CN109900673B - Method for improving detection sensitivity of heavy metal elements in biomass tar - Google Patents
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Abstract
The invention provides a method for improving detection sensitivity of heavy metal elements in biomass tar, which comprises the following steps: (1) dissolving a quantitative tar sample in a quantitative methanol solution; (2) adding a complexing agent solution into the solution prepared in the step (1) to obtain a solution to be detected; (3) placing the solution to be detected in a detection pool, and detecting the fluorescence spectrum performance of the solution to be detected; and (4) comparing the fluorescence spectrum performance of the solution to be detected with the fluorescence spectrum performance of the standard substance, and calculating the content of heavy metal elements in the tar. The method has high detection sensitivity and selectivity for heavy metal ions.
Description
Technical Field
The invention belongs to the technical field of detection, and particularly relates to a method for improving detection sensitivity of heavy metal elements in biomass tar.
Background
Compared with common oil products such as fuel oil and edible oil, the biomass tar has very complex components, contains various condensed ring compounds, phenolic compounds and the like, and also contains heavy metal ions, alkali metals, acids, gases, alkaline gases and the like. Measurement techniques for these contaminants enable the determination of tar cleanliness levels and assessment of quality for subsequent applications such as engine use. The nickel and vanadium elements in the biomass tar can cause the poisoning of a catalyst used in the subsequent deep processing of the coal tar, so that the catalyst loses activity and loses effectiveness, and on the other hand, the coal tar can generate corrosive products in the combustion process to cause equipment corrosion, so that the accurate determination of the nickel, iron and vanadium contents in the coal tar is particularly important. The commonly used test methods are spectrophotometry and atomic absorption, the two measurement methods are complicated to operate, various metal elements interfere with each other, and corresponding reagents are required to be added to eliminate the interference so as to measure the corresponding elements.
CN105466982B discloses a method for detecting heavy metals in water, which comprises the following steps: (A1) sending the liquid with the volume of V0 and containing the heavy metal ions to be detected to a detection pool to obtain the peak current value P01 for dissolving out the heavy metal ions to be detected; (A2) sending a water sample with the volume of V1 to the detection pool, and mixing the water sample with liquid in the detection pool to obtain a peak current value Ps for dissolving out the heavy metal ions to be detected; (A3) discharging the mixed liquid in the detection pool, and cleaning the detection pool; (A4) sending the liquid with the volume of V0 and containing the heavy metal ions to be detected to a detection pool to obtain the peak current value P02 for dissolving out the heavy metal ions to be detected; (A5) and (3) sending the heavy metal ion correction liquid to be detected with the volume of V1 to the detection pool, and mixing the heavy metal ion correction liquid with the liquid in the detection pool to obtain the peak current value Pb dissolved out by the heavy metal ions to be detected.
CN108051426A discloses a heavy metal detection method, which comprises the following steps: step 1, adopting electrode enrichment reaction to provide different voltage values, selecting a pure aluminum sheet with the length of 5cm and the width of 1cm as a cathode of a power supply, using a platinum wire electrode as an anode, and adding a reference electrode; in the electrode enrichment process, an electrochemical workstation provides electrons for a cathode, heavy metal cations in a solution can gather to the cathode under the action of an electric field to obtain electrons, and the cations are converted into simple substances from an ionic state and are attached to the surface of a cathode material; with the progress of the reaction process, a layer of uniform heavy metal attached film which is an object of LIBS laser ablation is formed on the surface of an aluminum sheet in the solution, and a sample is obtained after the aluminum sheet is dried for 5 min; and 2, performing laser ablation on the surface of the sample by adopting laser with enough power emitted by a laser, instantly gasifying surface substances and generating plasma signals, emitting characteristic spectra of elements by the plasma in the evolution process, and correspondingly obtaining the element composition and the content of the sample by analyzing information such as the wavelength, the intensity and the like of spectral lines.
CN108827890A discloses a method for detecting heavy metals in wastewater, which comprises the following steps: (1) collecting a water sample in wastewater, filtering impurities after collection, storing at normal temperature, adding 5mL of concentrated nitric acid into a test tube filled with the wastewater, shaking up, putting the test tube on an electric hot plate, heating and digesting the test tube to about 85mL, taking out the test tube, adding 5mL of concentrated nitric acid and 2mL of hydrogen peroxide, continuously putting the test tube on the electric hot plate, heating the test tube to about 75mL, taking out the test tube, cooling to the room temperature, adding 10mL of hydrochloric acid and 2mL of 10% of ammonium chloride, and transferring the test tube to a 100mL colorimetric tube; (2) putting the pretreated sample into a beaker, adding aminoacetic acid-HCl buffer solution to adjust the pH value of the solution to 3.0-4.0, putting the solution into a conical flask, and titrating with EDTA standard solution; (3) taking the solution, analyzing the overlapping problem of two absorption spectra by using a least square method by using a multivariate calibration-ultraviolet visible light photometry method and using the difference between the absorption spectra of the Cr (III) complex and the Cr (VI) per se, and simultaneously measuring the Cr (III) and the Cr (VI).
