阅读说明：本技术 一种用于水产干制食品中重金属的检测方法 (Detection method for heavy metals in aquatic product dried food ) 是由 曹峰 于 2020-07-20 设计创作，主要内容包括：本发明涉及食品检测技术领域,具体是涉及一种用于水产干制食品中重金属的检测方法,通过使用电化学沉积法制备石墨烯/Bi/Nafion复合材料,并将其作为工作电极用于检测消解液中的重金属Pb、Cd的痕量；和使用微波辐射法制备Au/石墨烯复合材料,并将其作为工作电极用于检测消解液中的重金属Hg的痕量的方法；利用阳极溶出伏安法测定干制水产品中重金属的痕量,相较于传统的汞电极,本发明设计的电极为“环境友好型”电极,对环境无二次污染；且本发明设计的检测方法与传统的光谱检测法相比,操作简单、分析时间短、仪器制备成本低的特点,因此本发明对干制水产中重金属的检测而言具有良好的应用前景。(The invention relates to the technical field of food detection, in particular to a detection method for heavy metals in aquatic product dried food, which comprises the steps of preparing a graphene/Bi/Nafion composite material by using an electrochemical deposition method, and using the graphene/Bi/Nafion composite material as a working electrode for detecting trace amounts of heavy metals Pb and Cd in digestion liquid; and a method for preparing the Au/graphene composite material by using a microwave radiation method and using the Au/graphene composite material as a working electrode for detecting the trace amount of heavy metal Hg in the digestion solution; the trace amount of heavy metal in the dried aquatic product is measured by using an anodic stripping voltammetry, and compared with the traditional mercury electrode, the electrode designed by the invention is an environment-friendly electrode, and has no secondary pollution to the environment; compared with the traditional spectrum detection method, the detection method designed by the invention has the characteristics of simple operation, short analysis time and low instrument preparation cost, so the method has good application prospect for detecting the heavy metal in the dried aquatic product.)

1. A method for detecting heavy metals in aquatic product dried food is characterized by mainly comprising the following steps:

s1 sample pretreatment

After the sample is collected, cleaning with deionized water, and infiltrating; taking soft tissue part from shellfish, removing head and shell from shellfish, taking edible part from fish, removing head, tail and bony spur from fish; respectively stirring and homogenizing the treated samples, placing the samples into sample cups, numbering and storing at-20 ℃;

s2 digestion treatment

Pretreatment for determination of S21, Pb and Cd

Weighing a quantitative pretreated sample, placing the sample in a digestion tank, adding MOS-grade nitric acid, carrying out constant-temperature heating treatment, cooling, and adding 30% H₂O₂Solution, after complete reaction, microwave digestion is carried out;

s22 pretreatment for Hg measurement

Weighing a quantitative pretreated sample, placing the sample in a digestion tank, adding MOS-grade nitric acid, standing for 24 hours, and then performing microwave digestion;

s3, acid-expelling and volume-fixing: respectively carrying out acid removal on digestion solutions in the digestion tanks for measuring Pb, Cd and Hg, and then carrying out constant volume treatment;

s4 preparation of working electrode

S41, preparing the graphene/Bi/Nafion composite material by using an electrochemical deposition method, and using the graphene/Bi/Nafion composite material as a working electrode for detecting the trace amount of heavy metals Pb and Cd in the digestion solution;

s42, preparing an Au/graphene composite material by using a microwave radiation method, and using the Au/graphene composite material as a working electrode for detecting the trace amount of heavy metal Hg in the digestion solution;

and S5, detecting trace amounts of heavy metals Pb, Cd and Hg in the digestion solution by using a stripping voltammetry method.

2. The method for detecting the heavy metals in the aquatic product dried food as claimed in claim 1, wherein the specific method for acid-expelling and volume-fixing in step S3 is as follows:

s31, Pb determination: opening the digestion tank, performing acid-dispelling treatment on the digestion solution at 140-160 ℃, cooling, and performing constant volume with ultrapure water for later use;

s32, Cd determination: opening the digestion tank, removing acid from the digestion solution at the temperature of 140-160 ℃ until the digestion solution is dried, and fixing the volume for later use by using a nitric acid solution;

s33, Hg determination: and (3) heating the digestion tank at 80 ℃, removing brown gas, taking out the digestion tank, and fixing the volume of the digestion solution by using ultrapure water for later use.

