pb 2+ Concentration detection sensor, device, preparation method and usage method

Abstract

The present invention discloses a Pb2+ concentration detection sensor, a device, a preparation method and a use method. The Pb2+ concentration detection sensor includes: a photonic crystal fiber, single-mode fibers connected to both ends of the photonic crystal fiber, and a sensitive film coated on the surface of the photonic crystal fiber, wherein the sensitive film has the function of causing a refractive index change after binding to Pb2+. In the Pb2+ concentration detection sensor of the present invention, the sensitive film can bind to Pb2+ in the solution, thereby causing a change in the refractive index. Furthermore, based on the change in the refractive index, the concentration of Pb2+ in the water quality can be effectively detected. The Pb2+ concentration detection sensor of the present invention has the advantages of high detection selectivity and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of pb 2+ concentration detection, and particularly to a pb 2+ concentration detection sensor, device, preparation method and usage method. Background Art

[0002] The most common heavy metals in the water environment are mercury (Hg), lead (Pb), cadmium (Cd), chromium (Cr), and arsenic (As), which are highly biotoxic even at low concentrations. Among them, Pb 2+ has attracted wide attention due to its chronic toxicity. Pb in water 2+ mainly comes from two aspects: on the one hand, from industrial and mining smelting, manufacturing and use, especially the high-concentration lead-containing wastewater discharged from non-ferrous metal smelting; on the other hand, from the lead-containing gas emitted by automobiles. Pb 2+ accumulation in the human body will cause serious damage to internal organs such as the brain and kidneys. The most serious one is Pb 2+ which can seriously affect the brain development of children and has an irreversible effect.

[0003] In recent years, in order to solve the harm of heavy metal pollution to humans and the environment, researchers need to conduct a large number of detections on heavy metal ions in the environment. Currently, the commonly used heavy metal detection methods mainly include: atomic absorption spectrometry (AAS), spectrophotometry, inductively coupled plasma mass spectrometry (ICP-MS), atomic fluorescence spectrometry (AFS), infrared spectrometry, electrochemistry method, etc. The detection instruments of atomic absorption spectrometry and inductively coupled plasma mass spectrometry are expensive. Spectrophotometry cannot distinguish heavy metal ions with similar structures and radii, resulting in low detection selectivity. The electrochemistry method requires prior chemical treatment of the sample, which may cause secondary pollution to the sample.

[0004] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0005] In view of the above deficiencies of the prior art, the purpose of the present invention is to provide a pb 2+ concentration detection sensor, device, preparation method and usage method, aiming to solve the problems of low detection selectivity and high price existing in the existing pb 2+ concentration measurement technology.

[0006] A pb 2+ concentration detection sensor, which includes:

[0007] A photonic crystal fiber, a single-mode fiber connected to both ends of the photonic crystal fiber, and a sensitive film coated on the surface of the photonic crystal fiber, wherein the sensitive film has the property of binding pb 2+Function that causes refractive index change later.

[0008] The said pb 2+ Concentration detection sensor, wherein the sensitive film is a composite film of chitosan and polyacrylic acid.

[0009] The said pb 2+ Concentration detection sensor, wherein the length of the photonic crystal fiber is 0.5 cm to 20 cm.

[0010] A kind of pb 2+ Concentration detection device, which includes:

[0011] The above-mentioned pb 2+ Concentration detection sensor;

[0012] Connected to the said pb 2+ Light source connected to the concentration detection sensor;

[0013] Connected to the said pb 2+ Spectrum analyzer connected to the concentration detection sensor.

[0014] A kind of the above-mentioned pb 2+ Preparation method of the concentration detection sensor, which includes:

[0015] Fuse a section of photonic crystal fiber between two single-mode fibers to obtain a sensing element;

[0016] Deposit sensitive film material on the surface of the said sensing element to obtain pb 2+ Concentration detection sensor.

[0017] The said pb 2+ Preparation method of the concentration detection sensor, wherein depositing the sensitive film material on the surface of the said sensing element includes:

[0018] Place the sensing element in a chitosan solution, take it out and dry it to obtain a sensing element coated with chitosan;

[0019] Place the sensing element coated with chitosan in a polyacrylic acid solution, take it out and dry it to obtain a sensing element deposited with sensitive film material.

