CN115753933A - Preparation method and application of carboxymethyl chitosan-based hydrogel modified electrode - Google Patents
Preparation method and application of carboxymethyl chitosan-based hydrogel modified electrode Download PDFInfo
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Abstract
The invention discloses a preparation method and application of a carboxymethyl chitosan-based hydrogel modified electrode, relating to the technical field of heavy metal ion detection and comprising the following steps: dissolving carboxymethyl chitosan in water, adding dopamine hydrochloride powder, adding ammonium persulfate solution after the dopamine hydrochloride powder is dissolved, uniformly mixing, dropwise adding the mixed solution onto the surface of a glassy carbon electrode, and standing at room temperature to obtain the carboxymethyl chitosan-based hydrogel modified electrode (CMCS-DA/GCE modified electrode) which can be used for simultaneously measuring Cd in water and soil 2+ And Pb 2+ To Cd 2+ And Pb 2+ The detection linear range of (2) is wide, the detection limit is respectively 6nM and 8nM, and the minimum detection standard of national standard drinking water is reached.
Description
Technical Field
The invention relates to the technical field of heavy metal ion detection, in particular to a preparation method and application of a carboxymethyl chitosan-based hydrogel modified electrode.
Background
Water and soil are important components of natural environment elements and are also important resources which are indispensable to human beings and animals and plants for survival. In recent years, due to the acceleration of the industrialization process, human activities such as mining, smelting, chemical engineering and the like cause the accumulation of water and soil heavy metals. Meanwhile, the application of a large amount of pesticides and fertilizers can cause water and soil heavy metal pollution, so the situation of heavy metal pollution to the environment is more and more severe. The soil pollution in part of areas is serious, the quality of the cultivated land soil environment is high, and the soil environment problem of industrial and mining waste land is prominent. The total overproof rate of soil pollution is 16.1%, the overproof rate of soil point positions of cultivated lands is 19.4%, the cultivated lands polluted by heavy metals account for about 20% of the total cultivated land area, and typical heavy metal pollutants comprise mercury, lead, copper, cadmium, arsenic, chromium, zinc, nickel and the like. The heavy metal pollution of the soil mainly affects the normal growth and development of plants by changing the composition, structure and function of the soil, so that harmful substances are accumulated in the plants and can enter human bodies through food chains, and the human health is harmed. Therefore, the development of a rapid detection technology for heavy metal ions in soil is urgently needed. At present, the detection techniques for heavy metal ions at home and abroad include atomic absorption spectrometry, atomic fluorescence spectrometry, inductively coupled plasma emission spectrometry, X-ray fluorescence spectrometry, ultraviolet-visible spectrophotometry, enzyme analysis, immunoassay, and the like. However, the large-scale instrumental analysis method is not suitable for field detection due to high price, high cost, complex operation and the like; the bioanalysis method has limited practical application because antigen and antibody are difficult to prepare and the detection result is greatly influenced by the environment. Therefore, the development of a rapid and low-cost heavy metal ion analysis technology has important practical significance and economic significance for the prevention, control and treatment of the heavy metal pollution of the soil.
The electrochemical method is a relatively mature modern instrument analysis method based on certain electrical parameters (such as conductance, resistance, potential, current, potential, etc.)The quantitative relation between the concentration of the substance to be detected and the method for analyzing the substance to be detected are widely used in the field of soil heavy metal detection. Compared with other analysis methods, the electrochemical analysis method has the following advantages: the device has the advantages of high sensitivity, simple operation, low detection limit, small instrument volume, short analysis time, wide measurement range, simultaneous determination of various metals, easy miniaturization and integration, portability, and realization of field detection and online real-time monitoring. For example, bui and the like use carbon nano tubes and gold nano particles to jointly modify electrodes and realize Pb control by SWV voltammetry 2+ And Cu 2+ The detection limit reaches 0.546 and 0.613 mu g/L respectively. The poly-tyrosine/bismuth composite film modified glassy carbon electrode is prepared by forest and the like, and the Pb is also modified 2+ The detection limit reaches 0.8nM. In the electrochemical determination process, heavy metal ions are enriched and dissolved out on the surface of the working electrode through the loss electrons on the surface of the electrode, chemical signals are converted into electric signals, and the relation between the concentration of the heavy metal ions and the current is obtained. In the measuring process, the property of the working electrode is crucial to the measuring result, and the surface of the working electrode is properly modified, so that the detection sensitivity and the detection limit can be improved.
