A method for accurate determination of 16 trace elements in tumorous stem mustard by inductively coupled plasma tandem mass spectrometry

Abstract

The present invention discloses a method for accurately determining 16 trace elements in stem mustard by inductively coupled plasma tandem mass spectrometry (ICP-MS / MS). The 16 trace elements are Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Cd, Hg, Pb. 27 Al, 51 V, 52 Cr, 55 Mn, 56 Fe, 59 Co, 60 Ni, 63 Cu, 66 Zn, 75 As, 78 Se, 88 Sr, 98 Mo, 111 Cd, 202 Hg, 206 Pb are used as analytical isotopes. Among them, the determination of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Sr, Pb adopts cold plasma technology, and NH3 is used as the reaction gas to eliminate mass spectrometry interference. For the determination of elements with relatively high first ionization energy such as Zn, As, Se, Mo, Cd, Hg, hot plasma technology is adopted to improve the sensitivity, and the mixed gas of O2 and H2 is used as the reaction gas to eliminate mass spectrometry interference. The method has high sensitivity, good accuracy and high precision.

Description

Technical Field

[0001] The invention relates to a method for determining elements in vegetables, and particularly to a method for accurately determining 16 trace elements in tumorous stem mustard by using inductively coupled plasma tandem mass spectrometry. Background Art

[0002] Tumored mustard (Brassica juncea var.tumida Tsen et Lee), also known as green mustard, is a stem mustard of the genus Brassica in the family Cruciferae. It is an important agricultural and economic crop in the Yangtze River Basin of my country. It has a long history of cultivation, high nutritional value, and delicious taste. It enjoys a high reputation in the world for its unique flavor of freshness, fragrance, tenderness and crispness. Fuling Zhacai, pickled with tumored mustard as raw material, is known as the world's three most famous pickled vegetables along with French pickles and German sweet and sour cabbage. The nutritional value of tumored mustard mainly depends on its organic components, but the composition and content of inorganic elements in tumored mustard play an important role in its nutritional value and safety. As the material basis for the growth of tumorous stem mustard, nutrients are important substances required for the development, maintenance and metabolism of tumorous stem mustard tissues, and are also an important source of essential trace elements for people to obtain through eating tumorous stem mustard; at the same time, the toxic elements contained in tumorous stem mustard can denature proteins after being ingested by the human body, and can gradually accumulate in the human body to cause chronic poisoning. Although the adverse effects of these toxic elements on health depend on the concentration, long-term exposure to toxic elements such as As, Cd, Hg, and Pb can cause toxic effects at relatively low levels. Therefore, establishing a multi-element analysis method that covers both nutrients and toxic elements in tumorous stem mustard is conducive to correctly evaluating the nutritional quality of tumorous stem mustard and the degree of harm of its toxic elements to human health.

[0003] At present, the research on tumorous stem mustard mainly focuses on the growth environment, physiological traits, genetic characteristics and virus control, while there are few reports on the research of various trace elements in tumorous stem mustard. The detection of trace elements in food mainly includes atomic fluorescence spectroscopy (AFS), atomic absorption spectroscopy (AAS), inductively coupled plasma optical emission spectroscopy (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma tandem mass spectrometry (ICP-MS / MS). Among them, AFS has high sensitivity and low detection limit, especially combined with hydride generation (HG) technology, which can reduce the detection limit by more than one order of magnitude, but the fluorescence quenching effect and the inherent scattered light interference reduce the theoretical advantages of AFS; the single element analysis characteristics of AAS cannot meet the requirements of high-throughput analysis of multiple elements in food, and elements whose resonance lines are in the vacuum ultraviolet region cannot be directly determined; the detection limit of ICP-OES is high, which is difficult to meet the detection requirements of trace elements in food. ICP-MS has lower detection limits and higher sensitivity than AFS, AAS and ICP-OES, and has become the most commonly used food analysis technology. However, ICP-MS still faces many challenges: for analytical elements with higher first ionization energies, the ionization efficiency is very low even under thermal plasma (ICP) conditions, resulting in low analytical sensitivity for these elements. ICP-MS makes up for the shortcomings of ICP-OES very well. Its extremely low detection limit is particularly suitable for the determination of trace elements in food. However, the diversity of food matrix composition leads to very complex mass spectrometric interferences, which are difficult to completely eliminate using conventional quadrupole ICP-MS (ICP-QMS). Cold plasma technology uses low-temperature plasma to suppress Ar ionization, thereby eliminating the interference of argon-based ions. Low-temperature plasma can also reduce the background signal of easily ionized elements, but water cluster ions will be formed under cold plasma conditions, and water cluster ions will still cause interference through rapid proton transfer reactions. The collision / reaction cell (CRC) provides a general technology for eliminating mass spectrometry interferences. Although the collision mode can eliminate polyatomic ion interferences, it cannot eliminate other mass spectrometry interferences. In the reaction mode, the byproduct ions formed by unknown reaction processes can easily generate new mass spectrometry interferences. Only by improving the selectivity of the reaction chemistry in the collision reaction cell can the potential of the reaction mode be fully realized.

