Quantitative detection model for multi-element heavy metals in paper packaging material and application of quantitative detection model

Abstract

The invention discloses a quantitative detection model for multi-element heavy metals in a paper packaging material and application of the quantitative detection model. According to the model, to-be-detected heavy metal elements in the paper food packaging material are calibrated by making a standard sample to obtain a standard curve, and through multiple times of test fitting, the influence of background noise on result accuracy is eliminated, and the detection limit is effectively reduced, so that the test sensitivity is improved; the sample is subjected to simple tabletting treatment, so that the X-ray excitation intensity can be enhanced, and the detection limit is effectively reduced; on the basis of a common energy spectrum X-ray fluorescence method, a bent crystal monochromatic X-ray fluorescence method is introduced, so that the detection limit of trace heavy metals can be effectively reduced. The method has the advantages of being simple in sample pretreatment, high in detection speed, high in accuracy and the like, the heavy metal detection capacity and efficiency in the paper packaging material can be remarkably improved, and the quality and safety of the paper packaging material are effectively guaranteed.

Description

Technical Field

[0001] This invention relates to a detection model for multiple heavy metals in paper materials, specifically a quantitative detection model for multiple heavy metals in paper packaging materials and its application, belonging to the field of sample processing and detection. Background Technology

[0002] Food safety encompasses both the safety of the food itself and the safety of packaging materials that come into direct contact with it. During direct contact with food, certain substances from packaging materials may migrate into the food, causing chemical contamination (contamination of food contact packaging materials). Plastics and paper are the most common food packaging materials. Due to the implementation of plastic bans, the demand for paper packaging products has increased dramatically, especially disposable paper tableware. Some paper packaging products may use contaminated recycled materials, causing these harmful contaminants to seep into the food, potentially causing unpredictable harm to human health. Heavy metal content is a product quality and safety indicator that requires strict control. Heavy metals in paper mainly originate from impurities in the pulp, additives, inks, and pigments. With increased regulation and awareness, the limits for these heavy metal elements are very stringent.

[0003] Currently, there are many methods for detecting heavy metals, with commonly used methods including atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS), inductively coupled plasma atomic emission spectrometry (ICP-AES), and inductively coupled plasma mass spectrometry (ICP-MS). These methods are accurate and effective elemental analysis methods, and numerous corresponding standard test methods have been published. However, these methods typically use liquid injection, requiring sample digestion or other complex and time-consuming pretreatment methods, thus hindering rapid detection. Furthermore, these pretreatment methods require hazardous reagents such as strong acids, placing high demands on experimental facilities and personnel. In addition, the high cost of these instruments, the complexity of operation and maintenance, and the inability of ordinary atomic spectrometry to simultaneously measure multiple elements also limit the application of these methods. Therefore, there is an urgent need to develop rapid, efficient, and high-throughput detection technologies for heavy metals in paper food packaging materials.

[0004] X-ray fluorescence spectrometry (XRF) is a widely used rapid method for heavy metal detection, offering advantages such as simple sample pretreatment, simple spectral lines, fast analysis speed, ability to measure multiple elements, and simultaneous multi-element analysis. However, when using this common energy-dispersive X-ray fluorescence spectrometer to test paper samples, the detection limit is generally above 2.0 μg / g, especially for Cr, where the detection limit is greater than 7 μg / g, approaching the limit of ordinary EDXRF and difficult to improve further. Summary of the Invention

[0005] To address the problems existing in the prior art, the first objective of this invention is to provide a quantitative detection model for multiple heavy metals in paper packaging materials. This model introduces curved crystal monochromatic X-ray fluorescence method on the basis of ordinary energy-dispersive X-ray fluorescence method, and performs quantitative analysis of samples by plotting XRF standard curves. The sample detection cycle is about 10 minutes, which greatly shortens the heavy metal detection cycle, and the detection limit of each heavy metal element is ≤1 ppm.

[0006] The second objective of this invention is to provide an application of a quantitative detection model for multiple heavy metals in paper packaging materials, enabling rapid detection of these metals. Based on the XRF detection model provided by this invention, this model achieves rapid and accurate quantitative analysis of multiple heavy metals in paper packaging materials. Its testing accuracy is essentially consistent with that of traditional ICP-MS detection, but its detection cycle is only about 10 minutes, significantly reducing the testing time.

