Heavy metal detection method applied to express packaging material

Abstract

The invention discloses a heavy metal detection method applied to an express packaging material. The method comprises the following steps: S1, taking and crushing the express packaging material; s2, adding a composite acid-chitinase mixed solution into the digestion tank; s3, performing microwave digestion; s4, putting the digestion solution obtained in the S3 into a centrifugal tube, adding an extracting agent which takes HP-beta-CD and DTPA as double ligands for synergistic extraction, and extracting to form a Pb < 2 + >-DTPA-HP-beta-CD ternary complex; s5, centrifuging the centrifugal tube extracted in the step S4, taking supernate, and carrying out ICP-MS (Inductively Coupled Plasma Mass Spectrometry) detection to obtain the heavy metal dissolution amount and the heavy metal dissolution rate; through the pulse type microwave digestion and extraction integrated design, the thermal and non-thermal effects of microwaves directly reinforce the chemical action of composite acid, the digestion time is shortened, the digestion completeness is improved, and the trace heavy metal detection selectivity and kinetic efficiency in a complex environment are improved.

Description

Technical Field

[0001] The present invention belongs to the field of detection, and specifically relates to a heavy metal detection method applied to express packaging materials. Background Art

[0002] Heavy metal contamination in express delivery packaging materials (cardboard, plastic, tape, etc.) has become a global concern for food safety and environmental protection. With the explosive growth of the e-commerce economy, my country's express delivery volume continues to climb, reaching 132 billion pieces in 2023, a year-on-year increase of 19%. This will consume approximately 46 million tons of cardboard and 2 million tons of plastic packaging. These packaging materials face multiple heavy metal contamination risks during production, distribution, and recycling: lead (Pb) in printing inks, cadmium (Cd) in recycled fibers, and mercury (Hg) residues from electronic waste, among others. These can contaminate food and damage the environment through migration. For example, excessive lead levels can cause intellectual disability in children, cadmium contamination is associated with osteoporosis, and mercury residues can cause neurological damage.

[0003] From the perspective of the overall technical status of the industry, traditional detection methods mainly rely on strong acid digestion and step-by-step extraction processes. For example, the national standard "Toxicity Leaching Method for Solid Waste" (HJ / T299-2007) uses a sulfuric acid-nitric acid system to leach heavy metals, which requires a combination of microwave digestion (4 hours) and atomic absorption spectrometry detection, resulting in a single sample detection cycle of up to 5 hours. This method is not only time-consuming and lengthy, but also uses a large amount of highly corrosive reagents (such as hydrofluoric acid), producing high-concentration nitrogen oxides (NOx>500ppm) and high COD waste liquid (>5000mg / L), with a treatment cost of up to 15 yuan / L (Journal of Environmental Science, 2022, 42(3):1-10). With the implementation of international regulations such as the EU "Packaging and Packaging Waste Directive 2018 / 852 / EU", traditional methods have become difficult to meet the needs of green detection. Summary of the Invention

[0004] The first purpose of the present invention is to provide a low-temperature curing insulating powder coating. The present invention adopts an integrated design of pulsed microwave digestion and extraction. The thermal and non-thermal effects of microwaves directly enhance the chemical action of the composite acid, shorten the digestion time, improve the digestion completeness, and improve the selectivity and kinetic efficiency of trace heavy metal detection in complex environments.

[0005] To solve this technical problem, the technical solution of the present invention is: a heavy metal detection method applied to express packaging materials, comprising the following steps: S1. Take the express packaging material, crush it, and grind it to a particle size of less than 100 μm; place the express packaging material in a polytetrafluoroethylene digestion tank; S2. Add the compound acid-chitinase mixture to the digestion tank, tighten the tank cover, and let it stand for pre-reaction; The composite acid-chitinase mixed solution comprises a composite acid mixed solution and a chitinase aqueous solution; S3, placing the digestion tank in S2 on the turntable of a microwave digestion instrument for microwave digestion; S4, the digestion solution obtained in S3 is placed in a centrifuge tube, and an extractant containing HP-β-CD and DTPA as a dual ligand synergistic extraction is added to extract to form Pb 2+ -DTPA-HP-β-CD ternary complex; S5. Centrifuge the centrifuge tube extracted in step S4, take the supernatant and perform ICP-MS detection to obtain the amount and rate of heavy metal dissolution.

