Total phosphorus flow injection merging band analysis system based on ultraviolet light catalytic digestion

Abstract

The application discloses a total phosphorus flow injection combined band analysis system based on ultraviolet light catalytic digestion, belongs to the technical field of chemical analysis and automatic quantification, and can be used for quantitative analysis of total phosphorus and phosphate in various water quality samples. The application uses the basic principle of the flow injection analysis technology, uses double-piston pumps to alternately guide liquid to replace traditional peristaltic pumps to realize carrier liquid continuous flow, uses two three-way electromagnetic valves as a group and a pipeline connected between the two interfaces as a quantitative ring to replace conventional switching valves to quantitatively control the volume of reagents or samples. Under the above scheme, a flow injection combined band analysis system is designed and built for a phosphate / ammonium molybdate / potassium antimonyl tartrate / ascorbic acid reaction system, and the ultraviolet light catalytic technology is introduced into the digestion process of total phosphorus, so that automatic, rapid and accurate determination of total phosphorus and phosphate is realized.

Description

Technical Field

[0001] This invention relates to a flow injection combined with band analysis system designed for online digestion and automated determination of total phosphorus and phosphate, belonging to the technical field of chemical analysis and automated quantification. It is suitable for the rapid and accurate determination of total phosphorus and phosphate in various water samples. Technical Background

[0002] Phosphorus is an essential nutrient for the growth of various plants in aquatic bodies. In nature, it exists not only as free phosphate ions and condensed phosphates (pyrophosphate, metaphosphate, and polyphosphate), but also, more often, as organic phosphorus bound to various organic matter. However, excessive discharge of phosphorus-containing substances into water bodies can lead to eutrophication, resulting in environmental problems such as the death of plankton and algae, and water quality deterioration. Therefore, the ability to rapidly, accurately, and in real-time measure the phosphate and total phosphorus content in water bodies is particularly important.

[0003] Traditional methods for determining total phosphorus all refer to the detection principle and manual experimental operation in GB / T 11893-1989, "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method." This method states that when the sample is digested with potassium persulfate at 120°C for 30 minutes under neutral conditions, all forms of phosphorus contained within it will be oxidized to orthophosphate. In an acidic medium, the orthophosphate reacts with ammonium molybdate, and in the presence of potassium antimony tartrate, it forms phosphomolybdic heteropolyacid, which is then immediately reduced by ascorbic acid to form a blue complex. The absorbance is measured at 700 nm after 15 minutes of this reaction. This method involves high heating temperatures, long processing times, and cumbersome operation, making it difficult to accurately determine large quantities of phosphorus-containing samples in practical work.

[0004] Flow injection analysis (FIA), as a technique connecting manual chemical reaction principles with instrumental analysis, can easily achieve automated quantitative analysis and online monitoring. It boasts advantages such as ease of operation, high automation, fast analysis speed, and good reproducibility. Therefore, applying FIA to total phosphorus / phosphate detection will greatly improve work efficiency and reduce human error. Furthermore, ultraviolet photocatalytic oxidation is a method that combines ultraviolet light irradiation with oxidant oxidation. Through ultraviolet light irradiation, the oxidant undergoes photodecomposition, generating more potent oxidizing free radicals such as hydroxyl groups. This reduces the temperature and time required for heating digestion, exhibiting advantages such as speed, efficiency, ability to be performed at room temperature and pressure, and no secondary pollution.

