PH test paper, preparation method thereof and water pH detection method

Abstract

The invention provides pH test paper, a preparation method thereof and a water pH detection method. The pH test paper is prepared from a test paper carrier and an indicator solution, the indicator solution comprises an indicator, a solvent, an acid-base regulator and a surfactant; the indicator comprises any one or a combination of at least two of phenol red, cresol red, neutral red, alpha-naphtholphthalein, thymol blue or bromothymol blue. When the pH test paper is used for detecting the pH of a water body, the color change is obvious, the detection sensitivity and accuracy are high, the reliability is high, and the pH test paper can be used for detecting the water body with low alkalinity and low buffer capacity.

Description

Technical Field

[0001] The invention belongs to the technical field of water body detection, and particularly relates to a pH test paper and a preparation method thereof, and a method for detecting the pH of a water body. Background Art

[0002] In daily life and public health, pH monitoring is of vital importance for ensuring water quality safety and maintaining public health. For example, the pH value of swimming pool water will directly affect its disinfection effect, water quality stability and irritation to swimmers' skin. Too high or too low pH values ​​may lead to deterioration of water quality and increase the risk of disease transmission. The pH value of tap water is also one of the important indicators for evaluating its safety and stability. Therefore, accurate and rapid monitoring of the pH value of these water bodies is crucial to protecting public health.

[0003] There are many ways to test the pH of water quality. Among them, pH test paper is a portable and economical detection method that can meet the needs of rapid screening. The pH value of water is detected by pH test paper through a chemical reaction between the indicator loaded on the test paper and the test liquid to develop color, and then compared with the standard color card to obtain the pH value of the test liquid. Usually, the acid-base indicator in the pH test paper belongs to an organic weak acid / weak acid salt, which has a dissociation equilibrium in the aqueous solution, and the indicator itself has a certain buffering capacity due to its weak acid properties. After the indicator comes into contact with the test liquid, it consumes the H + or OH - , the dissociation equilibrium shifts, the ratio of the acid form and the basic form of the indicator changes, and the color of the indicator and the test paper changes accordingly.

[0004] The H in the test solution + or OH - Consumption will also cause changes in its own pH: the highly buffered test solution can resist this change, making the indicator and H + or OH - After the reaction occurs, the test solution still maintains its original pH value. At this time, the test paper test result is the true pH value of the test solution. The test solution with low buffering cannot resist this change. + or OH -As the pH value of the liquid being tested changes, it will also change. Therefore, the test paper actually tests the pH value of the liquid to be tested after the change, which is different from the actual pH value of the liquid to be tested. The size of the gap depends on the buffering capacity of the liquid to be tested. For neutral, weakly acidic and weakly alkaline aqueous solutions, the buffering capacity is usually measured by the alkalinity index. For water bodies such as tap water, drinking water, and swimming pool water that are related to daily life and public health, the pH values ​​are mostly in the range of 5 to 9, that is, neutral, weakly acidic or weakly alkaline. These water bodies are usually very clean and contain few soluble substances. From a chemical point of view, the buffering capacity of these water bodies is very poor and the alkalinity is relatively low. However, most commercially available pH test papers, including broad pH test papers and precision pH test papers, are mainly used to measure buffered solutions in laboratory environments; when it is necessary to detect low-buffering and low-alkalinity water, especially when testing neutral water such as tap water and swimming pool water, they seem to be unable to do so. The measurement results are often inaccurate or difficult to interpret due to unclear color changes or insufficient response sensitivity. In addition, other components in low-alkalinity water (such as residual chlorine, hardness ions, etc.) may also interfere with the performance of the test paper, further affecting the reliability of the test results.

[0005] Normally, the pH of this type of water can only be accurately tested using a pH meter (electrode method), but the pH meter is relatively expensive, requires frequent calibration and maintenance, and cannot meet the needs of rapid testing in some scenarios.

