Method for determining 239Pu content in food based on inductively coupled plasma mass spectrometry

Abstract

The invention relates to the field of element content determination, in particular to a method for determining 239Pu content in food based on inductively coupled plasma mass spectrometry, which comprises the following steps: weighing a food sample to be determined, freeze-drying, crushing, and adding anhydrous sodium carbonate for saponification; carrying out ashing treatment on a to-be-detected food sample to obtain sample ash; adding anti-aqua regia and a screening agent into the sample ash to carry out digestion reaction; loading the digested solution to a two-stage series TK200 resin column for separation and purification to obtain a to-be-detected solution; and detecting the content of < 239 > Pu in the liquid to be detected through an inductively coupled plasma mass spectrometry equipped with a collision / reaction tank. When the method is used for detecting the ultra-trace < 239 > Pu in the food, the precision, the accuracy and the sensitivity are higher, the accurate measurement of the radioactive < 239 > Pu can be completed in a relatively short time, and the method is an ideal method for rapidly detecting the < 239 > Pu in the food.

Description

Technical Field

[0001] The present invention relates to the field of element content determination, and in particular to a method for determining the content of element in food based on inductively coupled plasma mass spectrometry. 239 Pu content method. Background Art

[0002] Plutonium-239 ( 239 Pu, half-life T 1 / 2 = 24110 y) is one of the most important transuranic (U) elements and is an artificial radionuclide commonly produced in human nuclear activities. Therefore, it can enter the ecosystem through nuclear accident emissions and global deposition. 239 Pu is the most important isotope of Pu and is considered one of the most toxic radioactive substances due to its high chemical toxicity and long persistence in the environment. 239 Pu can enter the plant body through plant root absorption or surface adsorption, and gradually accumulate in animals and humans along the food chain. 239 Pu easily accumulates in the liver and bones, causing cell damage and chromosomal aberrations, which may increase the incidence of cancer. 239 Pu has significant radiotoxicity and carcinogenicity risks. 239 Pu content is of great significance for protecting human health.

[0003] Currently, due to the 239 The content of Pu is usually at trace levels (0.06 ~ 3.38 mBq / kg·wet), and accurate detection of 239 The content of Pu in food is full of challenges. 239 Pu is usually measured by α spectrometer after the sample is ashed, chemically separated, and then the source is prepared by electrodeposition. However, the measurement process of α spectrometer is complicated and the measurement time is very long, usually taking several days or even a week. In addition, due to 239 Pu and 240 The energy of Pu's α-radiators is very close, 5.15MeV and 5.16MeV respectively, which is difficult to distinguish using an α-spectrometer. Therefore, we can only measure 239+240 In addition, whether it is an α spectrometer or a low-background α meter, the radioactivity count is measured. If the measurement time is not long enough, it may lead to poor accuracy. Moreover, the number of samples for a single α spectrum measurement is very limited. In the case of batch samples, multiple measurements are required, which means that 239 The time and economic costs of Pu testing are relatively high.

[0004] Inductively coupled plasma mass spectrometry (ICP-MS) has a much higher sensitivity (μBq / kg) than α-spectroscopy (mBq / kg), and has advantages such as a wide linear range, rapid detection, high resolution, and the ability to simultaneously detect a large number of samples, thus overcoming the inherent shortcomings of α-spectroscopy. In recent years, ICP-MS has made significant progress in the analysis and detection of Pu isotopes in environmental and human biological samples, such as soil, water, and urine. However, due to the wide variety of food samples and the complex matrix, especially the large amount of phosphorus (P) contained in the food matrix, which will form H3PO4 and HPO4 in acidic media, the ICP-MS technology has made significant progress in the analysis and detection of Pu isotopes in environmental and human biological samples, such as soil, water, and urine. 2- These phosphate compounds will react strongly with P to form precipitates, which will reduce the recovery rate of Pu. 239 The content of Pu is extremely low, requiring a large amount of sample (kilogram level) to be enriched. However, animal food has a high fat content, which is very easy to expand and overflow during the carbonization stage at 200~350℃, and produces thick white smoke, resulting in a low recovery rate of Pu and easy cross contamination, which puts extremely high demands on the sample processing process. In addition, when using ICP-MS detection, the mass number and 239 Pu is identical to the homogeneous uranium hydride ion ( 238 UH + ) will be 239 It greatly interferes with the determination of Pu. Summary of the Invention

