JP2007155494A - Twin flow cell and concentration measuring system using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flow cell to a piping line in the optical spectrometry of the concentration in a solution, and to also simply perform calibration for holding measuring precision. <P>SOLUTION: This twin flow cell is used in a spectrometric system and composed of a light pervious first flat plate on which light is incident, a light pervious second flat plate for emitting the incident light and three mutually parallel wall plates arranged between the first and second flat plates arranged parallel to each other. First and second spaces are constituted of the first and second flat plates and three wall plates. Preferably, the flow cell is further equipped with an attachment part, which fixes the first end part being the end part of a light emitting light path and the second end part opposed to the first end part so as to hold the flow cell, and a moving device capable of moving the position of the attachment part from a position where light is transmitted through one of the first and second spaces to a position where light is transmitted through the other one of them in relative relation to the flow cell. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to optical density measurement based on transmitted light intensity of a fluid, and more particularly to a flow cell and a density measurement system used therefor.

  In the concentration measurement of an aqueous solution or the like by spectroscopic analysis, the concentration can be measured by flowing a sample into a flow cell in the spectrometer and detecting the transmitted light of the flow cell (see, for example, JP-A-6-265471). Here, the absorbance of the transmitted light is obtained, and the concentration can be determined using a calibration curve formula obtained in advance. In the case of measurement over a long period of time, the spectroscopic measurement apparatus needs to be calibrated in order to maintain the measurement accuracy.

  In the manufacturing process of a semiconductor device, the concentration is controlled by measuring the concentration of a chemical solution to be used. Here, for example, a circulation line for taking out the chemical solution overflowing from the chemical solution tank and returning it to the original chemical solution tank is provided, and the pipe is branched from the middle of the circulation line to introduce the sample solution into the flow cell in the spectrometer. Light is transmitted through the sample solution flowing through the flow cell, the transmitted light is measured, and the concentration is determined by analyzing the measurement data. For example, it takes 5 minutes or more for one measurement. At the time of calibration, the removal of the chemical solution from the circulation line is stopped, and only the calibration solution is passed through the flow cell, and the transmitted light is measured.

There is also known a concentration measuring apparatus that can be measured in real time by providing a flow cell directly in the circulation line. For example, in the concentration measuring apparatus described in Japanese Patent Laid-Open No. 7-12713, a flow cell is provided in a pipe through which a fluid flows. The concentration of the substance in the liquid can be analyzed by transmitting light perpendicular to the direction of flow in the flow cell and measuring the transmitted light. Calibration is not described. In the spectroscopic analyzer described in JP-A-2005-164255, sample light, reference light, and dark light pass through different optical paths. Light passes through the flow cell sample only in the case of sample light.
JP-A-6-265471 JP 7-12713 A JP 2005-164255 A

  In the concentration measuring apparatus described in Japanese Patent Laid-Open No. 7-12713, a flow cell is attached to the piping line. However, since a sample of a known concentration for carrying out the accuracy check of the concentration measuring apparatus cannot be flowed, The accuracy of the measurement cannot be confirmed. Since calibration cannot be performed, the concentration measurement value gradually shifts.

  On the other hand, in the spectroscopic analyzer described in JP-A-2005-164255, an optical component is required for each of the measurement optical path and the reference optical path. Therefore, in order to attach the calibration mechanism, the entire apparatus becomes large, the number of parts increases, and the cost increases. In addition, since the sample optical path and the reference optical path are different, fluctuations in the optical components due to the environment cannot be removed when obtaining the absorbance from the transmitted light intensity. For this reason, even if calibration is performed, an error that cannot be removed appears in the concentration measurement value.

  An object of the present invention is to enable measurement to be performed quickly and with high accuracy in optical spectroscopic measurement of a concentration in a solution.

