A method for detecting the ethanol concentration of liquor using red light carbon quantum dot fluorescent probe

Abstract

A method for detecting the ethanol concentration in liquor using a highly water-soluble red light carbon quantum dot fluorescent probe belongs to the technical field of fluorescent probes. The present invention is to mix a red light carbon quantum dot solution with an ethanol-water solution of 0% to 100% ethanol concentration, and then measure the fluorescence emission spectrum of the mixed solution to establish a "fluorescence emission peak fluorescence intensity-ethanol concentration" relationship curve; then mix the red light carbon quantum dot solution with liquor of unknown ethanol concentration, add sodium hydroxide with a final concentration of 10 to 20 mM thereto, and then measure the fluorescence emission spectrum of the solution, substitute the emission peak fluorescence intensity value into the "fluorescence emission peak fluorescence intensity-ethanol concentration" relationship curve, calculate the liquor concentration, and thus realize the detection of the ethanol concentration in the liquor. After the present invention compensates the pH value of the liquor by adding alkali, the reaction system can be restored to the fluorescence intensity in the same ethanol-water system, and can be used as a fluorescent probe for accurate detection of the alcohol content of liquor.

Description

Technical Field

[0001] The invention belongs to the technical field of fluorescent probes, and in particular relates to a method for detecting ethanol concentration in liquor by utilizing a highly water-soluble red light carbon quantum dot fluorescent probe. Background Art

[0002] Chinese liquor is loved by consumers all over the world because of its long history and unique craftsmanship. Alcohol content is the volume percentage of ethanol content in liquor. It is an important indicator for identifying the quality of liquor and one of the main bases for consumers to buy liquor. As a qualified liquor, the alcohol content marked on it must be very accurate. However, the alcohol content marked by some unscrupulous merchants sometimes has a large deviation. Therefore, we can make a preliminary assessment of the quality of liquor by measuring the ethanol content in liquor. In order to standardize the quality of liquor in the market, my country has promulgated a series of standard methods for detecting the alcohol content of liquor, such as density bottle method, alcohol meter method, gas chromatography method and digital density meter method. However, these methods are complicated and time-consuming. Therefore, it is urgent to develop a simple, sensitive and efficient method for detecting the alcohol content of liquor.

[0003] Since its discovery in 2000, carbon quantum dots (CQDs) have become a research hotspot due to their excellent stability, low cost and good biocompatibility. [1] Carbon quantum dots are used in various fields, such as solar cells, capacitors, sensing and biological applications. [2-6] Researchers have tried to synthesize carbon quantum dots with different emission wavelengths using various raw materials and methods. However, under ultraviolet light, the emission wavelengths of carbon quantum dots are mostly in the blue or green light region, which limits the practical application of carbon quantum dots. Therefore, there is an urgent need to develop a cheap, environmentally friendly and simple method to prepare red light carbon quantum dots.

[0004] Previous inventions [7] Using paraphenylenediamine (PPD) and citric acid (CA) as raw materials, carbon quantum dots with red luminescence characteristics were synthesized. When applied to the detection of ethanol concentration in an ethanol-water system, it showed a good linear response. However, when it was further used to detect the ethanol concentration in actual liquor, it was found that when the ethanol concentration in the ethanol-water system was the same as that in the liquor, there was a certain difference in the fluorescence emission intensity of the carbon quantum dots (significantly lower). By investigating the effects of various additives and pH values ​​in liquor on the fluorescence intensity of carbon quantum dots, it was found that the fluorescence quenching of carbon quantum dots was mainly caused by the acidity in the liquor: the fluorescence intensity was significantly reduced as the pH value decreased. That is, the pH value of actual liquor is lower than the pH value of ethanol-water solution of the same concentration. Therefore, after adjusting and compensating the pH value of liquor, the fluorescent carbon quantum dots of the present invention can accurately detect the alcohol content of actual liquor. Summary of the invention