[0005] The present invention aims to provide a method for determining the content of 239 The method of Pu content is used to solve the above technical problems.

[0006] To achieve the above object, the present invention provides a method for determining the content of 239 A method for determining the content of Pu, the method comprising:

[0007] The food sample to be tested is weighed, freeze-dried, crushed, and anhydrous sodium carbonate is added to carry out saponification reaction;

[0008] Performing ashing treatment on the food sample to be tested to obtain sample ash;

[0009] adding aqua regia and a masking agent to the sample ash to carry out a digestion reaction;

[0010] The digested solution was loaded onto a two-stage TK200 resin column connected in series for separation and purification to obtain the test solution;

[0011] The inductively coupled plasma mass spectrometer equipped with a collision / reaction cell was used to measure the 239Pu content was detected.

[0012] Technical effects and advantages of the present invention:

[0013] The present invention adds an appropriate amount of anhydrous sodium carbonate to the food before ashing to carry out saponification reaction, converting the fat in the food sample into stearic acid, thereby effectively improving the ashing efficiency of animal food and reducing losses. In addition, by using a masking agent, such as a trivalent iron ion solution (such as FeCl3) as a masking agent for P, a large amount of P in the food matrix is ​​eliminated. 239 To remove interfering components such as uranium, a two-stage TK200 resin column was used in conjunction with the kinetic energy discrimination (KED) mode of ICP-MS, and the total decontamination factor of uranium reached 3.53×10 12 Therefore, the present invention detects ultra-trace amounts of food 239 Pu, with higher precision, accuracy and sensitivity.

[0014] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 The present invention is based on the inductively coupled plasma mass spectrometry to determine the 239 Flow chart of the method for Pu content;

[0017] Figure 2 This is a graph showing the retention performance of Pu(Ⅳ) and U(Ⅳ) by the TK200 resin column under different acidity conditions according to an embodiment of the present invention;

[0018] Figure 3 Graph showing the loss rate of Pu(IV) during secondary elution with HNO3 at different concentrations according to an embodiment of the present invention;

[0019] Figure 4 The different eluent pairs of the embodiment of the present invention 239 The elution of Pu and 239 Pu residual amount diagram;

[0020] Figure 5 The elution reagent pair containing the reducing agent NH2OH·HCl in the embodiment of the present invention is 239Pu elution effect and eluent consumption diagram;

[0021] Figure 6 For different He flow rates and concentrations in the embodiments of the present invention 238 Contribution of U to the signal intensity at m / z = 239. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0023] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for understanding and reading by those familiar with this technology, and are not used to limit the conditions for implementation of the present invention. Therefore, they have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose that can be achieved by the present invention. At the same time, terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0024] The present invention provides a method for determining the content of 239 Pu content method, such as Figure 1 As shown, the method includes:

[0025] 1. Take the food sample to be tested, weigh it, freeze-dry it, crush it, and add anhydrous sodium carbonate to carry out saponification reaction;

[0026] The mass ratio of the anhydrous sodium carbonate to the food sample to be tested is 1:800-1200, preferably 1:1000, for example, 1 g of anhydrous sodium carbonate is added per kilogram of fresh sample.

[0027] 2. Perform ashing treatment on the food sample to be tested to obtain sample ash.