CN108325508A discloses an adsorption film for heavy metal active states, wherein the active ingredient of the adsorption film is sodium alginate-polyglutamic acid SA-PGA gel, and the SA-PGA gel is prepared by the following steps: and placing SA-PGA resin powder into an acrylamide gel solution, uniformly stirring, adding an ammonium persulfate solution and tetramethylethylenediamine, injecting into a glass mold, culturing at a certain temperature, placing the glass mold in distilled water for a certain time, taking out gel formed in the glass mold, and hydrating with distilled water to obtain the SA-PGA gel.
The research of the heavy metal detection method, such as the creep culture and the like, the agriculture science of Anhui, 20 2013, comparatively analyzes the traditional method (such as an atomic absorption spectrometry, an atomic fluorescence photometry, a high performance liquid chromatography and the like) and the rapid detection method (an enzyme analysis method, an immunoassay technology and the like) of the heavy metal detection, and discusses the problems of the existing heavy metal detection technology and the development direction of the future detection technology.
For the detection of heavy metal ions in aqueous solutions, there are established measurement techniques. However, for the detection of heavy metal elements, especially heavy metal ions, in tar, there is no perfect measurement technique in the related art, and the conventional detection technique of heavy metal ions in aqueous solution is still used. However, when the conventional technology for detecting heavy metal ions in an aqueous solution is adopted, there is a case where a detection error is conspicuous due to insufficient detection sensitivity, which causes a great limitation in the detection of heavy metal ions in tar. In the prior art, reports on how to carry out high-sensitivity detection on heavy metal ions in biomass tar are not found.
Disclosure of Invention
The inventor carries out deep research and a large number of experiments aiming at the factors restricting the detection sensitivity of the heavy metal elements in the biomass tar through cooperative development on the basis of system research, and can effectively solve the problem of the detection sensitivity of the heavy metal ions in the biomass tar.
In one aspect of the invention, a method for improving the detection sensitivity of heavy metal elements in biomass tar is provided, and the method comprises the following steps: (1) dissolving a quantitative tar sample in a quantitative methanol solution; (2) adding a complexing agent solution into the solution prepared in the step (1) to obtain a solution to be detected; (3) placing the solution to be detected in a detection pool, and detecting the fluorescence spectrum performance of the solution to be detected; and (4) comparing the fluorescence spectrum performance of the solution to be detected with the fluorescence spectrum performance of the standard substance, and calculating the content of heavy metal elements in the tar.
Preferably, the pH of the solution to be tested is adjusted to 8-10, preferably 9, using a buffer in step (2).
As understood by those skilled in the art, the quantification is the basis of the final calculation, and those skilled in the art can select an appropriate quantification according to the actual detection needs, such as detection equipment and the like.
Preferably, prior to step (1), the tar is filtered.
Preferably, the filtration is performed using an organic membrane.
Preferably, the organic film is a polymer film.
Preferably, the filtration is capable of removing phenolics from the tar sample.
More preferably, the filtration is capable of removing 50 to 90 wt% of the phenolics in the tar sample.
More preferably, the phenolic substance comprises one or more of ethylphenol, m-cresol, phenol, methoxyphenol.
The inventor of the invention finds that, in the biomass tar, according to the biomass source, there may be contained ethyl phenol, m-cresol, phenol, methoxyphenol and other phenolic substances, and these phenolic substances have certain interference effect on the subsequent fluorescence detection. For example, the phenolic substance may affect the complexation of heavy metal ions by the complexing agent, and the phenolic substance may easily interact with the complexing agent, including hydrogen bonds, to deteriorate the fluorescence effect of the complexing agent. Thus, in the present application, it is preferred to remove or reduce the phenolic content of the biomass tar sample prior to detection.
Of course, as will be appreciated by those skilled in the art, for the detection of heavy metal elements in certain types of biomass tar, such filtration to remove phenolics is unnecessary or unnecessary.