3. The method for detecting the heavy metals in the aquatic dry food as claimed in claim 1, wherein the graphene/Bi/Nafion composite material electrode in the step S41 is prepared by the following specific method:

s411, ultrasonically dispersing graphene in a Nafion ethanol solution to prepare a suspension; after polishing the glassy carbon electrode, sequentially performing 1: 1 HNO₃Performing ultrasonic treatment in water for 5 min; dropwise adding the turbid liquid on the surface of a glassy carbon electrode, and evaporating at room temperature to obtain a graphene/Nafion modified electrode;

s412, taking the graphene/Nafion modified electrode as a working electrode, taking Ag/AgCl (3M NaCl) as a reference electrode, taking a platinum wire as a counter electrode, and putting the three-electrode system into an electrolytic cell containing a standard bismuth solution and metal ions to be detected;

s413, setting an enrichment voltage of-1.3V, after the enrichment time is 100S, standing the solution for 15S, and scanning the electrode potential from the negative positive potential direction between-1.3V and 0.0V to ensure that the metal deposited on the surface of the electrode is oxidized and dissolved out again;

and S414, after the dissolution is finished, setting the cleaning potential to be +0.3V, and cleaning the residual metal deposited on the surface of the electrode to obtain the graphene/Bi/Nafion composite material electrode.

4. The method for detecting the heavy metals in the aquatic dry food as claimed in claim 1, wherein the specific preparation method of the Au/graphene composite electrode in the step S42 is as follows:

s421, adding the graphene subjected to reflux purification by concentrated nitric acid into HAuCl with the mass concentration of 1.2%₄In the solution, placing in a microwave oven for heating for 1.5min after ultrasonic dispersion and dilution with distilled water;

s422, adding sodium acetate with the mass concentration of 1.2% into the hot solution, and performing microwave radiation for 4 min;

s423, cooling, centrifuging and filtering the suspension obtained in the step S422 to obtain a solid product, and drying the solid product at 130 ℃ for 20 hours to obtain the Au/graphene composite material;

s424, ultrasonically dispersing the Au/graphene composite material in a DMF (dimethyl formamide) solution to prepare a suspension; after polishing the glassy carbon electrode, sequentially performing 1: 1 HNO₃Performing ultrasonic treatment in water for 5 min; and dropwise adding the turbid liquid on the surface of a glassy carbon electrode, and evaporating at room temperature to obtain the Au/graphene composite material electrode.

Technical Field

The invention relates to the technical field of food detection, in particular to a detection method for heavy metals in aquatic product dried food.

Background

Food quality and safety issues have penetrated all aspects of society and are a focus topic in recent years. Heavy metals are cumulative pollutants that are widely present in ecological environments and, once ingested by animals, can be progressively transported and enriched through the food chain and, under certain conditions, can be converted into more toxic metal-organic compounds that affect human health. Aquatic products have strong enrichment capacity on heavy metals, particularly elements such as lead, cadmium, mercury, arsenic and the like, and particularly shellfish organisms. Therefore, the detection of the heavy metals in the aquatic products is carried out, and the method has important significance for evaluating the edible safety of the aquatic products.

At present, a plurality of methods for measuring the content of heavy metals in aquatic products exist, and commonly used measuring methods include an atomic absorption method, an inductively coupled plasma emission spectrometry, a spectrophotometry and the like. However, the former two devices are expensive, the testing cost is high, and the latter is not high in sensitivity and complicated in operation.

In view of the above problems, the invention aims to design a detection method which has the advantages of simple equipment, low price, simple and convenient operation, quick analysis, small reagent dosage and repeated measurement, and has practical significance for trace detection of heavy metals in dried aquatic products.

