CN114113249B - Heavy metal extraction and detection method for infant milk powder - Google Patents

Abstract

The invention discloses a method for extracting and detecting heavy metals in milk powder for infants and young children. The method steps include: weighing milk powder into a centrifuge tube with an analytical balance, adding deionized water, and vibrating to obtain a uniform solution; adding hydrogen peroxide to the uniform solution, and ultrasonically treating; adding hydrochloric acid and acetic acid, ultrasonically treating; The clear liquid is filtered through a cellulose membrane, and sodium hydroxide is added to adjust the pH to obtain the liquid to be tested and transferred to the electrochemical cell; the heavy metal ions in the liquid to be detected in the electrochemical cell are detected by using a nanoporous carbon-modified screen-printed electrode , the current response was detected by square wave voltammetry, and the heavy metal content in milk powder was obtained. The nanoporous carbon modified screen printing electrode constructed by the present invention is easy to manufacture and low in cost; the operation process of extracting heavy metals in infant milk powder is simple, low in cost and short in time, has high sensitivity and high selectivity, and realizes the extraction of heavy metals from Integrated technology to detection.

Description

Extraction and detection method for heavy metals in infant milk powder

technical field

The invention relates to a method for extracting and detecting heavy metals, an integrated method for measuring heavy metal content using nanoporous carbon-modified screen-printed electrodes as a simple electrochemical sensor, in particular to a method for extracting and detecting heavy metals in infant milk powder.

Background technique

Heavy metal detection techniques mainly include spectroscopic, optical and electrochemical methods. Spectroscopy techniques mainly include atomic absorption spectroscopy, atomic emission spectroscopy and X-ray fluorescence spectroscopy. Fluorescence, surface-enhanced Raman scattering, surface plasmon resonance, and fiber optic sensors are common optical techniques. Although these techniques are considered to be standard methods for detection, their large-scale instrumentation, high cost, and complicated pre-treatment hinder their field application, and matrix interferences also occur in actual samples. Compared with the aforementioned methods, electrochemical methods are widely used in the detection of heavy metal ions because of their portability, rapidity, and cheapness, as well as the inherent electrochemical activity of heavy metal ions.

In the field of electrochemistry, screen-printed electrodes integrate common three-electrode systems on polyvinyl chloride substrates or other insulating materials, and have attracted widespread attention due to their inherent small size, light weight, and ease of use, compared with other traditional electrodes. Compared with easy mass production and low cost, it is more suitable for rapid on-site detection. However, conductive inks such as carbon ink and gold ink are often used as the working area of screen-printed electrodes, and the non-conductive substances in commercial inks will lead to poor electrochemical performance of electrodes, thus limiting the sensitivity during electrochemical detection. Therefore, various modified materials have been combined with screen-printed electrodes to overcome these disadvantages. Nanoporous carbon, as a new type of carbon nanomaterial, is characterized by its low density, high specific surface area, high thermal stability, chemical stability, low cost, hierarchical porosity, fast electron transfer, fast charge conduction, efficient mass transfer, high electrical Properties such as active surface and large adsorption capacity have been widely used in the field of electrochemistry.

Milk and related products are the main source of nutrition for children, and milk powder is rich in vitamins, minerals and other nutrients that are crucial to the development of babies. In addition to the essential mineral elements, other heavy metal ions such as Pb(II) and Cd(II) are non-essential and can have toxic effects on infants even at very low concentrations. Exposure of dairy cows to the polluted environment around steel processing equipment or thermoelectric areas will also increase the concentration of heavy metal ions in milk, and it is of great significance to detect the content of heavy metals in infant milk powder.

Contents of the invention

In order to solve the problems in the background technology, the present invention uses nanoporous carbon-modified screen-printed electrodes as an electrochemical sensor to detect the heavy metal content in baby milk powder in real time.