[0020] The said pb 2+ Preparation method of the concentration detection sensor, wherein after obtaining the sensing element deposited with sensitive film material, it further includes: drying the sensing element deposited with sensitive film material at 60 °C.

[0021] The said pb 2+ Preparation method of the concentration detection sensor, which further includes in the said pb 2+The surface of the concentration detection sensor is repeatedly deposited with the sensitive film material for multiple times.

[0022] A pb as described above 2+ A method for using the concentration detection device, which includes:

[0023] Turn on the light source, and place the pb 2+ concentration detection sensor in the solution containing pb to be measured 2+ and measure the pb concentration through a spectral analyzer. 2+ Concentration.

[0024] The pb 2+ method for using the concentration detection device, wherein the solution containing pb 2+ has a Pb concentration of 200 μmol / L to 1000 μmol / L. 2+ Beneficial effects: In the pb concentration detection sensor of the present invention, the sensitive film can combine with Pb in the solution

[0025] to cause a change in refractive index, and then the concentration of Pb in the water quality can be effectively detected based on the change in refractive index. The pb concentration detection sensor of the present invention 2+ has the advantages of high detection selectivity and low cost. 2 + Thereby causing a change in refractive index, and then the concentration of Pb in the water quality can be effectively detected based on the change in refractive index. The pb 2+ concentration detection sensor of the present invention 2+ has the advantages of high detection selectivity and low cost. Description of the Drawings

[0026] Figure 1 is the schematic diagram of the pb concentration detection sensor of the present invention. 2+ Concentration detection sensor of the present invention

[0027] Figure 2 is the structural relationship diagram of the sensitive film and the photonic crystal fiber in the pb concentration detection sensor of the present invention. 2+ Concentration detection sensor of the present invention

[0028] Figure 3 is the structural schematic diagram of the pb concentration detection device of the present invention. 2+ Concentration detection sensor of the present invention

[0029] Figure 4 is the linear fitting diagram of the response of the sensing element without the coated sensitive film to different refractive index liquids.

[0030] Figure 5 is the linear fitting diagram of the response of the pb concentration detection sensor of the present invention to different concentrations of Pb. 2+ Concentration detection sensor of the present invention 2+ Concentration detection sensor of the present invention Detailed Embodiments

[0031] The present invention provides a pb 2+Concentration detection sensor, device, preparation method and usage method. To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] As Figure 1 and Figure 2 shown, the present invention provides a pb 2+ concentration detection sensor 1, which includes:

[0033] Photonic crystal fiber 102, single-mode fiber 101 connected to both ends of the photonic crystal fiber 102, and sensitive film 103 coated on the surface of the photonic crystal fiber 102, wherein the sensitive film 103 has the function of causing refractive index change after binding pb 2+ ions.

[0034] The pb 2+ concentration detection sensor 1 of the present invention is composed of a photonic crystal fiber 102 (PCF) and two ordinary single-mode fibers 101 (SMFs) to form a Mach-Zehnder Interferometer (MZI). Figure 1 The arrows shown are the propagation paths of light in the pb 2+ concentration detection sensor 1; at the same time, the sensitive film 103 coated on the surface of the photonic crystal fiber 102 has the function of causing refractive index change after binding pb 2+ ions, functionalizing the photonic crystal fiber 102. The sensitive film 103 of the present invention adsorbs Pb 2+ ions in the solution, thereby causing a change in refractive index, and then the concentration of Pb 2+ in the water quality can be effectively detected based on the change in refractive index.

[0035] The pb 2+ concentration detection sensor 1 of the present invention is an optical fiber sensor, which has the advantages of being portable, light in structure, anti-electromagnetic interference, low cost, etc., and can be used for heavy metal ion detection, solving the disadvantages of low detection selectivity and high price of traditional measurement technologies.

[0036] The photonic crystal fiber 102 (Photonic Crystal Fibers, PCF) is also called micro-structured fiber (Micro-Structured Fibers, MSF). The cross-section of the photonic crystal fiber 102 has a relatively complex refractive index distribution, usually containing air holes in different arrangements. The scale of these air holes is generally in the same order of magnitude as the wavelength of light waves and runs through the entire length of the device.

