Borax fluorescence detection method
By using discarded tobacco leaves as carbon sources to prepare carbon quantum dots and establishing fluorescence detection methods, the complexity of borax detection in food was solved, and low-cost and efficient borax detection was achieved. It is suitable for flour and its products, with a detection limit of 8μmol and stable conditions.
Patent Information
- Application Number
- CN202111301301.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2021-11-04
- Publication Date
- 2025-08-12
- Estimated Expiration
- 2041-11-04
AI Technical Summary
The prior art borax detection in food has problems such as complex operation, expensive equipment and troublesome sample preparation, and lacks simple, fast and effective detection methods.
Use discarded tobacco leaves as carbon sources to prepare carbon quantum dots (CQDs) by hydrothermal method, and use their fluorescent properties to establish a borax detection method, including preparing CQDs, establishing a regression equation and measuring the fluorescence intensity of the sample to be measured to determine the borax concentration.
It realizes low-cost, simple and fast borax detection, high sensitivity, wide linear range and high recovery rate. It is suitable for the detection of borax in flour and its products. The detection limit is 8μmol, and the applicable conditions are stable and not affected by interference factors.
Smart Images
Figure CN116067922B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of food additive detection, in particular to a borax fluorescence detection method. Background Art
[0002] Food additives are substances added to foods during manufacturing, processing, transportation, and storage to improve their quality and properties. Qualitative detection methods for borax, including turmeric test paper, infrared spectroscopy (IR), and inductively coupled plasma mass spectrometry (ICP-MS), all have drawbacks, including complex procedures, cumbersome sample preparation, and expensive equipment. Therefore, monitoring borax content in food through simple, rapid, and effective methods is crucial for ensuring food safety and consumer confidence.
[0003] Carbon quantum dots (CQDs) are spherical, zero-dimensional fluorescent nanomaterials with an average particle size of approximately 10 nm. CQDs have attracted widespread attention due to their high chemical stability, high hydrophilicity, and low toxicity, and have been widely used in chemical analysis, biosensing, and fluorescence imaging. However, the preparation of CQDs using waste materials and simple, green methods remains challenging. Summary of the Invention
[0004] To address these challenges, we developed a simple, green, and economical method for preparing CQDs using waste tobacco leaves as a carbon source. We established a fluorescence analysis method for the detection of borax in flour and flour-related products. Different concentrations of borax resulted in a linear increase in the fluorescence intensity of the CQDs. Experimental results demonstrate that this method is inexpensive, simple, rapid, and exhibits a wide linear range and high recovery, making it suitable for the determination of borax in flour and flour-related products (bread, instant noodles).
[0005] In order to achieve the purpose of the present invention, the following technical means are specifically adopted:
[0006] A borax fluorescence detection method, characterized in that it comprises the following steps:
[0007] (1) Preparation of CQDs: Tobacco leaves and water were mixed to obtain a mixture, and the mixture was heated at 170-190°C for 3-5 hours. After the reaction was completed, the mixture was cooled to room temperature and centrifuged to collect the CQDs supernatant;
[0008] (2) Establishing a regression equation for borax detection: Using the CQDs supernatant obtained in step (1) to detect the fluorescence intensity of a blank solution and borax solutions of different concentrations, a regression equation is fitted to obtain the relationship between the fluorescence intensity and the concentration of the borax solution;
[0009] (3) Measuring the sample to be tested: the sample to be tested was mixed with water, ultrasonicated for a period of time, and then centrifuged at 4000-5000 rpm for 9-11 min. The sample supernatant was collected and mixed with the CQDs supernatant. The fluorescence intensity was measured and substituted into the regression equation in step (2) to obtain the borax concentration in the sample to be tested.
[0010] In step (1) of preparing CQDs, the heating temperature must be determined, otherwise it is difficult to establish the regression equation.
[0011] Preferably, the mass volume ratio of tobacco leaves to water in step (1) is g / mL 1:80-120.
[0012] Preferably, in step (1), the heating temperature is 180° C., the heating time is 4 h, the centrifugal speed is 4000-5000 rpm, and the centrifugal time is 9-11 min.
[0013] Preferably, the fluorescence spectrum used in the operations of step (2) and step (3) is λex / λem=375 / 460nm.
[0014] Preferably, the pH value of the solution detected in step (2) and step (3) is 2 to 10.
[0015] Of course, a more preferred pH value is 5.5 to 8.0.
[0016] Preferably, the pH value of the solution detected in step (2) and step (3) is 6.0.
