On-site rapid detection method for heavy metal lead ions and / or cadmium ions in seawater by in-situ bismuth plating method

Abstract

The invention provides an on-site rapid detection method for heavy metal lead ions and / or cadmium in seawater through an in-situ bismuth plating method. The technical problems that in the prior art, operation is complex, and the method is not suitable for on-site application are solved. The method comprises the following steps: S1, assembling a three-electrode system sensor, and connecting an electrochemical workstation; s2, preparing a simulated seawater solution containing bismuth ions; s3, lead and cadmium ion standard solutions are added into the simulated seawater solution, and the optimal deposition voltage and deposition time are obtained through electrochemical testing; s4, dividing the simulated seawater solution into a plurality of parts, respectively adding lead ion and / or cadmium ion standard solutions with different concentrations, and detecting and drawing a standard working curve by adopting square wave anodic stripping voltammetry; and S5, carrying out suction filtration treatment on the seawater to be detected, adding the lead ion and / or cadmium ion standard solution, the bismuth ion solution, NaAc and HAc, preparing a weakly acidic water sample to be detected, carrying out electrochemical detection, comparing with the standard working curve, and calculating to obtain the content of lead ions and / or cadmium ions in the seawater to be detected. The method can be widely applied to the environment monitoring technology field.

Description

Technical Field

[0001] The present application relates to the technical field of environmental monitoring, and in particular to an on-site rapid detection method for heavy metal lead ions and / or cadmium in seawater by an in-situ bismuth plating method. Background Art

[0002] Heavy metals refer to metals with a density greater than 4.5 g / cm 3 Heavy metals are a class of metal elements. In recent years, due to the non-biodegradable nature and extremely high toxicity of heavy metal ions, even trace amounts of heavy metal ion pollution can have adverse effects on humans and aquatic life, and this issue has attracted serious attention. Since the ocean area accounts for two-thirds of the earth's surface and has an important impact on human survival and development, how to accurately and effectively detect heavy metals in the seawater environment is a key issue that researchers urgently need to solve, and it is of great significance to ensure the accurate acquisition of heavy metal information.

[0003] Commonly used physical methods for detecting heavy metals in seawater include atomic absorption spectrometry (AAS), inductively coupled plasma-atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), high performance liquid chromatography, fluorescence spectrometry and electrochemical analysis. Atomic absorption spectrometry has good selectivity and a wide range of applications, but the equipment is expensive, it cannot achieve simultaneous analysis of multiple elements and the measurement speed is slow; inductively coupled plasma-atomic emission spectrometry can perform simultaneous analysis of multiple elements, has high sensitivity and a wide linear range, but the equipment is expensive and requires complex sample pretreatment; inductively coupled plasma mass spectrometry has low detection limits, high sensitivity and strong anti-interference, and can perform simultaneous analysis of multiple elements, but the instrument is expensive, large in size, inconvenient to carry and has high requirements for operators; fluorescence spectrometry has high sensitivity and strong selectivity, but the detection limit is usually high and it is difficult to use for trace element analysis. High performance liquid chromatography has high sensitivity and selectivity, but it also faces the problems of high cost and complex operation.

[0004] The commonly used electrochemical methods for heavy metal detection in the ocean are polarography and voltammetry. The polarization electrode used in polarography usually uses a liquid electrode, mainly a mercury drop electrode. Polarography has the advantages of high accuracy and strong selectivity, but its application is relatively small due to the harm of mercury drops to the human body and the environment. The working electrode used in voltammetry is usually a stationary or solid electrode. Heavy metal detection mainly uses anodic stripping voltammetry. Carbon paste electrodes and glassy carbon electrodes are not suitable for field applications. Summary of the invention

[0005] The purpose of the present invention is to solve the deficiencies of the above-mentioned technology and provide an on-site rapid detection method for heavy metal lead ions and / or cadmium in seawater by an in-situ bismuth plating method, which reduces costs, is simple to operate, and is suitable for on-site application.

[0006] To this end, the present invention provides an on-site rapid detection method for heavy metal lead ions and / or cadmium in seawater by an in-situ bismuth plating method, comprising the following steps:

[0007] Step S1. Assembling a three-electrode system sensor, wherein the working electrode is a modified reduced graphene oxide-acidified multi-walled carbon nanotube-Nafion electrode, the counter electrode is a carbon-based electrode, and the reference electrode is an Ag / AgCl electrode, and the working electrode, the counter electrode, and the reference electrode are connected to an electrochemical workstation through the sensor respectively;

[0008] Step S2. preparing a simulated seawater solution containing bismuth ions;

[0009] Step S3. Take the simulated seawater solution prepared in step S2, and add a certain amount of lead ion standard solution and cadmium ion standard solution to the simulated seawater solution respectively; adopt the three-electrode system sensor of step S1, use an electrochemical workstation, and use square wave stripping voltammetry to perform current-voltage electrochemical tests at different deposition voltages and deposition times, and obtain the deposition voltage and deposition time when the peak current is maximum;

[0010] Step S4. Take the simulated seawater solution prepared in step S2, divide the simulated seawater solution into multiple portions, and add different concentrations of lead ion standard solution and / or cadmium ion standard solution into each portion of the simulated seawater solution; adopt the three-electrode system sensor of step S1, use an electrochemical workstation, and use square wave stripping voltammetry to detect the concentration of lead ions and / or cadmium ions, respectively, wherein the enrichment potential and enrichment time in the set detection parameters are respectively the deposition voltage and deposition time obtained in step S2; respectively draw the relationship curves corresponding to the peak current and the lead ion or cadmium ion concentration, that is, obtain the standard working curve diagram;

[0011] Step S5. Take a certain amount of seawater to be tested and perform filtration pretreatment; add a certain amount of lead ion and / or cadmium ion standard solution, bismuth ion solution, and detection reagent to the pretreated seawater to be tested to prepare a weakly acidic water sample to be tested; wherein the detection reagent includes NaAc and HAc; electrochemically detect the concentration of lead ions or cadmium ions by square wave anodic stripping voltammetry under the same experimental conditions as step S4; compare the standard working curve obtained in step S4 to obtain the concentration of lead ions and / or cadmium ions in the water sample to be tested; and finally calculate the content of lead ions and / or cadmium ions in the seawater to be tested.

