CN113820370A

CN113820370A - Method for detecting heavy metal As (III) in natural water body

Info

Publication number: CN113820370A
Application number: CN202111166014.7A
Authority: CN
Inventors: 黄行九; 蔡鑫; 林楚红
Original assignee: Hefei Institutes of Physical Science of CAS
Current assignee: Hefei Institutes of Physical Science of CAS
Priority date: 2021-09-30
Filing date: 2021-09-30
Publication date: 2021-12-21
Anticipated expiration: 2041-09-30
Also published as: CN113820370B

Abstract

The invention discloses a method for detecting heavy metal As (III) in natural water, which comprises the steps of pretreating the obtained natural water, adding detection reagents (NaAc, HAc and FeCl)₃) Pre-polishing a glassy carbon electrode, building a three-electrode system, detecting an electrochemical signal by using a square wave anodic stripping voltammetry, drawing a linear calibration curve corresponding to peak current and As (III) concentration, detecting the recovery rate of As (III) in a natural water body by using a standard addition method, and meeting the underground water quality standard GB/T14848 and 2017 specified by the national standard of the people's republic of China: and IV type water quality standard. The method uses a simple unmodified glassy carbon electrode, and only adds a detection reagent into the filtered natural water body, so that the detection of heavy metal As (III) (GB/T14848) -2017 (IV-type standard) below 50ppb can be realized. Compared with the method for synthesizing the electrode surface modification material for detecting As (III)Simple, practical, economic and good in repeatability and stability, and is suitable for rapid detection of non-professional technical operators.

Description

Method for detecting heavy metal As (III) in natural water body

Technical Field

The invention relates to the technical field of water quality detection, in particular to a detection method of heavy metals As (III) in natural water.

Background

The pollution problem of heavy metal ions is increasingly prominent, and the pollution to animals, plants and human beings is remarkableLife health and safety constitute a great threat. The main existing form of arsenic in natural ground water and surface water is inorganic H₃AsO₃、H₃AsO₄、HAsO₄ ^2-Wherein, As (III) has low content in drinking water but high toxicity, and the national standard of the people's republic of China stipulates the quality standard GB/T14848-19 of underground water: class IV, As (III) content should not exceed 50 ppb. Therefore, a rapid, simple, efficient and convenient detection method is urgently needed for detecting the concentration of heavy metal As (III) in natural water.

Due to the harmfulness and severity of heavy metal ions, the current detection methods for heavy metal ions are as follows: chemiluminescence (LC), ultraviolet-visible spectrophotometry (UV), High Performance Liquid Chromatography (HPLC), Ion Chromatography (IC), Atomic Absorption Spectroscopy (AAS), Atomic Fluorescence (AFS), Atomic Emission Spectroscopy (AES), X fluorescence spectroscopy (XRF), inductively coupled plasma mass spectrometry (ICP-MS), Electrochemical (EC) analysis methods, and the like. The electrochemical analysis method has the advantages of simple and portable instrument, low analysis cost, simple operation, low requirement on experimental environment, high sensitivity of an optical method, low detection limit, good selectivity and suitability for online detection of trace heavy metal ions in a natural water environment, effectively avoids pollution caused by a sample collection process, and is a detection method with great potential and rapid development. Hitherto, numerous electrochemical methods such as an ion selective electrode method, a polarographic analysis method, a potentiometric analysis method, a stripping voltammetry method and the like have been applied to the detection of heavy metal ions. Among them, stripping voltammetry is an electrochemical detection means integrating electrolysis enrichment and stripping detection, has high sensitivity and strong anti-interference capability, and is a means widely regarded as an effective means for detecting heavy metal ions due to its simple equipment and low price, which has been developed rapidly in recent years.

As is well known, heavy metal electroanalysis signals are limited by the overall environment of an electrode-solution two-phase interface, and in research work of about 20 years, a great deal of work has been carried out to change the properties of the electrode surface by promoting the redox reaction of heavy metal ions at the electrode solution interface through a nano material modified on the electrode surface, so as to improve the sensitivity and reduce the detection limit. Various nano materials such as carbon-based (e.g. carbon nanotube, graphene, carbon powder), noble metals (e.g. gold, platinum), metal oxides, etc. are used as electrode modifiers. However, the modification material on the surface of the electrode is easy to fall off, has poor reproducibility and stability, is expensive in cost, cannot be applied in large-scale practice, and the like, and attracts attention of people.

