CN107991336B - A rapid and simultaneous detection and separation of Pb2+ and Cu2+ in water based on magnetic sensing - Google Patents

Abstract

The invention discloses a magnetic sensing-based method for rapidly and simultaneously detecting and separating Pb²⁺And Cu²⁺The method of (1), comprising: 1) preparation of Quercetin-coated magnetic Fe₃O₄Nanoparticles, 2) making △ T₂‑Pb²⁺And Cu²⁺A standard curve of concentration; 3) coating magnetic Fe with quercetin₃O₄Nanoparticles (QmNPs) bound to Pb²⁺And Cu²⁺Determination of △ T₂According to △ T₂‑Pb²⁺And Cu²⁺Calculating Pb from the standard curve of the concentration²⁺And Cu²⁺The concentration of (c); 4) under the action of magnetic field, utilizing magnetic adsorption method to adsorb and combine Pb²⁺And Cu²⁺The quercetin-coated magnetic Fe₃O₄Nanoparticles to effect Pb removal²⁺And Cu²⁺. The invention is based on QmNPs system and Pb²⁺Or Cu²⁺The coordination is carried out, aggregation and precipitation are generated under the action of an external magnetic field, and therefore, the Pb in the water can be simultaneously treated²⁺And Cu²⁺The method can be successfully applied to water and urine samples by detection and removal, has the advantages of high recovery rate, strong adsorption capacity, no potential secondary pollution and the like, and has good practicability.

Description

A rapid and simultaneous detection and separation of Pb2+ and Cu2+ in water based on magnetic sensing

technical field

The invention belongs to the technical field of magnetic nanoparticles and their application, in particular to a method for rapid simultaneous detection and separation of Pb ²⁺ and Cu ²⁺ in water based on magnetic sensing.

Background technique

Heavy metal ion pollution has an important impact on the environment and biological development. Since excess heavy metal ions can pose serious threats to human health and the environment, it is critical to develop methods to detect and eliminate them. Therefore, the removal of heavy metal ions (such as Pb ²⁺ and Cu ²⁺ ) from sewage has attracted public attention. Among the heavy metal ions, Cu ²⁺ plays a crucial role in environmental, biological and chemical systems, etc., but high concentrations of Cu ²⁺ can cause damage to the liver and kidneys, and also have a serious impact on the self-purification function. Pb ²⁺ is a highly toxic heavy metal ion that poses a serious threat to human health and the environment even at low concentrations. Therefore, it is very necessary to remove Pb ²⁺ and Cu ²⁺ from contaminated water.

Different methods have been applied to detect these heavy metal ions, such as fluorescence spectroscopy, atomic absorption spectroscopy and gas chromatography. However, these methods have many shortcomings, such as small detection range, expensive equipment, complicated procedures, and must be operated by professionals, which obviously cannot fully meet the needs of use.

SUMMARY OF THE INVENTION

Purpose of the invention: Aiming at the deficiencies in the prior art, the present invention provides a method for rapid simultaneous detection and separation of Pb ²⁺ and Cu ²⁺ based on magnetic sensing, for simultaneous detection and Pb ²⁺ and Cu ^{2+ were} removed.

Technical scheme: In order to realize the above-mentioned purpose of the invention, the technical scheme adopted in the present invention is:

A method for rapid simultaneous detection and separation of Pb ²⁺ and Cu ²⁺ based on magnetic sensing, the steps are as follows:

1) Preparation of quercetin-coated magnetic Fe ₃ O ₄ nanoparticles;

2) Make standard curves of ΔT ₂ -Pb ²⁺ and Cu ²⁺ concentrations;

3) Using the properties of quercetin-coated magnetic Fe ₃ O ₄ nanoparticles (QMNPs) to combine Pb ²⁺ and Cu ²⁺ , ΔT ₂ was determined, according to the standard of ΔT ₂ -Pb ²⁺ and Cu ²⁺ concentrations Curve, calculate the concentration of Pb ²⁺ and Cu ²⁺ ;

4) Under the action of a magnetic field, magnetic Fe ₃ O ₄ nanoparticles are coated with quercetin combined with Pb ²⁺ and Cu ²⁺ by magnetic adsorption method to realize the removal of Pb ²⁺ and Cu ²⁺ .