[0007] To achieve the above-mentioned technical objectives, this invention provides a quantitative detection model for multiple heavy metals in paper packaging materials, comprising:

[0008] S1: The standard solutions of the various heavy metals to be detected in the paper packaging materials are diluted and brought to a constant volume according to the concentration gradient and then added to the ink to obtain a series of inks with standard concentrations of multiple heavy metals.

[0009] S2: The standard concentration ink is uniformly coated onto blank paper packaging material to obtain a series of paper samples with standard concentrations of multiple heavy metals;

[0010] S3: Perform X-ray fluorescence spectroscopy analysis on the paper samples with standard concentrations obtained in S2, and plot the standard curves for each heavy metal element to obtain the results.

[0011] The number of paper samples in the X-ray fluorescence spectroscopy analysis process is 40 to 200 layers.

[0012] As a preferred embodiment, the medium for the heavy metal standard solution is a 2-5% nitric acid solution.

[0013] As a preferred embodiment, the heavy metal is at least two of Pb, Cr, Cd, As, Se, and Hg.

[0014] As a preferred embodiment, the concentration range of the multi-metal standard concentration paper sample is 0.1–20 mg / kg, and the gradient value of the concentration gradient ranges from 0.1 to 4 mg / kg.

[0015] As a preferred embodiment, the process of adding the diluted and brought to volume standard solution to the ink is as follows: while stirring, add the alkaline solution to the ink, and then slowly drip the standard solution into the ink.

[0016] As a preferred embodiment, the alkaline solution is at least one of caustic soda solution, potassium hydroxide solution, concentrated ammonia solution, and sodium carbonate solution.

[0017] As a preferred embodiment, the alkaline solution has a pH > 11, and the amount added is 1 to 5 wt% of the ink mass, measured by the solute in the solution.

[0018] As a preferred embodiment, the X-ray fluorescence spectroscopy analysis process is as follows: the paper sample is pressed into a paper cake, flattened and placed into a sample cup with a support membrane, and then sent into the instrument for analysis.

[0019] As a preferred embodiment, the diameter of the paper cake is 10-30 mm and the thickness is 0.99-8 mm.

[0020] As a preferred embodiment, the conditions for pressing the paper cake are: pressure of 15-30t and time of 5-15s.

[0021] As a preferred embodiment, the support film is one of a Meyer film, a polycarbonate film, a polypropylene film, and a polyimide film.

[0022] As a preferred embodiment, the process of obtaining the calibration curve of the heavy metal element is as follows: with the heavy metal content in the paper sample as the abscissa x and the net peak intensity as the ordinate y, each sample with different content is tested 3 to 5 times, and the obtained data is fitted to obtain the calibration curve.

[0023] As a preferred option, the fitting method is at least one of interpolation, iteration, and least squares.

[0024] As a preferred embodiment, the fitting method is the least squares method, the process of which is as follows: The arithmetic mean of the net peak intensities obtained from multiple detections at the same heavy metal element content is used to obtain a discrete lattice of content-average peak intensity. This lattice is then fitted using the least squares method, and the calculation process is as follows:

[0025] Formula 1:

[0026] Formula 2:

[0027] Formula 3:

[0028] In equations 1 to 3: y ij For a concentration of x i At that time, the net peak intensity value obtained from the j-th test; For a concentration of x i The average net peak intensity at time; k and b are the parameters to be measured for the fitted curve.

[0029] This invention also provides an application of a quantitative detection model for multiple heavy metals in paper packaging materials, for the rapid detection of multiple heavy metals in paper packaging materials.

[0030] As a preferred option, the thickness of the paper sample to be tested should be the same as that of the standard concentration paper sample.

[0031] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0032] 1) The detection model provided by this invention accurately reflects the calibration curve of multi-component heavy metals in X-ray fluorescence spectroscopy analysis through multi-component mixed heavy metal standard samples. Through multiple test fittings, the influence of background noise on the accuracy of the results is eliminated, effectively reducing the detection limit of XRF test, thereby improving the sensitivity and accuracy of the test.

