A Fluorescent Ionic Liquid, Its Synthesis Method and Applications in Continuous Detection of Magnesium Ions and L-Ascorbic Acid

Abstract

The present invention discloses a fluorescent ionic liquid, its synthesis method, and its applications in continuously detecting magnesium ions and L-ascorbic acid. The chemical formula of the fluorescent ionic liquid is [HDQS][P 66614 , and the structural formula is as shown in formula (I). The present invention synthesizes an ionic liquid with green fluorescence emission by an ion exchange method. This method has simple synthesis steps and high synthesis yield. The synthesized fluorescent ionic liquid has good thermal stability, is not easily volatile, and has little environmental pollution. The ionic liquid has strong specificity and sensitivity to magnesium ions, and can detect magnesium ions within a relatively wide linear range. It has strong sensitivity and visual color change to L-ascorbic acid, and can achieve detection within a relatively wide linear range. The present invention can conduct qualitative analysis and quantitative detection of L-ascorbic acid in actual samples, providing the possibility for the detection of L-ascorbic acid in complex systems;

Description

Technical Field

[0001] The present invention relates to a fluorescent ionic liquid and a synthesis method thereof, and applications for rapid fluorescence / colorimetric detection of L-ascorbic acid in actual samples and for differentiating magnesium ions from common metal ions. Background Art

[0002] L-ascorbic acid (AA), also known as vitamin C, is an important micronutrient widely present in fresh vegetables and fruits and plays an important role in human health. L-ascorbic acid can enhance human metabolism, relieve the toxicity of heavy metals to a certain extent, and prevent cancer at the same time. Lack of L-ascorbic acid easily leads to scurvy and reduces the body's emergency response ability, but excessive AA can cause serious diseases. As a nutritional fortifier and additive, L-ascorbic acid is widely used in industries such as food, medicine, and cosmetics, and people usually obtain AA through exogenous intake. Therefore, it is crucial to detect the content of L-ascorbic acid in food to ensure human health.

[0003] At present, there are various detection methods for L-ascorbic acid, including capillary electrophoresis, chemometrics, electrochemistry, and fluorescence. Compared with other methods, fluorescence analysis has the advantages of simplicity, specificity, visualization, time-saving, etc., and can meet the requirements of on-site detection in actual scenarios. Currently, most of the materials for fluorescence sensors are carbon dots, quantum dots, and metal nanoclusters, which have certain adverse effects on food and the environment. Therefore, it is necessary to develop convenient, efficient, and environmentally friendly fluorescence sensors.

[0004] Ionic liquids, as environmentally friendly "green solvents and functional materials", have attracted extensive attention. They have negligible vapor pressure, high chemical and thermal stability, and adjustable properties, and have been successfully applied in various fields and are widely used in fields such as gas capture, solvents, catalysts, and extraction, achieving good results. More importantly, the adjustable properties of ionic liquids make it possible to meet specific requirements by combining various cations and anions, showing great potential as fluorescence probes for detecting target objects.

[0005] The present invention synthesizes a sulfonic acid group-modified 8-hydroxyquinoline ionic liquid ([HDQS][P 66614 ) through an acid-base neutralization reaction, forming a probe system for detecting magnesium ions and L-ascorbic acid. In the [HDQS][P 6614 -Mg 2+ system, the fluorescence of [HDQS][P 6614 can be selectively enhanced by magnesium ions and then further quenched by L-ascorbic acid, developing a fluorescence sensor capable of highly selectively, sensitively, and effectively detecting magnesium ions and L-ascorbic acid. Summary of the Invention

[0006] The present invention designs and synthesizes a novel ionic liquid-based fluorescent probe with high sensitivity and specificity, which can be used for the rapid detection of L-ascorbic acid in actual samples and the differential detection of magnesium ions and common metal ions. This method has a low detection limit for the analyte, high sensitivity, a wide linear range, and simple operation.

[0007] The present invention uses 5-sulfonic acid-8-hydroxyquinoline ionic liquid ([HDQS][P 66614 ) as a fluorescence / colorimetric probe, with magnesium ions and L-ascorbic acid as analytes. The specific binding of magnesium ions to [HDQS][P 66614 enhances the fluorescence of the probe, and through the re-complexation of L-ascorbic acid with magnesium ions, the magnesium ions dissociate from [HDQS][P 66614 , quenching the fluorescence of the probe.