The technical scheme adopted in the present invention is:

1) First, carry out heavy metal extraction:

1.1) Use an analytical balance to weigh the milk powder into a centrifuge tube, add deionized water to the centrifuge tube, and shake the deionized water and milk powder to obtain a uniform solution;

1.2) adding hydrogen peroxide to the homogeneous solution, followed by ultrasonic treatment to remove reduced substances in the homogeneous solution;

1.3) Continue to add hydrochloric acid and acetic acid, and perform ultrasonic treatment again to remove macromolecular substances in the homogeneous solution;

1.4) After centrifugation, collect the supernatant in another centrifuge tube, and centrifuge to remove small molecular interferences in the homogeneous solution; filter the supernatant through a cellulose membrane, add sodium hydroxide to adjust the pH, and obtain the solution to be tested. Transfer the liquid to be tested to the electrochemical cell;

2) Then, carry out electrochemical detection of heavy metal content:

2.1) Preparation of nanoporous carbon-modified screen-printed electrodes;

2.2) By square wave anodic stripping voltammetry, using nanoporous carbon-modified screen-printed electrodes to detect heavy metal ions in the liquid to be detected in the electrochemical cell, and detecting its current response, thereby detecting the heavy metal content in milk powder.

In the step 1.2), the concentration of hydrogen peroxide is 30%wt;

In the step 1.3), the concentration of hydrochloric acid is 36.5%wt, and the concentration of acetic acid is 50%wt.

In the steps 1.1)-1.3), the volume ratio among the homogeneous solution, hydrogen peroxide, hydrochloric acid and acetic acid is 1000:1:250:250.

In the step 1.4), the pH is adjusted to 4.5 by 0.1mol/L sodium hydroxide.

In said step 2.1), the method steps for preparing the screen-printed electrode modified by nanoporous carbon are as follows:

2.1.1) Disperse the nanoporous carbon powder NPC in the ethanol solution, perform ultrasonic treatment, remove the insoluble matter in the mixed solution; discard the precipitate after centrifugation, and centrifuge the supernatant again, collect the precipitate and dry it to obtain a powder, Disperse the powder into dimethylformamide DMF to modify the electrode to obtain a DMF-NPC dispersion;

2.1.2) Prepare a screen-printed electrode SPE, add the screen-printed electrode SPE into ultrapure water for ultrasonic activation and blow dry with nitrogen to obtain the activated screen-printed electrode;

2.1.3) DMF-NPC dispersion liquid is drop-coated to cover the working area of the activated screen-printed electrode, and the nanoporous carbon-modified screen-printed electrode is obtained after drying.

2.1.4) Use the screen-printed electrode as an electrochemical sensor to extract and detect the heavy metal content in milk powder.

In the step 2.1.1), the volume ratio of ethanol and water in the ethanol solution is 1:1.

In the step 2.1.1), the volume of the DMF-NPC dispersion is 6 μL, and the concentration is 1 mg/mL.

In the step 2.2), one end of the nanoporous carbon-modified screen printing electrode is connected to the electrochemical cell, and the other end is connected to the electrochemical workstation, and a voltage is applied to the liquid to be detected in the electrochemical cell, and the heavy metal ions in the liquid to be detected are quickly transferred To the surface of the screen-printed electrode modified by nanoporous carbon, the current response during the application of voltage is detected by the electrochemical workstation, and the content of heavy metal ions on the surface of the screen-printed electrode modified by nanoporous carbon is determined, and then the content of heavy metals in milk powder is determined .

The beneficial effects of the present invention are:

Firstly, the present invention extracts the heavy metals in the milk powder, the operation process is simple, the cost is low, and the time consumption is short;

Secondly, after the successful extraction of heavy metals in milk powder was achieved, the prepared nanoporous carbon modified screen-printed electrode was used to detect its content. Due to the high surface area of nanoporous carbon, chemical stability, low cost, fast electron transfer, Due to the inherent properties of fast charge conduction, efficient mass transfer, high electroactive surface, and large adsorption capacity, the constructed electrochemical sensor can achieve high selectivity and high sensitivity detection of heavy metal ions.

The present invention realizes the integrated technology from extraction to content determination of heavy metals in infant milk powder, and will open up a new processing method for the development of infant milk powder quality detection, and can provide a good quality evaluation for currently commercially available infant milk powder refer to.

