CN108181479B - Automatic analyzer for molecular weight cut-off of membrane - Google Patents
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N35/00—Automatic analysis not limited to methods or materials provided for in any single one of groups G01N1/00 - G01N33/00; Handling materials therefor
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- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
An automatic analyzer for molecular weight cut-off of membrane comprises a feed liquid unit (1), a membrane separation unit (2), a filtrate sampling unit (3), a concentration analysis unit (4), a control and data acquisition and calculation unit (5) and the like. The feed liquid unit (1) can automatically select a reference substance solution as a feed liquid; the membrane separation unit (2) realizes cross flow filtration of feed liquid and obtains filtrate; the filtrate sampling unit (3) can automatically select a filtrate sample; the concentration analysis unit (4) can measure the concentration of the filtrate; the control, data acquisition and calculation unit (5) controls the automatic operation of each unit and realizes the calculation of results.
Description
Technical Field
The patent relates to a detection instrument for ultrafiltration and nanofiltration membrane molecular weight cut-off and a related operation process, which are used for quickly and accurately detecting the molecular weight cut-off of a membrane filtration and separation material.
Technical Field
The ultrafiltration membrane is a porous filtration membrane with the pore diameter of 10-100nm, the organic ultrafiltration membrane material is mainly made of high polymer materials such as polyvinylidene fluoride, polysulfone, polyacrylonitrile, cellulose acetate and the like, and the inorganic ultrafiltration membrane is mainly made of ceramic materials such as alumina, titanium oxide, zirconia, silicon oxide, composite oxide and the like. The pore diameter of the nanofiltration membrane is generally 0.1-10 nm. Ultrafiltration and nanofiltration membranes are widely used in water treatment industries, such as seawater desalination, drinking water purification, wastewater treatment, etc., and are also widely used in separation processes in chemical industry, medicine, and food. With the wide application of ultrafiltration and nanofiltration membranes and the rapid growth of related industries, all countries in the world pay attention to the new production process of the membranes and the development of new materials, and the development and production of ultrafiltration and nanofiltration membranes with high performance and low cost become hot spots of industry competition. The detection of the membrane separation performance cannot be separated no matter the development of new membrane materials or the quality control of membrane production. At present, the evaluation indexes of the ultrafiltration and nanofiltration membrane filtration performance mainly include pure water flux, Molecular weight cut-off (MWCO), pore size distribution, backwashing performance, filling area, Zeta potential and the like. The molecular weight cut-off is the most important index which can directly reflect the cut-off effect of the ultrafiltration and nanofiltration membranes, and the cut-off performance of the ultrafiltration membrane can be usually detected by the pore size distribution.
The method for testing the pore size distribution of the ultrafiltration membrane is mainly a liquid-liquid displacement method, and other pore measurement methods such as a bubble point method (also called a capillary flow method, a bubble pressure method and a gas-liquid method), a BET method, a mercury pressure method and an electron microscope method are not applicable or have great limitation. The liquid-liquid displacement method is similar to the bubble point method in basic principle, and is characterized in that the ultrafiltration membrane is fully wetted by a wetting agent, and then the wetting agent is ejected out by compressed gas or another liquid which is not mutually soluble with the wetting agent and the pore channel of the membrane is opened. Wherein the larger the pore size, the smaller the pore opening pressure is required, i.e. the pore size is inversely proportional to the pore opening pressure, and the pore size can be calculated from the pore opening pressure and the interfacial tension of the wetting agent. Since the interfacial tension between two liquids is much smaller than the gas-liquid interfacial tension, the bubble point method is generally not suitable for measuring pore sizes below 100nm, i.e., the bubble point method is generally not suitable for ultrafiltration membranes. Although it is computationally possible to measure pore diameters below 10nm by increasing the test pressure by only a factor of 10, it is not practical because: the high-pressure test not only causes the problems of difficult sealing, high air resistance in the pore channel, large gas consumption, large measurement error and the like, but also puts high requirements on the strength of the sample, for example, the test pressure required for measuring the pore diameter of 10nm needs at least 5MPa, and the high pressure is enough to cause the deformation and even damage of the sample; most of the ultrafiltration membranes on the market are made of flexible polymer materials, and the test result is easy to be distorted due to the fact that a sample is deformed under pressure during high-pressure test. For the liquid-liquid displacement method, due to poor reproducibility of manual operation, automatic operation must be performed through a professional instrument, and the first domestic full-automatic ultrafiltration membrane pore size analyzer was developed by the Nanjing Hooji functional materials company. Although the liquid-liquid displacement method can measure smaller pore diameter, the method is still greatly limited in measuring the pore diameter of the nanofiltration membrane.