[0005] The present invention provides a method for detecting the ethanol concentration in liquor by using a highly water-soluble red-light carbon quantum dot fluorescent probe. The present invention uses p-phenylenediamine (PPD) and citric acid (CA) as raw materials, and directly prepares carbon quantum dots by a one-step hydrothermal method under high temperature and high pressure conditions. The optimal excitation wavelength of the carbon quantum dots is 500 nm, the emission wavelength is 620 nm, and the carbon quantum dots emit red light under the irradiation of ultraviolet light (365 nm); further, the carbon quantum dots are used for alcohol content detection of liquor. We observed that when the ethanol concentration in the ethanol-water system and the liquor is the same, the fluorescence intensity of the carbon quantum dots is significantly lower. In order to explain this quenching difference, we investigated the effects of various additives in liquor on the fluorescence intensity of carbon quantum dots. The results show that except for lactic acid, acetic acid and malic acid, which can quench the fluorescence intensity of carbon quantum dots, the other several commonly used liquor additives have no effect on the fluorescence intensity of carbon quantum dots. Moreover, when the pH value of the solution is artificially changed, the fluorescence intensity of the carbon quantum dots will also change accordingly; and the lower the pH value of the solution, the more the fluorescence intensity of the carbon quantum dots is quenched. Furthermore, after we compensated the pH value of liquor by adding alkali, we found that the fluorescence intensity of carbon quantum dots gradually increased and could be restored to the fluorescence intensity in the same ethanol-water system. The above results show that by compensating and regulating the pH value of liquor, the carbon quantum dots can be used as fluorescent probes for accurate detection of liquor alcohol content.

[0006] The method of the present invention for detecting the ethanol concentration in liquor by using a highly water-soluble red light carbon quantum dot fluorescent probe optical probe comprises the following steps:

[0007] (1) Weigh 0.01-0.03 g of p-phenylenediamine and dissolve it in 10 mL of water. After it is fully dissolved, add 8-15 mL of 1 mM citric acid aqueous solution, and then stir at room temperature for 8-15 min. Transfer the reaction solution to a high-pressure reactor with a polytetrafluoroethylene liner and react at 170-190 °C for 8-15 h to obtain a red light carbon quantum dot solution.

[0008] (2) diluting the red light carbon quantum dot solution obtained in step (1) with water by 50 to 150 times and then mixing with ethanol-water solutions with 0% to 100% ethanol concentration; the total volume of the mixed solution is 1000 μL, of which the volume of the diluted red light carbon quantum dot solution is 5 to 20 μL, and the rest is ethanol-water solution; then measuring the fluorescence emission spectrum of the mixed solution to establish a "fluorescence emission peak fluorescence intensity-ethanol concentration" relationship curve;

[0009] (3) The red light carbon quantum dot solution obtained in step (1) is diluted 50 to 150 times with water and then mixed with white wine of unknown ethanol concentration; the total volume of the mixed solution is 1000 μL, of which the volume of the diluted red light carbon quantum dot solution is 5 to 20 μL, and the rest is white wine; sodium hydroxide with a final concentration of 10 to 20 mM is then added to the mixed solution, and then the fluorescence emission spectrum of the solution is measured, and the emission peak fluorescence intensity value is substituted into the "fluorescence emission peak fluorescence intensity-ethanol concentration" relationship curve established in step (2) to calculate the white wine concentration, thereby realizing the detection of ethanol concentration in white wine. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 : Linear relationship between the fluorescence intensity difference of the fluorescence emission peak of the fluorescent probe solution and the ethanol concentration (0~100%) in ethanol-water solution and liquor under 500 nm excitation.

[0011] Figure 2 : Dot-line graph showing the fluorescence emission peak intensity of the fluorescent probe solution in ultrapure water under 500 nm excitation versus the concentration of common additives for light-flavor liquor (10-50 mM).

[0012] Figure 3 : Fluorescence emission spectra of the fluorescent probe solution in ultrapure water with the concentrations of lactic acid, malic acid, and acetic acid (10~50mM) under 500 nm excitation.

[0013] Figure 4 : Dot-line graph showing the fluorescence emission peak intensity of the fluorescent probe solution in ultrapure water changing with different concentrations of lactic acid, malic acid, and acetic acid (10-50 mM) under 500 nm excitation.