In recent years, hydrogels have characteristics of good heavy metal ion adsorption capacity and the like due to containing a large number of hydrophilic groups, and are gradually exposed in the field of biochemical analysis. For example, luo et al prepared a novel fluorescent chitosan-based hydrogel, which combined with titanate and carbon-modified cellulose nanofibers, had good adsorption properties and detection capability for Cr (VI), with a maximum adsorption of 228.2mg/g and a linear range of quantitative detection of 10-80mg/L. Han et al prepared carbon-composite acrylic hydrogel from modified carbon reed, sodium alginate and lysine, and studied hydrogel for Cu 2+ And Ni 2+ The hydrogel has a copper-copper removing ability to Cu 2+ And Ni 2+ The maximum adsorption amounts of (A) are 1245.27 and 1239.47mg/g respectively, which are superior to most reported documents. The research work of Luo, han and the like explains the adsorption mechanism of hydrogel on heavy metal ions, and mainly leads the hydrogel to be capable of chelating the heavy metal ions based on carboxyl, hydroxyl, amino and the like in the materialThe metal ions have good adsorption performance. However, most hydrogel materials directly adsorb heavy metal ions at present, and reports of the hydrogel materials as electrode modification materials are few.
Disclosure of Invention
Considering that the carboxymethyl chitosan chain contains rich amino, carboxyl and other groups, the carboxymethyl chitosan hydrogel modified electrode is prepared, the hydrogel forming conditions and the electrochemical test conditions are discussed, and the method for simultaneously measuring Cd is constructed 2+ And Pb 2+ The electrochemical sensing platform of (1).
In order to achieve the purpose, the invention provides the following scheme:
the invention provides a preparation method of a carboxymethyl chitosan-based hydrogel modified electrode, which comprises the following steps: dissolving carboxymethyl chitosan (CMCS) in water, adding dopamine hydrochloride (DA) powder, adding an ammonium persulfate solution (APS solution) after the dopamine hydrochloride (DA) powder is dissolved, uniformly mixing, dropwise adding the mixed solution to the surface of a Glassy Carbon Electrode (GCE), and standing at room temperature to obtain the carboxymethyl chitosan-based hydrogel modified electrode (CMCS-DA/GCE modified electrode).
Preferably, the glassy carbon electrode is further pretreated before the mixed solution is dripped on the surface of the glassy carbon electrode: the glassy carbon electrode was coated with 0.3 μm and 0.05 μm Al in this order 2 O 3 Pasting and polishing, then ultrasonically cleaning in nitric acid, absolute ethyl alcohol and water, and drying by nitrogen.
Preferably, the nitric acid is dilute nitric acid with the concentration of 0.5mol/L, and the volume ratio of the absolute ethyl alcohol to the water is 1.
Preferably, the mass ratio of the carboxymethyl chitosan to the dopamine hydrochloride is 1:1.
preferably, the carboxymethyl chitosan is O-carboxymethyl chitosan (CMCS), the carboxylation degree is more than or equal to 80 percent, the molecular weight is 15-80 ten thousand, and the carboxymethyl chitosan is purchased from Shanghai-sourced leaf Biotechnology Co., ltd. Dopamine hydrochloride (DA) with a content of >98% was purchased from the Shanghai Michelin Biotech, inc.; ammonium persulfate, acetic acid, and sodium acetate were all purchased from drugstore chemical agents, ltd. The cadmium nitrate standard solution (1 mg/mL) and the lead nitrate standard solution (0.1 mol/L) were purchased from Beijing northern great institute of metrological technology.