In step 1), the specific process is as follows: adding FeCl ₃ ·6H ₂ O and FeCl ₂ ·6H ₂ O into ultrapure water, stirring and heating to 100° C. until the solid is completely dissolved; then adding NH ₃ ·H ₂ O, A black precipitate was produced; magnetic Fe ₃ O ₄ nanoparticles were separated by centrifugal separation, and washed with water and ethanol; Fe ₃ O ₄ powder was added to ultrapure water, and ultrasonically dispersed for 1 h; then quercetin was added to the suspension system, Reacted with Fe ₃ O ₄ under ultrasonic dispersion conditions for 1 h; then, the functionalized magnetic quercetin nanoparticles were separated by centrifugation; finally, they were washed with clean water for several times, and dispersed in deionized water for long-term storage.

In step 1), the mass ratio of Fe ₃ O ₄ to quercetin is 1:1.

In step 2), the standard curve of ΔT ₂ -Pb ²⁺ concentration is Y=52.41458X-8.88188, R ² =0.9912.

In step 2), the standard curve position of ΔT ₂ -Cu ²⁺ concentration is Y=49.69175X-0.06574, and R ² =0.9983.

The linear range of Pb ²⁺ detection was 4.8×10 ^-6 mol L ^-1 to 10 ^-4 mol L ^-1 .

The linear range of Cu ²⁺ detection was 5.0×10 ^-6 mol L ^-1 to 10 ^-4 mol L ^-1 .

In the method, the adopted quercetin flavonoid is a natural product widely existing in plants, and belongs to the flavonoid compound with good biological activity. This quercetin has been shown to be an effective metal chelator with three possible competing chelation sites: 3-hydroxy-4-carbonyl catechol, 5-hydroxy-4-carbonyl catechol, 3',4'-dihydroxycatechol. The experiments of the present application confirmed that the complexation of metal ions Pb ²⁺ and Cu ²⁺ with the quercetin-coated Fe ₃ O ₄ system leads to nanoparticle aggregation and changes the spin relaxation time (T ₂ ), the change in T ₂ On the basis of the brightness enhancement of T2 _- weighted MR images, the concentrations of Pb ²⁺ and Cu ²⁺ can be detected. In addition, the functional magnetic nanoparticles can also remove Pb ²⁺ and Cu ²⁺ from polluted water by an external magnetic field, avoiding potential secondary pollution.

Beneficial effects: Compared with the prior art, the method of the present invention is based on the coordination of the QMNPs system with Pb ²⁺ or Cu ²⁺ , resulting in agglomeration of the QMNPs system and an increase in the relaxation time T ₂ . In the standard curve of ΔT ₂ -ion concentration, R ² of Pb ²⁺ = 0.9912, and R ² of Cu ²⁺ = 0.9983, which have good correlation, and the linear range of detection of Pb ²⁺ is 4.8×10 ^-6 mol L ^-1 ～10 ^-4 mol L ^-1 , Cu ²⁺ is at 5.0×10 ^-6 mol L ^-1 ～10 ^-4 mol L ^-1 . Since the ^QMNPs system coordinates with Pb ²⁺ or Cu ²⁺ under the action of an external magnetic field, aggregation and precipitation occur, so it can simultaneously detect and remove Pb ²⁺ and Cu ²⁺ in water, which can be successfully applied to water, urine It has the advantages of high recovery rate, strong adsorption capacity, no potential secondary pollution, etc., and has good practicability.

Description of drawings

Fig. 1 is the preparation route diagram of quercetin-coated Fe ₃ O ₄ nanoparticles;

Fig. 2 is the topography of QMNPs observed by transmission electron microscope; in the figure, a shows unmodified Fe ₃ O ₄ , b shows Fe ₃ O ₄ coated with quercetin, c shows the dispersed state of QMNPs, and d shows Pb ² added ⁺ the dispersion state of QMNPs;

Fig. 3 is the infrared spectrum of Fe ₃ O ₄ (a) and QMNPs (b);

Figure 4 is the XRD images of Fe ₃ O ₄ (a) and QMPNs (b);

Figure ₅ is the T2 relaxation time diagram of _Fe3O4 and _QMNPs ;

Fig. 6 is the relaxation time diagram of adding quercetin T ₂ to 100mL Fe ₃ O ₄ aqueous solution;

Figure 7 is a graph showing the effect of adding different metal ions to the QMNPs system on T ₂ ;