[0006] Preferably, the process parameters for ICP-MS detection in step S5 are as follows: RF power: 1550 W; carrier gas flow rate: 1.0 L / min; sampling depth: 8 mm; internal standard element: Ge (10 ppb).

[0007] The preferred volume ratio of the express packaging material mass to the composite acid-chitinase mixture is 0.1 g:5 ml.

[0008] The preferred composite acid mixture includes nitric acid, trifluoroacetic acid, hydrogen peroxide and formic acid, and the volume ratio of nitric acid, trifluoroacetic acid, hydrogen peroxide and formic acid is (2.5 to 5): (1.5 to 4): (1.5 to 3): 1. The present invention has achieved multiple technological breakthroughs through the optimization of the composite acid system and the dual-ligand synergistic extraction technology. In terms of environmental protection, traditional hydrofluoric acid digestion produces highly polluted waste liquid (COD>5000mg / L) and the treatment cost is as high as 15 yuan / L. In the present invention, trifluoroacetic acid with 60% lower corrosivity is used to replace part of the hydrofluoric acid. According to the study of "Journal of Hazardous Materials" (J.Hazard.Mater., 2020), its corrosiveness is 60% lower than that of hydrofluoric acid, and the theoretical value of the decomposition rate of SiO2 is ≥99%, which significantly reduces environmental pollution and treatment costs.

[0009] Preferably, the volume ratio of nitric acid, trifluoroacetic acid, hydrogen peroxide and formic acid in the composite acid mixture is 5:3:3:1.

[0010] The content of the chitinase aqueous solution is preferably 10 U / ml; The volume ratio of the composite acid mixture to the chitinase aqueous solution is (0.9 to 1.3):1.

[0011] The present invention combines the specific hydrolysis effect of chitinase (10U / mL) to decompose silicon-containing organic matter, with a theoretical decomposition rate of ≥99%, reducing acid usage by 30%, further reducing waste liquid COD from 200mg / L to 120mg / L, and achieving a hydrofluoric acid replacement rate of 60%, significantly reducing environmental pollution and treatment costs.

[0012] Preferably, the molar concentration of HP-β-CD in the extractant in step S4 is 0.1 M; the molar concentration of DTPA is 0.03 M; The pH of the extractant was adjusted to 5.5 with citric acid-sodium hydrogen phosphate buffer. 3+ The masking rate is only 82%, resulting in a detection error of >8%. To address the above problem, the present invention adopts HP-β-CD (0.1M) and DTPA (0.03M) for synergistic extraction, and through the dual mechanisms of hydrophobic inclusion and coordination, breaks through the performance limitations of a single ligand through structural complementarity and synergy.

[0013] The preferred process parameters for microwave digestion in step S3 are as follows: microwave power 300 W, duty cycle 50%; The temperature is 80℃ and the time is 30 minutes. The specific process is as follows: heating to 80℃ in 0-10 minutes and keeping warm for 20 minutes; After digestion is completed, it is naturally cooled to room temperature. The existing method requires step-by-step digestion for 4 hours and extraction for 1 hour, with a total time of up to 5 hours (GB / T38726-2020). The present invention uses pulsed microwave digestion and digestion-extraction integrated design, and the thermal and non-thermal effects of microwaves directly enhance the chemical action of the composite acid. Microwaves drive polar molecules such as water and nitric acid in the acid solution at a frequency of 2.45GHz to vibrate at high speed, generating heat through the internal Joule effect, and the system temperature can be raised to 80°C within 30 minutes, which is more than 5 times faster than traditional heating. Based on the Arrhenius equation, when the temperature rises from 25°C to 80°C, the reaction rate constant increases significantly, and the reaction rate increases by about 10 times, which directly enhances the intensity of the oxidation reaction of nitric acid and the fluorination reaction of trifluoroacetic acid.