The present inventors have found that a particularly effective and simple way of handling is to filter a tar sample using a filter membrane of a specific material. This filtration is carried out at normal temperature. Compared with the common distillation method, the method is simpler. In addition, if distillation separation is performed, on one hand, the separated substance is easy to form an azeotropic mixture with other substances and is difficult to remove by distillation, and on the other hand, other substances in the tar, such as a fused ring compound, can be decomposed due to heating, and the decomposition product can complex heavy metal ions and has certain fluorescence, so that the accuracy of subsequent fluorescence detection is influenced.
Particularly preferably, the material of the filter membrane is a material prepared by the following steps: dissolving 1-5 parts by weight of cyclodextrin, 20-50 parts by weight of PVC powder, 50-70 parts by weight of 2-nitrophenyl-octyl ether polar plasticizer and 50-70 parts by weight of potassium tetrakis (4-chlorophenyl) borate lipophilic ionic additive in THF, uniformly mixing, and evaporating THF.
More particularly preferably, 1g of dextrin, 30g of PVC powder, 66g of 2-nitrophenyl-octyl ether polar plasticizer, 120g of potassium tetrakis (4-chlorophenyl) borate lipophilic ionic additive are dissolved in 2000mL of THF, mixed until homogeneous, and the THF is evaporated off.
In the preparation of the membrane, the material can be dissolved in THF, then spread on a vessel, and the solvent is removed to obtain the filter membrane. Preferably, the solution is placed in a polytetrafluoroethylene vessel with the diameter of 20mm, and is slowly dried to obtain the filter membrane.
The filter membrane has a preferred adsorption function for biomass tar and is capable of removing 50 to 90 wt% of phenolic substances, preferably 60 to 90 wt% of phenolic substances, and more preferably 80 to 90 wt% of phenolic substances in a tar sample. The preparation method of the membrane is simple and has low cost.
In a preferred embodiment of the present invention, the methanol in step (1) contains MeCN and water, each independently in a volume of 5 to 20% of the total volume of methanol. That is, the volume percentages of MeCN and water are based on the total volume of methanol, MeCN and water.
Preferably, the complexing agent is a multidentate complex.
Particularly preferably, the complex is a complex represented by the following formula (1):
the complexing agent has particularly good complexing fluorescence property on heavy metal ions in tar. In particular in mixed aqueous-organic media, with heavy metal ions (e.g. Cr)3+、Pb2+、Ni2+) When combined, the fluorescent probe can show a fluorescence emission signal at 488nm and a fluorescence excitation signal at 388nm, and has a considerable fluorescence response in a visible light region, so that the fluorescent probe can be used as a heavy metal ion selective detection sensing platform.
The complexing agent of formula (I) may be prepared by the following method: the substituted aroylhydrazide (e.g. 4g, 2.32mmol) was dissolved in THF (60mL) and an equimolar amount of o-methoxyphenyl isothiocyanate (2.32mmol) was dissolved in 50mL of THF respectively, the two solutions were mixed slowly and stirred at room temperature for 20 h, the degree of reaction progress was monitored by thin layer chromatography, and at the end, THF was evaporated off to give the complexing agent of formula (I).
The compound is characterized as follows: mp 131-; rf 0.31 (n-hexane: ethyl acetate, 8: 2); FT-IR (v/cm)-1) 3331,3211(NH),1658, (C ═ O),1551,1536,1498(C ═ C),1254 (C ═ S); 1H NMR (400MHz, DMSO-d6) Δ 9.95(s,1H, NH),8.65(bs,1H, NH), 8.09(bs,1H, NH), 7.43-7.40 (s,1H, Ar-H), 7.39-7.23 (m,4H, Ar-H), 7.19-7.12 (m,3H, Ar-H),3.56(s,3H, OCH 3); 13C NMR (100MHz, DMSO-d6) delta 178.6, 162.4,159.3,158.7,135.6,131.5,130.5,129.8,125.4,119.7,118.2,114.24,114.1, 56.3; elemental analysis C15H14FN3O2S C56.41, H4.42, N13.16; the results were C55.32, H4.40, N13.21%.
The aroylhydrazide is commercially available and has a structural formula shown in the following formula (2):
the complex is found to form a fluorescent complex with heavy metal ions in the biomass tar. Formula (3) is represented by Ni2+The fluorescent complex structure is shown for example:
when the complex is used, heavy metal ions of the order of μmol/L can be detected, that is, the detection limit can be up to 1.0 μmol/L, for example, heavy metal ions of 5.0 μmol/L or less, preferably 2.0 μmol/L or less in biomass tar can be detected.
In another aspect of the invention, an application of a complexing agent in detecting heavy metal elements in biomass tar is provided, which is used for improving the detection sensitivity of the heavy metal elements in the biomass tar.
Preferably, the complexing agent and its method of use are as described above.
