A method for detecting methanol in an ethanol solution

Abstract

The application discloses a method for recognizing and detecting methanol in an ethanol solution. The method utilizes the transesterification reaction between methanol in a mixed solution and a reactive ester under the promotion of an amine to generate a p-nitrophenol negative ion with ultraviolet absorption. The ultraviolet intensity is detected by using an ultraviolet spectrometer, so that the methanol content can be measured. The method fully utilizes the principle of the transesterification reaction, a catalyst diethylamine, the generation of a p-nitrophenol negative ion (4-NP), the generation of ultraviolet absorption, the detection of the ultraviolet intensity by using the ultraviolet spectrometer, and the purpose of simply, sensitively and specifically detecting the methanol.

Description

Technical Field

[0001] This invention belongs to the field of chemical detection technology, specifically relating to a method for identifying and detecting methanol in ethanol solutions. Background Technology

[0002] Ethanol, also known as alcohol, anhydrous ethanol, or grain alcohol, is a clear, colorless liquid and a major component of alcoholic beverages such as beer, wine, and brandy. Ethanol's ability to homogenize food coloring makes it a common food additive to enhance the flavor of food extracts. For example, vanilla extract, a common food flavoring, is made by solidifying and processing vanilla beans in a solution of ethanol and water.

[0003] Methanol is a colorless, volatile liquid with a pungent odor. Ingestion of more than 0.3g can cause blurred vision, difficulty breathing, and damage to the nervous system, and in severe cases, may be life-threatening. Because of its low price, methanol is often added to alcoholic beverages to reduce brewing costs and increase profits, causing irreversible harm to human health. As a flammable substance, methanol vapor can mix with air and ignite violently upon contact with an open flame, potentially leading to a violent combustion and explosion. Therefore, effective detection of methanol in solutions has become a major focus of research.

[0004] Existing technologies for methanol detection mainly include colorimetric methods, gas chromatography, immobilized enzyme-flow injection analysis, immobilized enzyme FIA, enzyme electrode methods, laser Raman spectroscopy, and Fourier transform infrared spectroscopy. However, these methods have significant limitations, such as expensive instruments, complex processing, and time-consuming procedures, which are not conducive to detection. Therefore, developing a detection method for methanol identification under mild conditions has become a pressing issue. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for identifying and detecting methanol in ethanol solutions.

[0006] The technical solution of the present invention is as follows:

[0007] A method for identifying and detecting methanol in an ethanol solution, comprising the following steps:

[0008] (1) Add equal amounts of amine catalyst solution to methanol series standard working solutions of different volume ratios, and then add an active ester solution containing a strong electron-withdrawing nitro group. React in a constant temperature water bath at 24-26℃ for 15-25 min to obtain several reaction solutions corresponding to methanol baptism standard working solutions of different volume ratios. Measure the absorbance of these reaction solutions with an ultraviolet spectrophotometer, and then plot the standard working curve based on the absorbance and the methanol concentration in the methanol series standard working solutions. The solvent of the above methanol series standard working solutions is ethanol.

[0009] (2) Filter the ethanol solution to be tested to obtain the sample solution to be tested;

[0010] (3) Add the same and equal amount of amine catalyst solution as in step (1) to the above-mentioned sample solution to be tested, which is the same volume as the methanol series standard working solution in step (1). Then add the same and equal amount of active ester solution containing strong electron-withdrawing nitro groups as in step (1). React in a constant temperature water bath at 24-26℃ for 15-25 min to obtain the test solution. Measure the absorbance of the test solution with a UV spectrophotometer. Then substitute the absorbance of the test solution into the standard working curve obtained in step (1) to obtain the methanol concentration in the sample solution to be tested, and then obtain the methanol concentration in the ethanol solution to be tested.

[0011] In a preferred embodiment of the present invention, the amine catalyst is diethylamine.

[0012] More preferably, the concentration of the amine catalyst solution is 10-15 μM.

[0013] In a preferred embodiment of the present invention, the active ester containing the strongly electron-withdrawing nitro group is p-nitrophenol ethyl ester.

[0014] More preferably, the concentration of the active ester solution containing the strongly electron-withdrawing nitro group is 90-110 mM.

[0015] In a preferred embodiment of the present invention, the amine catalyst is diethylamine, and the active ester containing the strongly electron-withdrawing nitro group is ethyl p-nitrophenol.

[0016] More preferably, the concentration of the amine catalyst solution is 10-15 μM, and the concentration of the active ester solution containing the strongly electron-withdrawing nitro group is 90-110 mM.