Preferably, the concentration of the ammonium persulfate solution is 0.1g/mL.
Preferably, the amount of the mixed solution dropped on the surface of the glassy carbon electrode is 4. Mu.L.
A carboxymethyl chitosan-based hydrogel modified electrode is prepared according to the preparation method.
The carboxymethyl chitosan-based hydrogel modified electrode can be used for simultaneously detecting Cd 2+ And Pb 2+ The use of (1).
Preferably, cd is detected at the same time when the carboxymethyl chitosan-based hydrogel modifies the electrode 2+ And Pb 2+ The method comprises the following steps: assembling the carboxymethyl chitosan-based hydrogel modified electrode as a working electrode into a three-electrode, placing the three-electrode into HAc-NaAc buffer solution, and adding Cd after the system is stable 2+ And Pb 2+ The sample to be tested is enriched and then electrochemically tested by Square Wave Anodic Stripping Voltammetry (SWASV).
Preferably, the SWASV test parameters: the scanning range is-1.0 to-0.2V, the amplitude is 25mV/s, the enrichment potential is-1.2V, and the enrichment time is 240s.
Preferably, the electrode is tested for success using stripping voltammetry and AC impedance, cyclic Voltammetry (CV) and AC impedance test (EIS) at 5mM [ Fe (CN) 6 ]] 3-/4- In an electrolyte solution containing 0.1M KCl to enhance the conductivity of the electrolyte; the scanning range of CV is-0.1-0.5V, the scanning speed is 100mV/s; the frequency range of EIS test is 0.1Hz-10kHz, the amplitude is 50mV, and the bias voltage is open circuit voltage.
The invention discloses the following technical effects:
the invention constructs an electrochemical sensor based on carboxymethyl chitosan-based hydrogel modified electrode, which can be used for simultaneously determining Cd in water and soil 2+ And Pb 2+ . The CMCS-DA material has a large specific surface and rich active sites such as carboxyl, amino, hydroxyl and the like, and can improve the adsorption and pre-enrichment capacity of heavy metal ions. Under the optimal condition, the constructed sensing platform pair Cd 2+ And Pb 2+ The detection linear range of (2) is wide, the detection limit is respectively 6nM and 8nM, and the detection range is up toThe minimum detection standard of national standard drinking water. In addition, the electrochemical sensor has good selectivity, reproducibility and stability, and has wide application prospect in real sample detection as proved by experimental data of addition and recovery of tap water and soil samples of actual samples.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a diagram of a possible synthesis mechanism of CMCS-DA hydrogel;
FIG. 2, panel A is a scanning electron micrograph of a CMCS-DA hydrogel; panel B is the optical image of the hydrogel prepared, where a is DA + APS, B is CMCS + DA + APS, c is CMCS + APS, reaction time 5min; the C picture is an infrared test spectrum of CMCS-DA;
FIG. 3 is a graph of CV (A), EIS (B) and SWASV (C) curves for bare GCE (a) and CMCS-DA/GCE (B) electrodes, where: cd in SWASV test 2+ And Pb 2+ The concentration of (3) is 1. Mu.M;
fig. 4 is an experimental condition optimization: modifying the CMCS-DA on the surface of the working electrode by using the modification amount (A); the pH (B) of the SWASV test system; an accumulation potential (C); enrichment time (D), wherein Cd 2+ And Pb 2+ The test concentrations of (a) were all 1. Mu.M;
FIG. 5 shows CMCS-DA/GCE on Cd concentrations 2+ (0.01-5. Mu.M) and Pb 2+ SWASV plot (A) (0.05-5. Mu.M); cd [ Cd ] 2+ A relation (B) between concentration and peak current I and a standard working curve (C); pb 2+ A relationship (D) between concentration and peak current I and a standard working curve (E);
FIG. 6 shows the reproducibility (A) and stability (B) of CMCS-DA/GCE.
