A phosphate detection method combining colorimetry and electrochemical test paper

Abstract

The present invention discloses a phosphate detection method using a colorimetric method and electrochemical test paper, which belongs to the field of environmental monitoring. Specifically, the phosphate content in the water body is first semi-quantitatively detected by standard colorimetric test paper, and then the electrochemical test paper with a paper base is used to select cyclic voltammetry or square wave pulse voltammetry according to the colorimetric result to detect the phosphate concentration in the water body; when the phosphate content calculated as phosphorus in the colorimetric result is higher than 5 mg / L, the water sample is diluted by half and then detected by cyclic voltammetry; when the phosphate content calculated as phosphorus in the colorimetric result is within the range of 0.5 to 5 mg / L, cyclic voltammetry is used for detection; when the phosphate content calculated as phosphorus in the colorimetric result is lower than 0.5 mg / L, square wave pulse voltammetry is used for detection. The detection process of the present invention does not require the addition of other reagents, has a wide and accurate detection concentration range, and can achieve simple and fast in-situ detection of phosphate.

Description

Technical Field

[0001] The present invention relates to the field of environmental detection, and in particular to a phosphate detection method using a colorimetric method combined with electrochemical test paper. Background Art

[0002] Phosphate ions are a crucial component of living systems. Not only do they play important roles in biological systems, but their excessive presence can also have deleterious effects on aquatic ecosystems. Classical methods for phosphate determination include gravimetric analysis (where phosphate reacts to form magnesium pyrophosphate or ammonium magnesium phosphate hexahydrate, followed by weighing) and volumetric analysis (where ammonium phosphomolybdate is titrated with sodium hydroxide). Subsequently, with the development of various analytical instruments and measurement technologies, colorimetry, chromatography, and optical fluorescence methods have been gradually adopted for phosphate concentration determination. Colorimetry is the standard method for laboratory phosphate concentration determination. Ammonium molybdate, ascorbic acid, and antimony(III) are sequentially added to an orthophosphate sample, where they react to produce a blue phosphomolybdate complex. Colorimetry is complex and requires high equipment, power output, and space. Furthermore, colorimetry is susceptible to interference from dissolved silica and turbidity, and refractive index can also lead to deviations in measurement results at high temperatures.

[0003] Currently, a number of rapid phosphate test strips are available. These directly measure phosphate content in aqueous solutions using a colorimetric method based on the relationship between the color intensity of the test strips and the phosphorus content. These test strips are portable, inexpensive, and easy to use, making them suitable for on-site testing of water-based liquids such as surface water, domestic sewage, and industrial wastewater. However, they also have significant drawbacks: visual evaluation has certain limitations, providing only semi-quantitative detection of phosphate concentration in water.

[0004] Electrochemical analysis is a recognized rapid, sensitive, and accurate method for trace analysis. This method primarily utilizes the simple principle of electron transfer. Its instrumentation is lightweight, inexpensive, and widely applicable, making it easier to promote. Electrochemical voltammetry can be categorized into cyclic voltammetry (CV), square-wave voltammetry (SWV), differential pulse voltammetry (DPV), and linear sweep voltammetry (LSV). These techniques differ primarily in the temporal waveform changes observed after the application of a voltage or current pulse. A novel electrochemical platform for phosphate ion detection using electrochemical voltammetry has been reported. This method involves complexing molybdate with inorganic phosphate on the surface of a screen-printed electrode, forcing the electrochemically active phosphomolybdenum complex product to undergo a redox reaction, thereby indirectly determining the electrochemical concentration of phosphate ions. Cyclic voltammetry is applicable to studying phosphate detection systems and detecting higher phosphate concentrations. Square-wave voltammetry offers greater sensitivity, allowing phosphate ions to accumulate and scan on the working electrode surface, effectively lowering the detection limit and enabling ultrasensitive phosphate detection. Its disadvantage is that there is a certain working range for detecting the concentration of the target object. When the concentration of the target object is higher or lower than the range, the detection result is prone to deviation. Summary of the Invention

[0005] The present invention aims to address the problems existing in the prior art and provide a phosphate detection method that combines colorimetry with electrochemical test paper. This method uses colorimetric test paper to semi-quantitatively detect phosphate in water, and selects an appropriate electrochemical voltammetry method based on the colorimetric results to achieve accurate, simple, and in-situ detection of phosphate concentration in water.

