A method for ultra-trace mercury isotope analysis

Abstract

The application discloses a method for ultra-trace mercury isotope analysis and relates to the technical field of environmental analysis. The method comprises the following steps: blowing nitrogen to the liquid sample to be measured under the atmosphere of stannous chloride, and concentrating mercury into a gold trapping tube; pyrolyzing the gold trapping tube to release mercury vapor; mixing the pyrolyzed mercury vapor with thallium isotope internal standard aerosol, and then introducing the mixture into a multi-receiver inductively coupled plasma mass spectrometer as a sample; collecting mercury transient signals and thallium isotope signals; and calculating the mercury isotope ratio by using a least square linear regression fitting combined with a thallium internal standard ratio correction algorithm. The application generates transient mercury isotope signals by using the online combination of gold trapping and the multi-receiver inductively coupled plasma mass spectrometer, strategically collects and processes the transient signals, significantly improves the sensitivity of the isotope analysis by greatly reducing the determination concentration, and meets the direct determination of mercury isotope composition in 10 ng / L ‑1 grade concentration water samples.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental analysis, and particularly relates to a method for ultra-trace mercury isotope analysis. BACKGROUND

[0002] As the largest mercury exchange flux between the interfaces of the earth, the exchange of mercury between the atmosphere and water accounts for 32% to 54% of the global mercury cycle, and the exchange mechanism and influencing factors thereof need to be further studied. The effectiveness of mercury isotope fractionation fingerprinting in tracing the migration and transformation process of mercury in the environment has been widely proven, and accurate analysis of the mercury isotope composition in natural water bodies has become a key requirement of current research.

[0003] The method of introducing sample solution into a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) by using a cold vapor generation device is a conventional analysis method for mercury isotope analysis. This method has a relatively strict requirement for the mercury concentration in the sample, which is usually required to be higher than 1 μg L -1 to meet its determination accuracy, however, this concentration level is much higher than that of natural water (usually several to several tens of ng L -1 ). To solve this technical bottleneck, offline pre-concentration techniques such as purge / burning-oxidative solution absorption and ion exchange resin have been established to realize the extraction and concentration of mercury, but these offline operations are usually complicated, require a large amount of reagents and materials, manpower and time cost, and the total amount of sample needs to reach 5 ng Hg. Some studies have optimized the sample amount to 200 pg Hg, but it is still challenging to realize ultra-trace isotope composition analysis in natural water samples, and currently there is no method to directly determine 100 pg Hg of isotope.

[0004] In summary, the existing technology cannot meet the demand for ultra-trace mercury isotope analysis in natural water bodies, and an effective method needs to be established. SUMMARY

[0005] Therefore, the present application provides a method for ultra-trace mercury isotope analysis based on gold trapping tube pyrolysis sampling and internal standard correction synergy strategy, which can greatly improve the sensitivity of the method and maintain good internal precision by strategically collecting and processing transient signals, and can greatly reduce the sample amount of mercury isotope analysis from ng level to 50 pg, to solve the technical bottleneck that the existing technology cannot determine the extremely low concentration of mercury isotope in natural water samples. The method can directly analyze the mercury isotope of water samples with a concentration level of 10 ng L -1 , without the need for offline enrichment operation, and has the advantages of sensitivity, accuracy and speed.

[0006] Therefore, the present application provides a method for ultra-trace mercury isotope analysis, comprising the following steps:

[0007] The liquid sample to be tested is blown by nitrogen under stannous chloride atmosphere, and the mercury is captured and concentrated into a gold capture tube;

[0008] The gold capture tube is pyrolyzed to release mercury vapor;

[0009] The mercury vapor is mixed with a thallium isotope internal standard aerosol as an injection sample, and is introduced into a multi-receiver inductively coupled plasma mass spectrometer;

[0010] The mercury transient signal and the thallium isotope signal are collected;

[0011] The mercury isotope ratio is calculated by using a least squares linear regression fitting combined with a thallium internal standard ratio correction algorithm.