Description of drawings

Fig. 1 is the square wave anode stripping voltammetry current response curve figure of bare screen printing electrode and nanoporous carbon modified screen printing electrode to Pb(II), Cd(II) in the present invention;

Fig. 2 is the volume optimization diagram of nanoporous carbon modified screen printing electrode to Pb(II), Cd(II) detection parameter DMF-NPC dispersion liquid in the present invention;

Fig. 3 is the concentration optimization diagram of Bi(III) in the buffer solution of the nanoporous carbon modified screen printing electrode to Pb(II), Cd(II) detection parameters in the present invention;

Fig. 4 is the nanoporous carbon modified screen printing electrode pair Pb(II), Cd(II) detection parameter deposition time optimization figure in the present invention;

Fig. 5 is the nanoporous carbon modified screen-printed electrode pair Pb (II), Cd (II) detection parameter pH optimization diagram in the present invention;

Fig. 6 is the stripping curve figure that nanoporous carbon modified screen printing electrode detects to Pb(II), Cd(II) in the present invention;

Fig. 7 is the standard curve figure that nanoporous carbon modified screen printing electrode detects to Pb(II) in the present invention;

Fig. 8 is the standard graph of the detection of Cd(II) by the nanoporous carbon modified screen-printed electrode in the present invention;

Fig. 9 is a graph showing the selective detection of Pb(II) and Cd(II) by the nanoporous carbon modified screen-printed electrode in the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

Embodiments of the present invention are as follows:

Example 1

Electrochemical response of bare screen-printed electrodes and nanoporous carbon-modified screen-printed electrodes to heavy metal ions.

Prepare bare screen-printed electrodes and nanoporous carbon-modified screen-printed electrodes in advance. Add 10mL acetate buffer as electrolyte in the electrochemical cell, add 1mgL ^-1 of Bi(III) to promote the reduction process of heavy metal ions, then add 30μgL ^-1 of Pb(II) and Cd(II), through square wave Anodic stripping voltammetry was used to detect the current response of the two electrodes to heavy metal ions, and the results are shown in Figure 1. For the bare screen-printed electrode, there is no obvious voltammetry peak, but obvious voltammetry peaks are observed on the nanoporous carbon-modified screen-printed electrode, roughly located at -0.85V and -0.6V, indicating that the nanoporous carbon The nanoporous carbon film formed on the surface of the modified screen-printed electrode has abundant surface area and high conductivity, which facilitates the rapid electron transfer between heavy metal ions and the surface of the nanoporous carbon-modified screen-printed electrode. Therefore, it is feasible to modify the surface of screen-printed electrode with nanoporous carbon for the detection of heavy metals.

Example 2

Selective detection of heavy metals by nanoporous carbon-modified screen-printed electrodes.

Prepare nanoporous carbon-modified screen-printed electrodes in advance. Add 10mL acetic acid buffer solution to the electrochemical cell as electrolyte, add 1mgL ^-1 of Bi(III), and then add 30μgL ^-1 of Pb(II) and Cd(II), through square wave anodic stripping voltammetry, observe In response to the current change, the detected concentration of heavy metals is about 30μgL ^-1 , which is the concentration of Pb(II) and Cd(II);

After the current is stabilized, add Ca ²⁺ , Zn ²⁺ , Mg ²⁺ , Fe ³⁺ , fructose, glucose, sucrose, glycine and glutamine to the acetate buffer solution with Pb(II) and Cd(II) respectively. Acid, observe the change of response current again, that is, observe the change of the dissolution curve after adding interfering substances, as shown in Figure 9, for this selective detection experiment, after adding different interfering substances, the concentration of heavy metals is always about 30 μgL ^-1 , indicating that the current response of Pb(II) or Cd(II) was not significantly affected, indicating that these interferents are very useful for using nanoporous carbon-modified screen-printed electrodes as electrochemical sensors and for Pb(II) and Cd(II) The detection was performed with little interference, and the nanoporous carbon-modified screen-printed electrode exhibited excellent selectivity for the determination of heavy metals in complex samples such as milk powder.

Example 3

Extraction and concentration detection of heavy metals in infant milk powder.