Detailed Description
Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every intervening value, to the extent any stated or intervening value in a stated range, and every other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.
It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The description and examples are intended to be illustrative only.
As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.
In the present example, the water used was deionized water, supplied by Ekopu A2S-05-CE.
In the embodiment of the invention, the carboxymethyl chitosan is O-carboxymethyl chitosan (CMCS), the carboxylation degree is more than or equal to 80 percent, and the molecular weight is 15-80 ten thousand; dopamine hydrochloride (DA), content >98%.
The apparatus used in the examples of the present invention: scanning Electron Microscope (SEM), MIRA LMS, available from czech Tescan; infrared spectrometer (FTIR), spectrum 3, available from PerkinElmer, usa; electrochemical workstation, model CHI660E, was purchased from shanghai chenhua instruments ltd.
A glassy carbon electrode (3 mm diameter, working electrode), a silver chloride electrode (saturated KCl, reference electrode) and a platinum sheet electrode (counter electrode) were used to make up a three-electrode system.
The room temperature of the invention is 25 +/-2 ℃.
EXAMPLE 1 preparation of CMCS-DA/GCE modified electrode
Pretreatment of an electrode: glassy Carbon Electrode (GCE) 0.3 μm and 0.05 μm Al in this order 2 O 3 The paste was polished, and then ultrasonically cleaned in 0.5mol/L dilute nitric acid, absolute ethyl alcohol and water (volume ratio 1.
Preparing a CMCS-DA/GCE modified electrode: weighing 10mg of CMCS to dissolve in 1mL of water, then adding 10mg of DA powder, adding 100 mu L of 0.1g/mLAPS solution after the 10mg of DA powder is dissolved, and uniformly mixing by vortex oscillation to obtain the CMCS-DA hydrogel. And then dripping 4 mu L of the mixed solution on the surface of the GCE, and standing at room temperature for 10min to obtain the CMCS-DA/GCE modified electrode.
Example 2CMCS-DA/GCE modified electrode for simultaneous detection of Cd 2+ And Pb 2+
Pretreatment of an actual soil sample: carrying out digestion treatment on a soil sample: 0.100g of ground, sieved and air-dried soil sample was weighed into a polytetrafluoroethylene cup, and then 6.0mL of 1.5g/mL nitric acid solution, 4.0mL of 1.5g/mL hydrofluoric acid solution and 2.0mL of 1.6g/mL perchloric acid solution were added, followed by covering and placing at 180 ℃ for digestion for 5 hours. After the cover is opened, the acid gas in the cup is quickly removed, and a small amount of water is repeatedly added until the acid gas is completely removed. And finally, adding 1mL of nitric acid solution into the cup, transferring the digested sample solution into a 25mL volumetric flask, and fixing the volume to obtain the soil digestion solution.
Electrochemical testing: placing the three electrodes in 10mL of 0.1M HAc-NaAc buffer solution, adding heavy metal ion cadmium and lead standard samples (soil digestion solution) after the system is stabilized, enriching at a certain potential, and then feeding the heavy metal ion cadmium and lead standard samples through square wave anodic voltammetry (SWASV)And (6) performing electrochemical test. Electrochemical test parameters and conditions: the Cyclic Voltammetry (CV) and alternating current impedance test (EIS) were at 5mM [ Fe (CN) 6 ]] 3-/4- In an electrolyte solution containing 0.1M KCl to enhance the conductivity of the electrolyte. The scanning range of CV is-0.1-0.5V, the scanning speed is 100mV/s; the frequency range of EIS test is 0.1Hz-10kHz, the amplitude is 50mV, and the bias voltage is open circuit voltage. SWASV test parameters: the scanning range is-1.0 to-0.2V, the amplitude is 25mV/s, the enrichment potential is-1.2V, and the enrichment time is 240s.
