitive, highly accurate and stable optical spectrum measurement without being affected by the generation and growth of bubbles, even in a solution that contains bubbles. [Means for solving the problem]

[0008] The inventors of the present application have fundamentally reconsidered the concept and measurement method of diffuse reflectance analysis, which is generally a spectroscopic analysis method for powder or solid samples, and as a result of extensive research, have discovered that it is possible to provide a measurement method and apparatus that can stabilize the detection signal in time and space and increase the signal strength, even for liquid samples, particularly solutions in reaction systems that generate gas.

[0009] In detail, in the measurement of optical spectrum by the conventional diffuse reflection method, the object to be measured is generally a powder, and this powder has color and therefore absorbs light, and each particle functions as a carrier of light scattering. At this time, a colorless and transparent gas (gas) such as air, or a vacuum state by degassing, is interposed between the particles. Here, in the present invention, contrary to the concept of the conventional diffuse reflection method described above, the solution to be measured itself has color, that is, it has light absorption, and the basic idea of ​​diffusing or reflecting light by dispersing colorless and transparent powder particles in the solution has been conceived. In other words, compared to the conventional diffuse reflection method, it can be said to be a positive and negative relationship. Based on this idea, the present invention has been completed by combining it with the rotary stirring method described later.

[0010] That is, the method according to the present invention is a method for measuring the optical spectrum of a solution placed in a cell, which is characterized in that diffuse reflector particles are added to the solution, the solution is rotated and stirred around a rotation axis so as to form a dispersed flow of the diffuse reflector particles along the optical window of the cell, incident light is applied through the optical window, and the diffuse reflected light scattered by the diffuse reflector particles is obtained and its optical spectrum is measured.

[0011] According to this feature, it is possible to perform measurement of the solution near the optical window without being affected by the state of the other parts of the solution, and to perform highly sensitive, highly accurate and stable optical spectrum measurement. Measurement is possible even for high-concentration solutions and suspensions that could not be spectroscopically analyzed in the past, and furthermore, it is possible to measure optical spectra in a wide wavelength range, such as ultraviolet to visible to near infrared to infrared.

[0012] In the above-mentioned invention, the optical spectrum measuring device may further include a focusing means for focusing the diffuse reflected light scattered by the diffuse reflector particles. With this feature, the intensity of the reflected light can be increased, and the optical spectrum can be measured with high sensitivity and high accuracy.

[0013] In the above-mentioned invention, the solution may contain bubbles, and the bubbles may be unevenly distributed around the rotation axis by centrifugal force caused by the rotation and stirring. The bubbles may be generated by a reaction of the solution. According to this feature, even if the solution contains bubbles, it is possible to measure the optical spectrum with high sensitivity and high accuracy without being affected by the generation and growth of the bubbles.

[0014] In addition, an apparatus according to the present invention is an apparatus for measuring the optical spectrum of a solution containing added diffuse reflector particles by pouring the solution into a cell, and is characterized in that it includes a rotation mechanism that rotates and stirs the solution around a rotation axis so as to form a dispersed flow of the diffuse reflector particles along an optical window of the cell, and an optical system that applies incident light through the optical window and obtains diffuse reflected light scattered by the diffuse reflector particles, thereby measuring the optical spectrum of the solution.

[0015] According to this feature, it is possible to perform measurement of the solution near the optical window, and it is not affected by the state of the other parts of the solution, and it is possible to perform highly sensitive, highly accurate and stable optical spectrum measurement. It is now possible to perform measurement of high concentration solutions and suspensions, which could not be spectroscopically analyzed in the past, and it is also possible to measure optical spectra in a wide wavelength range, such as ultraviolet to visible to near infrared to infrared.

[0016] The above-mentioned invention may be characterized in that it includes a focusing means for focusing the diffuse reflected light scattered by the diffuse reflector particles. With this feature, it is possible to increase the intensity of the reflected light and perform highly sensitive, highly accurate and stable measurement of the optical spectrum.

[0017] In the above-mentioned invention, the solution may contain bubbles, and a control unit may be included that controls the rotation mechanism so that the bubbles are unevenly distributed around the rotation axis by centrifugal force caused by the rotation and stirring. According to this feature, even in the case of a solution containing bubbles, it is possible to perform highly sensitive, highly accurate and stable optical spectrum measurement without being affected by the generation and growth of the bubbles. [Brief description of the drawings]