[0033] 2) In the technical solution provided by this invention, based on the XRF detection model provided by this invention, rapid and accurate quantitative analysis of multiple heavy metals in paper packaging materials can be achieved. Its testing accuracy is basically consistent with the traditional ICP-MS detection results, but its detection cycle is only about 10 minutes, which greatly shortens the testing time. According to the test, the detection model provided by this invention has an RSD of <15% and a relative deviation of <10% at a concentration of <1ppm. In the concentration range of 1ppm to 10ppm, the test RSD is <10% and the relative deviation is <5%. It can be seen that the detection model provided by this invention has excellent testing sensitivity and accuracy. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the implementation of this invention, the accompanying drawings required in the embodiments of this invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on the content of the embodiments of this invention and these drawings without creative effort.

[0035] Figure 1 This is a flowchart of a method for detecting heavy metal content in paper packaging materials based on energy dispersive X-ray fluorescence spectroscopy provided by the present invention;

[0036] Figure 2 This is a schematic diagram of the energy-dispersive X-ray fluorescence spectrometer used in this invention;

[0037] Figure 3 This is a schematic diagram of sample cup loading;

[0038] Figure 4 This is a graph showing the relationship between the intensity of the characteristic spectral lines of the heavy metal element arsenic and its concentration in Example 2 of this invention.

[0039] Figure 5 This is a graph showing the relationship between the characteristic spectral intensity and concentration of lead, a heavy metal element, in Example 2 of this invention.

[0040] Figure 6 This is a graph showing the relationship between the characteristic spectral intensity and concentration of the heavy metal element cadmium in Example 2 of this invention.

[0041] Figure 7 This is the spectrum of arsenic and lead elements in Example 2 of the present invention;

[0042] Figure 8 This is the spectrum of cadmium in Example 2 of the present invention;

[0043] Figure 9 The graph shows the effect of different paper layers on the peak intensities of Cr, Ni, Hg, As and Pb.

[0044] Figure 10 The graph shows the effect of different paper layers on the peak intensity of Cd. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific examples.

[0046] The instrument used in this invention is the NX-1000 heavy metal detector (Steel Research Institute Nake Testing Technology Co., Ltd.). This detector includes dual X-ray sources: a 6.4keV bent crystal monochromatic X-ray source and a 70W W target X-ray source. The bent crystal X-ray source is used to excite Cr, while the W target X-ray source is used to excite Ni, Hg, As, Pb, and Cd. It uses a FAST SDD detector with an energy resolution of <129eV@Mn Kα and has sample spin and automatic sample introduction functions.

[0047] Example 1

[0048] There is a paper sample with unknown arsenic and lead content, and it is necessary to determine the arsenic and lead content in the paper.

[0049] The XRF conditions used were as follows: the qualitative and quantitative characteristic peak position of arsenic was As:Kα=10.543keV; the qualitative and quantitative characteristic peak position of lead was Pb:Lβ1=12.614keV. Excitation voltage: 35kV; excitation current: 200μA; scan time: 240s.

[0050] The specific process includes:

[0051] 1) Preparation of arsenic and lead-containing ink: NaOH solution with pH 12 is slowly added to the ink under stirring, and then standard solutions of arsenic and lead are added dropwise to the ink to obtain a series of inks containing arsenic and lead standard solutions. The NaOH solution accounts for 1 wt% of the ink mass based on the mass of NaOH.

[0052] 2) Preparation of arsenic and lead-containing paper standard samples: The ink containing arsenic and lead standard solutions is evenly coated on blank paper to obtain gradient standard samples containing arsenic and lead heavy metals.

[0053] 3) Standard sample loading and X-ray fluorescence spectroscopy analysis: Cut an appropriate length of polyimide film and clip it onto the sample cup. Take the standard sample prepared in step (1) and cut the paper sample into a circular shape using a cutting tool; use a manual or automatic sample press to press 40 layers of circular paper sample into a paper cake with a thickness of 0.99 mm; place the paper cake flat into the sample cup for testing; after the energy dispersive X-ray fluorescence spectrometer is preheated, open the sample inlet door of the instrument host, place the sample cup with the sample loaded into the chamber, close the sample inlet door, and start the measurement.

[0054] 4) Plotting standard curves and calibration curves for each heavy metal element: The external standard method was used to plot the standard curves for arsenic and lead; the measured content of the element obtained by ICP-MS was used as the x-axis and the net peak intensity obtained by XRF analysis was used as the y-axis. Each sample was measured 3 times, and the calibration curves for arsenic and lead were obtained by linear fitting.