[0037] The central glass core of the single-mode optical fiber 101 is very thin (the core diameter is generally 9 or 10 μm), and it is an optical fiber that can only transmit one mode. The intermodal dispersion of the single-mode optical fiber 101 is very small. Specifically, the single-mode optical fiber 101 can be one of a type 652 single-mode optical fiber, a type 653 single-mode optical fiber, and a type 655 single-mode optical fiber.

[0038] The sensitive film 103 has the function of causing a refractive index change after binding pb 2+ Specifically, the sensitive film 103 can adsorb pb 2+ ions in the solution, and after adsorbing pb 2+ ions in the solution, it can cause a change in its own refractive index. For example, the sensitive film 103 contains a group that binds to pb 2+ ions, and the group can be an amino group. Specifically, the sensitive film 103 contains chitosan, and the amino group of the chitosan chelates with Pb 2+ to thereby cause a change in the refractive index of the sensitive film 103.

[0039] In an embodiment of the present invention, the sensitive film 103 is a composite film of chitosan and polyacrylic acid. Among them, the carboxyl group on the chitosan binds to the chitosan through electrostatic interaction, increasing the network cross-linked structure of the chitosan, and the amino group in the chitosan chelates with Pb 2+ to thereby change the refractive index of the sensitive film 103. Tests show that the above-mentioned sensitive film 103 based on chitosan and polyacrylic acid materials can achieve a response to liquids with different refractive indices.

[0040] It should be noted that the sensitive film 103 is not limited to the composite film of chitosan and polyacrylic acid above, and can also be other sensitive films 103 that have the function of causing a refractive index change after binding pb 2+ For the composite film of chitosan and polyacrylic acid, when the composite film contains chitosan, it can all achieve the function of binding Pb 2+ Specifically, the chitosan content in the composite film of chitosan and polyacrylic acid can be 0.1 to 90%, such as 10%.

[0041] The length of the photonic crystal fiber 102 is determined according to the actual response effect to the pb 2+ concentration. In an embodiment of the present invention, the length of the photonic crystal fiber 102 is 0.5 cm to 20 cm. Specifically, the length of the photonic crystal fiber 102 is 2 cm.

[0042] In an embodiment of the present invention, the diameter of the photonic crystal fiber 102 is equal to the diameter of the single-mode optical fiber 101.

[0043] Optionally, the surface of the single-mode optical fiber 101 is also coated with the sensitive film 103 as described above.

[0044] As Figure 3 shown, the present invention provides a device for detecting the concentration of pb 2+ , which includes:

[0045] The pb 2+ concentration detection sensor 1 as described above;

[0046] A light source 2 connected to the pb 2+ concentration detection sensor 1;

[0047] A spectral analyzer 3 connected to the pb 2+ concentration detection sensor 1.

[0048] The light source 2 is used to generate light and transmit it to the pb 2+ concentration detection sensor 1. The spectral analyzer 3 is used to receive the light from the pb 2+ concentration detection sensor 1, analyze the spectrum of the light, and judge the pb 2+ concentration through the spectral analysis and data processing. For example, the judgment of the pb 2+ concentration through the spectrum can be that there is a pre-stored standard one-to-one correspondence between each pb 2 + concentration and the corresponding spectrum, and the pb 2+ concentration is obtained based on the detected spectrum of the light and according to the above relationship.

[0049] In an embodiment of the present invention, it further includes: a container 4 for the test solution, and the pb 2+ concentration detection sensor 11 is located inside the container 4 for the test solution. During the detection process, the test solution is introduced into the container 4 for the test solution, so that the pb 2+ concentration detection sensor 11 is immersed in the test solution to realize the detection of the pb 2+ concentration in the test solution.

[0050] In an embodiment of the present invention, the light source 2 is a broadband light source 2. The device for detecting the pb 2+ concentration of the present invention is composed of a broadband light source 2 (ASE), a spectral analyzer 3 (OSA) and the above-mentioned pb 2+ concentration detection sensor 1 (optical fiber heavy metal ion sensor), wherein the principle of the pb 2+ concentration detection sensor 1 is based on the refractive index change of the sensitive film on the optical fiber surface.