[0018] [Figure 1] 1 is a diagram showing the principle of measurement according to the present invention, in which (b) is a schematic enlarged view of part P in (a). [Diagram 2] FIG. 1 is a schematic plan view of an apparatus according to the present invention; [Diagram 3] FIG. 2 is a plan view of the essential parts of the device according to the present invention; [Figure 4] FIG. 2 is a side view of the essential parts of the device according to the present invention. [Diagram 5] 1 is a graph of absorbance versus wavelength according to one embodiment of the present invention. [Figure 6] 1 is a graph of absorbance versus solution concentration at each wavelength in accordance with one embodiment of the present invention. [Figure 7] 1 is a graph of absorbance versus wavelength according to a comparative example. [Figure 8] 13 is a graph of absorbance versus solution concentration at each wavelength according to a comparative example. [Figure 9] 1 is a graph showing (a) absorbance versus wavelength and (b) an expanded vertical axis for each concentration of a solution according to one embodiment of the present invention. [Figure 10] 1 is a graph showing (a) absorbance versus solution concentration at each wavelength according to one embodiment of the present invention, and (b) an expanded vertical axis. [Figure 11] 1 is a graph showing (a) absorbance versus wavelength and (b) an expanded vertical axis for each concentration of a diffuse reflector according to one embodiment of the present invention. [Figure 12] 1 is a graph showing (a) absorbance versus amount of diffuse reflector at each wavelength according to one embodiment of the present invention, and (b) an expanded vertical axis. [Figure 13] 1 is a graph of the light absorption spectrum for various amounts of diffuse reflector according to one embodiment of the present invention. [Figure 14] 1 is a structural formula of a catalyst used in one embodiment of the present invention. [Figure 15] 1 is a graph showing (a) absorbance versus wavelength at each measurement time according to one embodiment of the present invention, and (b) an expanded horizontal axis of the graph. [Figure 16] 1 is a graph showing (a) absorbance versus wavelength at various concentrations of an iridium complex, and (b) absorbance versus concentration of an iridium complex at various wavelengths, according to one embodiment of the present invention. [Figure 17] 1 is a graph of (a) absorbance versus wavelength and (b) absorbance versus measurement time according to one embodiment of the present invention. [Figure 18] 1 is a graph of absorbance versus wavelength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] As shown in FIG. 1(a), in order to uniformly disperse bubbles 110 in a solution S of a reaction system that generates gas, such as the decomposition reaction of formic acid, it is considered to rotate and stir the solution S around the rotation axis at high speed in a rotary stirring tank 100. Here, diffuse reflector particles 112, which are denser than the solvent, are added and suspended in the solution S. Then, due to centrifugal force, low-density bubbles 110 gather around the rotation axis (center axis) C of the rotary stirring tank 100, while high-density diffuse reflector particles 112 are unevenly distributed along the outer wall 100a of the rotary stirring tank 100 to form a dispersed flow, and the bubbles 110 are spatially separated. In this state, incident light (probe light) L0 is made incident on the rotary stirring tank 100 through the transparent outer wall 100a, and the reflected light (diffuse reflected light) L1 scattered by the diffuse reflector particles 112 is collected and the optical spectrum is measured, making it possible to measure the measurement without being affected by the bubbles 110. If the concentration of the diffuse reflector particles 112 is high, the distance between the particles that reflects light is shortened, and as a result, the light absorption by the solution between the particles is weakened, which is reflected in the diffuse reflectance spectrum. This will be described later in the Examples.

[0020] The above-mentioned method can measure high-concentration solutions and suspensions, whose optical spectra could not be measured in the past, regardless of whether or not gas is generated during the reaction and bubbles 110 are generated. The optical spectrum can be measured using light in a wide wavelength range, such as ultraviolet, visible, near infrared, and infrared, for the incident light L0, making it possible to measure the optical spectrum of reactions and solutions that could not be measured before. In addition, water is given as an example of the main solvent and hydrogen is given as the generated gas, but this combination is not limited to this, and the method can be applied to the measurement of optical spectra in systems in which gas (bubbles) that is mixed with the solution exists, such as enzyme reactions and generation of carbon dioxide from carbonated water, as well as methane, hydrogen sulfide, oxygen, etc. In addition, the solvent is not limited to water, and the method can be applied to inorganic, organic, and mixed solutions thereof.

[0021] FIG. 1(b) is a partially enlarged view of FIG. 1(a) and shows a schematic diagram of light diffusion by diffuse reflector particles 112. According to this, incident light L0 into the solution S, or light reflected by or transmitted through a certain diffuse reflector particle 112, is repeatedly reflected by or transmitted through other diffuse reflector particles 112. Here, the diffuse reflector particles 112 are made of a transparent material that does not absorb the incident light L0 etc., so the light transmitted through the particles 112 is not attenuated. In other words, the attenuation of light is due to the solution S present between the diffuse reflector particles 112.