[0012] Further, the pyrolysis temperature is 450-550°C.

[0013] Further, the carrier gas flow rate for transporting the mercury vapor is 0.16-0.21 L / min.

[0014] Further, the preparation method of the thallium isotope internal standard aerosol comprises:

[0015] The thallium standard solution is introduced into a membrane desolvation device for desolvation to form the thallium isotope internal standard aerosol; wherein the purge gas flow rate of the membrane desolvation device is 2.6-3.0 L / min.

[0016] Further, the make-up gas flow rate for introducing the injection sample is 0.9-1.1 L / min.

[0017] Further, in the collection of the mercury transient signal and the thallium isotope signal, the integration time for signal collection is 50-100 ms, and the sampling point number is 800-1200.

[0018] Further, the thallium internal standard ratio correction algorithm is to correct the mass discrimination by using the thallium internal standard isotope ratio, comprising: 205 Tl / 203 After screening and removing the thallium isotope ratio outliers exceeding 1 standard deviation in the determination time window, the average value of the thallium isotope ratio is calculated for correction. 205 Tl / 203 205 Tl / 203

[0019] Further, the calculation of the mercury isotope ratio is based on the signal value of 198 Hg as the reference, and the signal values of 199 Hg, 200 Hg, 201 Hg and 202 ​​Hg relative 198 The signal value of Hg is subjected to least square linear regression fitting, and the slope obtained by fitting is taken as the relative ratio of each isotope to 198 Hg.

[0020] Further, the method further comprises:

[0021] Using the standard-sample cross method, using mercury isotope standard solution NIST SRM 3133 as a reference material, performing mass discrimination correction, and requiring that the concentration of the sample solution matches the concentration of the adjacent standard solution within 10%.

[0022] Further, the method is used for direct mercury isotope analysis of natural water samples of 10 ng L -1 Concentration level, and / or for analyzing and determining the mercury isotope composition in natural water samples under the condition that the total amount of mercury is 50 pg~100 pg.

[0023] Compared with the prior art, the present application at least includes the following beneficial effects:

[0024] The ultra-trace mercury isotope analysis method of the present application uses gold trapping and multi-receiver inductively coupled plasma mass spectrometry online to generate transient mercury isotope signals, strategically collects and processes the transient signals, can greatly reduce the determination concentration of isotope analysis and significantly improve the sensitivity of the method, and meets the direct determination of mercury isotope composition in 10 ng L -1 Concentration level water samples. When processing transient signals to calculate mercury isotope ratios, a linear regression algorithm of least square fitting is applied, and the thallium isotope ratio algorithm for optimizing mass discrimination correction can greatly reduce the determination standard deviation of the method, and significantly improve the internal precision of the method. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can also be obtained by those skilled in the art according to these drawings.

[0026] Figure 1 The gold trapping-multi-receiver inductively coupled plasma mass spectrometry (P&T-MC-ICP-MS) system schematic diagram provided for the embodiments of the present application.

[0027] Figure 2 The purge-gold trapping-MC-ICP-MS combined system gas path parameter optimization diagram provided for the embodiments of the present application. DETAILED DESCRIPTION

[0028] For better understanding of the above technical solutions, the technical solutions of the embodiments of the present application are described in detail below through the drawings and specific embodiments. It should be understood that the specific features in the embodiments of the present application and the embodiments are detailed descriptions of the technical solutions of the embodiments of the present application, rather than limitations of the technical solutions of the present application. In the case of no conflict, the technical features in the embodiments of the present application and the embodiments can be combined with each other.