[0055] 5) Sample preparation and testing: Cut the paper sample into a circular shape using a cutting tool; use a manual or automatic sample press to press 40 layers of circular paper sample into a paper cake; place the paper cake flat into a sample cup for testing; use an XRF fluorescence spectrometer to analyze the sample, select the corresponding standard curve, run the detection program directly, and record the results.

[0056] Two parallel samples were prepared: Parallel sample 1 contained 0.44 mg / kg of arsenic and 2.33 mg / kg of lead; Parallel sample 2 contained 0.46 mg / kg of arsenic and 2.05 mg / kg of lead.

[0057] Example 2

[0058] There is a paper sample with unknown arsenic, lead, and cadmium content, and it is necessary to determine the arsenic, lead, and cadmium content in the paper.

[0059] The XRF conditions used were as follows: ① The qualitative and quantitative characteristic peak positions for arsenic were: As:Kα=10.543keV; the qualitative and quantitative characteristic peak positions for lead were: Pb:Lβ1=12.614keV. Excitation voltage: 35kV; excitation current: 200μA; scan time: 240s. ② The qualitative and quantitative characteristic peak positions for cadmium were: Cd:Kα=23.130keV. Excitation voltage: 64kV; excitation current: 800μA; scan time: 240s.

[0060] The specific process of this embodiment is exactly the same as that of Embodiment 1, except that:

[0061] 1) During the ink preparation process, standard solutions of arsenic, lead and cadmium were continuously added dropwise to obtain a series of inks containing arsenic, lead and cadmium standard solutions in gradients. The number of paper cake layers was 100 and the thickness was 2.43 mm.

[0062] 2) The test results of the prepared parallel samples are as follows: Parallel sample 1 has an arsenic content of 1.38 mg / kg, a lead content of 7.20 mg / kg, and a cadmium content of 1.21 mg / kg; Parallel sample 2 has an arsenic content of 1.31 mg / kg, a lead content of 6.91 mg / kg, and a cadmium content of 1.19 mg / kg.

[0063] The present invention also conducted a precision experiment on paper samples. Taking the paper sample in Example 2 as the object of study, the same sample was prepared and the RSD of 7 test results was calculated, which shows that the detection method described in the present invention has good precision. The test results are shown in Table 1.

[0064] Table 1

[0065]

[0066]

[0067] To verify the accuracy of this method, a batch of spiked positive samples was prepared. Four spiked samples were selected to examine the accuracy of the method. The spiked samples were first detected by EDXRF and then by ICP-MS. The relative deviations of the values ​​measured by EDXRF and ICP-MS are shown in Table 2. It can be seen that the EDXRF test results of As, Pb, and Cd in the actual samples are basically consistent with those of the traditional ICP-MS method, with a relative deviation within ±15%, which meets the requirements of GB / T 27404—2008 and can meet the requirements for on-site quality control and rapid screening of paper samples.

[0068] Table 2

[0069]

[0070] Furthermore, to verify the impact of the number of paper layers on the test results, the same paper as in Example 2 was selected in this invention, and the peak intensity of each heavy metal element in XRF detection was measured under different paper layer numbers. The results are shown in [Figure Number]. Figure 9 and Figure 10 According to the working principle of X-rays, when X-rays pass through matter, their intensity is weakened by absorption; when the thickness of the absorbing medium reaches a certain level, the X-rays will be completely absorbed, and this thickness is the infinite thickness of the absorbing medium. Before the sample thickness reaches infinity, the peak intensity increases with increasing medium thickness. Figure 9 It is known that for common elements such as Cr, Ni, Hg, As, and Pb, when the number of paper layers exceeds 40, the peak intensities of these elements remain essentially unchanged. This means that for these five elements, the infinite thickness is 40 layers. However, Cd exhibits the highest characteristic spectral energy and the greatest penetration depth. Figure 10 It can be seen that the peak intensity remains essentially unchanged after the number of layers reaches 200. According to the principle of the weakest link, as long as the infinite thickness requirement for Cd is met, the infinite thickness requirement for other heavy metals can also be met. Therefore, if Cd is not being tested, 40 layers of paper are sufficient. If the paper used in this invention contains Cd, then 200 layers can meet the requirement of infinite thickness, allowing the peak intensity of Cd to reach its maximum and the detection limit to be lowest. If the number of Cd samples is less than 200 layers, but the detection limit of the detection method already meets the detection requirements, then 100 layers are sufficient for Cd sample preparation.