The molecular weight cut-off method can detect the retention performance of various membranes (including nanofiltration membranes), and the test results and the bubble point method and the liquid-liquid displacement method can be mutually estimated according to practical experience [ Calvo J I, Peaadr R I, Pr a danos P, et al, liquid-liquid displacement measurement to estimate the molecular weight cut-off of the interaction membranes, 2011, 268268 (13): 174-181.]. The conventional detection method of molecular weight cut-off is: the rejection rate of the membrane to a series of standard substances with known molecular weights (namely, the percentage of the solute retained by the membrane to the total amount of the solute in the solution) is firstly measured, then a rejection rate-molecular weight relation curve is drawn, and when the rejection rate is 90%, the molecular weight of the corresponding standard substance is the molecular weight cut-off of the membrane. The accuracy of the retention molecular weight test result depends greatly on the selection of the reference substance, the selection of the detection method and the accuracy of the retention value.
The reference substance for detecting the molecular weight cut-off has the following conditions: the purity is high, and the molecular structure is definite; the molecular weight distribution is narrow, and the molecular weight coverage range is wide; the physical and chemical properties are stable and are not easy to be absorbed by the film material; the molecular shape is preferably spherical (the linear molecular retention is far lower than that of spherical molecules with the same molecular weight); low cost and easy availability. At present, the standards specified by the molecular weight cut-off detection standards at home and abroad are mainly polyethylene glycol, protein and glucan [ HY/T050-; ASTM E1343-90(2001), Standard test method for molecular weight cut off evaluation of flat sheet ultrafiltration membranes; GB/T32360-. According to the industry standard HY/T050-1999, the standards for measuring the retention performance of ultrafiltration membranes are polyethylene glycol (molecular weight 6000, 10000, 20000Da), cytochrome C (molecular weight 13000Da), ovalbumin (molecular weight 45000Da), bovine serum albumin (molecular weight 67000 Da). The detectable molecular weight cut-off range of these standards is limited to 6000-67000Da, and there is no comparable difference between the molecular weight cut-offs measured for the different standards [ Wufuke, Wangxin. Ultrafiltration Membrane cut-off Performance determination method. Tianjin chemical engineering, 2000 (2): 24-26; dawn, zheng civet. comparison of different standards characterizing ultrafiltration membrane rejection performance water treatment technology, 1993 (6): 319- & gt 323; 371540, loyalty, Dianthus superbus, Liangheng, etc. the comparative study of ultrafiltration membrane cutting molecular weight test using dextran and protein, membrane science and technology, 2015, 35 (3): 44-50; liuting, a major problem in the development of ultrafiltration, water treatment technology, 1988, 14 (4): 193-197 ], the application of which is greatly limited. In addition, proteins are also easily adsorbed by ultrafiltration membranes, which is expensive to test. In contrast, dextran is a more desirable standard substance, has a wide molecular weight distribution range (10000-: 103-108; research on a standardized method for measuring rejection rate of hollow fiber ultrafiltration membranes, water treatment technology, 1994, 20 (4): 192-196.].