[0006] The specific technical solutions adopted in the present invention are as follows:

[0007] The present invention provides a phosphate detection method using a colorimetric method combined with electrochemical test paper, which is as follows:

[0008] First, the phosphate content in the water was semi-quantitatively detected using standard colorimetric test paper. Then, paper-based electrochemical test paper was used to select cyclic voltammetry or square wave pulse voltammetry based on the colorimetric results to detect the phosphate concentration in the water.

[0009] When the phosphate content calculated as phosphorus in the colorimetric result is higher than 5 mg / L, the water sample is diluted by half and then detected by cyclic voltammetry; when the phosphate content calculated as phosphorus in the colorimetric result is within the range of 0.5 to 5 mg / L, the cyclic voltammetry is used for detection; when the phosphate content calculated as phosphorus in the colorimetric result is lower than 0.5 mg / L, the square wave pulse voltammetry is used for detection.

[0010] Preferably, the standard colorimetric test paper is purchased from commercial sources or prepared by the following method:

[0011] S11: using CorelDRAW Graphics Suite to design a first hydrophobic wax batch print pattern, the first hydrophobic wax batch print pattern including a circular color-developing area; then using a wax printing machine to print the first hydrophobic wax batch print pattern onto paper; heating the paper with the wax pattern to melt the wax and permeate the entire thickness of the paper, thereby obtaining a first paper and a second paper, each having a color-developing area;

[0012] S12: adding a first color developer to the color-developing area of ​​the first paper and a second color developer to the color-developing area of ​​the second paper, and drying the resulting color-developing areas to functionalize the color-developing areas. Then, cutting the functionalized first and second paper sheets, and attaching and fixing the color-developing areas of the two sheets to form a working area.

[0013] S13: preparing standard phosphate aqueous solutions of different concentrations;

[0014] S14: adding the prepared standard phosphate aqueous solution dropwise to the working area to completely soak the two layers of paper in the working area, leaving the solution for 2 to 10 minutes to observe the color change of the working area, collecting a color image with a camera, and then analyzing the image by grayscale intensity using Photoshop software;

[0015] S15: For each prepared standard phosphate aqueous solution of each concentration, react and photograph and analyze according to step S14, and then collect the reaction color pictures of all standard phosphate aqueous solutions of different concentrations together to obtain the standard colorimetric test paper.

[0016] Furthermore, the first developer is an aqueous solution including 1-20 g / L ammonium molybdate and / or its hydrate, 0.3-1 g / L potassium antimony tartrate and 0.2%-2% volume ratio of sulfuric acid; the second developer is 10-50 g / L ascorbic acid or stannous chloride solution; the addition amount of the first developer and the second developer is 20 μL.

[0017] Furthermore, the diameter of the color-developing area is 14.0 mm.

[0018] Furthermore, in step S13, potassium dihydrogen phosphate aqueous solutions with concentrations of 0.1 mg / L, 0.5 mg / L, 1.0 mg / L, 2.0 mg / L, 3.0 mg / L and 5.0 mg / L are respectively configured as standard phosphate aqueous solutions, and the addition amount of the standard phosphate aqueous solutions of each concentration is 20 μL.

