Ph test paper and preparation method therefor, and method for measuring ph of water

Abstract

The present application provides a pH test paper and a preparation method therefor, and a method for measuring the pH of water. The pH test paper is made of a test paper carrier and an indicator solution, wherein the indicator solution comprises an indicator, a solvent, a pH regulator and a surfactant, the indicator comprising any one or a combination of at least two of phenol red, cresol red, neutral red, α-naphtholphthalein, thymol blue and bromothymol blue. In the present application, when used for measuring the pH of water, the pH test paper exhibits obvious color changes, has a high detection sensitivity, accuracy and reliability, and can be used for detecting water having a low alkalinity and a low buffer capacity.

Description

A pH test strip and its preparation method, and a method for detecting pH in water. Technical Field

[0001] This application belongs to the field of water body detection technology, specifically relating to a pH test strip and its preparation method, and a method for detecting pH in water. Background Technology

[0002] In daily life and public health, pH monitoring is crucial for ensuring water quality safety and protecting public health. For example, the pH of swimming pool water directly affects its disinfection effectiveness, water quality stability, and skin irritation to swimmers. Excessively high or low pH levels can lead to water quality deterioration and increase the risk of disease transmission. The pH of tap water is also an important indicator for assessing its safety and stability. Therefore, accurate and rapid monitoring of the pH of these water bodies is essential for protecting public health.

[0003] There are many methods for testing the pH of water. Among them, pH test strips, as a portable and economical testing method, can meet the needs of rapid screening. pH test strips detect the pH value of water by reacting a chemical reaction between the indicator loaded on the strip and the test solution, resulting in a color change. The pH value of the test solution is then compared with a standard color chart. Typically, the acid-base indicators in pH test strips are organic weak acids / weak acid salts, which exist in dissociation equilibrium in aqueous solutions. The indicators themselves possess a certain buffering capacity due to their weak acid properties. When the indicator comes into contact with the test solution, it consumes H+ or OH- ions in the solution, shifting the dissociation equilibrium. This changes the ratio of the acidic and basic forms of the indicator, thus altering the color of both the indicator and the test strip.

[0004] The consumption of H+ or OH- in the test solution also causes a change in its pH. High-buffered test solutions can resist this change, so that after the indicator reacts with H+ or OH- and changes color, the test solution retains its original pH value. In this case, the test strip result is the true pH value of the test solution. Low-buffered test solutions cannot resist this change; as H+ or OH- are consumed, their own pH also changes. Therefore, the test strip actually measures the changed pH value of the test solution, which differs from the true pH value. The size of this difference depends on the buffering capacity of the test solution. For neutral, weakly acidic, and weakly alkaline aqueous solutions, buffering capacity is usually measured by alkalinity. For water bodies related to daily life and public health, such as tap water, drinking water, and swimming pool water, their pH values ​​are mostly in the range of 5 to 9, i.e., neutral, weakly acidic, or weakly alkaline. These water bodies are usually very clean, containing few dissolved substances. Chemically speaking, these water bodies have poor buffering capacity and low alkalinity. However, most commercially available pH test strips, including broad-spectrum and precision pH test strips, are primarily designed for measuring buffered solutions in laboratory settings. They fall short when testing for low-buffered, low-alkalinity water, especially neutral water such as tap water and swimming pool water. Often, the color change is not obvious or the response sensitivity is insufficient, leading to inaccurate or difficult-to-read results. Furthermore, other components in low-alkalinity water (such as residual chlorine and hardness ions) can also interfere with the performance of the test strips, further affecting the reliability of the test results.

[0005] Typically, pH in such water bodies can only be accurately measured using a pH meter (electrode method). However, pH meters are relatively expensive and require frequent calibration and maintenance, which cannot meet the needs of rapid detection in some scenarios.

[0006] Therefore, developing a test strip that can accurately, quickly, and conveniently detect the pH value of low-buffered, low-alkaline water is an urgent problem to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this application is to provide a pH test strip, its preparation method, and a method for detecting pH in water. The pH test strip exhibits a clear color change when detecting pH in water, demonstrating high sensitivity, accuracy, and reliability, and can be used to detect water with low alkalinity and low buffering capacity.

