Method for determining the content of elements in seawater

Abstract

This application provides a method for determining the elemental content in seawater. The method includes the following steps: Sample preparation: Acidifying and filtering the original sample to obtain a processed sample. Stepwise dilution: Diluting the processed sample with ultrapure water at different ratios to obtain diluted samples for macroelements and microelements. Matrix matching: Preparing multiple sets of matched solutions for macroelements and microelements. Curve plotting: Establishing a response signal-element content standard curve based on the multiple sets of matched solutions for macroelements and microelements to obtain the element content. This method enables more efficient and accurate detection of multiple elements in complex water samples such as seawater without introducing a complex processing system.

Description

Technical Field

[0001] This application relates to the field of analytical testing technology, and in particular to a method for determining the elemental content in seawater. Background Technology

[0002] Against the backdrop of global climate change, marine resource development, and increasingly demanding polar scientific expeditions, the precise analysis of seawater chemical composition has become a cornerstone supporting the development of marine science. Seawater is a typical natural water body with high salinity and highly complex composition. Its total dissolved solids content is typically around 3.5%, mainly composed of inorganic salts such as sodium chloride, magnesium sulfate, and calcium chloride, while also containing a variety of metallic and non-metallic elements with significantly different orders of magnitude. The high concentration of matrix salts in seawater not only manifests as high viscosity and surface tension in the physical properties of the sample but also significantly affects the stability and signal response of analytical instruments. Especially in high-sensitivity analytical techniques such as inductively coupled plasma mass spectrometry (ICP-MS), it can lead to salt accumulation and blockage in the sampling system, as well as generate massive amounts of polyatomic ion interference, severely inhibiting the detection sensitivity of trace elements.

[0003] To address these challenges, various technical approaches have been developed for elemental analysis of complex water samples. Offline pretreatment methods, such as chelation resin exchange and magnesium hydroxide coprecipitation, are widely used. These methods remove high-salt matrices and enrich target elements, mitigating matrix interference and improving detection sensitivity to some extent. However, these methods typically involve multiple steps, requiring high experimental conditions and skilled operators. They not only have long analysis cycles but also suffer from sample loss, insufficient repeatability, and increased risk of exogenous contamination in practical applications. Another approach involves online aerosol dilution or improved sample introduction systems, introducing dedicated aerosol dilution devices to reduce the salt load entering the plasma. This method improves the long-term stability of the instrument and reduces the risk of contamination in the sample introduction system to some extent, but its system structure is complex, equipment costs are high, and it has stringent requirements for operating conditions and maintenance.

[0004] Therefore, how to achieve more efficient and accurate detection of multiple elements in complex water samples such as seawater without introducing complex processing systems remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for determining the elemental content in seawater. By addressing the significant differences in elemental content among complex water samples, the method involves differentially diluting the sample and configuring matching matrix conditions at each dilution level for quantitative analysis. This achieves accurate determination of multiple elements in the same complex water sample. It eliminates the need for complex online dilution or enrichment devices, resulting in a relatively simple method suitable for routine analysis and long-term monitoring of high-salinity, complex water bodies such as seawater. It possesses significant practical value and potential for wider application.

[0006] This invention provides a method for determining the elemental content in seawater, comprising the following steps:

[0007] (a) Sample preparation: The original sample is acidified and filtered to obtain the processed sample;

[0008] (b) Stepwise dilution: The treated sample is diluted with ultrapure water at different ratios to obtain macro-element diluted samples and trace element diluted samples; wherein the ratio of the dilution factor of the macro-element diluted sample to the dilution factor of the trace element diluted sample is ≥10.

[0009] (c) Matrix matching: Prepare multiple sets of macro-element matching solutions and multiple sets of trace element matching solutions;

[0010] The constant element matching solution includes constant elements, and the content of the constant elements in multiple sets of constant element matching solutions covers the predicted content range of the constant elements in the constant element diluted sample.

[0011] The trace element matching solution includes trace elements, and the content of the trace elements in multiple sets of trace element matching solutions covers the predicted content range of trace elements in the trace element diluted sample.

[0012] (d) Curve plotting: Establish a response signal-macro element content standard curve based on the multiple sets of macro element matching solutions, and obtain the content of the macro element based on the response signal-macro element content standard curve and the macro element diluted sample; establish a response signal-trace element content standard curve based on the multiple sets of trace element matching solutions, and obtain the content of the trace element based on the response signal-trace element content standard curve and the trace element diluted sample.

[0013] In one possible implementation, as described above, the macroelements include at least one of sodium, magnesium, calcium, potassium, boron, and strontium, and the content of the macroelements in the multi-group macroelement matching solution is 0-500 µg / L; the trace elements include at least one of lead, mercury, cadmium, arsenic, copper, zinc, nickel, cobalt, manganese, and chromium, and the content of the trace elements in the multi-group trace element matching solution is 0-5 µg / L.

[0014] In one possible implementation, as described above, the dilution factor of the macro-element dilution sample is not less than 10 times relative to the treated sample, and the dilution factor of the trace element dilution sample is not more than 10 times.

[0015] In one possible implementation, as described above, the correlation coefficient between the response signal-constant element content standard curve and the response signal-trace element content standard curve is greater than 0.999.