[0005] The People's Republic of China National Environmental Protection Standard HJ 671-2013, "Determination of Total Phosphorus in Water - Flow Injection-Ammonium Molybdate Spectrophotometric Method," issued by the Ministry of Environmental Protection, proposes a flow injection analysis system for the determination of total phosphorus. This system mainly consists of a peristaltic pump, a rotary switching valve, a heating tank, an ultraviolet digestion device, a defoamer, a reaction coil, and a detector. This is also the technical solution for conventional flow injection analysis. In the implementation of this system, the phosphorus-containing sample is mixed with sulfuric acid solution and potassium persulfate digestion solution through continuous flow. It then enters the digestion path for heating and ultraviolet digestion. The digested sample is then injected into the analytical path through the rotary switching valve, where it sequentially merges with the continuously flowing colorimetric reagent and reducing agent, undergoing a chemical reaction to generate a response signal. Because the peristaltic pump used in this system can only maintain a constant flow rate for a very limited time and wears down with use, it needs to be replaced frequently, making it unsuitable for automated operation in unattended environments. Secondly, the continuous flow of digestion solution, chromogenic agent, and reducing agent also results in significant reagent waste during the analysis process. Furthermore, air bubbles are frequently introduced into the flow injection analysis path and adsorb onto the inner wall of the detector's flow cell, interfering with the measurement; therefore, manual removal of air bubbles is usually required periodically. These problems significantly limit the automation level and application scenarios of flow injection analysis. To address these issues and broaden the practicality of flow injection analysis technology, this invention proposes a novel combined flow injection analysis system for total phosphorus / phosphate based on ultraviolet photocatalytic digestion. Summary of the Invention

[0006] This invention utilizes the basic principles of flow injection analysis to design a combined flow injection analysis system for the phosphate / ammonium molybdate / potassium antimony tartrate / ascorbic acid reaction system. It also introduces ultraviolet photocatalysis into the digestion process of total phosphorus, thereby achieving automated, rapid, and accurate determination of total phosphorus and phosphate. The system features include: replacing the peristaltic pump commonly used in flow injection analysis with a dual-plunger pump assembly, achieving continuous carrier flow through alternating liquid delivery; using two three-way solenoid valves as a group and a pipeline connecting two of their interfaces as a quantitative loop for quantifying reagent or sample volume; injecting the sample, digestion solution, and chromogenic reagent into the system in the form of "solution plugs," and merging them through carrier flow to carry out the chemical reaction; adjusting the merging method by changing the on / off sequence of the two two-way solenoid valves, thus modifying the detection range of the analyte; and designing an automatic de-bubbling function for long-term unattended operation of this type of instrument.

[0007] The technical solution of the present invention consists of a flow injection combined with an analytical flow path, an analytical device based on the flow path, and an operating process.

[0008] The analytical system of the present invention comprises two miniature plunger pumps, eleven three-way solenoid valves, two normally closed solenoid valves, four reagent or sample quantitative loops, three storage coils, one digestion coil, one reaction coil, a miniature spectrophotometer equipped with a flow cuvette, an ultraviolet photocatalytic digester, a thermostat, a computer, and developed operating software to control the above components.

[0009] The operating flow of the analysis system involved in this invention is as follows: It should be noted that when the three-way solenoid valves (10-16, 18-20, 22) are de-energized, ports a and b are connected; when energized, ports a and c are connected. When the two-way solenoid valves (17, 21) are de-energized, they are both closed; when energized, they are connected.

[0010] Select the system baseline program on the operating software, and the analysis system will perform the following steps. First, all solenoid valve groups are de-energized, and the suction action of the first plunger pump (23) causes the carrier fluid (1) to enter the pump chamber; Second, the solenoid valve groups (10, 11, 17, 21) are energized, and the first plunger pump (23) pushes the carrier fluid in the chamber into the flow path system. At the same time, the second plunger pump (24) draws the carrier fluid (1) into the pump chamber; Third, all solenoid valve groups are de-energized, and the second plunger pump (24) pushes the carrier fluid in the chamber into the flow path system. At the same time, the first plunger pump (23) draws the carrier fluid (1) into the pump chamber; Repeat the above process to make the carrier fluid in the flow path flow continuously. When it passes the detector, the software in the computer (37) records a blank system baseline with zero absorbance; When the program ends, both plunger pumps will empty the carrier fluid in the chamber in turn.