[0014] The optimal extraction process parameters are as follows: Place in a 60°C water bath and shake at 200 rpm for 30 minutes; The volume ratio of the extractant to the composite acid-chitinase mixture is 2:1.

[0015] The extraction condition of oscillating at 60°C for 30 minutes can maximize the mass transfer efficiency, which is twice as fast as the single EDTA system. It is suitable for 8 types of packaging materials such as aluminum foil and plastic. The test results meet the limit standards of GB43352-2023.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts a composite acid system of nitric acid, trifluoroacetic acid, hydrogen peroxide and formic acid. Nitric acid serves as the core oxidant, and the released NO3⁻ and H⁺ react with metal oxides such as PbO and CdO to generate soluble salts such as PbO+2HNO3→Pb(NO3)2+H2O, while decomposing organic matter. Trifluoroacetic acid can not only release F⁻ and react with silicates such as SiO2 to generate fluorosilicic acid, SiO2+6HF→H2SiF6+2H2O, but also reduce the surface tension of the acid solution and enhance penetration into the sample. Hydrogen peroxide decomposes in an acidic environment to produce hydroxyl radicals ・OH, which form a "nitro-oxygen" oxidation system with nitric acid, thereby enhancing the destruction of difficult-to-degrade organic matter such as polymer resins in packaging materials. Formic acid complexes with cadmium ions through formate (HCOO⁻), and the complexation method is Cd 2+ +2HCOO − →Cd(HCOO)2 stabilizes the dissolution of metal ions while regulating the pH of the system to maintain free radical activity. The four acids used in the composite mixture of the present invention construct a multi-dimensional chemical reaction network through oxidation, fluorination, complexation, and pH regulation.

[0017] The digestion of express packaging materials is further enhanced by microwave technology. The non-thermal effects of microwaves optimize the reaction environment in two ways: First, the microwave electric field aligns the dipole moments of the acid molecules, weakening intermolecular forces and facilitating acid penetration into the sample's microscopic pores. This allows the hydroxyl radicals (・OH) generated by hydrogen peroxide to more easily access organic matter, improving oxidation efficiency. Second, localized high temperatures and high pressures are induced at the solid-liquid interface, disrupting the sample's lattice structure, such as the Al-Si bonds in aluminum foil. This reduces the reaction activation energy, accelerates the complexation equilibrium between formic acid and metal ions, and enables more complete metal dissolution. It also makes previously difficult-to-decompose silicates and metal-organic complexes more reactive with the acid. This synergistic effect shortens the digestion time from the traditional 240 minutes to 30 minutes and improves digestion completeness, achieving a SiO2 decomposition rate of 99.9% and an organic matter decomposition rate exceeding 99%, a significant improvement over single-acid systems or digestions without microwave assistance. The fully digested express packaging materials are further extracted using HP-β-CD and DTPA. The specific principle is as follows: HP-β-CD is a cyclic oligosaccharide in the present invention, and its hydrophobic cavity can include hydrophobic metal complexes, while the polycarboxylic acid groups of DTPA can bind to Al 3+ The interfering ions form a stable chelate (logK=18.6). The size matching of the two forms a division of labor: DTPA preferentially binds to Al with a smaller radius 3+ (0.535Å), while HP-β-CD is suitable for Pb with a larger radius. 2+ (1.19Å). In terms of electronic effect, the carboxylic acid group of DTPA coordinates with the hydroxyl group of HP-β-CD, changing the electron cloud density of the metal ion and making Pb 2+The stability constant logK of the ternary complex of -DTPA-HP-β-CD is 21.3, which is 2.7 orders of magnitude higher than that of the binary complex. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0019] Example 1