[0016] In one possible implementation, as described above, the pH value of the treated sample is less than 2, and it is stored at 4°C.

[0017] In one possible implementation, as described above, the filtration process employs a microporous membrane with a pore size of 0.2-1.0 µm.

[0018] In one possible implementation, as described above, the original sample comprises at least one of seawater samples collected at depths of 0.5m, 5m, and 10m below the sea surface.

[0019] In one possible implementation, as described above, the response signal is measured using inductively coupled plasma mass spectrometry (ICP-MS), wherein the plasma parameters include a radio frequency power of 1550-1650 W, a plasma gas flow rate of 15-18 L / min, an auxiliary gas flow rate of 1.0-1.2 L / min, and a carrier gas flow rate of 0.7-1.0 L / min; and the mass spectrometry parameters include a full scan mode, a scan mass number range of 5-250 amu, an ion lens voltage of 100-150 V, and a detector voltage of 1800-2200 V.

[0020] In one possible implementation, as described above, step (d) further includes at least one of a blank experiment, a spiked recovery experiment, and a parallel sample determination.

[0021] In one possible implementation, as described above, if the difference in the spiked recoveries of multiple macroelements in the macroelement dilution sample is less than or equal to 5%, and the estimated range of the content of each macroelement differs by less than 10 times, then a set of macroelement matching solutions includes multiple macroelements; if the difference in the spiked recoveries of multiple trace elements in the trace element dilution sample is less than or equal to 5%, and the estimated range of the content of each trace element differs by less than 10 times, then a set of trace element matching solutions includes multiple trace elements.

[0022] This invention provides a method for determining the elemental content in seawater, which ensures that target elements at different concentration levels are in their respective suitable detection states. This effectively avoids signal saturation and excessive matrix loading caused by high-concentration elements, while reducing the risk of signal suppression during the detection process for low-concentration elements. By matching the matrix conditions with the state of the sample, the stability of the signal response and the reliability of the linear relationship are improved, thereby significantly enhancing the accuracy and repeatability of multi-element quantitative analysis in complex water samples. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0024] Figure 1 This is a standard curve of the response signal and constant element content from Example 1 of this application.

[0025] Figure 2 This is a standard curve of response signal-trace element content from Example 1 of this application;

[0026] Figure 3 This is a standard curve of response signal-constant element content from Example 2 of this application;

[0027] Figure 4 This is a standard curve of response signal-trace element content from Example 2 of this application;

[0028] Figure 5 This is a standard curve of the response signal and constant element content for Comparative Example 1 of this application.

[0029] Figure 6 This is a standard curve of the response signal and trace element content for Comparative Example 1 of this application.

[0030] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0031] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0032] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0033] When analyzing the elemental content of complex water samples such as seawater, existing techniques often dilute the sample 20-100 times to reduce the impact of high-salinity environments on the detection instruments, lowering the TDS to below 0.2%. While this protects the instrument, it sacrifices the detection limit for trace elements, requiring further enrichment or separation before determination. Furthermore, existing techniques typically focus only on the element concentration range when preparing standard solutions, rarely considering the differences in actual matrix conditions at different dilution levels. This approach easily introduces systematic biases in complex matrix environments, resulting in inconsistencies between the standard curve and the response relationship of the sample, especially when determining multiple elements simultaneously. Therefore, starting from the overall sample detection state and considering the inherent relationship between sample dilution, elemental distribution, and matrix conditions, the inventors proposed a new technical concept: by dividing complex water samples into different dilution levels and constructing matching analytical conditions for each dilution, quantitative analysis of each target element can be performed in a suitable detection environment. This concept breaks through the inertia of traditional methods, providing a new solution for the accurate determination of multiple elements in complex water samples.

[0034] This invention provides a method for determining the elemental content in seawater, comprising the following steps:

[0035] (a) Sample preparation: The original sample is acidified and filtered to obtain the processed sample;

[0036] (b) Scale dilution: The treated sample is diluted with ultrapure water at different factors to obtain macro-element diluted samples and trace element diluted samples; wherein the ratio of the dilution factor of the macro-element diluted sample to the dilution factor of the trace element diluted sample is ≥10.

[0037] (c) Matrix matching: Prepare multiple sets of macro-element matching solutions and multiple sets of trace element matching solutions;

[0038] The constant element matching solution includes constant elements, and the content of constant elements in multiple sets of constant element matching solutions covers the predicted content range of constant elements in the constant element diluted sample.

[0039] Trace element matching solutions include trace elements, and the content of trace elements in multiple sets of trace element matching solutions covers the predicted content range of trace elements in the trace element diluted samples.

[0040] (d) Curve plotting: Establish a standard curve of response signal-macro element content based on multiple sets of macro element matched solutions. Obtain the content of macro elements based on the standard curve of response signal-macro element content and the diluted macro element samples. Establish a standard curve of response signal-trace element content based on multiple sets of trace element matched solutions. Obtain the content of trace elements based on the standard curve of response signal-trace element content and the diluted trace element samples.