[0004] Inductively coupled plasma tandem mass spectrometry (ICP-MS / MS) adopts a dual quadrupole mass spectrometry (MS / MS) structure. Through the dual quadrupole mass filters located before and after the octopole reaction cell system (ORS), the first-level quadrupole mass filter (Q1) extracts ions of specified mass-to-charge ratio (m / z) from the plasma and enters the ORS to react selectively with the reaction gas. The second-level quadrupole mass filter (Q2) extracts the reaction product ions of specified m / z from the ORS for measurement, giving full play to the potential of the reaction mode to eliminate mass spectrometry interference. Summary of the invention

[0005] In order to solve the above technical problems, the object of the present invention is to provide a method for accurately determining 16 trace elements in Brassica juncea by inductively coupled plasma tandem mass spectrometry, which has high sensitivity, good accuracy and high precision.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for accurately determining 16 trace elements in tumorous stem mustard by inductively coupled plasma tandem mass spectrometry, characterized in that the 16 trace elements are Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Cd, Hg, and Pb, respectively. 27 Al, 51 V. 52 Cr, 55 Mn, 56 Fe, 59 Co. 60 You, 63 Cu, 66 Zn, 75 As, 78 Se, 88 Sr. 98 Mo, 111 Cd, 202 Hg, 206 Pb is used as the analytical isotope.

[0007] The following steps are involved:

[0008] (1) Preparation of mixed standard solutions: use single element standard solutions to prepare a series of mixed calibration solutions with different concentration gradients;

[0009] (2) Preparation of sample solution and blank solution: fresh tuber parts of Brassica juncea were collected, rinsed with tap water and then with ultrapure water, drained and dried in a forced air drying oven to constant weight, and crushed to pass through a 40-mesh sieve; accurately weighed powder sample into a microwave digestion reaction tank, added with nitric acid and hydrogen peroxide, and digested; after digestion, transferred into a volumetric flask, fixed to the mark with ultrapure water, and shaken to obtain a sample solution; a blank solution was obtained using the same microwave digestion conditions;

[0010] (3) On-machine testing: the above-mentioned samples to be tested, standard samples, mixed standard solutions, and blank solutions were respectively measured by ICP-MS / MS, wherein Al, V, Cr, Mn, Fe, Co, Ni, Cu, Sr, and Pb were measured by cold plasma technology and NH3 was used as the reaction gas in MS / MS mode to eliminate mass spectrum interference; Zn, As, Se, Mo, Cd, and Hg with higher first ionization energy were measured by hot plasma technology and a mixed gas composed of O2 and H2 was used as the reaction gas in MS / MS mode to eliminate mass spectrum interference; the internal standard solution was added online through a standard T-type internal standard mixing joint to correct the matrix effect; the content of the analyzed element in the sample solution was calculated using the calibration curve.

[0011] The parameters of ICP-MS / MS are as follows:

[0012]

[0013]

[0014] In the above scheme: the digestion conditions are: power 1600W, heating to 120°C in 5 minutes, heating to 150°C in 3 minutes, maintaining for 5 minutes, heating to 190°C in 5 minutes, maintaining for 15 minutes.