[0008] To achieve this objective, the present application adopts the following technical solution:

[0009] In a first aspect, this application provides a pH test strip, the material of which includes a test strip carrier and an indicator solution; the indicator solution includes an indicator, a solvent, an acid-base adjuster, and a surfactant; the indicator includes any one or a combination of at least two of phenol red, cresol red, neutral red, α-naphtholphthalein, thymol blue, or bromothymol blue.

[0010] In this application, the acid-base adjuster can regulate the initial pH value of the indicator, allowing the indicator to be loaded onto the test paper carrier in a specific acidified or alkalized form. The color-changing pH range of the indicator is usually within the range of its dissociation constant pKa ± 1; if the initial pH of the indicator is not adjusted, the pH value after the reaction between the test solution and the indicator may not be within this range, causing the test paper to lack color-changing function. By controlling the ionization equilibrium of the indicator under specific initial pH conditions, the final pH value of the test solution falls within the indicator's colorimetric range, ensuring a significant color change and improving detection sensitivity and accuracy. Surfactants significantly reduce the surface tension of the test strip carrier, allowing the indicator solution to more easily penetrate the tiny pores and fibrous structure of the carrier. Furthermore, surfactants disperse indicator molecules uniformly in the solution, preventing agglomeration and ensuring even indicator distribution on the test strip, further enhancing detection sensitivity and accuracy. Therefore, pH test strips obtained using a specifically formulated indicator solution exhibit high detection sensitivity and accuracy, strong reliability, and can be used for pH detection in water bodies with low alkalinity and low buffering capacity.

[0011] Preferably, the concentration of the indicator in the indicator solution is 0.2–2 mM, for example, it can be 0.2 mM, 0.25 mM, 0.3 mM, 0.35 mM, 0.4 mM, 0.45 mM, 0.5 mM, 0.55 mM, 0.6 mM, 0.65 mM, 0.7 mM, 0.75 mM, 0.8 mM, 0.85 mM, 0.9 mM, 0.95 mM, 1 mM, 1.1 mM, 1.2 mM, 1.3 mM, 1.4 mM, 1.5 mM, 1.6 mM, 1.7 mM, 1.8 mM, 1.9 mM, 2 mM, etc.; preferably 0.5–1 mM.

[0012] In this application, the concentration of the indicator affects the amount of indicator loaded on the test strip carrier. For test solutions with low alkalinity, the buffering capacity of the indicator and the buffering capacity provided by the alkalinity of the test solution compete with each other. Since the buffering capacity of the indicator is directly related to its solution concentration, controlling the indicator concentration within a specific range allows for control of the indicator loading on the test strip carrier within that range, thus facilitating better color development of the indicator within the pH range of the test solution. If the indicator loading is too high, the color change will be indistinct; if the loading is too low, the color saturation of the test strip will be poor, making observation difficult.

[0013] Preferably, the solvent includes an organic solvent, or a mixture of an organic solvent and water, preferably an organic solvent; the organic solvent includes volatile organic solvents.

[0014] In this application, the advantages of volatile organic solvents are mainly reflected in three aspects: First, volatile organic solvents have low surface tension and good wettability, which allows the indicator solution to penetrate more effectively into the micropores and fiber structure of the test paper carrier, enhancing the capillary effect of the fiber structure in a wet state. This allows more indicator molecules to be carried by the solvent and adhere to the interior of the test paper carrier, thereby reducing the concentration of the indicator solution used. Second, since indicators are generally not heat-resistant, choosing low-boiling-point, volatile organic solvents results in lower drying temperatures, which is more conducive to the stability of the indicator, and also reduces the amount of solvent residue on the test paper carrier. Third... Volatile organic solvents vaporize rapidly during the drying process. As the solvent evaporates, the indicator molecules originally dissolved in the solvent migrate to the surface of the carrier due to the thermal motion of the solvent and the capillary action of the test paper carrier. This creates a longitudinal content gradient distribution within the carrier, resulting in more indicator distributed on the surface of the test paper carrier. Consequently, with the same load, the test paper exhibits higher color saturation, making color recognition easier. Furthermore, with the same color saturation on the test paper surface, a lower indicator load is required (less indicator in non-surface areas), which helps to increase the pH change value of the indicator, thereby presenting a better colorimetric range and effect.

[0015] Preferably, the organic solvent includes any one or a combination of at least two of ethanol, methanol, or acetone.

[0016] Preferably, the solvent includes a mixture of an organic solvent and water, wherein the volume ratio of the organic solvent to water is (0.1 to 10):1, and the specific values ​​of (0.1 to 10) can be, for example, 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, etc.