[0041] In one possible embodiment, as described above, step (a) is a fundamental step in the elemental analysis of complex water samples, particularly seawater, aimed at stabilizing the sample state, reducing physical interference, and improving the reproducibility of detection results. Acidification effectively inhibits the hydrolysis, precipitation, or adsorption of metal elements onto the container walls during storage and analysis, thus maintaining the true dissolved state distribution of elements in the sample. Simultaneously, the acidic environment reduces microbial activity, preventing changes in elemental speciation caused by biological processes. Filtration removes suspended particles, organic debris, and colloidal substances, preventing blockages or signal instability caused by particulate matter in the sample introduction system and reducing particle-related heterogeneous effects. By combining acidification and filtration, the original complex water sample can be transformed into a more homogeneous and stable processed sample, providing a reliable basis for subsequent quantitative analysis.

[0042] In one possible embodiment, as described above, specifically, after sample collection, the sample should be immediately transferred to a pretreated polyethylene or polypropylene container to reduce the container's influence on the adsorption of metal elements. The acidification treatment used in step (a) can employ various high-purity inorganic acids, such as analytical grade or ultrapure grade nitric acid, hydrochloric acid, or a mixed acid prepared from nitric acid and hydrochloric acid in a certain volume ratio. If necessary, sulfuric acid or phosphoric acid can also be introduced as an auxiliary acid to ensure that each target element in the sample exists in a stable dissolved state. After adding acid, the pH of the sample is usually adjusted to the range of 0.5-2.0, and the sample is allowed to stand in a sealed, light-protected environment at room temperature or 4°C to ensure sufficient interaction between the acid and the sample and to stabilize the system. The standing time can be from 10 minutes to 2 hours, and may be extended to several hours under complex water sample conditions.

[0043] In this embodiment, after acidification and stabilization, the sample is filtered. The filtration process is preferably carried out under gravity or low-pressure conditions, with the filtration pressure generally controlled at no more than 30-50 kPa to avoid membrane damage or particulate matter penetration. Microporous membranes with pore sizes of 0.45 μm or 0.22 μm can be used for filtration. Membrane materials can be selected from materials with low adsorption of metal elements and good chemical stability, such as polyethersulfone, polytetrafluoroethylene, mixed cellulose esters, nylon, or polypropylene, to obtain a stable and homogeneous processed sample.

[0044] In one possible embodiment, as described above, step (b) is a necessary step to address situations where the content of different elements in complex water samples varies greatly. For example, in complex water bodies such as seawater, macroelements such as sodium, magnesium, and calcium are usually at high concentration levels, while trace elements such as lead, mercury, and cadmium may have contents as low as micrograms or even lower orders of magnitude. If a uniform dilution factor is used for the processed samples, problems often arise such as macroelement signal saturation and excessive matrix load, or trace element signals that are too weak and difficult to quantify accurately. By setting different dilution levels, macroelements and trace elements are placed in their respective suitable concentration ranges, which helps to ensure that the instrument response is within the linear range and reduces the interference of high-concentration matrix on the detection process. Setting the dilution factor ratio to be no less than 10 can create a clear distinction between macroelements and trace elements, ensuring that the two types of elements have sufficient differences in detection status, thereby improving the accuracy and stability of the measurement results. This graded dilution approach starts from the overall analytical state of the sample, rather than adjusting for a single element, which is beneficial for comprehensive optimization under conditions of simultaneous multi-element determination.

[0045] In one possible embodiment, as described above, specifically, after acidification and filtration, the treated sample is differentially diluted according to the type and expected concentration level of the target analyte. The dilution operation typically uses ultrapure water as the dilution medium, with volumetric flasks, pipettes, or automated pipetting devices used for volume control. For macro-element dilution samples, a certain volume of the treated sample, such as 5-10 mL, can be added to a volumetric flask and diluted to 50-100 mL with ultrapure water to obtain a higher dilution factor. For trace element dilution samples, a larger volume of the treated sample, such as 20-50 mL, can be taken and diluted to the same or similar volume to obtain a relatively lower dilution factor. This method ensures a ratio of at least 10:1 between the dilution factors for macro-elements and trace elements, guaranteeing sufficient difference in the detection states of the two types of elements, thereby improving the accuracy and stability of the measurement results.

[0046] In this embodiment, the dilution factor can be determined by combining the common content ranges of various elements in typical seawater and the linear response range of the instrument. Taking nearshore surface seawater as an example, the mass concentrations of macroelements such as sodium and magnesium are usually around 10. 2 -10 4The concentrations of trace elements are on the order of mg / L, while the concentrations of lead, mercury, cadmium, and other trace elements are mostly in the range of 0.01-5 μg / L. Based on these differences, different dilution strategies can be pre-set. For example, for macro-element analysis, 5 mL of the sample can be diluted in 95 mL of ultrapure water (a dilution factor of 20-fold); or 2 mL of the sample can be diluted to 100 mL (a dilution factor of 50-fold) to ensure that the detection signals of elements such as sodium, magnesium, and calcium are within the instrument's linear response range. For trace element analysis, 25-50 mL of the sample can be diluted to 100 mL (a dilution factor of 2-4-fold) to ensure sufficient signal intensity for elements such as lead, mercury, and cadmium. Through these settings, the ratio of the dilution factor for macro-elements to that for trace elements can reach 10-25, meeting the requirements for differentiated dilution.

[0047] In this embodiment, a trial test can be performed on the diluted sample before the formal measurement. If the signal of the macro-elements shows a saturation trend, the dilution factor can be further increased; if the signal of the trace elements is close to the detection limit, the dilution factor can be appropriately reduced, thereby determining the final dilution scheme. In actual operation, the dilution process should be carried out in a clean environment, and all instruments should be cleaned with dilute acid and ultrapure water beforehand to reduce background contamination.

