CN103592356A - Method for quickly detecting lead and cadmium by adopting scanning anodic stripping voltammetry - Google Patents

Abstract

A method for quickly detecting ultra-trace heavy metals lead and cadmium by scanning anode stripping voltammetry, the steps are as follows: prepare a sample to be tested, prepare a lead or cadmium standard solution, assemble a glassy carbon electrode coated with mercury film, and a platinum wire For a three-electrode system consisting of a counter electrode and an Ag/AgCl reference electrode, set parameters and use scanning anode stripping voltammetry to measure the current values between the working electrode and the reference electrode of each standard solution in parallel until the relative standard deviation of the readings No more than 5%, the lead and cadmium heavy metals in the sample are determined by detecting the current value between the working electrode and the reference electrode, and the peak area of each curve is determined by automatic peak finding, and the workstation automatically calculates the detection result. The invention has the advantages of high sensitivity, good accuracy, reduced mercury pollution, high electrode stability and good reproducibility, and can be applied to the detection of conventional trace and ultra-trace heavy metals lead and cadmium.

Description

A method for rapid detection of lead and cadmium by scanning anodic stripping voltammetry

technical field

The invention belongs to the technical field of electrochemical analysis, in particular to a method for rapidly detecting lead and cadmium by scanning anode stripping voltammetry.

Background technique

Heavy metals refer to metal elements with atomic density greater than 5g/cm ³ , there are about 45 kinds, such as copper, lead, zinc, cadmium, manganese, iron, cobalt, mercury, gold, silver, etc. Although heavy metals such as manganese, copper, and zinc are trace elements needed for life activities, most heavy metals such as lead, cadmium, and mercury are not necessary for life activities, and all heavy metals exceeding a certain concentration will cause harm to the human body. With the expansion of cities and the development of large-scale industries, the heavy metal pollution in the atmosphere, soil and water environment is increasing day by day.

Because heavy metals are highly toxic, difficult to be metabolized in the environment, easy to be enriched by organisms, and have biomagnification effects, heavy metal pollution in the environment seriously threatens the survival of organisms and human health. Therefore, the monitoring and control of heavy metal content in the water environment has become an important issue related to environmental protection, sustainable development and improvement of residents' living standards. With the rapid development of analytical testing technology, not only more and more methods can be applied to the analysis of heavy metal content in different samples, but also the detection sensitivity and accuracy have been greatly improved. At present, the commonly used heavy metal analysis methods include atomic absorption spectrometry, inductively coupled plasma method, atomic fluorescence spectrometry, stripping voltammetry, biological enzyme inhibition method, immunoassay and biochemical sensor method.

The atomic absorption spectrometry in the above method cannot analyze multiple elements at the same time, and the light source lamp must be replaced if the measured elements are different, and the working range of the standard curve is narrow, which brings inconvenience to the actual analysis. The inductively coupled plasma method for the determination of heavy metals in water mainly includes inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). ICP-AES uses the high temperature generated by the high-frequency induction current to heat and ionize the reaction gas, and uses the characteristic spectral lines emitted by the elements for measurement. ICP-MS uses inductively coupled plasma to vaporize the sample, and the metal elements to be measured enter the mass spectrometer, and perform qualitative and quantitative analysis by measuring the charge-to-mass ratio. The inductive couple and plasma methods are complex in operation, high in cost, and not widely used. Atomic fluorescence spectrometry has the characteristics of high sensitivity, strong selectivity, small sample volume and simple method, but its disadvantage is that its application range is not wide enough. The relationship between the generation process of atomic fluorescence and the structure of compounds needs to be studied extensively and deeply. Although the biological enzyme inhibition method, immunoassay method and biochemical sensor method are conducive to the rapid detection of heavy metals on site, their sensitivity and accuracy are low, and the types of heavy metals detected are limited. Therefore, it is of great practical significance to study simple, fast and low-cost heavy metal rapid detection methods for effective assessment and early warning of pollution and protection of people's health and ecological security.