[0029] The embodiment of the present application provides a method for ultra-trace mercury isotope analysis, comprising the following steps:

[0030] The liquid sample to be measured is blown by nitrogen under a stannous chloride atmosphere, and mercury is captured and concentrated into a gold capture tube;

[0031] The gold capture tube is pyrolyzed to release mercury vapor;

[0032] The mercury vapor is mixed with a thallium isotope internal standard aerosol as a sample for injection, and is introduced into a multi-receiver inductively coupled plasma mass spectrometer;

[0033] The mercury transient signal and the thallium isotope signal are collected;

[0034] The least square linear regression fitting combined with the thallium internal standard ratio correction algorithm is used to calculate the mercury isotope ratio.

[0035] The method for ultra-trace mercury isotope analysis provided by the embodiment of the present application is aimed at the concentration limit of the method for ultra-trace mercury isotope analysis. Instantaneous mercury isotope signals are generated by using gold capture and multi-receiver inductively coupled plasma mass spectrometry online, and the instantaneous signals are strategically collected and processed. The determination concentration of isotope analysis can be greatly reduced, and the method sensitivity can be significantly improved, so as to meet the direct determination of mercury isotope composition in 10 ng L -1 grade concentration water sample. In order to solve the internal precision problem in establishing the method for ultra-trace mercury isotope analysis, the least square fitting linear regression algorithm is used when processing the instantaneous signal to calculate the mercury isotope ratio, and the thallium isotope ratio algorithm is optimized by mass discrimination correction, which can greatly reduce the determination standard deviation of the method and significantly improve the internal precision of the method.

[0036] Specifically, the gold capture tube is placed in a pyrolysis device, and the zero-valent mercury vapor generated by pyrolysis is mixed with a thallium isotope internal standard aerosol, and is introduced into a multi-receiver inductively coupled plasma mass spectrometer (MC-ICP-MS) for analysis of mercury isotope composition. Alternatively, the mercury in the solution is captured and concentrated into a gold capture tube by stannous chloride reduction-nitrogen blowing method, wherein the concentration of stannous chloride is 20% (in 10% HCl, v / v ), and the nitrogen blowing flow rate is 300 mL min -1The duration is 6 min. Optionally, an internal standard thallium isotope solution (NIST SRM 997, 100 μg / L) is prepared. -1 3% HNO3 v / v Stable thallium aerosols were generated using a membrane desolvation device (Aridus), with a 100 μL / min nebulizer selected. -1 Furthermore, online gold capture methods require the acquisition and processing of instantaneous signals, and their window time is relatively short. Careful selection of data acquisition and processing strategies is crucial for obtaining accurate isotope ratios.

[0037] In this embodiment of the invention, the sample introduction device for ultra-trace mercury isotope analysis includes: a gold trapping tube for collecting mercury; a pyrolysis device for heating the gold trapping tube to release mercury; a membrane desolvation device for introducing thallium internal standard aerosol; and a multi-receiver inductively coupled plasma mass spectrometer.

[0038] In some embodiments, the gold trap tube is thermally decomposed to release mercury vapor, wherein the pyrolysis temperature is 450°C to 550°C.

[0039] Specifically, under these pyrolysis conditions, instantaneous and complete mercury desorption can be achieved. The pyrolysis temperature optimization process involves using a stannous chloride-nitrogen purging method to concentrate 100 pg Hg into a gold trap, adjusting the resistance wire voltage to change the temperature, and using an atomic fluorescence detector (AFS) to determine the recovery rate. The preferred temperature is 450℃-550℃, and the recovery rate of added mercury reaches 100.5±1.8%. The mercury residue after secondary heating is negligible (<1%).

[0040] In some embodiments, the carrier gas flow rate for transporting the mercury vapor is 0.16 L / min to 0.21 L / min; preferably, the carrier gas flow rate for transporting the mercury vapor is 0.18 L / min.

[0041] Specifically, under the aforementioned carrier gas conditions, the highest mercury isotope signal response can be obtained. Experiments have shown that the highest response can be achieved when the carrier gas flow rate used to transport the mercury vapor is 0.18 L / min. 202 Hg signal sensitivity.

