Ultratrace mercury isotope analysis method

Abstract

The invention discloses an ultratrace mercury isotope analysis method, and relates to the technical field of environmental analysis. The method comprises the following steps: purging a liquid sample to be detected by nitrogen in a stannous chloride atmosphere, and trapping and concentrating mercury into a gold trapping tube; pyrolyzing the pyrolytic gold trapping tube to release mercury vapor; pyrolytic mercury vapor and thallium isotope internal standard aerosol are mixed to serve as a sample injection sample, and the sample injection sample is introduced into a multi-receiver inductively coupled plasma mass spectrometry; acquiring a mercury instantaneous signal and a thallium isotope signal; and calculating the mercury isotope ratio by adopting least square linear regression fitting in combination with a thallium internal standard ratio correction algorithm. According to the method, the instantaneous mercury isotope signal is generated by online combination of gold trapping and multi-receiver inductively coupled plasma mass spectrometry, the instantaneous signal is strategically collected and processed, the determination concentration of isotope analysis can be greatly reduced, the sensitivity of the method is remarkably improved, and direct determination of mercury isotope composition in a water sample with the concentration of 10 ng L <-1 > is met.

Description

Technical Field

[0001] This invention relates to the field of environmental analysis technology, and specifically to a method for ultra-trace mercury isotope analysis. Background Technology

[0002] As the largest mercury exchange flux among Earth's interfaces, the atmosphere-water interface accounts for approximately 32% to 54% of the global mercury cycle, and its exchange mechanisms and influencing factors urgently require in-depth research. The effectiveness of mercury isotope fractionation fingerprinting in tracking the migration and transformation of mercury in the environment has been widely demonstrated, and accurate analysis of the mercury isotope composition in natural water bodies has become a key research need.

[0003] Inductively coupled plasma mass spectrometry (MC-ICP-MS) using a cold vapor generator to introduce the sample solution is a routine method for mercury isotope analysis. This method has relatively strict requirements on the mercury concentration in the sample, typically requiring a concentration higher than 1 μg / L. -1 To meet its measurement accuracy, however, this concentration level is far higher than that of natural water (typically a few to tens of ng / L). -1 To address this technological bottleneck, offline pre-enrichment techniques such as purging / combustion-oxidizing solution absorption and ion exchange resins have been established for the extraction and concentration of mercury. However, these offline operations are typically cumbersome, requiring significant amounts of reagents, materials, manpower, and time, and the total sample volume must reach 5 ng Hg. Previous studies have optimized the sample volume to 200 pg Hg, but achieving ultra-trace isotopic composition analysis in natural water samples remains challenging; currently, there is no method to directly determine isotopes up to 100 pg Hg.

[0004] In summary, existing technologies are insufficient to meet the needs of isotopic analysis of ultra-trace mercury in natural water bodies, and there is an urgent need to establish effective methods. Summary of the Invention

[0005] Based on this, this invention proposes a method for determining ultra-trace mercury isotopes using a synergistic strategy of pyrolysis sampling with a gold trap and internal standard correction. By strategically collecting and processing the transient signal, the method's sensitivity is significantly improved while maintaining good internal accuracy. This drastically reduces the sample volume required for mercury isotope analysis from the ng level to 50 pg, thus overcoming the technical bottleneck of existing technologies that cannot determine extremely low concentrations of mercury isotopes in natural water samples. This method can determine ultra-trace mercury isotopes in samples as small as 10 ng / L. -1 Direct mercury isotope analysis of water samples at concentration levels offers advantages such as no need for offline enrichment operations, high sensitivity, accuracy, and speed.

[0006] Therefore, the present invention provides a method for ultra-trace mercury isotope analysis, comprising 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 trap 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 by using least squares linear regression fitting combined with a thallium internal standard ratio correction algorithm.

[0007] Furthermore, the pyrolysis is performed at a temperature of 450℃~550℃.

[0008] Furthermore, the carrier gas flow rate for transporting the mercury vapor is 0.16 L / min to 0.21 L / min.

[0009] Furthermore, the thallium isotope internal standard aerosol is prepared by a method comprising: 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.

[0010] Furthermore, the supplementary gas flow rate introduced into the sample is 0.9 L / min to 1.1 L / min.