  A flow cell according to the present invention is a flow cell used in a spectroscopic measurement apparatus, and includes a light-transmitting first flat plate on which light is incident, a light-transmitting second flat plate on which incident light is emitted, Between the 1st and 2nd plane board arrange | positioned in parallel, it consists of three mutually parallel wall boards arrange | positioned so that the 2nd independent 1st and 2nd space of the same shape may be partitioned off. First and second spaces are constituted by the first flat plate, the second flat plate, and the three wall plates. Preferably, for the first and second spaces, the distance between the first and second flat plates in the light transmission direction in one space, and the first and second in the light transmission direction in the other space. The difference from the distance between the second flat plates is 1 μm or less.

  The flow cell preferably further includes an attachment portion and a moving device. The attachment portion is a first end portion and a second end portion that are part of an optical path that makes light generated from a light source incident on the flow cell and guides light transmitted through the flow cell to a light receiving element, toward the flow cell. A moving device that fixes a first end that emits light and a second end that opposes the first end across the flow cell and that receives light transmitted through the flow cell. The position of the mounting portion can be moved relative to the flow cell from a position where light is transmitted to one of the first and second spaces to a position where light is transmitted to the other.

  The concentration analysis system according to the present invention generates a chemical liquid tank that contains a chemical liquid, the flow cell, a piping line that supplies the chemical liquid supplied from the chemical liquid tank to one space of the flow cell, and light having a plurality of wavelengths. And a concentration measuring device that measures transmitted light that is incident on the flow cell and transmitted through any space of the flow cell.

In the flow cell, the concentration can be measured quickly by flowing the sample solution in one space directly connected to the piping line, and even if a calibration solution such as pure water cannot flow in the piping line, a sample with a known concentration in the other space Therefore, it is possible to easily check (calibrate) the accuracy of the concentration measuring device.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows a mixed acid concentration monitoring system. For concentration monitoring, a part of the chemical solution (sample) overflowing from the chemical solution tank 10 containing the mixed acid is taken out and passed through a circulation line (piping line) including the flow cell 12, the filter 14 and the pump 16. The sample whose concentration is measured by the flow cell 12 is returned to the original chemical tank 10 by the pump 16. The flow cell 12 is connected to the concentration measuring device 18 by two optical fibers 13. The concentration measuring device 18 is a spectroscopic measuring device, generates light of a predetermined wavelength, and enters the flow cell 12 through the optical fiber 13. The light transmitted through the flow cell is detected by the concentration measuring device 18 through the optical fiber 13, and the concentration is determined based on the detected light. Thus, the flow cell 12 is directly connected to the circulation line. By measuring the chemical solution flowing through the flow cell 12, it can be measured at a plurality of time points in real time (in about 10 seconds for one measurement).

  When the flow cell is directly attached to the circulation line piping, the calibration line for flowing the calibration liquid cannot be attached. Therefore, as shown in FIG. 2, a twin cell including two cells 12 a and 12 b having the same structure is used as the flow cell 12. When switching from one cell to the other, only the position of the optical fiber 13 is shifted to switch the optical path. Therefore, when the optical path is switched, the optical system does not change except for the switching portion. The cells have the same structure, and the two cells are kept as parallel as possible so that the optical path lengths are the same. One of the twin cells (main cell 12a) is directly attached to the piping of the circulation line so that the sample liquid flows. Further, a calibration solution and a sample with a known concentration are allowed to flow through the other cell (subcell 12b). Therefore, calibration or confirmation measurement can be performed with the same configuration of the other optical system except that the optical path is switched from the main cell 12a side to the subcell 12b side. There is no need to install extra piping for calibration. In addition, it is easy to cope with exposure to drugs.