[0014] Figure 5 : Fluorescence emission spectra of the fluorescent probe solution with pH changes under 500 nm excitation.

[0015] Figure 6 : Dotted line graph of the fluorescence emission peak intensity of the fluorescent probe solution changing with pH under 500 nm excitation.

[0016] Figure 7 : Linear relationship between the fluorescence emission peak intensity of low-concentration fluorescent probe solution and the ethanol concentration (0~100%) in ethanol-water solution under 500 nm excitation.

[0017] Figure 8 : Fluorescence emission spectra of the fluorescent probe solution in light-flavor liquor with changes in sodium hydroxide concentration under 500 nm excitation.

[0018] Fig. 9: Dot-line graph showing the change of fluorescence emission peak fluorescence intensity of fluorescent probe solution in light-flavor liquor with sodium hydroxide concentration under 500 nm excitation.

[0019] Table 1: Comparison of pH values ​​of ethanol-water solutions and liquor with different alcohol contents.

[0020] Table 2: Evaluation of the alcohol content of commercially available light-flavor liquor using fluorescent probe solution.

[0021] Table 3: Comparison of the results of detecting the alcohol content of unknown liquor using fluorescent probe solution and the traditional method.

[0022] like Figure 1 As shown in the figure, when the ethanol concentration in the ethanol-water system and the ethanol concentration in the liquor are the same, there is a difference in the fluorescence enhancement amplitude of the fluorescence emission peak of the carbon quantum dots. This difference may be caused by the additives in the liquor. Figure 2 As shown, when carbon quantum dots are mixed with different types of additives, except for lactic acid, which can quench the fluorescence intensity of carbon quantum dots, the other liquor additives have no effect on the fluorescence intensity of carbon quantum dots. However, the other acids (malic acid, lactic acid) will also affect the fluorescence of carbon quantum dots. In addition, when the pH value of the solution is changed, the fluorescence intensity of the carbon quantum dots will change. As the pH value of the solution decreases, the fluorescence intensity of the carbon quantum dots will decrease. At the same time, the pH value of liquor is lower than the pH value of the ethanol-water solution of the same concentration. This result shows that pH may be the main factor causing the difference in the fluorescence intensity of carbon quantum dots in the two systems. By compensating the pH value of liquor, the fluorescence intensity of carbon quantum dots will gradually increase and return to the fluorescence emission intensity in the pure ethanol-water system. In summary, the results show that by compensating the pH value, the carbon quantum dots of the present invention can be used as a fluorescent probe to detect the alcohol content of liquor. DETAILED DESCRIPTION

[0023] The following examples further illustrate the present invention, but the present invention is not limited to these examples.

[0024] The p-phenylenediamine, citric acid, malic acid, lactic acid, acetal, methanol, ethyl acetate, 1-propanol, lactic acid, n-butanol, isobutanol, and isoamyl alcohol used in the present invention were purchased from Shanghai Aladdin Reagent Co., Ltd. Anhydrous ethanol was purchased from Shandong Yuwang Hetianxia New Materials Co., Ltd., Xinghuacun, Daqu original liquor, Beijing Erguotou, and Chinese liquor were purchased from local supermarkets, sodium hydroxide was purchased from Sinopharm Chemical Reagent Co., Ltd., and acetic acid was purchased from Beijing Chemical Plant. Deionized ultrapure water was used throughout the experiment.

[0025] Embodiment 1:

[0026] Preparation of red light carbon quantum dot fluorescent probe solution [7]Specifically, 0.02 g of p-phenylenediamine was weighed and dissolved in 10 mL of water. After it was fully dissolved, 10 mL of 1 mM citric acid aqueous solution was added, and then stirred at room temperature for 10 min; then the reaction solution was transferred to a high-pressure reactor with a polytetrafluoroethylene liner, and reacted at 180 °C for 10 h to obtain a red light carbon quantum dot fluorescent probe solution.