[0042] In some embodiments, the thallium isotope internal standard aerosol is prepared by a method comprising:

[0043] Specifically, a thallium standard solution is introduced into a membrane desolvation device for desolvation to form a thallium isotope internal standard aerosol; wherein the purge gas flow rate of the membrane desolvation device for thallium injection is 2.6 L / min to 3.0 L / min; preferably, the purge gas flow rate of the membrane desolvation device for thallium injection is 2.8 L / min.

[0044] Specifically, experiments prove that the highest Hg signal sensitivity can be obtained when the purge gas flow rate of the film desolventizing device is 2.8 L / min. 202 Hg signal sensitivity.

[0045] In some embodiments, the supplementary gas flow rate introduced by the sample introduction is 0.9 L / min to 1.1 L / min; preferably, the supplementary gas flow rate introduced by the sample introduction is 1.0 L / min.

[0046] Specifically, experiments prove that the highest Hg signal sensitivity can be obtained when the supplementary gas flow rate introduced by the sample introduction is 1.0 L / min. 202 Hg signal sensitivity.

[0047] In some embodiments, in the collection of the Hg transient signal and the Tl isotope signal, the integration time of signal collection is 50 ms to 100 ms, and the sampling point number is 800 to 1200; preferably, the data collection strategy is the integration time of 66 ms and 1000 sampling points, which can sensitively capture the rapidly changing isotope signal values.

[0048] Specifically, in the embodiments of the present application, the collection parameter optimization process uses the isotope composition result measurement method precision of NIST SRM 3177 relative to NIST SRM 3133 repeated N times, wherein N = 20 to 40. The collection parameters consider two groups of parameters (8 ms, 5000 cycles) and (66 ms, 1000 cycles), and the preferred parameters are the integration time of 66 ms and 1000 sampling points, which can effectively capture the rapidly changing Hg isotope signal values on the premise of minimizing the amount of data collection.

[0049] In some embodiments, the Tl internal standard ratio correction algorithm is a mass discrimination correction algorithm using the Tl internal standard, which includes: in the determination time window, after screening and removing the Tl isotope ratio abnormal values exceeding 1 times of the standard deviation, 205 Tl / 203 Tl isotope ratio, calculating the average value of the Tl isotope ratio is used for correction. 205 Tl / 203 Tl isotope ratio. 205 Tl / 203 Tl isotope ratio.

[0050] Specifically, in the embodiments of the present application, the Tl internal standard correction modification strategy is to correct the Tl internal standard in the determination time window, 205 Tl / 203The Tl values were optimized. We included the following correction strategies: 1) no screening, using all values for correction calculation; 2) screening to remove outliers with 2 times standard deviation; 3) screening to remove outliers with 1 times standard deviation, and compared the isotopic results obtained by several methods. The results showed that the correction strategy for thallium internal standard correction was preferably screening to remove outliers with 1 times standard deviation.

[0051] In some embodiments, the calculation of the mercury isotope ratio is based on 198 Hg signal values. 199 Hg, 200 Hg, 201 Hg and 202 Hg relative to 198 Hg signal values. 198 Hg.

[0052] Specifically, to obtain accurate and reliable isotopic ratios, a data processing strategy based on linear regression fitting (LRS) was developed. The mercury isotope ratio algorithm uses the least squares linear regression fitting of the 199 Hg, 200 Hg, 201 Hg and 202 Hg relative to 198 Hg signal values to obtain the slope (k) for obtaining , wherein is 199 Hg, 200 Hg, 201 Hg and 202 Hg.

[0053] In some embodiments, the method of ultra-trace mercury isotope analysis further comprises: using the standard-sample cross method, using mercury isotope standard solution NIST SRM 3133 as a reference material, performing mass discrimination correction, and requiring the concentration of the sample solution to match the concentration of the adjacent standard solution within 10%.