  FIG. 3 shows the structure of the flow cell 12 having a twin cell. In general, as described above, the flow cell is arranged in parallel with a light transmissive first flat plate on which light is incident and a light transmissive second flat plate on which incident light is emitted. It consists of three mutually parallel wall plates arranged so as to partition two independent first and second spaces having the same shape between the first and second flat plates, and the first flat plate and the second flat plate And the 1st and 2nd space is comprised from three wall boards. FIG. 3 shows a specific example of the flow cell. In FIG. 3, (a) is a plan view, (b) is a front view, and (c) is a sectional view taken along line A-A 'in (a). The twin flow cell 12 includes an upper surface portion 12c and a lower surface portion 12d capable of transmitting light, and a first side surface portion 12e, a central separation portion 12f, and a second side surface portion 12g therebetween, which are made of light such as quartz or sapphire. Made of permeable material. The light transmissive property refers to transmitting light in the infrared region, visible region, or ultraviolet region. The flow cell is manufactured by joining the glass substrates 12c to 12g constituting the flow cell 12 with an optical contact with high accuracy. Optical contact refers to a method in which each glass surface is polished to create two surfaces that are exactly suitable and have high flatness and smoothness, and are bonded by intermolecular force on the substrate surface. That is, it is a technique for joining two substrate surfaces polished with high accuracy without using an adhesive or the like. The glass substrates 12c to 12g are polished with a flatness capable of forming the main cell 12a and the subcell 12b with optical contacts, and they are joined with the optical contacts. The main cell 12a is surrounded by glass substrates 12c, 12d, 12e and 12f, and the subcell 12b is surrounded by glass substrates 12c, 12d, 12f and 12g. Therefore, the main cell 12a and the subcell 12b can be configured as the same shape, and are independent spaces. At the entrance and exit of the chemical solution, the shape is conically narrowed outward. As shown in (c), the main cell 12a and the subcell 12b have a rectangular cross section in the central portion that transmits light in the infrared region, visible region, or ultraviolet region, but in fact, at both ends, (a) As shown in (b), it becomes narrow and conical and opens to the outside. A sample to be measured is introduced from the opening and discharged from the other opening. The transmitted light is incident perpendicular to the sample flow in the cell.

  The cell length of the optical path between the glass substrates 12c and 12d constituting the main cell 12a and the subcell 12b is 1 to 20 mm. The cell length is set to an appropriate length according to the degree of light absorption of the measurement target. The glass substrates 12c and 12d have as much parallelism as possible with respect to the optical path. That is, the light transmitting surfaces of the glass substrates 12c and 12d are polished with a flatness that allows optical contact. Specifically, the difference in the total thickness of the cells at the light transmission portion is 1 μm or less, and the parallelism is 0.5 μm or less in the state of the glass substrate before being processed into cells. Thus, by maintaining the parallelism of the light transmission plate with high accuracy, there is almost no difference in optical path length, and the two cells 12a and 12b become substantially the same shape, and concentration measurement and calibration are performed in one cell. Calibration is now possible with a precision close to that required. Of course, it is desirable that the parallelism be further increased. In one example, the size of the optical path in each of the cells 12a and 12b is φ3 mm, the separation wall between the main cell 12a and the subcell 12b is 1.5 mm, and further, it is prevented from being near the center. Extra space is needed to do this.

  FIG. 4 shows the configuration of the concentration measuring device 18. The concentration measuring device 18 includes a spectroscopic unit 20, a sampling unit 40, and a data processing unit 50.

  The spectroscopic unit 20 includes two portions 20a and 20b. For example, emitted light from a light source 22 made of a tungsten / halogen lamp is collected by a convex lens 24 and passes through a diaphragm 26 disposed at the focal position of the convex lens 24. The rotating disk 30 holds a plurality of interference filters 28 at equal angular intervals, and is rotated by a driving motor 32 at, for example, 1000 rpm. The light that has passed through the diaphragm 26 and has passed through one of the interference filters 28 of the rotating disk 30 is collected by the convex lens 34. The collected light passes through the optical fiber 13 and enters one cell of the flow cell 12 in the sampling unit 40. The light transmitted through the flow cell 12 and returned through the other optical fiber 13 is collected by the convex lens 36 and enters the light receiving element 38. The light receiving element 38 converts incident light into photocurrent.

