CN112946048A - Method for directly detecting heavy metals in food through membrane electrochemical sensor - Google Patents
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Abstract
The invention discloses a method for directly detecting heavy metals in food by a membrane electrochemical sensor, which comprises the following steps: by passing
The solution growth method comprises depositing silicon dioxide nanochannel on the surface of the indium tin oxide conductive substrate, and removing the residual by adopting ethanol solution containing hydrochloric acid
Preparing a mesoporous silica-nanochannel film/indium tin oxide composite material by using the solution; modifying polydimethylsiloxane on the surface of the mesoporous silicon dioxide-nano channel film/indium tin oxide composite material by adopting a plasma deposition method to prepare plasma-triggered polyDimethyl siloxane modified mesoporous silica nanochannel @ indium tin oxide electrochemical sensor; and then the sensor is directly inserted into a complex matrix, and the concentration of the heavy metal in the sample is detected by differential pulse stripping voltammetry. The modified electrode disclosed by the invention has high selectivity and high sensitivity for determining heavy metals, is short in detection time, can be used for directly detecting the heavy metals in a complex sample, and is convenient and fast to operate.
Description
Technical Field
The invention belongs to the field of food detection, and particularly relates to a method for directly detecting heavy metals in food by a membrane electrochemical sensor.
Background
With the development of industry and agriculture, various fertilizers, micronutrients, pesticides and the like are widely used in order to ensure good growth and quality of agricultural products. However, the increasing use of these agrochemicals contaminates the ecosystem and can also be detected in food samples. The agricultural product has serious heavy metal pollution, and the quality and the health of the product are influenced. Among them, lead (Pb) and cadmium (Cd) are two important representatives, which cause serious food contamination and serious risks to human health. Pb has the characteristics of non-biodegradability, long half-life period, serious harm to human health and the like. Cd2+ has multiple toxic effects on the kidney, liver, nerves and cardiovascular system. Although their concentration in the natural environment is low, they accumulate in the human body through the food chain and prolonged exposure can lead to fatal diseases, including cancer.
The accumulation of Pb and Cd has been found in various foods such as rice, apple, strawberry, grape, pomegranate, kiwi and tomato. Although the Pb and Cd levels in fruits, berries and vegetables are generally low, consumption of these foods or juices and beverages in large quantities results in increased exposure to these heavy metals. The fruit juice mainly comprises minerals such as carbohydrates, proteins, fats, vitamins, salt and the like in water, and in the processes of raw material collection, processing and packaging, because the production process is unscientific and the quality control measures are not strict, the fruit juice can possibly face a greater heavy metal pollution risk, and the fruit juice still has a great food safety problem in the world. In addition, fruit and vegetable juices and beverages are becoming increasingly popular among young people due to their ready availability, processing and convenience of consumption. Therefore, the development of a detection analysis method for accurately detecting Pb and Cd in the samples with sensitivity, rapidness and low cost is urgently needed.
Traditional methods for detecting heavy metals in food samples include x-ray fluorescence spectroscopy (XRF), inductively coupled plasma optical emission spectroscopy (ICP-OES), atomic absorption spectroscopy (FAAS), and inductively coupled plasma mass spectroscopy (ICP-MS). However, these methods have disadvantages of high cost, complicated operation, long pretreatment steps, and limited industrial or market use. Thus, these techniques have difficulty meeting the ever-increasing demands for on-site monitoring and on-line analysis. In contrast, electrochemical methods, in particular Anodic Stripping Voltammetry (ASV), are widely used for their quantification due to the possible enrichment of metals at the electrode surface, with significant sensitivity even at trace/ultra-trace levels. The method can reduce cost, has high sensitivity, is compact and simple, and can be used for on-site rapid detection and trace analysis. In recent years, mesoporous silica-nanochannel membrane sensors have attracted increasing attention for their selective analytical capabilities for small analytes in complex samples. Such nanochannels exhibit osmo-selective through effects in size, charge and sensitivity to positively charged analytes due to enrichment effects caused by electrostatic attraction and spatial confinement within the channel. Steric hindrance has been widely used for nonspecific adsorption of macromolecules on electrodes, such as an antifouling effect, and has attracted great attention. The application of mesoporous silica materials in the fields of molecular separation, molecular detection, nanofluids, drug delivery, simulated biological membranes and the like has been reported.