There are two ways to detect the molecular weight cut-off on dextran basis. The first is gel chromatography, that is, a single ultrafiltration is carried out using a mixed solution of dextrans of different molecular weights, and the change in the concentration of dextran of each molecular weight in the mixed solution before and after ultrafiltration is measured by gel chromatography [ dunshenhua, tianyan, yanna, etc.. gel chromatography measures cut molecular weight distribution and characterizes ultrafiltration membrane. water treatment technology, 1990, 16 (4): 323-327; bottino A, Capanelli G, Imperato A, et al.Ultrafiltration of hydrosoluble polymers: effect of operating conditions on the performance of the Membrane. journal of Membrane Science, 1984, 21 (3): 247-267; dongbua, Zhengyingying gel chromatography characterizes the retention-molecular weight curves of several representative ultrafiltration membranes in China, water treatment technology, 1991, 17 (4): 268-271.]. Although gel chromatography is convenient, analytical instruments are expensive and difficult to popularize. Another method is more easily accepted by the market, namely, solutions of the glucan with different molecular weights are used for sequentially carrying out ultrafiltration experiments, and the concentration change of each glucan solution before and after ultrafiltration is respectively measured and calculated to obtain the retention rate. The method is simple, and comprises a turbidity method, a spectrophotometry method, a COD method and the like. Daihipin et al [ Daihipin, Zhanghuixin, Liangfu sea et al. simple method for determining cut molecular weight of ultrafiltration membrane with dextran. Membrane science and technology, 2005, 25 (4): 63-65 ] the proposed nephelometry is based on the principle of "water extraction and alcohol precipitation", where ethanol is added to precipitate the polysaccharide, resulting in an increase in turbidity. The solution turbidity was linear with dextran concentration when the dextran solution was mixed with equal volumes of ethanol and kept at room temperature for 30 min. A spectrophotometric method (namely a sulfuric acid-phenol method) is a classical polysaccharide quantitative detection method, furfural derivatives generated by hydrolysis and dehydration of glucan through concentrated sulfuric acid and phenol undergo a color reaction, and when the wavelength is 490nm, the absorbance of a solution and the concentration of glucan are in a linear relationship. The method is simple to operate, accurate in result, rapid in measurement and free of precision instruments, and therefore the method is the most universal method all over the world. The COD method determines the concentration of glucan by measuring the COD value of the glucan solution and comparing the value with a standard curve, and compared with the spectrophotometry, the reaction condition is more severe.
The increasing popularization of membrane materials and membrane technologies greatly motivate the research and development and production of membrane materials, and also motivate the development of membrane detection technologies and related instruments, and particularly the development of efficient, reliable and automatic membrane molecular weight cut-off testing processes and equipment is imperative. Zhang Hui Ping, Jiangxin, Lijunshan hollow fiber ultrafiltration membrane rejection rate detection device based on PLC design and application [ J ] instrument technology and sensor, 2016 (1): 37-40 ] a hollow fiber ultrafiltration membrane filtering device based on PLC control is designed, but the device only realizes membrane filtration operation, does not relate to automatic sampling of filtrate and automatic detection of concentration, still cannot solve the problems of time consumption and labor consumption of retention rate analysis, and has no report of a full-automatic molecular weight retention detection process and related equipment so far.
Disclosure of Invention
The purpose of this patent lies in developing the molecular weight cut-off automatic analyzer of membrane and relevant operation technology in order to analyze the molecular weight cut-off of various membrane materials, realizes including whole analytic process such as feed liquid selection, membrane separation, filtrating sampling, concentration analysis, data acquisition and molecular weight cut-off calculation, to given various membrane materials, can realize the test work of molecular weight cut-off automatically, swiftly.
The technical scheme of this patent: the automatic analyzer for molecular weight cut-off of membrane comprises 5 parts which are respectively: the device comprises a feed liquid unit, a membrane separation unit, a filtrate sampling unit, a concentration analysis unit and a control, data acquisition and calculation unit.
The membrane molecular weight cut-off automatic analyzer described in this patent is constructed as shown in FIG. 1. Wherein, the feed liquid unit (1) mainly comprises a sampler (101), a pure water bottle (102), a feed liquid bottle (103), a feed pipe (104) and a discharge pipe (105). The membrane separation unit (2) mainly comprises a constant flow pump (201), a pressure sensor (202) before the membrane, a membrane separator (203), a pressure sensor (204) after the membrane, an electric regulating valve (205) and a flowmeter (206). The filtrate sampling unit (3) mainly comprises a sampler (301), an electric rotary table (302), a sample cup (303), a sampling pipe (304), a pure water bottle (305) and a waste liquid bottle (306). The concentration analysis unit (4) mainly comprises a pure water bottle (401), an injection pump (402), a multi-way switching valve (403), an electric switch valve (404), a darkroom (405), a reaction pool (406), a photometric analysis light source (407), a light intensity sensor (408), a turbidity analysis light source (409), a turbidity light intensity sensor (410), a chemical reagent bottle (411), a waste liquid bottle (412) and a liquid storage coil pipe (413). The control, data acquisition and calculation unit (5) mainly comprises a computer (501) and a communication accessory (502). The communication accessory mainly comprises a data acquisition card, a driver, a controller and the like.