[0028] The conditions for the ashing treatment include: heating from room temperature to a first temperature, carbonizing at the first temperature, continuing to heat up to a second temperature, and ashing at the second temperature. Specifically, the first temperature is 220-270°C, preferably 230, 240, 250, and 260°C; the second temperature is 430-470°C, preferably 440, 450, and 460°C; the carbonization time is 2.5-3.5 hours, preferably 3 hours; the ashing time is 10-26 hours, preferably 12-24 hours, more preferably 10, 12, 15, 18, and 20 hours; the time for heating to the first temperature and heating to the second temperature is 0.3-0.7 hours, preferably 0.4, 0.5, and 0.6 hours.

[0029] 3. Add aqua regia and a masking agent to the sample ash to carry out a digestion reaction.

[0030] The shielding agent includes at least one of the following: aluminum nitrate, ferric chloride, or other substances capable of shielding phosphorus.

[0031] The sample ash and the reverse aqua regia are used in a ratio of 1 g to 8 ml to 12 ml, and the mass ratio of the sample ash to the masking agent is 1:0.8-1.2. Preferably, the sample ash, the reverse aqua regia, and the FeCl3 are used in a ratio of 1 g of sample ash to 10 ml of reverse aqua regia and 1 g of ferric chloride.

[0032] 4. Load the digested solution onto a two-stage TK200 resin column for separation and purification to obtain the test solution.

[0033] Specifically, the method includes: pretreating a first TK200 resin column and a second TK200 resin column with an acid solution; loading the digested solution onto the first TK200 resin column, and eluting the first TK200 resin column twice with HNO3 of different concentrations; adding an eluent to the first TK200 resin column for a first elution, loading the solution after the first elution onto a second TK200 resin column, and performing a second elution with the eluent to obtain a solution after a second elution; and mixing the solution after the first elution and the solution after the second elution to obtain a solution to be tested.

[0034] Among them, the model of TK200 resin is (10×2 mL, 50-100 μm particle size).

[0035] The HNO3 concentration in the digested solution is 2-10 M, preferably 4, 5, 6 and 8 M; the first eluent is 2-10 M HNO3, preferably 4, 5, 6 and 8 M HNO3; the secondary eluent is 2-6 M HNO3, preferably 3, 4 and 5 M HNO3; the eluent is a mixture of 0.001-0.05 M HF, 0.01-0.2 M NH2OH·HCl and 0.01-0.2 M HCl, preferably a mixture of 0.005-0.03 M HF, 0.05-0.15 M NH2OH·HCl and 0.05-0.15 M HCl, more preferably a mixture of 0.01 M HF-0.1 M NH2OH·HCl-0.1 M HCl.

[0036] The acid solution pretreated with the first TK200 resin column is the same as the first eluent; and the acid solution pretreated with the second TK200 resin column is the same as the eluent.

[0037] 5. The inductively coupled plasma mass spectrometer equipped with a collision / reaction cell is used to measure the 239 Pu content was detected.

[0038] Specifically, ICP-MS equipped with collision / reaction cell technology (CCT) was used to detect the presence of 239 High-precision detection of Pu.

[0039] Wherein, the collision gas in the collision / reaction cell is He, and the flow rate of the He is 4.5 mL / min-6.5 mL / min; 239 Pu content ≥ 3.6 fg / g sample ash.

[0040] In order to better understand the present solution, the following examples are also provided.

[0041] A method for the determination of iodine in food based on inductively coupled plasma mass spectrometry 239 The method for Pu content, the specific steps are as follows:

[0042] 1. Food sample pretreatment and ashing

[0043] The edible portion was weighed, freeze-dried, and crushed. 1 g of anhydrous sodium carbonate was added per kilogram of fresh sample, and the food sample was placed in a muffle furnace for ashing according to the procedure shown in Table 1. Then, 10 g of sample ash was digested with 100 mL of aqua regia (HNO3:HCl=3:1, v / v) at 200 °C for 3 h. During the digestion, 10 g of FeCl3 ( Figure 2After sample digestion, filter the sample, collect the filtrate, and rinse the residue with 8 M HNO3. Combine the filtrate and rinse, and then add 8 M HNO3 to 100 mL. Subsequently, add 2 g of NaNO2 to the sample solution at room temperature to adjust the other valence states of Pu to Pu(IV) for subsequent separation and purification.