[0008] The technical solution of the present invention is as follows:

[0009] A fluorescent ionic liquid with the chemical formula [HDQS][P 66614 , and its structural formula is shown in Formula (I):

[0010]

[0011] The synthesis method of the fluorescent ionic liquid described in the present invention is as follows:

[0012] [P 66614 [OH] is mixed with 5-sulfonic acid-8-hydroxyquinoline in anhydrous ethanol as a solvent, and stirred and reacted at 50 - 80 °C (preferably 60 °C) for 10 - 14 h (preferably 12 h). Then, the solvent is removed by rotary evaporation and dried in a nitrogen atmosphere at 50 - 80 °C (preferably 60 °C) to obtain the fluorescent ionic liquid [HDQS][P 66614 ;

[0013] The molar ratio of [P 66614 [OH] to 5-sulfonic acid-8-hydroxyquinoline is 1:1;

[0014] The [P 66614 [OH] is obtained by de-bromination treatment of trihexyl(tetradecyl)phosphonium bromide ([P 66614 [Br]) with a strongly basic anion exchange resin. The specific de-bromination treatment method is as follows:

[0015] The ethanol solution of [P 66614 [Br] is added to a chromatography column filled with a strongly basic anion exchange resin, and the effluent is collected as the ethanol solution of [P 66614 [OH] (without evaporation to dryness and can be directly used for the reaction).

[0016] The fluorescent ionic liquid of the present invention can be used as a fluorescence / colorimetric probe for the detection of magnesium ions and the detection of L-ascorbic acid in actual samples. The specific detection methods are as follows:

[0017] (1) Plot the standard fitting curve of magnesium ions

[0018] Dissolve the fluorescent ionic liquid [HDQS][P 66614 in absolute ethanol, add the standard magnesium chloride, prepare standard solutions with different magnesium chloride concentrations, and then record the peak height and corresponding peak position of the highest peak of the fluorescence emission spectrum of [HDQS][P 66614 under the conditions of an excitation wavelength of 370 nm, excitation and emission slit widths of 10 nm and 10 nm respectively. Take the fluorescence intensity of the highest peak as the ordinate and the magnesium chloride concentration as the abscissa to fit a linear curve (which can be used for the differential detection of magnesium ions);

[0019] (2) Plot the standard fitting curve of L-ascorbic acid

[0020] Dissolve the fluorescent ionic liquid [HDQS][P 66614 in absolute ethanol and mix it with the magnesium chloride solution to make its fluorescence intensity around 1000 a.u., add standard solutions of different concentrations of L-ascorbic acid, and then record the peak height and corresponding peak position of the highest peak of the fluorescence emission spectrum of the [HDQS][P 66614 -Mg 2+ solution system under the conditions of an excitation wavelength of 370 nm, excitation and emission slit widths of 10 nm and 10 nm respectively. Take the difference in fluorescence intensity before and after adding L-ascorbic acid as the ordinate and the L-ascorbic acid concentration as the abscissa to fit a linear curve;

[0021] (3) Detection of actual samples

[0022] Dissolve the fluorescent ionic liquid [HDQS][P 66614 in absolute ethanol and mix it with the magnesium chloride solution to make its fluorescence intensity around 1000 a.u., then add the sample to be tested, collect the fluorescence emission spectrum under the conditions of an excitation wavelength of 370 nm, excitation and emission slit widths of 10 nm and 10 nm respectively, and quantitatively analyze the concentration of L-ascorbic acid in the actual sample according to the linear curve fitted in step (2).