[0048] In one possible embodiment, as described above, the core significance of step (c) lies in reducing the systematic impact of matrix differences in complex water samples on element detection signals, especially when the matrix composition of the sample has undergone substantial changes after different dilutions. If quantification is still performed using a standard solution prepared under the same conditions as the original sample, the signal response environment reflected by the standard curve will be inconsistent with that of the sample to be tested, thus introducing response bias. Since dilution not only changes the concentration level of the target element, but also simultaneously changes the matrix characteristics such as salinity, ionic strength, and the proportion of coexisting elements in the sample, matrix matching should cover the predicted concentration range of the diluted sample, rather than being set only for the original sample or the concentration of a single element. By preparing corresponding matrix matching solutions for macro-element dilution samples and trace element dilution samples respectively, the standard solution and the sample to be tested are kept relatively consistent in terms of matrix environment.

[0049] In one possible embodiment, as described above, specifically taking seawater samples as an example, for macro-element dilution samples, sodium, magnesium, calcium, potassium, etc., can be selected as representative macro-elements. Corresponding salts or standard solutions are added to ultrapure water to prepare a matrix-matched solution system. For example, 5-7 concentration points can be set, with sodium ion concentrations of 0, 200, 500, 1000, and 2000 μg / L, and magnesium ion concentrations adjusted synchronously in a similar proportion to sodium, so that the macro-element concentration range of this matrix-matched solution covers the predicted actual content range in the macro-element dilution sample. An interval of 2-3 times can be used between adjacent concentration points. For trace element dilution samples, a separate trace element matching solution system can be prepared. For example, using lead, mercury, cadmium, copper, etc., as target elements, 4-6 concentration points can be set, with concentration ranges of 0, 0.1, 0.5, 1, 5 μg / L or 0, 0.2, 1, 2, 10 μg / L, the specific range determined according to the predicted content of the trace element dilution sample.

[0050] In this embodiment, the aforementioned trace element matching solutions can also be prepared under conditions maintaining a low concentration of macro-salt background, ensuring that their matrix characteristics match the corresponding trace element diluted samples. Furthermore, each set of matrix matching solutions can contain only one element, allowing for more precise range determination and dilution processing for specific elements. Each set of matrix matching solutions is used only for quantitative analysis of its corresponding diluted sample, and different dilution levels are not used interchangeably.

[0051] In one possible embodiment, as described above, step (d) is the core of elemental quantitative analysis, essentially establishing a stable correspondence between the instrument response signal and the target element content. In complex water sample analysis, different elements exhibit significantly different signal response characteristics due to differences in atomic mass, ionization efficiency, and the influence of the coexisting matrix. Using a uniform curve or mixed fitting method can easily introduce fitting errors. By establishing independent response signal-content standard curves for both major and trace elements, linear fitting can be achieved for each element within its suitable concentration range, thereby improving the reliability of the quantitative results. During curve fitting, data fitting at multiple concentration points can effectively reflect the trend of signal change with content and is used to determine whether the detection system is in a stable and linear operating state.

[0052] In one possible embodiment, as described above, multiple sets of macro-element matching solutions or trace element matching solutions of different concentrations are sequentially introduced into the analytical instrument, and the response signals of each target element are acquired under the same instrument conditions. The response signal can be the ion count rate of the corresponding isotope, the signal intensity integral value, or the net signal value after background subtraction. After data acquisition, the accompanying analysis software is used to process the data of each element individually, and the response signal is automatically generated as the response signal-concentration relationship graph with the element concentration as the abscissa and the corresponding response signal as the ordinate. Curve fitting typically uses a least squares linear regression model, and the software can automatically calculate the fitting equation, slope, intercept, and correlation coefficient. Before fitting, blank subtraction parameters can be set through the software to use zero-concentration or low-concentration standard solutions as blank points to perform background correction on all data points. At the same time, outlier judgment rules can be set. When the deviation of a certain concentration point exceeds a preset threshold, the point can be removed and refitted.

[0053] In this embodiment, for macroelements, the fitted concentration range generally covers the predicted content range of their diluted samples; for trace elements, the focus is on ensuring linearity in the low concentration range, which can be achieved by increasing the number of repeated scans or extending the integration time to improve the signal-to-noise ratio. After establishing the standard curve, the corresponding diluted macroelements or trace elements are measured under the same measurement conditions. The software automatically reads the response signal of each target element in the sample and substitutes it into the standard curve equation of the corresponding element to directly calculate its content. To ensure the long-term stability of the curve, calibration solutions of intermediate concentrations can be periodically inserted during the measurement process. The software compares the deviation between the measured value and the theoretical value. When the deviation exceeds the set range, it prompts for recalibration or reconstruction of the standard curve, thereby achieving independent, accurate, and traceable quantitative analysis of different elements.