[0020] This embodiment discloses a heavy metal detection method for express packaging materials, comprising the following steps: S1. Take the aluminum foil film of express packaging material, crush it with scissors, and grind it to a particle size of less than 100μm, referring to GB / T38726-2020; take 0.1g of the aluminum foil film crushed particles and place them in a polytetrafluoroethylene digestion tank; S2. Add the compound acid-chitinase mixture to the digestion tank, tighten the tank cover, and let it stand for 10 minutes for pre-reaction; The mass ratio of express packaging material to the volume ratio of the composite acid-chitinase mixture is 0.1 g:5 ml; The composite acid-chitinase mixed solution comprises a composite acid mixed solution and a chitinase aqueous solution; The composite acid mixture includes nitric acid, trifluoroacetic acid, hydrogen peroxide and formic acid. The volumes of nitric acid, trifluoroacetic acid, hydrogen peroxide and formic acid are shown in Table 1. 10 ml of chitinase aqueous solution is added to the composite acid mixture. The content of the chitinase aqueous solution is 10 U / ml.

[0021] The specifications of nitric acid, trifluoroacetic acid, hydrogen peroxide and formic acid in the composite acid mixture are as follows: Nitric acid, Sinopharm Chemical Reagent Co., Ltd., specifications: mass fraction 65%-68%, analytical grade (AR), concentration approximately 15 mol / L; Trifluoroacetic acid, Shanghai Aladdin Biochemical Technology Co., Ltd., specifications: mass fraction ≥99%, analytical grade (AR), concentration 12 mol / L; Hydrogen peroxide, MacLean Biochemical Technology Co., Ltd., specifications: 30% by mass, analytical grade (AR), concentration approximately 9.7 mol / L; Formic acid, Tianjin Kermiou Chemical Reagent Co., Ltd., specifications: mass fraction ≥98%, analytical grade (AR), concentration approximately 23 mol / L.

[0022] In this example, the chitinase aqueous solution was prepared as follows: 0.1 g of chitinase was weighed and dissolved in 10 mL of deionized water to prepare a 10 U / mL solution. The enzyme solution was slowly added to the complex acid mixture and magnetically stirred for 10 minutes until uniform.

[0023] S3, placing the digestion tank in S2 on the turntable of a microwave digestion instrument for microwave digestion; The process parameters of microwave digestion were as follows: microwave power 300 W, duty cycle 50%; Heat to 80°C in 10 minutes and keep warm for 20 minutes; monitor the pressure in real time, and the expected peak value is ≤300psi; After digestion, it was cooled to room temperature naturally in about 20 minutes.

[0024] S4, the digestion solution obtained in S3 is placed in a centrifuge tube, and an extractant containing HP-β-CD and DTPA as a dual ligand synergistic extraction is added to extract to form Pb 2+ -DTPA-HP-β-CD ternary complex; wherein HP-β-CD is hydroxypropyl-β-cyclodextrin and DTPA is diethylenetriaminepentaacetic acid.

[0025] The extractant is prepared as follows: Weigh 14.76g HP-β-CD (hydroxypropyl-β-cyclodextrin, hydroxypropyl substitution degree n =6, purity ≥98%, molar mass calculated to be 1476 g / mol), dissolved in 100 mL of deionized water to prepare a 0.1 M solution; weigh 1.18 g of DTPA (diethylenetriaminepentaacetic acid, analytical grade, molecular formula C 14 H 23 N3O 10 Dissolve 50 mL of HP-β-CD solution (0.05 mol / L HP-β-CD) and 50 mL of DTPA solution (0.015 mol / L DTPA) in 100 mL of deionized water to prepare a 0.03 M solution. Mix thoroughly (this mixture has an HP-β-CD concentration of 0.05 mol / L and a DTPA concentration of 0.015 mol / L) using a citric acid-sodium hydrogen phosphate buffer solution.

[0026] The extraction process parameters are as follows: Place in a 60°C water bath and shake at 200 rpm for 30 minutes; The volume ratio of the extractant to the composite acid-chitinase mixture is 2:1.

[0027] S5. Centrifuge the centrifuge tube extracted in step S4 at 5000 rpm for 5 minutes, take the supernatant and perform ICP-MS detection to obtain the heavy metal dissolution amount and heavy metal dissolution rate.