[0015] In the above scheme: prepare 0.0, 0.1, 0.5, 2.0, 10 μg L -1 A series of mixed standard solutions.

[0016] The present invention adopts cold plasma technology and uses NH3 as reaction gas in MS / MS mode, and utilizes in-situ mass method to eliminate mass spectrum interference of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Sr and Pb.

[0017] Thermal plasma technology was used and a mixture of O2 and H2 was used as the reaction gas in MS / MS mode. The mass-shift method was used to eliminate the mass spectral interference of As, Se, and Mo, and the in-situ mass method was used to eliminate the mass spectral interference of Zn, Cd, and Hg.

[0018] In the above scheme: select 1mg L -1 A mixed internal standard solution of Li, Sc, Ge, Y, In, Tb, and Bi.

[0019] In the above scheme: 1000mg L -1 A series of mixed standard solutions are prepared from single element standard solutions of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Cd, Hg and Pb.

[0020] In the above scheme: the detection instrument is Agilent 8800ICP-MS / MS.

[0021] The present invention adopts ICP-MS / MS to analyze the trace elements in the stem tumor mustard sample after microwave digestion, eliminates the mass spectrum interference of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Sr, and Pb in the cold plasma / NH3 reaction mode, and eliminates the mass spectrum interference of Zn, As, Se, Mo, Cd, and Hg in the hot plasma / O2 / H2 reaction mode. The detection limit (LOD) of the analyzed elements is 0.026-4.81ng L -1 Except for Se, the LOD of other elements is lower than 1.0 ng L -1 .The results of the analytical method are basically consistent with the certified values ​​of the standard reference materials, the spiked recoveries are 95.4%-110%, the relative standard deviations (RSDs) are 2.4%-6.2%, and at a confidence level of 95%, there is no significant difference between the analytical method and the SF-ICP-MS method for the test results of the standard reference materials. By fully controlling the chemical reactions of ions / molecules in the collision / reaction cell (CRC), the background equivalent concentration (BEC) of the analyzed elements can be reduced, and the long-term stability of the analytical process is good. The established analytical method has high sensitivity, good accuracy and high precision. ICP-MS / MS combined with reaction modes under different plasma conditions shows great potential for multi-element analysis in tumorous stem mustard. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Background equivalent concentrations (BECs) of the analyzed elements were obtained using SQ gas-free mode and MS / MS NH3 reaction mode under cold plasma conditions.

[0023] Figure 2 Shown are BECs for the analyte elements obtained under hot plasma conditions using SQ no gas mode and MS / MS in O2 / H2 mixed reaction gas mode.

[0024] Figure 3 This figure shows the effect of different NH3 flow rates on the BEC of the analyzed elements under cold plasma conditions.

[0025] Figure 4 This figure shows the effect of the flow rate changes of O2 and H2 on the BEC of the analyzed elements under thermal plasma conditions.

[0026] Figure 5 The stability of 10 analytical elements in spiked sample solution for 4 h under cold plasma conditions. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0028] Embodiment 1:

[0029] The instruments and reagents used in this example are as follows:

[0030] Agilent 8800ICP-MS / MS instrument, Agilent, USA. MARs 5 microwave digestion system, CEM, USA. Milli-Q ultrapure water machine, Millipore, USA. Sector magnetic field double focusing (SF)-ICP-MS.

[0031] The operating conditions of Agilent 8800ICP-MS / MS and SF-ICP-MS are shown in Tables 1 and 2 respectively.

