CN110172148B - Preparation method of non-conjugated fluorescent polymer and application of non-conjugated fluorescent polymer in picric acid detection - Google Patents
Preparation method of non-conjugated fluorescent polymer and application of non-conjugated fluorescent polymer in picric acid detection Download PDFInfo
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- SPSSULHKWOKEEL-UHFFFAOYSA-N 2,4,6-trinitrotoluene Chemical compound CC1=C([N+]([O-])=O)C=C([N+]([O-])=O)C=C1[N+]([O-])=O SPSSULHKWOKEEL-UHFFFAOYSA-N 0.000 description 4
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Abstract
The invention discloses a preparation method of a non-conjugated fluorescent polymer and application thereof in picric acid detection, wherein the preparation method of the non-conjugated fluorescent polymer comprises the following steps: the non-conjugated fluorescent polymer is prepared by taking polyethyleneimine and citric acid as raw materials and deionized water as a solvent, heating, stirring and reacting to obtain a product solution, dialyzing, concentrating and drying. When a trace amount of picric acid is added to the aqueous solution of the non-conjugated fluorescent polymer, the fluorescence of the non-conjugated fluorescent polymer is quenched due to electron transfer and internal filtering effects between the picric acid and the non-conjugated fluorescent polymer, and the quenching degree is in a linear relationship with the concentration of the picric acid within a certain range. Therefore, the method for detecting picric acid is established, is simple to operate, has high sensitivity and good selectivity, and can be used for quickly detecting picric acid in real time.
Description
Technical Field
The invention relates to a preparation method of a non-conjugated fluorescent polymer and application of the non-conjugated fluorescent polymer in picric acid detection.
Background
Picric acid is a strong acid, similar to many other nitroaromatics, and is a powerful explosive even more explosive than trinitrotoluene (TNT), and is widely used in world war ii for the first time. Meanwhile, picric acid is also an important raw material for dyes, medicaments and chemical reagents. On the other hand, similar to its importance in various fields, picric acid is also very harmful to the human body, it is strongly irritating to the skin and eyes, and it is liable to cause damage to organic body weight proteins in the respiratory system. As picric acid is very easy to dissolve in water, underground water and soil are very easy to be polluted when the picric acid is exposed, and the health of surrounding residents is harmed, so that the picric acid in water can be detected with important and practical significance.
Although many methods for detecting picric acid exist so far, some traditional methods are time-consuming, low in sensitivity, poor in selectivity, complex in synthesis steps of some fluorescent probes and the like. Therefore, the development of a new fluorescent material which has simple preparation, no toxicity and high sensitivity and selectivity for TNP detection has important theoretical value and application value.
Disclosure of Invention
The invention aims to provide a preparation method of a non-conjugated fluorescent polymer and application of the non-conjugated fluorescent polymer in picric acid detection. The non-conjugated fluorescent polymer with high fluorescence and good water solubility can be prepared through one-step reaction, and the preparation condition is mild; the non-conjugated fluorescent polymer prepared by the invention can generate electron transfer and internal light filtering effect with picric acid, so that the fluorescence intensity of the non-conjugated fluorescent polymer is reduced, the phenomenon can be utilized to realize quantitative detection of the picric acid, the detection method has high sensitivity and low detection limit, and can eliminate the interference of other substances.
The technical scheme adopted by the invention is as follows:
a method of preparing a non-conjugated fluorescent polymer, the method comprising the steps of:
(1) heating, stirring and reacting Polyethyleneimine (PEI) and citric acid serving as raw materials and deionized water serving as a solvent to obtain a product solution;
(2) and dialyzing, concentrating and drying the product solution to obtain the non-conjugated fluorescent polymer (NFP).
The mass ratio of the polyethyleneimine to the citric acid is 1: 170-200, and the obtained NFP has the maximum fluorescence intensity within the range of the ratio.
The heating reaction conditions are as follows: stirring and reacting for 7-10 h at 65-80 ℃.
Further, the step (1) specifically includes the steps of: mixing the water solution of polyethyleneimine with the water solution of citric acid, adding distilled water to obtain a mixed solution, and stirring and reacting the mixed solution at 65-80 ℃ for 7-10 hours to obtain a product solution.