  The interference filter 28 of the rotating disk 30 separates incident light at a specific wavelength, and as the wavelength, in the near infrared region where the characteristic absorption band of water appears prominently, the fluctuation of the spectrum with respect to the concentration change of the specific component. A wavelength that is large and is less affected by interference and interference from other components is selected. Specifically, the fluctuation of the near-infrared absorption spectrum in each of the ionic species at 980 nm and its vicinity, which is a characteristic absorption band of water, at 1400 nm and its vicinity, 1460 nm and its vicinity, 1940 nm and its vicinity, 2500 nm and its vicinity Gives a unique spectrum. Further, acetic acid has characteristic absorption at 1680 nm, 1720 nm, 2260 nm, 2480 nm, and 2510 nm. Therefore, as the interference filter 28, for example, eight wavelengths are selected from wavelengths in the range of 800 nm to 2600 nm including light of these wavelengths according to the mixed acid to be measured, and light of these eight wavelengths is transmitted. Eight interference filters 28 to be used are used. Here, although the spectrum in the near infrared region has been described, it is needless to say that an interference filter 28 that spectrally separates light in the infrared region, visible region, or ultraviolet region may be used.

(Configuration of sampling unit 40)
As shown in FIG. 2, the sampling unit 40 includes a flow cell 12 directly connected to a part of the circulation line, and two optical fibers 13 for transmitting light to the flow cell 12. The flow cell 12 has a twin cell structure including a main cell 12a and a subcell 12b. The main cell 12a is directly connected to the circulation line using an O-ring or the like. The pair of optical fibers 13 is usually positioned in the main cell 12a so as to transmit light in a direction orthogonal to the flow, and the concentration of the chemical solution from the circulation line is measured. On the other hand, in the subcell 12b, a calibration solution or a sample with a known concentration can be flowed for calibration. For example, a pure water line is connected. Moreover, you may connect the tube which enclosed the pure water. Thereby, the liquid for calibration can be easily introduced into the subcell 12a. Therefore, the time required for calibration is shortened by providing the subcell 12b.

  A connector (not shown) for connecting to the optical fiber 13 is provided on the pair of optical fiber mounting portions 44 positioned with the flow cell 12 in between, and the optical fiber 13 is connected thereto. A moving device that moves smoothly is used to switch the optical path. Here, an air actuator 42 (not shown because it is installed below FIG. 2) is used. The moving distance of this switching is preferably as short as possible and 15 mm or less in order to maintain parallelism. Thus, even if a mechanical moving means such as an actuator is used, if the parallelism is maintained, even if there is a positional reproducibility shift, it can be regarded as the same optical path. By smoothly moving the optical fiber mounting portion 44 to a predetermined position by the air actuator 42 in the direction perpendicular to the optical path, the optical path passing through the menin cell 12a and the optical path passing through the subcell 12b are switched. The optical path switching by the air actuator 42 is controlled by the data processing device 53. In the concentration measurement, the optical fiber attachment portion 44 is positioned so that the optical path between the pair of optical fibers 13 passes through the main cell 12a. When calibrating the concentration measurement, the optical fiber attachment portion 44 is positioned so that the optical path between the pair of optical fibers 13 passes through the subcell 12b. As described above, the measurement can be performed by transmitting light through the fluid in the cell with the optical fiber 13 and switching the optical path with the air actuator 42 to perform calibration and maintenance measurement.

(Configuration of data processing unit 50)
In the data processing unit 50, as shown in FIG. 4, the amplifier 51 amplifies the transmitted light intensity signal corresponding to the intensity of the transmitted light of the flow cell 12 output from the light receiving element 38 as the photocurrent, and performs A / D conversion. The unit 52 converts the output of the amplifier 51 into a digital signal. The data processing device 53 calculates the absorbance of light of a plurality of wavelengths from the transmitted light intensity signal input from the A / D converter 52, and calculates and stores the calculated absorbance of each wavelength of light and as described later. Based on the calibration curve formula, the concentration of acid in the mixed acid is calculated from the absorbance at each wavelength.