[0006] Therefore, developing a test paper that can accurately, quickly and conveniently detect the pH value of low-buffered, low-alkalinity water is a problem to be solved urgently in the art. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention aims to provide a pH test paper and a preparation method thereof, and a method for detecting the pH of a water body. When the pH test paper detects the pH of a water body, the color changes significantly, the detection sensitivity and accuracy are high, the reliability is strong, and it can be used to detect water bodies with low alkalinity and low buffering capacity.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a pH test paper, wherein the material of the pH test paper includes a test paper 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 of phenol red, cresol red, neutral red, α-naphtholphthalein, thymol blue or bromothymol blue, or a combination of at least two thereof.

[0010] In the present invention, the acid-base regulator can adjust the initial pH value of the indicator so that the indicator is loaded in the test paper carrier in a specific acidified or alkaline form. The color development pH range of the indicator is usually within the interval of its dissociation constant pKa±1; if the initial pH of the indicator is not adjusted, it is likely that the pH value after the reaction between the test liquid and the indicator is not within this interval, resulting in the test paper not having the color change function. The ionization equilibrium of the indicator is controlled under specific initial pH conditions so that the final pH value of the test liquid can fall within the color development range of the indicator, thereby ensuring that the indicator can undergo obvious color changes and improving the detection sensitivity and accuracy; the surfactant can significantly reduce the surface tension of the test paper carrier, making it easier for the indicator solution to penetrate into the tiny pores and fiber structure of the test paper carrier; and the surfactant can disperse the indicator molecules evenly in the solution through its dispersing effect, prevent the formation of agglomerates, and ensure that the indicator on the test paper is evenly distributed, which is conducive to further improving the detection sensitivity and accuracy; therefore, by adopting a specific formula of indicator solution, the obtained pH test paper has high detection sensitivity and accuracy, strong reliability, and can be used for the detection of pH 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, 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 the present invention, the concentration of the indicator affects the load of the indicator on the test paper carrier. For the test liquid with lower alkalinity, since the buffering property of the indicator and the buffering property brought by the alkalinity of the test liquid are in a competitive relationship, and the buffering property of the indicator is directly related to the concentration of its solution, therefore, by controlling the concentration of the indicator within a specific range, the load of the indicator on the test paper carrier can be controlled within a specific range, which is conducive to better color development of the indicator in the pH range of the test liquid. If the indicator load is too high, the color change of the indicator is not obvious; if the load is too low, the color saturation of the test paper will be poor and it will be unfavorable for observation.

[0013] Preferably, the solvent comprises an organic solvent, or a mixed solvent of an organic solvent and water, preferably an organic solvent; and the organic solvent comprises a volatile organic solvent.

[0014] In the present invention, the advantages of the volatile organic solvent are mainly reflected in three aspects: first, the volatile organic solvent has a lower surface tension and good wettability, which can make the indicator solution more effectively penetrate into the tiny pores and fiber structure of the test paper carrier, enhance the effect of the capillary action of the fiber structure in a wet state, so that more indicator molecules are carried by the solvent and attached to the inside of the test paper carrier, thereby reducing the use concentration of the indicator solution; second, since the indicator is usually not resistant to high temperature, a low-boiling point volatile organic solvent is selected, and the drying temperature is low, which is more conducive to the stability of the indicator, and the residual amount of the solvent on the test paper carrier is lower; third, The volatile organic solvent vaporizes quickly 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, forming a longitudinal content gradient distribution inside the carrier. More indicators are distributed on the surface of the test paper carrier, making the color saturation of the test paper surface higher and easier to identify the color when the test paper load is the same; when the color saturation of the test paper surface is the same, the indicator load required for the test paper is lower (less indicator in the non-surface area), which is beneficial to increase the pH change value of the indicator, thereby presenting a better color development range and effect.

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

[0016] Preferably, the solvent comprises a mixed solvent of an organic solvent and water, and the volume ratio of the organic solvent to water is (0.1-10):1, wherein the specific value in (0.1-10) 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 regulator 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 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.

[0019] Preferably, the mass percentage of the surfactant in the indicator solution is 0.2-2%, 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% and the like.