Despite good steric hindrance properties, direct electrochemical detection remains challenging in real food samples due to interference from large amounts of interfering substances. Small electroactive molecules in food (e.g. antioxidants, vitamins) can enter traditional nanochannels and generate interfering electrochemical signals. At present, no nano sensor with high sensitivity, convenient treatment and low cost is developed for detecting heavy metals Pb and Cd in food samples.
Disclosure of Invention
The invention provides a method for directly detecting heavy metals in food by a membrane electrochemical sensor, and the electrochemical sensor prepared by the invention can directly detect the heavy metals in a complex sample, and has the characteristics of high sensitivity, low detection limit, wide dynamic range, strong anti-interference capability, short detection time and the like.
A method for direct detection of heavy metals in food products by a membrane electrochemical sensor comprising:
(1) by passing
The solution growth method comprises depositing silicon dioxide nanochannel on the surface of the indium tin oxide conductive substrate, and removing the residual by adopting ethanol solution containing hydrochloric acid
Preparing a mesoporous silica-nanochannel film/indium tin oxide composite material by using the solution;
(2) modifying polydimethylsiloxane on the surface of the mesoporous silica-nanochannel film/indium tin oxide composite material by adopting a plasma deposition method to prepare a plasma-triggered polydimethylsiloxane-modified mesoporous silica nanochannel @ indium tin oxide electrochemical sensor, and then detecting heavy metals in a sample by adopting a differential pulse stripping voltammetry method.
Polydimethylsiloxane is deposited on a silicon dioxide nanochannel @ indium tin oxide electrode to prepare the electrochemical sensor, the nanochannel of the electrochemical sensor is filled with dense polydimethylsiloxane, so that most molecules can be inhibited from passing through, only small heavy metal ions can pass through, heavy metal ions can be directly detected in a complex environment, hydrophilic substances, hydrophobic substances and macromolecular substances in a sample cannot be adsorbed on the surface of the indium tin oxide electrode, and only small heavy metal ions can be adsorbed on the electrode, so that the sensitivity and selectivity of heavy metal compound detection are improved.
In the step (1), the
The solution is prepared by dissolving cetyl trimethyl ammonium bromide in a mixed solution of water and ethanol and adding an ammonia solution and tetraethyl orthosilicate, wherein the mass ratio of the cetyl trimethyl ammonium bromide to the ammonia solution to the tetraethyl orthosilicate is 15-24:0.91-1.12: 7.45.
In the step (1), further, ethanol solution containing hydrochloric acid is adopted to remove residual
Cetyl trimethylammonium bromide in solution.
The concentration of the hydrochloric acid in the ethanol solution containing the hydrochloric acid is not less than 0.1 mol/L.
Adding an ethanol solution containing hydrochloric acid to remove residual hexadecyl trimethyl ammonium bromide in the silicon dioxide nano channel, so that the silicon dioxide nano channel has hydrophilicity, the residual hexadecyl trimethyl ammonium bromide cannot be completely removed due to too low concentration of the hydrochloric acid in the ethanol solution of the hydrochloric acid, the residual hexadecyl trimethyl ammonium bromide can remain in the silicon dioxide nano channel, the hydrophilicity of the silicon dioxide nano channel is influenced, and the selectivity of detecting the small molecular compound is reduced.
In the step (2), the plasma deposition method is to place the indium tin oxide/silicon dioxide composite material on a glass plate, surround the polydimethylsiloxane monomer on the periphery of the glass plate, and place the glass plate in a plasma cleaner for plasma deposition for 10-35 s.
The polydimethylsiloxane has a length of 1.8-2.3cm and a width of 0.2-0.4 cm.
In step (3), before the heavy metal detection by the differential pulse stripping voltammetry, the sample solution is filtered by adding it to a filter membrane with a pore size of 0.40-0.45 μm (Millipore).
Compared with the method for detecting the heavy metal, which is finally determined after the samples are filtered, extracted, enriched and subjected to microwave digestion in the inductively coupled plasma mass spectrometry (ICP-MS) determination, the method for detecting the heavy metal provided by the invention has the advantages that the samples do not need to be further pretreated, and the developed field electrochemical sensor is simple, rapid and convenient.