[0012] Among them, it is important to point out that:

[0013] The main purpose of the above step S3 is to optimize the deposition voltage and deposition time of simulated seawater to determine the preferred electrochemical parameters, and the optimization of the deposition voltage and deposition time can significantly improve the sensitivity, selectivity and accuracy of the detection. The optimized deposition voltage can effectively enrich the target ions while reducing the influence of interfering ions, thereby enhancing the signal strength and detection sensitivity. The optimized deposition time can avoid the co-deposition of too many interfering substances while increasing the enrichment amount, thereby improving the selectivity. By optimizing these two parameters, the background noise and interference can also be reduced, and the reproducibility and accuracy of the data can be improved. In addition, the optimized deposition time can save experimental time and improve detection efficiency.

[0014] The main purpose of the filtration pretreatment in step S5 is that the real seawater after filtration can effectively remove suspended particles, organic matter and biological substances, reduce the interference of these impurities on electrochemical detection, and thus improve the sensitivity, accuracy and stability of detection. Filtration can reduce the adsorption of heavy metal ions by particles and organic matter, ensure that the sample is purer, and reduce the influence of biological substances on the deposition of electrode surfaces, reducing the risk of electrode contamination or passivation. In addition, filtration can also reduce the noise in the detection, make the signal more stable, and improve the reproducibility and reliability of the detection results.

[0015] Preferably, in step S1, the preparation method of the working electrode comprises: drop coating an acidified multi-walled carbon nanotube-graphene mixed solution on the surface of a bare electrode of a screen-printed electrode, and drying, to prepare a modified reduced graphene oxide-acidified multi-walled carbon nanotube electrode; then drop coating a Nafion solution on the surface of the modified reduced graphene oxide-acidified multi-walled carbon nanotube electrode, and drying, to obtain a modified reduced graphene oxide-acidified multi-walled carbon nanotube-Nafion electrode, i.e., a working electrode.

[0016] Preferably, the method for preparing the acidified multi-walled carbon nanotube-graphene mixed solution comprises:

[0017] Preparation of acidified multi-walled carbon nanotubes: multi-walled carbon nanotubes, concentrated nitric acid and concentrated sulfuric acid are mixed to form a suspension, subjected to ultrasonic treatment, diluted with water and centrifuged to obtain a centrifuged solid, the centrifuged solid is fully washed with water, ultrasonicated and centrifuged, and the finally obtained centrifuged solid is dried and ground into fine powder particles with a particle size controlled at 0.1-10 μm to obtain acidified multi-walled carbon nanotubes;

[0018] Preparing an acidified multi-walled carbon nanotube solution: stirring and mixing the prepared acidified multi-walled carbon nanotubes, ethanol and water to prepare an acidified multi-walled carbon nanotube solution for later use;

[0019] Preparing a reduced graphene oxide solution: stirring and mixing the reduced graphene oxide, ethanol and water to prepare a reduced graphene oxide solution for later use;

[0020] Preparation of an acidified multi-walled carbon nanotube-graphene mixed solution: stirring and mixing the prepared acidified multi-walled carbon nanotube solution, the prepared reduced graphene oxide solution, ethanol and water to prepare an acidified multi-walled carbon nanotube-graphene mixed solution.

[0021] Preferably, the method for preparing the Nafion solution includes: stirring and mixing the Nafion standard solution, ethanol, and distilled water to prepare the Nafion solution.

[0022] Preferably, in step S2, each 500 mL of simulated seawater solution contains 12.36 g of sodium chloride, 0.335 g of potassium chloride, 0.68 g of calcium chloride, 2.33 g of magnesium chloride, 3.145 g of magnesium sulfate, and 0.09 g of sodium bicarbonate.

[0023] Preferably, in step S2, 500 μL of 1000 μg / mL bismuth ion solution is added to every 500 mL of simulated seawater solution.

[0024] Preferably, in step S3, 50 μL of a 10 μg / mL lead ion standard solution and a 10 μg / mL cadmium ion standard solution are added to the container, and then the prepared simulated seawater solution is added to dilute to 10 mL; an electrochemical test is performed to obtain a deposition voltage of -1.2 V and a deposition time of 220 s at the maximum peak current value.

[0025] Preferably, in step S4, when heavy metal ions and lead ions are detected separately, the detection parameters are set as follows: amplitude of 25 mV, potential increment of 5 mV, frequency of 15 Hz, enrichment potential of -1.2 V, enrichment time of 220 s, stirring rate of 300 r / min, static time of 10 s, dissolution starting potential of -0.8 V, and termination potential of -0.4 V;

[0026] When the heavy metal ion cadmium ion is detected alone, the detection parameters are set as follows: amplitude of 25mV, potential increment of 5mV, frequency of 15Hz, enrichment potential of -1.2V, enrichment time of 220s, stirring rate of 300r / min, static time of 10s, dissolution starting potential of -1.1V, and termination potential of -0.75V;

[0027] When detecting heavy metal ions lead ions and cadmium ions, the detection parameters were set as follows: amplitude of 25 mV, potential increment of 5 mV, frequency of 15 Hz, enrichment potential of -1.2 V, enrichment time of 220 s, stirring rate of 300 r / min, static time of 10 s, dissolution starting potential of -1.2 V, and ending potential of -0.4 V.

[0028] Preferably, in step S5, the seawater to be tested is pre-treated by filtration, wherein the pore size of the filter membrane is ≤1.0 μm.

[0029] Preferably, in step S5, the method for configuring the water sample to be tested includes:

[0030] Add 750 μL of 1000 μg / mL bismuth ion solution into the container, then add 3.4546 g of NaAc, 1.016 mL of HAc, and the pretreated seawater to be tested to dilute to 500 mL to prepare a seawater mixture for standby use;

[0031] Take another container, add 20 μL of 10 μg / mL lead ion standard solution and / or 20 μL of 10 μg / mL cadmium ion standard solution into the container respectively, then add the seawater mixture to dilute to 10 mL to prepare the water sample to be tested with a pH of 4.5.