The material line connections between the different units are shown in figure 1. The feeding pipeline of the membrane separator (203) is provided with a constant flow pump (201) and a pressure sensor (202) before the membrane, and the reflux pipeline is provided with a pressure sensor (204) after the membrane, an electric regulating valve (205) and a flowmeter (206). The feed pipe (104) at the end of the feed pipeline and the discharge pipe (105) at the end of the reflux outlet pipeline are both fixed on a slide block of the sampler (101), and the slide block can move up and down, left and right, thereby being capable of taking liquid from each liquid feeding bottle (103) for testing. The filtrate of the membrane separator (203) is discharged into a sample cup (303) on an electric turntable (302), the electric turntable (302) rotates the sample cup (303) filled with the filtrate to be analyzed to the lower part of a sampling pipe (304), and the sampling pipe (304) is fixed on a slide block of the sampler (301), and the slide block can move up and down. Thus, the sampler 301 may extend the sampling tube 304 into the sample cup 303, drawing the sample through the syringe pump 402 and the multi-way switching valve 403.
The pump opening pipeline of the injection pump (402) is connected with a tee joint, one end of the tee joint extends into the pure water bottle (401) through an electric switch valve (404), and the other end of the tee joint is connected with a central channel of the multi-way switching valve (403) through a liquid storage coil pipe (413). The central channel of the multi-way switching valve (403) can be communicated with any branch channel in pairs, but the branch channels cannot be communicated with each other, and the number of the branch channels is not less than 5. An air vent is reserved in a channel of the multi-way switching valve (403), and the rest of the air vent is respectively connected with the reaction tank (406), the chemical reagent bottle (411), the waste liquid bottle (412) and the sampling pipe (304). A photometric analysis light source (407) and a turbidity analysis light source (409) are arranged in the darkroom (405), after light passes through the reaction liquid, the intensities of transmitted light and scattered light are respectively detected by a light intensity sensor (408) and a turbidity light intensity sensor (410), then collected light intensity signals are converted into concentration values through a standard curve arranged in the computer (501), the rejection rate of the membrane on each feed liquid is calculated according to the original concentration of each feed liquid and the concentration of filtrate, and the rejection molecular weight of the filter membrane can be calculated by drawing a relation curve between the rejection rate and the molecular weight of a standard filter medium. The electronic device and the electric element are connected with a computer (501) through a communication accessory (502).
The liquid pipeline used by the automatic analyzer of the membrane molecular weight cut-off should be made of plastic as much as possible, wherein the region where concentrated sulfuric acid reaches must be made of corrosion-resistant material such as polytetrafluoroethylene. Therefore, when the reaction involves concentrated sulfuric acid, the pipelines connected with all the channels of the multi-way switching valve (403) are made of polytetrafluoroethylene. The internal diameter of the liquid storage coil (413) is 0.5-4mm, but in order to reduce the influence of the diffusion of the solution while moving in the tube, the internal diameter of the line is preferably 1-2 mm. The volume of the liquid storage coil (413) is determined by the inner diameter and the total length of the pipeline, but is not lower than the volume of the injection pump (402). Since a plurality of liquids can flow through the liquid storage coil (413), in order to improve the cleaning effect of the liquid storage coil (413), the inner surface of the pipe wall should be smooth, and preferably has certain hydrophobicity. In order to reduce the liquid residue of the liquid pipeline system of the instrument and improve the cleaning effect, the absolute roughness of the inner wall of the pipeline is less than 10 mu m.
The main function of each unit of the membrane molecular weight cut-off automatic analyzer. Feed liquid unit (1): automatically selecting feed liquid for the membrane separation unit; membrane separation unit (2): realizing cross flow filtration of the feed liquid and obtaining filtrate; filtrate sampling unit (3): automatically selecting a filtrate sample; concentration analysis unit (4): measuring the concentration of the filtrate; a control, data acquisition and calculation unit (5): and according to the set program and the acquired signals, controlling the automatic operation of each unit and realizing the calculation of results.