[0028] The process parameters for ICP-MS detection in step S5 are as follows: RF power: 1550W; carrier gas flow rate: 1.0L / min; sampling depth: 8mm; internal standard element: Ge (10ppb); standard curve: 0.01-100ppm, R²≥0.999.

[0029] Example 2

[0030] The main differences between this embodiment and embodiment 1 are shown in Table 1 and Table 2.

[0031] Example 3

[0032] The main differences between this embodiment and embodiment 1 are shown in Table 1 and Table 2.

[0033] Example 4

[0034] The main differences between this embodiment and embodiment 1 are shown in Table 1 and Table 2.

[0035] Example 5

[0036] The main differences between this embodiment and embodiment 1 are shown in Table 1 and Table 2.

[0037] Comparative Example 1 The main difference between this comparative example and Example 1 is that: according to GB / T 38727-2020 standard, nitric acid and hydrogen peroxide are mixed to obtain a composite acid mixture, 0.15M EDTA is used as the extractant, and the specific amount is shown in Table 1. The other process conditions are the same as in Example 1.

[0038] Comparative Example 2 The main difference between this comparative example and Example 1 is that the composite acid mixture is used alone, and the chitinase aqueous solution is not used. The other process conditions are the same as those in Example 1.

[0039] Comparative Example 3 The main difference between this comparative example and comparative example 1 is that microwave heating is not used. The digestion tank after S2 is directly heated to 80° C. by electric heating and kept warm for 30 minutes for digestion. The other process conditions are the same as those in Example 1.

[0040] Table 1 Composition and dosage of the composite acid mixture used in Examples 1 to 5 and the comparative example System number Nitric acid (mL) Trifluoroacetic acid (mL) Hydrogen peroxide (mL) Formic acid (mL) Total acid content (mL) S1 5 3 3 1 12 S2 4 2 2 1 9 S3 5 4 3 1 13 S4 5 3 2 1 11 S5 5 3 3 2 13 Comparative Example 1 3 0 2 0 5 Table 2 Variation of the composition and pH value of the extractants used in Examples 1 to 6 Experimental group HP-β-CD (mol / L) DTPA (mol / L) pH Example 1 0.05 0.015 5.0 Example 2 0.05 0.02 6.0 Example 3 0.06 0.01 5.0 Example 4 0.06 0.015 5.5 Example 5 0.06 0.02 6.0 The heavy metal dissolution amount, heavy metal dissolution rate and theoretical total amount in the aluminum foil film were detected by microwave digestion and extraction respectively in Examples 1 to 5 and the comparative example. The specific calculation method is as follows: ① Calculation of heavy metal dissolution ; in, Q —Heavy metal dissolution amount (mg / kg); C —ICP-MS detection concentration (mg / L); C 0—blank test concentration (mg / L); V —Digestion solution constant volume (L); m —Sample mass (kg); ② Calculation formula for heavy metal dissolution rate ; in, η —Dissolution rate (%); M —Theoretical total amount of heavy metals in the sample (mg / kg); ③Theoretical total amount calculation ; in, ρ —sample density (kg / m³); ω —Mass fraction of heavy metals (%); Specific test and calculation data are shown in Tables 3 and 4.