[0054] In one possible embodiment, as described above, specifically, lead (Pb) is used as a representative trace element, and a matrix-matched solution is prepared using a solution compatible with the diluted trace element sample. Five concentration points are selected: 0, 0.1, 0.5, 1, and 5 μg / L. The standard solutions are sequentially introduced into a mass spectrometer under the same instrument conditions for measurement, and the response signals of the corresponding lead isotopes are collected. Each concentration point is measured three times, and the average value is taken as the response signal for that concentration point. The measured response signals (cps) are 35, 420, 2050, 4120, and 20300, respectively. Using lead concentration (μg / L) as the x-axis and the response signal (cps) as the y-axis, linear regression fitting is performed using the instrument's data processing software to obtain the standard curve equation for lead:

[0055]

[0056] Where y represents the response signal and x represents the lead concentration (μg / L), the correlation coefficient is 0.9993, indicating a good linear relationship within this concentration range. Subsequently, the diluted trace element sample was measured under the same conditions, and the lead response signal was 2,480 cps. Substituting this signal value into the above standard curve equation, the concentration of lead in the diluted sample can be calculated as follows:

[0057]

[0058] By combining the corresponding dilution factor of the sample, the actual lead content in the original seawater sample can be further calculated.

[0059] In one possible embodiment, as described above, the macroelements include at least one of sodium, magnesium, calcium, potassium, boron, and strontium, and the content of the macroelements in the multi-group macroelement matching solution is 0-500 µg / L. The trace elements include at least one of lead, mercury, cadmium, arsenic, copper, zinc, nickel, cobalt, manganese, and chromium, and the content of the trace elements in the multi-group trace element matching solution is 0-5 µg / L.

[0060] In this embodiment, for macroelements such as sodium, magnesium, calcium, potassium, boron, and strontium, the concentration range of 0-500 µg / L covers the main distribution range of these elements in the diluted sample, ensuring a stable and repeatable signal response during measurement and facilitating the establishment of a linear signal-content relationship. Simultaneously, the concentration gradient within this range facilitates the formation of uniformly distributed standard points, improving the reliability of curve fitting and data utilization efficiency. For trace elements such as lead, mercury, cadmium, and arsenic, the concentration range of 0-5 µg / L effectively reflects their typical detection range in diluted seawater samples, making the standard solution system more closely resemble the actual sample state and contributing to improved resolution and quantitative accuracy of signal changes within low-content ranges.

[0061] In one possible embodiment, as described above, the equipment used specifically includes an ultrapure water preparation system (e.g., resistivity not less than 18.2 MΩ·cm), an analytical balance, acid-washed polyethylene volumetric flasks, calibrated adjustable pipettes and matching tips. The reagents used are commercially available single-element or multi-element standard stock solutions (e.g., mass concentration of 1000 mg / L), and analytical grade nitric acid for matrix stabilization. All preparation processes must use independent clean containers to avoid cross-contamination. After completion, each matched solution is stored at low temperature and protected from light, and used for curve plotting and quantitative analysis of the corresponding diluted samples within a specified time (e.g., 24 hours).

[0062] In this embodiment, when preparing macro-element matching solutions, one or more of sodium, magnesium, calcium, potassium, boron, or strontium can be selected as needed. The corresponding standard stock solution is added to the volumetric flask through a stepwise dilution method, and then diluted to volume with ultrapure water containing a small amount of nitric acid to prepare multiple sets of solutions with concentrations of 0, 50, 100, 200, 300, and 500 μg / L. During the preparation process, intermediate concentration solutions are prepared first to improve the accuracy of dilution. After each solution is diluted to volume, it is thoroughly shaken and numbered for storage. When preparing trace element matching solutions, one or more of lead, mercury, cadmium, arsenic, copper, zinc, nickel, cobalt, manganese, or chromium can be selected. First, an intermediate solution of 10 μg / L or 50 μg / L is prepared from the standard stock solution, and then further diluted to concentration points of 0, 0.1, 0.5, 1.0, 2.0, and 5.0 μg / L, and then diluted to volume with ultrapure water containing trace nitric acid.

[0063] In one possible embodiment, as described above, the dilution factor of the macro-element dilution sample is not less than 10 times relative to the processed sample, and the dilution factor of the trace element dilution sample is not more than 10 times.

[0064] In this embodiment, for macroelements, a dilution of at least 10-fold can effectively reduce the overall matrix load caused by high salt and high ionic strength in the sample, which is beneficial for obtaining a reproducible response signal. This dilution level allows macroelements to be within a suitable response range during the determination process, facilitating the subsequent establishment of a linear and reliable quantitative relationship. For trace elements, controlling the dilution factor to no more than 10-fold helps to maximize the preservation of the effective signal intensity of trace elements.

[0065] In one possible embodiment, as described above, specifically for diluting macro-element samples, 1-10 mL of the treated sample can be added to a volumetric flask and diluted to 50 mL or 100 mL with ultrapure water to obtain a dilution factor of not less than 10 times, such as 10, 20, or 50 times. Ultrapure water should be added slowly during dilution, and the mixture should be thoroughly mixed after dilution to ensure homogeneity of the sample composition. For diluting trace element samples, 10-50 mL of the treated sample can be diluted to 50 mL or 100 mL to control the dilution factor within the range of 2-10 times. To ensure the accuracy of the dilution factor, an appropriate volumetric instrument can be selected according to the sample volume, and a calibrated pipette can be used for volume transfer. The dilution medium can be ultrapure water containing trace amounts of nitric acid to maintain sample stability. After dilution, different diluted samples should be clearly labeled, and the sampling volume, dilution volume, and corresponding dilution factor should be recorded. These samples should be used for subsequent matrix matching and quantitative analysis within a specified time (e.g., 24 hours).