Anodic stripping voltammetry is the most sensitive method in stripping voltammetry. Heavy metals are dissolved after pre-enrichment, which greatly improves the Faraday electrolysis current component. Under stirring, the trace substances in the sample are reduced and deposited on the anode; then a reverse scanning voltage is applied on the two electrodes to oxidize and dissolve the metal ions deposited on the anode, forming a large peak current. proportional to the concentration of the substance being measured. Anode stripping voltammetry directly obtains electrical signals, so it can be output without conversion. Not only is the instrument simple and portable, but it also has low energy consumption, high degree of automation, convenient operation, low cost, and high sensitivity (PPB-PPT level). The mercury film electrode has both the characteristics of a mercury electrode and a high area/volume ratio. During dissolution, the peak current is high, the peak is sharp, and the resolution is good. It can form amalgam with most other heavy metal ions and has a low hydrogen evolution potential. Mercury film electrodes are still widely used in electrochemical detection.

In recent years, many reports at home and abroad have confirmed that anodic stripping voltammetry is easy to operate, low in cost, can continuously measure multiple heavy metal ions at one time, and has high test sensitivity. It has become one of the important development directions of on-site rapid detection technology for heavy metals. However, in terms of sensitivity, it still cannot be compared with methods such as atomic emission spectrometry, inductive couple and plasma method. This brings inconvenience to the on-site detection of ultra-trace heavy metals in some samples. In the conventional stripping voltammetry test, it is required to eliminate the background current as much as possible and increase the peak height of the stripping to increase the signal-to-noise ratio. However, the electric double layer capacitance of the pre-mercury-plated film electrode basically does not change during the test. The number of electrons on the electrode surface increases, and in the presence of ultra-trace heavy metal ions, an obvious dissolution peak can also appear, which improves the test sensitivity. The high-speed scanning makes the metal ions deposited on the mercury membrane electrode hardly lose during the dissolution and mass transfer process, and the dissolution process is extremely short. Under the premise of ensuring the test accuracy, every small scanning step within the scanning range can be The scanning speed of 500V/S can be reached within 1mS, and the dissolution test can be completed within a few milliseconds. Therefore, the electrochemical workstation can run and collect data at a high scanning speed, which provides a practical basis for the low-cost detection of ultra-trace heavy metals lead and cadmium.

Contents of the invention

The purpose of the present invention is to address the above-mentioned problems and provide a method for quickly detecting lead and cadmium using scanning anode stripping voltammetry. The method can accurately detect the content of PPT-level heavy metal lead and cadmium in the sample, and the instrument is simple and convenient It is easy to carry, simple to operate and low in cost, and has a wide detection range, which can be widely used in actual detection in various fields.

Technical scheme of the present invention:

A method for rapidly detecting lead and cadmium by scanning anode stripping voltammetry, the steps are as follows:

1) Pretreatment of samples to be tested

Add perchloric acid solution and nitric acid solution to the sample to be tested, place the jar in a microwave digestion instrument after sealing it, and digest it for 20 minutes under the power of the microwave digestion instrument at 900w. M, pH is that the acetic acid-sodium acetate buffer solution of 4 is settled in the 50mL volumetric flask;

2) Preparation of standard solution

Soak the test beakers in 5w% nitric acid for 8-10 hours, then rinse them with double distilled water, dry them and number them, measure 50mL of 0.1M acetic acid-sodium acetate buffer solution with a pH of 4, and add them to each test beaker , and then add lead or cadmium standard solutions with volume accuracy of uL level to prepare 0.01, 0.05, 0.1, 0.5, 1, 5ug/L series standard solutions;

3) Assemble the three-electrode system

The three-electrode system consists of a glassy carbon electrode coated with mercury film, a platinum wire counter electrode and an Ag/AgCl reference electrode. The working electrode is a glassy carbon electrode, the counter electrode is a platinum wire electrode, and the reference electrode is an Ag/AgCl electrode. In the mercury ion solution with a concentration of 50mg/L, the preparation method of the glassy carbon electrode coated with mercury film is: the _glassy carbon electrode with a diameter of _3mm ) is polished to Smooth mirror surface, ultrasonically cleaned with ethanol for 5 minutes to remove impurities, rinsed with double distilled water, blown dry with nitrogen, then performed 25 times of cyclic voltammetry scanning activation treatment in the potential range of -1 to 1V, and deposited at -0.2V potential for 240s , stirred by a magnetic stirrer, and a layer of uniform silver-gray mercury film without spots is plated on the surface of the glassy carbon electrode;