[0011] Select the total phosphorus determination program on the operating software. The analysis system will perform the following steps. First, the solenoid valve group (13) is energized. The first plunger pump (23) draws the carrier liquid (1) into the pump chamber. The second plunger pump (24) draws in the actual water sample (2) or standard solution (3, only when the solenoid valve group (13, 14) is energized) and fills the sample quantitative loop (28). Excess sample enters the first storage coil (25). Then, the solenoid valve group (10, 11, 12) is energized. The first plunger pump (23) pushes the carrier liquid in the chamber and discharges the excess sample solution in the first storage coil (25) from the waste liquid port (5). This completes the loading step of the sample quantitative loop (28). In the second step, the solenoid valve assembly (16) is energized, and the first plunger pump (23) draws the carrier liquid (1) into the pump chamber. The second plunger pump (24) draws in the digestion liquid (4) and fills the digestion liquid metering loop (29). Excess digestion liquid enters the second storage coil (26). Subsequently, the solenoid valve assembly (10, 11, 15) is energized, and the first plunger pump (23) pushes the carrier liquid in the chamber, discharging the excess digestion liquid in the second storage coil (26) from the waste liquid outlet (5). This completes the loading step of the digestion liquid metering loop (29). In the third step, the solenoid valve assembly (17) is energized, and the second plunger pump (24) pushes the carrier liquid in the chamber, simultaneously pushing the sample solution in the sample metering loop (28) and the digestion liquid in the digestion liquid metering loop (29) into the digestion coil (32), causing them to merge and form a mixed sample band. In the fourth step, during the digestion reaction of the sample solution and digestion solution in the digestion coil (32) of the UV photocatalytic digester (33), the first plunger pump (23) continues to draw the carrier liquid (1) into the pump chamber. When the solenoid valve group (20) is energized, the second plunger pump (24) draws in the second colorimetric reagent (7) and fills the second reagent metering ring (31). When the solenoid valve group (19) is energized, the second plunger pump (24) draws in the first colorimetric reagent (6) and fills the first reagent metering ring (30). The excess colorimetric reagents 2 and 1 enter the third storage coil (27) in sequence. Subsequently, the first plunger pump (23) pushes the carrier liquid in the chamber to discharge the excess colorimetric reagent in the third storage coil (27) from the waste liquid port (5). This completes the loading step of the reagent metering rings (30, 31). In the fifth step, after the sample solution digestion is completed, the solenoid valve group (17, 21) is energized, and the second plunger pump (24) pushes the carrier liquid in the chamber to simultaneously push the digested sample solution in the digestion coil (32) and the colorimetric reagent in the reagent metering loop (30, 31) into the reaction coil (34) placed in the thermostat (35) to merge and carry out a chemical colorimetric reaction. At the same time, the first plunger pump (23) draws the carrier liquid (1) into the pump chamber. Then, the first plunger pump (23) pushes the carrier liquid in the chamber to continuously push the colorimetric sample strip into the detector (36) to the waste liquid port (9), and the response signal is recorded by the operating software on the computer (37).

[0012] When the phosphate determination program is selected in the operating software, the analytical system will perform all the steps described above except for the loading of the digestion solution quantitative loop and the digestion step. Additionally, for the determination of total phosphorus and phosphate, the energizing sequence of the solenoid valve assembly (17, 21) can be changed in step five above to adjust the merging method of the sample band and the chromogenic reagent band, as well as to change the current carrying capacity, thereby increasing or decreasing the detection sensitivity.

[0013] When the device is placed in an unattended environment for long-term operation, if air bubbles appear in the flow path and remain in the flow cuvette of the detector (36), the air bubbles can be automatically discharged through the following procedure. The specific steps are as follows: the solenoid valve group (17, 21, 22) is energized, the second plunger pump (24) draws air (8) into the detector (36) and the reaction coil (34), and at the same time, the first plunger pump (23) draws the carrier liquid into the cavity. Finally, the solenoid valve group (10, 11, 17, 21) is energized, and the first plunger pump (23) pushes the carrier liquid to discharge the air in the pipeline from the waste liquid port two (9).

[0014] The advantages and positive effects of this invention are as follows: The use of a dual-plunger pump alternating liquid delivery scheme replaces the conventional peristaltic pump, allowing the solution to flow continuously at a constant speed while avoiding frequent replacements due to pump tube wear; Volumetric quantification of samples and reagents is achieved through a quantitative loop, rather than relying on the suction action of a plunger pump or syringe pump, improving the accuracy of sample or reagent volume quantification and reducing the requirements for pump stroke accuracy, thereby lowering costs and saving pump cleaning time; Furthermore, it allows for automated adjustment of the analyte detection range and eliminates the common problem of residual air bubbles in flow analysis methods. Attached Figure Description

[0015] Figure 1 Schematic diagram of a flow injection combined with analysis system for total phosphorus based on ultraviolet photocatalytic digestion.