[0017] Preferably, the acid-base adjuster adjusts the pH of the indicator solution to 6-9, for example, 6, 6.2, 6.4, 6.6, 6.8, 7, 7.2, 7.4, 7.6, 7.8, 8, 8.2, 8.4, 8.6, 8.8, 9, etc.

[0018] Preferably, the acid-base regulator comprises a strong acid or a strong base; the strong acid comprises dilute hydrochloric acid and / or dilute sulfuric acid; the strong base comprises sodium hydroxide and / or potassium hydroxide.

[0019] Preferably, the surfactant in the indicator solution has a mass percentage content of 0.2% to 2%, for example, it can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, etc.

[0020] Preferably, the surfactant comprises at least one or a combination of at least two of the following: quaternary ammonium salt surfactant, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, fatty alcohol polyoxyethylene ether, or alkylphenol polyoxyethylene ether.

[0021] In this application, the quaternary ammonium salt surfactant includes n-N-alkyltrimethylammonium halide, wherein N is 10 to 22, representing the number of carbon atoms in the alkyl group, for example, 10, 12, 14, 16, 18 or 22; the halogen atom in the ammonium halide is chlorine or bromine.

[0022] Preferably, the test paper carrier comprises filter paper or cellulose membrane.

[0023] The thickness of the test strip carrier is 0.2–0.5 mm, for example, it can be 0.2 mm, 0.22 mm, 0.25 mm, 0.28 mm, 0.3 mm, 0.32 mm, 0.35 mm, 0.38 mm, 0.4 mm, 0.42 mm, 0.45 mm, 0.48 mm, 0.5 mm, etc.; the density of the test strip carrier is ≥0.35 g / cm³. 3 For example, it can be 0.35 g / cm³. 3 0.4g / cm 3 0.45g / cm 3 0.5g / cm 3 0.55g / cm 3 wait.

[0024] Secondly, this application provides a method for preparing pH test paper according to the first aspect, the method comprising the following steps:

[0025] The pH test paper is obtained by loading the indicator solution onto the surface of the test paper carrier.

[0026] Preferably, the loading method includes: immersing the test paper carrier in an indicator solution, squeezing it dry, and obtaining a test paper that has undergone one immersion and squeezing.

[0027] In this application, the drying process is performed using rubber rollers to remove excess liquid from the test paper carrier.

[0028] Preferably, the soaking time is 5 to 30 seconds, for example, 5 seconds, 6 seconds, 8 seconds, 10 seconds, 11 seconds, 12 seconds, 13 seconds, 14 seconds, 15 seconds, 16 seconds, 18 seconds, 20 seconds, 22 seconds, 24 seconds, 26 seconds, 28 seconds, 30 seconds, etc.; more preferably, it is 8 to 15 seconds.

[0029] Preferably, the number of impregnation cycles is 1 to 5, for example, 1, 2, 3, 4, 5, etc.; more preferably, the number of impregnation cycles is 2 to 3.

[0030] In this application, when the number of immersions and rolls is greater than 1, the loading method includes: immersing the test paper carrier in an indicator solution, rolling it dry, and then repeating the immersion and rolling dry steps to obtain the pH test paper.

[0031] In this application, the liquid retention rate of the test paper after a single drying is 50% to 150%, for example, it can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 105%, 110%, 115%, 120%, 125%, 130%, 135%, 140%, 145%, 150%, etc.

[0032] In this application, the liquid carrying rate of the test paper after a single roll-drying is 50% to 150%, which means that after each roll-drying, the liquid carrying rate of the test paper needs to be controlled within the range of 50% to 150%, and the liquid carrying rate refers to the percentage of liquid carried by the test paper relative to the mass of the dried test paper.

[0033] In this application, if the liquid carry-over rate is too high, the indicator may move with the excess liquid during the drying process, resulting in uneven distribution of the indicator; if the liquid carry-over rate is too low, the indicator loading may be insufficient, affecting the color development effect.

[0034] Preferably, after loading the indicator solution onto the surface of the test paper carrier, a drying step is also included.

[0035] Preferably, the drying temperature is 40 to 70°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, etc.

[0036] In this application, the drying is carried out in a vacuum oven; on the one hand, drying in a vacuum environment can significantly reduce the temperature required for the drying process, avoiding excessively high temperatures from damaging the indicator molecules and causing the test paper to fail; on the other hand, during the rapid heating process, the organic solvent evaporates faster, and the indicator molecules migrate to the carrier surface more quickly, thereby increasing the load of the indicator on the carrier surface and improving the color development effect.