A possible mechanism for the synthesis of CMCS-DA hydrogels is shown in FIG. 1. As is clear from FIG. 1, the bond between C-N and C-O in the CMCS ring is broken into radicals by the action of ammonium persulfate, which is a strong oxidant, and the hydrogen in the hydroxyl group and the amino group is abstracted to form radicals, and the hydrogen in the DA benzene ring is abstracted to change into a radical state, so that the radicals between CMCS and DA bond to each other to form a new chemical bond, and crosslink to form a hydrogel.
FIG. 2, panel A, is a scanning electron micrograph of a CMCS-DA hydrogel after lyophilization; panel B is an optical image of the prepared hydrogel, where a is DA + APS, B is CMCS + DA + APS, c is CMCS + APS, reaction time 5min; and the C picture is an infrared test spectrum of the CMCS-DA. The specific method of DA + APS is as follows: dissolving dopamine hydrochloride (DA) in water, adding ammonium persulfate solution (APS solution) after the dopamine hydrochloride (DA) is dissolved, and uniformly mixing for 5min. The specific method of CMCS + APS is as follows: dissolving carboxymethyl chitosan (CMCS) in water, adding ammonium persulfate solution (APS solution) after the carboxymethyl chitosan (CMCS) is dissolved, and uniformly mixing for 5min. From a diagram in fig. 2, it can be seen that the hydrogel has a porous structure, and can provide enough heavy metal ion adsorption sites for subsequent electrochemical tests. As can be seen from the B diagram in FIG. 2, when CMCS is mixed with APS (a) or DA is mixed with APS (c), the mixture is in solution state, and only when CMCS and DA are simultaneously present (B), the two will be crosslinked into gel state, which indicates that CMCS alone or DA alone will not form gel. As can be seen from the C diagram in FIG. 2, 3200cm -1 Nearby are the stretching vibration absorption bands belonging to-O-H and-N-H; 1725cm -1 Is a C = O stretching vibration absorption peak, 1620cm -1 Is a C = C stretching vibration absorption peak, and indicates that CMCS-DA contains hydroxyl, carboxyl, amino, benzene ring and the likeThe functional group is beneficial to the electrochemical enrichment process.
CV and EIS are two important electrochemical testing means for characterizing the surface modification condition of the electrode, the CV and EIS testing methods are adopted to research the surface properties of naked GCE and CMCS-DA/GCE, and the testing result is shown in figure 3. As can be seen from graph A in FIG. 3, there is a significant pair of CV graphs for both the bare GCE and the CMCS-DA/GCE [ Fe (CN) ] 6 ] 3-/4- Redox peak. However, [ Fe (CN) 6 ] 3-/4- The peak redox current of the hydrogel is slightly reduced on CMCS-DA/GCE, which shows that carboxyl groups and other groups on the hydrogel have certain inhibition effect on redox couple. FIG. 3B is an EIS diagram of different electrodes, where the semi-circular diameter of the high frequency region in the EIS diagram represents the electron transfer impedance of electrons on the electrode, and it can be seen that the EIS diagram of CMCS-DA/GCE shows a larger semi-circular arc compared to the bare electrode, which indicates that the charge transfer resistance of the electrode surface is slightly increased after the CMCS-DA hydrogel is modified, which is consistent with the CV results and demonstrates that the hydrogel has been successfully modified on the working electrode surface.