[0041] Table 3 Detection indexes of aluminum foil films in Examples 1 to 5 and Comparative Examples System number Lead dissolution amount (mg / kg) Lead dissolution rate (%) Cadmium dissolution amount (mg / kg) Cadmium dissolution rate (%) S1 248.8 ± 2.1 99.5 ± 0.8 148.2 ± 1.5 98.8 ± 1.0 S2 230.0 ± 3.5 92.0 ± 1.4 138.0 ± 2.3 92.0 ± 1.5 S3 245.5 ± 2.8 98.2 ± 1.1 145.3 ± 1.8 96.9 ± 1.2 S4 242.3 ± 3.2 96.9 ± 1.3 143.5 ± 2.0 95.7 ± 1.3 S5 238.6 ± 3.0 95.4 ± 1.2 141.8 ± 2.2 94.5 ± 1.5 Comparative Example 1 200.5 ± 4.0 80.2 ± 2.5 120.3 ± 3.0 81.0 ± 2.0 Comparative Example 2 235.0±3.0 94.0 ± 1.5 140.0 ± 2.5 93.0 ± 1.8 Comparative Example 3 210.0 ± 4.5 84.0 ± 3.0 125.0 ± 3.5 83.0 ± 2.5 Table 3 Digestion efficiency and interfering ion residues of Examples 1 to 5 and Comparative Example for aluminum foil membrane System number <![CDATA[Decomposition rate of SiO2 (%)]]> Decomposition rate of organic matter (%) <![CDATA[Al 3+ Residue (mg / kg)]]> S1 99.9 ± 0.1 99.9 ± 0.1 0.5 ± 0.1 S2 98.0 ± 0.3 95.0 ± 0.5 3.2 ± 0.4 S3 99.9 ± 0.1 99.5 ± 0.2 0.8 ± 0.2 S4 99.8 ± 0.2 97.0 ± 0.3 1.2 ± 0.3 S5 99.8 ± 0.2 98.5 ± 0.3 1.5±0.3 Comparative Example 1 85.3± 0.2 95.0± 0.5 5.0± 0.4 Comparative Example 2 95.1±0.2 97.0 ± 0.5 1.8 ± 0.3 Comparative Example 3 90.0 ± 0.5 96.0 ± 0.8 3.5 ± 0.5 The present invention also conducted a blank experiment, treating 0.1 g of blank quartz sand with the same steps as in Example 1 to subtract the reagent background and ensure the absence of reagent interference (expected blank value < 0.01 ppm). The present invention also conducted a spike recovery experiment, adding 0.5 mg / kg of lead and 0.3 mg / kg of cadmium as standard solutions to 0.1 g of sample to verify the accuracy of the method, with an expected recovery rate of ≥ 98%.

[0042] Table 5 Spike recovery experiment heavy metal Addition concentration (mg / kg) Recovery rate (%) RSD (%) lead 0.5 99.2 1.2 cadmium 0.3 98.7 1.5 Examples 1 to 5 were compared with comparative examples 1 to 3. The results showed that the S1 group with a volume ratio of nitric acid, trifluoroacetic acid, hydrogen peroxide and formic acid of 5:3:3:1 performed best in terms of heavy metal dissolution efficiency and digestion effect: the lead dissolution rate reached 99.5% ± 0.8%, the cadmium dissolution rate was 98.8% ± 1.0%, the SiO2 decomposition rate was 99.9% ± 0.1%, the organic matter decomposition rate was 99.9% ± 0.1%, and the Al 3+ The residual amount is only 0.5mg / kg±0.1. This ratio provides strong oxidizing ability through nitric acid (ΔH=-55.2kJ / mol), trifluoroacetic acid releases fluoride ions (0.6M) to promote fluorine decomposition reaction (ΔG=-87.3kJ / mol), hydrogen peroxide generates hydroxyl radicals (yield 0.085min⁻¹) to enhance the oxidation of organic matter, and formic acid stabilizes metal complexes (logK=21.3), forming a hydrogen bond network (an average of 2.3 hydrogen bonds per molecule) and a three-dimensional effect of synergy with free radicals. Statistical analysis showed that the lead dissolution rate in group S1 was significantly higher than that in other groups (p<0.001), and response surface fitting confirmed that its ratio combination maximized the dissolution rate. The spiked recovery rates were 99.2% for lead and 98.7% for cadmium, with RSD<2%, verifying the accuracy and precision of the method. The present invention uses dual ligand synergistic extraction, and the experimental data in Tables 3 to 5 show that the synergistic system makes Al 3+ The masking rate increased from 82% to 95%, the lead recovery rate increased from 90% to 99.5%, and the detection limit dropped to 0.01 ppm, all remaining stable within the pH range of 5.0-6.0. This synergistic mechanism not only improves selectivity and kinetic efficiency, but also enhances resistance to matrix interference, providing a highly effective solution for trace heavy metal detection in complex environments.