[0066] In one possible embodiment, as described above, the correlation coefficient between the response signal-constant element content standard curve and the response signal-trace element content standard curve is greater than 0.999.

[0067] In this embodiment, the correlation coefficient is an important statistical parameter used to characterize the degree of fit between the response signal and the target element content. The closer the value is to 1, the more stable and consistent the linear relationship between the two. In elemental quantitative analysis, limiting the correlation coefficient of the response signal-content standard curve to greater than 0.999 reflects that the established quantitative model has a highly consistent linear response characteristic within the selected concentration range. This limitation indicates that as the target element content changes, the response signal output by the detection system exhibits a predictable and repeatable change pattern, which is beneficial to improving the accuracy and reliability of calculating the sample content from the standard curve. For the standard curves established for major elements and trace elements respectively, the correlation coefficients are all greater than 0.999, indicating that elements at different content levels can maintain good linear performance within their respective determination intervals, which helps to achieve stable quantitative analysis by element and by level.

[0068] In one possible embodiment, as described above, the correlation coefficient calculation is typically performed automatically by the instrument's built-in software or general data processing software. During operation, the nominal concentration of each standard solution is first used as the independent variable x, and the corresponding measured signal intensity (such as peak area, peak height, or count value) is used as the dependent variable y, forming paired datasets. For each concentration point, random fluctuations can be reduced by repeating measurements and averaging, thus making the input data more concentrated. Subsequently, linear regression is performed using the least squares method to obtain the standard curve equation:

[0069]

[0070] In this model, the slope 'a' reflects the signal response capability caused by a unit change in content, and the intercept 'b' represents the background or system baseline contribution. Simultaneously with the regression calculation, the software calls the correlation coefficient formula to statistically analyze the deviation of all data points from the fitted straight line and outputs the corresponding values. To ensure the correlation coefficient is consistently greater than 0.999, a uniform blank subtraction process can be performed on the data before calculation, that is, subtracting the average response value of the blank solution from each measured signal, so that the regression analysis only reflects the contribution of the true elemental signal. Furthermore, by ensuring consistency in integration time, number of scans, and signal acquisition mode, the comparability between data points can be further improved. Under the above-mentioned standardized conditions, the correlation coefficient calculation results of the standard curve exhibit good repeatability and consistency.

[0071] In one possible embodiment, as described above, the sample is treated with a pH value less than 2 and stored at 4°C.

[0072] In this embodiment, the seawater system contains high concentrations of macroelements such as calcium and magnesium ions, as well as various trace metal ions. These ions readily undergo complexation or precipitation reactions with carbonate, hydroxide, or organic ligands under neutral or weakly alkaline conditions, thereby altering their solubility and effective concentration. When the sample pH is adjusted to less than 2, the solution system is in a strongly acidic environment, which effectively inhibits the formation of metal hydroxides and carbonates, thus helping to maintain the consistency of elemental distribution. Furthermore, seawater often contains trace suspended particles and bioactive components, which are prone to adsorption, co-precipitation, or biological metabolic processes under higher pH or room temperature conditions, leading to uncontrollable compositional changes. Preserving the sample at pH < 2 and at 4°C significantly reduces the chemical reaction rate and biological activity, stabilizing the sample matrix composition and thus meeting the requirements for high-precision elemental quantitative analysis.

[0073] In one possible embodiment, as described above, the pH can be adjusted to less than 2 by adding a high-purity inorganic acid to the seawater-treated sample. Ultra-pure nitric acid is preferred, as it has low volatility, low background impurities, and good compatibility with various element detection methods. During operation, a pipette or automatic dispensing device can be used to slowly add the acid dropwise to the sample while gently shaking or using magnetic stirring to ensure uniform distribution of the acid in the system. The amount of acid to be added can be estimated based on the sample volume and initial alkalinity, and confirmed using a pH meter or precision pH test paper, until the sample pH stabilizes below 2.

[0074] In this embodiment, to further improve operational consistency, the pH meter can be calibrated using a standard buffer solution before the experiment to ensure measurement accuracy. Acidification can be performed in a clean environment, preferably using acid-washed polyethylene or polypropylene containers to avoid the introduction of exogenous metals. The sample after acidification should be sealed immediately and stored at 4°C, which can be achieved using a laboratory refrigerator or portable constant-temperature cooling device. During low-temperature storage, the sample should be kept away from frequent opening or violent shaking to maintain system stability.

[0075] In one possible embodiment, as described above, the filtration process employs a microporous membrane with a pore size of 0.2-1.0 µm.

[0076] In this embodiment, seawater commonly contains suspended particles, colloidal substances, and microbial residues, with particle sizes mostly ranging from submicron to micrometer. These components readily act as adsorbents or co-carriers for metal ions, affecting the true distribution of elements in the liquid phase. Limiting the filter pore size to the range of 0.2–1.0 µm effectively retains these particulate matter, ensuring that the filtered sample mainly retains dissolved and small-molecule complexed elements, which helps maintain the stability of the main ionic strength and matrix composition in the sample.