[0027] Fluorescence response of the fluorescent probe solution to ethanol in ethanol-water solution and liquor: anhydrous ethanol was added to deionized ultrapure water to prepare ethanol-water mixed solutions of different concentrations (the volume concentrations of ethanol were 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%, respectively). Then, 950 µL of the ethanol-water mixed solutions of different concentrations and 50 µL of the red light carbon quantum dot fluorescent probe solution were added to the cuvette. After thorough mixing, the fluorescence emission spectra of the solutions were measured.

[0028] By diluting and increasing the concentration of ethanol, different concentrations of liquor were prepared (the volume concentrations of ethanol were 26.5%, 50.35%, 63%, 73%, 83%, and 93%, respectively), and then 950 µL of the above-mentioned liquor of different concentrations and 50 µL of red light carbon quantum dot fluorescent probe solution were added to the cuvette. After fully mixing, the fluorescence emission spectra of the above solutions were measured.

[0029] By plotting the difference in fluorescence intensity (FF) of the two systems of carbon quantum dots 0 , F 0 represents the peak fluorescence intensity of the fluorescence emission spectrum before adding ethanol / liquor; F represents the peak fluorescence intensity of the fluorescence emission spectrum after adding ethanol / liquor) and the relationship curve between ethanol concentration ( Figure 1 ). It can be clearly seen that when the ethanol concentration in the ethanol-water system and the liquor is the same, there is a large difference in the fluorescence intensity of the carbon quantum dots.

[0030] Embodiment 2:

[0031] pH of ethanol-water solution and liquor: A series of ethanol-water mixed solutions with the same alcohol content as liquor (42%, 53%, 56%, 65.8%) were prepared, and the pH values ​​of ethanol-water solution and liquor were tested respectively. The results are listed in Table 1. The results show that the pH value of liquor is lower than the pH value of ethanol-water solution with the same concentration.

[0032] Table 1: Comparison of pH values ​​of ethanol-water solutions and liquor with different alcohol contents.

[0033]

[0034] Embodiment 3:

[0035] Effect of additives in liquor on the fluorescence intensity of fluorescent probe solution: prepare 1.0 M liquor additive mother liquor (2-phenylethanol, methanol, 1-propanol, n-butanol, isobutanol, isoamyl alcohol, acetal, furfural, ethyl acetate, lactic acid, and the solvent is water); dilute the red carbon quantum dot fluorescent probe solution prepared in Example 1 100 times with water, and divide it into multiple portions (1.0 mL each), add different volumes and types of liquor additive mother liquor to each dilution, so that the final concentrations of liquor additives are 10, 20, 30, 40, and 50 mM, respectively. Then, use a fluorescence spectrometer to record the fluorescence emission spectrum of the solution. Figure 2 As shown, except for lactic acid which can quench the fluorescence intensity of carbon quantum dots, the other liquor additives have no significant effect on the fluorescence intensity of carbon quantum dots.

[0036] Embodiment 4:

[0037] Effect of common acids on the fluorescence intensity of fluorescent probe solutions: prepare lactic acid, acetic acid, and malic acid mother liquors (1.0 M) of the same concentration respectively; mix 990 µL of a 53% ethanol-water mixed solution and 10 µL of a red carbon quantum dot fluorescent probe solution (the red carbon quantum dot fluorescent probe solution prepared in Example 1 was diluted 100 times with water) as the test solution, and drop different volumes of lactic acid, acetic acid, and malic acid mother liquors into the above-mentioned multiple test solutions to make the final concentrations 10, 20, 30, 40, and 50 mM, respectively. After fully mixing, measure the fluorescence emission spectrum of the above solutions. Figure 3 The experimental results show that as the concentrations of lactic acid (Figure a), acetic acid (Figure b), and malic acid (Figure c) increase, the fluorescence intensity of the fluorescence emission peak of the carbon quantum dots gradually weakens. At the same time, by drawing a graph showing the relationship between the fluorescence emission peak intensity of the carbon quantum dots in the system and the concentrations of lactic acid, acetic acid, and malic acid ( Figure 4 ) It can be clearly seen that lactic acid, acetic acid and malic acid can quench the fluorescence intensity of carbon quantum dots.