The patent has the obvious advantages that:
1. the automation of the operation processes of feed liquid switching, membrane separation, filtrate sampling, sample introduction, pipeline cleaning, chemical reaction, signal acquisition, result calculation and the like not only saves manpower and avoids human errors, but also improves the test efficiency.
2. Through the ingenious cooperation of syringe pump, stock solution coil and multi-way diverter valve, the feed liquor volume of quantitative control reaction has improved the reproducibility and the accuracy of test result accurately. When the chemical reagent and the filtrate are extracted, the pump body only takes pure water as a carrier fluid, the interior of the pump body is not polluted and corroded, and the gas column in the liquid storage coil can also isolate the pure water from the chemical reagent or the filtrate, so that the cross contamination is avoided.
3. The instrument integrates spectrophotometry and turbidity method concentration analysis, and improves the test applicability.
4. This patent instrument degree of automation is high, easy operation. The unitized design can realize the overall operation of each operation step, and save the operation time.
Drawings
Fig. 1 is a schematic diagram of the structure of the apparatus described in this patent. Wherein: 101-a sampler; 102-a plain water bottle; 103-liquid medicine bottle; 104-a feed pipe; 105-a discharge pipe; 201-a constant flow pump; 202-pressure sensor before membrane; 203-a membrane separator; 204-a behind-the-membrane pressure sensor; 205-electric regulating valve; 206-a flow meter; 301-a sampler; 302-an electric turntable; 303-sample cup; 304-a sample tube; 305-a plain water bottle; 306-waste solution bottle; 401-pure water bottle; 402-a syringe pump; 403-multi-way switching valve; 404-an electric switch valve; 405-darkroom; 406-a reaction cell; 407-photometric analysis light source; 408-a light intensity sensor; 409-turbidity analysis light source; 410-turbidity light intensity sensor; 411-chemical reagent bottle; 412-waste bottle; 413-liquid storage coil pipe; 501-computer; 502-communication accessory.
Detailed Description
Dextran standard substance solutions with different molecular weights are placed in a solution bottle (103) of a solution unit (1) as a solution, pure water is injected into pure water bottles (102), (401) and (305), and concentrated sulfuric acid, a 5% phenol solution and absolute ethyl alcohol are respectively placed in a chemical reagent bottle (411) of a concentration analysis unit (4). The anhydrous ethanol can be omitted if turbidity is not used, and the concentrated sulfuric acid and phenol solution can be omitted if spectrophotometry is not used. The amount of water in the pure water bottle (102) is not less than 500 ml. The feed liquid is pumped into a membrane separator (203) in a cross-flow filtration mode, the flow rate and transmembrane pressure difference are controlled by a constant flow pump (201) and an electric regulating valve (205), the reflux liquid returns to an original feed liquid bottle (103), and the filtrate is collected by a sample cup (303). After the collection is finished, the constant flow pump (201) pumps all the feed liquid in the pipeline back to the feed liquid bottle (103). Therefore, the constant flow pump (201) needs to have a bidirectional infusion function. As shown in figure 1, the end of the feed pipe (104) is lower than the discharge pipe (105), and the feed pipe (104) is extended below the liquid level and the discharge pipe (105) is kept above the liquid level during operation, so that the frequent lifting operation of the sampler (101) can be avoided during the output and the recovery of the feed liquid, and the short circuit phenomenon caused by the approach of the end of the feed pipe (104) and the discharge pipe (105) can be avoided. After the filtering operation is finished, different feed liquids can be tested and filtrate can be collected through the samplers (101), (301) and the electric rotary table (302). In order to prevent the pollution between different feed liquids, the system is cleaned in the following modes when the feed liquids are switched: water is pumped from the pure water bottle (102) by using a constant flow pump (201) and the water is used as feed liquid to operate, and the washing water flowing out of the filtrate side enters a waste liquid bottle (306), and the initial water amount in the pure water bottle (102) is not less than 500 ml. In order to improve the cleaning effect, 2-3 pure water bottles (102) can be arranged to realize multi-time cleaning. Or the number of the pure water bottles (102) is equal to that of the liquid feeding bottles (103), and a new pure water bottle is automatically selected during each cleaning.