[0011] Furthermore, in the acquisition of the instantaneous mercury signal and the thallium isotope signal, the integration time for signal acquisition is 50 ms to 100 ms, and the number of sampling points is 800 to 1200.

[0012] Furthermore, 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.

[0013] Furthermore, 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. 198The ratio of Hg.

[0014] Furthermore, the method also 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%.

[0015] Furthermore, the method is used for 10 ng L -1 Direct mercury isotope analysis was performed on natural water samples at concentration levels, and / or the mercury isotope composition in natural water samples was analyzed and determined under conditions where the total amount of mercury injected was 50 pg to 100 pg.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: The method for ultra-trace mercury isotope analysis of this invention utilizes online coupling of gold trapping and multi-receiver inductively coupled plasma mass spectrometry to generate transient mercury isotope signals. Strategic collection and processing of these transient signals allows for a significant reduction in the concentration to be measured in isotope analysis, thereby substantially improving the method's sensitivity and meeting the requirements of 10 ng / L. -1 Direct determination of mercury isotope composition in water samples of varying concentrations. When processing instantaneous signals to calculate mercury isotope ratios, a least-squares fitting linear regression algorithm is applied. Furthermore, by optimizing the thallium isotope ratio algorithm with quality discrimination correction, the standard deviation of the method can be significantly reduced, resulting in a substantial improvement in the method's internal accuracy. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in the embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0018] Figure 1 A schematic diagram of a gold trapping-multiple receiver inductively coupled plasma mass spectrometry (P&T-MC-ICP-MS) system provided in an embodiment of the present invention.

[0019] Figure 2 An optimized diagram of the gas path parameters for the purge-gold capture-MC-ICP-MS combined system provided in an embodiment of the present invention. Detailed Implementation

[0020] To better understand the above technical solutions, the technical solutions of the embodiments of this application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of this application and the specific features in the embodiments are detailed descriptions of the technical solutions of the embodiments of this application, rather than limitations on the technical solutions of this application. In the absence of conflict, the embodiments of this application and the technical features in the embodiments can be combined with each other.

[0021] This invention provides a method for ultra-trace mercury isotope analysis, comprising 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 trap 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 by using least squares linear regression fitting combined with a thallium internal standard ratio correction algorithm.

[0022] The method for ultra-trace mercury isotope analysis provided in this invention addresses the concentration limitations of traditional methods. It utilizes online coupling of gold trapping and multi-receiver inductively coupled plasma mass spectrometry to generate transient mercury isotope signals. Strategic collection and processing of these transient signals significantly lowers the required concentration for isotope analysis, thereby substantially improving method sensitivity and meeting the requirements of 10 ng / L. -1 Direct determination of mercury isotope composition in water samples of varying concentrations. Addressing the internal accuracy issues in establishing ultra-trace mercury isotope analysis methods, a least-squares fitting linear regression algorithm is applied when calculating mercury isotope ratios using instantaneous signals. Furthermore, by optimizing the thallium isotope ratio algorithm with quality discrimination correction, the standard deviation of the method can be significantly reduced, thus substantially improving the method's internal accuracy.

[0023] Specifically, the gold collecting tube is placed in a pyrolysis apparatus. The zero-valent mercury vapor generated by pyrolysis is mixed with a thallium isotope internal standard aerosol and introduced into a multi-detector inductively coupled plasma mass spectrometry (MC-ICP-MS) system to analyze the mercury isotope composition. Optionally, stannous chloride reduction-nitrogen purging is used to collect and concentrate the mercury in solution into the gold collecting tube, wherein the concentration of stannous chloride is 20% (in 10% HCl). v / v The nitrogen purging flow rate was 300 mL / min. -1 The duration is 6 min. Optionally, an internal standard thallium isotope solution (NIST SRM 997, 100 μg / L) is prepared. -1 3% HNO3 v / vStable 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.

[0024] 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.

[0025] In some embodiments, the gold trap tube is thermally decomposed to release mercury vapor, wherein the pyrolysis temperature is 450°C to 550°C.

[0026] 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%).

[0027] 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.

[0028] 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.

[0029] In some embodiments, the thallium isotope internal standard aerosol is prepared by a method comprising: 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.