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

[0021] In the present invention, the quaternary ammonium salt surfactant includes normal N-alkyl trimethyl ammonium halide, wherein N is 10 to 22, representing the number of carbon atoms in the alkyl group, for example, it can be 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 paper carrier is 0.2-0.5 mm, for example, 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 paper carrier is ≥ 0.35 g / cm 3 , for example, it can be 0.35 g / cm 3 , 0.4g / cm 3 , 0.45g / cm 3 , 0.5g / cm 3 , 0.55g / cm 3 wait.

[0024] In a second aspect, the present invention provides a method for preparing the pH test paper according to the first aspect, the preparation method comprising the following steps:

[0025] The indicator solution is loaded on the surface of the test paper carrier to obtain the pH test paper.

[0026] Preferably, the loading method comprises: soaking the test paper carrier in an indicator solution, and rolling it dry to obtain a test paper that has been dipped once.

[0027] In the present invention, the squeezing is performed by a rubber roller to remove excess liquid in the test paper carrier.

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

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

[0030] In the present invention, when the number of times of padding is greater than 1, the loading method comprises: soaking the test paper carrier in the indicator solution, rolling dry, and then repeating the soaking and rolling dry steps to obtain the pH test paper.

[0031] In the present invention, the liquid carrying rate of the test paper after a single rolling is 50-150%, 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 the present invention, the liquid carrying rate of the test paper after a single squeeze is 50-150%, which means that after each squeeze, the liquid carrying rate of the test paper needs to be controlled within the range of 50-150%, and the liquid carrying rate refers to the percentage of the liquid carried by the test paper to the mass of the dry test paper.

[0033] In the present invention, if the liquid carrying 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 carrying rate is too low, the indicator may not be loaded sufficiently, affecting the color development effect.

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

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

[0036] In the present invention, the drying is carried out in a vacuum oven; on the one hand, drying in a vacuum environment can greatly reduce the temperature required for the drying process, avoiding excessively high temperatures that damage the indicator molecules and cause the test paper to fail; on the other hand, during the rapid heating process, the organic solvent evaporates faster, and the indicator molecules accelerate their migration to the carrier surface, thereby increasing the loading amount of the indicator on the carrier surface, thereby improving the color development effect.

[0037] In the present invention, the pH test paper adopts a specific preparation process, which is conducive to improving the detection sensitivity and accuracy, and realizing accurate and rapid measurement of the pH of low-alkalinity water bodies.

[0038] In a third aspect, the present invention provides a method for detecting pH of water, the detection method comprising using the pH test paper described in the first aspect for detection.

[0039] Preferably, the detection method comprises: contacting the test liquid with the test paper, identifying the color using a visual recognition method, and thus determining the pH value.

[0040] Preferably, the contacting method includes: dropping the liquid to be tested onto the surface of the test paper; or, immersing the test paper in the liquid to be tested.

[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 immersion 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 the present invention, the detection method can directly contact the test paper with the test liquid, or the test paper can be attached to the surface of the substrate to prepare a test block, and the test liquid is contacted with the test paper on the surface of the test block.

[0043] Preferably, the detection method comprises:

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

[0045] (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 obtain the pH value of the test liquid by algorithm comparison. In the present invention, the pH test paper in step (1) is a square with a side length of 2 to 10 mm, preferably a side length of 5 mm.

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

[0047] Preferably, the volume of the test liquid added is 2 to 50 μL, and the amount of liquid dropped varies according to the size of the test 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., more preferably 10 to 20 μL; the immersion time is 2 to 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 the present invention, 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 the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] The pH test paper provided by the present invention can detect the pH of water bodies with relatively low alkalinity by adopting a specific indicator solution formula, and has high sensitivity and accuracy; it can produce clearly discernible color changes within the pH range of 6.0 to 9.0, thereby realizing rapid and portable measurement of low-alkalinity water; the detection sensitivity of the pH test paper can reach 0.2 or above. DETAILED DESCRIPTION

[0052] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0053] Example 1

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

[0055] This embodiment provides a method for preparing a pH test paper, which specifically comprises the following steps:

[0056] The chromatography filter paper is immersed in the indicator solution, and the excess liquid is rolled out with a rubber roller to make the liquid rate of the test paper 85%; the above steps are repeated once (i.e., the immersion and rolling are performed twice), and the pH test paper is dried in a vacuum oven at 45°C to obtain the pH test paper.