[0032] Table 1 ICP-MS / MS operating conditions

[0033]

[0034]

[0035] Table 2 SF-ICP-MS operating conditions

[0036]

[0037] 1000mg L -1 Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Cd, Hg, Pb single element standard solution, 10 mg L -1 A mixed internal standard solution of Li, Sc, Ge, Y, In, Tb, and Bi, 65% (w / w) ultrapure nitric acid, 30% (w / w) ultrapure hydrogen peroxide, Merck, Germany; 8 mustard samples were collected in February 2023 in Chongqing Fuling (107°29′56″E, 29°50′10″N, 225-418m above sea level), Tuojiang, Sichuan (104°78′15″E, 29°28′25″N, 270-350m above sea level) and Liuyang, Hunan (113°60′22″E, 28°01′56″N, 202-369m above sea level), including 3 in Chongqing Fuling, 3 in Sichuan Tuojiang, and 2 in Hunan Liuyang.

[0038] (1) Preparation of mixed standard solutions: single element standard solutions were used to prepare 0.0, 0.1, 0.5, 2.0, and 10 μg L -1 A series of mixed standard solutions.

[0039] (2) Preparation of internal standard solution: 10 mg L -1 Dilute the mixed internal standard solution to prepare 1 mg L -1A mixed internal standard solution of Li, Sc, Ge, Y, In, Tb, and Bi.

[0040] (3) Preparation of sample solution and blank solution: The tuber of fresh stem mustard was collected, rinsed with tap water and then washed with ultrapure water, drained and dried in a forced air drying oven to constant weight, and crushed to pass through a 40-mesh sieve; 0.25 g of powder sample was accurately weighed into a microwave digestion reaction tank, 8 mL of nitric acid (mass concentration 65%) and 2 mL of hydrogen peroxide (mass concentration 30%) were added, and the mixture was left open for 15 min. The reaction tank was covered and placed in a microwave digestion system for digestion; the digestion conditions were: power 1600 W, heating to 120° C. in 5 min, heating to 150° C. in 3 min, holding for 5 min, heating to 190° C. in 5 min, and holding for 15 min.

[0041] After digestion, transfer to a 250 mL volumetric flask, dilute to the mark with ultrapure water, and shake well to obtain a sample solution. The standard reference substance solution and blank solution were prepared using the same microwave digestion conditions.

[0042] (4) On-machine testing: the above-mentioned samples to be tested, standard samples, mixed standard solutions, and blank solutions were respectively measured by ICP-MS / MS, wherein Al, V, Cr, Mn, Fe, Co, Ni, Cu, Sr, and Pb were measured by cold plasma technology and NH3 was used as the reaction gas in MS / MS mode to eliminate mass spectrum interference; Zn, As, Se, Mo, Cd, and Hg with higher first ionization energy were measured by hot plasma technology and a mixed gas composed of O2 and H2 was used as the reaction gas in MS / MS mode to eliminate mass spectrum interference; the internal standard solution was added online through a standard T-type internal standard mixing joint to correct the matrix effect; the content of the analyzed element in the sample solution was calculated using the calibration curve.

[0043] (5) Mass spectrometric behavior of elements analyzed under different modes

[0044] After plasma ionization, the matrix elements in Brassica juncea, the sample solvent and the plasma Ar gas will form a large number of complex mass spectrometry interferences, which will affect the accurate determination of the analyzed elements, especially the analysis of the elements with a mass-to-charge ratio (m / z) ≤ 80amu. Cold plasma uses a relatively low temperature plasma to eliminate the interference of argon-based ions and argon-containing polyatomic ions, but low-energy plasma is more susceptible to ionization suppression effects, and has low sensitivity for the determination of elements with higher first ionization energies. Therefore, this experiment uses cold plasma technology to eliminate mass spectrometry interference for the determination of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Sr, and Pb, and uses thermal plasma technology (RF power of 1600W) to eliminate mass spectrometry interference for the determination of elements with higher first ionization energies such as Zn, As, Se, Mo, Cd, and Hg.

