Analysis method for measuring pH value of aqueous solution by using methyl red
By mixing methyl red solution with a standard solution to establish an absorbance curve and calculating the pH value of the water sample to be tested, the problem of inaccurate pH measurement of aqueous solutions in existing technologies is solved, and accurate measurement and online monitoring are achieved.
Patent Information
- Application Number
- CN202511576897.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-31
- Publication Date
- 2025-12-02
AI Technical Summary
Existing technologies cannot accurately measure the pH value of aqueous solutions, especially in ultrapure water where the readings are unstable. Furthermore, pH electrodes require calibration and replacement, leading to inaccurate measurements.
Methyl red solution was mixed with standard solutions of different pH values. A working curve was established by detecting the absorbance curve of the colorimetric solution. The pH value of the water sample to be tested was calculated using this curve and measured by spectrophotometry.
It enables accurate measurement of pH values in aqueous solutions, broadens the application range of acid-base indicators, overcomes the measurement inaccuracy problem caused by pH electrode aging, and is suitable for online monitoring.
Smart Images
Figure CN121049240A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of pH measurement technology, and more particularly to an analytical method for measuring the pH of aqueous solutions using methyl red. Background Technology
[0002] pH value is a common indicator in daily production and life, and it needs to be measured in many situations. Our commonly used method on-site is the pH electrode method, but the performance of pH electrodes changes over time, requiring calibration and replacement. Furthermore, there are still some problems with measuring pH in ultrapure water; the pH readings used for ultrapure water testing are generally very unstable. We utilize the principle of acid-base indicators changing color with pH, combined with our spectrophotometric measuring device, to measure the pH value of solutions.
[0003] Generally, we use pH indicators to measure whether the pH of a solution is within a certain range. For example, under laboratory conditions, methyl red's color change range is roughly between pH 4.4 and 6.2. Within this range, methyl red will change color with changes in the solution's acidity or alkalinity. As the pH changes, its color will gradually transition from red to yellow or orange. We use methyl red to test whether the solution's pH is within the 4.4~6.2 range. We cannot know the specific pH value of the solution.
[0004] Therefore, it is very important to provide an analytical method that can specifically indicate the pH value of a solution. Summary of the Invention
[0005] The purpose of this invention is to provide an analytical method for measuring the pH value of an aqueous solution using methyl red, thereby solving the technical problem that existing technologies cannot measure the specific pH value of a solution.
[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides an analytical method for measuring the pH value of an aqueous solution using methyl red, comprising the following steps: 1) Mix standard solutions with different pH values and methyl red solution to obtain a colorimetric solution. Then, use a detection device to detect the absorbance curve of the colorimetric solution, read the absorbance, and plot a working curve with the pH value of the colorimetric solution as the x-axis and the absorbance as the y-axis. 2) Mix the water sample to be tested with methyl red solution and then test to obtain the absorbance value. Substitute the absorbance value into the working curve to calculate the pH value of the water sample to be tested and display its pH value.
[0007] Furthermore, the working curve is: y = 0.0748x 2 -1.0591x+3.7646.
[0008] Furthermore, the pH value of the standard solution is 4 to 7.2.
[0009] Furthermore, in step 1), the volume ratio of the standard solution to the methyl red solution is 8~12:0.5.
[0010] Furthermore, in step 2), the volume ratio of the water sample to be tested to the methyl red solution is 8~12:0.5.
[0011] Furthermore, the effective optical path of the detection device is 20~40mm, and the wavelength is 500~600nm.
[0012] Furthermore, in steps 1) and 2), the mass concentration of the methyl red solution is independently 0.002~0.006%.
[0013] The beneficial effects of this invention are: The analytical method of this invention enables online determination of the pH value of a solution, thereby broadening the application range of acid-base indicators. Existing acid-base indicators can only be used to estimate pH values over a relatively wide range, while the analytical method of this invention uses the acid-base indicator as a precise pH meter, overcoming measurement inaccuracies caused by factors such as pH electrode aging. Furthermore, this invention is also suitable for online monitoring, particularly in situations where color changes are used as the endpoint determination criterion for titration. Attached Figure Description
[0014] Figure 1 This is a schematic diagram of an instrument for measuring the pH value of a solution using methyl red. Figure 2 Chemical flow diagram for an instrument that uses methyl red to measure the pH of a solution; Figure 3 A diagram illustrating the measurement steps of an instrument for measuring the pH value of a solution using methyl red; Figure 4 The scan curves of methyl red at different pH values; Figure 5 The working curve of the instrument for measuring the pH value of a solution using methyl red. Detailed Implementation
[0015] This invention provides an analytical method for measuring the pH value of an aqueous solution using methyl red, comprising the following steps: 1) Mix standard solutions with different pH values and methyl red solution to obtain a colorimetric solution. Then, use a detection device to detect the absorbance curve of the colorimetric solution, read the absorbance, and plot a working curve with the pH value of the colorimetric solution as the x-axis and the absorbance as the y-axis. 2) Mix the water sample to be tested with methyl red solution and then test it. Substitute the mixture into the working curve to calculate the pH value of the water sample to be tested and display its pH value.