[0044] The reason for adding FeCl3 is as follows: In the subsequent separation and purification process of Pu(IV), Pu(IV) is dissolved in 8M HNO3 and reacts with NO3 – Coordination to form ionic complex [Pu(NO3) n ] 4–n (n=1~6), these complexes are adsorbed on the resin, thereby achieving the retention of Pu(IV) on the resin column. At the same time, under acidic conditions, P in food will be converted to HPO4 2- 、H2PO4 1- and H3PO4, while HPO4 2- and H2PO4 1- Can coordinate with Pu(IV) to form a precipitate, which will cause 239 In addition, H3PO4 molecules have a stronger coordination ability with Pu(IV) than NO3 – Easy to form a more stable complex [Pu(H3PO4)] 4+ , which hinders the adsorption of Pu(IV) on the resin column. However, under acidic conditions, iron ions can exist stably and react with HPO4 2- 、H2PO4 1- Therefore, an appropriate amount of FeCl3 is added during the digestion process to mask the interference of P in food samples, thereby improving 239 Recovery rate of Pu.

[0045] Table 1 Food sample ashing procedure

[0046]

[0047] 2. 239 Separation and enrichment of Pu

[0048] ICP-MS in the detection 239 Pu is faced with problems such as matrix interference, polyatomic ion interference and peak tailing. Among them, the most noteworthy is the uranium hydrogen ion ( 238 UH + ) for target ions 239 Pu + Studies have shown that isobaric interference in food samples 238 U content ratio 239 Pu is more than four orders of magnitude higher. In addition, during ICP-MS measurement238 UH + The formation rate is about 10 -3 ( 238 UH + / 238 U + ), which will interfere with the 239 Therefore, the enrichment of Pu in food samples 239 Pu and effectively eliminate 238 U and 238 UH + The interference of 239 Accurate quantification of Pu is crucial.

[0049] The present invention uses two-stage series TK200 resin columns to separate and purify food samples 239 Pu. Specifically, the Pu(IV) sample solution was loaded onto the first TK200 resin column (pretreated with 10 mL of 8 M HNO₃ solution). Subsequently, the column was washed sequentially with 10 mL of 8 M HNO₃ and 40 mL of 3 M HNO₃, and eluted with 20 mL of 0.01 M HF-0.1 M NH₂OH·HCl-0.1 M HCl solution. The eluate was directly loaded onto a second TK200 resin column (pretreated with 10 mL of 0.01 M HF-0.1 M NH₂OH·HCl-0.1 M HCl solution), and eluted with 20 mL of 0.01 M HF-0.1 M NH₂OH·HCl-0.1 M HCl solution. The eluates from the first and second columns were combined, evaporated to dryness at 200°C, and dissolved in 5 mL of concentrated HNO₃. The solution was evaporated to dryness again at 200°C, and the residue was dissolved in 10 mL of 1% HNO3 (v / v) for testing. The following details the optimization measures for this step in this protocol:

[0050] 2.1. Optimization of loading solution

[0051] While Pu is reduced to Pu(IV), U may also be reduced to U(IV). Since TK200 resin has good retention capacity for both Pu(IV) and U(IV) in HNO3 medium. However, the acidity of the sample solution will affect the retention effect of TK200 resin on Pu(IV) and U(IV). Therefore, in order to maximize the retention capacity of Pu(IV) and at the same time reduce the retention rate of U(IV), the present invention studied the retention performance of TK200 resin column for Pu(IV) and U(IV) under different acidity conditions. The results are as follows Figure 2 shown.