[0045] Usually, Ar ionization under hot plasma conditions will form a large number of argon-based ions, among which 40 Ar 12 C + , 36 Ar 16 O + , 38 Ar 14 C + , 36 Ar 15 NH + constitutes 52 Cr + The main interference is that the matrix elements Cl and S in the mustard are ionized to form polyatomic ions ( 35 Cl 16 OH + , 37 Cl 15 N + , 34 S 18 O + , 36 S 16 O + ) constitutes a secondary interference; under low temperature cold plasma conditions, due to the suppression of Ar, Cl, S ionization, the argon-based ions are completely eliminated, 35 Cl 16 OH + and 37 Cl 15 N + right 52 Cr + Even in single quadrupole (SQ) mode without using a reagent gas, the corresponding background equivalent concentrations (BECs) are at a low level, but a small amount of 34 S 18 O + and 36 S 16 O + , thus interfering 52 Cr + In the MS / MS mode, NH3 was selected as the reaction gas. Due to the mass transfer reaction between the highly reactive NH3 and the small amount of interfering ions formed under the low temperature cold plasma conditions, 52 Cr + It hardly reacts with NH3, and the interference is eliminated by NH3 on-site mass method. 52 Cr + Similarly, for interferences mainly from argon-based ions 51 V + , 55 Mn+ , 56 Fe + , 59 Co + , 60 Ni + , 65 Cu + , using cold plasma / NH3 reaction mode to eliminate interference and further reduce 51 V + , 52 Cr + , 55 Mn + , 56 Fe + , 59 Co + , 60 Ni + , 65 Cu + BEC( Figure 1 ).

[0046] Under cold plasma conditions, due to the suppression of 12 C 15 N + and 12 C 14 NH + The formation of 27 Al + There will be almost no interference, and 88 Sr + and 206 Pb + The interference is negligible, but through Figure 1 It can be seen that in the NH3 reaction mode, the 27 Al + , 88 Sr + , 206 Pb + BEC.

[0047] Figure 2 The figure shows the background equivalent concentration (BEC) of the analyzed elements using SQ gasless mode and MS / MS O2 / H2 mixed reaction gas mode under hot plasma conditions. It can be seen that in SQ mode, all ions from the plasma enter the octopole collision / reaction cell (ORS). Since no reaction gas is used to eliminate interference, the BECs of the analyzed elements Zn, As, and Se are very large; 98 Mo + The interference mainly comes from 41 K2 16 O + ,Although 41The abundance of K is low (6.7%), but due to the high content of K in stem mustard and the fact that K is an easily ionized element, the 41 K2 16 O + Serious interference 98 Mo + The determination of Mo results in a larger BEC; 111 Cd + The interference mainly comes from the interference of Mo-based ions ( 95 Mo 16 O + , 98 Mo 13 C + , 96 Mo 14 N + ), since the Mo content in tumorous stem mustard is much higher than that of Cd, the BEC of Cd is also at a high level; 202 Hg + The interference mainly comes from 186 W 16 O, but due to the low W content in stem mustard, the BEC of Hg is at a low level. In MS / MS mode, O2 / H2 mixed reaction gas was added to ORS. 66 Zn + , 111 Cd + , 202 Hg + It hardly reacts with O2, but the interfering ions react with O2 / H2, and the interference is eliminated by in-situ mass method; 75 As + , 78 Se + , 98 Mo + It undergoes an efficient mass transfer reaction with O2 in O2 / H2, and uses the mass transfer method to eliminate interference, thereby further reducing the BEC of Zn, As, Se, Mo, Cd, and Hg.

[0048] By eliminating interferences in cold plasma / NH3 reaction mode and hot plasma / O2 / H2 reaction mode, extremely low BECs were obtained for all analyzed elements (see Table 3). The sensitivity of the analyzed elements in the two modes was investigated. As can be seen from Table 3, even under low-temperature cold plasma conditions, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Sr, and Pb have high sensitivity, while high-temperature hot plasma promotes the ionization of elements with higher first ionization energy in plasma, making Zn, As, Se, Mo, Cd, and Hg also have high sensitivity. Therefore, in view of the differences in the first ionization energies of the analyzed elements, plasmas of different temperatures were used to achieve high-sensitivity determination of all analyzed elements.