Opening an electric switch valve (404), adjusting a multi-way switching valve (403) to close a central channel, and starting a syringe pump (402) to pump water from a pure water bottle (401); closing the electric switch valve (404), adjusting the multi-way switching valve (403) to enable the central channel to be communicated with the waste liquid bottle (412), injecting water in the injection pump (402) into the liquid storage coil pipe (413), and discharging redundant water into the waste liquid bottle (412); controlling the electric rotary table (302) to rotate a sample cup (303) filled with the filtrate to be analyzed to a position below the sampler (301), and extending a sampling pipe (304) into the filtrate by the sampler (301); adjusting a multi-way switching valve (403) to enable the central channel to be communicated with air, and sucking a small amount of air by using a syringe pump (402) to enable a section of air column to be generated in a liquid storage coil (413); adjusting a multi-way switching valve (403) to enable an injection pump (402) to be communicated with a sampling pipe (304) and pump filtrate into a liquid storage coil pipe (413), adjusting the multi-way switching valve (403) to enable a central channel to be communicated with a reaction tank (406), pumping the filtrate into the reaction tank (406) by the injection pump (402), similarly, pumping chemical reagents corresponding to the detection method into the reaction tank (406) by the injection pump (402), analyzing the concentration of the filtrate by a spectrophotometry method or a turbidity method after reaction, namely measuring a standard curve between the concentration and absorbance and turbidity in advance, and converting collected absorbance and turbidity signals into concentration values by a computer. The wavelength of the photometric analysis light source (407) is 480-. The retention rate of the membrane can be calculated according to the original concentration of each feed liquid and the concentration of the filtrate, and then the relationship curve of the retention rate and the molecular weight of the standard filter medium is drawn, so that the molecular weight retention of the filter membrane can be calculated.
Claims (12)
1. An automatic analyzer for molecular weight cut-off of membrane comprises a feed liquid unit (1), a membrane separation unit (2), a filtrate sampling unit (3), a concentration analysis unit (4) and a control, data acquisition and calculation unit (5); the feed liquid unit (1) automatically selects a reference substance solution as a feed liquid, the membrane separation unit (2) realizes cross-flow filtration of the feed liquid and obtains filtrate, the filtrate sampling unit (3) automatically selects a filtrate sample, the concentration analysis unit (4) determines the concentration of the filtrate, and the control, data acquisition and calculation unit (5) controls the automatic operation of each unit and realizes the calculation of results; the feed liquid unit (1) comprises a sampler (101), a pure water bottle (102), a feed liquid bottle (103), a feed pipe (104) and a discharge pipe (105); the membrane separation unit (2) comprises a constant flow pump (201), a pressure sensor (202) in front of the membrane, a membrane separator (203), a pressure sensor (204) behind the membrane, an electric regulating valve (205) and a flowmeter (206); the filtrate sampling unit (3) comprises a sampler (301), an electric rotary table (302), a sample cup (303), a sampling pipe (304), a pure water bottle (305) and a waste liquid bottle (306); the concentration analysis unit (4) comprises a pure water bottle (401), an injection pump (402), a multi-way switching valve (403), an electric switch valve (404), a darkroom (405), a reaction pool (406), a photometric analysis light source (407), a light intensity sensor (408), a turbidity analysis light source (409), a turbidity light intensity sensor (410), a chemical reagent bottle (411), a waste liquid bottle (412) and a liquid storage coil pipe (413); the control and data acquisition and calculation unit (5) comprises a computer (501) and a communication accessory (502), and the working process of the automatic analyzer for the molecular weight cut-off of the membrane is as follows: the method comprises the following steps of selecting feed liquid in a feed liquid bottle (103) through a sampler (101), driving the feed liquid into a membrane separator (203) in a cross flow filtering mode, controlling flow and transmembrane pressure difference by using a constant flow pump (201) and an electric regulating valve (205), returning backflow liquid to an original feed liquid bottle (103), collecting filtrate by using a sample cup (303), after the filtrate is collected, sucking the feed liquid in a pipeline into the backflow liquid bottle (103) by using the constant flow pump (201), and then analyzing the