[0051] The present invention provides a preparation method of the pb 2+ concentration detection sensor 1 as described above, which includes:

[0052] S100. Fusion splice a section of photonic crystal fiber 102 between two single-mode fibers 101 to obtain a sensing element;

[0053] S200. Deposit the material of the sensitive film 103 on the surface of the sensing element to obtain the pb 2+ concentration detection sensor 1.

[0054] In the preparation method of the pb 2+ concentration detection sensor 1, deposit the material of the sensitive film 103 on the surface of the sensing element, so as to form the sensitive film 103 on the sensing element. Similarly, the sensitive film 103 has the function of causing a refractive index change after binding pb 2+ The sensitive film 103 is specifically coated on the surface of the photonic crystal fiber 102. Of course, the single-mode fiber 101 can be optionally coated with the sensitive film 103.

[0055] Through the preparation method of the pb 2+ concentration detection sensor 1 of the present invention, a sensor based on the refractive index change of the sensitive thin film on the fiber surface can be prepared, and further, the detection of the pb 2+ concentration in the solution can be realized.

[0056] In S100, the sensing element of the present invention is composed of two single-mode fibers 101 and a section of photonic crystal fiber 102 sandwiched between the two single-mode fibers 101. The preparation method of the sensing element is not limited to fusion splicing.

[0057] S100 specifically includes:

[0058] S101. Fusion splice a section of photonic crystal fiber 102 between two single-mode fibers 101 to obtain a sensing element;

[0059] S102. Remove the impurities on the surface of the sensing element.

[0060] By removing the impurities on the surface of the sensing element, the adverse effects of the impurities on the preparation of the sensitive film 103 can be avoided.

[0061] Specifically, S102 includes:

[0062] S1021. Immerse the sensing element in piranha solution (70% sulfuric acid and 30% hydrogen peroxide) for 60 minutes to remove the organic impurities on its surface;

[0063] S1022. Rinse the sensing element several times with deionized water to remove the residual piranha solution and impurities, and finally dry it in an oven.

[0064] S200 is to coat a layer of sensitive film 103 on the surface of the sensing element to obtain the pb2+ Concentration detection sensor 1.

[0065] In an embodiment of the present invention, the materials for depositing the sensitive film 103 on the surface of the sensing element include:

[0066] S201: Place the sensing element in a chitosan solution, take it out and dry it to obtain a sensing element coated with chitosan;

[0067] S202: Place the sensing element coated with chitosan in a polyacrylic acid solution, take it out and dry it to obtain a sensing element with the material of the sensitive film 103 deposited.

[0068] The present invention uses chitosan and polyacrylic acid (PAA) as the sensitive film 103. Chitosan is a biopolymer obtained by deacetylating chitin widely existing in nature. The chitosan contains abundant active functional groups, amino groups (-NH 2 ) and hydroxyl groups (-OH), and has strong chelating coordination with metal ions. The chitosan has good compatibility and biodegradability. The chitosan is also used in industries such as wastewater treatment, food, and medicine. Polyacrylic acid is a light yellow liquid, which is negatively charged in a neutral solution, and chitosan is positively charged under acidic conditions. Therefore, chitosan and polyacrylic acid can form a homogeneous polymer film through electrostatic adsorption.

[0069] In S201, by immersing the sensing element in the chitosan solution, the chitosan is adsorbed on the surface of the sensing element to form a layer of chitosan.

[0070] The soaking time of the sensing element in the chitosan solution will affect the effect of chitosan adsorbed on the surface of the sensing element. In an embodiment of the present invention, the soaking time of the sensing element in the chitosan solution is 3 - 30 min, specifically 5 min.

[0071] In S201, the drying is carried out in air for 1 minute. Through this drying, the binding force between the chitosan layer and the sensing element can be improved, the chitosan molecules can be fixed, and the excess water can be removed.

[0072] In an embodiment of the present invention, after obtaining the sensing element coated with chitosan, it is soaked in deionized water to wash away the chitosan with weak binding ability on the surface of the sensing element coated with chitosan. Optionally, the soaking time is 1 minute.

[0073] In S202, by placing the sensing element coated with chitosan in the polyacrylic acid solution, chitosan and polyacrylic acid can form a homogeneous polymer film through electrostatic adsorption.