When studying the action mechanism between the electrode surface modification material and the heavy metal ion, researchers often neglect the action of the solution phase species in the process. Interface species of the solution phase, such as metal ions fe (ii), fe (iii), etc., may participate in the reaction, or interfere with the reaction process in such a way as to affect the electric double layer, change the active site composition, etc., and the mechanism of action in heavy metal detection is yet to be explored. The ferric salt flocculation-precipitation method for removing arsenic is often applied to the treatment of arsenic in wastewater due to the technical advantages of simple operation, low cost and the like. Researches find that the detection of As (III) is often interfered by iron ions, and the invention designs a novel detection reagent to realize the detection of As (III) in natural water by utilizing the interference effect between iron and arsenic.

Disclosure of Invention

In view of the above, the invention provides an electrochemical detection method for heavy metal As (III) in natural water, aiming at the problems of instability, poor repeatability, complex and easily-agglomerated modified material, easy shedding, low utilization rate of active sites and the like in the existing electrochemical detection of heavy metal As (III), and promoting the practicability of the detection method in the field of natural water detection. The detection method researched by the invention has high sensitivity, and also has good repeatability and stability. The invention adopts a simple unmodified glassy carbon electrode, only adds a detection reagent, designs a novel, simple, economic, practical, good-repeatability and stable detection system by utilizing the promotion effect of solution phase ions, realizes the detection of As (III), and reaches the practical application of national standard (GB/T14848) -2017, below 50 ppb) of water quality detection of IV water.

In order to achieve the purpose, the invention provides the following technical scheme:

a method for detecting heavy metal As (III) in natural water comprises the following steps:

s1: pretreating a laboratory water sample, adding a detection reagent into the laboratory water sample, and preparing a mixed solution with the pH value of 4.5; wherein the detection reagent is NaAc, HAc and FeCl₃；

S2: polishing, cleaning and drying the glassy carbon electrode for later use;

s3: and (4) forming a three-electrode system by taking the glassy carbon electrode obtained in the step (S2) as a working electrode, a platinum wire as a counter electrode and Ag/AgCl as a reference electrode, and performing electrochemical detection by adopting a square wave anodic stripping voltammetry, wherein the method specifically comprises the following steps:

connecting a three-electrode system with an electrochemical workstation, immersing a working electrode into a mixed solution, setting an enrichment voltage of-1.1V, adding an equal amount of As (III) into the mixed solution one by one under the stirring condition, wherein the enrichment time is 180s each time, detecting an electroanalysis signal by adopting a square wave anodic stripping voltammetry, and drawing a corresponding relation curve of peak current and As (III) concentration;

s4: taking a natural water sample to be detected, pretreating the natural water sample as in the step S1, and performing As (III) electrochemical detection by adopting a square wave anodic stripping voltammetry under the same experimental conditions in the step S3; comparing the relation curve to obtain the content of As (III) in the natural water sample.

As a further scheme of the invention: in step S1, the preprocessing is: the water sample was filtered using a 220nm microfiltration membrane.

As a further scheme of the invention: in step S1, NaAc, HAc and FeCl are added to the mixed solution₃The concentrations of (A) and (B) were 0.1M, 0.1M and 10ppm in this order.

As a further scheme of the invention: in step S3, after each electrochemical detection, the working electrode is subjected to a desorption experiment and then to the next electroanalytical signal detection.

As a further scheme of the invention: the desorption experiment specifically comprises the following steps: the working electrode was kept in the mixed solution, the working voltage was set at 0.8V, the running time was 90s, and the stirring speed was 500 rpm.

As a further scheme of the invention: in step S3, the parameter setting of the square wave anodic stripping voltammetry further includes: frequency 25 Hz; amplitude 25 mV; the incremental potential was 4 mV.

As a further scheme of the invention: the diameter of the glassy carbon electrode is 3 mm.