[0030] Specifically, experiments have shown that the highest efficiency can be obtained when the purge gas flow rate of the membrane desolvation device is 2.8 L / min. 202 Hg signal sensitivity.

[0031] In some embodiments, the supplementary gas flow rate introduced for the sample injection is 0.9 L / min to 1.1 L / min; preferably, the supplementary gas flow rate introduced for the sample injection is 1.0 L / min.

[0032] Specifically, experiments have shown that the highest efficiency can be achieved when the supplementary gas flow rate introduced into the sample is 1.0 L / min. 202 Hg signal sensitivity.

[0033] In some embodiments, the integration time for acquiring instantaneous mercury signals and thallium isotope signals is 50 ms to 100 ms, and the number of sampling points is 800 to 1200. Preferably, the data acquisition strategy is an integration time of 66 ms and 1000 sampling points, which can sensitively capture rapidly changing isotope signal values.

[0034] Specifically, in this embodiment of the invention, the acquisition parameter optimization process uses the NIST SRM 3177's isotopic composition results from N repeated measurements relative to the NIST SRM 3133 to measure method accuracy, where N = 20 to 40. Two sets of acquisition parameters are considered: (8 ms, 5000 cycles) and (66 ms, 1000 cycles). The preferred parameters are an integration time of 66 ms and 1000 sampling points, which can effectively capture rapidly changing mercury isotope signal values ​​while minimizing the amount of data acquisition.

[0035] In some embodiments, the thallium internal standard ratio correction algorithm employs 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.

[0036] Specifically, in this embodiment of the invention, the thallium internal standard correction strategy is for the thallium internal standard within the measurement time window. 205 Tl / 203 We optimized the thallium (Tl) values. We used the following correction strategies: 1) no filtering, using all values ​​for correction calculation; 2) filtering and removing out-of-bounds values ​​by 2 times the standard deviation; 3) filtering and removing out-of-bounds values ​​by 1 time the standard deviation. We compared the isotope results obtained by these methods. The results showed that the optimal correction strategy for thallium internal standard correction was to filter and remove out-of-bounds values ​​by 1 time the standard deviation.

[0037] In some embodiments, the calculation of mercury isotope ratios is based on... 198 The Hg signal value is the reference, for199 Hg, 200 Hg, 201 Hg and 202 Hg relative 198 The Hg signal value was fitted using least-squares linear regression, and the slope (k) obtained from the fitting was used as the slope of each isotope relative to the signal. 198 The ratio of Hg.

[0038] Specifically, to obtain accurate and reliable isotope ratios, a data processing strategy based on linear regression fitting (LRS) was developed. The mercury isotope ratio algorithm utilizes data collected within a time window. 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 (k) was obtained for use in obtaining... ,in, for 199 Hg, 200 Hg, 201 Hg and 202 Hg.

[0039] In some embodiments, the method for ultra-trace mercury isotope analysis further includes: using a standard-sample cross-reference method, with the mercury isotope standard solution NIST SRM 3133 as a reference, performing mass discrimination correction, requiring the concentration of the sample solution to match the concentration of the adjacent standard solution within 10%.

[0040] In some embodiments, the above-described method for ultra-trace mercury isotope analysis can be used for 10 ng / L of mercury isotopes. -1 Direct mercury isotope analysis of water samples at concentration levels is applicable to the analysis and determination of mercury isotope composition in natural water samples with a total mercury content of 50 pg to 100 pg.

[0041] Specifically, in order to obtain accurate and reliable isotope ratios and further reduce the lower limit of the determination concentration of the method, this invention has developed a correction algorithm based on linear regression fitting and thallium internal standard correction. Under the condition of injection volume ≤100 pg, or even as low as 50 pg, accurate isotope composition results can still be obtained.