[0074] The step S202 specifically includes placing the mixture in a polyacrylic acid solution for reaction for 3 to 30 minutes and in dry air for 1 minute. Optionally, placing the mixture in a polyacrylic acid solution for reaction for 5 minutes.

[0075] In one embodiment of the present invention, the chitosan solution is a mixed solution containing acetic acid and chitosan. Optionally, in the chitosan solution, the mass percentage of chitosan is 1%. Specifically, the preparation process of the chitosan solution is: dilute 36% acetic acid solution to 4% with deionized water; dissolve 100 mg chitosan in 10 ml 4% acetic acid solution; stir continuously for 2 hours at 100° C. with a magnetic stirrer to obtain a 1% chitosan solution.

[0076] In one embodiment of the present invention, the mass percentage of the polyacrylic acid in the polyacrylic acid solution is 10%. Optionally, the preparation process of the polyacrylic acid solution is: dilute the mass percentage of polyacrylic acid of 35% to 10% with deionized water.

[0077] In one embodiment of the present invention, after obtaining the sensor element on which the sensitive film 103 material is deposited, the method further includes: S203, drying the sensor element (the coated fiber structure) on which the sensitive film 103 material is deposited at 60°C.

[0078] In step S203, chitosan and polyacrylic acid are allowed to fully react during the drying process. Optionally, the sensing element deposited with the sensitive film 103 material is placed in an oven and dried at 60° C. for 4 hours.

[0079] In one embodiment of the present invention, the method further comprises: S204, in the pb 2+ The sensitive film 103 material is repeatedly deposited on the surface of the concentration detection sensor 1 for multiple times.

[0080] The thickness of S204 is increased, and a multi-layer structure of the sensitive film 103 is formed to improve the detection of pb 2+ sensitivity.

[0081] It can be seen that the detection of Pb 2+ The preparation method of the ion sensor uses a dip coating method to coat chitosan / polyacrylic acid on the optical fiber sensing area to functionalize it, thereby obtaining a high-sensitivity optical fiber Pb based on MZI. 2+ Ion sensor.

[0082] The present invention also provides a pb as described above 2+ A method for using a concentration detection device, comprising:

[0083] Turn on light source 2 and set the pb 2+The concentration detection sensor 1 is placed in a solution containing Pb to be measured 2+ and the Pb concentration is measured by a spectral analyzer 3 2+ .

[0084] In the method for using the Pb concentration detection device of the present invention, after turning on the light source 2, the light is transmitted to the Pb 2+ concentration detection sensor 1, and then transmitted to the spectral analyzer 3 for spectral analysis of the light, and the Pb 2+ concentration is measured 2+ .

[0085] In an embodiment of the present invention, in the solution containing Pb 2+ , the Pb 2+ concentration is 200 μmol / L to 1000 μmol / L. Tests show that when the Pb 2+ concentration is in the range of 200 μmol / L to 1000 μmol / L, the sensitivity of the sensor is 0.0031 nm / mol, that is, when the Pb 2+ concentration is in the range of 200 μmol / L to 1000 μmol / L, the sensitivity of the described Pb 2+ concentration detection device is better

[0086] The technical solution of the present invention will be described below through specific embodiments

[0087] Example 1

[0088] The acetic acid solution with a mass percentage of 36% is diluted to 4% with deionized water. 100 mg of chitosan is dissolved in 10 ml of 4% acetic acid solution. Continuously stir with a magnetic stirrer at 100 °C for 2 hours to obtain a 1 wt% chitosan solution. Dilute 35% polyacrylic acid to 10% with deionized water

[0089] A 2-cm-long photonic crystal fiber 102 is fusion spliced between two standard single-mode optical fibers 101 as a sensing element. Then the sensor is immersed in a piranha solution (70% sulfuric acid and 30% hydrogen peroxide) for 60 minutes to remove organic impurities on its surface, then rinsed several times with deionized water, and finally dried in an oven

[0090] The sensing element was placed in the chitosan solution for 5 minutes, dried in air for 1 minute, and then soaked in deionized water for 1 minute to wash off the chitosan with weak surface binding ability. Then it was placed in the polyacrylic acid solution for 5 minutes and dried in dry air for 1 minute to achieve a coating (deposition) process for the sensitive film 103 of the sensing element. The above coating process was repeated multiple times to obtain a multi-layer polymer sensitive film 103. The coated fiber structure (the sensing element coated with the sensitive film 103) was put into an oven and dried at 60 °C for 4 hours to allow the chitosan and polyacrylic acid to react fully.