As a further scheme of the invention: in step S3, the stirring speed of the mixed solution was 500 rpm.

Compared with the prior art, the invention has the beneficial effects that:

(1) the invention only uses a simple unmodified glassy carbon electrode as a working electrode, has the characteristics of good conductivity, high chemical stability, hard texture, wide potential application range, wide application and the like, solves the problems of complexity, easy agglomeration, easy shedding, low utilization rate of active sites and the like of the traditional modified electrode, and has simple detection method, good repeatability and stability. The method is suitable for rapid detection of non-professional technical operators, can be used for rapid quantitative detection of heavy metals As (III) in natural water, and provides a new method for rapid quantitative detection and practical application of heavy metals As (III) in natural water.

(2) The method can be suitable for detection of natural water and experimental water samples, and is simple to operate, easy to control conditions, low in price, good and stable in repeatability and suitable for batch production.

(3) As an actual detection mode, the iron source is environment-friendly and pollution-free, and the detected reagent does not need to be recovered and can be directly discharged after detection; for natural water with As (III) content in the range of 20ppb to 200ppb, the interference of Cu (II) to the detection result is not obvious, and the method has good sensitivity and recovery rate.

(4) The experimental conditions optimized in the invention are that the pH is 4.5, the enrichment potential is-1.1V and the FeCl content is 10ppm₃In a 0.1MHAc-NaAc supporting electrolyte solution, the square wave anode dissolution signal is evaluated; the calibration curve, the sensitivity, the standard recovery rate and the reproducibility of the electrode are obtained by optimizing experimental parameters, and technical reference is provided for the detection method for heavy metal ions As (III) in natural water.

Drawings

FIG. 1 shows the square wave anodic stripping voltammetry response signal under different experimental conditions; wherein, fig. 1a is a situation of a square wave anode stripping voltammetry response signal when the pH value is changed alone under optimized experimental conditions; FIG. 1b is a graph showing the square wave anodic stripping voltammetry response signal when the enrichment time is varied alone under optimized experimental conditions; FIG. 1c is a graph showing the response signal of square wave anodic stripping voltammetry when the enrichment potential is changed alone under optimized experimental conditions, and the inset shows the comparison of the response signal of the stripping potential when the enrichment potential is at-1.1V and-1.2V; FIG. 1d is a square wave anodic stripping voltammetry response signal of whether the supporting electrolyte was replenished in the presence of 200ppb As (III) under optimized experimental conditions; the inset corresponds to the response signal in the presence of 20ppb As (III);

FIG. 2 is a comparison of the effect of stripping voltammetry peaks of Cu (II) on As (III) under optimized experimental conditions, wherein FIG. 2a is a response signal of square wave anodic stripping voltammetry detection on As (III) in deionized water to be tested in a laboratory; FIG. 2b is a graph of the response signal for 10ppb As (III) in deionized water in the presence of 1-10ppb Cu (II), with the inset showing the change in the response signal for As (III) As the Cu (II) concentration increases.

FIG. 3 is a graph showing response signals of mixed solution 1 and mixed solution 2 in examples when different concentrations of As (III) are added; wherein, fig. 3a is As (III) of the detection mixed solution 2, and fig. 3b is As (III) in the mixed solution 1; the inset of fig. 3a and 3b are both linear calibration curves of the respective peak currents versus as (iii) concentration.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the following specific embodiments and accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

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. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

The specific information of the raw materials used in the examples is as follows:

anhydrous ferric chloride, [ FeCl ]₃，>99％]From the Aladdin industries, Inc. (Shanghai, China). Other reagents were purchased from chinese medicinal chemicals limited. All chemicals involved were of analytical grade and were used without further treatment or purification.

All aqueous solutions used a resistivity of 18.2 M.OMEGA.cm^-1The deionized water of (4). A0.1M HAc-NaAc buffer was prepared by mixing a solution of 0.1M HAc and 0.1M NaAc. All solutions to be used were measured for their concentration by inductively coupled plasma atomic emission spectroscopy (ICP-MS), and all the solutions prepared were placed in a low temperature refrigerator to prevent changes in the form and valence stability of the metal ions.