Further, the concentration of the water solution of the polyethyleneimine is 0.5-2.0 g/L; the concentration of the citric acid aqueous solution is 0.001-0.1M; the volume ratio of the polyethyleneimine aqueous solution to the citric acid aqueous solution to the distilled water is 1: 10-30: 60-90.
Further, the step (1) specifically includes the following steps: 400. mu.L of a 1g/L aqueous solution of polyethyleneimine and 8mL of a 0.05M aqueous solution of citric acid were mixed, and then distilled water was added thereto to make the mixture 40mL, followed by stirring and reacting at 70 ℃ for 8 hours.
The invention also provides the application of the non-conjugated fluorescent polymer prepared by the preparation method in quantitative detection of picric acid.
The invention also provides a picric acid detection method, which comprises the following steps:
(a) preparing a series of aqueous solutions of non-conjugated fluorescent polymers containing picric acid with different concentrations, adjusting the pH value of each system, standing, and testing to obtain a fluorescence spectrogram of each system; the non-conjugated fluorescent polymer is prepared according to the preparation method of any one of claims 1 to 5;
(b) and (3) drawing a standard curve by taking the concentration of the picric acid as a horizontal coordinate and the fluorescence intensity of each system as a vertical coordinate to obtain a linear equation, and calculating the concentration of the picric acid to be detected corresponding to any fluorescence intensity value according to the linear equation.
Further, in the step (a), the concentration of the aqueous solution of the non-conjugated fluorescent polymer is 0.16 g/L; the picric acid concentrations were 0, 0.5, 2.5, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150 μ M, respectively.
In the step (a), a phosphate buffer solution is used to adjust the pH of each system to 8.0-8.5, preferably 8.5, the lower pH value can reduce the deprotonation degree of picric acid (TNP), the higher pH value can reduce the protonation degree of amine groups on the surface of NFP, and at pH8.5, NFP can adsorb TNP more easily to form a non-luminous complex, so that at pH8.5, the fluorescence quenching degree is maximum, which is the most favorable test condition.
In the step (a), the test conditions are as follows: the excitation wavelength is 360nm, and the excitation slit and the emission slit are both 10.0 nm.
In the step (a), the standing time is 5 min.
In the step (b), the fluorescence intensity is the fluorescence intensity at a wavelength of 450 nm; the standard curve is Y-1943.4 +24.3C, where Y is the fluorescence intensity at a wavelength of 450nm and C is the picric acid concentration in μ M. The linear correlation coefficient of the standard curve is 0.991, and the detection limit of the method can reach 0.7 mu M at the lowest.
According to the invention, PEI and citric acid are used as raw materials, and the water-soluble polymer NFP with strong fluorescence emission is synthesized in one step through amidation reaction. When a trace amount of picric acid is added to an aqueous NFP solution, fluorescence of NFP is quenched due to electron transfer and internal light filtering effects between picric acid and NFP, and the degree of quenching is linear with the concentration of picric acid within a certain range. Therefore, the method for detecting picric acid is established, is simple to operate, has high sensitivity and good selectivity, and can be used for quickly detecting picric acid in real time.
The non-conjugated fluorescent polymer (NFP) prepared by the invention can also realize qualitative detection of picric acid, before the picric acid is not added, the aqueous solution of the NFP is light yellow under natural light, and emits strong blue fluorescence under the irradiation of an ultraviolet lamp; after the picric acid is added, the NFP aqueous solution gradually changes from light yellow to dark yellow under natural light along with the increase of the added amount of the picric acid, and under the irradiation of an ultraviolet lamp, the blue fluorescence gradually weakens along with the increase of the concentration of the added picric acid until the NFP aqueous solution disappears.
Drawings
FIG. 1 shows the process of NFP synthesis and the mechanism of quenching picric acid;
FIG. 2 is a chart of the infrared spectra of Polyethyleneimine (PEI) (a), citric acid (b) and NFP (c);
FIG. 3 is a graph of UV-VIS absorption spectra of PEI, citric acid and NFP;
FIG. 4 is a fluorescence spectrum of the corresponding NFP at different excitation wavelengths;
FIG. 5 is a graph showing the change in fluorescence intensity of the detection system after picric acid of different concentrations was added;
FIG. 6 is a graph showing the relationship between the fluorescence intensities of picric acid at different concentrations in a test system;
FIG. 7 is a linear relationship chart of picric acid concentration in the range of 0 to 30 μ M;
FIG. 8 is a graph of the effect of pH on the degree of fluorescence quenching;
FIG. 9 is a graph of a selectivity experiment for NFP detection of picric acid;
FIG. 10 is a diagram showing an excitation spectrum, an emission spectrum and an ultraviolet absorption spectrum of picric acid in NFP.
