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

Heavy metal extraction and detection method for infant milk powder Download PDF

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CN114113249B
CN114113249B CN202111412673.4A CN202111412673A CN114113249B CN 114113249 B CN114113249 B CN 114113249B CN 202111412673 A CN202111412673 A CN 202111412673A CN 114113249 B CN114113249 B CN 114113249B
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平建峰
陈涵
姚瑶
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Abstract

The invention discloses a method for extracting and detecting heavy metals in infant milk powder. The method comprises the following steps: weighing milk powder in a centrifuge tube by using an analytical balance, adding deionized water, and oscillating to obtain a uniform solution; adding hydrogen peroxide into the uniform solution, and carrying out ultrasonic treatment; adding hydrochloric acid and acetic acid, and performing ultrasonic treatment; centrifuging, collecting supernatant, filtering with cellulose membrane, adding sodium hydroxide to adjust pH value to obtain solution to be detected, and transferring to electrochemical cell; heavy metal ions of the liquid to be detected in the electrochemical cell are detected by using the screen printing electrode modified by the nano porous carbon, and the current response of the heavy metal ions is detected by using a square wave voltammetry method, so that the content of the heavy metal in the milk powder is obtained. The nano porous carbon modified silk-screen printing electrode constructed by the invention is simple and convenient to manufacture and low in cost; the method has the advantages of simple operation process, low cost, short time consumption, high sensitivity and high selectivity, and realizes the integrated technology of extracting heavy metals from infant milk powder to detect the heavy metals.

Description

Heavy metal extraction and detection method for infant milk powder
Technical Field
The invention relates to a heavy metal extraction and detection method, in particular to an integrated method for determining the content of heavy metals by using a nano porous carbon modified screen printing electrode as a simple electrochemical sensor, and specifically relates to a heavy metal extraction and detection method for infant milk powder.
Background
The heavy metal detection technology mainly comprises three methods, namely a spectroscopic method, an optical method and an electrochemical method. Spectroscopic 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 technologies. Although these techniques are considered as standard methods of detection, the large scale, high cost, complex pre-processing, and their field application are hindered, and in practical samples, matrix interference may also occur. Compared with the aforementioned method, the electrochemical method is widely applied to heavy metal ion detection due to the characteristics of portability, rapidness and low price and the inherent electrochemical activity of heavy metal ions.
In the electrochemical field, a common three-electrode system is integrated on a polyvinyl chloride base plate or other insulating materials by a screen printing electrode, the screen printing electrode is widely concerned due to the characteristics of small inherent size, light weight, easy use and the like, and compared with other traditional electrodes, the screen printing electrode is easy to produce in mass and low in cost and is more suitable for rapid field detection. However, conductive inks such as carbon ink, gold ink, etc. are often used as the working area of screen-printed electrodes, and non-conductive substances in commercial inks can cause the electrochemical performance of the electrodes to deteriorate, thereby limiting the sensitivity during electrochemical detection. Therefore, various modifying materials have been combined with screen printed electrodes to overcome these disadvantages. As a novel carbon nanomaterial, the nanoporous carbon has been widely applied in the electrochemical field due to the characteristics of low density, high specific surface area, high thermal stability, chemical stability, low cost, hierarchical porosity, rapid electron transfer, fast charge conduction, efficient mass transfer, high electroactive surface, large adsorption capacity and the like.
Milk and related products are main nutrient sources of children, and the abundant nutrient components such as vitamins, minerals and the like in the milk powder are important for the development of babies. In addition to essential mineral elements, other heavy metal ions such as Pb (II), cd (II), etc. are not essential and, even at low concentrations, can have toxic effects on infants. The milk cow exposed to the polluted environment around the steel processing device or the thermoelectric area can also increase the concentration of heavy metal ions in the milk, and the detection of the content of the heavy metal in the infant milk powder has important significance.
Disclosure of Invention
In order to solve the problems in the background technology, the invention uses the nano porous carbon modified silk-screen printing electrode as an electrochemical sensor to detect the heavy metal content in the infant milk powder in real time.