concentration of the filtrate: firstly, opening an electric switch valve (404), adjusting a multi-way switching valve (403) to close a central channel, and starting a syringe pump (402) to pump water from a pure water bottle (401); closing the electric switch valve (404), adjusting the multi-way switching valve (403) to enable the central channel to be communicated with the waste liquid bottle (412), injecting water in the injection pump (402) into the liquid storage coil pipe (413), and discharging redundant water into the waste liquid bottle (412); controlling the electric rotary table (302) to rotate a sample cup (303) filled with the filtrate to be analyzed to a position below the sampler (301), and extending a sampling pipe (304) into the filtrate by the sampler (301); adjusting a multi-way switching valve (403) to enable the central channel to be communicated with air, and sucking a small amount of air by using a syringe pump (402) to enable a section of air column to be generated in a liquid storage coil (413); adjusting a multi-way switching valve (403) to enable a syringe pump (402) to be communicated with a sampling pipe (304) and pump filtrate into a liquid storage coil pipe (413), adjusting the multi-way switching valve (403) to enable a central channel to be communicated with a reaction tank (406), driving the filtrate into the reaction tank (406) by the syringe pump (402), driving a chemical reagent into the reaction tank (406) by the syringe pump (402), and analyzing the concentration of the filtrate by a spectrophotometry or a turbidity method after reaction.
2. The automatic membrane molecular weight cut-off analyzer according to claim 1, characterized in that: in order to prevent pollution between different feed liquids, before the feed liquid is selected, a constant flow pump (201) is used for pumping water from a pure water bottle (102) and taking water as the feed liquid to operate, cleaning water flowing out of a filtrate side enters a waste liquid bottle (306), and the initial water amount in the pure water bottle (102) is not lower than 500 ml; 2-3 pure water bottles (102) are arranged to improve the cleaning effect so as to realize multi-time cleaning; or the number of the pure water bottles (102) is equal to that of the liquid feeding bottles (103), and a new pure water bottle is automatically selected during each cleaning.
3. The automatic membrane molecular weight cut-off analyzer according to claim 1, characterized in that: the constant flow pump (201) has a bidirectional infusion function.
4. The automatic membrane molecular weight cut-off analyzer according to claim 1, characterized in that: when the sampler (101) selects feed liquid or pure water, the inlet pipe (104) needs to extend into the liquid level, and the outlet pipe (105) needs to be above the liquid level.
5. The automatic membrane molecular weight cut-off analyzer according to claim 1, characterized in that: the liquid pipeline is made of plastic materials, and the absolute roughness of the inner wall is less than 10 mu m.
6. The automatic membrane molecular weight cut-off analyzer according to claim 1, characterized in that: a photometric analysis light source (407) and a turbidity analysis light source (409) are arranged in the darkroom (405), and after light passes through the reaction liquid, transmitted light and scattered light are detected by a light intensity sensor (408) and a turbidity light intensity sensor (410).
7. The automatic membrane molecular weight cut-off analyzer according to claim 1, characterized in that: the inner diameter of the pipeline of the liquid storage coil pipe (413) is 0.5-4 mm.
8. The membrane molecular weight cut-off autoanalyzer according to claim 1, wherein: the central channel of the multi-way switching valve (403) can be communicated with any branch channel in pairs, but the branch channels cannot be communicated with each other, and the number of the branch channels is not less than 5.
9. The automatic membrane molecular weight cut-off analyzer according to claim 1, characterized in that: the feed solution is dextran solution.
10. The automatic membrane molecular weight cut-off analyzer according to claim 9, wherein: the wavelength of the photometric analysis light source (407) is 480-.
11. The automatic membrane molecular weight cut-off analyzer according to claim 10, wherein: when the detection method uses a spectrophotometry, the corresponding chemical reagents are concentrated sulfuric acid and 5% phenol solution respectively; when the detection method uses a turbidity method, the corresponding chemical reagent is absolute ethyl alcohol.
12. The automatic membrane molecular weight cut-off analyzer according to claim 11, wherein: all pipelines connected with all channels of the multi-way switching valve (403) are made of polytetrafluoroethylene materials.
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