[0017] More preferably, the volume ratio of the amine catalyst solution to the active ester solution containing the strongly electron-withdrawing nitro group is 0.8-1.2:0.8-1.2.

[0018] In a preferred embodiment of the present invention, in steps (1) and (3), the temperature of the constant temperature water bath reaction is 25°C and the time is 20 min, and the measurement wavelength of the ultraviolet spectrophotometer is 390 nm.

[0019] In a preferred embodiment of the present invention, the standard working curve is y = 0.00059x - 0.00065, R 2 =0.98, where x is the percentage of methanol by volume and y is the UV absorbance.

[0020] The beneficial effects of this invention are as follows: This invention utilizes the transesterification reaction between methanol and an active ester in a mixed solution, driven by an amine, to generate p-nitrophenol anions with ultraviolet absorption. The methanol content is then determined by detecting the ultraviolet intensity using an ultraviolet spectrometer. This method fully utilizes the principle of transesterification reaction, using diethylamine as a catalyst to generate p-nitrophenol anions (4-NP), which produce ultraviolet absorption. The ultraviolet intensity is then detected using an ultraviolet spectrometer, thus achieving the purpose of simple, sensitive, and specific detection of methanol. Attached Figure Description

[0021] Figure 1 The standard working curve is plotted for Embodiment 1 of the present invention.

[0022] Figure 2 This is a selective result diagram of Embodiment 2 of the present invention.

[0023] Figure 3 This is a comparison diagram of the active ester types in Example 3 of the present invention.

[0024] Figure 4 This is a comparison diagram of amine types in Example 4 of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will be further explained and described below with reference to specific embodiments and accompanying drawings.

[0026] Example 1

[0027] 15 μL of 100 mM diethylamine solution was added to methanol standard working solutions (ethanol as solvent) at different volume ratios, followed by 15 μL of 2 mM p-nitrophenol ethyl ester solution, maintaining a total volume of 3 mL. The solutions were reacted in a constant temperature water bath at 25 °C for 20 min to obtain several reaction solutions corresponding to different volume ratios of methanol baptism standard working solutions. The absorbance of these reaction solutions was measured at 390 nm using a UV spectrophotometer. A standard working curve was then plotted based on the absorbance and the methanol concentration in the methanol standard working solutions. Figure 1 As shown, the standard working curve is y = 0.00059x - 0.00065, R0 2 =0.98, where x is the volume percentage of methanol, y is the UV absorbance, and the detection limit for methanol is 4.2%.

[0028] Example 2

[0029] 15 μL of 100 mM diethylamine solution was added to different test solutions (ethanol as solvent, solutes were methanol, n-propanol, isopropanol, acetonitrile, acetone, and tetrahydrofuran, respectively), followed by 15 μL of 2 mM p-nitrophenol ethyl ester solution, controlling the total volume to 3 mL. The mixture was reacted in a constant temperature water bath at 25 °C for 20 min to obtain several reaction solutions corresponding to different test solutions. The absorbance of these reaction solutions was measured at 390 nm using a UV spectrophotometer to study the effect of different test solutions on the UV absorption reaction of transesterification. Figure 2 As shown, n-propanol, isopropanol, acetonitrile, acetone and tetrahydrofuran did not respond to the system, verifying that the present invention can achieve specific detection of methanol in ethanol.

[0030] Example 3

[0031] 15 μL of 100 mM diethylamine solution was added to methanol (ethanol as solvent, solutes were methanol, n-propanol, isopropanol, acetonitrile, acetone, and tetrahydrofuran, respectively), followed by 15 μL of 2 mM nitroactive ester solution (ethyl p-nitrophenol, phenyl p-nitrophenol, or hexyl p-nitrophenol), controlling the total volume to 3 mL. The reaction was carried out in a constant temperature water bath at 25 °C for 20 min, yielding several reaction solutions. The absorbance of these reaction solutions was measured at 390 nm using a UV spectrophotometer to study the effect of different nitroactive esters on the UV absorption of transesterification. The results are as follows. Figure 3 As shown, the rate of p-nitrophenol ethyl ester is faster than that of p-nitrophenol hexyl ester and p-nitrophenol phenyl ester, verifying the importance of selecting p-nitrophenol ethyl ester as the active ester in this invention.