  The data processing unit 53 includes a microprocessor 54 that performs the above-described calculation of the acid concentration in the mixed acid, a RAM 55 that stores a calibration curve type and various data, a ROM 56 that stores a program for operating the microprocessor 54, data, An input device 57 such as a keyboard for inputting various commands, an output device 58 such as a printer or a display for outputting the results of the data processing, and the like are included. The microprocessor 54 also generates drive control signals such as the drive motor 32 that rotates the rotary disk 30.

  Note that the detector 38 and the above-described arithmetic unit may be provided on the light emission side of the flow cell 12.

  For the data processing for concentration determination in the data processing unit 50, a known method described in JP-A-6-265471 is used. FIG. 5 shows more specific contents of data processing by the microprocessor 54 of the data processing device 53. In the light receiving element 38 of FIG. 4, when the rotary disk 30 is driven to rotate by the rotation of the drive motor 32, light having a transmission wavelength of the eight interference filters 28 held by the rotary disk 30 is transmitted to the main cell 12a. A signal proportional to the transmitted light transmitted through the mixed acid is generated. These signals are amplified by the amplifier 51 and then converted into digital signals by the A / D converter 52. This digital signal is input (step S1).

Next, the calculation of the following equation (1) is executed for this digital signal to calculate the absorbance A _i (step S2).

ここで、ｉ＝１〜８、Ｒ_ｉ＝測定対象サンプルのｉ波長目の透過強度値、Ｂ_ｉ＝基準濃度の混酸（たとえば、フッ酸＋硝酸＋酢酸）をサブセル１２ｂに入れたときのｉ波長の透過強度値、Ｄ_ｉ＝メインセル１２ａを遮光したときのｉ波長目の透過強度値。Ｂ_ｉおよびＤ_ｉは予め測定しておき、キーボード等の入力装置５７からデータ処理装置５３のＲＡＭ５５に格納されている。

Here, i = 1 to 8, R _i = the transmission intensity value of the _i -th wavelength of the sample to be measured, B _i = the mixed acid of the reference concentration (for example, hydrofluoric acid + nitric acid + acetic acid) i in the subcell 12b The transmission intensity value of the wavelength, D _i = the transmission intensity value of the _i -th wavelength when the main cell 12a is shielded from light. B _i and D _i are measured in advance and stored in the RAM 55 of the data processing device 53 from the input device 57 such as a keyboard.

Next, the following equation (2) is converted to the absorbance A _i obtained by the calculation of equation (1) (step S3).

この変換を行なうのは次の理由による。式（１）により演算される吸光度Ａ_ｉは、光源２２の明るさの変動、受光素子３８の感度変動、光学系のひずみ等により変化する。しかしこの変化はあまり波長依存性はなく、８波長の各吸光度データに同相、同レベルで重畳する。したがって、式（２）のように、各波長間の差を取ることにより、上記変化を相殺できる。また、サンプル自体の温度変動による吸光度Ａ_ｉの変動もあるが、この変動の除去には、たとえば本出願人の出願に係る特開平３−２０９１４９号公報に記載の方法を採用できる。

This conversion is performed for the following reason. The absorbance A _i calculated by the equation (1) varies depending on the brightness variation of the light source 22, the sensitivity variation of the light receiving element 38, the distortion of the optical system, and the like. However, this change is not very wavelength-dependent, and is superimposed in the same phase and at the same level on each absorbance data of 8 wavelengths. Therefore, the above change can be canceled by taking the difference between the wavelengths as shown in Equation (2). There is also a variation of absorbance A _i due to temperature variations of the sample itself, the removal of this variation may be employed a method described in JP-A-3-209149 discloses according to the example the applicant's application.