[0019] Preferably, the preparation method of the electrochemical test paper is as follows:

[0020] S21: Designing a second hydrophobic wax batch printing pattern and a working electrode, reference electrode, counter electrode, and wire screen printing pattern matching the wax printing pattern using CorelDRAW Graphics Suite; the second hydrophobic wax batch printing pattern includes an electrochemical reaction area with a size of 14.0 mm*14.0 mm;

[0021] S22: Printing a second hydrophobic wax batch printing pattern onto paper using a wax printing machine;

[0022] S23: heating the paper with the wax pattern so that the wax melts and permeates the entire thickness of the paper;

[0023] S24: adding an electrolyte buffer dropwise to the electrochemical reaction area of ​​the paper obtained in step S23 to perform functional modification;

[0024] S25: Printing a working electrode, a reference electrode, a counter electrode, and a wire on the functionally modified paper according to the pattern designed in step S21 using screen printing technology; then cutting, folding, and assembling according to the pattern designed in step S21 to obtain the electrochemical test paper.

[0025] Furthermore, the working electrode is a circular structure with a diameter of 4.0 mm, the reference electrode has a diameter of 10. mm and a width of 1.0 mm, the counter electrode has a diameter of 10. mm and a width of 1.0 mm, and the wire has a length of 17.0 mm and a width of 1.0 mm.

[0026] Furthermore, the electrolyte buffer is a 0.2 mol / L potassium chloride solution whose pH is adjusted to 1.1 using sulfuric acid.

[0027] Furthermore, in the screen printing technology, the screen is made of nylon with a mesh size of 200 to 300, the conductive material for printing the working electrode is carbon paste doped with nanomaterials, the conductive material for printing the counter electrode is pure carbon paste, and the conductive material for printing the reference electrode is silver paste; the nanomaterials include 0.5% to 10% by mass of ammonium molybdate and / or its hydrate and 5% to 20% by mass of multi-walled carbon nanotubes.

[0028] Preferably, the amount of the sample added to the electrochemical test paper is 10 μL; the parameters of the cyclic voltammetry are set as: potential range -0.1 to 6.0 V, scan rate 50 mV / s; the parameters of the square wave pulse voltammetry are set as: deposition potential -0.1 V, deposition time 3 minutes, potential range -0.1 to 6.0 V, scan rate 50 mV / s, and pulse height of 25 mV.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) The present invention uses a dual-mode device to visually predict and accurately detect phosphate. It can visually predict the concentration range of phosphate ions and select the corresponding appropriate electrochemical voltammetry method to specifically detect phosphate, thereby improving the accuracy of detection and achieving full coverage of phosphate concentration detection in common water bodies.

[0031] 2) Leveraging the hydrophilicity of paper, the ions required for the reaction are pre-stored within the paper's fiber network. Furthermore, when the test sample is dripped onto the back of the paper-based electrochemical chip, the paper's pores automatically block large particles, enabling reagent-free operation and facilitating simple in-situ testing.

[0032] 3) The white background of paper reduces interference signals and allows for clear color rendering, making it easier to observe with the naked eye. Compared to traditional glassy carbon and glass electrodes, paper substrates are made from abundant raw materials, are lightweight, inexpensive, easily foldable, biodegradable, and less likely to pollute the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The test paper designed for the present invention has a batch printing pattern of hydrophobic wax (a), a reference electrode and wire screen printing template (b), a working electrode and counter electrode screen printing template (c), and an electrochemical test paper batch preparation effect diagram for use with colorimetry (d);

[0034] Figure 2 Schematic diagram (a) and a comparison diagram (b) of an electrochemical test paper for phosphate detection used in conjunction with a colorimetric method according to the present invention;

[0035] Figure 3 Schematic diagram of the standard colorimetric card required for the phosphate colorimetric detection method of the present invention;

[0036] Figure 4 This is a flow chart of the use of an electrochemical test paper for phosphate detection in combination with a colorimetric method according to the present invention;

[0037] Figure 5 The cyclic voltammetric curve responses of phosphates of different concentrations according to the present invention are shown;

[0038] Figure 6 The square wave pulse voltammetric curve responses of phosphates of different concentrations according to the present invention are shown. DETAILED DESCRIPTION

[0039] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention may be combined accordingly, provided that there is no conflict between them.