[0071] The precision and accuracy tests above demonstrate that the method described in this invention for analyzing the arsenic, lead, and cadmium content in paper samples using XRF fluorescence spectroscopy is convenient and feasible. This method has high precision, good reproducibility, high accuracy, and good repeatability. It only requires simple sample pretreatment, which greatly reduces the analysis time.

Claims

1. A quantitative detection model for multiple heavy metals in paper packaging materials, characterized in that, include: S1: The standard solutions of the various heavy metals to be detected in the paper packaging materials are diluted and brought to a constant volume according to the concentration gradient and then added to the ink to obtain a series of inks with standard concentrations of multiple heavy metals. S2: The standard concentration ink is uniformly coated onto blank paper packaging material to obtain a series of paper samples with standard concentrations of multiple heavy metals; S3: Perform X-ray fluorescence spectroscopy analysis on the paper samples with standard concentrations obtained in S2, and plot the standard curves for each heavy metal element to obtain the results. The number of paper samples in the X-ray fluorescence spectroscopy analysis process is 40 to 200 layers.

2. The quantitative detection model for multiple heavy metals in paper packaging materials according to claim 1, characterized in that: The heavy metal is at least two of Pb, Cr, Cd, As, Se and Hg; the concentration range of the multi-element heavy metal standard concentration paper sample is 0.1 to 20 mg / kg, and the gradient value of the concentration gradient ranges from 0.1 to 4 mg / kg.

3. The quantitative detection model for multiple heavy metals in paper packaging materials according to claim 1, characterized in that: The process of adding the diluted and brought to volume standard solution to the ink is as follows: while stirring, add the alkaline solution to the ink, and then slowly drip the heavy metal standard solution into the ink.

4. The quantitative detection model for multiple heavy metals in paper packaging materials according to claim 3, characterized in that: The alkaline solution is at least one of caustic soda solution, potassium hydroxide solution, concentrated ammonia solution, and sodium carbonate solution.

5. The quantitative detection model for multiple heavy metals in paper packaging materials according to claim 3, characterized in that: The alkaline solution has a pH > 11, and the amount added is 1 to 5 wt% of the ink mass, measured by the solute in the solution.

6. The quantitative detection model for multiple heavy metals in paper packaging materials according to claim 1, characterized in that: The X-ray fluorescence spectroscopy analysis process is as follows: the paper sample is pressed into a paper cake, flattened and placed into a sample cup with a support membrane, and then sent into the instrument for analysis.

7. The quantitative detection model for multiple heavy metals in paper packaging materials according to claim 6, characterized in that: The diameter of the paper cake is 10-30 mm and the thickness is 0.99-8 mm; the pressing conditions of the paper cake are: pressure of 15-30 t and time of 5-15 s.

8. The quantitative detection model for multiple heavy metals in paper packaging materials according to claim 6, characterized in that: The supporting membrane is one of the following: a Meyer membrane, a polycarbonate film, a polypropylene film, and a polyimide film.

9. The quantitative detection model for multiple heavy metals in paper packaging materials according to claim 1, characterized in that: The process of obtaining the calibration curve of the heavy metal element is as follows: with the heavy metal content in the paper sample as the x-axis and the net peak intensity as the y-axis, each sample with a certain content is tested 3 to 5 times, and the obtained data is fitted to obtain the calibration curve.

10. The quantitative detection model for multiple heavy metals in paper packaging materials according to claim 9, characterized in that: The fitting method is at least one of interpolation, iteration, and least squares.

11. The quantitative detection model for multiple heavy metals in paper packaging materials according to claim 10, characterized in that: The fitting method is the least squares method, and the process is as follows: The arithmetic mean of the net peak intensities obtained from multiple tests with the same heavy metal element content is used to obtain a discrete lattice of content-average peak intensity. This lattice is then fitted using the least squares method, yielding the final result. The calculation process is as follows: Formula 1: Formula 2: Formula 3: In equations 1 to 3: y ij For a concentration of x i At that time, the net peak intensity value obtained from the j-th test; For a concentration of x i The average net peak intensity at time; k and b are the parameters to be measured for the fitted curve.

12. The application of the quantitative detection model for multiple heavy metals in paper packaging materials according to any one of claims 1 to 11, characterized in that: This method is used for the rapid detection of multiple heavy metals in paper packaging materials; the thickness of the paper sample to be tested should be consistent with that of the standard concentration paper sample.

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