Next, the following equation (3) is calculated based on _Si obtained in equation (2). When the mixed acid is, for example, (hydrofluoric acid + nitric acid + acetic acid), the hydrofluoric acid concentration C ₁ The nitric acid concentration C ₂ and the acetic acid concentration C ₃ are calculated (step S4).

In the formula (3), F (S i ) is a calibration curve type hydrofluoric acid, with including higher-order terms from each of the first-order of S _i, in each multiplication of S _i and S _{i + 1} or higher order terms that It includes a certain cross term and constant term, and is expressed by the following equation (4).

In Expression (4), S _i and S _{i + 1} are data obtained by Expressions (1) and (2), α, β, and γ are coefficients of a calibration curve equation, and Z ₀ is a constant term. Equation (4) is obtained in advance by the mixed acid concentration measuring apparatus shown in FIG. 1 using a standard sample of a mixed acid (hydrofluoric acid + nitric acid + acetic acid) having a known concentration, and stored in the RAM 55.

In the formula (3), G (S _i ) and H (S _i ) are a calibration curve formula for nitric acid and a calibration curve formula for acetic acid, respectively, and both are the same formulas as the formula (4). Similarly, these calibration curve types are obtained in advance by the mixed acid concentration measuring apparatus shown in FIG. 1 using a standard sample of a mixed acid (hydrofluoric acid + nitric acid + acetic acid) having a known concentration, and stored in the RAM 55.

Next, the concentration C _{1 of} hydrofluoric acid, the concentration C _{2 of} nitric acid and the concentration C ₃ of acetic acid obtained by the calculation of equation (4) are displayed on a CRT screen, or printed on an output device 58 such as a printer. Is output as a hard copy or transmitted to the outside (step S5).

Also, based on the data of hydrofluoric acid concentration C ₁ , nitric acid concentration C ₂ and acetic acid concentration C ₃ obtained above, the current state of the chemical bath 10 (see FIG. 1) is ascertained, and from these data The parameter values necessary for management of the chemical tank 10 that can be calculated, for example, the stock solution addition amount, the stock solution addition time, the waste solution amount, and the waste solution time are calculated, and the results are output to the output device 58 (step S6).

  In the above example, since the mixed acid is composed of three components of hydrofluoric acid + nitric acid + acetic acid, a correction coefficient represented by a matrix of 3 rows × 3 columns was used. For example, in the case of a two-component mixed acid such as hydrofluoric acid + nitric acid, the correction coefficient can be obtained in the same manner except that the correction coefficient is 2 rows × 2 columns.

  Japanese Patent Application Laid-Open No. 6-265471 describes correction of a change due to a temperature change of a concentration calculation value, distortion of an optical system, and the like when the concentration measuring apparatus is used for a long time. This can be applied when a sample having a known concentration is measured by the subcell 12b. The correction calculation performed by the data processing device 53 will be described. Expression (5) is an expression used for the correction calculation.

この式（５）において、Ｃ₁，Ｃ₂およびＣ₃は式（３）により得られた値であり、また、Ｃ₁´，Ｃ₂´およびＣ₃´は補正後の各酸の濃度である。さらに、ｐ_ij（ｉ＝１〜３，ｊ＝１〜３）は補正係数である。

In this equation (5), C ₁ , C ₂ and C ₃ are values obtained by equation (3), and C ₁ ′, C ₂ ′ and C ₃ ′ are the concentrations of each acid after correction. is there. Further, p _ij (i = 1 to 3, j = 1 to 3) is a correction coefficient.

The correction coefficient p _ij has the following relationship when a long time has not elapsed since the expression (3) was obtained and correction is not necessary. p ₁₁ = p ₂₂ = p ₃₃ = 1, p ₁₂ = p ₁₃ = p ₂₁ = p ₂₃ = p ₃₁ = p ₃₂ = 0, C ₁ '= C ₁ , C ₂ ' = C ₂ , C ₃ '= C ₃ .