The technical scheme adopted by the invention is as follows:
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 into the homogeneous solution, and then ultrasonic treatment is carried out to remove the reduction type substances in the homogeneous solution;
1.3 Continuously adding hydrochloric acid and acetic acid, and performing ultrasonic treatment again to remove macromolecular substances in the uniform solution;
1.4 Centrifuging, collecting the supernatant in another centrifuge tube, and centrifuging to remove small molecule interferents in the uniform solution; filtering the supernatant by a cellulose membrane, adding sodium hydroxide to adjust the pH value to obtain a solution to be detected, and transferring the solution to be detected into 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;
2.2 By square wave anodic stripping voltammetry, heavy metal ions in the liquid to be detected in the electrochemical cell are detected by using a screen printing electrode modified by nano porous carbon, and the current response of the electrode is detected, so that the content of heavy metals in the milk powder is detected.
In said step 1.2), the concentration of hydrogen peroxide is 30% by weight;
in the step 1.3), the concentration of hydrochloric acid was 36.5% by weight, and the concentration of acetic acid was 50% by weight.
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.
in the step 1.4), the pH value is adjusted to 4.5 by 0.1mol/L of sodium hydroxide.
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 Nano porous carbon powder NPC is dispersed into ethanol solution, ultrasonic treatment is carried out, and insoluble substances in the mixed solution are removed; centrifuging again, removing the precipitate, centrifuging the supernatant again, collecting the precipitate, drying to obtain powder, dispersing the powder into dimethyl formamide DMF (dimethyl formamide) for modifying an electrode to obtain a DMF-NPC dispersion liquid;
2.1.2 Preparing a screen printing electrode SPE, adding the screen printing electrode SPE into ultrapure water for ultrasonic activation, and drying by using nitrogen to obtain an activated screen printing electrode;
2.1.3 DMF-NPC dispersion liquid is dripped and covered on a working area of the activated screen printing electrode, and the screen printing electrode modified by the nano porous carbon is obtained after drying.
2.1.4 Using a screen printing electrode as an electrochemical sensor to extract and detect the content of heavy metals in the milk powder.
In the step 2.1.1), the volume ratio of the ethanol to the water in the ethanol solution is 1:1.
In the step 2.1.1), the volume of the DMF-NPC dispersion liquid is 6 mu L, and the concentration is 1mg/mL.
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 rapidly 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.
The invention has the beneficial effects that:
firstly, the invention extracts the heavy metals in the milk powder, and has simple operation process, low cost and short time consumption;
secondly, after the successful extraction of heavy metal in milk powder is realized, the prepared nano porous carbon modified screen printing electrode is used for detecting the content of the heavy metal, and the constructed electrochemical sensor can realize the high selectivity and high sensitivity detection of heavy metal ions due to the inherent properties of the nano porous carbon, such as high surface area, chemical stability, low cost, rapid electron transfer, rapid charge conduction, efficient mass transfer, high electroactive surface, large adsorption capacity and the like.
The invention realizes the integrated technology of extraction and content determination of heavy metals in infant milk powder, opens up a new processing mode for the development of infant milk powder quality detection, and can provide good reference for the quality evaluation of the infant milk powder sold in the market at present.
Drawings
FIG. 1 is a square wave anodic stripping voltammetry current response curve diagram of a bare screen printing electrode and a nanoporous carbon modified screen printing electrode to Pb (II) and Cd (II) in the invention;
FIG. 2 is a volume optimization diagram of a nanoporous carbon modified screen printing electrode for detecting parameters of DMF-NPC dispersion liquid for Pb (II) and Cd (II) in the invention;
FIG. 3 is a graph of the concentration optimization of Bi (III) in buffer solution for detecting parameters of Pb (II) and Cd (II) by using the nanoporous carbon modified silk-screen printing electrode;
FIG. 4 is a graph of optimizing the deposition time of the nanoporous carbon modified screen printing electrode for Pb (II) and Cd (II) detection parameters in the invention;
FIG. 5 is a diagram of pH value optimization of detection parameters of Pb (II) and Cd (II) by a nanoporous carbon modified silk-screen printing electrode in the invention;
FIG. 6 is a dissolution curve diagram of a nanoporous carbon modified silk-screen printing electrode for Pb (II) and Cd (II) detection in the invention;
FIG. 7 is a standard curve diagram of Pb (II) detection by a nanoporous carbon modified screen-printed electrode in the invention;
FIG. 8 is a standard curve diagram of Cd (II) detection by a nanoporous carbon modified screen-printed electrode in the invention;
FIG. 9 is a selective detection diagram of a nanoporous carbon modified screen printing electrode for Pb (II) and Cd (II) in the invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the embodiments.