[0052] according to Figure 2It can be seen that when the HNO3 concentration is in the range of 2-10 M, the TK200 resin column maintains a high retention rate (>86%) for Pu(Ⅳ) and U(Ⅳ). This is attributed to the fact that in media with HNO3 concentrations greater than 0.2 M, Pu(Ⅳ) and U(Ⅳ) have high distribution coefficients on TK200 resin. In addition, Figure 2 It can be observed that the retention rate of Pu(IV) does not change significantly across different HNO3 concentrations, while the retention rate of U(IV) gradually decreases with increasing HNO3 concentration, which is consistent with previous research results. Notably, when the HNO3 concentration in the sample solution is 8 M, the retention rate of Pu(IV) reaches its highest value (98.4%), while the retention rate of U(IV) drops to its lowest value (86%). At this point, the difference in the retention rates of Pu(IV) and U(IV) is the greatest, with the ratio of their retention rates being 1.13. Therefore, in this protocol, the HNO3 concentration of the sample solution is preferably set to 8 M.

[0053] 2.2. Optimization of eluent

[0054] After sample loading, the TK200 resin will adsorb both Pu(IV) and impurities. Therefore, the elution process requires the removal of impurities as much as possible while ensuring strong Pu(IV) adsorption. The choice of elution solution is a key factor influencing recovery; it must effectively remove impurities while maximizing Pu(IV) retention, thereby improving detection accuracy and sensitivity. Therefore, this method utilizes a two-step rinsing process: first, the TK200 resin is rinsed with HNO3 at the same concentration as the loading solution to maintain stable Pu(IV) adsorption and prevent Pu(IV) loss due to changes in acidity. A second rinsing step is then performed with HNO3 at a different concentration to remove impurities.

[0055] The present invention studies the loss rate of Pu(IV) during secondary elution with different concentrations of HNO3 (2 M, 3 M, 4 M, 5 M and 6 M). The results show that when the HNO3 concentration is in the range of 2-6 M, the loss of Pu(IV) does not change significantly and is less than 10%. Figure 3 In addition, previous studies have shown that various interfering elements such as Hg, Pb, and Tl can be effectively removed in 3 M HNO3. Therefore, 3 M HNO3 is the preferred second-step eluent in this protocol.

[0056] 2.3. Selection of eluent

[0057] The retention capacity of TK200 resin for Pu(IV) and U(IV) is closely related to the type and concentration of acid. In 4-9 M HCl solutions and 0.1-8 M HNO3 solutions, the resin exhibits extremely strong retention for Pu(IV). However, in HCl solutions below 4 M, Pu(IV) retention is relatively weak, with retention decreasing with lower acidity. Notably, the resin exhibits extremely strong retention for U(IV) in both 0-10 M HCl and 0-10 M HNO3 solutions. Based on this characteristic, the use of low-concentration HCl solutions as eluents may enable efficient separation of Pu(IV) from U(IV).

[0058] By examining the elution effects of Pu(IV) and U(IV) with different concentrations of HCl, it was found that when 4 M HCl was used for elution, only a small amount of Pu(IV) was eluted (<20%). Even when the HCl concentration was as low as 0.1 M, a large amount of Pu(IV) could not be eluted, and the recovery rate was only 32.6%, indicating that a single low-concentration HCl solution could not achieve complete elution of Pu(IV). Considering that TK200 resin has a strong adsorption capacity for Pu(IV) and a weak adsorption capacity for Pu(III), the reducing agent NH2OH·HCl was added to the eluent to reduce Pu(IV) to Pu(III), and HF was added in synergistically to enhance the elution capacity. The results showed that after adding 0.1 M NH2OH·HCl to 0.1 M HCl, the recovery rate of Pu(IV) reached more than 90%; after further adding HF, the recovery rate increased to more than 95%, as shown in Figure 2. Figure 4 As shown. Among them, Figure 4 Among the eluent types, A represents 4 M HCl, B represents 0.1 M HCl, C represents 0.1 M NH2OH·HCl-0.1 M HCl, D represents 0.1 M HF-0.1 M HCl-0.1 M NH2OH·HCl; and E represents 0.01 M HF-0.1 M HCl-0.1 MNH2OH·HCl.