[0022] Therefore, when the concentration of the diffuse reflector particles 112 is high, the average interparticle distance becomes small, and the attenuation of light due to the light absorption of the solution S is less likely to occur, and the light absorption intensity of the obtained spectrum is observed to be weaker. On the other hand, when the concentration of the diffuse reflector particles 112 is low, the light absorption intensity is observed to be stronger. For these reasons, if the concentration of the diffuse reflector particles 112 is made too low, the frequency of diffuse reflection by the diffuse reflector particles 112 decreases, and the effect of the air bubbles 110 increases relatively. In addition, the incident light L0 may pass through the solution S and reach the opposite side of the rotating stirring tank (cell). For this reason, it should be considered that the measurement accuracy of the wavelength dependency of the light absorption intensity may decrease. This will be described later.

[0023] 2 shows the concept of a measuring device that houses the above-mentioned rotary stirring tank 100 as a cell 30. The device 1 is composed of a light source section 10 including a light source 10a, reflectors 11 and 12, a sample chamber 20 that houses a cell 30, and a spectroscopic section 40, and guides incident light (probe light) L0 from the light source 10a of the light source section 10 via the reflector 11 to the cell 30 in the sample chamber 20. Also, reflected light L1 from the cell 30 is guided via the reflector 12 to the spectroscopic section 40 for spectroscopic analysis.

[0024] 3 and 4 show a more detailed configuration of the optical system around the cell 30. Second reflecting mirrors 11a and 12a are inserted in the optical paths of the incident light L0 and the reflected light L1, respectively, to form optical paths from the sample chamber 25 to the cell 30 and to the spectroscopic section 40.

[0025] Here, the light source 10a of the light source unit 10 is a light source that is selected according to the purpose of measurement and generates light with wavelengths in the ultraviolet-visible-near infrared-infrared range or in a range spanning these ranges. The light source can be selected according to the purpose from light sources such as halogen lamps, deuterium lamps, xenon lamps, and Globar lamps, as well as monochromatic, high-brightness, and high-coherence light sources such as lasers.

[0026] The light from the light source 10a can be collected by the reflecting mirror 11 and irradiated onto the cell 30. If necessary, a lens, an optical fiber, or the like may be interposed instead of the reflecting mirror 11. When the incident light L0 is irradiated, the sample in the cell 30, which is a mixture of the solution S and the diffuse reflector particles 112, emits reflected light L1. By collecting this light at as large a solid angle as possible by a collecting means such as the reflecting mirror 12, the detection sensitivity can be increased. As in the case of light irradiation, the diffuse reflected light L1 may be collected by a lens, an optical fiber, or the like. The collected light is introduced into the spectroscopic section 40, where the light intensity corresponding to the wavelength is detected. The spectroscopic section 40 may be selected according to the purpose, for example, a high-performance dual spectrometer with low stray light or a highly sensitive two-dimensional detector in the case of fluorescence and Raman scattering spectrum measurement.

[0027] Incident light L0 from the light source unit 10 is irradiated onto the sample (solution) S in the cell 30, and the reflected light L1 is split to detect the light intensity. However, for example, in optical absorption spectrum measurement, a known measurement method may be used in which the cell 30 is irradiated with the split monochromatic light rather than irradiating the cell 30 with white light and splitting it. Also, in fluorescence measurement, monochromatic light can be irradiated, but the spectroscopic unit 40 is also provided with a spectroscopic function. Furthermore, in optical absorption spectra in the infrared light region, modulated light that has passed through an interferometer (typically, a Michelson interferometer) may be used as the incident light L0.

[0028] Here, a concave reflecting mirror 12 is used, but for the purpose of collecting the diffuse reflected light L1 from the sample in the cell 30 and guiding it to the spectroscopic section 40, an integrating sphere coated with white powder such as barium sulfate or alumina, or with a metal such as aluminum or gold may be used instead of the reflecting mirror 12 to collect the diffuse reflected light L1 over an even larger solid angle. However, when the solution (sample) has strong light absorption, it is also required to prevent the reflected light L2 from the surface of the cell 30 (see FIG. 4 in particular) from mixing with the reflected light L1 from the solution (sample) in the cell 30, thereby improving the measurement accuracy.

[0029] In general, when a flat solid powder is irradiated with light, the diffuse reflected light is emitted at a solid angle of 2π. Therefore, as long as the solution in the cell 30 can be irradiated with light, there are no conditions for the angle of incidence. The same applies to the direction of the detected reflected light L1. However, since the angle dependency of the intensity distribution of the reflected light L1 is maximum when the angle of incidence and the angle of reflection are the same, as in the case of light reflection in a normal smooth, flat continuous material, it is preferable to collect the diffuse reflected light L1 near that angle. In this case, since the angle of reflection is close to the angle of reflection of the specular reflected light from the surface of the cell 30, it is necessary to pay attention to the mixing of the specular reflected light, as mentioned above.