4) Connect the three-electrode system to the electrochemical workstation and fix it in the beaker for detection. Set the parameters of the electrochemical workstation as: deposition potential -1V, step height 1-10mV, step time 20-1000uS, deposition time 480s, The waiting time is 20s, the cleaning time is 240s, then add the standard solution and use scanning anode stripping voltammetry to measure the current value between the working electrode and the reference electrode of each standard solution in parallel until the relative standard deviation of the reading does not exceed 5%;

5) Determination of lead and cadmium heavy metals

Transfer the sample to be tested to a beaker, add 5mg/L, 1mg/L, 0.5mg/L, 0.1mg/L, 0.05mg/L, 0.01mg/L lead or cadmium standard solution 100uL, detect the working electrode and The current value between the reference electrodes is used to obtain the linear scanning curve of the sample to be tested, and the standard addition method is used for quantification, and the test is repeated four times to obtain the linear scanning test curves of four standard solutions with different concentrations;

6) Information result processing

Determine the peak area of each curve through automatic peak finding, and the workstation automatically calculates the detection result.

The concentration of the perchloric acid solution is 70-72w%, the concentration of the nitric acid solution is 65-68w%, and the volume ratio of the perchloric acid solution to the nitric acid solution is 1:3.

Working mechanism of the present invention:

Using pre-mercury film method and rapid scanning anode stripping voltammetry as the basic principle of detection, the mercury film electrode conduction terminal is connected to the self-developed electrochemical workstation through wires, and the application includes electrochemical workstation, computer and software systems. The advanced data acquisition and processing system can detect whether the sample to be tested contains lead, cadmium and ultra-trace lead and cadmium content.

The rapid scanning anodic stripping voltammetry of the pre-mercury-coated film is divided into four steps: deposition, waiting, stripping, and cleaning. The deposition process refers to that in the measuring solution, under the deposition potential selected by Pb ²⁺ and Cd ²⁺ , the two ions are deposited on the surface of the electrode to form an amalgam with the mercury film. The waiting process means that after the deposition process is over, the magnetic stirring is controlled by the workstation to suspend the operation, so that the liquid in the solution remains still during the dissolution, and the interference of the solution during the dissolution of heavy metal ions is reduced. The dissolution process is to wait for the end of the process, and scan the electrode potential forward. When the potential reaches the equilibrium electrode potential, lead and cadmium will generate a dissolution current. Because the stripping potential of mercury is corrected, it will not be stripped out earlier than lead and cadmium to cause interference.

The stripping peak potential in stripping voltammetry is the basis of qualitative analysis. Use the inventive method in 0.1mol/L, pH be in the acetic acid-sodium acetate buffer solution of 4, lead, cadmium ion appear a sensitive stripping voltammetry peak at-0.46V,-0.63V place respectively, stripping voltammogram waveform better.

The stripping peak area has a linear relationship with the corresponding ion concentration, so the content of lead and cadmium can be quantitatively detected.

In order to overcome the matrix effect of the standard curve method, the standard addition method can be used for quantification.

Through the single factor test of stripping peak height and linear scanning parameters, the test conditions of the fast scanning anodic stripping voltammetry selected by the present invention are: deposition potential-1V, step height 0.1-1mV, pulse time 10us-1ms, deposition time 480s, waiting time 20s, cleaning time 240s.

The technical effect of the present invention compared with the prior art: 1) The sensitivity is high, and the lowest lead and cadmium content can be detected to 50ppt. 2) The accuracy is good, and the rapid scanning anodic stripping voltammetry is used for detection, and the metal ions deposited on the electrode are scanned within tens of microseconds, which reduces the loss of the ion mass transfer process during the stripping process. 3) Mercury film electrodes are used instead of mercury plating in situ to reduce mercury pollution. 4) The electrode has high stability and good reproducibility, which not only meets the needs of heavy metal pollution inspection, but also can be applied to the separate or simultaneous detection of conventional trace and ultra-trace heavy metals lead and cadmium. 5) There is a cleaning and activation process before the test deposition process, which can ensure the stability of the electrode state, and the cleaning, activation, deposition, waiting, testing, and cleaning processes are connected one by one and fully automatic control.