[0023] In the above detection method,

[0024] The conditions for fluorescence spectrum determination are all an excitation wavelength of 370 nm, excitation and emission slit widths of 10 nm and 10 nm respectively, and the emission wavelength measurement range is 400 - 610 nm;

[0025] The L-ascorbic acid in the actual sample was quantitatively analyzed based on the linear curve fitted with the fluorescence intensity difference before and after the addition of L-ascorbic acid as the ordinate and the L-ascorbic acid concentration as the abscissa; [HDQS][P 66614 Fluorescent / colorimetric probes can be used to detect L-ascorbic acid in coconut juice, orange juice, grape juice, broccoli, potatoes, and spinach;

[0026] The present invention uses fluorescent ionic liquid [HDQS][P 66614 ] is a fluorescent / colorimetric probe, magnesium ions and L-ascorbic acid are used as analytes, and the magnesium ions react with [HDQS][P 66614 ] specific binding enhances the fluorescence of the probe, and the magnesium ions are re-complexed with L-ascorbic acid, so that the magnesium ions are transferred from [HDQS][P 66614 ] falls off, quenching the fluorescence of the probe.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention develops a new type of fluorescent ionic liquid and provides a method for rapid and visual detection of L-ascorbic acid in actual samples and a method for distinguishing magnesium ions from common metal ions. The prepared ionic liquid [HDQ][P 66614 ] as a fluorescent / colorimetric probe, prepare a fixed concentration of ethanol solution, add the actual sample to be tested and mix well. Record the [HDQS][P 66614 ] fluorescence excitation spectrum, and the quantitative detection of magnesium ions and L-ascorbic acid in actual samples was achieved according to the fitted linear curve.

[0029] The present invention synthesizes an ionic liquid with green fluorescence emission by an ion exchange method, which has simple synthesis steps and high synthesis yield; the synthesized [HDQS][P 66614 ] Fluorescent ionic liquids have good thermal stability, are not volatile, and have little environmental pollution; ionic liquids [HDQ][P 66614 ] has strong specificity and sensitivity to magnesium ions and L-ascorbic acid, and can realize the detection of magnesium ions and L-ascorbic acid in a wide linear range; the present invention can perform qualitative analysis and quantitative detection of L-ascorbic acid in actual samples, providing a possibility for the detection of L-ascorbic acid in food. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 For the present invention in [HDQS][P 66614Fluorescence emission spectra of adding magnesium chloride solutions with different concentrations (0.1 μM, 0.2 μM, 0.4 μM, 0.6 μM, 0.8 μM, 0.9 μM, 2 μM, 3 μM, 4 μM, 6 μM, 8 μM, 9 μM, 15 μM, 20 μM, 25 μM, 30 μM, 35 μM, 40 μM, 45 μM) into ethanol solutions of

[0031] Figure 2 For the present invention in [HDQS][P 66614 Visual photos taken under ultraviolet light irradiation of adding magnesium chloride solutions with different concentrations (0, 1 μM, 2 μM, 4 μM, 6 μM, 8 μM, 10 μM) into ethanol solutions of

[0032] Figure 3 For the present invention with [HDQS][P 66614 with the fluorescence intensity as the ordinate and the magnesium chloride concentration (0.1 - 45 μM) as the abscissa to fit a linear curve.

[0033] Figure 4 For the present invention in [HDQS[P 66614 Bar graph comparing the fluorescence intensities of adding magnesium chloride solution (0.01 mM) and other common metal salts into ethanol solutions of

[0034] Figure 5 For the present invention in [HDQS][P 66614 -Mg 2+ Fluorescence emission spectra of adding L - ascorbic acid solutions with different concentrations (0.1 μM, 1 μM, 2 μM, 10 μM, 20 μM, 30 μM, 40 μM, 60 μM, 80 μM, 100 μM, 200 μM) into the solution system of

[0035] Figure 6 For the present invention with the difference in fluorescence intensity before and after adding L - ascorbic acid in the solution system of [HDQS][P 66614 -Mg 2+ as the ordinate and the L - ascorbic acid concentration (0 - 200 μM) as the abscissa to fit a linear curve.

[0036] Figure 7 For the present invention with [HDQS][P 66614 -Mg 2+ Color change diagrams of adding L - ascorbic acid solutions with different concentrations (0, 0.05 mM, 0.1 mM, 5 mM) under sunlight for portable paper devices prepared based on the solution of

[0037] Figure 8 The spike - recovery results of L - ascorbic acid in actual samples (coconut juice, orange juice, grape juice, broccoli, potato, and spinach) for the present invention. Detailed implementation manners

[0038] To better understand the present invention, the content of the present invention will be further elaborated through specific embodiments below. However, the content of the present invention is not limited to the following embodiments, and the following content should not be understood as a limitation to the protection scope of the present invention.