[0017] Preferably, the sample to be tested is selected from flour or flour products.
[0018] Preferably, the specific steps of the detection are:
[0019] (1) Preparation of CQDs: Tobacco leaves and water were mixed to obtain a mixture, and the mixture was heated at 180°C for 4 h. After the reaction, the mixture was cooled to room temperature and centrifuged to collect the CQDs supernatant. The mass volume ratio of the tobacco leaves to water was g / mL 1:80-120;
[0020] (2) Establishing a borax detection regression equation: Take the CQDs supernatant obtained in step (1), take borax standard solutions of different concentrations, mix the CQDs supernatant with equal volumes of blank solution and borax standard solutions of different concentrations to obtain a mixed solution, then dilute the mixed solution to 1.5 times the volume with water, adjust the pH to 6.0, let it stand for 5 to 15 minutes, and then perform fluorescence spectrum detection at λex / λem=375 / 460nm to obtain the borax-fluorescence regression equation: (F-F0) / F0=0.0171Borax+0.0222, where F0 is the fluorescence intensity of the diluted mixed solution of the CQDs supernatant and the blank solution; F is the fluorescence intensity of the diluted mixed solution of the CQDs supernatant and the borax standard solutions of different concentrations, and Borax is the concentration of the borax standard solution;
[0021] (3) Measuring the sample to be tested: the crushed sample to be tested was mixed with water, the mass volume ratio of the sample to be tested to water was 1:4-6 g / mL, and after ultrasonication for 5-15 minutes, the mixture was centrifuged at 4000-5000 rpm for 5-15 minutes, and the supernatant of the sample to be tested was collected; the CQDs supernatant obtained in step (1) and the supernatant of the sample to be tested prepared by the above method were mixed in equal volumes and diluted with water to 1.5 times the volume, the pH was adjusted to 6.0, and after standing for 5-15 minutes, the fluorescence intensity was measured at λex / λem=375 / 460 nm.
[0022] Beneficial effects
[0023] (1) The present invention only requires discarded tobacco leaves to prepare CQDs for fluorescence analysis. The experimental raw materials are cheap and easy to obtain, and the experimental cost is low.
[0024] (2) The method for preparing CQDs is a one-step hydrothermal method with few operating steps, simple experimental conditions and low experimental difficulty.
[0025] (3) The fluorescence analysis method established using CQDs as fluorescent probes is efficient and sensitive, and can detect a minimum borax concentration of 8 μmol. In addition, the overall scheme of the present invention is simple and green, and the recovery rate of the target is at a high level.
[0026] (4) The detection system of the present invention is stable and can maintain good detection results under various conditions without being affected by interfering factors.
[0027] (5) This technology is suitable for the detection of borax residues in flour-based foods, providing a new approach for the detection of illegal food additives and can be used as a reliable method for monitoring borax residues. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 Schematic diagram of the principle of this method;
[0029] Figure 2 Performance test diagram of CQDs;
[0030] Figure 3 is the graph showing the change of fluorescence intensity with borax concentration;
[0031] Figure 4 is the regression line graph of fluorescence intensity and borax concentration;
[0032] Figure 5 This is a graph showing the effects of pH, Xe light irradiation time, NaCl concentration, and incubation temperature on the stability of CQDs solution;
[0033] Figure 6 This is the result diagram of the effect of pH and reaction time on borax fluorescence detection;
[0034] Figure 7 This is a diagram of the specific experimental detection of fluorescent carbon quantum dots. DETAILED DESCRIPTION
[0035] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.
[0036] The schematic diagram of the principle of this method is shown in Figure 1 As shown, fluorescent carbon quantum dots are first extracted from tobacco leaves, and then the concentration of the borax solution is measured using the fluorescent carbon quantum dots.
[0037] Example 1
[0038] The reactions in Example 1 were all carried out at room temperature, which was approximately 25°C.
[0039] (1) Preparation of CQDs: Carbon quantum dots (CQDs) were prepared by a hydrothermal method using waste tobacco leaves as a carbon source. An appropriate amount of tobacco leaves was pulverized, and 0.4 g of the pulverized tobacco leaves was mixed with 40 mL of purified water. The mixture was transferred to a 50 mL reactor and heated in an oven at 180°C for 4 h. After the reaction, the reactor was cooled to room temperature. After centrifugation at 4500 rpm for 10 min, 200 mL of the CQD supernatant was collected for further use.