In the step (3), the differential pulse stripping voltammetry adopts a three-electrode system, wherein a silver chloride/silver electrode is a reference electrode, a platinum wire electrode is a counter electrode, and a plasma-triggered polydimethylsiloxane-modified silicon dioxide nanochannel @ indium tin oxide electrode is a working electrode.
In the step (3), the differential pulse stripping voltammetry for heavy metal detection mainly comprises electrochemical deposition and stripping, and comprises the following steps:
(1) depositing heavy metal ions on the plasma-triggered polydimethylsiloxane-modified mesoporous silica nanochannel @ indium tin oxide electrochemical sensor at a voltage of-0.95V to-0.2V by adopting a method for reducing heavy metals;
(2) carrying out anodic dissolution on the electro-deposited Pb and Cd by adopting a differential pulse voltammetry under the voltage of-0.95 to-0.2V;
(3) applying a potential of +0.3 to +0.6V for 60-90s to remove the deposited residual species from the surface and recovering the used electrode for the next test.
In the step (3), the experimental conditions of the differential pulse stripping voltammetry are as follows: the scanning potential range is-0.95 to-0.2V, the increment potential is 0.01V, the amplitude is 0.05V, the pulse width is 0.05s, and the balance period is 30 s.
In the step (3), the electrolyte solution adopted in the differential pulse stripping voltammetry is a potassium chloride-hydrochloric acid solution, acetic acid-sodium acetate is a buffer solution, and the pH value of the electrolyte solution is adjusted to be 5-6.
Under the condition of proper pH, the inner wall of the pore channel can be deprotonated and has negative charges, so that the mass transfer process of heavy metal ion signals can be accelerated, the detection sensitivity of the small molecular compound is enhanced, the potassium sulfate-sulfuric acid or potassium chloride-hydrochloric acid solution has small influence on the heavy metal ion signals, and the interference on the transmission of the heavy metal ion signals is reduced.
The invention provides a plasma-triggered polydimethylsiloxane-modified silicon dioxide nanochannel @ indium tin oxide electrode prepared by a method for detecting heavy metals by using an electrochemical modified electrode, wherein the modified electrode has higher selectivity and sensitivity, and the minimum detection limits of lead ions and cadmium ions are 4 mug/L and 2 mug/L.
The invention has the following beneficial effects:
(1) the invention provides a plasma-triggered polydimethylsiloxane-modified silicon dioxide nanochannel @ indium tin oxide electrode, wherein a nanochannel is filled with a dense polymer, so that most molecules including hydrophilic molecules and hydrophobic molecules can be inhibited, only small heavy metal ions can pass through the nanochannel, and therefore, in the process of detecting small-size compounds in a complex sample, the nanochannel has high selective permeability for the small-size compounds, and the concentration of the nanochannel can be detected to be 4-1500 mu g L-1Lead ion of 30-900 mu g L-1And thus has high sensitivity and selectivity.
(2) The method for detecting the heavy metal in the indium tin oxide/silicon dioxide surface by the plasma deposition method has the advantages that the polydimethylsiloxane group is modified on the indium tin oxide/silicon dioxide surface by the plasma deposition method, the deposition method is simple and rapid, the preparation efficiency is improved, the detection can be directly carried out in a complex sample without carrying out complicated pretreatment, the method for detecting the heavy metal in the sample only needs 8-15min, and the detection time is far shorter than that of the prior art.