[0059] In addition, the elution curve ( Figure 5 ) showed that 0.01 M HF-0.1 M HCl-0.1 M NH2OH·HCl and 0.1 M HF-0.1 M HCl-0.1 M NH2OH·HCl can elute Pu(IV) earlier than 0.1 M HCl-0.1 M NH2OH·HCl solution, and only 20 mL can elute most of the plutonium Pu(IV) (>95%). However, at a higher HF concentration (0.1 M), although Pu(IV) can be fully eluted, the uranium eluted is much higher than that of other eluents. When the added HF concentration is 0.01 M, the uranium elution rate is not significantly different from the elution rate when no HF is added ( Figure 4 Therefore, this protocol prefers 0.01 M HF-0.1 MHCl-0.1 M NH2OH·HCl as the eluent.

[0060] 3. 239 Determination of Pu

[0061] This study used a separation and purification scheme with two TK200 resin columns in series to achieve 238 High efficiency removal of U. However, the double column system still cannot completely remove 238 U, residual trace 238 U will interfere with the measurement.

[0062] remove 238 UH + In addition to the contribution to the peak intensity at m / z=239, 238 The single-atom tailing peak of U may also affect the mass-to-charge ratio signal. Since the peak tail contribution at m-1 is usually higher than that at m+1, a conservative estimate can be made by monitoring the m / z=237 signal. 238 U contributes to the peak tail at m / z=239. Experimental determination of 10 ng / mL 238 U standard solution found that the m / z=237 signal was extremely weak and close to the process blank value, indicating that 238 The contribution of the peak tail of U at m / z=239 can be ignored. 239 The main interference sources at Pu are 238 UH + . For trace 238 UH + In order to solve the interference problem, this scheme uses ICP-MS equipped with collision / reaction cell technology (CCT) to achieve the detection of ions in food by kinetic energy discrimination mode (KED). 239 High-precision detection of Pu. This technology effectively suppresses 238 UH + The selectivity of the method was significantly improved by eliminating polyatomic interferences.

[0063] In the kinetic energy discrimination (KED) mode, the collision gas He selectively blocks interfering ions with specific kinetic energy, effectively eliminating 238 UH + This method investigates the interference of different concentrations of He at different He flow rates. 238 The contribution of U to the signal intensity at m / z=239 is as follows: Figure 6 In standard mode (STD, no gas is introduced), even if 238 U concentrations as low as 0.01 ng / mL still significantly interfere with the signal response at m / z = 239 (>10 cps). 239It is worth noting that the introduction of the KED mode of He can effectively suppress such interference. 238 When the U concentration is lower than 0.1 ng / mL and the He flow rate is 6.5 mL / min, 238 UH + The signal is significantly reduced, and its contribution to the m / z=239 signal is less than 0.1 cps. However, subsequent experiments found that as the He flow rate increases, 239 The signal intensity of the Pu standard solution decreased synchronously, indicating that the introduction of He would weaken the detection sensitivity of the target ion. 239 Pu detection sensitivity and 238 UH + For the removal effect, the preferred He flow rate is 5.5 mL / min. Under this condition, 0.1 ng / mL 238 The test results of U standard solution showed that 238 UH + The counts were <1 cps, confirming that the interference was effectively suppressed.