[0043] This method reduces digestion time to 30 minutes and total detection time to 1.5 hours, three times faster than traditional methods. Compared to the two-hour calcination-nitric acid digestion method described in Chinese patent CN112326575A, this method is expected to reduce digestion time by 87.5%. Furthermore, the simultaneous extraction process, which eliminates the need for digestion solution transfer, further reduces operational steps and contamination risks. With a theoretical organic matter decomposition rate of >99.9% and a lead recovery rate of 99.5% (RSD <2.5%), it meets the high-throughput requirements of the logistics industry, which requires over 300 samples per day.

Claims

1. A heavy metal detection method for express packaging materials, characterized by: The following steps are involved: S1. Take the express packaging material, crush it, and grind it to a particle size of less than 100 μm; place the express packaging material in a polytetrafluoroethylene digestion tank; S2. Add the compound acid-chitinase mixture to the digestion tank, tighten the tank cover, and let it stand for pre-reaction; The composite acid-chitinase mixed solution comprises a composite acid mixed solution and a chitinase aqueous solution; S3, placing the digestion tank in S2 on the turntable of a microwave digestion instrument for microwave digestion; S4, the digestion solution obtained in S3 is placed in a centrifuge tube, and an extractant containing HP-β-CD and DTPA as a dual ligand synergistic extraction is added to extract to form Pb 2+ -DTPA-HP-β-CD ternary complex; S5. Centrifuge the centrifuge tube extracted in step S4, take the supernatant and perform ICP-MS detection to obtain the amount and rate of heavy metal dissolution.

2. The heavy metal detection method for express packaging materials according to claim 1, characterized in that: The process parameters for ICP-MS detection in step S5 are as follows: RF power: 1550W; Carrier gas flow rate: 1.0L / min; Sampling depth: 8mm; Internal standard element: Ge (10 ppb).

3. The heavy metal detection method for express packaging materials according to claim 1, characterized in that: The mass ratio of the express packaging material to the volume of the composite acid-chitinase mixture is 0.1 g:5 ml.

4. The heavy metal detection method for express packaging materials according to claim 1, characterized in that: The composite acid mixture includes nitric acid, trifluoroacetic acid, hydrogen peroxide and formic acid, and the volume ratio of nitric acid, trifluoroacetic acid, hydrogen peroxide and formic acid is (2.5 to 5): (1.5 to 4): (1.5 to 3):

1.

5. The heavy metal detection method for express packaging materials according to claim 4, characterized in that: The volume ratio of nitric acid, trifluoroacetic acid, hydrogen peroxide and formic acid in the composite acid mixture is 5:3:3:

1.

6. The heavy metal detection method for express packaging materials according to claim 1, characterized in that: The content of chitinase aqueous solution was 10 U / ml; The volume ratio of the composite acid mixture to the chitinase aqueous solution is (0.9 to 1.3):

1.

7. The heavy metal detection method for express packaging materials according to claim 1, characterized in that: The molar concentration of HP-β-CD in the extractant in step S4 is 0.05M to 0.06M; The molar concentration of DTPA is 0.01M to 0.02M; The pH of the extractant was adjusted to 5.0 to 6.0 with citric acid-disodium hydrogen phosphate buffer.

8. The heavy metal detection method for express packaging materials according to claim 1, characterized in that: The process parameters of microwave digestion in step S3 are as follows: microwave power 300 W, duty cycle 50%; The temperature is 80℃ and the time is 30 minutes. The specific process is as follows: heating to 80℃ in 0-10 minutes and keeping warm for 20 minutes; After digestion, cool naturally to room temperature.

9. The heavy metal detection method for express packaging materials according to claim 1, characterized in that: The extraction process parameters are as follows: Place in a 60°C water bath and shake; The volume ratio of the extractant to the composite acid-chitinase mixture is 2:1.