[0040] The performance of the fluorescent carbon quantum dots obtained by the above method was characterized, and the results were as follows Figure 2 As shown, where:
[0041] Figure 2 a is the transmission electron microscopy (TEM) image of CQDs, which shows that all CQDs are spherical and well dispersed;
[0042] Figure 2 b is the particle size distribution diagram of CQDs, which shows that the average diameter of the prepared CQDs is 14.2 nm;
[0043] Figure 2 c is the Fourier transform infrared (FTIR) spectrum of CQDs, which clearly shows that the surface of the CQDs is full of hydrophilic groups (-OH and -COOH), which makes the CQDs have good water dispersibility and good fluorescence properties.
[0044] (2) Establishment of borax detection regression equation: Borax was determined at room temperature. Take the CQDs solution obtained in step (1) and take 1 mL of borax standard solution of different concentrations: 0 mmol·L -1 , 0.025mmol·L -1 , 0.05mmol·L -1 , 0.1mmol·L -1 , 0.25mmol·L -1 , 0.5mmol·L -1 , 1mmol·L -1 , 2.5mmol·L -1 , 5mmol·L -1 、10mmol·L -1 Then, 1 mL of CQDs solution and borax standard solutions of different concentrations were added to a series of 4 mL colorimetric tubes to obtain a mixed solution of 1 mL CQDs solution + 1 mL of borax standard solution of a determined concentration. The mixed solution was then diluted to 3 mL with purified water and mixed thoroughly. The pH of the mixed solution was adjusted to 6.0. After 10 minutes, the fluorescence spectrum was detected at λex / λem=375 / 460 nm. Each concentration of borax standard solution was prepared in triplicate, and the final fluorescence intensity was averaged by taking the three replicates. Finally, the fluorescence intensity was obtained as the concentration of the borax solution changes as shown in the figure below. Figure 3 As shown in the figure, the curves from top to bottom are the fluorescence intensities corresponding to the borax concentration from high to low, respectively, showing that the fluorescence intensity of CQDs increases with the increase of borax concentration.
[0045] Further study of the regression equation relationship between fluorescence intensity and borax solution concentration yielded Figure 4The relationship shown is: (F-F0) / F0=0.0171Borax+0.0222, where F0 is the fluorescence intensity of the mixed solution of CQDs supernatant and blank solution after dilution, that is, the blank group; F is the fluorescence intensity of the mixed solution of CQDs supernatant and different concentrations of borax solution after dilution, Borax is the borax concentration of the borax standard solution, and the determination coefficient r of this equation is 2 is 0.9963. This proves that the fitting degree of the equation is very high. As can be seen from the figure, when the concentration of borax is increased from 0.025mmol·L -1 Increased to 10mmol·L -1 When the concentration of borax is 0.05, the fluorescence intensity of CQDs increases linearly, and the fluorescence intensity of CQDs has a good linear correlation with the concentration of borax. 2 =0.9963, and the detection limit (LOD) was 8.0 μmol·L -1 , calculated as: LOD = 3σ / S (σ is the standard deviation of 11 blank samples, S is the slope of the linear correlation). Therefore, the CQDs can be used as a fluorescent probe to effectively detect borax with good sensitivity.
[0046] Verification of the regression equation
[0047] The following experiments were performed at room temperature.
[0048] Step S1: Flour, bread, and instant noodles were selected as test samples because borax can be added to these foods as a food additive. All samples were purchased from a local supermarket. 10 g of the crushed sample was mixed with 50 mL of purified water, sonicated for 10 minutes, and centrifuged at 4500 rpm for 10 minutes. The supernatant was collected for further use.
[0049] Step S2: Take 1.0 mL of the CQDs supernatant liquid prepared in the previous step, and 1.0 mL of the supernatant liquid of different noodle samples are added to a series of 4 mL colorimetric tubes in sequence and diluted to 3 mL with pure water. Mix thoroughly, adjust the pH to 6.0, and after 10 minutes, measure the fluorescence spectrum at λex / λem=375 / 460 nm. The measurement experiment of each noodle product is repeated three times, and the average value is taken to obtain the borax concentration A0 of the sample supernatant liquid of different noodle products after three-fold dilution.