Figure 8 is a schematic diagram of agglomeration;

Figure 9 is a graph of the change of T ₂ and MRI of the QMNPs system with Cu ²⁺ added;

Figure 10 is a graph of the change of T ₂ and MRI of QMNPs system adding Pb ²⁺ ;

Figure 11 is a T ₂ -weighted MR image of QMNPs system with increasing Pb ²⁺ or Cu ²⁺ concentration;

Figure 12 is a standard curve diagram of the concentration of ΔT ₂ -Pb ²⁺ in the QMNPs system;

Figure 13 is a standard curve diagram of the concentration of ΔT ₂ -Cu ²⁺ in the QMNPs system;

Fig. 14 is a graph showing the adsorption results of quercetin-coated Fe ₃ O ₄ system on Cu ²⁺ and Pb ²⁺ ;

FIG. 15 is a graph of the results of Example 6. FIG.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments.

In the following examples, T ₂ (spin relaxation time) was measured by a 0.47T nuclear magnetic resonance apparatus (Shanghai Niumag Company), and a transmission electron microscope (TEM, JEM-1400) was used to study the quercetin-coated magnetic Fe ₃ O Morphology and structure of ₄ -nanometer core-shell particle nanoparticles (QMNPs). The system was investigated with Bruker D8Venture series single crystal X-ray diffractometer and Bruker VERTEX 80V series Fourier transform infrared spectroscopy (FTIR), and the content of Pb ²⁺ and Cu ²⁺ was determined with Perkin Elmer AA900T AAS.

Example 1

The synthesis route of functionalized magnetic quercetin nanoparticles (QMNPs) is shown in Figure 1. The specific process is: adding FeCl ₃ ·6H ₂ O (10.85g) and FeCl ₂ ·6H to 250mL ultrapure water ₂ O (3.99 g), stir, heat to 100 °C until the solids are completely dissolved. _NH3.H2O ( ₅ mL, 28%) was then added, resulting in a black precipitate. Magnetic _Fe3O4 nanoparticles _were isolated by centrifugation and washed three times with water and ethanol. 1 mg of Fe ₃ O ₄ powder was added to 100 mL of ultrapure water, and dispersed by ultrasonic (40 KHz, 30 °C) for 1 h. Then a certain amount of quercetin (10 ^-5 mol·L ^-1 ) was added to the suspension system, and it was reacted with Fe ₃ O ₄ under ultrasonic (40KHz, 30℃) dispersion conditions for 1 h. Next, the functionalized magnetic quercetin nanoparticles (QMNPs) were isolated by centrifugation (15 min, 15000 rmp). Finally, the product is rinsed several times with clean water and dispersed in deionized water for long-term storage.

The morphology of QMNPs was observed by transmission electron microscopy (TEM). Figure 2a shows unmodified Fe ₃ O ₄ with particle sizes ranging from 20 nm to 30 nm. Figure 2b shows the morphologies of QMNPs, which were successfully coated with quercetin _on the surface of _Fe3O4 nanoparticles. Figures 2c and d show the dispersed state of QMNPs with or without Pb ²⁺ in the water samples, respectively. It can be clearly seen from the figure that after the addition of Pb ²⁺ , the phenomenon of agglomeration, agglomeration and agglomeration of the magnetic sensor occurs. This indirectly indicates that quercetin has been successfully intercalated into the surface of _{Fe3O4 .}

The Fourier transform infrared (FTIR) spectra of Fe ₃ O ₄ (a) and QMNPs (b) are shown in Fig. 3 . In Fig. 3a, the peaks at 567 cm ^-1 and 1632 cm- ¹ are characteristic peaks of Fe–O bonds and FeOO– bonds. The peak at 3500 cm ^-1 is the O–H stretching vibration peak. In Figure 3b, the peaks at 2900 cm- ¹ and 1640 cm ^-1 are stretching vibrations of C=O. The peak at 1320-1210 cm ^-1 is characteristic of the C–O bond of the carbonyl group. Therefore, according to the above results, it is confirmed that the magnetic QMNPs structure has been successfully synthesized in this example, and the coating of quercetin _on the surface of _Fe3O4 nanoparticles is also effective.