[0049] Table 3 Sensitivity and BECs of analytes in different modes

[0050]

[0051] (6) Optimization of reaction gas flow rate

[0052] Under cold plasma conditions, 1 μg L -1 The NH3 flow rate was optimized for the standard solutions of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Sr, and Pb, and the effect of different NH3 flow rates on the BEC of the analyzed elements was investigated. Figure 3 It can be seen that as the NH3 flow rate increases, the interfering ions gradually undergo mass transfer reactions with NH3, which results in a gradual decrease in the BEC of the analyzed element and a gradual removal of the interference. When the NH3 flow rates reach 1.3, 0.9, 1.4, 1.1, 1.5, 1.4, 1.0, 1.5, 1.3, and 1.2 mL min -1 When the BEC of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Sr, and Pb reached the minimum, indicating that the interference had been removed to the greatest extent at this time. Then, the NH3 flow rate was increased continuously, and the BEC of the analyzed elements began to increase slowly. In order to ensure that the BEC of all analyzed elements was kept at a low level, the present invention selected the NH3 flow rate of 1.5 mL min -1 .

[0053] Under thermal plasma conditions, 1 μg L -1 The flow rates of O2 and H2 were optimized by using standard solutions of Zn, As, Se, Mo, Cd and Hg. The effect of O2 flow rate on the BEC of the analyzed elements was investigated. Figure 4 As can be seen from (a), with the increase of O2 flow rate, the BEC of As, Se, Mo, Cd, and Hg decreased rapidly, while the BEC of Zn hardly changed, indicating that the mass spectral interference of As, Se, Mo, Cd, and Hg can be quickly eliminated in the O2 reaction mode, but the mass spectral interference of Zn cannot be eliminated. When the O2 flow rate reaches 0.30, 0.25, 0.30, 0.25, and 0.20 mL min, respectively -1 When the O2 flow rate is increased, the BEC of As, Se, Mo, Cd, and Hg begins to increase slowly. The fixed O2 flow rate of the present invention is 0.30 mL min -1 In order to reduce the BEC of Zn, H2 was added to ORS to form a reaction gas mixture O2 / H2 with O2. The effect of H2 flow rate on the BEC of the analyzed element was investigated. Figure 4As can be seen from (b), with the increase of H2 flow rate, the BEC of As, Se, and Cd still slightly decreases, indicating that the addition of H2 eliminates the interference that cannot be eliminated in the O2 reaction mode; the BEC of Mo and Hg is almost unchanged, indicating that all interferences have been eliminated in the O2 reaction mode; and the BEC of Zn decreases rapidly with the increase of H2 flow rate, which is due to 66 Zn + The main source of interference comes from 40 Ar 24 Mg + and 38 Ar 14 N + H2 can react with argon-based ions at a relatively fast rate, but has low reactivity with other element ions. The addition of H2 quickly eliminates 40 Ar 24 Mg + and 38 Ar 14 N + right 66 Zn + The interference was manifested as a rapid decrease in the BEC of Zn. When the H2 flow rate reached 7.0 mL min -1 When the H2 flow rate is increased, the BEC of Zn reaches the minimum. Then, the BEC of Zn begins to increase slowly. Therefore, the flow rate of O2 is selected as 0.3 mL min -1 , the flow rate of H2 is 7.0 mL min -1 , ensuring that Zn, As, Se, Mo, Cd, and Hg all have low BEC.

[0054] (7) Stability of the analysis process under cold plasma conditions

[0055] Compared with hot plasma, cold plasma can provide lower BEC. However, the lower the cold plasma energy, the lower the matrix decomposition efficiency. It has poor tolerance to high-matrix samples. Over time, deposits may form on the interface cone and ion lens, affecting the stability of the analytical signal. In this example, a 1000-fold dilution was performed during sample processing to maintain a low element concentration in the mustard sample solution to reduce the risk of precipitation. The stability of the analytical process was confirmed by monitoring the signal stability over a long period of time. 50 μg L was added to the mustard sample solution. -1 Al, Mn, Fe, Cu, Sr and 1μg L -1 The long-term stability test of V, Cr, Co, Ni, and Pb standard solutions was carried out, and the signal intensity was measured every 30 minutes to investigate the stability of the 10 analytical elements in the spiked sample solution under cold plasma conditions for 4 hours. Figure 5It can be seen that the recoveries of all analyzed elements were between 95% and 105%, and the relative standard deviation (RSD) was less than 5%, indicating that the stability of the analysis process was very good.