Disclosure of Invention

Objects of the invention

Generally, electrodes used by anodic stripping voltammetry are mainly mercury membrane electrodes or mercury drop electrodes, mercury is a toxic heavy metal element, and is easy to pollute the environment when being frequently used, and the electrodes are limited in many areas and countries, even the electrodes are forbidden to be used. Therefore, new electrodes are being studied to replace the mercury electrodes.

Second, the specific scheme design

In order to achieve the aim, the invention provides a detection method for heavy metals in aquatic product dried food, which greatly increases the detection speed, reduces the detection time and improves the detection sensitivity for trace heavy metals in aquatic products compared with the existing dried aquatic product detection method, and the specific technical scheme is as follows:

1. sample pretreatment

After the sample is collected, cleaning with deionized water, and infiltrating; taking soft tissue part from shellfish, removing head and shell from shellfish, taking edible part from fish, removing head, tail and bony spur from fish; and (3) stirring the processed sample finely, homogenizing, placing in a sample cup, numbering and storing at-20 ℃.

2. Digestion treatment

21. Pretreatment for Pb and Cd determination

Weighing a quantitative pretreated sample, placing the sample in a digestion tank, adding MOS-grade nitric acid, carrying out constant-temperature heating treatment, cooling, and adding 30% H₂O₂Solution, and microwave digestion is carried out after complete reaction.

22. Pretreatment for Hg measurement

Weighing a quantitative pretreated sample, placing the sample into a digestion tank, adding MOS-grade nitric acid, standing for 24 hours, and then performing microwave digestion.

3. Acid-expelling constant volume

31. And (3) Pb determination: and opening the digestion tank, performing acid-dispelling treatment on the digestion solution at 140-160 ℃, cooling, and performing constant volume with ultrapure water for later use.

32. And (3) Cd determination: and opening the digestion tank, removing acid from the digestion solution at the temperature of 140-160 ℃ until the digestion solution is dried, and fixing the volume for later use by using a nitric acid solution.

33. And (3) measuring Hg: and (3) heating the digestion tank at 80 ℃, removing brown gas, taking out the digestion tank, and fixing the volume of the digestion solution by using ultrapure water for later use.

4. Preparation of working electrode

In 2000, data show that the bismuth membrane electrode is used for replacing a mercury membrane electrode to carry out anodic stripping voltammetry and cathodic stripping voltammetry measurement, the bismuth membrane electrode has the advantages of high sensitivity, good reproducibility, complete stripping peak separation, wide cathode voltage range, no interference of dissolved oxygen and the like, and bismuth ions are environment-friendly metal elements and have no secondary pollution to the environment.

However, the bismuth membrane electrode generally uses a glassy carbon electrode as a substrate, and when the bismuth membrane electrode is directly detected by using a bare glassy carbon electrode, the surface of the electrode is easily affected by interfering substances in a solvent, so that the electrode is passivated, and the reproducibility and the sensitivity are reduced. This is one of the most important problems faced in electrochemical detection, and the key to solving this problem is to find a substance that eliminates or reduces this interference.

41. Nafion is a high ion exchange polymeric membrane that is stable both thermally and chemically, has the structure of sodium sulfonate and dissociates in water. Because the affinity between metal ions in the test solution and Nafion is stronger than that between Nat and Nafon, the Nafion modified electrode and the metal ions can generate ion exchange in the test solution, and the purpose of enriching the metal ions is achieved by utilizing the ion exchange. In addition, the Nafion polymer has small impedance and small solubility in water, can well eliminate the influence of interference substances in a test solution, and is a good electrode modification material.

Therefore, the graphene/Bi/Nafion composite material is prepared by using an electrochemical deposition method, and is used as a working electrode for detecting the trace amount of heavy metals Pb and Cd in the digestion solution.

The preparation method comprises the following specific steps:

411. ultrasonically dispersing graphene in a Nafion ethanol solution to prepare a turbid liquid; after polishing the glassy carbon electrode, sequentially performing 1: 1 HNO₃Performing ultrasonic treatment in water for 5 min; and dropwise adding the turbid liquid on the surface of a glassy carbon electrode, and evaporating at room temperature to obtain the graphene/Nafion modified electrode.