[0039] The chemical reagents and solvents used in the embodiments are all of analytical grade.

[0040] The conditions for fluorescence spectrum determination are that the excitation wavelength is 370 nm, the emission wavelength is 400 - 610 nm, and the excitation and emission slit widths are 10 nm and 10 nm respectively.

[0041] Example 1

[0042] The synthesis of a fluorescent ionic liquid is as follows:

[0043] (1) Debromination treatment of [P 66614 [Br]:

[0044] Slowly add the ethanol solution of [P 66614 [Br] to the chromatography column filled with strongly basic anion exchange resin (Aladdin, Shanghai, AR) ([P 66614 [Br] and the strongly basic anion exchange resin have a mass ratio of 1:6), and collect the effluent ethanol solution of [P 66614 [OH].

[0045] (2) Synthesis of the fluorescent ionic liquid [HDQS][P 66614 :

[0046] Add 0.2252 g of 5-sulfonic acid-8-hydroxyquinoline and the above-obtained ethanol solution of [P 66614 [OH] (containing 5.1847 g of [P 66614 [OH]) into a 250 mL round-bottom flask, add 50 mL of anhydrous ethanol as the solvent, and react under stirring in an oil bath at 60 °C for 12 h, where the molar ratio of [P 66614 [OH] to 5-sulfonic acid-8-hydroxyquinoline is 1:1. After removing the solvent ethanol from the reaction product using a rotary evaporator, heat it to 60 °C in a nitrogen atmosphere and dry it for 30 min to remove trace ethanol and water in the product, and finally obtain a brown viscous liquid. Store it sealed at room temperature. The reaction formula is as follows:

[0047]

[0048] Example 2

[0049] The ionic liquid is used as a colorimetric / fluorescent probe for the rapid detection of magnesium ions. The specific steps include:

[0050] (1) Fluorescence / colorimetric probe for the detection of magnesium ions:

[0051] Weigh 0.0354 g of [HDQS][P 66614 and dissolve it in anhydrous ethanol as the solvent to prepare a 1 mM stock solution. Add 100 μL of different concentrations (0.1 μM, 0.2 μM, 0.4 μM, 0.6 μM, 0.8 μM, 0.9 μM, 2 μM, 3 μM, 4 μM, 6 μM, 8 μM, 9 μM, 15 μM, 20 μM, 25 μM, 30 μM, 35 μM, 40 μM, 45 μM) of magnesium ion solution to 100 μL of the [HDQS][P 66614 stock solution. Collect the fluorescence emission spectra under the conditions of an excitation wavelength of 370 nm, and excitation and emission slit widths of 10 nm and 10 nm respectively. The results are as Figure 1 shown.

[0052] As can be seen from Figure 1 , when the magnesium ion concentration gradually increases from 0.1 μM to 45 μM, the fluorescence intensity of the fluorescence probe gradually increases.

[0053] (2) Accurately add 200 μL of the stock solution to several centrifuge tubes, and then add magnesium ion solutions with different concentrations (0, 1 μM, 2 μM, 4 μM, 6 μM, 8 μM, 10 μM). Take visual photos under ultraviolet light irradiation at 365 nm. As Figure 2 shown.

[0054] (3) Plotting the standard curve

[0055] Perform quantitative analysis with a linear curve fitted with fluorescence intensity as the ordinate and magnesium chloride concentration as the abscissa. The results are as Figure 3 shown. When the magnesium ion concentration is 0.1 - 45 μM, the equation obtained by linear fitting is y = 188.6314x - 18.2674 (R 2 = 0.994).

[0056] (4) Interference of common metal ions on the detection of magnesium ions by [HDQS][P 66614

[0057] Mix 100 μL of the stock solution with 100 μL of 0.01 mM magnesium chloride solution or 100 μL of a solution of other metal salts (Co(NO3)2, BaCl2, Cr(NO3)3, Na2S, Mn(Ac)4, Cu(NO3)2, KCl, AgNO3, NiCl3, Pb(NO3)2, CdCl2, Zn(NO3)2, CaCl2, MnCl2, Al(NO3)3, FeSO4, FeCl3) at 0.1 mM, and make up the volume to 1 mL with absolute ethanol. Collect the fluorescence emission spectrum under the conditions of an excitation wavelength of 370 nm, an excitation slit width of 10 nm, and an emission slit width of 10 nm. Plot a bar chart with the fluorescence intensity as the ordinate and the type of metal salt as the abscissa, as Figure 4 .