[0037] In this application, the pH test paper is prepared using a specific process, which helps to improve detection sensitivity and accuracy, and enables accurate and rapid measurement of pH in low-alkalinity water.

[0038] Thirdly, this application provides a method for detecting the pH of a water body, the method comprising using the pH test paper described in the first aspect for detection.

[0039] Preferably, the detection method includes: contacting the test liquid with the test strip, and using a visual recognition method to identify the color, thereby determining the pH value.

[0040] Preferably, the contact method includes: adding the test liquid to the surface of the test paper; or immersing the test paper in the test liquid.

[0041] The volume of the test liquid added is 2–50 μL, for example, it can be 2 μL, 5 μL, 8 μL, 10 μL, 12 μL, 15 μL, 18 μL, 20 μL, 22 μL, 25 μL, 28 μL, 30 μL, 32 μL, 35 μL, 38 μL, 40 μL, 42 μL, 45 μL, 48 μL, 50 μL, etc., more preferably 10–20 μL; the soaking time is 2–5 s, for example, it can be 2 s, 2.5 s, 3 s, 3.5 s, 4 s, 4.5 s, 5 s, etc.

[0042] In this application, the detection method can either directly contact the test strip with the test liquid, or the test strip can be bonded to the surface of a substrate to form a test block, and the test liquid can be brought into contact with the test strip on the surface of the test block.

[0043] Preferably, the detection method includes:

[0044] (1) The pH test paper is attached to the surface of a white plastic base plate to obtain a test block;

[0045] (2) The test solution is added to the surface of the test block obtained in step (1), and the RGB values ​​of the test block are obtained using a visual recognition device. The pH value of the test solution is obtained by comparison using an algorithm. In this application, the pH test paper in step (1) is a square with a side length of 2 to 10 mm, preferably with a side length of 5 mm.

[0046] Preferably, the method of adding in step (2) includes: adding the test liquid to the surface of the test paper of the test block; or immersing the test block with the test paper attached in the test liquid.

[0047] Preferably, the volume of the test liquid added is 2–50 μL, and the amount of liquid added varies depending on the size of the test block area. For example, it can be 2 μL, 5 μL, 8 μL, 10 μL, 12 μL, 15 μL, 18 μL, 20 μL, 22 μL, 25 μL, 28 μL, 30 μL, 32 μL, 35 μL, 38 μL, 40 μL, 42 μL, 45 μL, 48 μL, 50 μL, etc., and more preferably 10–20 μL; the soaking time is 2–5 s, for example, it can be 2 s, 2.5 s, 3 s, 3.5 s, 4 s, 4.5 s, 5 s, etc.

[0048] In this application, the alkalinity of the test solution is 100-200 ppm, for example, it can be 100 ppm, 110 ppm, 120 ppm, 130 ppm, 140 ppm, 150 ppm, 160 ppm, 170 ppm, 180 ppm, 190 ppm, 200 ppm, etc.

[0049] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0050] Compared with the prior art, the beneficial effects of this application are as follows:

[0051] The pH test strip provided in this application, by using a specific indicator solution formulation, can achieve pH detection of water with low alkalinity and has high sensitivity and accuracy; it can produce a clear and distinguishable color change in the pH range of 6.0 to 9.0, realizing rapid and portable measurement of low alkalinity water; the detection sensitivity of the pH test strip can reach 0.2 or higher. Detailed Implementation

[0052] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0053] Example 1

[0054] This embodiment provides a pH test strip, the materials of which include a test strip carrier and an indicator solution; the test strip carrier has a thickness of 0.45 mm and a density of 0.4 g / cm³. 3 The chromatographic filter paper; the indicator solution comprises 200 mL anhydrous ethanol, 125 mg bromothymol blue (1 mM), 0.8 g Tween-80 (0.5% of the total mass of the indicator solution), and sodium hydroxide solution; the concentration of the sodium hydroxide solution is 1 M, and the content is used to adjust the pH of the indicator solution to 8.0.

[0055] This embodiment provides a method for preparing pH test strips, specifically including the following steps:

[0056] The chromatography filter paper was immersed in the indicator solution, and excess liquid was squeezed out using a rubber roller to make the liquid carrying rate of the test paper 85%; the above steps were repeated once (i.e., immersion and squeezing twice), and then dried in a vacuum oven at 45°C to obtain the pH test paper.