[0040] The present invention provides a phosphate detection method using a colorimetric method combined with electrochemical test paper, which is as follows:

[0041] First, the phosphate content in the water is semi-quantitatively detected using standard colorimetric test paper. Then, using paper-based electrochemical test paper, cyclic voltammetry or square wave pulse voltammetry is selected based on the colorimetric results obtained by the standard colorimetric test paper to detect the phosphate concentration in the water.

[0042] Specifically, when the phosphate colorimetric result of the water sample is higher than 5 mg / L (in terms of P), the water sample is diluted with ultrapure water in a volume ratio of 1:1 and then detected by cyclic voltammetry; when the phosphate colorimetric result of the water sample is within the range of 0.5 to 5 mg / L (in terms of P), cyclic voltammetry can be selected for direct detection; when the phosphate concentration in the water sample is lower than 0.5 mg / L (in terms of P), square wave pulse voltammetry is selected for detection.

[0043] In the present invention, the standard colorimetric test paper can be purchased through commercial channels or prepared by oneself. The preparation method is as follows:

[0044] S11: using CorelDRAW Graphics Suite to design a first hydrophobic wax batch-printed pattern, the first hydrophobic wax batch-printed pattern including a circular color-developing area; then using a wax printing machine to print the first hydrophobic wax batch-printed pattern onto paper; heating the paper with the wax pattern to melt the wax and penetrate the entire thickness of the paper, thereby obtaining a first paper and a second paper, each having a color-developing area.

[0045] In actual application, the diameter of the color development area is preferably 14.0 mm, and the paper used is one of the common filter paper, chromatography paper, and A4 office paper available on the market; the heating temperature is 60-120°C, and the heating time is 0.5-3 minutes, which can be adjusted according to the selected paper and actual conditions.

[0046] S12: Add a first color developer to the color development area of ​​the first paper, and add a second color developer to the color development area of ​​the second paper. After drying, the color development area is functionalized. Then, the functionalized first paper and the second paper are cut, and the color development areas of the two are attached and fixed to form a working area.

[0047] The reason why two papers are functionalized with different color developers is that the two color developers are not easy to stabilize after mixing, which will affect the accuracy of the test results.

[0048] In practical applications, the first developer is an aqueous solution comprising 1-20 g / L ammonium molybdate and / or its hydrate (i.e., ammonium molybdate, its hydrate, or a mixture thereof), 0.3-1 g / L potassium antimony tartrate, and 0.2%-2% by volume sulfuric acid. The second developer is a 10-50 g / L ascorbic acid or stannous chloride solution. The first and second developer are added in a 20 μL dropwise amount each, preferably not in excess, to ensure uniform fixation.

[0049] S13: Prepare standard phosphate aqueous solutions of different concentrations.

[0050] In actual application, potassium dihydrogen phosphate aqueous solutions with concentrations of 0.1 mg / L, 0.5 mg / L, 1.0 mg / L, 2.0 mg / L, 3.0 mg / L and 5.0 mg / L can be prepared as standard phosphate aqueous solutions, and the addition amount of the standard phosphate aqueous solutions of each concentration is 20 μL.

[0051] S14: Add the prepared standard phosphate aqueous solution dropwise to the working area to allow the standard phosphate aqueous solution to completely penetrate the two layers of paper in the working area. Let it stand for 2 to 10 minutes to observe the color change of the working area, collect a color image with a camera, and then analyze it by grayscale intensity using Photoshop software.

[0052] S15: For each prepared standard phosphate aqueous solution of each concentration, react and photograph and analyze according to step S14, and then collect the reaction color pictures of all standard phosphate aqueous solutions of different concentrations together to obtain the standard colorimetric test paper.

[0053] In the present invention, the electrochemical test paper can be prepared by the following method:

[0054] S21: Using CorelDRAW Graphics Suite, design a second hydrophobic wax batch printing pattern and a working electrode, reference electrode, counter electrode, and wire screen printing pattern that match the wax printing pattern; wherein the second hydrophobic wax batch printing pattern includes an electrochemical reaction area with a size of 14.0 mm*14.0 mm.