Detailed Description
The invention is described in detail below with reference to the following examples and the accompanying drawings.
Example 1
A preparation method of a non-conjugated fluorescent polymer comprises the following steps:
mixing 400 mu L of 1g/L PEI and 8mL of 0.05M citric acid, adding the mixture into a conical flask, adding water to 40mL, heating and stirring the mixed solution at 70 ℃ for 8h to obtain a product solution of polymer NFP with strong fluorescence emission, putting the product solution into a dialysis bag with the cut-off molecular weight of 3500Da for dialysis for 6h, removing unreacted micromolecule citric acid by using ultrapure water as dialysis liquid, collecting the solution in the dialysis bag, concentrating the solution, and drying for later use to obtain the non-conjugated fluorescent polymer material (NFP).
The product obtained in this example was characterized by uv, ir and fluorescence spectra, respectively, with the following results:
the infrared characterization is shown in FIG. 2, in which a, b, and c represent PEI and lemon, respectivelyFT-IR spectra of citric acid and NFP. 1261cm in PEI-1～1660cm-1Several characteristic absorptions in the region are associated with the stretching vibration of the N-H bond. The strength of the N-H bond in NFP is reduced, indicating that part of the amino groups are reacted with citric acid. 2930cm in PEI-1And 2850cm-1The absorption peak at (A) corresponds to CH2The stretching vibration of (2). 3495cm in citric acid-1The stretching vibration peak of-OH is located, and the stretching vibration of-OH in NFP disappears because-OH reacts with amino in PEI. 1703cm-1And 1743cm-1Characteristic absorption corresponding to C ═ O, 1396cm-1Is of CH21178cm of bending vibration of-1And (b) is asymmetric stretching of the C-O bond. 1724cm in NFP-1A stretching vibration peak of 1625cm-1The weak stretching vibration peak of C ═ O connected with-NH shows that amido bond is formed. 1396cm-1Is represented by CH2Bending vibration of 1222cm-1The peak at the C-N bond is a vibration peak, further illustrating the formation of the amide.
The UV characterization is shown in FIG. 3, which is a UV-VIS spectrum of PEI, citric acid and NFP, respectively. The UV-VIS spectrum shows that NFP has a new absorption peak around 358nm, while PEI and citric acid do not absorb significantly here, and this new absorption band is due to the newly formed amide bond.
The fluorescence characterization is shown in fig. 4, and it can be seen from the figure that, as the excitation wavelength is increased from 330nm to 410nm, the position of the highest peak of the NFP fluorescence spectrum is not changed and always remains at 450nm, which indicates that the NFP synthesized by the present invention is different from the carbon quantum dot obtained by high temperature carbonization reported in the prior art. In general, the wavelength position corresponding to the fluorescence intensity maximum in the emission spectrum of the carbon quantum dot changes with the change of the excitation wavelength, but the wavelength position corresponding to the fluorescence intensity maximum of the NFP synthesized in this experiment does not change with the change of the excitation wavelength. And it can be seen from the figure that the fluorescence intensity at 450nm is maximum when the excitation wavelength is 360nm, so 360nm is selected as the excitation wavelength in the experiment. This stationary nature of the emission spectrum is mainly attributed to the fact that the crosslinking of polyethyleneimine by citric acid reduces the fluidity of the polymer and the formation of large amounts of amide on the polymer surface. The fluorescence characteristics of NFP indicate that NFP can be used as an excellent fluorescent probe.