The embodiment of the invention is as follows:
example 1
And the bare screen printing electrode and the nano porous carbon modified screen printing electrode perform electrochemical response on heavy metal ions.
A bare screen printing electrode and a nanoporous carbon-modified screen printing electrode were prepared in advance. 10mL of acetic acid buffer solution is added into the electrochemical cell as electrolyte, and 1mgL is added -1 Promoting the reduction process of heavy metal ions, and adding 30 mu g L of Bi (III) -1 The current responses of the two electrodes to heavy metal ions are detected by square wave anodic stripping voltammetry, and the result is shown in figure 1. For the bare screen-printed electrode, no significant voltammetric peak was observed, but significant voltammetric peaks were observed on the nanoporous carbon modified screen-printed electrode, approximately at-0.85V and-0.6V, indicating that in the nanoporous carbon modified screen-printed electrodeThe nano-porous carbon film formed on the surface of the screen printing electrode has rich surface area and higher conductivity, which is beneficial to the rapid electron transfer between the heavy metal ions and the surface of the screen printing electrode modified by the nano-porous carbon. Therefore, the detection of heavy metal by modifying the nano porous carbon on the surface of the screen printing electrode is feasible.
Example 2
And (3) selectively detecting the heavy metal by the nano porous carbon modified screen printing electrode.
A nanoporous carbon modified screen-printed electrode was prepared in advance. 10mL of acetic acid buffer solution is added into the electrochemical cell as electrolyte, and 1mgL is added -1 And 30. Mu.g L of Bi (III) are added -1 Pb (II) and Cd (II), observing the change of response current by square wave anodic stripping voltammetry, and detecting the concentration of heavy metal to be about 30 mu gL -1 That is, the concentration of Pb (II) and Cd (II);
after the current is stabilized, respectively adding Ca into acetic acid buffer solution added with Pb (II) and Cd (II) 2+ 、Zn 2+ 、Mg 2+ 、Fe 3+ Fructose, glucose, sucrose, glycine and glutamic acid, and the change in response current, i.e., the change in dissolution profile after the addition of the interferents, was observed again, as shown in fig. 9, for this selective assay, the concentration of heavy metals was always about 30 μ gL after the addition of different interferents -1 The interference of the interferents on the electrochemical sensor using the screen-printed electrode modified by the nanoporous carbon as well as the detection of Pb (II) and Cd (II) is very small, and the screen-printed electrode modified by the nanoporous carbon shows excellent selectivity and can be used for determining the content of heavy metal in a complex sample, such as milk powder.
Example 3
Extracting heavy metals from infant milk powder and detecting the concentration of the heavy metals.
A screen-printed electrode decorated with nanoporous carbon is prepared in advance. Randomly selecting 5 infant milk powders of different brands, preparing the milk powders into liquids to be detected, adding 10mL of the liquids to be detected into an electrochemical cell, and adding the five liquids to be detected into an electrochemical cell during detectionInto 1mgL -1 And 30. Mu.g L of Bi (III) -1 The Pb (II) and Cd (II) were measured by square wave anodic stripping voltammetry with response to current changes, and the results are shown in Table 1, where the concentrations of the heavy metals were about 30. Mu.gL -1 The concentration of Pb (II) and Cd (II) shows that the detection of the concentration of the heavy metal in the milk powder by using the screen printing electrode modified by the nano porous carbon has higher accuracy; and the heavy metal ions adsorbed on the surface of the screen printing electrode modified by the nanoporous carbon are recovered, the recovery rates of Cd (II) in five solutions to be detected are 71.5%, 86.1%, 93.2%, 77.9% and 105.2%, and the recovery rates of Pb (II) are 110.4%, 113.6%, 103.5%, 120.5% and 128.6%, respectively. During the detection, the detection limit of Pb (II) is 0.1, and the detection limit of Cd (II) is 1.67.