Prepare nanoporous carbon-modified screen-printed electrodes in advance. Randomly select 5 different brands of infant milk powder, make it into the test solution, and add 10mL to the electrochemical cell. When testing, add 1mgL ^-1 Bi(Ⅲ) and 30μgL -1 to the five test solutions respectively ^{. 1} of Pb(II) and Cd(II), through square wave anodic stripping voltammetry, observe the change of response current, the test results are shown in Table 1, the detected concentration of heavy metals is about 30μgL ^-1 , that is, Pb( II) and the concentration of Cd (II), show that the heavy metal concentration in milk powder detected by the screen printing electrode modified by nanoporous carbon has higher accuracy; The ions are recovered and processed. The recovery rates of Cd(II) in the five liquids to be detected are 71.5%, 86.1%, 93.2%, 77.9% and 105.2%, respectively, and the recovery rates of Pb(II) are respectively 110.4%, 113.6%, 103.5%, 120.5%, and 128.6%. During the detection process, the detection limit of Pb(II) was 0.1, and that of Cd(II) was 1.67.

Table 1

In the specific experiment, in order to make the detection performance better, the relevant heavy metal detection parameters were optimized, including the volume of DMF-NPC dispersion, the concentration of Bi(III) in the buffer, the deposition time, and the pH value of the buffer.

The volume of the DMF-NPC dispersion was optimized during the experiment. In the prepared DMF-NPC dispersion, if the nanoporous carbon powder NPC content is not enough, the best performance cannot be achieved. If the content is too much, the particles may accumulate with each other and cause the surface of the nanoporous carbon modified screen printing electrode surface to be damaged. The conductivity decreased; when 6 μL of DMF-NPC dispersion liquid was deposited on the nanoporous carbon-modified screen printing electrode working area, the response current was observed by square wave anodic stripping voltammetry, and the maximum peak current appeared during detection, as shown in the figure 2, when more DMF-NPC dispersion was dispensed, the reproducibility became worse. Therefore, 6 μL of DMF-NPC dispersion was used for detection in all experiments.

The concentration of Bi(III) in the buffer was optimized during the experiment. The content of Bi(III) in the acetic acid buffer was continuously increased. With the increase of the concentration of Bi(III), the overall trend of the stripping current first increased and then decreased. When 1mgL ^-1 of Bi(III) was added, the anode Stripping voltammetry, observing the response current change, and detecting the maximum peak current, as shown in Figure 3, the alloy formed by heavy metal ions and Bi(III) promotes the deposition process of Pb(II) and Cd(II), and when When the concentration of Bi(III) is too high, a thicker film will be formed, hindering the process of metal enrichment. Therefore, 1 mgL ^-1 of Bi(III) was selected for detection in the experiments.

The pH was optimized during the experiment. When the pH value of the acetic acid buffer was increased from 4 to 4.5, the response current was observed by square wave anodic stripping voltammetry, and the current intensity increased. After continuing to increase the pH value, the current intensity showed a downward trend, as shown in Figure 5 , which may be caused by the hydrolysis of Bi(III) in acetate buffer at higher pH. Therefore, the acetic acid buffer solution with a pH value of 4.5 was used for detection in the experiments; the pH value of the liquid to be tested prepared from milk powder was also adjusted to 4.5 in the experiments.

The deposition time was optimized during the experiment. With the increase of the deposition time, the change of the response current was observed by square wave anodic stripping voltammetry, and the current gradually increased. After 150 seconds, the content of heavy metals enriched on the nanoporous carbon-modified screen-printed electrode reached saturation, as shown in Figure 4 As shown, the current changes slightly. Therefore, 150 seconds of deposition was selected for detection in the experiment.

The standard curve for detecting Pb(II) and Cd(II) was established by square wave anodic stripping voltammetry in the experiment. Using the standard addition method, different concentrations of Pb( ^II ) and Cd(II) (1μgL ^-1 , 3μgL ^-1 , 5μgL ^-1 , 10μgL ^-1 , 20μgL ^-1 , 30μgL ^-1 , 40μgL ^-1 , 50μgL ^-1 , 60μgL ^-1 , 70μgL ^-1 ), obtain the dissolution curve, as shown in Figure 6, and obtain the standard curve after fitting the dissolution current response curve, construct The equation between heavy metal concentration and stripping response current is established, as shown in Figure 7 and Figure 8. It can be seen from the figure that the use of nanoporous carbon-modified screen-printed electrodes as electrochemical sensors exhibits excellent electrocatalytic ability for heavy metal ions, and has a good linear response range and high sensitivity. There is a good linear relationship between the dissolution response current and the concentration of heavy metal ions. The linear equation is: I _pb =0.01772C _pb +0.24964, I _cd =0.03958C _cd -0.12592, and the correlation coefficients are 0.9884 and 0.99577, respectively. In the experiment, a linear equation was used to obtain the heavy metal content in infant milk powder.