The method utilizes the SWASV method to simultaneously determine Cd 2+ And Pb 2+ Therefore, the electrochemical response capacities of the naked GCE and the CMCS-DA/GCE to different heavy metal ions are evaluated, and the corresponding electrochemical sensing curves are shown as a graph C in figure 3. It can be seen that the test curves, whether for bare GCE (curve a) or CMCS-DA/GCE (curve b), have two anodic peaks, located near-0.8V and-0.55V, corresponding to Cd, respectively 2+ And Pb 2+ Anode dissolution peak of (4). Compared with naked GCE, CMCS-DA/GCE shows more obviously enhanced peak current intensity. Bare GCE vs Cd 2+ And Pb 2+ The electrochemical response peak current of (a) is 1.53. Mu.A and 1.61. Mu.A, respectively, while that of CMCS-DA/GCE for Cd 2+ And Pb 2+ The electrochemical response peak current of (2.10 muA) and (3.07 muA) respectively, which are improved by 37.25% and 90.68% respectively. The result is probably that CMCS-DA has rich porous structure and active groups such as carboxyl, amino and the like, and plays an important role in the enrichment of heavy metal ions. In addition, the two dissolution peaks of the CMCS-DA/GCE test curve are both sharp peaks and are well separated, indicating that CMCS-DA/GCE can be used for simultaneously determining Cd 2+ And Pb 2+ The sensing platform of (1).
Different test conditions will be applied to Cd 2+ And Pb 2+ The determination of (2) has important influence, and in order to obtain the optimal electrochemical detection performance, the CMCS-DA/GCE is simultaneously used for detecting Cd 2+ And Pb 2+ Several important experimental conditions of the electrochemical enrichment are optimized, including the modification dosage of the CMCS-DA to the working electrode, the pH of the test system, the deposition potential and the deposition time in the electrochemical enrichment process, and the optimization result is shown in figure 5.
CMCS-DA Pair Cd 2+ And Pb 2+ Has enrichment effect, the modification dosage of the modified CMCS-DA on the surface of the electrode has important influence on the analysis and detection performance, but the more the modification dosage of the modified CMCS-DA on the electrode is, the better the modification dosage is, and different CMCS-DA modification dosages can be used for Cd 2+ And Pb 2+ The effect of detection of (2) is shown in graph a in fig. 4. Cd with the increase of the amount of the CMCS-DA modification 2+ And Pb 2+ The electrochemical response current of (2) is gradually increased, and when the addition amount of CMCS-DA/GCE is 4 mu L, the electrochemical sensor obtains the optimal response peak current. When the amount of CMCS-DA continues to increase, the CMCS-DA/GCE is paired with Cd 2+ And Pb 2+ Because the addition amount of the CMCS-DA is increased when the use amount of the CMCS-DA is small, the electrochemical detection signal of (1) is reduced for Cd 2+ And Pb 2+ Also gradually increases, but when increased to a certain extent, it acts on Cd as the modification amount of CMCS-DA continues to increase 2+ And Pb 2+ The larger the diffusion resistance, the unfavorable electrochemical enrichment and dissolution, so the optimal dosage of CMCS-DA for the electrode modification process in the experimental process is 4 muL.
The pH value of the electrolyte is one of important factors influencing the electrochemical response of heavy metal ions. Exploring different pH pairs of Cd pairs of a test system in 0.5M HAc-NaAc test buffer solution with the pH value of 3.5-6.0 2+ And Pb 2+ The result is shown in the graph B in fig. 4. It can be seen that as the pH is increased from 3.5 to 5 2+ And Pb 2+ Gradually increases the peak current. Cd as pH continued to increase from 5 to 6 2+ And Pb 2+ Gradually decreases, and the peak current is maximal at pH = 5. This is becauseThe hydrogen evolution reaction can occur during the electrodeposition due to over-strong acidity, which influences the electrochemical enrichment of metal ions; and the excessive alkalinity can hydrolyze heavy metal ions and influence the enrichment and dissolution processes. It was thus shown from the experimental results that the electrolyte solution used in the subsequent experiments had a pH of 5.
In FIG. 4, C is a deposition potential pair Cd 2+ And Pb 2+ The peak current of (a). It is known that different metal ions have different deposition potentials, and the more negative the deposition potential is, the more favorable the metal ion enrichment is, the faster the deposition rate is, and thus the larger the dissolution peak current is. The experimental result shows that Cd 2+ And Pb 2+ The response current of (a) gradually increases as the deposition potential changes from-0.8V to-1.2V. However, when the deposition potential is further shifted negative, cd 2+ And Pb 2+ The response current of (2) is decreased because the deposition of metal ions on the electrode surface is hindered by the hydrogen evolution reaction when the deposition potential is too negative. From the above experimental results, the optimum deposition potential of the present invention was-1.2V.