[0057] Example 2

[0058] This embodiment provides a pH test paper, which differs from Embodiment 1 only in that 200 mL of anhydrous ethanol is replaced by 200 mL of a mixed solvent of anhydrous ethanol and water, and the volume ratio of the two (anhydrous ethanol: water) is 7:3, and the other components, amounts and preparation methods are the same as those in Embodiment 1.

[0059] Example 3

[0060] This embodiment provides a pH test paper, the material includes a test paper carrier and an indicator solution; the test paper carrier has a thickness of 0.45 mm and a density of 0.4 g / cm 3 The indicator solution comprises 200 mL of anhydrous ethanol, 0.6 mM bromothymol blue, 1% hexadecyltrimethylammonium bromide and a sodium hydroxide solution; the concentration of the sodium hydroxide solution is 1 M, and the content is adjusted to adjust the pH of the indicator solution to 7.8; the preparation method of the pH test paper is the same as that of Example 1.

[0061] Example 4

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

[0063] Example 5

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

[0065] Example 6

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

[0067] Example 7

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

[0069] This embodiment provides a method for preparing a pH test paper, which specifically comprises the following steps:

[0070] The chromatography filter paper is immersed in the indicator solution, and the excess liquid is squeezed out by a rubber roller to make the liquid carrying rate of the test paper 85%; and then the test paper is 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 Embodiment 7 only in that, in the preparation method, the number of immersion and rolling is 2 times, that is, the chromatography filter paper is immersed in the indicator solution, and the excess liquid is rolled out with a rubber roller so that the liquid carrying rate of the test paper is 85%; then the immersion and rolling steps are repeated, and the liquid carrying rate of the test paper after each rolling is 85%. Other components, amounts and processes are the same as those in Embodiment 7.

[0073] Example 9

[0074] This embodiment provides a pH test paper, which differs from Embodiment 7 only in that, in the preparation method, the number of immersion and rolling is 5 times, that is, the chromatography filter paper is immersed in the indicator solution, and the excess liquid is rolled out with a rubber roller so that the liquid carrying rate of the test paper is 85%; then the immersion and rolling steps are repeated 4 times, and the liquid carrying rate of the test paper after each rolling is 85%. Other components, amounts and processes are the same as those in Embodiment 7.

[0075] Example 10

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

[0077] This embodiment provides a method for preparing a pH test paper, which specifically comprises the following steps:

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

[0079] Embodiment 11

[0080] This embodiment provides a pH test paper, which is different from Embodiment 10 only in that, in the preparation method, the liquid carrying rate of the test paper after each rolling is 100%, and other components, dosages and processes are the same as those in Embodiment 10.

[0081] Example 12

[0082] This embodiment provides a pH test paper, which is different from Example 10 only in that, in the preparation method, the liquid carrying rate of the test paper after each rolling is 120%, and other components, dosages and processes are the same as those in Example 10.

[0083] Comparative Example 1

[0084] This comparative example provides a pH test paper, which is different from Example 1 only in that there is no sodium hydroxide in the indicator solution, and other components, dosages and processes are the same as those in Example 1.

[0085] Comparative Example 2

[0086] This comparative example provides a pH test paper, which is different from Example 1 only in that Tween-80 is not contained in the indicator solution, and other components, dosages and processes are the same as those in Example 1.

[0087] Comparative Example 3

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

[0089] Comparative Example 4

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

[0091] Application Examples

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

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

[0094] (2) The pH test papers provided in Examples 1 to 12 and Comparative Examples 1 to 4, cut into 5 mm × 5 mm pieces, were respectively attached to the surface of white polyvinyl chloride plastic to obtain test blocks; then, 15 μL of the test solution was dripped into the center of the test block, and the test block was placed in a color recognition device. A photo was taken 15 seconds after dripping the solution, and the RGB value of the test block was automatically obtained according to the algorithm, and the pH value of the test solution was obtained; the pH value obtained by the test was compared with the standard pH value to know the test accuracy of the detection method provided by the present invention.