[0054] In some embodiments, the above-mentioned method of ultra-trace mercury isotope analysis can directly analyze water samples with a concentration level of 10 ng L -1 The method is suitable for analyzing and determining the mercury isotope composition in natural water samples under the condition that the total mercury amount of the sample is 50 pg~100 pg.

[0055] Specifically, to obtain accurate and reliable isotope ratio and further reduce the lower limit of the determination concentration of the method, a linear regression fitting and thallium internal standard correction algorithm is developed. Under the condition of sample injection amount ≤100 pg, even as low as 50 pg, accurate isotope composition results can still be obtained.

[0056] Example 1 Construction of gold trapping tube trapping-pyrolysis-MC-ICP-MS combined system and optimization of gas path parameters

[0057] 1) The divalent mercury standard solution was prepared by stepwise dilution of the stock solution (GSB 04-1729-2004, 1000 μg mL -1 ) with deionized water, and was prepared immediately before use. The working solution concentration gradient was 10 μg mL -1 , 100 μg L -1 , 1 μg L -1 , 10 ng L -1 , respectively. The standard solution was only used to evaluate the recovery of the process of enriching zero-valent mercury to the gold tube by reduction-nitrogen sweeping. The mercury isotope standard solutions NIST SRM 3133 and NIST SRM 3177 were both prepared by stepwise dilution of the stock solution. The stock solution was diluted from the stock solution (100 μg mL -1 ) to 1 μg mL -1 , and bromine chloride (0.2 N, 5 ‰) was added to avoid light. The working solution was prepared by stepwise dilution of the stock solution, and the concentration gradient was 10 μg L -1 and 100 ng L -1 , respectively. The matrix was hydrochloric acid (10%, v / v ). The reducing agent was stannous chloride (SnCl2) solution for complete conversion of Hg(II) to Hg(0), with a concentration of 20% (20% SnCl2, w / v , 10% HCl, v / v ) when used in sweeping-gold trapping determination, and a concentration of 5% (5% SnCl2, w / v , 10% HCl, v / v ) when used in MC-ICP-MS tuning.

[0058] 2) The mercury in the solution was enriched to the gold trapping tube by stannous chloride reduction-nitrogen sweeping. The sweeping process was carried out in a borosilicate glass ground mouth bubble bottle, the outlet of the sweeping bottle was connected to a drying tube with built-in sodium lime using a silica gel sleeve, and finally connected to the gold trapping tube. 20 mL of stannous chloride solution was added to the sweeping bottle, followed by the addition of an appropriate amount of divalent mercury standard solution (such as 100 ng L -1 1 mL of standard solution 1, a total of 100 pg Hg), and the ground mouth bottle cap was tightly sealed. High-purity nitrogen gas was used as the sweeping gas, and the flow rate was 300 mL min-1 , and the purge duration was 6 min. The recovery of the purge-gold trapping process was evaluated using cold vapor atomic fluorescence spectrometry (CVAFS). After the recovery was confirmed, the mercury solution used in the subsequent purge-gold trapping processes was isotopic standard solution NIST SRM 3133 and NIST SRM 3177.

[0059] 3) The mercury isotope analysis used NIST SRM 3133 and NIST SRM 3177 mercury isotope standard solutions (1 μg L -1 , 10% HCl, v / v ) as internal standards. The thallium internal standard solution was diluted from the stock solution to 100 μg L -1 , and the matrix was 3% HNO3 ( v / v ). In the present embodiment, the concentration of the thallium solution was 100 μg L 205 The Tl signal response should be greater than 20 V, and if it is insufficient, the concentration of the thallium solution needs to be increased.