Description of drawings

Accompanying drawing is the peak shape figure that embodiment 1 quick scan obtains.

In the figure: a is the test curve of the sample solution, b is the test curve of the sample adding 10ug/L lead ion standard solution, c is the test curve of the sample adding 20ug/L lead ion standard solution, d is the test curve of the sample adding 30ug/L lead ion The test curve of the ion standard solution, e is the test curve of the sample with 40ug/L lead ion standard solution.

Detailed ways

Example 1:

A method for rapid detection of lead and cadmium by scanning anode stripping voltammetry is characterized in that it comprises the following steps:

1) Soak the test beaker in 5% nitric acid overnight, rinse it with double distilled water, and then dry the number. Measure 50mL of 0.1M acetic acid-sodium acetate buffer solution (pH=4), transfer it to the test beaker, and add lead standard solution Prepare 0.01, 0.05, 0.1, 0.5, 1, 5ug/L series of standard solutions (since the volume of the lead standard solution added is uL level, it can be considered that the volume of the solution to be tested is always constant), and add clean and dry magnets to the on a magnetic stirrer.

2) Connect the three-electrode system consisting of mercury film electrode, platinum wire counter electrode and Ag/AgCl reference electrode to the electrochemical workstation and move it into the beaker to fix it.

3) Set the electrochemical workstation parameters: deposition potential -1V, step height 1mV, step time 20uS, deposition time 480s, waiting time 20s, cleaning time 240s. Rapid scan anodic stripping voltammetry were measured respectively, and standard addition method was used for quantification.

4) Each standard solution was measured in parallel 10 times, and the measured results were 0.01031, 0.05028, 0.10509, 0.50237, 1.03115, 5.16382ug/L.

Accompanying drawing is the peak shape chart that embodiment 1 quick scan obtains, shows in the figure: peak shape is obvious, consistency is good, accuracy is high, and the relative standard deviation of reading is all no more than 5%.

Example 2:

A method for rapid detection of lead and cadmium by scanning anode stripping voltammetry is characterized in that it comprises the following steps:

1) Soak the test beaker in 5% nitric acid overnight, rinse it with double distilled water, and then dry the number. Measure 50mL of 0.1M acetic acid-sodium acetate buffer solution (pH=4), transfer it to the test beaker, and add cadmium standard solution Prepare 0.01, 0.05, 0.1, 0.5, 1, 5ug/L series of standard solutions (since the volume of the cadmium standard solution added is uL level, it can be considered that the volume of the solution to be tested is always constant), and add clean and dry magnets to the on a magnetic stirrer.

2) Connect the three-electrode system consisting of mercury film electrode, platinum wire counter electrode and Ag/AgCl reference electrode to the electrochemical workstation and move it into the beaker to fix it.

3) Set the electrochemical workstation parameters: deposition potential -1V, step height 1mV, step time 20uS, deposition time 480s, waiting time 20s, cleaning time 240s. Rapid scan anodic stripping voltammetry were measured respectively, and standard addition method was used for quantification.

4) Each standard solution was measured in parallel 10 times, and the measured results were 0.01020, 0.05018, 0.01042, 0.52164, 0.99862, and 5.10237.

The profile obtained by the quick scan is similar to that of Example 1, the conclusion is consistent and the relative standard deviation of the readings is no more than 4%.

Example 3:

A method for rapid detection of lead and cadmium by scanning anode stripping voltammetry is characterized in that it comprises the following steps:

1) Soak the test beaker in 5% nitric acid overnight, rinse it with double distilled water, and then dry the number. Measure 50mL of 0.1M acetic acid-sodium acetate buffer solution (pH=4), transfer it to the test beaker, and add lead and cadmium. Prepare standard solutions of 0.01, 0.05, 0.1, 0.5, 1, 5ug/L series of standard solutions (since the volume of lead and cadmium standard solutions added is uL level, it can be considered that the volume of the solution to be tested is always constant), and add clean and dry The magnet is placed on a magnetic stirrer.