[0030] The sample chamber 20 is a room (space) in which the temperature and pressure of the cell 30 can be kept constant. The sample chamber 20 and the cell 30 may be integrated, and the temperature and pressure ranges can be selected appropriately depending on the temperature and pressure conditions required for the measurement, the medium to be introduced into the cell 30, etc.

[0031] For example, to cool the temperature of the cell 30, a cryostat or the like is used to control the temperature using liquid helium, liquid nitrogen, liquid oxygen, liquid carbon dioxide, or the like, and the temperature can be controlled at temperatures of -269°C, -196°C, -183°C, or higher. At this time, it is necessary that the solution to be measured does not solidify (freeze). In addition, the temperature can be controlled using a heat transfer medium such as Dowtherm A, silicone oil, or water, and the temperature can be controlled at temperatures of 257°C, 150°C, or lower than 100°C.

[0032] The pressure is also reduced by 10 -5 Pa, 0.1Pa, 10Pa, 1.01325×10 5 It can be controlled to negative pressures of 1 Pa (normal pressure) or higher. Furthermore, it can be controlled to positive pressures of 1 MPa, 10 MPa, 100 MPa, 1 GPa, and 1 PPa (petapascal) by using a pressure pump.

[0033] The inner wall of the sample chamber 20 can be selected to be a metal such as aluminum or a material with high reflectivity and metallic luster. For example, if the density of the diffuse reflector particles 112 is low, the incident light L0 introduced into the cell 30 is unlikely to be scattered by the diffuse reflector particles 112, and may reach the inner surface of the sample chamber 20 containing the cell 30. In the case of the near-infrared to visible to ultraviolet light range, the reflected light intensity can be increased by reflecting this light by aluminum and returning it to the surface of the cell 30 to be irradiated with light. In other words, the inner wall of the sample chamber 20 can be made to also function as an integrating sphere. However, if the amount of bubbles 110 generated is large or the size of the bubbles 110 is large, the reflected light intensity may fluctuate over time.

[0034] The shape of the cell 30 in the sample chamber 20 is preferably such that at least the surface on which the incident light L0 is incident is either spherical, flat, or cylindrical, and can be selected according to the conditions required for the measurement, such as spherical, quadrangular prism, triangular prism, and cylindrical. Furthermore, as described above, in the diffuse reflection measurement, it is necessary that the reflected light L2 from the surface of the cell 30 is not on the same optical path as the diffuse reflected light L1 from the target solution S and is not guided to the spectroscopic section 40. If this condition is satisfied and high-speed stirring is possible without causing the diffuse reflector particles 112 to settle, a cylindrical (columnar) cell having an axis of rotational symmetry is more suitable. Note that the reflected light L2 is likely to spread on a spherical surface and is likely to follow the same optical path as the diffuse reflected light L1, so that the optical path design, such as the relative angle between the incident light L0 and the cell 30, must be fully considered.

[0035] The material of the cell 30 in the sample chamber 20 or the optical window part of the cell 30 irradiated with the incident light L0 may be transparent to the wavelength to be used, and is not particularly limited, but may be any material generally used as a window material for spectroscopy and chemically stable to the solvent. For example, borosilicate glass, quartz glass, synthetic quartz glass, non-fluorescent quartz glass, black quartz glass, infrared synthetic quartz glass, chalcogenite glass, plastic (main components of polystyrene (PS), polymethyl methacrylate (PMMA), polyacrylic acid (PAA), etc.), zinc sulfide (ZnS), zinc selenide (ZnSe), thallium bromoiodide (KRS-5), calcium fluoride (CaF2), barium fluoride (BaF2), potassium bromide (KBr), sapphire (Al2O3), diamond (C), germanium (Ge), silicon (Si), etc. may be appropriately used.

[0036] The solution (medium) S in the cell 30 varies depending on the reaction system, and the material of the diffuse reflector particles 112 is selected according to each solution, but it is necessary that the diffuse reflector particles 112 themselves are made of a transparent powder material that does not absorb light in the wavelength range to be measured. In addition, since the diffuse reflected light by the diffuse reflector particles 112 is observed, it is preferable that the material has a refractive index significantly different from that of the solution S. Furthermore, a material should be selected that is chemically stable with respect to the solvent used and does not affect the reaction. For example, various ceramics (alumina, zirconia, silica, ceria, calcia, titania, hafnium oxide, magnesia, barium oxide, tungsten oxide, barium titanate, boron nitride, aluminum nitride, hydroxyapatite), various salts (lithium chloride, sodium chloride, potassium chloride, calcium chloride, magnesium chloride, barium chloride, lithium fluoride, sodium fluoride, potassium fluoride, calcium fluoride, magnesium fluoride, barium fluoride, magnesium sulfate, calcium sulfate, barium sulfate, magnesium carbonate, calcium carbonate, barium carbonate), diatomaceous earth, carbon, various glasses (quartz, soda lime glass, crystal glass, etc.), various plastics (polytetrafluoroethylene (PTFE), polystyrene (PS), polymethyl methacrylate (PMMA), polyacrylic acid (PAA), etc.), polymer fine particles, or composite materials thereof can be used. Furthermore, the diffuse reflector particles 112 made of these materials may be appropriately combined with other functional particles and dispersed in the solution S for use.