[0064] The decontamination factor of uranium in food samples after separation and purification by two-stage TK200 resin columns can reach 4.1×10 7 In ICP-MS measurement, using KED mode and adjusting the collision gas (He) flow rate to 5.5 mL / min can effectively eliminate the residual U 238 UH + right 239 Pu + interference, 238 UH + / 238 U + The ratio is 1.16×10 -5 Combining chemical separation with two TK200 resin columns in series, 238 The overall decontamination factor of U interference reached 3.53×10 12 , which can achieve the detection of trace amounts of uranium from high uranium (162.1 mg / kg) food environments. 239 Accurate determination of Pu.

[0065] It should be noted that the specific working conditions of ICP-MS are shown in Table 2. 1% HNO3 (v / v) was used as the cleaning solution, and 0.1 pg / mL 209 Bi was used as an internal standard.

[0066] Table 2 ICP-MS specific working conditions

[0067]

[0068] The following are the sensitivity, precision, recovery and repeatability of this method:

[0069] 1. Detection limit and linearity

[0070] 1.1. Preparation of standard solution

[0071] Take appropriate amount 239 Place the Pu standard solution in a 10 mL volumetric flask and dilute to the mark with 1% nitric acid (v / v) to prepare a standard stock solution with a concentration of 1 ng / mL. Store at 4°C. Take 1.0 mL of the standard stock solution and place it in a 100 mL volumetric flask. Add 1% nitric acid (v / v) to the mark and shake well to obtain a standard working solution with a concentration of 10 pg / mL. Store at 4°C. Immediately before use, dilute the standard working solution with 1% nitric acid (v / v) to prepare calibration solutions with concentrations of 0.1, 0.5, 1.0, 2.0, and 5.0 pg / mL.

[0072] 1.2. Evaluate by drawing a calibration curve containing 5 concentration levels (excluding matrix) 239 The linear relationship between Pu and process blank samples was prepared by the same method as the actual analysis samples. 239 The detection limit (LOD) was calculated based on the detection sensitivity of Pu and three times the standard deviation of the process blank measurement results (n=10) (Formula 1)

[0073] (1)

[0074] Where: S: standard deviation of blank measurement value (cps); V: volume before analysis (mL); SI: instrument 239 Sensitivity of Pu (cps / (ng / mL)); γ: method recovery (%); m: food sample mass (g).

[0075] 1.3. In the concentration range of 0.1-5.0 pg / mL, the correlation coefficient (r) of the calibration curve exceeded 0.999, indicating a good linear relationship. The linear equation was y=178x (where y is 239 Pu count value, x is 239 concentration of Pu). 239 The difference between the calibration value and the nominal value of Pu is within ±10%. The detection limit (LOD) of this method for ash samples is 3.6 fg / g (ash content). 239 The detection limit of Pu can be obtained by converting the measured ash-to-fresh ratio.

[0076] 2. Recovery and Repeatability

[0077] The accuracy and precision of the present invention were evaluated by using a spike recovery experimental system: representative food ash samples (fish, shrimp, crab, algae, and chicken) were selected and spiked with three concentration levels of low (0.120 pg), medium (0.367 pg), and high (0.561 pg) of ash. 239 Pu standard solution. Recovery was evaluated by calculating the ratio of the average detected concentration of spiked samples to the theoretical concentration. Repeated analyses (n = 4) of spiked samples at each fortification level were performed, and the reproducibility of the method was evaluated by calculating the relative standard deviation. The experimental results are shown in Table 3.

[0078] Table 3 Recovery rate and repeatability experimental data

[0079]

[0080] According to Table 3, 239 The spiked recovery of Pu was 54.9%-83.7%, with an average recovery of 74% and relative standard deviations (RSDs) ranging from 1.4% to 6.6%, indicating that this quantitative analysis method has good recovery and repeatability.