[0050] Step S3: Then take 1.0mL of low, medium and high concentration borax standard solutions respectively: 0.025mmol·L -1 , 0.5mmol·L -1 、10mmol·L -11.0 mL of low-, medium-, and high-concentration borax standard solutions were mixed with 1.0 mL of the supernatant of different noodle samples and 1.0 mL of CQD supernatant, respectively. The mixture was added to a series of 4 mL colorimetric tubes, thoroughly mixed, and the pH was adjusted to 6.0. After 10 minutes, the fluorescence spectra were measured at λex / λem = 375 / 460 nm. Each measurement was repeated three times, and the average value was taken. This yielded the total borax solution concentration A1 (the total concentration of the noodle sample solution plus the low-, medium-, and high-concentration borax standard solutions in the 3 mL mixed solution). Furthermore, the spiked concentration A2 of the original borax standard solution was obtained, which is also the detection value shown in the table below.
[0051] The results of the above experiments are shown in the following table:
[0052] Table 1 Recovery of borax at three levels in three actual samples (n=3)
[0053]
[0054] The addition amount in the table above refers to the known concentration of the borax standard solution, and the detection amount in the table above refers to the concentration of the added borax standard solution measured in step S3 after the above steps S1 to S3. The recovery rate is the detection amount / addition amount, and the RSD is the relative standard deviation of three repeated experiments at each concentration. As can be seen from the table above, the recovery results of the present invention ranged from 85.2% to 105.8%, with an RSD of less than 9.0% (n=3). Therefore, we can see that this method is reliable and can be used for the determination of borax in actual samples.
[0055] (3) Determination of borax content in actual samples: Actual samples such as flour, bread, and instant noodles were selected as test samples because borax can be added to these foods as a food additive. 10 g of crushed sample was mixed with 50 mL of purified water, ultrasonicated for 10 min, and centrifuged at 4500 rpm for 10 min. The sample supernatant was collected for further use. 1.0 mL of CQDs supernatant solution and 1.0 mL of sample were added to a 4 mL colorimetric tube in sequence. The mixed solution was then diluted to 3 mL with purified water and mixed thoroughly. The pH was adjusted to 6.0. After 10 min, the fluorescence spectrum was detected at λex / λem=375 / 460 nm to obtain the fluorescence intensity, thereby obtaining the borax concentration. Finally, the borax content in the sample was calculated.
[0056] Example 2
[0057] In order to further explore the wide applicability of the fluorescent carbon quantum dots in the detection of borax, the following series of experiments were conducted to investigate the stability of the carbon quantum dots.
[0058] The stability of the obtained carbon quantum dots (CQDs) was investigated. Taking fluorescence intensity as an indicator, the effects of pH, Xe light irradiation time, NaCl concentration and incubation temperature on the stability of CQDs solution were investigated.
[0059] like Figure 5 As shown in Figure a, when the pH range of the buffer solution is 2.06-10.06, the fluorescence intensity changes steadily, but decreases sharply with the increase of pH. That is, the CQDs have good stability under acidic and neutral conditions, but are extremely unstable in strong alkaline solutions.
[0060] like Figure 5 As shown in (b), the fluorescence intensity of CQDs basically does not fluctuate with the increase of ultraviolet irradiation time, indicating that it has good photostability.
[0061] This experiment also studied the effects of NaCl concentration and incubation temperature on its fluorescence intensity. Figure 5 c, as shown in 5d. Figure 5 c shows that the fluorescence intensity of CQDs does not change significantly with the increase of NaCl concentration, indicating that CQDs can be stably preserved in high concentration salt solution. Figure 5 d shows that the fluorescence intensity remains unchanged at different temperatures.
[0062] Example 3
[0063] Optimizing conditions for borax testing
[0064] The CQDs solution and the borax solution were mixed to obtain a mixed solution, the pH of the mixed solution was adjusted, and the fluorescence intensity at different pH values was measured. Figure 6 As shown in a, it shows that in the presence of borax, when the pH is 2-10, the fluorescence intensity is higher, especially when the pH is 5.5-8.0, the fluorescence intensity is higher, and when the pH is 6.0, the fluorescence intensity is the highest, so pH = 6.0 should be selected as the optimal solution pH.
[0065] After the CQDs solution and borax solution were mixed, they were left to stand for a certain period of time. Then the relationship between different standing times and fluorescence intensity was measured. The results are as follows: Figure 6 As shown in b, it can be seen that the reaction time of CQDs and borax has no effect on the fluorescence intensity, proving that the reaction system is relatively stable.
[0066] Example 4
[0067] Specificity experiments
[0068] When testing actual samples, there may be other interfering substances, such as metal ions. Therefore, in order to ensure the stability of the test, it is necessary to verify whether the interfering substances will cause measurement errors.