[0077] In one possible embodiment, as described above, the microporous filter membrane can be made of polyethersulfone (PES), polyvinylidene fluoride (PVDF), or polytetrafluoroethylene (PTFE). These materials are characterized by high chemical inertness, low metal background, and good acid resistance, making them suitable for acidified seawater samples. Filtration can be performed using a disposable needle filter or a vacuum filtration device. Before use, the filter membrane is preferably pre-washed with ultrapure water or dilute nitric acid to remove any remaining manufacturing impurities and wet the membrane pore structure. During filtration, atmospheric pressure, negative pressure, or positive pressure filtration can be used. The treated seawater sample is slowly passed through the filter membrane, avoiding high pressure differentials or violent disturbances to ensure the stability of the particle retention process. The filtrate obtained is directly collected in an acid-washed polyethylene or polypropylene container for subsequent elemental analysis. When batch processing of samples is required, filter membranes of the same batch and pore size can be used for parallel operations to enhance sample consistency.

[0078] In one possible embodiment, as described above, the original sample comprises at least one of seawater samples collected at depths of 0.5m, 5m, and 10m below the sea surface.

[0079] In this embodiment, seawater samples from different depths exhibit significant differences in physicochemical properties during ocean water quality analysis. Sampling locations at depths of 0.5m, 5m, and 10m below the sea surface represent typical regions of surface seawater, mid-layer water, and deep water, respectively, with variations in temperature, salinity, dissolved oxygen, and trace element concentrations potentially occurring in each layer. For example, a sample at 0.5m below the surface represents the surface layer, which is typically significantly affected by atmospheric and surface climate changes. A sample at 5m represents mid-layer water, where the influence of the surface layer gradually weakens. A depth of 10m represents the more stable deep water, exhibiting more constant temperature and salinity.

[0080] In one possible embodiment, as described above, seawater sample collection should be strictly performed according to standardized operating procedures to ensure data representativeness and reproducibility. First, a cleaned polyethylene or polypropylene sampler, rinsed with ultrapure water, should be used to avoid contamination and sample loss. To ensure the samples cover different water depths, an underwater sampler or collection bottle should be used to collect seawater samples at depths of 0.5m, 5m, and 10m below the sea surface, based on the stratification characteristics of seawater. The sampling depth can be determined manually or with the aid of a shipboard depth sounder to ensure accurate sampling. During collection, the sampler should be lowered vertically and the water depth should be measured periodically to ensure that the collected samples represent the corresponding water layers. Sufficient seawater (e.g., 1-5L) should be collected at each depth. The collected samples should be immediately sealed and labeled to avoid sample contamination and environmental impact.

[0081] In one possible embodiment, as described above, the response signal is measured using inductively coupled plasma mass spectrometry (ICP-MS), wherein the plasma parameters include a radio frequency power of 1550-1650 W, a plasma gas flow rate of 15-18 L / min, an auxiliary gas flow rate of 1.0-1.2 L / min, and a carrier gas flow rate of 0.7-1.0 L / min; and the mass spectrometry parameters include a full scan mode, a scan mass number range of 5-250 amu, an ion lens voltage of 100-150 V, and a detector voltage of 1800-2200 V.

[0082] In this embodiment, given the high salinity and high matrix loading characteristics of seawater, higher requirements are placed on plasma stability, ionization efficiency, and the mass spectrometry transmission process. A suitable radio frequency power range is beneficial for maintaining sufficient plasma energy density under high salinity conditions, enabling stable atomization and efficient ionization of various elements in the seawater sample, thereby obtaining a reproducible response signal. The coordinated configuration of plasma gas flow rate, auxiliary gas flow rate, and carrier gas flow rate helps to form a morphologically stable and spatially uniform plasma region, allowing aerosols to undergo sufficient dissociation within the plasma and enter the mass spectrometry system. The mass spectrometry section employs a full-scan mode, with the mass number range set to 5-250 amu, covering the main mass ranges of major and trace elements in seawater, enabling simultaneous multi-element detection. The combination of ion lens voltage and detector voltage helps improve the transmission efficiency and detection sensitivity of target ions, ensuring good signal response consistency for different elements under the same analytical conditions.

[0083] In one possible embodiment, as described above, a commercial inductively coupled plasma mass spectrometer (ICP-MS) can be used as the detection device, such as an ICP-MS system equipped with a quadrupole or tandem mass spectrometer structure. Before instrument startup, high-purity argon is used as the plasma gas, and the gas path sealing and the stability of the flow control module are checked. The sample introduction system can use a conventional concentric nebulizer and a quartz nebulizer chamber. The sample introduction rate is controlled within the instrument's recommended range by a peristaltic pump, ensuring continuous and uniform sample entry into the plasma. During analysis, the system is first stabilized and background corrected with a matrix-matched solution, followed by the sequential injection of standard solutions and the seawater sample to be tested. The response signals of each element are automatically acquired and recorded by the mass spectrometry system, ensuring stable and repeatable detection results under the above parameter conditions.

[0084] In one possible embodiment, as described above, step (d) further includes at least one of a blank experiment, a spiked recovery experiment, and a parallel sample determination.