[0091] Before coating, the refractive index of the sensing element was calibrated, and the spectral images of the uncoated optical fiber structure (sensing element) immersed in glycerol aqueous solutions with different refractive indices were obtained. The relationships of different wavelengths were very similar through the transmittance of the uncoated optical fiber structure (sensing element) immersed in glycerol aqueous solutions with different refractive indices. An automatic Abbe refractometer (WYA-Z) was used to measure the refractive index of the glycerol aqueous solution. When the external refractive index increased from 1.33252 to 1.35051, the central wavelength of the interference peak shifted towards the longer wavelength direction. The sensitivity was 87.507 nm / R.I. as Figure 4 shown.

[0092] The sensor coated with 15 layers of chitosan / PAA sensitive film 103 was tested in Pb 2+ solutions with different concentrations, and the corresponding spectral response diagrams were obtained. It can be seen from the diagrams that when the Pb 2+ concentration increased from 10 μmol / L to 100 μmol / L, the interference peak shifted towards the longer wavelength direction. This is because the carboxyl groups on PAA bind to chitosan through electrostatic interaction, increasing the network cross-linking structure of chitosan, and the amino groups in chitosan chelate with Pb 2+ , thus increasing the refractive index of the sensitive film 103. Figure 5 is the spectral linear fitting diagram of the fiber optic sensor after coating for different concentrations of Pb 2+ . When the Pb 2+ concentration is less than 200 μmol, the sensitivity of this sensor is 0.0769 nm / mol; when the Pb 2+ concentration is in the range of 200 μmol / L - 1000 μmol / L, the sensitivity of the sensor is 0.0031 nm / mol, and the displacement of the central wavelength gradually decreases. This is because the binding sites on the surface of chitosan are occupied by more and more Pb 2+ , resulting in the saturation of the sensor response and the decrease of the refractive index of the sensitive film 103.

[0093] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or changes can be made according to the above description, and all such improvements and changes shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A pb 2+ concentration detection sensor, It is characterized in that It consists of a photonic crystal fiber, single-mode fibers connected to both ends of the photonic crystal fiber, and a sensitive film coated on the surface of the photonic crystal fiber, wherein the sensitive film has the function of causing a refractive index change after binding pb 2+ ; the sensitive film is a composite film of chitosan and polyacrylic acid; the length of the photonic crystal fiber is 2 cm; The said Pb 2+ The concentration detection sensor is used to detect Pb 2+ The solution containing Pb with a concentration of 200 μmol / L to 1000 μmol / L 2+ ; The described pb 2+ A method for preparing a concentration detection sensor, comprising the following steps: a section of photonic crystal fiber is fusion spliced between two single-mode fibers to obtain a sensing element; the sensing element is immersed in a chitosan solution for 3 - 30 min, taken out and dried to obtain a sensing element coated with chitosan; the mass percentage of chitosan in the chitosan solution is 1%; the sensing element coated with chitosan is placed in a polyacrylic acid solution and reacted for 3 - 30 minutes, taken out and dried to obtain a sensing element deposited with sensitive film material; the mass percentage of polyacrylic acid in the polyacrylic acid solution is 10%; Dry the sensing element of the deposition-sensitive film material at 60 °C to obtain pb 2+ concentration detection sensor, and repeatedly deposit the deposition-sensitive film material on the surface of the pb 2+ concentration detection sensor for multiple times.

2. A pb 2+ concentration detection device It is characterized in that including: pb as described in claim 1 2+ Concentration detection sensor; The light source connected to the pb 2+ concentration detection sensor; The spectrometer connected to the pb 2+ concentration detection sensor.

3. A pb as described in claim 2 2+ Method for using a concentration detection device It is characterized in that including: Turn on the light source and place the pb 2+ concentration detection sensor in the solution to be measured containing pb 2+ and measure the pb 2+ concentration through a spectral analyzer; The solution containing Pb 2+ has a Pb 2+ concentration of 200 μmol / L to 1000 μmol / L.

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