[0038] Embodiment 5:

[0039] Effect of pH value on fluorescence intensity of fluorescent probe solution: Prepare HEPES-NaOH buffer solutions with pH values ​​of 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 9, 9.5, and 10. Add 900 µL of HEPES-NaOH buffer solutions with different pH values ​​and 100 µL of red carbon quantum dot fluorescent probe solution (the red carbon quantum dot fluorescent probe solution prepared in Example 1 was diluted 10 times with water) to the cuvette, mix thoroughly, and measure the fluorescence emission spectrum of the above solution. Figure 5It shows that the peak fluorescence intensity of carbon quantum dots is closely related to pH value. As pH increases, the peak fluorescence intensity of carbon quantum dots gradually becomes stronger. At the same time, by drawing a graph showing the relationship between the peak fluorescence intensity of carbon quantum dots and pH value ( Figure 6 ), it can be clearly seen that the lower the pH value, the weaker the fluorescence intensity of the carbon quantum dots.

[0040] Embodiment 6:

[0041] Fluorescence response of low-concentration fluorescent probe solution to ethanol in ethanol-water solution: prepare ethanol-water mixed solutions of different volume concentrations (0%, 10%, 20%, 30%, 40%, 50%, 52%, 53%, 60%, 65.8%, 70%, 80%, 90%, 100%), then add 990 μL of ethanol-water mixed solutions of different concentrations and 10 μL of red carbon quantum dot fluorescent probe solution (the red carbon quantum dot fluorescent probe solution prepared in Example 1 was diluted 100 times with water) to the cuvette, and measure the fluorescence emission spectrum of the above solution after thorough mixing. By plotting the relationship between the fluorescence intensity of the carbon quantum dot fluorescence emission peak and the ethanol concentration of the system ( Figure 7 ) It can be clearly seen that when the ethanol concentration is in the range of 20%~90%, there is a good linear response relationship between the fluorescence emission peak intensity (F) of carbon quantum dots and the ethanol concentration (Ethanol) (R 2 =0.99107), and its linear response equation is: F=6.22507[Ethanol]-8.29971.

[0042] Embodiment 7:

[0043] Detection of alcohol content of liquor by fluorescent probe solution: 10 µL of red light carbon quantum dot fluorescent probe solution (the red light carbon quantum dot fluorescent probe solution prepared in Example 1 was diluted 100 times with water) was mixed with 990 µL of liquor of different concentrations (42%, 53%, 56%, 65.8%), and then sodium hydroxide solution was added dropwise to the above solution (the final concentration range was 2~20 mM, and the final concentrations were 2 mM, 4 mM, 6 mM, 8 mM, 10 mM, 12 mM, 14 mM, 16 mM, 18 mM, 20 mM, respectively), and the fluorescence emission spectrum of the above solution was detected. Figure 8 It shows that the peak fluorescence intensity of carbon quantum dots in liquor increases with the increase of sodium hydroxide concentration. By drawing a graph showing the relationship between the peak fluorescence intensity of carbon quantum dots in liquor and the concentration of sodium hydroxide ( Fig. 9) It can be clearly seen that when the concentration of sodium hydroxide is greater than 10 mM, as the concentration of sodium hydroxide increases, the fluorescence intensity of the fluorescence emission peak of carbon quantum dots remains basically unchanged. Therefore, the final concentration of sodium hydroxide in the appropriate fluorescent probe solution is 10~20 mM.

[0044] Finally, 10 µL of red light carbon quantum dot fluorescent probe solution (the red light carbon quantum dot fluorescent probe solution prepared in Example 1 was diluted 100 times with water), 990 µL of liquor and sodium hydroxide (final concentration 10.0 mM) were added to the cuvette, and the fluorescence emission intensity of the above solution was measured. The results showed that the recovery rate was between 95.8% and 101.0%, indicating that the carbon quantum dots can be used to detect the alcohol content of liquor (Table 2). In order to further prove the accuracy of this method, we compared the alcohol content detected by carbon quantum dots with the traditional method (liquid chromatography). The results showed that the degree of agreement was between 96.1% and 98.8% (Table 3), further indicating that this method can quickly and accurately detect the alcohol content of liquor.