[0037] The particle size of the diffuse reflector particles 112 is required to be a size that effectively diffuses and reflects in the wavelength range to be measured. If the particle size is smaller than the wavelength, the scattering due to specular reflection on the particle surface of the diffuse reflector particles 112 occurs, but the effects of Mie scattering and Rayleigh scattering occur. Therefore, although the particle size is appropriately selected according to the wavelength, it is preferable that the particle size of the diffuse reflector particles 112 is approximately the same as the wavelength to be measured or larger. On the other hand, if it is too large, it becomes difficult to disperse in the solution S by stirring, and it will settle. In addition, multiple reflection and transmission that cause diffuse reflection may not be obtained within the cell 30 of a finite size. In this case, the intensity of the diffuse reflected light may be weak, and it may not be possible to approximate it as diffuse reflection. For this reason, when using diffuse reflector particles 112 with a large particle size, it is necessary to devise a way to adjust the size of the cell 30 in the depth direction with respect to the incident light L0, the spot size of the incident light L0 irradiated on the cell 30, and the range of the detected diffuse reflected light L1 on the surface of the cell 30. Typically, for example, when ultraviolet to visible light with wavelengths of 190 to 700 nm is used for measurement, the particle size of the diffuse reflector particles 112 may be about 1 μm. When near-infrared to infrared wavelengths are used, the particle size may be about 700 nm to about 1000 μm (1 mm). Therefore, particles having a size or size range of 1 μm to 1000 μm, which is the size of powders of various ceramics and the like, may be used.

[0038] Regarding the concentration of the diffuse reflector particles 112 to be put into the cell 30, as the concentration of the diffuse reflector particles 112 increases, the intensity of the diffuse reflected light L1 increases, improving the measurement sensitivity and reducing the effect of the air bubbles 110, but on the other hand, the amount of the solution S decreases, making it difficult to obtain the optical spectrum itself. Therefore, it is preferable to adjust the concentration appropriately depending on the reaction conditions. Typically, the optimum concentration condition can be selected and used within the range of 0.001% by weight or more and 100% by weight or less in the reaction solution.

[0039] The solution S in the cell 30 can be rotated and stirred to generate centrifugal force, which can promote the separation of the bubbles 110, but the required rotation speed depends on the viscosity of the reaction solution and the amount of gas generated. Typically, it can be appropriately adjusted within a range of 1 to 10,000 rpm.

[0040] The solution S inside the cell 30 is rotated and stirred by a rotation mechanism controlled by the control unit, and the method is not particularly limited, but includes, for example, a stirrer 32 made of a magnetic stirrer and a stirring unit 33. Alternatively, various methods such as a method using a mechanical stirrer or a method rotating the cell 30 may be used.

[0041] By rotating and stirring the solution S inside the cell 30, it is possible to prevent the bubbles 110 from adhering to the inner wall of the cell 30. In addition, since the solution S is mechanically stimulated by stirring, the bubbles 110 are generated throughout the solution S, not just on the inner wall of the cell 30 where the bubbles 110 are likely to be generated in a stationary state. This prevents the bubbles 110 from growing, and prevents the grown, large bubbles 110 from affecting the measurement. In other words, although many small bubbles 110 are generated, they are gathered at the center of rotation inside the cell 30 by the rotation and stirring, and the bubbles 110 that are about the same size as or smaller than the diffuse reflector particles 112 may be mixed in with the diffuse reflector particles 112 and have the same effect.

[0042] The diffuse reflector particles 112 in the cell 30 and the bubbles 110 that are generated undergo microscopic dynamic changes as the solution S is stirred. This may cause temporal intensity fluctuations in the diffuse reflected light L1, but it has been confirmed that this does not cause any particular problem in the observation sensitivity of the embodiment described below if the reflected light L1 detected in the spectroscopic section 40 is subjected to a time smoothing process and the time constant is set to 0.1 to 1 second. This is a situation in which the area of ​​the surface of the cell 30 irradiated with the incident light L0 and the depth to which the incident light L0 penetrates into the cell 30 are sufficient, and the dynamic changes described above are averaged spatially and temporally. As described above, when a finite number of large bubbles 110 exist in the spatial region that is the optical path of the incident light L0, it may not be considered as a dynamic change that can be averaged. EXAMPLES

[0043] Example 1: (Measurement of dye: alizarin solution) Diffuse reflector particles made of alumina powder were added to an aqueous solution of alizarin, known as a dye, and then placed in a cylindrical quartz cell, where the diffuse reflectance spectrum was measured while stirring and suspending. Here, alumina is insoluble in water and is chemically stable in the solution (solvent), and the refractive indexes of alumina and water are 1.77 and 1.33, respectively, which is a large difference in refractive index, so that the aqueous solution in which the alumina particles are dispersed becomes cloudy. In other words, it meets the requirements suitable for the above-mentioned diffuse reflector particles. Note that, although a representative example using alumina is shown here, similar results are obtained with diffuse reflector particles made of the same material.