Example 2
Application of non-conjugated fluorescent polymer prepared in example 1 in quantitative detection of picric acid
The method for detecting picric acid comprises the following steps:
(a) a series of aqueous solutions of the unconjugated fluorescent polymer obtained in example 1, containing picric acid at different concentrations, were prepared, the pH of each system was adjusted to 8.5 using 10mM phosphate buffer solution and left at room temperature for 5min, and fluorescence spectra of each system were obtained by testing using a Hitachi F-4500 fluorescence spectrophotometer under an excitation wavelength of 360nm and an excitation and emission slit of 10.0nm, as shown in FIGS. 5 and 6, from which it can be seen that, when picric acid was added to the system, the fluorescence intensity of the NFP polymer originally having strong fluorescence emission gradually decreased and the degree of decrease of fluorescence increased with the increase in the amount of picric acid added.
The concentration of the aqueous solution of the non-conjugated fluorescent polymer is 0.16 g/L; the concentrations of picric acid are 0, 0.5, 2.5, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150 μ M, respectively;
(b) drawing a standard curve by taking the concentration of picric acid as an abscissa and the fluorescence intensity of each system as an ordinate, and obtaining a linear equation Y of 1943.4+24.3C as shown in FIG. 7, wherein Y is the fluorescence intensity at a wavelength of 450nm, and C is the concentration of picric acid and has a unit of μ M; the linear correlation coefficient is R0.991, and the lowest detection limit can reach 0.7 mu M. The concentration of the picric acid to be detected under any fluorescence intensity value can be calculated according to a linear equation. The picric acid concentration is within the range of 0-30 mu M, and the picric acid concentration and the fluorescence intensity at 450nm are in a linear relation.
Example 3
Optimization of pH of detection system in application of non-conjugated fluorescent polymer in quantitative detection of picric acid
Formulation 0.16g L-1Non-conjugated fluorescent Polymer obtained in example 1 containing 50. mu.M picric acidThe pH of each system is adjusted to 4.2, 5.3, 5.72, 6.0, 6.5, 7.0, 7.4, 8.0, 8.5, 9.1, 10.0 and 10.5 respectively by using 10mM phosphate buffer solution, the system is placed at room temperature for 5min, a fluorescence spectrum of each system is tested by using a Hitachi F-4500 fluorescence spectrophotometer under an excitation wavelength of 360nm and an excitation and emission slit of 10.0nm, the fluorescence quenching value of the system at 450nm before and after adding picric acid is plotted by taking the pH as an abscissa, as shown in FIG. 8, the fluorescence quenching degree of the picric acid on NFP is influenced by the pH, and the fluorescence quenching degree of the picric acid on the NFP is maximum when the pH of the system is 8.5. Therefore, the pH of the detection system is controlled to be 8.5, so that the detection is sensitive.
Example 4
Application of non-conjugated fluorescent polymer in quantitative detection of picric acid, and selectivity experiment of non-conjugated fluorescent polymer for picric acid
A stable and excellent fluorescent probe must have good selectivity and anti-interference capability. In order to investigate the anti-interference capability of the fluorescent polymer, some common substances such as trinitrotoluene, catechol, resorcinol, toluene and Cl are selected as interferents in the experiment-、Br-、I-、S2 -、NO3 -、CO3 2-、Mg2+、Ca2+Interference experiment is carried out, in the detection system, the picric acid concentration is 25 MuM, the trinitrotoluene concentration is 50 MuM, the rest interferent concentrations are 250 MuM, and the NFP aqueous solution concentration is 0.16g L-1In (iii). As shown in FIG. 9, the addition of picric acid maximizes the quenching of NFP fluorescence, and the quenching of NFP fluorescence by other substances except picric acid is negligible. The experimental result shows that the NFP polymer nanoparticles have good selectivity and anti-interference performance when used for detecting picric acid.
Example 5
Mechanism discussion of bitter acid detection by non-conjugated fluorescent polymer
In order to research the quenching mechanism of picric acid on NFP, the invention researches related fluorescence and ultraviolet spectra. As can be seen from fig. 10, the excitation spectrum (λ ex ═ 360nm), the emission spectrum (λ em ═ 450nm) of NFP and the ultraviolet absorption spectrum of picric acid overlap to a large extent, so that the internal fluorescence filtering effect (IEF) can be effectively generated, i.e. the excitation light of NFP and the emission light generated by NFP by the fluorescence instrument are absorbed by the detection object picric acid. The absorption of the excitation light of the instrument by picric acid means that the NFP acquires less excitation light energy and the resulting emission light becomes weaker.