[0016] In the figure, (1) carrier liquid, (2) actual water sample, (3) standard solution, (4) digestion solution, (5) waste liquid outlet one, (6) colorimetric reagent one, (7) colorimetric reagent two, (8) air, (9) waste liquid outlet two, (10)~(16), (18)~(20), (22) three-way solenoid valve, (17), (21) two normally closed solenoid valves, (23) first plunger pump, (24) second plunger pump, (25) first storage coil, (26) second storage coil, (27) third storage coil, (28) sample quantitative loop, (29) digestion solution quantitative loop, (30) reagent quantitative loop, (31) reagent two quantitative loop, (32) digestion coil, (33) ultraviolet photocatalytic digester, (34) reaction coil, (35) thermostat, (36) flow-through photometric detector, (37) computer and operating software.

[0017] Figure 2 Example 1: Response curve recording of multiple parallel determinations of total phosphorus standard sample solution

[0018] Figure 3 Example 2: Response curve recording of total phosphorus standard sample solution

[0019] Figure 4 Example 3: Effect of carrier flow rate on phosphate standard curve

[0020] Figure 5 Example 4: Effect of the merging method of phosphate sample band and reagent band on phosphate response value Detailed Implementation

[0021] The embodiments of the present invention will be further described with reference to the accompanying drawings:

[0022] Example 1

[0023] The analysis system of the present invention (see) Figure 1 Under optimized system parameters (including optimal quantitative loop volume, storage coil length, reaction coil length, and reagent and sample injection rates), reaction reagent conditions (including optimal concentrations of ammonium molybdate, ascorbic acid, sulfuric acid, potassium antimony tartrate, and potassium persulfate), and measurement procedures, a 5 mg / L total phosphorus standard sample solution was repeatedly measured 11 times, and its response curve was obtained as shown below. Figure 2 As shown, the results indicate that the system has good precision (the relative standard deviation of absorbance detection is 1.49%).

[0024] Example 2

[0025] Under the above conditions, total phosphorus standard sample solutions of 0–5 mg / L were measured, and the response curves of different concentrations of total phosphorus were obtained as follows: Figure 2 As shown.

[0026] Example 3

[0027] By varying the flow rate of the carrier fluid during operation, the phosphate standard curves were investigated at different flow rates. The results are as follows: Figure 4 As shown.

[0028] Example 4

[0029] Keeping the injection rate constant, the merging pattern of the sample and chromogenic reagent bands in the flow path was adjusted by changing the energizing time difference between the two normally closed solenoid valves, transitioning from "head-to-head" merging to "head-to-tail" merging. The resulting trend of the effect of the energizing time difference on the 5 mg / L phosphate response value is shown below. Figure 5 As shown.