The natural water sample is taken from a reservoir paved on board of Hefei city, Anhui province, China.

The electrochemical experiments were all performed on a CHI 760E electrochemical workstation (shanghai chenhua instruments ltd, china).

In order to avoid the interference of external factors and the reproducibility of experimental results, all electrochemical experiments use the same glassy carbon electrode, and each experiment is repeated three times and is carried out under the condition of constant-temperature water bath at 25 ℃.

It is understood that the above raw material reagents are only examples of some specific embodiments of the present invention, so as to make the technical scheme of the present invention more clear, and do not represent that the present invention can only adopt the above reagents, particularly, the scope of the claims is subject to.

In the examples, the following steps are used for detecting the content of As (III):

s1: filtering deionized water by using a 220nm microporous filter membrane, adding 2.945mL of glacial acetic acid into 500mL of filtered deionized water to prepare 0.1M HAc solution; 1000mL of the filtered deionized water was added with 8.203g of NaAc to prepare a 0.1M NaAc solution, and the HAc solution and the NaAc solution were mixed in an appropriate ratio to prepare a 0.1M HAc-NaAc buffer solution having a pH of 4.5. 10ml of this buffer solution was taken and 260. mu.L of 384.5ppm FeCl was added₃Prepared into 10ppm FeCl₃，pH＝4.5，0.1M HAc-NaAc mixed solution 1.

S2: removing pollutants on the surface of the glassy carbon electrode by using wet absorbent cotton, and sequentially taking polishing powder alpha-Al with the grain diameters of 1.0 mu m, 0.3 mu m and 0.05 mu m₂O₃And (3) dropwise adding a small amount of deionized water on the chamois, uniformly mixing the mixture with polishing powder, polishing the mixture in a 8-shaped manner in a manner of ensuring that the glassy carbon electrode is always kept vertical until the surface of the glassy carbon electrode is smooth, and washing the glassy carbon electrode by using the deionized water.

The method comprises the following steps of (1) measuring the state of a glassy carbon electrode in a 5mM potassium ferricyanide solution and a 0.1M potassium chloride mixed solution 1 by using an electrochemical workstation and adopting a cyclic voltammetry scanning mode, wherein when the difference of oxidation-reduction peak potentials is less than or equal to 85mV, the surface of the glassy carbon electrode is completely treated, and the surface reversibility of the electrode is good; finally, placing the glassy carbon electrodes in HNO in sequence₃Respectively performing ultrasonic treatment in ethanol and deionized water for 0.5-1min, and drying with nitrogen flow for later use.

S3: nitrogen gas was continuously introduced into the mixed solution 1 for 15 minutes to remove dissolved oxygen. And performing electrochemical detection on As (III) in the mixed solution 1 by square wave anodic stripping voltammetry. Immersing a simple unmodified glassy carbon electrode into the mixed solution 1, setting the enrichment potential of a working electrode to be-1.1V (relative to an Ag/AgCl reference electrode) under the condition of stirring speed of 500rpm, gradually adding 1ppb of As (III) into the mixed solution 1, keeping the enrichment time for 180s each time to deposit ions to be detected on the surface of the electrode, recording the detection data of each time, and drawing a corresponding relation curve of peak current and As (III) concentration. The stripping potential was continuously varied from-1 to 1V, and other parameters were set as follows: frequency 25 Hz; amplitude 25 mV; the incremental potential was 4 mV. After each square wave anodic stripping voltammetry measurement, stirring at the rotating speed of 500rpm for 90s under the working voltage of 0.8V for carrying out desorption experiments, and ensuring that the deposits remained on the surface of the glassy carbon electrode are completely removed.

S4: taking a natural water sample to be detected, filtering the natural water sample by using a 220nm microporous filter membrane, adding 2.945mL of glacial acetic acid into 500mL of the filtered natural water sample to prepare 0.1M HAc solution, adding 8.203g of NaAc into 1000mL of the filtered natural water sample to prepare 0.1M NaAc solution, mixing the two solutions in a proper ratio to prepare the mixtureBecomes a buffer solution of 0.1M HAc-NaAc with pH 4.5. 10ml of this mixed water sample was taken and 260. mu.L of 384.5ppm FeCl was added₃Prepared into 10ppm FeCl₃pH 4.5,0.1M HAc-NaAc mixed solution 2.