Claims (7)

1. A method for extracting and detecting heavy metals in infant milk powder is characterized by comprising the following steps:

1) Firstly, heavy metal extraction is carried out:

1.1 Weighing milk powder in a centrifuge tube by using an analytical balance, adding deionized water into the centrifuge tube, and oscillating the deionized water and the milk powder to obtain a uniform solution;

1.2 Hydrogen peroxide is added to the homogeneous solution, followed by sonication;

1.3 Adding hydrochloric acid and acetic acid continuously, and carrying out ultrasonic treatment again;

1.4 Centrifuging, collecting supernatant in another centrifuge tube, filtering the supernatant with cellulose membrane, adding sodium hydroxide to adjust pH value to obtain solution to be detected, and transferring the solution to be detected to an electrochemical cell;

2) Then, carrying out electrochemical detection on the heavy metal content:

2.1 Preparing a screen-printed electrode modified by nano porous carbon;

in the step 2.1), the method for preparing the screen printing electrode modified by the nano porous carbon comprises the following steps:

2.1.1 Dispersing NPC into ethanol solution, performing ultrasonic treatment, centrifuging again, discarding precipitate, centrifuging supernatant again, collecting precipitate, oven drying to obtain powder, and dispersing the powder into DMF to obtain DMF-NPC dispersion solution;

2.1.2 Preparing a screen printing electrode SPE, adding the screen printing electrode SPE into ultrapure water for ultrasonic activation, and drying by blowing with nitrogen to obtain an activated screen printing electrode;

2.1.3 Dropping and coating DMF-NPC dispersion liquid on a working area of the activated screen printing electrode, depositing for 150s after dropping and coating, and drying to obtain the screen printing electrode modified by the nano porous carbon;

2.1.4 Using a screen-printed electrode as an electrochemical sensor to extract and detect the heavy metal content in the milk powder;

2.2 Using a screen-printed electrode modified by nanoporous carbon to detect heavy metal ions in a liquid to be detected in an electrochemical cell, adding an acetic acid buffer solution as an electrolyte and trivalent Bi ions into the electrochemical cell, and detecting the current response of the electrochemical cell, thereby detecting the heavy metal content in the milk powder.

2. The method for extracting and detecting the heavy metals in the infant milk powder according to claim 1, wherein the method comprises the following steps:

in said step 1.2), the concentration of hydrogen peroxide is 30% by weight;

in said step 1.3), the concentration of hydrochloric acid is 36.5% wt, the concentration of acetic acid is 50% wt.

3. The method for extracting and detecting the heavy metals in the infant milk powder according to claim 1, wherein the method comprises the following steps:

in the steps 1.1) -1.3), the volume ratio of the uniform solution, the hydrogen peroxide, the hydrochloric acid and the acetic acid is 1000:1:250:250.

4. the method for extracting and detecting heavy metals in infant milk powder according to claim 1, wherein the method comprises the following steps:

in the step 1.4), the pH value is adjusted to 4.5 by 0.1mol/L of sodium hydroxide.

5. The method for extracting and detecting the heavy metals in the infant milk powder according to claim 4, wherein the method comprises the following steps:

in the step 2.1.1), the volume ratio of the ethanol to the water in the ethanol solution is 1:1.

6. The method for extracting and detecting heavy metals in infant milk powder according to claim 4, wherein the method comprises the following steps:

in the step 2.1.1), the concentration of the DMF-NPC dispersion is 1mg/mL.

7. The method for extracting and detecting heavy metals in infant milk powder according to claim 1, wherein the method comprises the following steps:

in the step 2.2), one end of the screen printing electrode modified by the nano porous carbon is connected with the electrochemical cell, the other end of the screen printing electrode modified by the nano porous carbon is connected with the electrochemical workstation, voltage is applied to the liquid to be detected in the electrochemical cell, heavy metal ions in the liquid to be detected are transferred to the surface of the screen printing electrode modified by the nano porous carbon, current response in the voltage applying process is detected through the electrochemical workstation, the content of the heavy metal ions on the surface of the screen printing electrode modified by the nano porous carbon is determined, and then the content of the heavy metal in the milk powder is determined.

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