[0032] The present invention provides an on-site rapid detection method for heavy metal lead ions and / or cadmium ions in seawater by an in-situ bismuth plating method, and the main beneficial effects are as follows:

[0033] (1) When determining heavy metal ions in seawater, since seawater contains a large amount of salts and organic matter, the prior art usually requires the use of strong acids such as concentrated nitric acid, hydrofluoric acid, and hydrochloric acid to digest the sample; however, the present invention adopts electrochemical stripping voltammetry, which does not require complex sample digestion steps, and directly uses electrodes to enrich and detect heavy metal ions, avoiding the treatment of seawater matrix, simplifying the operation process, reducing costs, and can quickly detect heavy metal lead ions and cadmium ions. The seawater to be tested is pre-filtered, which is simple to operate, has a fast response, and the data has high timeliness. It is fast and convenient, does not cause environmental pollution, and is suitable for field applications.

[0034] (2) The in-situ bismuth plating method has significant advantages in detecting heavy metals in seawater. First, it uses non-toxic bismuth ions, avoiding the environmental and health risks of traditional mercury-based electrodes and being highly environmentally friendly. The method is easy to operate and can simultaneously electrodeposit the bismuth film during the detection process. There is no need to prepare the electrodes in advance, which improves the experimental efficiency. Compared with mercury electrodes, bismuth electrodes have a wider potential window and can work stably under complex matrices and adapt to high-salinity seawater environments. The in-situ bismuth plating method also has good repeatability and stability. A fresh bismuth film can be generated each time the test is performed, ensuring the reliability of the test results.

[0035] In addition, this method is suitable for integration into portable sensors for rapid on-site detection and is particularly suitable for real-time monitoring of heavy metals in seawater. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application.

[0037] Figure 1 The SEM images of the bare electrode (a), the acidified carbon nanotubes (b), and the acidified multi-walled carbon nanotube-reduced graphene oxide hybrid material (c);

[0038] Figure 2 The stripping voltammograms (a) and linear relationship diagrams (b) of different concentrations of lead ions in simulated seawater;

[0039] Figure 3 The stripping voltammograms (a) and linear relationship diagrams (b) of cadmium ions with different concentrations in simulated seawater;

[0040] Figure 4 The peak current-voltage linear relationship diagram for simulating different deposition voltages in seawater;

[0041] Figure 5 It is the peak current-voltage linear relationship diagram for different deposition times in simulated seawater;

[0042] Figure 6 This is a flow chart of the real seawater pretreatment process;

[0043] Figure 7 The linear relationship diagram of the simulated seawater lead ion concentration and its peak current (a), and the linear relationship diagram of the cadmium ion concentration and its peak current (b). DETAILED DESCRIPTION

[0044] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. The methods used in the present invention are conventional methods unless otherwise specified; the raw materials and devices used are conventional commercial products unless otherwise specified.

[0045] Example 1

[0046] This embodiment provides a method for preparing a working electrode, assembling a three-electrode system sensor, and connecting an electrochemical workstation, the steps of which include:

[0047] (1) Preparation of acidified multi-walled carbon nanotubes

[0048] Weigh 50 mg of multi-walled carbon nanotubes, add 12.5 mL of concentrated nitric acid and then 37.5 mL of concentrated sulfuric acid, ultrasonicate the prepared suspension in an ultrasonic cleaner for 6 hours, add purified water to dilute and centrifuge after the ultrasonication, and repeat the water washing-ultrasonication-centrifugation process 4 times. Put the material after centrifugation into a vacuum drying oven and dry it at a temperature of 50°C. After drying, grind it into fine powder particles with a particle size controlled at 0.1-10 μm to obtain acidified multi-walled carbon nanotubes.

[0049] (2) Preparation of 1 mg / mL acidified multi-walled carbon nanotube solution

[0050] Weigh 2 mg of the acidified multi-walled carbon nanotubes prepared in step (1) into a centrifuge tube, add 1 mL of ethanol and 1 mL of distilled water, stir and mix, and prepare a 1 mg / mL acidified multi-walled carbon nanotube solution for use.

[0051] (3) Prepare 1 mg / mL reduced graphene oxide solution

[0052] Weigh 2 mg of reduced graphene oxide into a centrifuge tube, add 1 mL of ethanol and 1 mL of distilled water, stir and mix, and prepare a 1 mg / mL reduced graphene oxide solution for use.

[0053] (4) Preparation of 250 μg / mL acidified multi-walled carbon nanotube-graphene mixed solution

[0054] Take 1 mL of the 1 mg / mL acidified multi-walled carbon nanotube solution prepared in step (2) and 1 mL of the 1 mg / mL reduced graphene oxide solution prepared in step (3) in a centrifuge tube, add 1 mL of ethanol and 1 mL of distilled water, stir and mix, and prepare a 250 μg / mL acidified multi-walled carbon nanotube-graphene mixed solution.

[0055] (5) Preparation of 0.5% Nafion solution

[0056] Take 200 μL of a 5% by volume Nafion standard solution in a centrifuge tube, add 900 μL of ethanol and 900 μL of distilled water, stir and mix, and prepare a 0.5% by volume Nafion solution for use.

[0057] (6) Preparation of modified reduced graphene oxide-acidified multi-walled carbon nanotube-Nafion working electrode

[0058] Take 3 μL of the 250 μg / mL acidified multi-walled carbon nanotube-graphene mixed solution prepared in step (4) and drop it on the bare electrode surface of the screen-printed electrode, and dry it for 30 minutes; then take 3 μL of the 0.5% Nafion solution prepared in step (5) and drop it on the surface of the screen-printed electrode, and dry it for 30 minutes to obtain a modified reduced graphene oxide-acidified multi-walled carbon nanotube-Nafion working electrode.

[0059] (7) Assemble the three-electrode system sensor and connect it to the electrochemical workstation

[0060] The screen-printed electrode is a three-electrode system, which includes a counter electrode, a reference electrode, and a working electrode obtained in step (5). The counter electrode is a carbon-based electrode, and the reference electrode is an Ag / AgCl electrode. The counter electrode, the reference electrode, and the working electrode are connected to the electrochemical workstation through sensors, respectively.