412. The graphene/Nafion modified electrode is used as a working electrode, Ag/AgCl (3M NaCl) is used as a reference electrode, a platinum wire is used as a counter electrode, and the three-electrode system is placed in an electrolytic cell containing standard bismuth solution and metal ions to be detected.

413. Setting an enrichment voltage of-1.3V, standing the solution for 15s after the enrichment time is 100s, and scanning the electrode potential from the negative positive potential direction between-1.3V and 0.0V to ensure that the metal deposited on the surface of the electrode is oxidized and dissolved out again.

414. And after the dissolution is finished, setting the cleaning potential to be +0.3V, and cleaning the residual metal deposited on the surface of the electrode to obtain the graphene/Bi/Nafion composite material electrode.

42. The Au/graphene composite material is prepared by using a microwave radiation method and is used as a working electrode for detecting the trace amount of heavy metal Hg in digestion solution, and the specific preparation steps are as follows:

421. adding graphene subjected to reflux purification of concentrated nitric acid into HAuCl₄Dispersing the solution (1.2%) by ultrasonic, diluting with distilled water, and heating in a microwave oven for 1.5 min;

422. adding sodium acetate (1.2%) into the hot solution, and performing microwave radiation for 4 min;

423. cooling, centrifuging and filtering the suspension obtained in the step 422 to obtain a solid product, and drying the solid product at 130 ℃ for 20 hours to obtain an Au/graphene composite material;

424. ultrasonically dispersing the Au/graphene composite material in a DMF (dimethyl formamide) solution to prepare a turbid liquid; after polishing the glassy carbon electrode, sequentially performing 1: 1 HNO₃Performing ultrasonic treatment in water for 5 min; and dropwise adding the turbid liquid on the surface of a glassy carbon electrode, and evaporating at room temperature to obtain the Au/graphene composite material electrode.

5. The trace amounts of heavy metals Pb, Cd and Hg in the digestion solution are detected by using a stripping voltammetry, and the basic principle of the detection is as follows:

under a certain external negative voltage, bismuth ions in an electrolyte solution and metal ions to be detected are simultaneously reduced and deposited on the surface of an electrode, a bismuth film is easy to form an alloy with lead, cadmium and zinc, and reactions (1) and (2) are simultaneously carried out: after the electrodeposition process is finished, the working electrode scans from the direction of negative positive potential, and then the deposited metal is oxidized and dissolved out again from the electrode, and the reaction (3) occurs, which is a quick process, so that a large dissolution current is obtained. The reaction equation for the electrode surface is as follows:

Bi³⁺+3e→Bi⁰(1)

Mⁿ⁺+ne→M(Bi) (2)

M(Bi)-ne→Mⁿ⁺+Bi (3)

compared with the existing detection method for heavy metals in dried aquatic products, the method has the beneficial effects that:

(1) compared with the traditional spectrum detection method, the detection method designed by the invention has the advantages of simple operation, short analysis time and low instrument preparation cost.

(2) Compared with the traditional mercury electrode, the electrode designed by the invention is an environment-friendly electrode, has no secondary pollution to the environment, and has good application prospect for detecting heavy metals in dried aquatic products.

Drawings

FIG. 1 is a voltammogram of trace Pb and Cd in dried aquatic products detected by a graphene/Bi/Nafion composite material electrode of the invention;

FIG. 2 is a voltammogram of the Au/graphene composite material electrode for detecting trace Hg in dried aquatic products.

In fig. 1: the dissolution curve is a dissolution voltammogram of the sample (a) and the Pb and Cd continuously added standard solution (b → d) from bottom to top;

in fig. 2: a is blank, b is 0.5, c is 1.0, d is 1.5, e is 2.0, f is 3.0, g is 4.0, h is the dissolution voltammogram at 5.0nM Hg.

Detailed Description

To further illustrate the manner in which the present invention is made and the effects achieved, the following description of the present invention will be made in detail and completely with reference to the accompanying drawings.