The deposition time also has important influence on the electrochemical enrichment process, and the invention researches Cd in different deposition times 2+ And Pb 2+ The result is shown in fig. 4, D. Cd when the electrochemical enrichment time increased from 180s to 270s 2+ And Pb 2+ Gradually increases and provides the maximum peak current signal at 270 s. But as the deposition time continued to increase to 300s 2+ And Pb 2+ A slight decrease in peak current signal, which may be due to accumulation of large amounts of heavy metal ions, leading to saturation of the electrode active sites or competing reactions between different metal ions. However, it can be seen that the peak current difference between the deposition times of 240s and 270s is not large, and 240s is selected as the optimum deposition time in consideration of the present invention.
Under the optimal test condition, the CMCS-DA/GCE modified electrode pairs with different concentrations of Cd are explored 2+ And Pb 2+ The electrochemical response SWASV curve and the linear relationship of (a) are shown in fig. 5. It can be seen that with Cd 2+ And Pb 2+ The concentration is increased, the dissolution current of the system is gradually increased and is in the range of 0.01-5 mu M (figure)Panel B and C in FIG. 5), cd 2+ Shows a good linear relation between the response peak current of (1) and the logarithm of the concentration, and the linear regression equation is I =0.40 × logC (Cd) 2+ )+2.10,R 2 =0.994; in the range of 0.05-5. Mu.M (FIGS. 5D and E), pb 2+ Shows a good linear relation between the response peak current of (2) and the logarithm of the concentration, and the linear regression equation is I =1.35 × logC (Pb) 2+ )+2.99,R 2 =0.993, I in equation means electrochemical response peak current (μ a), R 2 Is a linear correlation coefficient. Estimating the pair Cd of the electrochemical sensor based on a method of S/N =3 of a signal-to-noise ratio 2+ And Pb 2+ The detection limits of the cadmium ion detection reagent are 6nM and 8nM respectively, and the requirement of national standard on the lowest detection concentration of cadmium ions and lead ions in drinking water is met.
In the determination of 1. Mu.M Cd 2+ And Pb 2+ When in use, the selectivity of the electrode is examined by respectively adding common coexisting substances into a sample, and the specific method is to test Cd 2+ And Pb 2+ While adding Ca 2+ 、Mn 2+ 、Zn 2+ 、Na + 、K + 、Cl - 、SO 4 2- And NO 3 - . The test results showed 100 times Ca with less than 5% change in the dissolution peak current 2+ ，Mn 2+ ，Zn 2+ Non-interfering, 1000 times Na + ，K + ，Cl - ，SO 4 2- ，NO 3 - And no interference is caused. The above shows that the prepared CMCS-DA/GCE sensing platform pair Cd 2+ And Pb 2+ Has better selectivity in the determination.
Detection of Cd to evaluate CMCS-DA/GCE 2+ And Pb 2+ The reproducibility of the method is that the electrochemical test is carried out on 5 parallel electrodes, the specific method is consistent with the preparation method of CMCS-DA/GCE, and the test result is shown as a picture A in figure 6. Wherein each group of electrode pairs is used for measuring 1 mu M Cd 2+ And Pb 2+ The relative standard deviations of the response currents of (1) and (3.17%) are 4.61% and 3.17%, respectively, indicating good reproducibility of the CMCS-DA/GCE electrode.
To investigate the stability of the electrochemical sensor, the CMCS-DA/GCE electrode prepared in example 1 was placed at 4 ℃Stored in a refrigerator for three weeks and then used to determine 1. Mu.M Cd 2+ And Pb 2+ The electrochemical response results are shown in graph B of fig. 6. Cd (cadmium-doped cadmium) 2+ And Pb 2+ The electrochemical response current of the electrode still keeps 93.84% and 92.86% of the newly prepared electrode, and the prepared CMCS-DA/GCE electrode has good stability.