[0042] Example 1: Construction and gas path parameter optimization of a gold trapping tube-pyrolysis-MC-ICP-MS combined system. 1) The divalent mercury standard solution was prepared from the stock solution (GSB 04-1729-2004, 1000 μg / mL). -1 (1 M HNO3) should be diluted stepwise with deionized water, and prepared fresh each time. The concentration gradient of the working solution should be 10 μg / mL.-1 100 μg L -1 1 μg L -1 10 ng L -1 This standard solution is used only to evaluate the recovery rate of the reduction-nitrogen purging process that enriches zero-valent mercury into the gold tube. Both NIST SRM 3133 and NIST SRM 3177 mercury isotope standard solutions were serially diluted from the stock solutions. The stock solutions were prepared from the mother solution (100 μg / mL). -1 Dilute to 1 μg mL -1 Add bromine chloride (0.2 N, 5‰) and store protected from light. The working solution is prepared by serial dilution of the stock solution, with a concentration gradient of 10 μg / L. -1 and 100 ng L -1 The matrix is ​​hydrochloric acid (10%). v / v Prepare fresh before use. Stannous chloride (SnCl2) solution is used as the reducing agent for the complete conversion of Hg(II) to Hg(O), with a concentration of 20% when using purge-gold trapping for determination. w / v 10% HCl v / v The concentration used for MC-ICP-MS tuning is 5%. w / v 10% HCl v / v ).

[0043] 2) Mercury in the solution is enriched into the gold collecting tube by stannous chloride reduction followed by nitrogen purging. The purging process is carried out in a borosilicate glass ground glass bubble flask. The outlet of the flask is connected to a drying tube with a built-in soda lime using a silicone sleeve, and finally connected to the gold collecting tube. Add 20 mL of stannous chloride solution to the flask, followed by an appropriate amount of divalent mercury standard solution (e.g., 100 ng / L). -1 Add 1 mL of standard solution (total volume is 100 pg Hg) and seal the bottle tightly with the ground glass stopper cap. Use high-purity nitrogen as the purge gas at a flow rate of 300 mL / min. -1 The purge duration was 6 min. The recovery rate of the purge-gold capture process was evaluated using the cold vapor deposition method (CVAFS). After confirming the recovery rate, the mercury solutions used in subsequent purge-gold capture processes were the isotope standard solutions NIST SRM 3133 and NIST SRM 3177.

[0044] 3) Mercury isotope analysis was performed using daily prepared NIST SRM 3133 and NIST SRM 3177 mercury isotope standard solutions (1 μg / L). -1 10% HCl v / v The thallium isotope standard solution NIST SRM 997 was used as an internal standard. The thallium internal standard solution was diluted from the stock solution to 100 μg / L. -1 The matrix is ​​3% HNO3 (v / v In this embodiment of the invention, the generated thallium aerosol... 205 The Tl signal response should be greater than 20 V; if it is insufficient, the thallium solution concentration needs to be increased.

[0045] Cold vapor generator-multiple receiver inductively coupled plasma mass spectrometry (CV-MC-ICP-MS) was used for instrument tuning. A peristaltic pump was used to deliver the mercury isotope solution NIST SRM 3133 (1 μg / L). -1 10% HCl v / v ) and reducing agent stannous chloride solution (5%) m / v 10% HCl v / v The mercury vapor, after reduction and gas-liquid separation, is introduced into a cold vapor generator (HGX-200) for thorough mixing. The resulting mercury vapor is then mixed with thallium aerosol and introduced into the ion source. The data acquisition parameters for the tuning process are an integration time of 2 s, 30 cycles, and 2 blocks. On one hand, the parameters of the Inlet System are adjusted to obtain the strongest and most stable isotopic response. Under the optimal parameter combination, the following can be obtained: 202 The Hg response was 2 V (NIST SRM 3133, 1 μg L). -1 Pump speed 0.56 mL / min -1 On the other hand, adjust the parameters of Source Lenses and Zoom Optics to obtain the optimal peak shape.

[0046] During isotope determination, a standard-sample cross-reference (SSB, using NIST SRM 3133 as the reference) and a thallium internal standard were used for simultaneous mass discrimination correction. The concentration of the sample solution was matched to the concentration of the adjacent isotope standard solution NIST 3133 within 10%. Mercury isotope mass fractionation (MDF) in the sample was performed using δ¹⁸O₅. xxx Hg is represented by the following formula:

[0047] 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:

[0048] 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 1This 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).

[0049] Table 1. Parameters of the combined MC-ICP-MS system for purging-gold capture

[0050] Example 2: Data Processing Method for Instantaneous Signals 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.