[0056] (8) Analytical performance evaluation of the method

[0057] The calibration curve of the analyte was established using the calibration solution, and linear regression was performed. The detection limit (LOD) and quantification limit (LOQ) of the analyzed elements were obtained by repeatedly measuring the concentration corresponding to 3 times and 10 times the standard deviation of the blank solution 10 times. The results are shown in Table 4. It can be seen that the linear correlation system of the analyzed elements is ≥0.9997, indicating a good linear relationship. The LOD of the analyzed elements is 0.026-4.81ng L -1 Except for Se, the LOD of other elements is lower than 1.0 ng L -1 .The LOD of the analyzed elements in the cold plasma / NH3 reaction mode was lower than 0.5 ng L -1 This indicates that the method can meet the requirements of ng L -1 Determination of multiple trace elements.

[0058] Table 4 Linearity, LOD and LOQ of the method

[0059]

[0060]

[0061] In order to evaluate the accuracy and reliability of this method, the standard reference material SRM1547 (peach leaves) was repeatedly measured 6 times using this method and SF-ICP-MS method, and the t-test method was selected to perform statistical analysis on the measurement results of the two analytical methods. At the same time, the standard solution of the analytical element was added to the sample solution of the standard reference material, and the spike recovery rate of the analytical element was calculated. The results are shown in Table 5. It can be seen that the measured values ​​of all analytical elements in this method are basically consistent with the certified values ​​of the standard reference material, with RSD between 2.4% and 6.2%, and the spike recovery rate is 95.4%-110%. Statistical analysis shows that at a confidence level of 95%, there is no significant difference between the measured values ​​of this method and the SF-ICP-MS method (p>0.05), which verifies that the analytical method has good accuracy and high precision.

[0062] Table 5 Accuracy and precision of the method

[0063]

[0064]

[0065] (9) Analysis of Tumorous Mustard Samples

[0066] The analytical method was used to measure 8 samples of tumorous stem mustard from Chongqing Fuling (sample numbers CQFL1-3), Sichuan Tuojiang (sample numbers SCTJ1-3) and Hunan Liuyang (sample numbers HNLY1-2). Each sample was measured 6 times. The results are shown in Table 6. The content of trace elements in tumorous stem mustard from different origins varies greatly. The content of trace elements in tumorous stem mustard is not only controlled by its genetic characteristics, but also related to factors such as its growth geographical environment and cultivation conditions. The content range of 16 trace elements in the 8 tumorous stem mustard samples is: Al content is 1.45-2.87 mg kg -1 The content of V is between 151-516 μg kg -1 The Cr content is between 10.5-32.2 μg kg -1 The content of Mn is between 26.2-82.5 mg kg -1 The Fe content is between 39-152 mg / kg -1 The content of Co is between 1.51-3.20 mg kg -1 The Ni content is between 0.86-2.28 mg kg -1 The Cu content is between 7.90-15.3 mg kg -1 The Zn content is between 51.8-157 mg kg -1 The As content is between 1.06-4.08 μg kg -1 The Se content is between 15.0-31.2 μg kg -1 The Sr content is between 161-405 μg kg -1 The Mo content is between 19.8-80.5 μg kg -1 The Cd content is between 1.45-3.97 μg kg -1 The Hg content is between 0.95-307 μg kg -1 The content of Pb is between 46.6-178 μg kg -1 The contents of Cr, As, Cd, Hg, and Pb in the eight tumorous mustard samples were much lower than the limit of contaminants in food in China (GB 2762-2022). Although GB 2762-2022 does not set a limit for Al, which has potential hazards, the contents of Al in the eight tumorous mustard samples were all lower than 2.0 mg kg -1 , ensuring its food safety.