On the other hand, as can be seen from fig. 10, picric acid also absorbs part of the NFP emission spectrum. Under this dual absorption, the apparent emission intensity of the NFP will be effectively quenched. This absorption increases gradually with increasing picric acid concentration, as evidenced by a gradual decrease in the intensity of the NFP fluorescence emission.
Picric acid, also known as trinitrophenol, is a typical electron withdrawing species, whereas a large number of electron donating group amines are present on the NFP surface. Under the dipole effect, free picric acid in solution is adsorbed to the surface of NFP to form a non-fluorescing complex, thereby quenching NFP fluorescence, as shown in fig. 1. Therefore, the fact that picric acid can effectively quench the fluorescence emission of NFP is mainly attributed to the fact that the internal light filtering effect and the adsorption effect of NFP on picric acid form a non-luminous complex, thereby showing that NFP has higher sensitivity on picric acid.
The above detailed description of the preparation of a non-conjugated fluorescent polymer and its use in picric acid detection with reference to the examples is illustrative and not restrictive, and several examples may be cited within the limits set forth, so that variations and modifications may be made without departing from the general inventive concept and, therefore, fall within the scope of the appended claims.
Claims (9)
1. A preparation method of a non-conjugated fluorescent polymer is characterized by comprising the following steps:
(1) heating, stirring and reacting polyethyleneimine and citric acid serving as raw materials and deionized water serving as a solvent to obtain a product solution;
(2) dialyzing, concentrating and drying the product solution to obtain a non-conjugated fluorescent polymer (NFP);
in the step (1), the mass ratio of the polyethyleneimine to the citric acid is 1: 170-200; the heating reaction condition is that the stirring reaction is carried out for 7-10 h at 65-80 ℃.
2. The preparation method according to claim 1, wherein the step (1) specifically comprises the steps of: mixing the water solution of polyethyleneimine with the water solution of citric acid, adding distilled water to obtain a mixed solution, and stirring and reacting the mixed solution at 65-80 ℃ for 7-10 hours to obtain a product solution.
3. The method according to claim 2, wherein the concentration of the aqueous solution of polyethyleneimine is 0.5 to 2.0 g/L; the concentration of the citric acid aqueous solution is 0.001-0.1M; the volume ratio of the polyethyleneimine aqueous solution to the citric acid aqueous solution to the distilled water is 1: 10-30: 60-90.
4. The preparation method according to claim 1, wherein the step (1) specifically comprises the steps of: 400. mu.L of a 1g/L aqueous solution of polyethyleneimine and 8mL of a 0.05M aqueous solution of citric acid were mixed, and then distilled water was added thereto to make the mixture 40mL, followed by stirring and reacting at 70 ℃ for 8 hours.
5. Use of the non-conjugated fluorescent polymer prepared according to the preparation method of any one of claims 1 to 4 for the quantitative detection of picric acid.
6. A method for detecting picric acid is characterized by comprising the following steps:
(a) preparing a series of aqueous solutions of non-conjugated fluorescent polymers containing picric acid with different concentrations, adjusting the pH value of each system, standing, and testing to obtain a fluorescence spectrogram of each system; the non-conjugated fluorescent polymer is prepared according to the preparation method of any one of claims 1 to 4;
(b) and (3) drawing a standard curve by taking the concentration of the picric acid as a horizontal coordinate and the fluorescence intensity of each system as a vertical coordinate to obtain a linear equation, and calculating the concentration of the picric acid to be detected corresponding to any fluorescence intensity value according to the linear equation.
7. The detection method according to claim 6, wherein in the step (a), the concentration of the aqueous solution of the non-conjugated fluorescent polymer is 0.16 g/L; the picric acid concentrations were 0, 0.5, 2.5, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150 μ M, respectively.
8. The detection method according to claim 6, wherein in the step (a), the pH of each system is adjusted to 8.0-8.5 by using a phosphoric acid buffer solution, and the test conditions are as follows: the excitation wavelength is 360nm, and the excitation slit and the emission slit are both 10.0 nm.
9. The detection method according to claim 6, wherein in the step (b), the standard curve is Y-1943.4 +24.3C, wherein Y is fluorescence intensity at a wavelength of 450nm, and C is picric acid concentration in μ M.
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