[0060] Cold vapor generation-multiple collector inductively coupled plasma mass spectrometry (CV-MC-ICP-MS) was used for instrument tuning. The mercury isotope solution NIST SRM 3133 (1 μg L -1 , 10% HCl, v / v ) and the reducing agent stannous chloride solution (5%, m / v , 10% HCl, v / v ) were introduced into the cold vapor generation device (HGX-200) for mixing, reduction, and gas-liquid separation. The mercury vapor after reduction and gas-liquid separation was mixed with the thallium aerosol and introduced into the ion source. The data acquisition parameters for the tuning process were integration time 2 s, 30 cycles, and 2 blocks. On the one hand, the parameters of the Inlet System were adjusted to obtain the strongest and most stable isotope response. Under the optimal combination of parameters, the 202 Hg response was 2 V (NIST SRM 3133, 1 μg L -1 , pump speed 0.56 mL min -1 ). On the other hand, the parameters of the Source Lenses and Zoom Optics were adjusted to obtain the optimal peak shape.

[0061] During the isotope determination process, the standard-sample bracketing method (SSB, with NIST SRM 3133 as the reference material) and the thallium internal standard were used to simultaneously correct the concentration of the sample solution. The concentration of the sample matched the concentration of the adjacent isotope standard solution NIST 3133 within 10%. The mercury isotope mass fractionation (MDF) in the sample was represented by δ xxx Hg, and the calculation formula was as follows:

[0062]

[0063] Massless fractionation (MIF) using Δ xxx Hg represents the measured δ xxx The difference between Hg and the predicted value based on the MDF law:

[0064]

[0065] 4) Connect the gold collection tube pyrolysis module to the membrane desolvation device and MC-ICP-MS. Use PFA material for the pipeline to avoid mercury adsorption. Figure 1 This is a schematic diagram of the overall process of the gold capture-pyrolysis-MC-ICP-MS system. The gas path parameters of the coupled system were optimized in detail to obtain the highest isotopic response and thus lower the detection limit of the method. The steps are as follows: First, measurements were performed using a NIST SRM 3133 isotope standard solution with a single injection volume of 1000 pg Hg. The flow rates of the sample gas carrying zero-valent mercury, the sweep gas used to generate the thallium aerosol membrane desolvation system, and the added gas introduced to the sample were optimized. The optimization process of the gas path parameters is as follows: Figure 2 As shown. Preferably, the sample carrier gas flow rate is 0.18 L / min. -1 The supplemental airflow rate is 1.0 L / min. -1 The purge gas flow rate of the membrane desolvation system is 2.8 L / min. -1 The optimal parameter combination yields the strongest response. Under the aforementioned injection conditions, 202 The peak value of the Hg signal reached 10 to 16 V. The above parameters were fine-tuned for each experiment, and the fluctuation range of the mercury isotope response value between each ignition and extinguishing was within 10% (all setting parameters are shown in Table 1).

[0066] Table 1. Parameters of the combined MC-ICP-MS system for purging-gold capture

[0067]

[0068] Example 2: Data Processing Method for Instantaneous Signals

[0069] Solution preparation and gold capture - MC-ICP-MS preliminary setup and gas path parameter optimization methods are the same as steps 1) to 4) of Example 1.

[0070] 5) Due to the transient signal generated by the pyrolysis of the gold trap tube, the data acquisition and processing methods are crucial for obtaining accurate isotope ratios. Gradient concentrations of isotope standard solutions (NIST SRM 3177 vs. NIST SRM 3133) were used to optimize the data strategy. In systems using transient signals, shorter integration times effectively record rapidly changing mercury isotope signals, yielding accurate isotope results (NIST SRM 3177, injection volume 1000 pg Hg, δ¹²). 202 Hg -0.51 ± 0.17‰, Δ 199 Hg -0.01 ± 0.08‰, Δ 200 Hg 0.01 ± 0.06‰, Δ 201 Hg -0.03 ± 0.08‰, mean ± 2SD, N = 48). However, using this set of parameters to collect data resulted in a large amount of data, causing software overload and abnormalities. In the acquisition software, the accuracy did not significantly decrease (δ) even with the second shortest integration time (66 ms, 1000 cycles). 202 Hg -0.55 ± 0.21‰, Δ 199 Hg -0.02 ± 0.12‰, Δ 200 Hg -0.01 ± 0.16‰, Δ 201 Hg -0.02 ± 0.19‰, mean ± 2SD, N = 49). Based on this, the preferred data acquisition parameters are as follows.