[0057] Example 2

[0058] This embodiment provides a pH test strip, which differs from Example 1 only in that 200 mL of anhydrous ethanol is replaced with a mixed solvent of 200 mL of anhydrous ethanol and water, with a volume ratio of anhydrous ethanol to water of 7:3. All other components, amounts, and preparation methods are the same as in Example 1.

[0059] Example 3

[0060] This embodiment provides a pH test strip, the materials of which include a test strip carrier and an indicator solution; the test strip carrier has a thickness of 0.45 mm and a density of 0.4 g / cm³. 3 The chromatographic filter paper; the indicator solution comprises 200 mL anhydrous ethanol, 0.6 mM bromothymol blue, 1% cetyltrimethylammonium bromide and sodium hydroxide solution; the concentration of the sodium hydroxide solution is 1 M, and the content is used to adjust the pH of the indicator solution to 7.8; the preparation method of the pH test paper is the same as in Example 1.

[0061] Example 4

[0062] This embodiment provides a pH test strip, the materials of which include a test strip carrier and an indicator solution; the test strip carrier has a thickness of 0.45 mm and a density of 0.4 g / cm³. 3 The chromatographic filter paper; the indicator solution comprises 200 mL anhydrous ethanol, 1.5 mM bromothymol blue, 1.5% Tween-60 and sodium hydroxide solution; the concentration of the sodium hydroxide solution is 1 M, and the content is used to adjust the pH of the indicator solution to 8.2; the preparation method of the pH test paper is the same as in Example 1.

[0063] Example 5

[0064] This embodiment provides a pH test strip, which differs from Example 1 only in that the concentration of bromothymol blue in the indicator solution is 0.1 mM, while the other components, dosages, and preparation methods are the same as in Example 1.

[0065] Example 6

[0066] This embodiment provides a pH test strip, which differs from Example 1 only in that the concentration of bromothymol blue in the indicator solution is 2.5 mM, while the other components, dosages, and preparation methods are the same as in Example 1.

[0067] Example 7

[0068] This embodiment provides a pH test strip, the materials of which include a test strip carrier and an indicator solution; the test strip carrier has a thickness of 0.45 mm and a density of 0.4 g / cm³. 3 The chromatographic filter paper; the indicator solution comprises 200 mL anhydrous ethanol, 1 mM phenol red, 0.5% Tween-80 and sodium hydroxide solution; the concentration of the sodium hydroxide solution is 1 M, and the content is used to adjust the pH of the indicator solution to 7.9.

[0069] This embodiment provides a method for preparing pH test strips, specifically including the following steps:

[0070] The chromatography filter paper was immersed in the indicator solution, and the excess liquid was squeezed out with a rubber roller to make the liquid carrying rate of the test paper 85%; then it was dried in a vacuum oven at 45°C to obtain the pH test paper.

[0071] Example 8

[0072] This embodiment provides a pH test paper, which differs from Example 7 only in that the preparation method involves two immersion and rolling processes. Specifically, the chromatography filter paper is immersed in the indicator solution, and excess liquid is rolled off using a rubber roller to achieve a liquid-carrying rate of 85%. The immersion and rolling steps are then repeated, with the liquid-carrying rate of the test paper remaining at 85% after each rolling. Other components, dosages, and processes are the same as in Example 7.

[0073] Example 9

[0074] This embodiment provides a pH test strip, which differs from Example 7 only in that the preparation method involves 5 immersion and rolling cycles. Specifically, the chromatography filter paper is immersed in the indicator solution, and excess liquid is rolled off using a rubber roller to achieve a liquid-carrying rate of 85%. The immersion and rolling steps are then repeated 4 times, with the liquid-carrying rate of the test strip remaining at 85% after each rolling. Other components, dosages, and processes are the same as in Example 7.

[0075] Example 10

[0076] This embodiment provides a pH test strip, the materials of which include a test strip carrier and an indicator solution; the test strip carrier has a thickness of 0.45 mm and a density of 0.4 g / cm³. 3The chromatographic filter paper; the indicator solution comprises 200 mL anhydrous ethanol, 0.75 mM thymol blue, 0.5% Tween-80 and sodium hydroxide solution; the concentration of the sodium hydroxide solution is 1 M, and the content is used to adjust the pH of the indicator solution to 8.0.