The correction coefficient p _ij is obtained as follows. That is, n types (n = 3 or more) of sample 1 to sample n of known mixed concentrations having different concentration ratios are prepared. Assume that these samples 1 to n have a known concentration of the value represented by the following equation (6).

  The measured concentration before correction in which the concentration of the mixed acid is measured by the data processing device 53 is represented by the following equation (7).

  At this time, the relationship represented by the following equation (8) is established between the known concentration and the measured concentration of samples 1 to n.

  Each of the three matrices in equation (8)

とおくと、式（８）はＣ´＝ＰＣで表わされ、補正係数ｐ_ijは、次の式（１２）（ｎが３の場合）および式（１３）（ｎが３よりも大の場合）により求められる。ここで、行列Ｃ^Ｔは行列Ｃの転置行列であり、行列Ｃ^-1は行列Ｃの逆行列である。

The expression (8) is expressed by C ′ = PC, and the correction coefficient p _ij is expressed by the following expression (12) (when n is 3) and expression (13) (where n is larger than 3). If). Here, the matrix C ^T is a transposed matrix of the matrix C, and the matrix C ⁻¹ is an inverse matrix of the matrix C.

In the correction, samples 1 to 3 (when n = 3) having a known density are inserted into the optical path of the transmitted light of the subcell 12b, and the value of Expression (7) is obtained. Further, the value of equation (6) is stored in advance in the RAM 55 of the data processing device 53, the correction value is calculated from equations (9) to (13), and the deviation from the true value is calculated from equation (5). A density value corrected for is obtained.

Diagram of mixed acid concentration monitoring system Diagram showing twin flow cell structure Diagram showing twin flow cell structure Diagram showing the configuration of the concentration measuring device Flow chart of data processing by microprocessor of data processor

Explanation of symbols

10 chemical tank, 12 flow cell, 12a main cell, 12b subcell, 13 optical fiber, 18 concentration measuring device, 20 spectroscopic unit, 40 sampling unit, 50 data processing unit, 53 data processing device.

Claims (5)

A flow cell used in a spectrometer,
A light transmissive first flat plate on which light is incident; a light transmissive second flat plate on which incident light is emitted;
It consists of three mutually parallel wall plates arranged so as to partition two independent first and second spaces of the same shape between the first and second plane plates arranged in parallel,
A flow cell in which first and second spaces are constituted by a first flat plate, a second flat plate, and three wall plates.   The first plane plate, the second plane plate, and the three wall plates are polished with a flatness capable of forming the first and second spaces with optical contacts, and the first plane plate, the second plane plate, and The three wall plates are joined by optical contact, and the light transmitting surfaces of the first plane plate and the second plane plate are polished with a flatness that allows optical contact. Item 2. The flow cell according to Item 1. further,
Light emitted from the light source is incident on the flow cell, and the first end and the second end are part of an optical path that guides the light transmitted through the flow cell to the light receiving element, and emits light toward the flow cell. An attachment for fixing one end and a second end opposite to the first end across the flow cell, the second end receiving light transmitted through the flow cell;
A moving device capable of moving the position of the mounting portion relative to the flow cell from a position where light is transmitted to one of the first and second spaces to a position where light is transmitted to the other. The flow cell according to claim 1 or 2.   For the first and second spaces, the distance between the first and second flat plates in the light transmission direction in one space and the first and second flat plates in the light transmission direction in the other space. The flow cell according to any one of claims 1 to 3, wherein a difference from the interval is 1 µm or less. A chemical tank for storing the chemical,
A flow cell according to any one of claims 1 to 4,
A piping line for supplying a chemical solution supplied from a chemical tank to one space of the flow cell;
A concentration measurement system comprising: a concentration measurement device that generates light of a plurality of wavelengths, enters the flow cell, and measures transmitted light that has passed through any space of the flow cell.

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