[0067] Table 6 Sample analysis results (mg kg -1 ,n=6)

[0068]

[0069]

[0070] “*”:μg kg -1

[0071] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for accurately determining 16 trace elements in tumorous stem mustard by inductively coupled plasma tandem mass spectrometry, characterized in that: The 16 trace elements are Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Cd, Hg, and Pb. 27 Al, 51 V. 52 Cr, 55 Mn, 56 Fe, 59 Co. 60 You, 63 Cu, 66 Zn, 75 As, 78 Se, 88 Sr. 98 Mo, 111 Cd, 202 Hg, 206 Pb as analytical isotope; The following steps are involved: (1) Preparation of mixed standard solutions: use single element standard solutions to prepare a series of mixed calibration solutions with different concentration gradients; (2) Preparation of sample solution and blank solution: collect the tuber part of fresh tumorous stem mustard, rinse it with tap water and then with ultrapure water, drain the water, dry it in a forced air drying oven to constant weight, and grind it through a 40-mesh sieve; accurately weigh the powder sample into a microwave digestion reaction tank, add nitric acid and hydrogen peroxide, and digest it; after the digestion is completed, transfer it to a volumetric flask, dilute it to the scale with ultrapure water, and shake it well to prepare the sample solution; use the same microwave digestion conditions to prepare a blank solution; (3) On-machine testing: samples to be tested, standard samples, mixed standard solutions, and blank solutions were measured using ICP-MS / MS. Cold plasma technology was used for the determination of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Sr, and Pb, and NH3 was used as the reaction gas in MS / MS mode to eliminate mass spectrometric interference. Thermal plasma technology was used for the determination of elements with higher first ionization energy, such as Zn, As, Se, Mo, Cd, and Hg, and a mixed gas consisting of O2 and H2 was used as the reaction gas in MS / MS mode to eliminate mass spectrometric interference. Internal standard solution was added online through a standard T-type internal standard mixing joint to correct for matrix effects. The parameters of ICP-QQQ are as follows: The parameters in the cold plasma ammonia environment were: RF power 600 W, sampling depth 18 mm, nebulizer gas flow rate 0.70 L min -1 , compensation gas flow rate 0.80 L min -1 , extraction voltage 1 -160 V, extraction voltage 2 -15 V, reaction gas flow rate 1.5 mL min -1 , octopole bias voltage -18 V, kinetic energy discrimination voltage 13 V; The parameters in the cold plasma-gasless state were: octopole bias voltage -18 V, kinetic energy discrimination voltage 13 V; The parameters under the O2 / H2 reaction conditions were as follows: RF power 1600 W, sampling depth 8 mm, and compensation gas flow rate 0.40 L min -1 , extraction voltage 1 5V, extraction voltage 2 -250 V, reaction gas flow rate O2 0.3 mL min -1 , H2 7.0 mL min -1 , octopole bias voltage -10 V, kinetic energy discrimination voltage -10 V; Select 1 mg L -1 A mixed internal standard solution of Li, Sc, Ge, Y, In, Tb, and Bi.

2. The method for accurately determining 16 trace elements in tumorous stem mustard by inductively coupled plasma tandem mass spectrometry according to claim 1, characterized in that: The digestion conditions were as follows: power 1600 W, heating to 120°C in 5 min, heating to 150°C in 3 min, maintaining for 5 min, heating to 190°C in 5 min, maintaining for 15 min.

3. The method for accurately determining 16 trace elements in tumorous stem mustard by inductively coupled plasma tandem mass spectrometry according to claim 1, characterized in that: Prepare 0.0, 0.1, 0.5, 2.0, 10 μg L -1 A series of mixed standard solutions.

4. The method for accurately determining 16 trace elements in tumorous stem mustard by inductively coupled plasma tandem mass spectrometry according to claim 3, characterized in that: Using 1000 mg L -1 A series of mixed standard solutions are prepared from single element standard solutions of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Cd, Hg and Pb.

5. The method for accurately determining 16 trace elements in tumorous stem mustard by inductively coupled plasma tandem mass spectrometry according to claim 4, characterized in that: The detection instrument is Agilent 8800 ICP-MS / MS.

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