[0044] Specifically, 2.56 mg of alizarin was dissolved in 25 mL of sodium bicarbonate aqueous solution (manufactured by Wako Pure Chemical Industries, Ltd.), and the solutions were prepared at 0.249, 0.189, 0.122, 0.0387, and 0.0104 mmol / L. 200 mg of α-alumina powder (particle size: average particle diameter about 1 μm, manufactured by Kojundo Chemical Laboratory Co., Ltd.) was added to each solution as a diffuse reflector. These were sequentially placed in a quartz cylindrical cell with an outer diameter of φ25 mm, an inner diameter of φ23.5 mm, and a length of 200 mm, and the temperature was set to 18°C. The mixture was stirred and suspended at a speed of 800 rpm with a Teflon (registered trademark) stirrer (cylindrical φ5 mm × length 20 mm) to measure the reflected light spectrum. The 100% diffuse reflectance was obtained by placing only the α-alumina powder in the cylindrical cell and measuring it. The diffuse reflectance of 0% was obtained by placing a shielding plate in the middle of the scattered light path to prevent scattered light from entering the detector of the spectrophotometer. The measured diffuse reflectance spectrum was divided by the diffuse reflectance spectrum of only the sodium bicarbonate aqueous solution without alizarin, and the value was calculated using the Kubelka-Munk formula (KM=(1-r) 2 The diffuse reflectance r was converted to absorbance (KM: Kubelka-Munk), which is a dimensionless quantity proportional to the absorption coefficient, according to the equation (1 / 2r).

[0045] For spectroscopy, a Cary 5000 UV-Vis spectrophotometer manufactured by Agilent Technologies was used. The irradiation area of ​​the irradiated light was adjusted to approximately φ5 mm on the cell surface, and the size of the mirror was a concave mirror with a diameter of 100 mm. The measurement range was the wavelength range from 900 nm to 200 nm, and the scan speed was 100 nm / min.

[0046] On the other hand, as a comparative example, an aqueous solution of alizarin without the addition of a diffuse reflector was placed in a quartz square cell and a transmission type measurement was performed. As above, 2.27 mg of alizarin was dissolved and diluted in 25 mL of an aqueous sodium bicarbonate solution (manufactured by Wako Pure Chemical Industries, Ltd.) to prepare solutions of 0.0378, 0.0189, 0.00378, 0.00189, and 0.000378 mmol / L, respectively. Each solution was placed in a quartz square cell with a side length of 10 mm, and the temperature was set to 18°C, and the transmitted light absorption spectrum was measured using a Cary 60 UV-Vis spectrophotometer manufactured by Agilent Technologies, Inc.

[0047] FIG. 5 shows the light absorption spectrum obtained by converting the measured diffuse reflectance spectrum using the Kubelka-Munk formula. FIG. 6 shows a graph showing the concentration dependence of the light absorption spectrum, with the absorbance at wavelengths of 520 nm, 330 nm, and 261 nm set on the vertical axis and the solution concentration set on the horizontal axis. Furthermore, as a comparative example, FIGS. 7 and 8 show graphs showing the light absorption spectrum and concentration dependence measured using a general transmission cell. As can be seen from these, the results obtained in the examples correspond to the transmitted light absorption spectrum measured using a general transmission cell in the comparative example. Furthermore, the signal intensity according to the concentration also increased linearly, reflecting the measurement of the transmitted light absorption spectrum using a general transmission cell. In other words, it can be seen that the method of the present invention can measure the light absorption spectrum in the same way as the conventional method.

[0048] Example 2: (Substrate concentration dependence) As in Example 1, a diffuse reflector consisting of α-alumina powder was added to an aqueous solution of cobalt (II) nitrate, which was then placed in a cylindrical quartz cell and the reflected light spectrum was measured while stirring and suspending the solution.