Drawings
FIG. 1 is a diagram of PDMS-PDMS (polydimethylsiloxane, MSF-mesoporous silica nanochannel, ITO-indium tin oxide) before plasma deposition treatment of a PDMS-modified mesoporous silica nanochannel/indium tin oxide electrode;
FIG. 2 is a graph of electrochemical sensing properties (cyclic voltammetry) of indium tin oxide, mesoporous silica nanochannel/indium tin oxide, plasma-triggered polydimethylsiloxane-modified mesoporous silica nanochannel/indium tin oxide electrodes in 0.5M KCl containing (a) Ru (NH3)63+, (b) Fe (CN)63-, (c) Fc-MeOH, (d) ascorbic acid, (e) retinol, (f) melatonin scan rate of 50mV s-1 (CVs);
FIG. 3 is a graph comparing electrochemical signals on a plasma-triggered PDMS-modified mesoporous silica nanochannel/indium tin oxide electrode and an indium tin oxide electrode in a lead ion solution of the same concentration;
FIG. 4 is a linear relationship graph of the current signal change and the heavy metal ion concentration of the plasma-triggered polydimethylsiloxane-modified mesoporous silica nanochannel/indium tin oxide electrode prepared in example 1 in standard solutions with different lead ion and cadmium ion concentrations;
FIG. 5 plasma-triggered PDMS modified mesoporous silica nanochannel/ITO electrode detection pb2+And Cd2+The interference immunity evaluation effect map of (1);
FIG. 6 is a picture (a) of direct electrochemical detection of Cd in grape juice, grape beverage, apple juice, and rice fermented beverage samples by using plasma-triggered polydimethylsiloxane-modified mesoporous silica nanochannel/indium tin oxide electrode (b) of Cd in grape juice, grape beverage, apple juice, and rice fermented beverage samples by using plasma-triggered polydimethylsiloxane-modified mesoporous silica nanochannel/indium tin oxide electrode2+Working curve diagram of (2). (c) Method for measuring Pb in grape juice, grape beverage, apple juice and rice fermented beverage samples by using plasma-triggered polydimethylsiloxane-modified mesoporous silica nanochannel/indium tin oxide electrode2+Working curve diagram of (2).
Detailed Description
The invention is further illustrated by the following specific examples:
(1) cleaning the electrode: firstly, an indium tin oxide electrode is immersed in an ethanol solution containing 1mol/L of sodium hydroxide and is subjected to ultrasonic treatment for 1 hour, then the electrode is immersed in acetone and ethanol in sequence and is subjected to ultrasonic treatment for 15 minutes respectively, then the electrode is cleaned with deionized water for 15 minutes, the ultrasonic treatment is repeated twice, and finally, the electrode is dried by nitrogen for standby.
(2) Depositing a silicon dioxide nano-channel film on the surface of the indium tin oxide electrode:
1. configuration of
Solution: 0.16g of cetyltrimethylammonium bromide was dissolved in 100mL of a water/ethanol mixed solution (70mL/30mL), and after the cetyltrimethylammonium bromide was completely dissolved, an ammonia solution (100. mu.L, 2.5 wt%) and tetraethylorthosilicate (80. mu.L) were separately added to the solutionSlowly adding the mixture into a hexadecyl trimethyl ammonium bromide solution under stirring;
2. soaking indium tin oxide electrode in the solution
Heating in water bath at 60 ℃, avoiding vibration in the whole process as much as possible, taking out the electrode after 24 hours, washing with a large amount of water, drying with nitrogen, putting the electrode in a dry box, and aging at 100 ℃ for 12 hours, wherein the nano pore channel of the obtained electrode is filled with a surfactant;
3. the surfactant cetyl trimethyl ammonium bromide in the nano-channel is removed by soaking in ethanol solution containing 0.1mol/L hydrochloric acid, and the indium tin oxide/silicon dioxide nano-channel composite material of the silicon dioxide nano-channel array with the pore vertical to the substrate deposited on the surface of the indium tin oxide conductive substrate is obtained.
(3) Plasma cleaner deposition: placing the indium tin oxide/silicon dioxide nanochannel composite material at 12.5cm2And surrounding 1g of polydimethylsiloxane monomer on three sides of the glass plate, specifically putting the glass frame into a plasma cleaner, and treating at low power for 30 seconds to obtain the plasma-triggered polydimethylsiloxane-modified mesoporous silica nano-channel/indium tin oxide electrode, as shown in FIG. 1.
(4) The electrochemical detection adopts a classical three-electrode system: and taking a standard silver chloride/silver electrode as a reference electrode, a platinum wire electrode as a counter electrode, and a modified indium tin oxide electrode as a working electrode. The electrolyte background of the detection system is 0.5mol/L potassium chloride solution, the buffer solution is acetic acid-sodium acetate solution, the pH of the solution is 5.5, the probe molecule/ion concentration is 200 mu mol/L, the electrochemical sensing characteristics (cyclic voltammetry) of indium tin oxide, mesoporous silica nano-channel/indium tin oxide and plasma-triggered polydimethylsiloxane modified mesoporous silica nano-channel/indium tin oxide electrode are compared, and the three electrodes contain (a) Ru (NH-N) in the presence of (a)3)6 3+，(b)Fe(CN)6 3-(c) Fc-MeOH, (d) ascorbic acid, (e) retinol, and (f) melatonin scan at a rate of50mVs-1Cyclic Voltammograms (CVs) in 0.5M KCl, see FIG. 2.