[0055] In actual application, the working electrode is a circular structure with a diameter of 4.0 mm, the reference electrode has a diameter of 10. mm and a width of 1.0 mm, the counter electrode has a diameter of 10. mm and a width of 1.0 mm, and the wire has a length of 17.0 mm and a width of 1.0 mm.

[0056] S22: Printing the second hydrophobic wax batch printing pattern onto paper using a wax printing machine.

[0057] S23: The paper with the wax pattern is heated so that the wax melts and permeates the entire thickness of the paper.

[0058] In actual application, the paper used is one of the common filter paper, chromatography paper, and A4 office paper available on the market; the heating temperature is 60-120°C, and the heating time is 0.5-3 minutes, which can be adjusted according to the selected paper and actual conditions.

[0059] S24: adding an electrolyte buffer solution dropwise to the electrochemical reaction area of ​​the paper obtained in step S23 to perform functional modification.

[0060] In practical applications, the electrolyte buffer is a 0.2 mol / L potassium chloride solution adjusted to pH 1.1 using sulfuric acid.

[0061] S25: Printing a working electrode, a reference electrode, a counter electrode, and a wire on the functionally modified paper according to the pattern designed in step S21 using screen printing technology; then cutting, folding, and assembling according to the pattern designed in step S21 to obtain the electrochemical test paper.

[0062] In actual application, in the screen printing technology, the screen is made of nylon with a mesh size of 200 to 300, the conductive material for printing the working electrode is carbon paste doped with nanomaterials, the conductive material for printing the counter electrode is pure carbon paste, and the conductive material for printing the reference electrode is silver paste; the nanomaterials include 0.5% to 10% by mass of ammonium molybdate and / or its hydrate and 5% to 20% by mass of multi-walled carbon nanotubes.

[0063] In the present invention, the amount of sample added to the electrochemical test paper is 10 μL; the parameters of the cyclic voltammetry are set as follows: potential range of -0.1 to 6.0 V, scan rate of 50 mV / s; the parameters of the square wave pulse voltammetry are set as follows: deposition potential of -0.1 V, deposition time of 3 minutes, potential range of -0.1 to 6.0 V, scan rate of 50 mV / s, and pulse height of 25 mV.

[0064] In practical applications, to facilitate comparison, standard colorimetric test paper and electrochemical test paper can be integrated onto a single large test paper as a single device. For example, the device's overall dimensions are 16.0mm*60.0mm, and the pattern arrangement can be adjusted based on the paper size. During measurement, the test paper leads are connected to an electrochemical workstation, and the sample is then dripped onto the hydrophilic areas of the standard colorimetric and electrochemical test paper, respectively, within the device. The colorimetric results are then compared with a standard colorimetric card, and the appropriate electrochemical voltammetry method is selected based on the colorimetric results to achieve sensitive detection of the sample.

[0065] Example 1

[0066] This example prepares a phosphate standard colorimetric card, and the specific method is as follows:

[0067] 1) Use CorelDRAW Graphics Suite on the computer to design a batch printing pattern of hydrophobic wax, the style is as follows Figure 1 As shown, filter paper is placed in a wax printing machine for batch printing, and then the paper printed with the wax pattern is placed in an oven for heating at a temperature of 100°C for 2 minutes to melt the wax and penetrate the entire thickness of the paper.

[0068] 2) Prepare the first color developer. Specifically, measure 10g of analytically pure ammonium molybdate tetrahydrate, 10mL of analytically pure sulfuric acid, and 5g of the catalyst potassium antimony tartrate. Then, measure 1L of ultrapure water. Add the measured molybdate, acid, and catalyst to the ultrapure water and stir evenly to prepare the first color developer. Next, add 20μL of the first color developer dropwise to the first color development zone, and dry in a desiccator to complete the functionalization of the circular hydrophilic working area of ​​the first color development zone.