To evaluate the applicability of the developed electrochemical sensing platform in actual sample testing, spiking recovery tests were performed on both local water source tap water and soil digestion solution samples. HAc-NaAc solutions were prepared using tap water and soil digestion solutions, respectively, and three concentrations (0,0.1 and 0.5. Mu.M) of Cd were prepared by standard addition methods 2+ And Pb 2+ The tap water and soil digestion liquid samples of (1) were used for recovery rate evaluation, and the test results are shown in table 1.Cd (cadmium-doped cadmium) 2+ And Pb 2+ The recovery rates in tap water are respectively 96-98% and 101.6-102%; the recovery rates in the soil digestion solution are respectively 104-105% and 102-103%, and the Cd can be seen from the table 2+ And Pb 2+ The relative standard deviation of the measured results is less than 5 percent, which shows that the electrochemical detection platform provided by the invention has wide application prospect in real water samples and soil samples.
TABLE 1 Cd in actual samples 2+ And Pb 2+ Experimental results on the recovery rate
The above-described embodiments are only intended to illustrate the preferred embodiments of the present invention, and not to limit the scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims (10)
1. A preparation method of a carboxymethyl chitosan-based hydrogel modified electrode is characterized by comprising the following steps: dissolving carboxymethyl chitosan in water, adding dopamine hydrochloride powder, adding an ammonium persulfate solution after the dopamine hydrochloride powder is dissolved, uniformly mixing, dropwise adding the mixed solution onto the surface of the glassy carbon electrode, and standing at room temperature to obtain the carboxymethyl chitosan-based hydrogel modified electrode.
2. The method for preparing the carboxymethyl chitosan-based hydrogel modified electrode according to claim 1, wherein the glassy carbon electrode is further pretreated before the mixed solution is dripped on the surface of the glassy carbon electrode: the glassy carbon electrode is sequentially coated with 0.3 μm Al and 0.05 μm Al 2 O 3 Polishing, ultrasonic cleaning in nitric acid, absolute ethyl alcohol and water, and drying by nitrogen.
3. The method for preparing a carboxymethyl chitosan-based hydrogel modified electrode according to claim 2, wherein the volume ratio of absolute ethyl alcohol to water is 1.
4. The method for preparing the carboxymethyl chitosan-based hydrogel modified electrode according to claim 1, wherein the mass ratio of the carboxymethyl chitosan to the dopamine hydrochloride is 1:1.
5. the method for preparing a carboxymethyl chitosan-based hydrogel modified electrode according to claim 1, wherein the concentration of the ammonium persulfate solution is 0.1g/mL.
6. The method for preparing the carboxymethyl chitosan-based hydrogel modified electrode according to claim 1, wherein the dropping amount of the mixed solution on the surface of the glassy carbon electrode is 4 μ L.
7. A carboxymethyl chitosan-based hydrogel modified electrode, characterized in that it is prepared by the preparation method according to any one of claims 1 to 6.
8. The carboxymethyl chitosan-based hydrogel modified electrode of claim 7 for simultaneously detecting Cd 2+ And Pb 2+ The use of (1).
9. Use according to claim 8, characterized in that it comprises the following method: assembling the carboxymethyl chitosan-based hydrogel modified electrode as a working electrode into a three-electrode, placing the three-electrode into HAc-NaAc buffer solution, and adding Cd into the three-electrode after the system is stable 2+ And Pb 2+ And enriching a sample to be tested, and then carrying out electrochemical test by square wave anodic stripping voltammetry.
10. Use according to claim 9, characterized in that square-wave anodic stripping voltammetry test parameters: the scanning range is-1.0 to-0.2V, the amplitude is 25mV/s, the enrichment potential is-1.2V, and the enrichment time is 240s.
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