In the lead ion solution with the same concentration, electrochemical signals on the mesoporous silica nanochannel/indium tin oxide electrode and the indium tin oxide electrode are compared and modified by polydimethylsiloxane triggered by plasma, and the graph is shown in fig. 3.
As can be seen from FIG. 2, in order to study the electrochemical behavior of plasma-triggered PDMS modified mesoporous silica nanochannel/ITO electrode, Cyclic Voltammetry (CVs) was applied to typical Ru (NH)3)6 3+，Fe(CN)6 3-Electrochemical studies were performed with Fc-MeOH probes. As shown in fig. 2, a well-defined current wave was observed for all three redox probes on the bare indium tin oxide electrode. When indium tin oxide is modified by mesoporous silica nanochannels, the nanochannel electrodes also exhibit a distinct current peak, however, no molecule can penetrate the nanochannels filled with plasma-triggered polydimethylsiloxane, as all the redox peaks on the plasma-triggered polydimethylsiloxane-modified mesoporous silica nanochannels/indium tin oxide electrodes disappear. Similar phenomena are observed for electroactive molecules (i.e., ascorbic acid, retinol, and melatonin) commonly found in food, which can also enter mesoporous silica-modified indium tin oxide nanochannels and generate significant peak signals, while no signal can be observed on plasma-triggered polydimethylsiloxane-modified nanochannel electrodes, which is much better than previous heating methods (heating 12h deposits polydimethylsiloxane, which still allows small neutral or hydrophobic molecules to pass through the nanochannels. these results clearly show that plasma-triggered polydimethylsiloxane-modified mesoporous silica nanochannels can significantly inhibit the passage of most molecules, including hydrophilic and hydrophobic molecules, while allowing smaller heavy metal ions to pass, as shown in figure 3, in which case, the plasma-triggered polydimethylsiloxane modified mesoporous silicon dioxide nano-channel/indium tin oxide electrode shows the capability of resisting surface pollution and pollution, and allows heavy metal ions to be inElectrochemical analysis in real or complex media.
(5) Drawing a working curve:
20mL of acetic acid buffer (0.1M, Pb2+ pH 6.0, Cd2+ pH5.5) was used as a medium for detecting heavy metal ions. The effective area of the working electrode immersed in the electrolyte is 1cm x 1 cm. Preparation of 1000. mu.g mL-1 of Pb2+And Cd2+Gradually diluting the standard stock solution to obtain different concentrations, and depositing heavy metal ions on a p-PDMS @ MSF/ITO electrode for 300s under-0.9V; subsequently, the electrodeposited Pb and Cd were subjected to anodic stripping using Differential Pulse Voltammetry (DPV) under the following conditions: the scanning potential range is-0.1V, the increment potential is 0.01V, the amplitude is 0.05V, the pulse width is 0.05s, and the balance period is 30 s. Mixing the peak current signal with Pb2+And Cd2+The concentration data were fitted linearly and the standard curve was plotted as shown in FIG. 4, Cd 2+30 mu g/L-900 mu g/L and Pb2+The linear relation between 4 mug/L and 1500 mug/L is better, and the linear correlation coefficients are respectively 0.9991 and 0.9883. Then adding a set volume of the solution to be detected into acetic acid-sodium acetate + potassium chloride solution, triggering response currents of the polydimethylsiloxane modified mesoporous silica nano-channel/indium tin oxide electrode and the polydimethylsiloxane modified indium tin oxide electrode to heavy metal lead and cadmium ions according to the plasma, and obtaining the concentration of the heavy metal ions in the solution to be detected through calculation by combining a linear relation curve of the current and the concentration, so as to realize the determination of the concentration of the heavy metal in the solution to be detected; during electrodeposition and pretreatment, the test solution was stirred with a magnetic stirrer. Furthermore, after each measurement, the used electrode can be recovered for the next detection by applying a pre-step of potential +0.3V, for 60s, to clean the surface of the deposited residual species.