[0049] 200 mg of α-alumina powder (manufactured by Kojundo Chemical Laboratory Co., Ltd.) was dispersed in 20.039 g of water as a diffuse reflector. Then, 37.77, 56.43, 83.47, and 165.16 mg of cobalt (II) nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) were added to prepare solutions. As in Example 1, each solution was sequentially placed in a quartz cylindrical cell, the temperature was set to 18°C, and the solution was stirred and suspended at a speed of 800 rpm with a Teflon stirrer, and the diffuse reflectance spectrum was measured using a Cary 5000 UV-Vis spectrophotometer manufactured by Agilent Technologies, Inc. The measured diffuse reflectance spectrum was divided by the diffuse reflectance spectrum of alumina alone, and the value was converted into absorbance (KM), which is a dimensionless quantity proportional to the diffuse reflectance r and the absorption coefficient, according to the above-mentioned Kubelka-Munk formula.

[0050] Figure 9 shows the optical absorption spectrum converted from the measured diffuse reflectance spectrum. Note that Figure 9(b) shows an enlarged vertical axis showing absorbance in (a). Note that the absorption peak appearing at 300 nm in the figure is due to nitrate ions (NO3 - ), and the absorption at 500 nm is due to cobalt ions (Co 2+ ) is the result of the above. Figure 10 shows a graph plotting the concentration and absorbance of a cobalt nitrate solution at wavelengths of 221, 305, and 527 nm. From these, it can be seen that the signal strength is proportional to the concentration. In Figure 10(a), it appears that there is a tendency for the signal to saturate above a certain light intensity (approximately 20 km), but this is due to the dynamic range of the spectrometer.

[0051] Example 3: (Diffuse Reflector Concentration) The reflectance spectrum of the aqueous solution of cobalt (II) nitrate was measured while varying the amount of a diffuse reflector made of α-alumina powder and stirring the solution in a cylindrical quartz cell.

[0052] 164.59 milligrams of cobalt(II) nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 20.029 g of water, and 51, 102, 153, 203, 303, and 403 mg of α-alumina powder (manufactured by Kojundo Chemical Laboratory Co., Ltd.) were added as a diffuse reflector to create solutions (corresponding to 0.25, 0.50, 0.75, 1.00, and 2.00 wt% α-alumina ratios, respectively). Solutions containing only cobalt(II) nitrate were also created without adding α-alumina powder. Each solution was placed in a quartz cylindrical cell and measured as above. The measured diffuse reflectance spectrum of the solution containing cobalt(II) nitrate was divided by the diffuse reflectance spectrum measured for a solution containing only alumina without the addition of cobalt(II) nitrate, and the resulting value was converted to absorbance (KM), a dimensionless quantity proportional to the absorption coefficient, according to the Kubelka-Munk equation.

[0053] Figure 11 shows the converted optical absorption spectrum. Figure 11(b) is an enlarged view of the vertical axis showing the light intensity in (a). In the solution that did not contain alumina as a diffuse reflector, almost no diffuse reflected light was obtained. As a result, a spectrum with a low S / N ratio was obtained over the entire measurement range. In particular, in the wavelength range below 320 nm, no spectrum corresponding to nitrate ions was obtained. On the other hand, when the diffuse reflector was added at 0.25 wt% (50 mg alumina / 20 g water) or more, a diffuse reflectance spectrum due to cobalt (II) nitrate was obtained.

[0054] Figure 12 shows a graph plotting the concentration and absorbance of a cobalt nitrate solution at wavelengths of 221, 305, and 527 nm. As shown in Figure 12(a) and its enlarged vertical axis, Figure 12(b), solutions containing 0.5 wt% or more alumina as a diffuse reflector show concentration dependency.

[0055] Here, although the concentration of the cobalt nitrate solution remains unchanged, a tendency is observed in which the apparent absorbance (light absorption intensity) gradually decreases as the concentration of α-alumina increases. As mentioned above, this is due to the change in the average distance between the diffuse reflector particles. It is considered that the light absorption by cobalt ions in the solution is not that strong to begin with, and at an alumina concentration of 0.5 wt% or less, the contribution of the diffuse reflector particles is small, so that the incident light reaches the back surface of the solution cell, making it impossible to accurately measure the diffuse reflectance spectrum, resulting in weak light absorption. In other words, there is an optimal concentration of diffuse reflector particles for accurate measurement of the diffuse reflectance spectrum.

[0056] Note that Figure 13 shows the intensity of the light absorption spectrum (diffuse reflectance) for each concentration of alumina used as a diffuse reflector. As can be seen from this, it is necessary to perform baseline correction of the intensity of the light absorption spectrum for each concentration of the diffuse reflector.

[0057] Example 4: (Decomposition reaction of formic acid) Using a catalyst made of an iridium complex as shown in Figure 14, a diffuse reflector made of α-alumina powder was added to an aqueous solution of formic acid, and the solution was then placed in a cylindrical quartz cell. The solution was stirred and suspended while decomposing the formic acid to produce carbon dioxide and hydrogen, and the diffuse reflectance spectrum was measured.