[0058] Example 3

[0059] The detection system formed by the ionic liquid as a colorimetric / fluorescent probe is used for the rapid detection of L-ascorbic acid in actual samples. The specific steps include:

[0060] (1) Detection of L-ascorbic acid by the fluorescent / colorimetric probe:

[0061] Mix 100 μL of the stock solution of [[HDQS]][[P 66614 with 6 μM magnesium chloride solution to make the fluorescence intensity around 1000 a.u., and then add 100 μL of L-ascorbic acid solutions with different concentrations (0.1 μM, 1 μM, 2 μM, 10 μM, 20 μM, 30 μM, 40 μM, 60 μM, 80 μM, 100 μM, 200 μM). Collect the fluorescence emission spectrum under the conditions of an excitation wavelength of 370 nm, an excitation slit width of 10 nm, and an emission slit width of 10 nm. The results are as Figure 5 shown.

[0062] It can be seen from Figure 5 that when the concentration of L-ascorbic acid gradually increases from 0 μM to 200 μM, the fluorescence intensity of the fluorescent probe gradually weakens and exhibits a blue shift.

[0063] (2) Plotting of the standard curve

[0064] Perform quantitative analysis using a linear curve fitted with the difference in fluorescence intensity before and after adding L-ascorbic acid as the ordinate and the concentration of L-ascorbic acid as the abscissa. The results are as Figure 6 shown. When the concentration of L-ascorbic acid is 0 - 200 μM, the equation obtained by linear fitting is y = 3.5704x - 289.6028 (R 2 = 0.992).

[0065] (3) A portable paper-based device was prepared by the impregnation method. Obvious color changes occurred under sunlight when different concentrations (0, 0.05 mM, 0.1 mM, 5 mM) of L-ascorbic acid solution were added, as Figure 7 shown.

[0066] (4) Detection of L-ascorbic acid in actual samples

[0067] Homogenize 1 ml of the beverage and then pass it through a 0.45 μm membrane filter. Dilute the filtered juice with 9 ml of ethanol. Weigh 0.3 g of fresh vegetables accurately and homogenize them, then juice, centrifuge, and dilute the liquid sample 100-fold for the standard addition recovery experiment. Add L-ascorbic acid solution to the actual sample as the test solution, add 100 μL of the stock solution to the test solution, and collect the fluorescence emission spectrum under the conditions of an excitation wavelength of 370 nm, excitation and emission slit widths of 10 nm and 10 nm respectively. Analyze the L-ascorbic acid in the actual sample by the standard addition recovery method, and the results are as Figure 8 shown.

Claims

1. Application of a fluorescent ionic liquid as a fluorescent / colorimetric probe in the detection of magnesium ions and L-ascorbic acid in real samples; The chemical formula of the fluorescent ionic liquid is [HDQS][P 66614 ], the structural formula is shown in formula (I):

2. The use according to claim 1, characterized in that The synthesis method of the fluorescent ionic liquid is: [P 66614 ][OH] and 5-sulfonic acid-8-hydroxyquinoline were mixed in anhydrous ethanol, stirred at 50-80 ° C for 10-14 h, and then the solvent was removed by rotary evaporation and dried in a nitrogen atmosphere at 50-80 ° C to obtain a fluorescent ionic liquid [HDQS][P 66614 ].

3. The use according to claim 2, characterized in that The [P 66614 The molar ratio of ][OH] to 5-sulfonic acid-8-hydroxyquinoline is 1:

1.

4. The use according to claim 2, characterized in that The [P 66614 ][OH] by [P 66614 ][Br] is obtained by debromination treatment with a strong alkaline anion exchange resin, wherein the debromination treatment method is: [P 66614 The ethanol solution of ][Br] was added to a chromatography column containing a strong alkaline anion exchange resin, and the effluent was collected as [P 66614 ][OH] in ethanol solution.

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