[0051] 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 201Hg -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.

[0052] 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.

[0053]

[0054] Among them, 2.38714 is the absolute isotopic ratio of NIST SRM 997.

[0055] 7) To further lower the detection limit and achieve analysis of extremely low concentrations of mercury isotopes in natural water samples, the thallium isotope ratio algorithm used for mass discrimination correction was further improved. The injection volumes of the NIST SRM 3133 and NIST SRM 3177 isotope standard solutions were gradually decreased at gradients of 1000 pg, 500 pg, 200 pg, 100 pg, and 50 pg. Comparing the accuracy and precision of the measurement results, the decrease in injection volume significantly reduced the measurement precision. In the linear fitting calculation, R0 was used to evaluate the linear fitting effect of mercury isotopes. 2 There was no significant decrease; all values ​​were above 0.99999, while those used for quality discrimination correction... 205 Tl / 203 The relative standard deviation of the Tl ratio has increased. Therefore, the values ​​used for calculation have been adjusted. 205 Tl / 203 Tl ratio, screening to remove outliers can effectively improve accuracy (Table 2). δ¹⁸O values ​​of the isotope standard solution NIST SRM 3177. 202The Hg measurements were adjusted from -0.42 ± 1.26‰ to -0.46 ± 0.52‰ (removing 2SD out-of-bounds values) and -0.50 ± 0.29‰ (removing 1SD out-of-bounds values), resulting in significant improvements in all isotope measurements. Using the 1SD out-of-bounds removal strategy, the NIST SRM 3177 isotope standard solution measurement results were 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).

[0056] Table 2. Mercury isotope composition of NIST SRM 3177 under different thallium isotope ratio algorithms.

[0057] Example 3: Validation in ultra-trace mercury isotope analysis The solution preparation, gold capture-MC-ICP-MS setup, and parameter optimization methods are the same as steps 1) to 7) in Examples 1 and 2.

[0058] Spiking experiments were conducted using national primary standard reference material, seawater (GBW13150), to verify the feasibility of this invention in complex matrices and its isotopic fidelity, and to systematically evaluate the stability of mercury isotopic composition in multiple parallel experiments. All six experiments used NIST SRM 3133 and NIST SRM 3177 isotopic standard solutions as spiking sources, and mixing and pretreatment were performed according to different settings (solution concentration set at 4 ng / L). -1 The stability of the isotope determination results was investigated using 20 mL of NIST 3133. The specific settings were: ① NIST 3133 80 pg; ② NIST 3133 64 pg, NIST 3177 16 pg; ③ NIST 3133 48 pg, NIST 3177 32 pg; ④ NIST 3133 32 pg, NIST 3177 48 pg; ⑤ NIST 3133 16 pg, NIST 3177 64 pg; ⑥ NIST 3177 80 pg. The determination results are shown in Table 3, δ 202 The measured Hg values ​​(-0.11‰ to -0.46‰) generally fluctuated around the corresponding standard values ​​(0‰ to -0.53‰), with an overall deviation range of ±0.2‰, consistent with literature reports. This indicates that there was no significant mass fractionation (MDF) during seawater spiking, enrichment, and isotope determination. Regarding mass non-mass fractionation (MIF), Δ... 199 Hg, Δ 200 Hg and Δ201 The measured Hg values ​​were generally close to 0‰, with the vast majority falling within ±0.20‰, and no significant non-mass fractionation was observed. These results demonstrate the reproducibility of this invention for ultra-trace mercury isotope composition analysis in complex matrix samples.

[0059] Table 3. Isotopic composition of standard seawater (GBW13150) spiked experiments

[0060] It will be readily understood by those skilled in the art that the above-described advantageous methods can be freely combined and superimposed without conflict. The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this 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 trap 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 by using least squares linear regression fitting combined with a thallium internal standard ratio correction algorithm.

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 thallium internal standard ratio correction algorithm uses thallium internal standards. 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.

8. 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.

9. 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%.

10. The method for ultra-trace mercury isotope analysis according to any one of claims 1-9, 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, and / or the mercury isotope composition in natural water samples was analyzed and determined under conditions where the total amount of mercury injected was 50 pg to 100 pg.

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