[0069] The blank aqueous solution and the concentration of 10mmol·L -1 of each interfering substance aqueous solution, 10mmol·L -1 The borax aqueous solution was mixed with the CQDs solution in equal volumes and thoroughly mixed at room temperature to obtain a mixed aqueous solution of blank aqueous solution + CQDs, sodium carboxymethyl cellulose + CQDs, carbonate ions + CQDs, magnesium ions + CQDs, sodium ions + CQDs, calcium ions + CQDs, potassium ions + CQDs, zinc ions + CQDs, vitamin A + CQDs, vitamin B6 + CQDs, and borax + CQDs. The pH of the solution was 6.0, and then the fluorescence intensity was measured at λex / λem=375 / 460nm, respectively. The results are as follows: Figure 7 As shown, borax (10 mmol.L -1 ) after addition of borax, the fluorescence intensity of CQDs increased by 15.6%. When other metal ions were added, the fluorescence intensity increased by a maximum of 0.2%. Therefore, it can be concluded that CQDs have significant selectivity for the detection of borax.
[0070] The above description is only a preferred 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 scope of protection of the present invention.
Claims
1. A borax fluorescence detection method, characterized in that, The steps include: (1) Preparation of CQDs: Tobacco leaves and water were mixed to obtain a mixture, and the mixture was heated at 170°C-190°C for 3 h-5 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, and the CQDs supernatant was collected; (2) Establishing a regression equation for borax detection: Using the CQDs supernatant obtained in step (1) to detect the fluorescence intensity of a blank solution and borax solutions of different concentrations, a regression equation is fitted to obtain the relationship between the fluorescence intensity and the concentration of the borax solution; (3) Measuring the sample to be tested: the sample to be tested was mixed with water, sonicated, and then centrifuged at 4000-5000 rpm for 9-11 min. The sample supernatant was collected and mixed with the CQDs supernatant obtained in step (1). The fluorescence intensity was measured and the fluorescence intensity was substituted into the regression equation obtained in step (2) to obtain the borax concentration in the sample supernatant.
2. The detection method according to claim 1, characterized in that The mass volume ratio of tobacco leaves to water in step (1) is g / mL 1:80-120.
3. The detection method according to claim 1, wherein In the step (1), the heating temperature is 180° C., the heating time is 4 h, the centrifugal speed is 4000-5000 rpm, and the centrifugal time is 9-11 min.
4. The detection method according to claim 1, wherein The fluorescence spectrum used in the operations of steps (2) and (3) is λex / λem=375 / 460nm.
5. The detection method according to claim 1, wherein The pH value of the solution detected in step (2) and step (3) is 2-10.
6. The detection method according to claim 5, characterized in that The pH value of the solution detected in step (2) and step (3) is 6.
0.
7. The detection method according to claim 1, characterized in that The sample to be tested is selected from flour or flour products.
8. The detection method according to claim 1, wherein The specific steps of the detection are: (1) Preparation of CQDs: Tobacco leaves and water were mixed to obtain a mixture, and the mixture was heated at 180°C for 4 h. After the reaction, the mixture was cooled to room temperature and centrifuged to collect the CQDs supernatant. The mass volume ratio of the tobacco leaves to water was g / mL 1:80-120; (2) Establishing a borax detection regression equation: Take the CQDs supernatant obtained in step (1), take borax standard solutions of different concentrations, mix the CQDs supernatant with equal volumes of blank solution and borax standard solutions of different concentrations to obtain a mixed solution, then dilute the mixed solution to 1.5 times the volume with water, adjust the pH to 6.0, and perform fluorescence spectrum detection at λex / λem=375 / 460nm to obtain the borax-fluorescence regression equation: (F-F0) / F0=0.0171Borax+0.0222, where F0 is the fluorescence intensity of the diluted mixed solution of the CQDs supernatant and the blank solution; F is the fluorescence intensity of the diluted mixed solution of the CQDs supernatant and the borax standard solutions of different concentrations, and Borax is the concentration of the borax standard solution; (3) Measuring the sample to be tested: the crushed sample to be tested was mixed with water, the mass volume ratio of the sample to be tested to water was 1:4-6 g / mL, and after ultrasonication for 5-15 minutes, the mixture was centrifuged at 4000-5000 rpm for 5-15 minutes, and the supernatant of the sample to be tested was collected; the CQDs supernatant obtained in step (1) and the supernatant of the sample to be tested prepared by the above method were mixed in equal volumes and diluted with water to 1.5 times the volume, the pH was adjusted to 6.0, and after standing for 5-15 minutes, the fluorescence intensity was measured at λex / λem=375 / 460 nm.