[0061] Scanning electron microscope (SEM) tests were performed on the bare electrode in Example 1 (i.e., the electrode without screen-printed electrode modification material, specifically the bare electrode in the above step (6)), the acidified carbon nanotubes (the bare electrode was directly modified with acidified carbon nanotubes, specifically the acidified multi-walled carbon nanotube solution prepared in the above step (2) was directly drop-coated on the surface of the bare electrode and dried), and the acidified multi-walled carbon nanotube-reduced graphene oxide mixed material (the bare electrode was directly modified with acidified multi-walled carbon nanotube-graphene, specifically the acidified multi-walled carbon nanotube-graphene mixed solution in the above step (6) was directly drop-coated on the surface of the bare electrode and dried), and SEM images (a), (b), and (c) were obtained, respectively. Figure 1 As shown. Among them:

[0062] from Figure 1 (a) It can be seen that the unmodified electrode surface is relatively flat and uniform with low surface roughness. Figure 1 (b) The modified electrode surface shows an obvious nanotube network structure with higher surface roughness and complex surface morphology. Figure 1 (c) It can be found that the strip-shaped acidified carbon nanotubes grow on the sheet-shaped reduced graphene oxide and are evenly distributed. The acidified multi-walled carbon nanotube-reduced graphene oxide is a porous material with an obvious network structure, higher surface roughness and complex morphology. This surface morphology can increase the effective surface area of ​​the electrode. When it is dripped on the electrode, it can provide more active sites, making it easier for the metal to be enriched on the electrode, which is beneficial to the subsequent dissolution detection.

[0063] Example 2

[0064] This embodiment provides a method for configuring a simulated seawater solution and determining a preferred deposition voltage / deposition time, the steps of which include:

[0065] (1) Prepare a simulated seawater solution containing bismuth ions

[0066] Add 12.36 g of sodium chloride, 0.335 g of potassium chloride, 0.68 g of calcium chloride, 2.33 g of magnesium chloride, 3.145 g of magnesium sulfate, and 0.09 g of sodium bicarbonate into a beaker, then add 500 μL of 1000 μg / mL bismuth ion standard solution, and dilute to 500 mL with distilled water to complete the preparation of the simulated seawater solution containing bismuth ions.

[0067] (2) Determine the optimal deposition voltage and deposition time

[0068] Add 50 μL of 10 μg / mL lead ion standard solution and 10 μg / mL cadmium ion standard solution to a small beaker, and then add the simulated seawater solution prepared in step (1) to dilute to 10 mL. Set the enrichment voltages to -0.6 V, -0.9 V, -1.2 V, -1.5 V, and -1.8 V respectively, use the three-electrode system sensor of Example 1 above, and use an electrochemical workstation to perform current-voltage electrochemical tests at different deposition voltages. The test results are as follows: Figure 4 As shown, the peak current increases from -0.6V to -1.2V when the deposition voltage is increased. After reaching -1.2V, the peak current decreases. It can be seen that the peak current is the highest when the deposition voltage is -1.2V.

[0069] Take another small beaker, add 50 μL of 10 μg / mL lead ion standard solution and 10 μg / mL cadmium ion standard solution respectively, and then add the prepared simulated seawater solution to dilute to 10 mL. Set the enrichment time to 60s, 100s, 140s, 180s, 220s, and 260s respectively, use the three-electrode system sensor of Example 1 above, and use an electrochemical workstation to perform current-voltage electrochemical tests at different deposition times. The test results are as follows: Figure 5 As shown, the deposition time is from 60s to 220s. As the deposition time increases, the peak current increases successively. After exceeding 220s, the peak current decreases. It can be seen that the peak current is the highest when the deposition time is 220s.

[0070] Therefore, the deposition voltage is preferably -1.2 V, and the deposition time is preferably 220 s.

[0071] Example 3

[0072] This embodiment provides a method for rapid on-site detection of heavy metal lead (Pb) ions in seawater by an in-situ bismuth plating method, the steps of which include:

[0073] (1) Obtaining the standard working curve

[0074] 20 μL, 40 μL, 60 μL, and 80 μL of 10 μg / mL lead ion standard solution were added to 4 small beakers, respectively, and then the simulated seawater solution prepared in Example 2 was added to dilute to 10 mL. After calculation, the lead ion concentrations in the solutions in the 4 small beakers were 20 μg / L, 40 μg / L, 60 μg / L, and 80 μg / L, respectively; set aside.

[0075] The three-electrode system sensor of Example 1 was used, and an electrochemical workstation was used to detect the change of the current of the simulated seawater added with different concentrations of lead ion standard solution as the voltage increased using square wave stripping voltammetry (SWASV). The detection results are as follows: Figure 2 (a), wherein the deposition voltage of -1.2 V measured in Example 2 is used as the enrichment potential, the deposition time of 220 s is used as the enrichment time, and the detection parameters are set as follows: amplitude of 25 mV, potential increment of 5 mV, frequency of 15 Hz, enrichment potential of -1.2 V, enrichment time of 220 s, stirring rate of 300 r / min, static time of 10 s, dissolution starting potential of -0.8 V, and termination potential of -0.4 V. A standard working curve is prepared according to the detection results, as shown in FIG. Figure 2 (b) as shown.

[0076] See also Figure 2 (a) According to the potential value of the dissolution peak, the type of heavy metal detected can be determined. The dissolution peak potential of lead ions is about -0.60V. As the concentration of heavy metal lead ions increases, the peak current of the dissolution peak also increases; please refer to Figure 2 (b) The lead ion concentration and its peak current showed a good linear correlation in the range of 20 to 80 μg / L, and the linear equation of peak current (I) and concentration (C) was obtained as follows: I = 0.08678C-0.7571(R 2 =0.98795).

[0077] (2) Detection of lead ion concentration in real seawater

[0078] See also Figure 6 , take seawater from a bathing beach, use a filter membrane with a pore size of 1.0 μm to filter, and obtain the treated seawater from a bathing beach. Add 750 μL of 1000 μg / mL bismuth ion solution to a beaker, then add 3.4546 g of NaAc, 1.016 mL of HAc, and the treated seawater from a bathing beach to dilute to 500 mL to prepare a seawater mixture.

[0079] Take 5 small beakers, add 20 μL of 10 μg / mL lead ion standard solution to each small beaker, and then pour the prepared seawater mixture into each small beaker to dilute to 10 mL, and prepare the water sample to be tested for use. Among them, the concentration of NaAc-HAc in the water sample to be tested is 0.1 mol / L, and the pH is 4.5.

[0080] The three-electrode system sensor of the above-mentioned embodiment 1 is used, an electrochemical workstation is used, and square wave stripping voltammetry (SWASV) is used to detect the peak current of the water samples to be tested in the above-mentioned five small beakers. The detection parameters are set the same as step (1) and are not repeated here.