TABLE 1
Figure BDA0003374807120000051
In a specific experiment, in order to ensure better detection performance, relevant heavy metal detection parameters are optimized, including the volume of DMF-NPC dispersion liquid, the concentration of Bi (III) in buffer liquid, deposition time and the pH value of the buffer liquid.
The volume of the DMF-NPC dispersion was optimized during the experiment. In the prepared DMF-NPC dispersion liquid, if the NPC content of the nano porous carbon powder is insufficient, the optimum performance cannot be achieved, and if the NPC content is excessive, the mutual accumulation of particles can cause the reduction of the conductivity of the surface of the screen printing electrode modified by the nano porous carbon; when 6 μ L of DMF-NPC dispersion was deposited on the nanoporous carbon modified screen-printed electrode work area, the maximum peak current appeared during detection in response to current change observed by square wave anodic stripping voltammetry, as shown in fig. 2, when more DMF-NPC dispersion was dispensed, reproducibility became poor. Therefore, 6. Mu.L 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 solution is increased continuously, and the general trend of stripping current is firstly along with the increase of the concentration of Bi (III)Ascending and descending, when adding 1mgL -1 And when the concentration of Bi (III) is too high, a thick film is formed, so that the process of metal enrichment is hindered, as shown in fig. 3, the alloy formed by heavy metal ions and Bi (III) promotes the deposition process of Pb (II) and Cd (II). Therefore, bi (III) is selected to be 1mgL in the experiment -1 And (6) detecting.
The pH value is optimized during the experiment. When the pH of the acetate buffer was increased from 4 to 4.5, the current intensity was observed to increase in response to the change in current by square-wave anodic stripping voltammetry, and after continuing to increase the pH, the current intensity showed a tendency to decrease, as shown in fig. 5, which may be caused by the hydrolysis of Bi (III) in the acetate buffer at higher pH. Therefore, the acetic acid buffer solution with the pH value of 4.5 is used for detection in the experiment; the pH values of the solutions to be tested, which were prepared from milk powder during the experiment, were also adjusted to 4.5.
The deposition time was optimized during the experiment. With the increase of the deposition time, the current is gradually increased by observing the change of the response current through the square wave anodic stripping voltammetry, and after 150 seconds, the content of the heavy metal enriched on the nano porous carbon modified screen printing electrode reaches saturation, and as shown in fig. 4, the current slightly changes. Therefore, 150 seconds of deposition was selected for detection in the experiment.
During the experiment, a standard curve for detecting Pb (II) and Cd (II) is established by using a square wave anodic stripping voltammetry method. By adopting a standard addition method, bi (III) is 1mgL -1 Respectively adding Pb (II) and Cd (II) (1. Mu.g L) with different concentrations into the acetic acid buffer solution -1 、3μgL -1 、5μgL -1 、10μgL -1 、20μgL -1 、30μgL -1 、40μgL -1 、50μgL -1 、60μgL -1 、70μgL -1 ) A dissolution curve was obtained as shown in fig. 6, and a standard curve was obtained by fitting the dissolution current response curve, and an equation between the heavy metal concentration and the dissolution response current was constructed as shown in fig. 7 and 8. From the figure, it can be seen that the screen-printed electrode modified by the nano porous carbon is used as an electrochemical sensor and represents heavy metal ionsHas excellent electrocatalytic capacity, good linear response range and high sensitivity. The dissolution response current and the concentration of the heavy metal ions have a good linear relation, and the linear equation is as follows: I.C. A pb ＝0.01772C pb +0.24964，I cd ＝0.03958C cd 0.12592 with correlation coefficients of 0.9884 and 0.99577, respectively. In the experiment, the content of heavy metal in the infant milk powder is obtained by using a linear equation.

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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