S5: and performing electrochemical detection on As (III) in the mixed solution 2 by square wave anodic stripping voltammetry. A simple unmodified glassy carbon electrode is immersed in the mixed solution 2, the dissolution potential is continuously changed from-1 to 1V under the condition that the stirring speed is 500rpm, and other parameters are set as follows: frequency 25 Hz; amplitude 25 mV; the incremental potential is 4mV, the enrichment potential of the working electrode is set to be-1.1V (relative to an Ag/AgCl reference electrode), the enrichment time is kept for 180s, ions to be detected are deposited on the surface of the electrode, and the corresponding relation curve of peak current and As (III) concentration is compared according to measurement data to obtain the As (III) content. The desorption experiment was carried out with stirring at 500rpm for 90s at an operating voltage of 0.8V to ensure complete removal of the deposits remaining on the glassy carbon electrode surface.

Referring to FIG. 1, the square wave anodic stripping voltammetry response signals under different experimental conditions of the present invention include individually changing pH (FIG. 1a), enrichment time (FIG. 1b), enrichment potential (FIG. 1c) and whether supporting electrolyte is added (FIG. 1 d). The optimized experimental conditions of this example were: pH 4.5HAc-NaAc buffer solution, enrichment potential-1.1V, enrichment time 180s, no addition of NaClO₄Supporting the electrolyte. Specifically, the inset in FIG. 1c is the response signal of the enrichment potential at-1.1V and-1.2V, and it can be seen that the enrichment potential at-1.2V has a significant interference peak compared to-1.1V, so the scheme selects-1.1V as the optimal enrichment potential. Figure 1d shows the square wave anodic stripping voltammetry response signals for whether the supporting electrolyte is replenished in the presence of 200ppb As (III), while the inset corresponds to the response signals in the presence of 20ppb As (III), it can be seen that replenishing the supporting electrolyte has an accelerating effect on the stripping of high concentrations of As (III), while suppressing the stripping of low concentrations of As (III). Therefore, when the As (III) below 20ppb is selected to be detected, no extra electrolyte is required.

Referring to FIG. 2, FIG. 2a shows the experimental conditions optimized for the laboratory test of dissociation in the present embodimentIn the sub-water, response signals to As (III) are detected by square wave anodic stripping voltammetry; FIG. 2b is a graph showing the response signal for 10ppb As (III) in the presence of 1-10ppb Cu (II) in deionized water; the inset shows the response signal of As (III) as the concentration of Cu (II) increases. From FIG. 2b, it can be seen that as (III) response signal varies with increasing Cu (II) concentration. Specifically, with the addition of Cu (II), the peak current at 0V is increased and then decreased, and the peak current at about-0.4V is obviously increased. The detection sensitivity of the detection reagent in deionized water in a laboratory is 0.296 mu A/ppb, and the corresponding linear relation R²0.989, and the addition of the interfering ions Cu (II) has a great influence on the stripping voltammetry peak shape of As (III), namely the Cu (II) has certain interference on the detection of As (III).

Therefore, interference analysis was performed on cu (ii): the Cu elution potential and As elution potential of the glassy carbon electrode are close to each other and are both near 0V. (E)^θ(Cu²⁺/Cu⁰) 0.119V, Ag/AgCl reference; e^θ(HAsO₂/As⁰) 0.018V, Ag/AgCl reference) for dissolution process: the dissolution of Cu promotes the dissolution of Fe: fe + Cu²⁺＝＝Fe²⁺+ Cu; due to the existence of high concentration of Fe (III), low concentration of Cu (II) and Fe (II) or Fe (III) have metal replacement, so that Cu can not be dissolved out; the concentration of Cu (II) is increased, so that the response signal of As is not interfered by low concentration of Cu (II), and the dissolution peak of Fe (0) is increased (E) about-0.4V due to high concentration of Cu (II)^θ(Fe²⁺/Fe⁰) -0.662V, Ag/AgCl reference; e^θ(Fe³⁺/Fe⁰) -0.2594V, Ag/AgCl reference). It is concluded that the method has no obvious interference effect on Cu (II) of natural water with As (III) content in the range of 20ppb-200ppb, and has good sensitivity and recovery rate.