[0081] The test results are as follows: the peak currents I of the water samples to be tested in the above five small beakers are 1.083 μA, 1.109 μA, 1.048 μA, 1.100 μA, and 1.057 μA, respectively. Substituting the peak current (I) and concentration (C) into the linear equation I=0.08678C-0.7571 in step (1), the lead ion concentrations C are calculated to be 21.2 μg / L, 21.5 μg / L, 20.8 μg / L, 21.4 μg / L, and 20.9 μg / L, respectively. The lead ion concentration C in the water samples to be tested (average value) is 21.16 μg / L.

[0082] The water sample to be tested contains a known mass of lead ion standard solution added additionally. After calculation, the concentration of the additional lead ions contained in the water sample to be tested is 20 μg / L. Therefore, the concentration of lead ions in the seawater of a certain bathing beach (i.e., real seawater) in the water sample to be tested is 1.16 μg / L.

[0083] The water sample to be tested is 10 mL. The mass of lead ions in the seawater of a certain beach contained in the water sample to be tested is 1.16×10 -2 μg.

[0084] 500mL of seawater mixture contains 750μL of bismuth ion solution and 1.016mL of Hac (the added 3.4546g of NaAc is negligible for the volume), so the volume of seawater in a certain bathing beach after the treatment is 498.234mL. Ignoring the effect of filtration treatment on the real seawater volume, the volume of seawater in a certain bathing beach tested is 498.234mL.

[0085] According to calculations, the concentration of lead ions in the seawater at a certain bathing beach is 0.023 μg / L.

[0086] In this embodiment, sampling and testing were carried out on site at a certain bathing beach, and the time required from sampling to obtaining the lead ion concentration value was about 20 minutes.

[0087] Example 4

[0088] This embodiment provides a method for rapid on-site detection of heavy metal cadmium (Cd) ions in seawater by an in-situ bismuth plating method, the steps of which include:

[0089] (1) Obtaining the standard working curve

[0090] Add 20 μL, 40 μL, 60 μL and 80 μL of 10 μg / mL cadmium ion standard solution to 4 small beakers, respectively, and then add the simulated seawater solution prepared in Example 2 to dilute to 10 mL. After calculation, the cadmium ion concentrations in the solutions in the 4 small beakers are 20 μg / L, 40 μg / L, 60 μg / L and 80 μg / L, respectively; set aside.

[0091] The three-electrode system sensor of Example 1 was used, and an electrochemical workstation was used to detect the change of the current of the simulated seawater added with different concentrations of cadmium ion standard solution as the voltage increased. The detection results are as follows: Figure 3 (a), wherein the deposition voltage of -1.2 V measured in Example 2 is used as the enrichment potential, the deposition time of 220 s is used as the enrichment time, and the detection parameters are set as follows: amplitude of 25 mV, potential increment of 5 mV, frequency of 15 Hz, enrichment potential of -1.2 V, enrichment time of 220 s, stirring rate of 300 r / min, static time of 10 s, dissolution starting potential of -1.1 V, and termination potential of -0.75 V. A standard working curve is prepared according to the detection results, as shown in FIG. Figure 3 (b) as shown.

[0092] See also Figure 3 (a) According to the potential value of the dissolution peak, the type of heavy metal detected can be determined; the dissolution peak potential of cadmium ions is about -0.85V. Figure 3 (b) With the increase of heavy metal cadmium ion concentration, the peak current of the dissolution peak also increases. The cadmium ion concentration of 20-80 μg / L and its peak current show a good linear correlation. The linear equation of peak current (I) and concentration (C) can be obtained: I = 0.16903C-2.38169 (R 2 =0.99728).

[0093] (2) Detection of cadmium ion concentration in real seawater

[0094] See also Figure 6 , take seawater from a bathing beach, use a filter membrane with a pore size of 1.0 μm to filter, and obtain the treated seawater from a bathing beach. Add 750 μL of 1000 μg / mL bismuth ion solution to a beaker, then add 3.4546 g of NaAc, 1.016 mL of HAc, and the treated seawater from a bathing beach to dilute to 500 mL to prepare a seawater mixture.

[0095] Take 5 small beakers, add 20 μL of 10 μg / mL cadmium ion standard solution to each small beaker, and then pour the prepared seawater mixture into each small beaker to dilute to 10 mL, and prepare the water sample to be tested for use. Among them, the concentration of NaAc-HAc in the water sample to be tested is 0.1 mol / L, and the pH is 4.5.

[0096] The three-electrode system sensor of the above-mentioned embodiment 1 is used, an electrochemical workstation is used, and square wave stripping voltammetry (SWASV) is used to detect the peak current of the water samples to be tested in the above-mentioned five small beakers. The detection parameters are set the same as step (1) and are not repeated here.

[0097] The test results are as follows: the peak currents I of the water samples to be tested in the above five small beakers are 1.134 μA, 1.151 μA, 1.236 μA, 1.100 μA and 1.219 μA respectively. Substituting the peak current (I) and concentration (C) into the linear equation of step (1): I = 0.16903C-2.38169, the cadmium ion concentrations C are calculated to be 20.8 μg / L, 20.9 μg / L, 21.4 μg / L, 20.6 μg / L and 21.3 μg / L respectively. The cadmium ion concentration C in the water samples to be tested (average value) is 21.00 μg / L.

[0098] The water sample to be tested contains a known mass of cadmium ion standard solution added additionally. After calculation, the concentration of the additional cadmium ions contained in the water sample to be tested is 20 μg / L. Therefore, the concentration of cadmium ions in the seawater of a certain bathing beach (i.e., real seawater) in the water sample to be tested is 1.00 μg / L.

[0099] The water sample to be tested is 10 mL. The mass of cadmium ions in the seawater of a certain beach contained in the water sample to be tested is 1.00×10 -2 μg.

[0100] 500mL of seawater mixture contains 750μL of bismuth ion solution and 1.016mL of HAc (the added 3.4546g of NaAc is negligible for the volume), so the volume of seawater in a certain bathing beach after the treatment is 498.234mL. Ignoring the effect of filtration treatment on the real seawater volume, the volume of seawater in a certain bathing beach tested is 498.234mL.

[0101] According to calculations, the concentration of cadmium ions in the seawater at a certain bathing beach is 0.020 μg / L.