[0069] 3) Prepare the second colorimetric reagent. Specifically, measure 30 g / L of analytically pure ascorbic acid and stir evenly in 1 L of ultrapure water to prepare the second colorimetric reagent. Next, add 20 μL of the second colorimetric reagent dropwise to the second colorimetric zone and place in a desiccator to dry. This completes the functionalization of the circular hydrophilic working area within the second colorimetric zone.

[0070] 4) Cut the dried color test paper into a 16mm*32mm rectangle, fold the first color development area and the second color development test paper in half, and secure with a clip.

[0071] 5) Prepare standard potassium dihydrogen phosphate solutions with concentrations of 0.1, 0.5, 1.0, 2.0, 3.0, and 5.0 mg / L, respectively. Take 20 μL of each concentration of standard solution and drop it onto the surface of the color-developing area of ​​the test paper to evenly disperse the solution in the first and second color-developing areas. Let it stand for 5 minutes to observe the color change, collect the color image with a camera, and then use Photoshop software to analyze it by grayscale intensity. React and photograph the standard phosphate aqueous solution of each concentration, then collect the reaction colors of the standard orthophosphate aqueous solutions of different concentrations and print them to obtain the standard colorimetric card, as shown in the attached figure. Figure 3 shown.

[0072] Example 2

[0073] In this example, a phosphate-sensitive electrochemical paper-based electrode was prepared and its working curve was established. The specific method is as follows:

[0074] 1) Using CorelDRAW Graphics Suite on a computer, design the electrochemical hydrophobic wax batch printing pattern and the working electrode, reference electrode, counter electrode and wire screen printing pattern that match the wax printing pattern, such as Figure 1 The second hydrophobic wax pattern was printed in batches onto the filter paper using a wax printing machine, and the paper with the wax pattern printed was placed in an oven and heated at 100°C for 2 minutes to melt the wax and penetrate the entire thickness of the paper.

[0075] 2) A potassium chloride solution with a pH of 1.1 and a concentration of 0.2 mol / L was added dropwise to the electrochemical reaction area of ​​the obtained paper, and the paper was placed in a drying container to dry for functional modification.

[0076] 3) Screen printing a working electrode, reference electrode, counter electrode, and conductor onto the functionalized paper using a 300-mesh nylon screen. The working electrode is printed using a carbon paste doped with 5% by weight of ammonium molybdate tetrahydrate and 10% by weight of multi-walled carbon nanotubes. The counter electrode is printed using pure carbon paste, and the reference electrode is printed using silver paste. The electrochemical test paper is then cut, folded, and assembled.

[0077] 4) Establish a working curve for cyclic voltammetry detection of phosphate ions: Prepare standard potassium dihydrogen phosphate solutions with concentrations of 0.5, 1.0, 3.0, and 5.0 mg / L, respectively. Measure 10 μL of each standard solution and drip it onto the surface of the test paper electrode. Connect the test paper wire end to the electrochemical workstation and select cyclic voltammetry for analysis. The parameters are set as follows: potential range -0.1 to 6.0 V, scan rate 50 mV / s, and repeat 3 times for each concentration. Calculate the linear relationship between the response current and phosphate concentration. The cyclic voltammetry response curves for different phosphate concentrations are shown in the attached figure. Figure 5 shown.

[0078] 5) Establish a working curve for detecting phosphate ions by square wave pulse voltammetry: prepare standard potassium dihydrogen phosphate solutions with concentrations of 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 mg / L, respectively. Measure 10 μL of each standard solution and drop it onto the surface of the test paper electrode. Connect the test paper wire end to the electrochemical workstation and select square wave pulse voltammetry for analysis. The parameters are set as follows: deposition potential -0.1 V, deposition time 3 minutes, potential range -0.1 to 6.0 V, scan rate 50 mV / s, pulse height 25 mV. Repeat 3 times for each concentration and calculate the linear relationship between the response current and phosphate concentration. The square wave pulse voltammetry curve response of different phosphate concentrations is shown in the attached figure. Figure 6 shown.