[0032] Example 4

[0033] 15 μL of different amine catalyst solutions (100 mM) were added to methanol, followed by 15 μL of 2 mM p-nitrophenol ethyl ester solution, bringing the total volume to 3 mL. The mixtures were reacted in a constant-temperature water bath at 25 °C for 20 min to obtain several reaction solutions. The absorbance of these solutions was measured at 390 nm using a UV spectrophotometer to investigate the effect of different amine catalysts on the UV absorption of the transesterification reaction. The results are as follows: Figure 4 As shown, ethyl p-nitrophenol reacts with DEA, EDA, PPA, and TEA mixtures, respectively. However, the reaction rate of the ethyl p-nitrophenol and DEA mixture is the fastest, which verifies the superiority of using the ethyl p-nitrophenol and DEA mixture as a method for methanol identification in ethanol solutions.

[0034] Example 5

[0035] ① Purchase two samples of industrial alcohol randomly and store them at room temperature;

[0036] ② Remove the precipitate from the industrial alcohol by vacuum distillation, and transfer a small amount to a clean test tube and store at room temperature for later use.

[0037] Detection: 15 μL of 100 mM diethylamine solution was added to the treated industrial alcohol test solution, followed by 15 μL of 2 mM p-nitrophenol ethyl ester solution, maintaining a total volume of 3 mL. The mixture was reacted in a constant temperature water bath at 25 °C for 20 min to obtain several reaction solutions corresponding to different test solutions. The absorbance of each reaction solution was measured at 390 nm using a UV spectrophotometer. The methanol content in the test solution was calculated using the standard working curve from Example 1. The experiment was conducted in triplicate.

[0038] The results are shown in Table 1 below. It can be seen that under the same experimental conditions, the results of the methanol content identification and detection study in industrial alcohol show that the methanol content in industrial alcohol 1 is 4.5-4.6%, and the methanol content in industrial alcohol 2 is 4.3-4.4%. The RSD values ​​for both are 0.13%. Therefore, this invention has good application prospects.

[0039] Table 1. Experimental results of methanol content in industrial alcohol (n=3)

[0040]

[0041]

[0042] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for identifying and detecting methanol in an ethanol solution, characterized in that: Includes the following steps: (1) Add equal amounts of amine catalyst solution to methanol series standard working solutions of different volume ratios, and then add an active ester solution containing a strong electron-withdrawing nitro group. React in a constant temperature water bath at 24-26℃ for 15-25 min to obtain several reaction solutions corresponding to methanol series standard working solutions of different volume ratios. Measure the absorbance of these reaction solutions with an ultraviolet spectrophotometer, and then plot the standard working curve based on the absorbance and the methanol concentration in the methanol series standard working solutions. The solvent of the above methanol series standard working solutions is ethanol; the amine catalyst is diethylamine; and the active ester containing a strong electron-withdrawing nitro group is p-nitrophenol ethyl ester. (2) Filter the ethanol solution to be tested to obtain the sample solution to be tested; (3) Add the same and equal amount of amine catalyst solution as in step (1) to the above sample solution to be tested with the same volume as the methanol series standard working solution in step (1), and then add the same and equal amount of active ester solution containing strong electron-withdrawing nitro groups as in step (1). React in a constant temperature water bath at 24-26℃ for 15-25 min to obtain the test solution. Measure the absorbance of the test solution with an ultraviolet spectrophotometer. Then substitute the absorbance of the test solution into the standard working curve obtained in step (1) to obtain the methanol concentration in the sample solution to be tested, and then obtain the methanol concentration in the ethanol solution to be tested.

2. The method for identifying and detecting methanol in an ethanol solution as described in claim 1, characterized in that: The concentration of the amine catalyst solution is 10-15 µM.

3. The method for identifying and detecting methanol in an ethanol solution as described in claim 1, characterized in that: The concentration of the active ester solution containing the strongly electron-withdrawing nitro group is 90-110 mM.

4. The method for identifying and detecting methanol in an ethanol solution as described in claim 1, characterized in that: The concentration of the amine catalyst solution is 10-15 µM, and the concentration of the active ester solution containing the strongly electron-withdrawing nitro group is 90-110 mM.

5. The method for identifying and detecting methanol in an ethanol solution as described in claim 4, characterized in that: The volume ratio of the amine catalyst solution to the active ester solution containing the strongly electron-withdrawing nitro group is 0.8-1.2: 0.8-1.

2.

6. The method for identifying and detecting methanol in an ethanol solution as described in claim 1, characterized in that: In steps (1) and (3), the temperature of the constant temperature water bath reaction is 25°C and the time is 20 min. The wavelength of the ultraviolet spectrophotometer is 390 nm.

7. A method for identifying and detecting methanol in an ethanol solution as described in any one of claims 1 to 6, characterized in that: The standard working curve is y = 0.00059x - 0.00065, R0 2 =0.98, where x is the percentage of methanol by volume and y is the UV absorbance.

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