[0102] In this embodiment, sampling and testing were carried out at a certain bathing beach, and the time required from sampling to obtaining the cadmium ion concentration value was about 20 minutes.

[0103] Example 5

[0104] This embodiment provides a method for rapid on-site detection of heavy metal lead and cadmium ions in seawater by an in-situ bismuth plating method, the steps of which include:

[0105] (1) Obtaining the standard working curve

[0106] In 4 small beakers, 10 μg / mL of lead ion standard solution and 10 μg / mL of cadmium ion standard solution were added to a total of 20 μL, 40 μL, 60 μL, and 80 μL (the volumes of lead ion standard solution and cadmium ion standard solution added to each small beaker were the same), and then the simulated seawater solution prepared in Example 2 was added to dilute to 10 mL. After calculation, the lead ion concentrations in the solutions in the 4 small beakers were 20 μg / L, 40 μg / L, 60 μg / L, and 80 μg / L, and the cadmium ion concentrations were 20 μg / L, 40 μg / L, 60 μg / L, and 80 μg / L, respectively; set aside.

[0107] The three-electrode system sensor of Example 1 was used, and an electrochemical workstation was used to detect the change in current as the voltage increased when the lead ion standard solution and the cadmium ion standard solution with different concentrations were added, respectively, using square wave stripping voltammetry (SWASV), wherein the deposition voltage of -1.2V measured in Example 2 was used as the enrichment potential, and the deposition time of 220s was used as the enrichment time. The detection parameters were set as follows: amplitude of 25mV, potential increment of 5mV, frequency of 15Hz, enrichment potential of -1.2V, enrichment time of 220s, stirring rate of 300r / min, static time of 10s, dissolution starting potential of -1.2V, and termination potential of -0.4V. A standard working curve was prepared according to the detection results, as shown in FIG. Figure 7 (a) and Figure 7 (b) as shown.

[0108] See also Figure 7 (a) As the lead ion concentration increases, the peak current of the dissolution peak increases continuously. The lead ion concentration of 20-80 μg / L and its peak current show a good linear correlation. The linear equation of peak current (I) and concentration (C) is: I = 0.08474C-0.97479 (R 2 =0.98795).

[0109] See also Figure 7 (b) With the increase of cadmium ion concentration, the peak current of the dissolution peak increases continuously. The cadmium ion concentration of 20-80 μg / L and its peak current show a good linear correlation. The linear equation of peak current (I) and concentration (C) can be obtained: I = 0.19412C-2.49572 (R 2 =0.99392).

[0110] (2) Detection of lead and cadmium ion concentrations in real seawater

[0111] See also Figure 6 , take seawater from a bathing beach, use a filter membrane with a pore size of 0.22μm to filter, and obtain the treated seawater from a bathing beach. Add 750μL of 1000μg / mL bismuth ion solution to a beaker, then add 3.4546g of NaAc, 1.016mL of HAc, and the treated seawater from a bathing beach to dilute to 500mL to prepare a seawater mixture.

[0112] Take 5 small beakers, add 20 μL of 10 μg / mL lead ion standard solution and 10 μg / mL cadmium ion standard solution to each small beaker, and then pour the prepared seawater mixture into each small beaker to dilute to 10 mL, and prepare the water sample to be tested for later use. Among them, the concentration of NaAc-HAc in the water sample to be tested is 0.1 mol / L, and the pH is 4.5.

[0113] The three-electrode system sensor of the above-mentioned embodiment 1 is used, an electrochemical workstation is used, and square wave stripping voltammetry (SWASV) is used to detect the peak current of the water samples to be tested in the above-mentioned five small beakers. The detection parameters are set the same as step (1) and are not repeated here.

[0114] The test results are:

[0115] In the water samples to be tested in the above five small beakers, the peak current I of lead ions were 0.830μA, 0.839μA, 0.788μA, 0.881μA, and 0.754μA, respectively, and the peak current I of cadmium ions were 1.561μA, 1.503μA, 1.658μA, 1.580μA, and 1.464μA, respectively.

[0116] Substituting the peak current I values ​​of the above lead ions into the linear equation of the peak current (I) and concentration (C) of the lead ions in step (1) I=0.08474C-0.97479, the ion concentrations of the lead ions were calculated to be 21.3 μg / L, 21.4 μg / L, 20.8 μg / L, 21.9 μg / L, and 20.4 μg / L, respectively. The lead ion concentration C (average value) in the water sample to be tested is 21.16 μg / L.

[0117] Substituting the peak current I value of the above cadmium ion into the linear equation of the peak current (I) and concentration (C) of the cadmium ion in step (1) I=0.19412C-2.49572, the cadmium ion concentration C is calculated to be 20.9μg / L, 20.6μg / L, 21.4μg / L, 21.0μg / L, and 20.4μg / L, respectively. The cadmium ion concentration C in the water sample to be tested (average value) is 20.86μg / L.

[0118] The water sample to be tested contains additionally added lead ion standard solution and cadmium ion standard solution of known mass. After calculation, the concentrations of the additionally added lead ion standard solution and cadmium ion in the water sample to be tested are both 20 μg / L. Therefore, the concentration of lead ions in the water sample to be tested (i.e., real seawater) at a certain bathing beach is 1.16 μg / L, and the concentration of cadmium ions in the water sample to be tested is 0.86 μg / L.

[0119] The water sample to be tested is 10 mL. The mass of lead ions in the seawater of a certain beach contained in the water sample to be tested is 1.16×10 -2 μg, the mass of cadmium ion is 0.86×10 -2 μg.

[0120] 500mL of seawater mixture contains 750μL of bismuth ion solution and 1.016mL of HAc (3.4546g of NaAc added is negligible for the volume), so the volume of the seawater in a certain bathing beach after the treatment is 498.234mL. Ignoring the effect of the filtration treatment on the real seawater volume, the volume of the tested bathing beach is 498.234mL.

[0121] According to calculations, the concentration of lead ions in the seawater at a certain bathing beach was 0.023 μg / L, and the concentration of cadmium ions was 0.017 μg / L.

[0122] In this embodiment, sampling and testing were carried out on site at a certain bathing beach, and the time required from sampling to obtaining the lead ion and cadmium ion concentration values ​​was about 20 minutes.

[0123] Comparative Example 1

[0124] Comparative Example 1 provides an on-site rapid detection method for heavy metal lead ions in seawater using an in-situ bismuth plating method.