2) Connect the three-electrode system consisting of mercury film electrode, platinum wire counter electrode and Ag/AgCl reference electrode to the electrochemical workstation and move it into the beaker to fix it.

3) Set the electrochemical workstation parameters: deposition potential -1V, step height 1mV, step time 20uS, deposition time 480s, waiting time 20s, cleaning time 240s. Rapid scan anodic stripping voltammetry were measured respectively, and standard addition method was used for quantification.

4) Each standard solution was measured in parallel 10 times, the measured lead results were 0.01051, 0.05139, 0.10275, 0.51863, 1.01253, 5.01068, and the measured cadmium results were 0.01022, 0.05087, 0.10469, 0.52006, 1.04971, 5.03889.

The peak shape obtained by the quick scan is similar to that of Example 1, and the conclusion is consistent.

Claims (2)

1. a method that adopts scan anode stripping voltammetry fast detecting lead, cadmium, is characterized in that step is:

1) sample to be tested pre-service

In sample to be tested, add perchloric acid solution and salpeter solution, tinning is airtight to be placed in microwave dissolver, at microwave dissolver power, be to clear up 20min under 900w, after clearing up, remove spent acid, with acetic acid-sodium-acetate buffer that the 0.1M, the pH that prepare are in advance 4, be settled in 50mL volumetric flask;

2) preparation of standard solution

Test is soaked after 8-10 hour with beaker in 5w% nitric acid, with redistilled water, rinse well again, numbering after drying, measure 0.1M, pH and be acetic acid-sodium-acetate buffer 50mL of 4, add and respectively test in beaker, then adding respectively volume accuracy is that the lead of uL level or cadmium mark liquid make 0.01,0.05,0.1,0.5,1,5ug/L series standard solution;

3) assembling three-electrode system

Three-electrode system is comprised of electrode and Ag/AgCl contrast electrode the glass-carbon electrode, the platinum filament that are coated with mercury film, working electrode is glass-carbon electrode, to electrode, it is platinum electrode, contrast electrode is Ag/AgCl electrode, being placed in concentration is the mercury ion solution of 50mg/L, described in be coated with the glass carbon electricity of mercury film preparation method be: the Al of 1.5 μ m particle diameters for the glass-carbon electrode that is 3mm by diameter ₂o ₃be polished to smooth mirror surface, with ethanol ultrasonic cleaning 5min, remove impurity, redistilled water is rinsed well, with nitrogen, dry up, then in-1 to 1V potential region, carry out after 25 cyclic voltammetry scan activation processing, under-0.2V current potential, deposit 240s, magnetic stirrer, obtains the even immaculate silver gray mercury film of one deck at glass-carbon electrode plated surface;

4) three-electrode system is connected on electrochemical workstation and is fixed on and detect with in beaker, electrochemical workstation parameter is set is: sedimentation potential-1V, step height 1-10mV, snap time 20-1000uS, sedimentation time 480s, stand-by period 20s, scavenging period 240s, then add standard solution and adopt scan anode stripping voltammetry to each mark liquor working electrode and the current value between contrast electrode carries out replicate determination respectively until reading relative standard deviation is no more than 5%;

5) plumbous, cadmium determining heavy metals

Sample to be tested is transferred in beaker, the lead or the cadmium standard solution 100uL that add 5mg/L, 1mg/L, 0.5mg/L, 0.1mg/L, 0.05mg/L, 0.01mg/L, current value between testing electrode and contrast electrode, obtain the linear sweep curve of sample to be tested, employing standard addition method is quantitative, repeat four tests, obtain the linear sweep test curve of the standard solution of four variable concentrations;

6) information result is processed

By automatic Peak Search, determine each curve peak area, workstation calculates testing result automatically.

2. the method that adopts according to claim 1 scan anode stripping voltammetry fast detecting lead, cadmium, is characterized in that: described perchloric acid solution concentration is 70-72w%, salpeter solution concentration is 65-68w%, and the volume ratio of perchloric acid solution and salpeter solution is 1:3.

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