[0095] Performance Testing

[0096] (1) Sensitivity: According to the detection method provided in the application example, the RGB values ​​of the test liquids with different pH values ​​(the same type of tap water) are tested, and the sum of the RGB differences is calculated, which is recorded as △. The calculation formula is △=|R1-R2|+|G1-G2|+|B1-B2|; wherein |R1-R2|, |G1-G2|, and |B1-B2| are the absolute values ​​of the differences between the maximum and minimum values ​​of the R value, the absolute values ​​of the differences between the maximum and minimum values ​​of the G value, and the absolute values ​​of the differences between the maximum and minimum values ​​of the B value obtained by testing 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 discrimination degree of the test paper for the pH of the test liquid, and the better the sensitivity of the test paper.

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

[0098] The specific test results are shown in Tables 1 and 2; Table 1 shows that the pH value of the test liquid is 6.5-8.5, and Table 2 shows that the pH value of the test liquid is 6-9. The pH values ​​in Tables 1 and 2 are all obtained by testing with a pH meter; wherein, “ / ” in Table 1 indicates that no test was performed; Table 2 takes the pH test paper provided in Example 1 of the present invention as an example, and compares its sensitivity and accuracy with the pH test paper provided in Comparative Example 4 in testing the test liquid with a pH value of 6-9.

[0099] Table 1

[0100]

[0101]

[0102] Table 2

[0103]

[0104] As can be seen from Tables 1 and 2, the pH test paper provided by the present invention uses an indicator solution with a specific formula, and the obtained test paper can be used to detect low-alkalinity water bodies, and has high detection sensitivity and high accuracy; compared with commercially available pH test papers, the pH test papers provided by the present invention have high △ values.

[0105] It can be seen from Table 1 that the pH test paper provided by the present invention tests the test liquid with a pH value of 6.5 to 8.5, and the △ value is ≥19, and can even reach 65 or above; it can be seen from Table 2 that the pH test paper provided by the present invention tests the test liquid with a pH value of 6 to 9, and the △ value reaches 128, which is significantly higher than the commercially available test paper, and the test accuracy is higher than that of the commercially available test paper.

[0106] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

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

2. pH test paper according to claim 1, characterized in that, The concentration of the indicator in the indicator solution is 0.2-2 mM, preferably 0.5-1 mM.

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

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

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

1.

6. 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. 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. pH test paper according to claim 1, characterized in that, The mass percentage of the surfactant in the indicator solution is 0.2-2%.

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

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

11. A method for preparing a pH test paper according to any one of claims 1 to 10, characterized in that: The preparation method comprises the following steps: The indicator solution is loaded on the surface of the test paper carrier to obtain the pH test paper.

12. The preparation method according to claim 11, characterized in that: The loading method comprises: soaking the test paper carrier in an indicator solution, and rolling it to obtain the test paper after one-time rolling.

13. The preparation method according to claim 12, characterized in that: The soaking time is 5 to 30 seconds, preferably 8 to 15 seconds.

14. The preparation method according to claim 12, characterized in that: The number of padding is 1 to 5 times; The liquid content of the test paper after a single rolling is 50-150%.

15. The preparation method according to claim 11, characterized in that: After the indicator solution is loaded on the surface of the test paper carrier, a drying step is also included; The drying temperature is 40-70°C.

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

17. The detection method according to claim 16, characterized in that: The detection method comprises: contacting the test liquid with the test paper, identifying the color by a visual recognition method, and thus determining the pH value.

18. The detection method according to claim 17, characterized in that: The contact method includes: dropping the test liquid onto the surface of the test paper; or, immersing the test paper in the test liquid; The volume of the test liquid added is 2 to 50 μL; the soaking time is 2 to 5 seconds.

19. The detection method according to claim 18, characterized in that: The detection method comprises: (1) attaching the pH test paper 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 obtain the pH value of the test liquid through algorithm comparison.

20. The preparation method according to claim 16, characterized in that: The alkalinity of the liquid to be tested is 100-200 ppm.

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