[0058] 200 mg of α-alumina powder (manufactured by Kojundo Chemical Laboratory Co., Ltd.) was dispersed in 20 g of 3.7 mol / L formic acid solution as a diffuse reflector, and 5.68 mg of iridium complex (see Figure 14) was dissolved and placed in a cylindrical quartz cell. The temperature of this cell was adjusted to 50°C, and the inside was stirred at a speed of 1000 rpm with a Teflon stirrer. After confirming the generation of bubbles, the diffuse reflectance spectrum was measured after a predetermined time (0, 14, 50, and 88 minutes) had elapsed. The obtained spectrum was converted using the Kubelka-Munk equation to obtain an optical absorption spectrum.

[0059] The converted optical absorption spectrum is shown in Figure 15. Note that Figure 15(b) is a graph in which the horizontal axis of (a) is enlarged.

[0060] Measurements were also performed at different catalyst concentrations. In detail, 200 mg of α-alumina powder (manufactured by Kojundo Chemical Laboratory Co., Ltd.) was dispersed in 20 g of 0.1 mol / L formic acid solution as a diffuse reflector, and 5.12 mg of iridium complex (see Figure 14) was dissolved, followed by an additional 4.80 mg (total 9.92 mg), and the solution was placed in a cylindrical quartz cell as above, the temperature was adjusted to 50°C, and the solution was stirred at 1000 rpm with a Teflon stirrer, and measurements were performed after 10 minutes. The obtained spectrum was converted using the Kubelka-Munk equation to obtain an optical absorption spectrum.

[0061] Figure 16(a) shows the optical absorption spectrum for each concentration of the iridium complex catalyst, and Figure 16(b) shows a graph plotting the absorbance at wavelengths of 240, 330, 299, and 259 nm. As can be seen from these figures, there is a proportional relationship between the catalyst concentration and the absorbance.

[0062] Figure 17(a) shows the optical absorption spectrum of only the solution of the iridium complex catalyst, superimposed on the optical absorption spectrum of a solution in which formic acid has been completely decomposed and no longer generates bubbles. Furthermore, Figure 17(b) shows the change over time in absorbance at a wavelength of 222 nm, which corresponds to the absorption of formic acid. This shows that the decrease in absorbance due to the decomposition of formic acid is proportional to the absorbance. In other words, it is clear that this method can be used to observe the progress of formic acid decomposition by the catalyst.

[0063] Furthermore, Figure 18 shows a comparison with the measurement by the permeation method. Due to the difference in catalyst concentration (this method: 5.00 × 10 -4 mol / L, transmission method: 1.00×10 -4 mol / L and 2.50×10 -4 mol / L) and the optical spectral absorption intensity are different, but the shapes of the spectral lines are almost the same, and it can be seen that this method can be used for measurements in the same way as the transmission method.

[0064] Although the representative embodiments of the present invention and modified examples based thereon have been described above, the present invention is not necessarily limited thereto, and a person skilled in the art will be able to find various alternative embodiments without departing from the scope of the appended claims. [Explanation of symbols]

[0065] 1 device 10 Light source section 10a light source 11, 12 Reflector 20 Sample Room 30 cells 40 Spectroscopic section 100 Rotating Mixer 110 Bubbles 112 Diffuse Reflector Particles

Claims

1. 1. A method for measuring the optical spectrum of a solution provided in a cell, comprising the steps of: A method for measuring the optical spectrum of a solution, comprising the steps of adding diffuse reflector particles to the solution, rotating and stirring the solution around a rotation axis so as to form a dispersed flow of the diffuse reflector particles along the optical window of the cell, applying incident light through the optical window, obtaining diffuse reflected light scattered by the diffuse reflector particles, and measuring the optical spectrum of the light.

2. 2. The method for measuring an optical spectrum according to claim 1, further comprising a focusing means for focusing the diffuse reflected light scattered by the diffuse reflector particles.

3. 3. The method for measuring an optical spectrum according to claim 1, wherein the solution contains air bubbles, and the air bubbles are unevenly distributed around the rotation axis by centrifugal force caused by the rotation and stirring.

4. 4. The method of claim 3, wherein the bubbles are generated by a reaction of the solution.

5. 5. A method for measuring an optical spectrum according to claim 1, wherein the cell is cylindrical and has an axis of rotational symmetry, the axis of rotational symmetry being aligned with the axis of rotation.

6. 6. A method for measuring an optical spectrum according to claim 1, wherein the diffuse reflector particles are made of a transparent powder material that has no optical absorption for the incident light and has a refractive index different from that of the solution.

7. 7. The method for measuring an optical spectrum according to claim 1, wherein the optical spectrum is an optical absorption spectrum.

8. 7. The method for measuring an optical spectrum according to claim 1, wherein the optical spectrum is a fluorescence / Raman scattering spectrum.

Images