[0079] Example 3

[0080] This example uses the standard colorimetric card prepared in Example 1 and the electrochemical test paper prepared in Example 2 to detect the phosphate concentration of surface runoff water samples from the environmental monitoring point of the agricultural product production area in Kaihua County. The overall use process is as shown in the attached figure. Figure 4As shown, the details are as follows:

[0081] 1) Take 20 μL of surface runoff water sample from the environmental monitoring point of agricultural product production area in Kaihua County and add it dropwise to the double-layer colorimetric area of ​​the test paper of the present invention (such as the attached Figure 2 After standing for 5 minutes, observe the color change and compare it with the standard color card. The colorimetric result shows that the phosphate concentration is about 0.3 mg / L, which is lower than 0.5 mg / L.

[0082] 2) Take 10 μL of water sample and evenly drip it onto the working electrode surface of the test paper. Connect the test paper wire end to the electrochemical workstation. After checking the circuit, turn on the electrochemical workstation.

[0083] 3) Based on the colorimetric results, square wave pulse voltammetry was selected to detect phosphate. The parameters were set as follows: deposition potential of -0.1 V, deposition time of 3 minutes, potential range of -0.1 to 6.0 V, sweep rate of 50 mV / s, and pulse height of 25 mV. Based on the working curve for phosphate ion detection by square wave pulse voltammetry in Example 2, the phosphate concentration in the water sample was calculated to be 0.171 mg / L based on the response current value.

[0084] 4) Using the classic method for detecting phosphate, ammonium molybdate-potassium antimony tartrate-ascorbic acid spectrophotometry, surface runoff water samples from the environmental monitoring point of the agricultural product production area in Kaihua County were measured, and the phosphate concentration of the water sample was 0.169 mg / L, which was consistent with the results of colorimetry and cyclic voltammetry, indicating that the colorimetric / electrochemical method combined with the test paper of the present invention has an accurate detection effect.

[0085] The detection process of the present invention does not require the addition of other reagents, has a wide and accurate detection concentration range, and can achieve simple and rapid in-situ detection of phosphate.