[0081] In summary, after separation and purification by the double-stage TK200 resin column, the sample 238 The decontamination factor (DF) of U was 4.1×10 7 When using ICP-MS, the KED mode was used and the collision gas (He) flow rate was adjusted to 5.5 mL / min, which can effectively eliminate the residual U. 238 UH + right 239 Pu + Interference ( 238 UH + / 238 U + The ratio dropped to 1.16×10 -5 ). Combined with the chemical separation of double columns in series, 238 The overall DF of U interference is increased to 3.53×10 12 , theoretically achievable 238 U content (162.1 mg / kg) trace amounts in food 239 The accurate quantification of Pu was achieved. Moreover, the linearity was good within the concentration range (correlation coefficient r>0.999), the limit of detection (LOD) in the ash matrix was 3.6 fg / g, the average recovery rate exceeded 74%, and the relative standard deviation was less than 6.6%. 239 The quantitative analysis of Pu verified the applicability of the method, and the results showed that the method is fast, accurate and sensitive. 239 An ideal method for Pu detection. Compared with traditional α spectrometer measurement, this method can complete radioactivity in a shorter time.239 Accurate measurement of Pu with a turnaround time of less than three days for fresh food sample analysis, while alpha spectrometer measurements typically require more than a week.

[0082] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for determining the content of chlorinated paracetamol in food based on inductively coupled plasma mass spectrometry 239 The method for Pu content is characterized in that The method comprises: The food sample to be tested is weighed, freeze-dried, crushed, and anhydrous sodium carbonate is added to carry out saponification reaction; Performing ashing treatment on the food sample to be tested to obtain sample ash; adding aqua regia and a masking agent to the sample ash to carry out a digestion reaction; The digested solution was loaded onto a two-stage TK200 resin column connected in series for separation and purification to obtain the test solution; The inductively coupled plasma mass spectrometer equipped with a collision / reaction cell was used to measure the 239 Pu content was detected.

2. The method according to claim 1, characterized in that The mass ratio of the anhydrous sodium carbonate to the food sample to be tested is 1:800-1200.

3. The method according to claim 1, characterized in that The usage ratio of the sample ash and the anti-aqua regia is: 1g:8ml-12ml; the mass ratio of the sample ash and the shielding agent is 1:0.8-1.

0.

4. The method according to claim 1, wherein The ashing treatment conditions include: heating from room temperature to a first temperature, performing carbonization at the first temperature, continuing to heat to a second temperature, and performing ashing at the second temperature.

5. The method according to claim 4, characterized in that The first temperature is 220-270°C; the second temperature is 430-470°C; the carbonization time is 2.5-3.5 hours; the ashing time is 10-26 hours; and the time for heating to the first temperature and the time for heating to the second temperature are both 0.3-0.7 hours.

6. The method according to claim 1, characterized in that The digested solution is loaded onto a two-stage TK200 resin column connected in series for separation and purification to obtain a test solution, comprising: Pretreating the first TK200 resin column and the second TK200 resin column with acid solution; The digested solution was loaded onto the first TK200 resin column, and the first TK200 resin column was eluted twice with HNO3 of different concentrations; Adding an eluent to the first TK200 resin column for a first elution, loading the solution after the first elution onto a second TK200 resin column, and performing a second elution with the eluent to obtain a second elution solution; The solution after the first elution and the solution after the second elution are mixed to obtain a test solution.

7. The method according to claim 6, characterized in that The HNO3 concentration in the digested solution is 2-10 M; the first eluent is 2-10 M HNO3; the second eluent is 2-6 M HNO3; and the eluent is a mixture of 0.001-0.05 M HF, 0.01-0.2 M NH2OH·HCl and 0.01-0.2 M HCl.

8. The method according to claim 7, characterized in that The acid solution pretreated with the first TK200 resin column is the same as the first eluent; the acid solution pretreated with the second TK200 resin column is the same as the eluent.

9. The method according to claim 1, characterized in that The collision gas in the collision / reaction cell is He, and the flow rate of the He is 4.5 mL / min-6.5 mL / min; the shielding agent includes at least one of the following: aluminum nitrate and ferric chloride.

10. The method according to claim 1, characterized in that described 239 Pu content ≥ 3.6 fg / g sample ash.

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