Preferably, the method for detecting the heavy metal elements in the biomass tar adopts fluorescence spectroscopy, wherein the excitation is carried out at 388nm, and the emission maximum is 488 nm.
The complexing agent shown in formula (1) of the present application alone does not show any significant fluorescence signal at 488nm under excitation at 388nm in the fluorescence emission spectrum, and does not show any significant fluorescence signal at 388nm in the same fluorescence excitation spectrum when the 488nm emission is fixed in the absence of nickel ions, whereas it has a very significant signal with an emission maximum of 488nm and an excitation maximum of 388nm after the addition of nickel ions is detected. This provides the possibility of detection of heavy metal ions such as nickel ions.
Description of the drawings:
FIG. 1 shows the complexation of different equivalents of Ni by the complex according to the invention2+Fluorescence spectrum of (5.0) μ M ligand, Ni 2+1 to 6 equivalents thereof;
FIG. 2 shows the fluorescence intensity at 488nm with and without the complexing agent of formula (1) according to the invention.
Detailed description of the preferred embodiments
The present invention will be described in further detail below with reference to the following examples and corresponding comparative examples, but the embodiments of the present invention are not limited thereto.
Example 1
2.0ml of tar sample standard (obtained from the laboratory of the institute of energy and Power engineering, university of Nanjing, containing 5.0. mu.M Ni)2+) Dissolving in 20ml of methanol solution containing 10 v% MeCN and 10 v% water, adding 2.0ml of a solution of a complexing agent represented by the formula (1) in methanol, wherein the concentration of the complexing agent in methanol is 5.0 μ M, to obtain a solution to be measured, adjusting the pH of the solution to be measured to 9.0 with a PBS buffer solution, placing the solution to be measured in a detection cell, detecting the fluorescence spectrum performance of the solution to be measured with an RF-5301PC type fluorescence spectrometer (RF-5301PC type fluorescence spectrometer), and subjecting the solution to be measured toFluorescence spectrum performance of (2) and calibrated Ni-containing2+Comparing the fluorescence spectrum performance of the standard substance, calculating the content of heavy metal elements in the tar, and measuring the Ni in the tar sample2+The content was 4.68. mu.M.
Comparative example 1
Detection by conventional flame atomic absorption spectrometry (Thermo Scientific M series-iCE 3000) failed to detect Ni distinctively2+。
Comparative example 2
The same preparation as in example 1 was followed, except that calcein (available from Amresco, USA) was selected as the fluorescent complexing agent, and Ni was detected2+The content was 0.84. mu.M.
As is clear from the above examples and comparative examples, when conventional elemental analysis is employed, Ni ions are not detected selectively well, which is an inherent disadvantage of flame atomic absorption spectrometry, which cannot simultaneously analyze multiple elements, is unsatisfactory in the sensitivity of measurement of a sparingly soluble element, and requires enrichment and separation for the measurement of trace amounts, particularly ultra trace amount components, due to the low sensitivity of flame atomic absorption.
In addition, as can be seen from comparative example 2, when the conventional fluorescent complexing agent was used, the detection result error was large because the fluorescence property of the formed complex was weak, and thus the detection sensitivity was also significantly low as compared with example 1.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. All citations referred to herein are incorporated herein by reference to the extent that no inconsistency is made.
Claims (7)
1. A method for improving detection sensitivity of heavy metal elements in biomass tar comprises the following steps:
(1) dissolving a quantitative tar sample in a quantitative methanol solution, wherein the methanol solution contains MeCN and water, and the volumes of the MeCN and the water are respectively and independently 5-20% of the volume of the methanol;
(2) adding a complexing agent solution into the solution prepared in the step (1) to obtain a solution to be detected;
the complexing agent is a complex shown as the following formula (1):
(3) placing the solution to be detected in a detection pool, and detecting the fluorescence spectrum performance of the solution to be detected; and
(4) and comparing the fluorescence spectrum performance of the solution to be detected with the fluorescence spectrum performance of the standard substance, and calculating the content of heavy metal elements in the tar.
2. The method of claim 1, wherein said tar is filtered prior to step (1).
3. The method of claim 2, wherein the filtering is performed using an organic membrane.
4. The method of claim 3, wherein the organic film is a polymer film.
5. The method of any of claims 2 or 3, wherein said filtering is capable of removing phenolics from the tar sample.
6. The method of claim 5, wherein said filtering is capable of removing 50-90 wt% of phenolics in the tar sample.
7. The method of claim 6, wherein the phenolic material comprises one or more of ethylphenol, m-cresol, phenol, methoxyphenol.
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