[0077] This embodiment provides a method for preparing pH test strips, specifically including the following steps:

[0078] The chromatography filter paper is immersed in the indicator solution, and excess liquid is squeezed out using a rubber roller to make the liquid content of the test paper 80%; the above steps are repeated once (i.e., immersion and squeezing twice); then it is dried in a vacuum oven at 45°C to obtain the pH test paper.

[0079] Example 11

[0080] This embodiment provides a pH test strip, which differs from Example 10 only in that, in the preparation method, the test strip has a liquid content of 100% after each drying, while the other components, dosages, and processes are the same as in Example 10.

[0081] Example 12

[0082] This embodiment provides a pH test strip, which differs from Example 10 only in that, in the preparation method, the liquid content of the test strip after each drying is 120%, while the other components, dosages, and processes are the same as in Example 10.

[0083] Comparative Example 1

[0084] This comparative example provides a pH test strip, which differs from Example 1 only in that the indicator solution does not contain sodium hydroxide; all other components, amounts, and processes are the same as in Example 1.

[0085] Comparative Example 2

[0086] This comparative example provides a pH test strip, which differs from Example 1 only in that the indicator solution does not contain Tween-80, while the other components, dosages, and processes are the same as in Example 1.

[0087] Comparative Example 3

[0088] This comparative example provides a pH test strip, which is a commercially available ordinary laboratory pH test strip with a nominal pH testing range of 6.0-10.0.

[0089] Comparative Example 4

[0090] This comparative example provides a pH test strip, which is a commercially available pH test strip for testing swimming pool water, and can detect pH in the range of 6.2-8.4.

[0091] Application examples

[0092] This application example provides a method for detecting the pH of tap water, specifically including the following steps:

[0093] (1) Adjust the pH of the tap water with an initial alkalinity of 160 ppm (i.e. the test solution) to 6-9. The specific pH value is measured by a pH meter, and the obtained pH value of the test solution is used as the standard pH value.

[0094] (2) The pH test strips provided in Examples 1-12 and Comparative Examples 1-4, cut to 5mm×5mm, are respectively attached to the surface of white polyvinyl chloride plastic to obtain test blocks; then, 15μL of the test solution is dropped into the center of the test block, placed in a color recognition device, and a photo is taken 15 seconds after the liquid is dropped. The RGB values ​​of the test block are automatically obtained according to the algorithm, and the pH value of the test solution is obtained; by comparing the pH value obtained by the test with the standard pH value, the test accuracy of the detection method provided in this application can be known.

[0095] Performance testing

[0096] (1) Sensitivity: According to the detection method provided in the application example, test the RGB values ​​of the test liquid (the same tap water) with different pH values, and calculate the sum of the RGB differences, denoted as △. The calculation formula is △=|R1-R2|+|G1-G2|+|B1-B2|; where |R1-R2|, |G1-G2|, and |B1-B2| are the absolute values ​​of the difference between the maximum and minimum R values, the difference between the maximum and minimum G values, and the difference between the maximum and minimum B values ​​obtained for the test liquids with different pH values, respectively. Taking Example 1 as an example, △=|140-99|+|139-127|+|118-135|; the larger the △ value, the higher the resolution of the test strip for the pH of the test liquid, and the better the sensitivity of the test strip.

[0097] (2) Accuracy: According to the detection method provided in the application example, test the pH value of the test solution and compare it with the standard pH value. The closer the two are, the higher the accuracy. Accuracy is characterized by the difference between the pH value of the test solution and the standard pH value.

[0098] The specific test results are shown in Tables 1 and 2. Table 1 shows the pH values ​​of the test solutions from 6.5 to 8.5, and Table 2 shows the pH values ​​of the test solutions from 6 to 9. The pH values ​​in both Tables 1 and 2 were obtained using a pH meter. In Table 1, “” indicates that no test was performed. Table 2 uses the pH test strip provided in Example 1 of this application as an example to compare its sensitivity and accuracy with the pH test strip provided in Comparative Example 4 when testing test solutions with pH values ​​from 6 to 9.

[0099] Table 1

[0100] Table 2

[0101] As shown in Tables 1 and 2, the pH test strips provided in this application use an indicator solution with a specific formula. The resulting test strips can be used to detect water bodies with low alkalinity, and have high detection sensitivity and accuracy. Compared with commercially available pH test strips, the pH test strips provided in this application all have high Δ values.