[0125] Take seawater from a bathing beach that is the same as that in Example 3. The only difference from Example 3 is that the seawater is not filtered through a filter membrane when configuring the water sample to be tested. The other contents are the same and will not be repeated.

[0126] The test results are as follows: the peak currents I of the water samples to be tested in the five small beakers are 1.274 μA, 1.048 μA, 0.987 μA, 1.274 μA, and 0.935 μA, respectively. Substituting the peak current (I) and concentration (C) linear equation I=0.08678C-0.7571 in step (1) of Example 3, the lead ion concentrations C are calculated to be 23.4 μg / L, 20.8 μg / L, 20.1 μg / L, 23.4 μg / L, and 19.5 μg / L, respectively. The lead ion concentration C in the water samples to be tested (average value) is 21.44 μg / L.

[0127] According to the calculation method of Example 3, the concentration of lead ions in the seawater of the bathing beach in Comparative Example 1 without suction filtration treatment is 0.029 μg / L.

[0128] The lead ion concentration in the bathing beach seawater treated by filtration with a filter membrane in Example 3 was 0.023 μg / L.

[0129] It can be seen that impurities such as suspended matter in seawater have a greater impact on the peak current. The present invention removes impurities such as suspended matter in seawater by performing membrane filtration on seawater, thereby making the detection result more accurate.

[0130] Comparative Example 2

[0131] Comparative Example 2 provides an on-site rapid detection method for heavy metal cadmium ions in seawater by an in-situ bismuth plating method. The source of the real seawater to be detected is the same as that in Example 4. The difference between the detection process and Example 4 is that the seawater is not filtered through a filter membrane. Other details are the same and will not be repeated.

[0132] The test results are as follows: the peak currents I of the water samples to be tested in the 5 small beakers are 1.320 μA, 3.162 μA, 0.965 μA, 2.503 μA, and 1.219 μA, respectively. Substituting the peak current (I) and concentration (C) linear equation I=0.16903C-2.38169 in step (1) of Example 4, the cadmium ion concentrations C are calculated to be 21.9 μg / L, 32.8 μg / L, 19.8 μg / L, 28.9 μg / L, and 21.3 μg / L, respectively. The cadmium ion concentration C in the water samples to be tested (average value) is 24.94 μg / L.

[0133] According to the calculation method of Example 4, the concentration of cadmium ions in the seawater of the bathing beach in Comparative Example 2 without suction filtration treatment is 0.099 μg / L.

[0134] The concentration of cadmium ions in the seawater of the bathing beach treated by filtration with a filter membrane in Example 4 was 0.020 μg / L.

[0135] It can be seen that impurities such as suspended matter in seawater have a greater impact on the peak current. The present invention removes impurities such as suspended matter in seawater by performing membrane filtration on seawater, thereby making the detection result more accurate.

[0136] It should be noted that:

[0137] (1) In the present invention, in the preparation of acidified multi-walled carbon nanotubes, the preparation of acidified multi-walled carbon nanotube solutions, the preparation of reduced graphene oxide solutions, the preparation of acidified multi-walled carbon nanotube-graphene mixed solutions, and the preparation of Nafion solutions, the proportions of the relevant raw materials can be appropriately adjusted by those skilled in the art according to actual conditions.

[0138] (2) After obtaining the concentration of lead ions and / or cadmium ions in the water sample to be tested, the present invention obtains the mass of lead ions or cadmium ions in the seawater to be tested and the volume of the seawater to be tested by conventional calculation, thereby finally obtaining the concentration of lead ions or cadmium ions in the seawater to be tested.

[0139] (3) The present invention can use existing simulated seawater solution or specially configured simulated seawater solution. + , Cl - Mg 2+ , Ca 2+ , K + The simulated seawater prepared by the present invention and its concentration ratio are close to real seawater. At the same time, compared with the artificial seawater of ASTM D1141-98 standard, the main ion concentration of the simulated seawater is different from that of real seawater and the concentration ratio of the artificial seawater in ASTM D1141-98 standard within a reasonable range (±5%), and the macroscopic physical and chemical properties such as salinity, density, and conductivity are close to those of real seawater.

[0140] (4) Electrochemical detection of lead (Pb) in seawater 2+ ) and cadmium (Cd 2+ ) ions, the water sample to be tested is weakly acidic (usually pH range is 4.5-6.5), which can prevent Pb 2+ and Cd 2+ With OH - The combination generates hydroxide precipitation, thereby maintaining the stability of metal ions in the solution. In addition, weak acidic conditions can enhance the electrochemical activity of target ions and improve detection sensitivity, while avoiding strong acid corrosion of electrode materials, ensuring the accuracy and stability of the experiment.

[0141] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for rapid on-site detection of heavy metal lead ions and / or cadmium in seawater by in-situ bismuth plating, characterized in that: The steps include: Step S1. Assembling a three-electrode system sensor, wherein the working electrode is a modified reduced graphene oxide-acidified multi-walled carbon nanotube-Nafion electrode, the counter electrode is a carbon-based electrode, and the reference electrode is an Ag / AgCl electrode, and the working electrode, the counter electrode, and the reference electrode are respectively connected to an electrochemical workstation through a sensor; Step S2. preparing a simulated seawater solution containing bismuth ions; Step S3. Take the simulated seawater solution prepared in step S2, and add a certain amount of lead ion standard solution and cadmium ion standard solution into the simulated seawater solution respectively; Using the three-electrode system sensor of step S1, using an electrochemical workstation, and using square wave stripping voltammetry to perform current-voltage electrochemical tests at different deposition voltages and deposition times, respectively, to obtain the deposition voltage and deposition time at the maximum value of the peak current; Step S4. Take the simulated seawater solution prepared in step S2, divide the simulated seawater solution into multiple portions, and add different concentrations of lead ion standard solution and / or cadmium ion standard solution into each portion of the simulated seawater solution; adopt the three-electrode system sensor of step S1, use an electrochemical workstation, and use square wave stripping voltammetry to detect the concentration of lead ions and / or cadmium ions, wherein the enrichment potential and enrichment time in the set detection parameters are the deposition voltage and deposition time obtained in step S2 respectively; The relationship curves between the peak current and the lead ion or cadmium ion concentration are respectively drawn to obtain the standard working curve diagram; Step S5. Take a certain amount of seawater to be tested and perform filtration pretreatment; add a certain amount of lead ion and / or cadmium ion standard solution, bismuth ion solution, and detection reagent to the pretreated seawater to be tested to prepare a weakly acidic water sample to be tested; wherein the detection reagent includes NaAc and HAc; electrochemically detect the concentration of lead ions or cadmium ions by square wave anodic stripping voltammetry under the same experimental conditions as in step S4; compare the standard working curve obtained in step S4 to obtain the concentration of lead ions and / or cadmium ions in the water sample to be tested; and finally calculate the content of lead ions and / or cadmium ions in the seawater to be tested.