Claims

1. A fluid analysis method based on ultraviolet photocatalytic digestion of total phosphorus / phosphate by flow injection combined with an analytical system, characterized in that: The analytical system comprises a first micro plunger pump (23), a second micro plunger pump (24), eleven three-way solenoid valves (10-16, 18-20, 22), a first two normally closed solenoid valves (17), a second two normally closed solenoid valves (21), a sample metering loop (28), a digestion solution metering loop (29), a first reagent metering loop (30), a second reagent metering loop (31), a first storage coil (25), a second storage coil (26), a third storage coil (27), a digestion coil (32), a reaction coil (34), a micro spectrophotometer (36) equipped with a flow cuvette, an ultraviolet photocatalytic digester (33), a thermostat (35), and a computer (37). The computer includes controls for each component. The operating software controls the components, including eleven three-way solenoid valves: the first three-way solenoid valve (10), the second three-way solenoid valve (11), the third three-way solenoid valve (12), the fourth three-way solenoid valve (13), the fifth three-way solenoid valve (14), the sixth three-way solenoid valve (15), the seventh three-way solenoid valve (16), the eighth three-way solenoid valve (18), the ninth three-way solenoid valve (19), the thirteenth three-way solenoid valve (20), and the eleventh three-way solenoid valve (22). Its fluid analysis method includes: selecting the total phosphorus determination program on the operating software; the analysis system will then perform the following steps: First, the sample loading process; at this time, the fourth three-way solenoid valve (13) is energized, and the first micro plunger pump (23) draws the carrier liquid (1) into the pump chamber, the second micro... The first step is to use a plunger pump (24) to draw in the actual water sample (2) and fill the sample metering loop (28). Excess sample enters the first storage coil (25). Then, the first three-way solenoid valve (10), the second three-way solenoid valve (11), and the third three-way solenoid valve (12) are energized. The first micro plunger pump (23) pushes the carrier liquid in the cavity and discharges the excess sample solution in the first storage coil (25) from the waste liquid outlet (5). This completes the loading step of the sample metering loop (28). The second step is the digestion solution loading process. At this time, the seventh three-way solenoid valve (16) is energized. The first micro plunger pump (23) draws the carrier liquid (1) into the pump cavity, and the second micro plunger pump (24) draws in the digestion solution (4) and fills the digestion solution metering loop (29). The remaining digestion solution enters the second storage coil (26); then the first three-way solenoid valve (10), the second three-way solenoid valve (11), and the sixth three-way solenoid valve (15) are energized, and the first micro plunger pump (23) pushes the carrier liquid in the cavity to discharge the excess digestion solution in the second storage coil (26) from the waste liquid port (5), thus completing the loading step of the digestion solution metering loop (29); the third step is the total phosphorus digestion process. At this time, the first two normally closed solenoid valves (17) are energized, and the second micro plunger pump (24) pushes the carrier liquid in the cavity to push the sample solution in the sample metering loop (28) and the digestion solution in the digestion solution metering loop (29) into the digestion coil (32) simultaneously, so that they merge and form a mixed sample band, and the digestion reaction takes place in it;The fourth step, the loading process of the colorimetric reagent, involves the first micro plunger pump (23) continuing to draw the carrier liquid (1) into the pump chamber while the sample undergoes digestion. When the thirteenth solenoid valve (20) is energized, the second micro plunger pump (24) draws in the second colorimetric reagent (7) and fills the second reagent metering loop (31). When the ninth three-way solenoid valve (19) is energized, the second micro plunger pump (24) draws in the first colorimetric reagent (6) and fills the first reagent metering loop (30). Excess colorimetric reagents 2 and 1 enter the third storage coil (27) in sequence. Subsequently, the first micro plunger pump (23) pushes the carrier liquid in the chamber, discharging the excess colorimetric reagent in the third storage coil (27) from the waste liquid port (5). This completes the loading steps of the first reagent metering loop (30) and the second reagent metering loop (31). The five-step process for colorimetric reaction and determination of total phosphorus sample involves energizing the first and second normally closed solenoid valves (17 and 21) after the sample solution digestion is complete. The second micro plunger pump (24) pushes the carrier liquid in the chamber, simultaneously pushing the colorimetric reagents from the first reagent quantitative loop (30) and the second reagent quantitative loop (31) in the digestion coil (32) into the reaction coil (34) placed in the thermostat (35) for merging and chemical colorimetric reaction. Simultaneously, the first micro plunger pump (23) draws the carrier liquid (1) into the pump chamber. Then, the first micro plunger pump (23) pushes the carrier liquid in the chamber, continuously pushing the colorimetric sample strip into the micro spectrophotometer (36) to the waste outlet (9). The response signal is simultaneously recorded by the operating software on the computer (37) for quantitative analysis of total phosphorus.

2. The fluid analysis method for total phosphorus / phosphate based on ultraviolet photocatalytic digestion combined with an analytical system as described in claim 1, characterized in that: When the analysis system is in the "injection" step, that is, the carrier liquid drives the sample and reagent in the quantitative loop to flow. By controlling the energizing time between the first two normally closed solenoid valves (17) and the second two normally closed solenoid valves (21), the merging mode of the "sample band" and the "colorimetric reagent band" is changed, thereby adjusting the detection sensitivity and detection range of the sample to be tested.

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