[0102] As shown in Table 1, the pH test strip provided in this application can test test solutions with a pH value of 6.5 to 8.5 with a Δ value ≥ 19, and can even reach 65 or above. As shown in Table 2, the pH test strip provided in this application can test test solutions with a pH value of 6 to 9 with a Δ value of 128, which is significantly higher than that of commercially available test strips, and the testing accuracy is also higher than that of commercially available test strips.

[0103] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A pH test strip, characterized in that, The pH test strip is made of a test strip carrier and an indicator solution; The indicator solution includes an indicator, a solvent, an acid-base regulator, and a surfactant; The indicator includes any one or a combination of at least two of phenol red, cresol red, neutral red, α-naphtholphthalein, thymol blue, or bromothymol blue.

2. The pH test paper according to claim 1, characterized in that, The concentration of the indicator in the indicator solution is 0.2–2 mM.

3. The pH test paper according to claim 1, characterized in that, The solvent includes organic solvents, or a mixture of organic solvents and water; The organic solvents include volatile organic solvents.

4. The pH test paper according to claim 3, characterized in that, The organic solvent includes any one or a combination of at least two of ethanol, methanol, or acetone.

5. The pH test paper according to claim 3, characterized in that, The solvent includes a mixture of an organic solvent and water, wherein the volume ratio of the organic solvent to water is (0.1 to 10):

1.

6. The pH test paper according to claim 1, characterized in that, The acid-base regulator adjusts the pH of the indicator solution to 6-9.

7. The pH test paper according to claim 1, characterized in that, The acid-base regulator includes a strong acid or a strong base; The strong acid includes dilute hydrochloric acid and / or dilute sulfuric acid; the strong base includes sodium hydroxide and / or potassium hydroxide.

8. The pH test paper according to claim 1, characterized in that, The surfactant in the indicator solution has a mass percentage content of 0.2% to 2%.

9. The pH test paper according to claim 1, characterized in that, The surfactant includes at least one or a combination of at least two of the following: quaternary ammonium salt surfactant, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, fatty alcohol polyoxyethylene ether, or alkylphenol polyoxyethylene ether.

10. The pH test paper according to claim 1, characterized in that, The test paper carrier includes filter paper or cellulose membrane; The thickness of the test strip carrier is 0.2–0.5 mm, and the density of the test strip carrier is ≥0.35 g / cm³. 3 .

11. A method for preparing pH test paper according to any one of claims 1 to 10, characterized in that, The preparation method includes the following steps: The pH test paper is obtained by loading the indicator solution onto the surface of the test paper carrier.

12. The method for preparing pH test paper according to claim 11, characterized in that, The loading method includes: immersing the test paper carrier in an indicator solution, squeezing it dry, and obtaining a test paper that has undergone one immersion and squeezing.

13. The method for preparing pH test paper according to claim 12, characterized in that, The soaking time is 5 to 30 seconds.

14. The method for preparing pH test paper according to claim 12, characterized in that, The number of impregnation cycles is 1 to 5; The liquid retention rate of the test paper after a single drying cycle is 50%–150%.

15. The method for preparing pH test paper according to claim 11, characterized in that, After the indicator solution is loaded onto the surface of the test paper carrier, the process also includes a drying step; The drying temperature is 40–70°C.

16. A method for detecting the pH of water, characterized in that, The detection method includes using pH test paper according to any one of claims 1 to 10 for detection.

17. The method for detecting pH in water according to claim 16, characterized in that, The detection method includes: contacting the test liquid with the test strip, and using a visual recognition method to identify the color, thereby determining the pH value.

18. The method for detecting pH in water according to claim 17, characterized in that, The contact method includes: adding the test liquid to the surface of the test strip; or immersing the test strip in the test liquid; The volume of the test liquid added is 2–50 μL; the soaking time is 2–5 s.

19. The method for detecting pH in water according to claim 18, characterized in that, The detection method includes: (1) The pH test paper is attached to the surface of a white plastic base plate to obtain a test block; (2) Add the test liquid to the surface of the test block obtained in step (1), use a visual recognition device to obtain the RGB value of the test block, and use an algorithm to compare and obtain the pH value of the test liquid.

20. The method for detecting pH in water according to claim 16, characterized in that, The alkalinity of the test solution is 100–200 ppm.

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