2. The on-site rapid detection method for heavy metal lead ions and / or cadmium in seawater by an in-situ bismuth plating method according to claim 1, characterized in that: In the step S1, the preparation method of the working electrode comprises: dripping an acidified multi-walled carbon nanotube-graphene mixed solution on the surface of a bare electrode of a screen-printed electrode, and drying, to prepare a modified reduced graphene oxide-acidified multi-walled carbon nanotube electrode; and then dripping a Nafion solution on the surface of the modified reduced graphene oxide-acidified multi-walled carbon nanotube electrode, and drying, to obtain a modified reduced graphene oxide-acidified multi-walled carbon nanotube-Nafion electrode, i.e., the working electrode.

3. The on-site rapid detection method for heavy metal lead ions and / or cadmium in seawater by an in-situ bismuth plating method according to claim 2, characterized in that: The method for preparing the acidified multi-walled carbon nanotube-graphene mixed solution comprises: Preparation of acidified multi-walled carbon nanotubes: multi-walled carbon nanotubes, concentrated nitric acid and concentrated sulfuric acid are mixed to form a suspension, subjected to ultrasonic treatment, diluted with water and centrifuged to obtain a centrifuged solid, the centrifuged solid is fully washed with water, ultrasonicated and centrifuged, and the finally obtained centrifuged solid is dried and ground into fine powder particles with a particle size controlled at 0.1-10 μm to obtain acidified multi-walled carbon nanotubes; Preparing an acidified multi-walled carbon nanotube solution: stirring and mixing the prepared acidified multi-walled carbon nanotubes, ethanol and water to prepare the acidified multi-walled carbon nanotube solution for later use; Preparing a reduced graphene oxide solution: stirring and mixing the reduced graphene oxide, ethanol and water to prepare the reduced graphene oxide solution for later use; The acidified multi-walled carbon nanotube-graphene mixed solution is prepared by stirring and mixing the prepared acidified multi-walled carbon nanotube solution, the prepared reduced graphene oxide solution, ethanol and water to prepare the acidified multi-walled carbon nanotube-graphene mixed solution.

4. The on-site rapid detection method for heavy metal lead ions and / or cadmium in seawater by an in-situ bismuth plating method according to claim 2, characterized in that: The method for preparing the Nafion solution includes: stirring and mixing the Nafion standard solution, ethanol and distilled water to prepare the Nafion solution.

5. The on-site rapid detection method for heavy metal lead ions and / or cadmium in seawater by an in-situ bismuth plating method according to claim 1, characterized in that: In the step S2, every 500 mL of the simulated seawater solution contains 12.36 g of sodium chloride, 0.335 g of potassium chloride, 0.68 g of calcium chloride, 2.33 g of magnesium chloride, 3.145 g of magnesium sulfate, and 0.09 g of sodium bicarbonate.

6. The on-site rapid detection method for heavy metal lead ions and / or cadmium in seawater by an in-situ bismuth plating method according to claim 5, characterized in that: In the step S2, 500 μL of 1000 μg / mL bismuth ion solution was added to every 500 mL of the simulated seawater solution.

7. The on-site rapid detection method for heavy metal lead ions and / or cadmium in seawater by an in-situ bismuth plating method according to claim 1, characterized in that: In the step S3, 50 μL of a 10 μg / mL lead ion standard solution and a 10 μg / mL cadmium ion standard solution are added to the container, and then the prepared simulated seawater solution is added to dilute to 10 mL; an electrochemical test is performed to obtain a deposition voltage of -1.2 V and a deposition time of 220 s at the maximum value of the peak current.

8. The on-site rapid detection method for heavy metal lead ions and / or cadmium in seawater by an in-situ bismuth plating method according to claim 1, characterized in that: In step S4, when heavy metal ions and lead ions are detected alone, the detection parameters are set as follows: amplitude of 25 mV, potential increment of 5 mV, frequency of 15 Hz, enrichment potential of -1.2 V, enrichment time of 220 s, stirring rate of 300 r / min, static time of 10 s, dissolution starting potential of -0.8 V, and termination potential of -0.4 V; When the heavy metal ion cadmium ion is detected alone, the detection parameters are set as follows: amplitude of 25mV, potential increment of 5mV, frequency of 15Hz, enrichment potential of -1.2V, enrichment time of 220s, stirring rate of 300r / min, static time of 10s, dissolution starting potential of -1.1V, and termination potential of -0.75V; When detecting heavy metal ions lead ions and cadmium ions, the detection parameters were set as follows: amplitude of 25 mV, potential increment of 5 mV, frequency of 15 Hz, enrichment potential of -1.2 V, enrichment time of 220 s, stirring rate of 300 r / min, static time of 10 s, dissolution starting potential of -1.2 V, and ending potential of -0.4 V.

9. The on-site rapid detection method for heavy metal lead ions and / or cadmium in seawater by an in-situ bismuth plating method according to claim 1, characterized in that: In the step S5, the seawater to be tested is pre-treated by filtration, wherein the pore size of the filter membrane is ≤1.0 μm.

10. The on-site rapid detection method for heavy metal lead ions and / or cadmium in seawater by an in-situ bismuth plating method according to claim 1, characterized in that: In the step S5, the configuration method of the water sample to be tested includes: Add 750 μL of 1000 μg / mL bismuth ion solution into the container, then add 3.4546 g of NaAc, 1.016 mL of HAc, and the pretreated seawater to be tested to dilute to 500 mL to prepare a seawater mixture for standby use; Take another container, add 20 μL of 10 μg / mL lead ion standard solution and / or 20 μL of 10 μg / mL cadmium ion standard solution into the container respectively, then add the seawater mixture to dilute to 10 mL, and prepare the water sample to be tested with a pH of 4.5.

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