[0071] 6) The method of isotope data processing has a significant impact on the isotope analysis results of the acquired instantaneous signals. Compared to methods such as calculating the mean or peak area integral for each data point, the linear regression slope (LRS) algorithm performs better in terms of accuracy. Preferably, the linear regression slope method is used to calculate... xxx Hg and 198 The isotope ratio of Hg is corrected according to formulas (4) and (5) using Russell correction.

[0072]

[0073] Among them, 2.38714 is the absolute isotopic ratio of NIST SRM 997.

[0074] 7) To further reduce the lower limit of determination and achieve the analysis of ultra-low concentration of mercury isotopes in natural water samples, the thallium isotope ratio algorithm for mass discrimination correction was further improved. The sample amount of thallium isotope standard solution NIST SRM 3133 and NIST SRM 3177 was gradually reduced, with a gradient of 1000 pg, 500 pg, 200 pg, 100 pg, and 50 pg. By comparing the accuracy and precision of the determination results, the decrease in sample amount led to a significant decrease in determination precision. When linear fitting was calculated, the R 2 There was no significant decrease, all of which were higher than 0.99999, and the relative standard deviation of the Tl 205 203 Tl ratio for mass discrimination correction increased. Accordingly, the Tl 205 203 Tl ratio used for calculation was adjusted, and the screening of outliers could effectively improve the precision (Table 2). The δ 202 Hg determination value was adjusted from -0.42 ± 1.26 ‰ to -0.46 ± 0.52 ‰ (removing 2SD outliers) and -0.50 ± 0.29 ‰ (removing 1SD outliers), and all isotope determination values were significantly improved. Using the processing strategy of removing 1SD outliers, the isotope standard solution NIST SRM 3177 determination result was δ 202 Hg -0.50 ± 0.29 ‰, Δ 199 Hg -0.05 ± 0.31 ‰, Δ 200 Hg -0.01 ± 0.22 ‰, Δ 201 Hg 0.00 ± 0.21 ‰ (N = 36).

[0075] Table 2 NIST SRM 3177 mercury isotope composition under different thallium isotope ratio algorithms

[0076]

[0077] Example 3 Verification in ultra-trace mercury isotope analysis

[0078] Solution configuration and gold trapping-MC-ICP-MS setup and parameter optimization method same as example 1 and 2 steps 1) to 7).

[0079] ​​The application feasibility and isotope fidelity of the application in a complex matrix were verified by using a national primary standard substance standard seawater (GBW13150) to carry out a spiking experiment, and the stability of the mercury isotope composition in multiple parallel experiments was systematically evaluated. Six groups of experiments were carried out by using two isotope standard solutions of NIST SRM 3133 and NIST SRM 3177 as the spiking source, and mixing and pretreatment was carried out according to different settings (the solution concentration was set to 4 ng L -1 20 mL), and the stability of the isotope determination results was investigated. The specific settings were as follows: ① NIST 3133 80 pg; ② NIST 3133 64 pg and NIST 3177 16 pg; ③ NIST 3133 48 pg and NIST 3177 32 pg; ④ NIST 3133 32 pg and NIST 3177 48 pg; ⑤ NIST 3133 16 pg and NIST 3177 64 pg; and ⑥ NIST 3177 80 pg. The determination results are shown in Table 3, and δ 202 The Hg determination values (-0.11 ‰ to -0.46 ‰) fluctuated around the corresponding standard values (0 ‰ to -0.53 ‰) basically, and the deviation range was ±0.2 ‰ as a whole, which was consistent with the literature report, indicating that there was no obvious mass fractionation (MDF) in the seawater spiking, enrichment and isotope determination processes. In terms of non-mass fractionation (MIF), Δ 199 Hg, Δ 200 Hg and Δ 201 The determination values of Hg, Δ