The anti-interference properties are of great importance for the practical application of electrochemical sensors, especially for complex food samples. The presence of common interferents such as food additives, amino acids, starch, antioxidants and minerals can have a serious impact on the detection of heavy metal ions. The anti-interference property is crucial to the practical application of electrochemical sensors. By detecting plasma contactPolydimethylsiloxane modified mesoporous silica nano-channel/stannic oxide electrochemical sensor pair other possible Pb and/or Sn oxide electrochemical sensors2+And Cd2+Coexisting interferent (Fe)3+Glycine (Gly), glucose, fructose, sucrose, vitamin c (vc), glutamic acid (Glu), citric acid and starch, and the interference of the sensor was determined. Pb2+And Cd2+The result of the interference rejection evaluation is shown in FIG. 5, which shows the evaluation on the interference-free substrate (I) or the interference-free substrate (I)0) Time, relative signal change (I/I) calculated using peak current0). With Pb2+And Cd2+Observed I/I0The significant response of the values is comparable to the change in response obtained when adding other interference, which is negligible. Even when containing Pb2+(100. mu.g/L) and Cd2+(100. mu.g/L) of a solution of each interfering substance (1000. mu.g/L) in a large amount of Pb2+And Cd2+There is little significant change in the peak current of (a). The result shows that the plasma-triggered polydimethylsiloxane-modified mesoporous silica nano-channel/tin oxide electrochemical sensor has equivalent anti-interference performance on food additives, amino acids, starch and minerals and has good Pb resistance2+And Cd2+Has high selectivity.
The plasma-triggered polydimethylsiloxane-modified mesoporous silica nanochannel/indium tin oxide electrode prepared in this embodiment detects heavy metal ions in a real sample, and comparative analysis of the obtained working curve is shown in fig. 6 and table 1.
TABLE 1 Pb in juice and beverage samples2+And Cd2+Calibration curve and statistical contrast analysis for detection
Fermentation of commercially available grape juice, grape beverage, apple juice and riceThe beverage sample was used as a heavy metal ion analysis sample. Commercial juice and beverage samples were filtered through 0.45 μm (Millipore) pore size filters, adjusted for pH and electrolyte concentration by the addition of acetic acid buffer, and analyzed. The prepared sample is directly detected without other complicated pretreatment. Since no Pb was found in the collected sample2+And Cd2+So that the final concentrations were 35. mu. g L-1And 40 μ g L-1Pb of2+And final concentrations of 40. mu. g L, respectively-1And 55 μ g L-1Cd (2)2+Respectively adding the components into actual food samples, and measuring pb in grape juice, grape beverage, apple juice and rice fermented beverage by adopting a plasma-triggered polydimethylsiloxane modified mesoporous silica nano-channel/oxidized fume tin electrochemical sensor differential pulse stripping voltammetry method and an inductively coupled plasma mass spectrometry (ICP-MS) method2+And Cd2+The content comparison is shown in Table 2.
TABLE 2 Pb in juices and beverages2+And Cd2+Direct electrochemical detection of
As can be seen from Table 2, pb of the four actual food samples (commercial juices and beverages)2+And Cd2+The result of electrochemical detection of (1). Determination of 35. mu.g/L Pb2+The relative recovery rate of (B) is 98.98-103.43%, and the determination of Pb is 40 mug/L2+Has a relative standard deviation (RSD%, n is 3) of 0.96 to 5.72, and measures Pb at 40. mu.g/L2+The relative recovery rate of the Cd is 95.40-102.93%, and 55 mug/L Cd is measured2+The relative recovery rate of the Cd is 95.27-101.98 percent2+The relative recovery rate of the Cd is 95.40-102.93 percent2+The relative recovery rate is 95.27% -101.98%, and 40 mug/L Cd is detected2+Has a relative standard deviation (RSD%, n is 3) of0.91-6.54, detecting 55 mug/L Cd2+The relative standard deviation of (A) is 1.93-9.08. The detection of the heavy metals in the sample takes 8-15min, and in the measurement of inductively coupled plasma mass spectrometry (ICP-MS), the final measurement is carried out after the sample is subjected to filtration, extraction, enrichment and microwave digestion treatment, but in the method established by the invention, the sample does not need to be further pretreated. It is worth noting that the recovery rate of heavy metal ions detected in juice and beverage samples is very high, which indicates that the mesoporous silica nano-channel/tin oxide electrode modified by polydimethylsiloxane triggered by plasma can enrich heavy metal ions, and has excellent removal performance on starch, food additives, organic matters and other interfering substances in actual food. The results show that the method is used for detecting pb in the actual food sample2+And Cd2+The detection has higher accuracy and has higher application prospect in food industry, environmental protection and clinical research. In addition, the developed on-site electrochemical sensor is simple, quick, convenient and low in cost, and is a feasible solution. In contrast, existing inductively coupled plasma mass spectrometry (ICP-MS) for heavy metal detection is entirely a laboratory-based instrument, expensive, time consuming, requires training and high operating costs.