Figure ₄ is the XRD images of _Fe3O4 and QMPNs. The different diffraction peaks (a) on the curve can be considered as the face-centered cubic phase of Fe ₃ O ₄ (JCPDS card 65–3107). After coating with quercetin coating, the diffraction pattern of QMNPs (b) is significantly different from Fe ₃ O ₄ (a), and the change in crystallinity may be caused by the quercetin layer.

Example 2

In order to compare the states of _QMNPs and _Fe3O4 nanoparticles in water for the two samples, the T2 of the _two samples was determined separately: the sample solution was put into a 5 mm glass tube, and the T2 was measured by a _0.55T NMR spectrometer (TE =1000s,TR=1500ms). The measurement interval for T2 was ₅ min with 3 scans per sample.

The resulting graph is shown in Fig. ₅ , the T2 of _Fe3O4 increased significantly within ₂₂ min, indicating that _Fe3O4 nanoparticles aggregated into clusters in water under the magnetic field condition _. Although only small changes occurred in the QMNPs, it indicated that the quercetin _- coated _Fe3O4 could be dispersed in water. _In the quercetin structure, ₅ hydroxyl groups can form hydrogen bonds with _Fe3O4 , making _Fe3O4 nanoparticles better dispersed in water. However, the content of quercetin could affect the stability of QMNPs. Four different mass of quercetin (0.5mg, 1.0mg, 1.5mg, 2.0mg) were added to 100mL Fe ₃ O ₄ aqueous solution to test the changes of T2 relaxation time of four different QMNPs systems. The results are shown in Fig. 6, indicating that with the increase of quercetin content, the T of _QMNPs first decreased and then increased, which indicated the stability of the QMNPs system when 1.0 mg quercetin was contained in 100 mL Fe ₃ O ₄ aqueous solution it's the best. A small amount of quercetin was added to the Fe ₃ O ₄ aqueous solution, and a hydrogen bond was formed between quercetin and Fe ₃ O ₄ , which improved the stability of the QMNPs system. When the content of quercetin increased to a certain extent, the hydrogen bonding interaction of quercetin coated _on the surface of _Fe3O4 nanoparticles increased, resulting in the tendency of the QMNPs system to aggregate state. Therefore, the quercetin content is important when preparing QMNPs.

Example 3 Identification of metal ions by QMNPs

In order to detect the T ₂ of QMNPs system for different metal ions, 1 mL of QMNPs solution was mixed with 10 μL of different metal ions (Co ²⁺ , K ⁺ , Zn ²⁺ , Na ⁺ , Ni ²⁺ , Cd ²⁺ , Li ⁺ , Fe ^{3 )} . ⁺ , Fe ²⁺ , Mn ²⁺ , Mg ²⁺ , La ²⁺ , Cu ²⁺ , Pb ²⁺ ) in acetic acid/nitrate standard solution (1×10 ^-3 mol·L ^-1 ), and then the sample The solution was put into a 5 mm glass tube, and T2 was measured by a _0.55T NMR apparatus (TE=1000s, TR=1500ms).

Each metal ion was separately added to the prepared detection system and the T _relaxation time was recorded. The results are shown in Fig. ₇ , which show that only Pb ²⁺ and Cu ²⁺ cause significant changes in the T relaxation time.

When Pb 2+ or Cu ²⁺ was added to the ^QMNPs solution, the coordination reaction between QMNPs and Pb ²⁺ or Cu ²⁺ occurred, resulting in the dispersion of QMNPs into clusters, as shown in Figure 8. Larger nanoparticles alter the magnetic relaxation properties of surrounding water protons, thereby increasing the T relaxation time, as shown in Figures ₉ and 10, a phenomenon that can be explained by the T2 _- weighted magnetic relaxation (MR) of MRI. The brightness changes show that, at the same time, the QMNPs system is precipitated under the action of an external magnetic field.

Example 4 Detection of Pb ²⁺ and Cu ²⁺ by QMNPs system

In order to determine the effect of different concentrations of Pb ²⁺ and Cu ²⁺ on T ₂ , the test solution was obtained by mixing 1 mL of the solution as a detector with standard solutions of different concentrations of Pb ²⁺ and Cu ²⁺ , and injected into a test tube to measure T ₂ . A weighted image of T ₂ can be obtained after T ₂ is measured.