[0045] Table 2: Detection of alcohol content of liquor using fluorescent probe solution (liquor samples from supermarkets)

[0046] sample Nominal alcohol content of raw materials (%) The method of the present invention detects alcohol content (%) Recovery rate (%) <![CDATA[1 # ]]> 42 42.4 101.0 <![CDATA[2 # ]]> 53 52.0 98.2 <![CDATA[3 # ]]> 56 53.7 95.8 <![CDATA[4 # ]]> 65.8 64.1 97.4

[0047] Table 3: Comparison of the results of using fluorescent probe solution to detect the alcohol content of unknown liquor with the results of traditional methods (liquor samples come from the winery)

[0048] sample Carbon quantum dots detect alcohol content (%) Alcohol content detected by traditional methods (%) Degree of conformity (%) <![CDATA[1 # ]]> 32.4 32.8 98.8 <![CDATA[2 # ]]> 44.2 46.0 96.1 <![CDATA[3 # ]]> 57.3 59.0 97.1 <![CDATA[4 # ]]> 64.1 65.8 97.4

[0049] In addition, it should be noted that the specific embodiments listed in this specification are only used to illustrate the contents of the present invention and do not limit the protection scope of the present invention in any way; relevant technical personnel in the field can make improvements or changes based on some of the above descriptions, but all these improvements and changes should fall within the protection scope of the claims of the present invention.

[0050] References:

[0051] [1] Y. Jiang, Z. Dai Sensors Actuators B Chem 234 (2016) 15–20.

[0052] [2] R. Guo, H. Hou Energy Stor. Mater. 37 (2021) 8–39.

[0053] [3] Y. Jin, L. Dai Adv. Funct. Mater. 28 (2018) 1804630.

[0054] [4] L. Cai, F. Cui J Fluorescence 30 (2020) 11–20.

[0055] [5] S. Bian, X. Dong Sensors Actuators B Chem 242 (2017) 231–2.

[0056] [6] P. Shen, J. Yao ChemistrySelect 1 (2016) 1314–1317.

[0057] [7] Wu Yuqing. A fluorescent probe based on red light carbon quantum dots and its application in detecting ethanol concentration in ethanol-water system [P]. Chinese Patent: 202210244301.3.

Claims

1. A method for detecting the ethanol concentration in liquor using a highly water-soluble red light carbon quantum dot fluorescent probe, the steps of which are as follows: (1) Weigh 0.01-0.03 g of p-phenylenediamine and dissolve it in 10 mL of water. After it is fully dissolved, add 8-15 mL of 1 mM citric acid aqueous solution, and then stir at room temperature for 8-15 min. Transfer the reaction solution to a high-pressure reactor with a polytetrafluoroethylene liner and react at 170-190 °C for 8-15 h to obtain a red light carbon quantum dot solution. (2) diluting the red light carbon quantum dot solution obtained in step (1) with water by 50 to 150 times and then mixing with ethanol-water solutions with ethanol concentrations of 0% to 100%; then measuring the fluorescence emission spectrum of the mixed solution to establish a "fluorescence emission peak fluorescence intensity-ethanol concentration" relationship curve; (3) diluting the red light carbon quantum dot solution obtained in step (1) with water by 50 to 150 times and then mixing it with liquor of unknown ethanol concentration; then adding sodium hydroxide with a final concentration of 10 to 20 mM to the mixed solution, and then measuring the fluorescence emission spectrum of the solution, substituting the emission peak fluorescence intensity value into the "fluorescence emission peak fluorescence intensity-ethanol concentration" relationship curve established in step (2), and calculating the liquor concentration, thereby realizing the detection of ethanol concentration in liquor; in, The total volume of the mixed solution in step (2) is 1000 μL, of which the volume of the diluted red light carbon quantum dot solution is 5-20 μL, and the rest is ethanol-water solution; the total volume of the mixed solution in step (3) is 1000 μL, of which the volume of the diluted red light carbon quantum dot solution is 5-20 μL, and the rest is liquor; the volume of the diluted red light carbon quantum dot solution in step (2) and step (3) is the same.

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