Claims (10)
1. A method for direct detection of heavy metals in food products by a membrane electrochemical sensor comprising:
(1) by passing
The solution growth method comprises depositing silicon dioxide nanochannel on the surface of the indium tin oxide conductive substrate, and removing the residual by adopting ethanol solution containing hydrochloric acid
Preparing a mesoporous silica-nanochannel film/indium tin oxide composite material by using the solution;
(2) modifying polydimethylsiloxane on the surface of the mesoporous silica-nanochannel film/indium tin oxide composite material by adopting a plasma deposition method to prepare a plasma-triggered polydimethylsiloxane-modified mesoporous silica nanochannel @ indium tin oxide electrochemical sensor, and then detecting heavy metals in a sample by adopting a differential pulse stripping voltammetry method.
2. The method for preparing an electrochemically modified electrode according to claim 1, wherein in step (1), the electrochemical modification is performed
The solution is prepared by dissolving cetyl trimethyl ammonium bromide in a mixed solution of water and ethanol and adding an ammonia solution and tetraethyl orthosilicate, wherein the mass ratio of the cetyl trimethyl ammonium bromide to the ammonia solution to the tetraethyl orthosilicate is 15-24:0.91-1.12: 7.45.
3. The method for directly detecting heavy metals in foods by using the membrane electrochemical sensor as claimed in claim 2, wherein the residual metal is removed by using ethanol solution containing hydrochloric acid in the step (1)
Cetyl trimethylammonium bromide in solution.
4. The method for directly detecting the heavy metals in food through the membrane electrochemical sensor according to claims 1-3, wherein the concentration of hydrochloric acid in the ethanol solution containing hydrochloric acid is not less than 0.1 mol/L.
5. The method for directly detecting the heavy metals in the food through the membrane electrochemical sensor according to claim 1, wherein in the step (2), the indium tin oxide/silicon dioxide composite material is placed on the glass plate, the polydimethylsiloxane monomer is surrounded on the periphery of the glass plate, and the glass plate is placed in a plasma cleaner for plasma deposition for 10-35 s.
6. The method for direct detection of heavy metals in food products by membrane electrochemical sensors according to claim 5, wherein said polydimethylsiloxane is 1.8-2.3cm long and 0.2-0.4cm wide.
7. The method for directly detecting the heavy metals in the food through the membrane electrochemical sensor according to claim 1, wherein in the step (3), the sample solution is filtered by a filter membrane with a pore size of 0.40-0.45 μm before the heavy metals are detected by using the differential pulse stripping voltammetry.
8. The method according to claim 1, wherein in the step (3), the differential pulse stripping voltammetry adopts a three-electrode system, wherein the silver chloride/silver electrode is a reference electrode, the platinum wire electrode is a counter electrode, and the plasma-triggered polydimethylsiloxane-modified silica nanochannel @ indium tin oxide electrode is a working electrode.
9. The method for directly detecting heavy metals in food through the membrane electrochemical sensor according to claim 1, wherein in the step (3), the method for detecting heavy metals through differential pulse stripping voltammetry comprises:
(1) depositing heavy metal ions on the plasma-triggered polydimethylsiloxane-modified mesoporous silica nanochannel @ indium tin oxide electrochemical sensor at a voltage of-0.95V to-0.2V by adopting a method for reducing heavy metals;
(2) carrying out anodic dissolution on the electro-deposited Pb and Cd by adopting a differential pulse voltammetry under the voltage of-0.95 to-0.2V;
(3) applying a potential of +0.3 to +0.6V for 60-90s to remove the deposited residual species from the surface and recovering the used electrode for the next test.
10. The method for directly detecting the heavy metals in the food through the membrane electrochemical sensor according to claim 1, wherein in the step (3), the electrolyte solution adopted in the differential pulse stripping voltammetry is potassium chloride-hydrochloric acid solution, acetic acid-sodium acetate is buffer solution, and the pH of the electrolyte solution is adjusted to 5-6.
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