The system can detect different concentrations of Pb ²⁺ or Cu ²⁺ . It can be observed from Fig. 11 that as the concentration of Pb ²⁺ and Cu ²⁺ in the sample increases, the MR image of the sample also gradually becomes brighter, and the T _relaxation time increases accordingly.

Add 1 mL of magnetic sensor to the glass tube for testing, and record its T2 value with a low _- field NMR instrument; then add lead salt solutions and copper salt solutions of different concentrations dropwise into it, and record them with a low-field NMR instrument. ΔT _{2 is obtained by subtracting the T 2 values} measured before and after, and the working curve of ΔT ₂ and different concentrations of Pb ²⁺ and Cu ²⁺ is drawn _{: ΔT 2 -Pb} ²⁺ concentration The standard curve is shown in Figure 12, Y=52.41458X-8.88188, R2= ^0.9912 . The standard curve of ΔT ₂ -Cu ²⁺ concentration is shown in Figure 13, Y=49.69175X-0.06574, R ² =0.9983, they have a good correlation, the linear range of detection Pb ²⁺ is 4.8×10 ^-6 mol L ^-1 ～10 ^-4 mol L ^-1 , Cu ²⁺ at 5.0×10 ^-6 mol L ^-1 ～10 ^-4 mol L ^-1 . The detection limit of Pb ²⁺ is 1.6×10 ^-6 mol L ^-1 , and the detection limit of Cu ²⁺ is 2×10 ^-6 mol L ^-1 .

Example 5 Application of QMNPs system in water and urine samples

1 mmol/L of Pb ²⁺ or Cu ²⁺ was added to 3.0 mL of water, followed by QMNPs. When the mixture was subjected to an external magnetic field, precipitation appeared immediately, as shown in Figure 14. After half an hour, the suspension was carefully removed and the concentration of Pb ²⁺ or Cu ²⁺ was determined. The adsorption formula per gram of the system: M=[(C ₀ -C)×V]×m ^-1 , C ₀ and C are the initial and final concentrations of Pb ²⁺ or Cu ²⁺ in the solution (mg·L ^-1 ) , V is the sample volume (L), and m is the weight (g) of the QMNPs. After calculation, the maximum adsorption capacity of Pb ²⁺ and Cu ²⁺ is 68 mg and 71 mg, respectively, which is better than the existing method (shown in Table 1). Therefore, the magnetic adsorption method of QMNPs is feasible to remove Pb ²⁺ and Cu ²⁺ in aqueous solution.

Table 1 The adsorption amount of Cu ²⁺ and Pb ²⁺ in the literature

Note: The specific references are as follows:

1. Y.Chen,R.C.Haddon,S.Fang,A.M.Rao,P.C.Eklund,Chemical attachment oforganic functional groups to single-walled carbon nanotube material,J.Mater.Res.13(1998)2423–2431.

2. N. Chiron, R. Guilet, E. Deydier, Adsorption of Cu(II) and Pb(II) onto agrafted silica: isotherms and kinetic models, Water Res. 37(2003) 3079-3086.

3. L. Curkovic, S. Cerjan-Stefanovic, A. Rastovean Mioe, Batch Pb ²⁺ and Cu ²⁺ removal by electric furnace slag, Water Res. 35 (2001) 3436–3440.

4. C. Zhang, J. Sui, J. Li, Y. Tang, W. Cai, Efficient removal of heavy metalions by thiol-functionalized superparamagneticcarbon nanotubes, Chem.Eng.J.210(2012) 45–52.

A.Veronovski,Z.Novak,Z.Knez,Silica aerogels modifiedwith mercapto functional groups used for Cu(II)and Hg(II)removal from aqueoussolutions, Desalination 269(2011)223-230.5. S.

A. Veronovski, Z. Novak, Z. Knez, Silica aerogels modified with mercapto functional groups used for Cu(II) and Hg(II) removal from aqueoussolutions, Desalination 269 (2011) 223-230.

This example is also designed to evaluate the detection performance and removal ability of QMPNs system for Pb ²⁺ and Cu ²⁺ in water and urine samples (after acid digestion). First, 10 μL of water or urine samples containing Pb ²⁺ and Cu ²⁺ were added to the solution of 1 mL of the QMNPs system. The presence of Pb ²⁺ and Cu ²⁺ was detected by low-field NMR, and the concentrations of Pb ²⁺ and Cu ²⁺ were measured by AAs method. The statistics of the results are shown in Table 2 and Table 3. The measured results are basically the same as those measured by the AAs method, which proves that QMNPs can be used as magnetic sensors for qualitative and quantitative analysis of Pb ²⁺ and Cu ²⁺ .