[0086] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A method for detecting phosphate using a colorimetric method combined with electrochemical test paper, characterized in that: The details are as follows: First, the phosphate content in the water was semi-quantitatively detected using standard colorimetric test paper. Then, paper-based electrochemical test paper was used to select cyclic voltammetry or square wave pulse voltammetry based on the colorimetric results to detect the phosphate concentration in the water. When the phosphate content calculated as elemental phosphorus in the colorimetric result is higher than 5 mg / L, the water sample is diluted by half and then tested by cyclic voltammetry; when the phosphate content calculated as elemental phosphorus in the colorimetric result is within the range of 0.5-5 mg / L, the cyclic voltammetry is used for testing; when the phosphate content calculated as elemental phosphorus in the colorimetric result is lower than 0.5 mg / L, the square wave pulse voltammetry is used for testing; The standard colorimetric test paper is prepared by the following method: S11: using CorelDRAW Graphics Suite to design a first hydrophobic wax batch print pattern, the first hydrophobic wax batch print pattern including a circular color-developing area; then using a wax printing machine to print the first hydrophobic wax batch print pattern onto paper; heating the paper with the wax pattern to melt the wax and permeate the entire thickness of the paper, thereby obtaining a first paper and a second paper, each having a color-developing area; S12: adding a first color developer to the color-developing area of ​​the first paper and a second color developer to the color-developing area of ​​the second paper, and drying the resulting color-developing areas to functionalize the color-developing areas. Then, cutting the functionalized first and second paper sheets, and attaching and fixing the color-developing areas of the two sheets to form a working area. S13: preparing standard phosphate aqueous solutions of different concentrations; S14: adding the prepared standard phosphate aqueous solution dropwise to the working area to completely soak the two layers of paper in the working area, leaving the solution for 2 to 10 minutes to observe the color change of the working area, collecting a color image with a camera, and then analyzing the image by grayscale intensity using Photoshop software; S15: For each prepared standard phosphate aqueous solution of each concentration, react and photograph and analyze according to step S14, and then collect the reaction color pictures of all standard phosphate aqueous solutions of different concentrations together to obtain the standard colorimetric test paper; The first developer is an aqueous solution comprising 1-20 g / L ammonium molybdate and / or its hydrate, 0.3-1 g / L potassium antimony tartrate, and 0.2%-2% by volume sulfuric acid; the second developer is a 10-50 g / L ascorbic acid or stannous chloride solution; the dropwise addition amount of the first developer and the second developer is 20 μL each; The preparation method of the electrochemical test paper is as follows: S21: Designing a second hydrophobic wax batch printing pattern and a working electrode, reference electrode, counter electrode, and wire screen printing pattern matching the wax printing pattern using CorelDRAW Graphics Suite; the second hydrophobic wax batch printing pattern includes an electrochemical reaction area with a size of 14.0 mm*14.0 mm; S22: Printing a second hydrophobic wax batch printing pattern onto paper using a wax printing machine; S23: heating the paper with the wax pattern so that the wax melts and permeates the entire thickness of the paper; S24: adding an electrolyte buffer dropwise to the electrochemical reaction area of ​​the paper obtained in step S23 to perform functional modification; S25: Printing a working electrode, a reference electrode, a counter electrode, and a wire on the functionally modified paper using a screen printing technique according to the pattern designed in step S21; Then, cutting, folding, and assembling are performed according to the pattern designed in step S21 to obtain the electrochemical test paper; The electrolyte buffer is a 0.2 mol / L potassium chloride solution whose pH is adjusted to 1.1 using sulfuric acid; In the screen printing technology, the conductive material of the printed working electrode is a carbon paste doped with nanomaterials, wherein the nanomaterials include 0.5% to 10% by mass of ammonium molybdate and / or its hydrate and 5% to 20% by mass of multi-walled carbon nanotubes; The amount of sample added to the electrochemical test paper was 10 μL.

2. The phosphate detection method according to claim 1, wherein the colorimetry method is coupled with an electrochemical test paper. The diameter of the color development area is 14.0 mm.

3. The phosphate detection method according to claim 1, wherein the colorimetry method is combined with electrochemical test paper, In step S13, potassium dihydrogen phosphate aqueous solutions with concentrations of 0.1 mg / L, 0.5 mg / L, 1.0 mg / L, 2.0 mg / L, 3.0 mg / L and 5.0 mg / L are respectively prepared as standard phosphate aqueous solutions, and the addition amount of the standard phosphate aqueous solutions of each concentration is 20 μL.

4. The phosphate detection method according to claim 1, wherein the colorimetric method is coupled with an electrochemical test paper. The working electrode is a circular structure with a diameter of 4.0 mm, the reference electrode has a diameter of 10. mm and a width of 1.0 mm, the counter electrode has a diameter of 10. mm and a width of 1.0 mm, and the lead has a length of 17.0 mm and a width of 1.0 mm.

5. The phosphate detection method according to claim 1, wherein the colorimetric method is coupled with an electrochemical test paper. In the screen printing technology, the screen is made of nylon with a mesh size of 200 to 300, the conductive material for printing the counter electrode is pure carbon paste, and the conductive material for printing the reference electrode is silver paste.

6. The phosphate detection method according to claim 1, wherein the colorimetric method is combined with electrochemical test paper, The parameters of the cyclic voltammetry method are set as follows: potential range -0.1 to 6.0 V, scan rate 50 mV / s; the parameters of the square wave pulse voltammetry method are set as follows: deposition potential -0.1 V, deposition time 3 minutes, potential range -0.1 to 6.0 V, scan rate 50 mV / s, and pulse height 25 mV.

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