With reference to fig. 3, fig. 3a is a diagram illustrating as (iii) of the mixed solution 2, and fig. 3b is a diagram illustrating as (iii) of the mixed solution 1; the inset of fig. 3a and 3b are both linear calibration curves of the respective peak currents versus as (iii) concentration. The comparison shows that compared with deionized water, the natural water sample has obvious impurity peak near-0.2V. Therefore, the natural water sample can effectively detect more than 20ppb of As (III), and the effect is similar to that of deionized waterThe properties in the sample detection reagents are similar. As can be seen from the figure, the corresponding linear relationship R in the laboratory deionized water²0.974, sensitivity 0.237 μ A/ppb; corresponding linear relation R in natural water sample²The detection sensitivity is 0.985, the sensitivity is 0.155 mu A/ppb, the detection effects are good, the linear correlation is not obviously reduced, and the detection sensitivity is good.

FeCl is added₃The actual effect of the present detection method was evaluated by analyzing the concentration of as (iii) (standard addition method, variance of 3 times) in a natural water sample using HAc and NaAc as detection reagents, and calculating the recovery rate, and the detection results are shown in table 1.

TABLE 1

As can be seen from Table 1, for the detection performance, the detection method of the invention obtains excellent effects on the two performances of sensitivity and the range of standard recovery rate, and the detection method is proved to have good technical effects by calculating that the recovery rates of different addition amounts are between 90 and 100 percent.

Any range recited herein is intended to include the endpoints and any number between the endpoints and any subrange subsumed therein or defined therein.

Although the present description is described in terms of embodiments, not every embodiment includes only a single embodiment, and such description is for clarity only, and those skilled in the art should be able to integrate the description as a whole, and the embodiments can be appropriately combined to form other embodiments as will be understood by those skilled in the art.

Therefore, the above description is only a preferred embodiment of the present application, and is not intended to limit the scope of the present application; all changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

1. The method for detecting the heavy metal As (III) in the natural water body is characterized by comprising the following steps:

S2: polishing, cleaning and drying the glassy carbon electrode for later use;

connecting a three-electrode system with an electrochemical workstation, immersing a working electrode into a mixed solution, enriching the mixed solution at a voltage of-1.1V, adding an equal amount of As (III) into the mixed solution one by one under the stirring condition, wherein the enrichment time is 180s each time, detecting an electroanalysis signal by adopting a square wave anodic stripping voltammetry method, and drawing a corresponding relation curve of peak current and As (III) concentration;

2. The method for detecting heavy metals As (III) in natural water according to claim 1, wherein in step S1, the pretreatment is: the water sample was filtered using a 220nm microfiltration membrane.

3. The method for detecting heavy metals As (III) in natural water according to claim 1, wherein in step S1, NaAc, HAc and FeCl are contained in the mixed solution₃The concentrations of (A) and (B) were 0.1M, 0.1M and 10ppm in this order.

4. The method according to claim 1, wherein in step S3, after each electrochemical detection, the working electrode is subjected to a desorption experiment and then subjected to next electroanalysis signal detection.

5. The method for detecting heavy metals As (III) in natural water according to claim 4, wherein the desorption experiment specifically comprises: the working electrode was kept in the mixed solution, the working voltage was set at 0.8V, the running time was 90s, and the stirring speed was 500 rpm.

6. The method for detecting heavy metal As (III) in natural water according to claim 1, wherein in step S3, the parameter setting of the square wave anodic stripping voltammetry further comprises: frequency 25 Hz; amplitude 25 mV; the incremental potential was 4 mV.

7. The method for detecting the heavy metal As (III) in the natural water body according to claim 1, wherein the diameter of the glassy carbon electrode is 3 mm.

8. The method for detecting heavy metals As (III) in natural water according to claim 1, wherein in step S3, the stirring speed of the mixed solution is 500 rpm.