Table 2 The detection and removal ability of QMNPs system to Pb ²⁺

In addition, 60 μg of QMNPs was added to water or urine to coordinate with Pb ²⁺ or Cu ²⁺ , and adsorbed metal ions under the condition of an external magnetic field. After 30 min, the mixture was filtered, and the Pb in the filtrate was determined by atomic absorption spectrometry. ²⁺ or Cu ²⁺ concentration. The results (Table 2 and Table 3) show: 90.24-92.00% Pb ²⁺ and 88.2-91.9% Cu ²⁺ in water samples, 90.90-92.00% Pb ²⁺ and 91.8-91.9% Cu ² in urine samples ⁺ was adsorbed and removed by the QMNPs system.

Table 3 Detection and removal ability of QMNPs system for Cu ²⁺

Example 6

The preparation method of the kaempferol-modified magnetic Fe ₃ O ₄ nanoparticle system is the same as in Example 1, in which kaempferol is used instead of quercetin, and the prepared products are detected and removed in water for different ions, the method is the same as that in Example 3, and the results are shown in the figure As shown in Figure 15, its selectivity for different ions is poor, and it cannot meet the needs of simultaneous detection and removal of Pb ²⁺ and Cu ²⁺ .

Claims (4)

1. Magnetic sensing-based rapid simultaneous detection and separation method for Pb²⁺And Cu²⁺The method is characterized by comprising the following steps:

1) preparation of Quercetin-coated magnetic Fe₃O₄A nanoparticle; the specific process is as follows: adding FeCl into ultrapure water₃·6H₂O and FeCl₂·6H₂O, stirring and heating to 100 ℃ until the solid is completely dissolved; then adding NH₃·H₂O, producing a black precipitate; magnetic Fe separation by centrifugal separation₃O₄Nano particles, and washing with water and ethanol; mixing Fe₃O₄Adding the powder into ultrapure water for ultrafiltrationSound dispersion is carried out for 1 h; then adding quercetin to the suspension system, mixing with Fe₃O₄Reacting for 1h under the condition of ultrasonic dispersion; then, centrifugally separating out functionalized magnetic quercetin nanoparticles; finally, washing the magnetic quercetin nanoparticles for multiple times by using clear water, and dispersing the magnetic quercetin nanoparticles in deionized water for long-term storage;

2) make △ T₂-Pb²⁺And Cu²⁺Standard curve of concentration △ T₂-Pb²⁺The standard curve of concentration is Y = 52.41458X-8.88188, R²=0.9912；△T₂-Cu²⁺The standard curve of concentration is Y = 49.69175X-0.06574, R²=0.9983, wherein, △ T₂-difference between adjacent relaxation times, Y being △ T₂X is the ion concentration, 10^-5mol·L^-1；

3) Coating magnetic Fe with quercetin₃O₄Nanoparticle bound Pb²⁺And Cu²⁺△ T was determined₂According to △ T₂- Pb²⁺And Cu²⁺Calculating Pb from the standard curve of the concentration²⁺And Cu²⁺The concentration of (c);

4) under the action of magnetic field, utilizing magnetic adsorption method to adsorb and combine Pb²⁺And Cu²⁺The quercetin-coated magnetic Fe₃O₄Nanoparticles to effect Pb removal²⁺And Cu²⁺。

2. Magnetic sensing based rapid simultaneous detection and separation of Pb according to claim 1²⁺And Cu²⁺Characterized in that, in step 1), Fe₃O₄The mass ratio of the quercetin to the quercetin is 1: 1.

3. magnetic sensing based rapid simultaneous detection and separation of Pb according to claim 1²⁺And Cu²⁺Characterized by the fact that Pb is²⁺Has a linear range of 4.8 × 10^-6mol L^-1~10^-4mol L^-1。

4. According to the rightMagnetic sensing based rapid simultaneous detection and separation of Pb according to claim 1²⁺And Cu²⁺Characterized in that Cu^{2 +}Has a linear range of 5.0 × 10^-6mol L^-1~10^-4mol L^-1。

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