[0016] In this invention, the working curve is: y = 0.0748x 2 -1.0591x+3.7646.
[0017] In this invention, the pH value of the standard solution is 4 to 7.2.
[0018] In this invention, in step 1), the volume ratio of the standard solution to the methyl red solution is 8~12:0.5, preferably 9~11:0.5, and more preferably 10:0.5.
[0019] In this invention, in step 2), the volume ratio of the water sample to be tested to the methyl red solution is 8~12:0.5, preferably 9~11:0.5, and more preferably 10:0.5.
[0020] In this invention, the effective optical path of the detection device is 20-40 mm, preferably 25-35 mm, and more preferably 30 mm; the wavelength is 500-600 nm, preferably 520-580 nm, and more preferably 550 nm.
[0021] In this invention, in steps 1) and 2), the mass concentration of the methyl red solution is independently 0.002~0.006%, preferably 0.003~0.005%, and more preferably 0.004%.
[0022] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0023] Example 1
[0024] 10 mL of standard solutions with pH values of 4, 4.4, 4.8, 5.2, 5.6, 6, 6.4, 6.8, and 7.2 were mixed with 0.5 mL of 0.004% methyl red solution to obtain colorimetric solutions. The absorbance curves of these solutions were then measured using a detection device. Figure 4 As shown, the cuvette of this device has an effective optical path of 30 mm and a wavelength of 550 nm. The absorbance values are shown in Table 1.
[0025] Table 1. Absorbance values of standard solutions at different pH values
[0026] A working curve was plotted with the pH value of the colorimetric solution on the x-axis and the absorbance on the y-axis. The working curve was obtained as: y = 0.0748x 2 -1.0591x+3.7646, as Figure 5 As shown, R 2 =0.9991; 10 mL of the water sample to be tested was mixed with 0.5 mL of 0.004% methyl red solution and the absorbance was measured. The absorbance was 0.170. The pH value of the water sample was calculated by substituting the absorbance value into the working curve and the pH value was shown to be 5.6.
[0027] Figure 4 To obtain 10 mL solutions with pH values of 4.0, 4.4, 4.8, 5.2, 5.6, 6.0, 6.4, 6.8, and 7.2, 0.5 mL of 0.004% methyl red solution was added. Using a cuvette with an effective path length of 30 mm, absorbance curves were scanned from 400 nm to 700 nm. Figure 4 It can be seen that selecting a wavelength of 550nm and reading the absorbance is the optimal choice.
[0028] Figure 5 The working curve is obtained by plotting pH on the x-axis and the absorbance at 500 nm (effective optical path length is 30 mm) at the corresponding pH value on the y-axis.
[0029] As shown in the above embodiments, this invention provides an analytical method for measuring the pH value of an aqueous solution using methyl red, comprising the following steps: mixing standard solutions with different pH values and methyl red solution to obtain a colorimetric solution; then using a detection device to detect the absorbance curve of the colorimetric solution, reading the absorbance, and plotting a working curve with the pH value of the colorimetric solution on the x-axis and the absorbance on the y-axis; mixing the water sample to be tested with the methyl red solution and detecting the pH value, substituting the result into the working curve, calculating the pH value of the water sample to be tested, and displaying the pH value. This analytical method of the present invention uses an acid-base indicator as a precise pH meter, enabling online measurement of the pH value of a solution, thereby broadening the application range of acid-base indicators.
[0030] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. An analytical method for measuring the pH value of an aqueous solution using methyl red, characterized in that, Includes the following steps: 1) Mix standard solutions with different pH values and methyl red solution to obtain a colorimetric solution. Then, use a detection device to detect the absorbance curve of the colorimetric solution, read the absorbance, and plot a working curve with the pH value of the colorimetric solution as the x-axis and the absorbance as the y-axis. 2) Mix the water sample to be tested with methyl red solution and then test to obtain the absorbance value. Substitute the absorbance value into the working curve to calculate the pH value of the water sample to be tested and display its pH value.
2. The analytical method for measuring the pH value of an aqueous solution using methyl red according to claim 1, characterized in that, The working curve is: y = 0.0748x 2 -1.0591x+3.7646.
3. The analytical method for measuring the pH value of an aqueous solution using methyl red according to claim 2, characterized in that, The pH value of the standard solution is 4 to 7.
2.
4. The analytical method for measuring the pH value of an aqueous solution using methyl red according to claim 3, characterized in that, In step 1), the volume ratio of the standard solution to the methyl red solution is 8~12:0.
5.
5. The analytical method for measuring the pH value of an aqueous solution using methyl red according to claim 4, characterized in that, In step 2), the volume ratio of the water sample to be tested to the methyl red solution is 8~12:0.
5.
6. The analytical method for measuring the pH value of an aqueous solution using methyl red according to claim 5, characterized in that, The effective optical path of the detection device is 20~40mm, and the wavelength is 500~600nm.
7. The analytical method for measuring the pH value of an aqueous solution using methyl red according to claim 6, characterized in that, In steps 1) and 2), the mass concentration of the methyl red solution is independently 0.002~0.006%.