[0080] Table 3 Isotope composition of the standard seawater (GBW13150) spiking experiment

[0081]

[0082] It is easy for those skilled in the art to understand that the above advantageous modes can be freely combined and superimposed without conflict. The above is only a preferred embodiment of the present application and does not limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application. The above is only a preferred embodiment of the present application, and it should be pointed out that, for ordinary skilled in the art, without departing from the technical principles of the present application, a number of improvements and modifications can be made, and these improvements and modifications should be regarded as the protection scope of the present application.

Claims

1. A method for ultra-trace mercury isotope analysis, characterized in that, Includes the following steps: The liquid sample to be tested was purged with nitrogen under a stannous chloride atmosphere to collect and concentrate mercury into a gold collection tube; The gold trapping tube is thermally decomposed to release mercury vapor; The mercury vapor was mixed with a thallium isotope internal standard aerosol and used as the injection sample, which was then introduced into a multi-receiver inductively coupled plasma mass spectrometer. Acquire instantaneous mercury signals and thallium isotope signals; The mercury isotope ratios were calculated using a combination of least squares linear regression fitting and thallium internal standard ratio correction algorithm. The thallium internal standard ratio correction algorithm uses a thallium internal standard. 205 Tl / 203 Quality discrimination correction was applied to Tl isotope ratios, including: within the measurement time window, filtering out values ​​exceeding one standard deviation. 205 Tl / 203 After the Tl isotope ratio anomaly, calculate 205 Tl / 203 The average value of the Tl isotope ratios was used for correction; The method described herein is used to analyze and determine the mercury isotope composition in natural water samples when the total amount of mercury injected is between 50 pg and 100 pg.

2. The method for ultra-trace mercury isotope analysis according to claim 1, characterized in that, The pyrolysis temperature is 450℃~550℃.

3. The method for ultra-trace mercury isotope analysis according to claim 1, characterized in that, The carrier gas flow rate used to transport the mercury vapor is 0.16 L / min to 0.21 L / min.

4. The method for ultra-trace mercury isotope analysis according to claim 1, characterized in that, The thallium isotope internal standard aerosol is prepared by the following method: A thallium standard solution is introduced into a membrane desolvation device for desolvation to form the thallium isotope internal standard aerosol; wherein the purge gas flow rate of the membrane desolvation device is 2.6 L / min to 3.0 L / min.

5. The method for ultra-trace mercury isotope analysis according to claim 1, characterized in that, The supplementary gas flow rate introduced into the sample is 0.9 L / min to 1.1 L / min.

6. The method for ultra-trace mercury isotope analysis according to claim 1, characterized in that, In the acquisition of instantaneous mercury signals and thallium isotope signals, the integration time for signal acquisition is 50 ms to 100 ms, and the number of sampling points is 800 to 1200.

7. The method for ultra-trace mercury isotope analysis according to claim 1, characterized in that, The calculation of the mercury isotope ratio is based on 198 The Hg signal value is the reference, for 199 Hg, 200 Hg, 201 Hg and 202 Hg relative 198 The Hg signal value was fitted using least-squares linear regression, and the slope obtained from the fitting was used as the ratio of each isotope to the Hg signal. 198 The ratio of Hg.

8. The method for ultra-trace mercury isotope analysis according to claim 1, characterized in that, The method further includes: Using the standard-sample cross-reference method, with the mercury isotope standard solution NIST SRM 3133 as the reference, mass discrimination correction was performed, requiring the concentration of the sample solution to match the concentration of the adjacent standard solution within 10%.

9. The method for ultra-trace mercury isotope analysis according to any one of claims 1-8, characterized in that, The method is used for 10 ng / L -1 Direct mercury isotope analysis was performed on natural water samples at concentration levels.

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