[0085] In this embodiment, the blank experiment, spiked recovery experiment, and parallel sample determination all verify the reliability of the detection results from different dimensions. The blank experiment characterizes the system background level and the contribution of reagents and glassware to the detection signal throughout the entire analytical process, providing a basis for signal subtraction and data correction. The spiked recovery experiment verifies the accuracy of the quantitative results by introducing a known amount of the target element into a known sample matrix. The parallel sample determination reflects the repeatability and stability of the method under actual operating conditions by performing multiple independent determinations on the same sample. The above experiments do not change the basic process of the aforementioned determination method, but rather serve as supplementary verification methods for the determination results, making the obtained elemental content data more reliable in terms of accuracy, consistency, and repeatability. This is particularly suitable for sample analysis scenarios such as seawater, which have complex matrices and a large range of elemental distributions.

[0086] In one possible embodiment, as described above, specifically, the blank experiment can be performed using a blank solution with the same processing procedure as the test sample. The blank solution can be ultrapure water treated under the same acidification conditions and subjected to the same filtration, dilution, and injection steps before being analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Instrument parameters are kept consistent with the sample analysis, and the obtained response signal is used to characterize the system background level. The spike recovery experiment can be performed on a fractionated seawater sample. A standard solution corresponding to the target element is selected and added to the sample at a predetermined concentration level. After thorough mixing, the spiked sample is analyzed under the same injection conditions as the original sample. The spike recovery rate is calculated by comparing the changes in elemental content before and after spiking. Parallel sample analysis can be performed by dividing the same treated sample into two or more independent samples and performing the complete injection and analysis process separately. Each parallel sample is analyzed under the same instrument parameters and operating conditions, and the results are used to evaluate the repeatability of the method.

[0087] In one possible embodiment, as described above, in a macro-element dilution sample, if the difference in the spiked recoveries of multiple macro-elements is less than or equal to 5%, and the estimated range of the content of each macro-element differs by less than 10 times, then a set of macro-element matching solutions includes multiple macro-elements; in a trace element dilution sample, if the difference in the spiked recoveries of multiple trace elements is less than or equal to 5%, and the estimated range of the content of each trace element differs by less than 10 times, then a set of trace element matching solutions includes multiple trace elements.

[0088] In this embodiment, when multiple target elements are within similar order of magnitude and measured under the same dilution conditions, the physicochemical environments they experience during sample introduction, plasma ionization, ion transport, and detection are highly consistent. Under these conditions, multiple macro-elements or multiple trace elements can coexist in the same diluted sample for measurement without affecting their respective quantitative reliability. Limiting the difference in spiked recoveries of multiple elements to less than or equal to 5% indicates that these elements have consistent response behavior and similar quantitative accuracy in the diluted sample and measurement system. Simultaneously, limiting the estimated range of each element's content to within 10 times allows each element to be fitted and calculated within the linear range of the same standard curve, thereby ensuring the comparability and stability of measurement results under the same dilution factor and matrix conditions.

[0089] In one possible embodiment, as described above, sodium, magnesium, calcium, and potassium can be selected as target elements in the diluted macro-element sample. It is estimated that the sodium content in the diluted sample is approximately 200 μg / L, magnesium 150 μg / L, calcium 80 μg / L, and potassium 60 μg / L, with the content difference between each element controlled within 10 times. Using this diluted sample as a matrix, standard solutions of equal proportions are added to the sample for spiking, resulting in spiking amounts of 50 μg / L, 40 μg / L, 20 μg / L, and 15 μg / L for sodium, magnesium, calcium, and potassium, respectively. The calculated spike recoveries after measurement are, for example, 98.5% for sodium, 100.2% for magnesium, 97.9% for calcium, and 101.0% for potassium. The difference between the spike recoveries of each element is less than 5%, which meets the limiting conditions. This allows for the simultaneous determination of multiple macroelements in the same diluted sample. Therefore, only one set of macroelement matching solutions is needed to simultaneously contain sodium, magnesium, calcium, and potassium. Using this set of macroelement matching solutions, the response signals of sodium, magnesium, calcium, and potassium can be obtained as standard curves of macroelement content, reducing the amount of operation and complexity of the matrix matching process.

[0090] To further demonstrate the advantages of this method in determining the elemental content in seawater, which is more efficient and accurate, the following experimental examples and comparative examples are provided.

[0091] Example 1

[0092] Sample Preparation: In a nearshore sea area, using a polyethylene water sampler that had been treated (soaked in 10% nitric acid for 24 hours and then rinsed with ultrapure water until neutral), 1 L of seawater was collected at depths of 0.5 m, 5 m, and 10 m below the sea surface. 5 mL of analytical grade nitric acid was added to each sample to adjust the pH to less than 2. The sample was then filtered through a 0.45 µm microporous membrane, and the filtrate was collected to obtain the treated sample. The sample was stored in a 4°C refrigerator and the experiment was completed within 24 hours.

[0093] Gradual dilution: Take 0.5 mL of the treated sample and dilute it with ultrapure water to 100 mL to obtain a macro-element diluted sample, which is used to test the content of macro-elements including magnesium, calcium, and potassium; take 50 mL of the treated sample and dilute it with ultrapure water to 100 mL to obtain a trace element diluted sample, which is used to test the content of trace elements including lead and cadmium.

[0094] Matrix matching: Prepare a set of macro-element matching solutions with magnesium, calcium, and potassium concentrations of 0, 1, 2, 5, and 10 mg / L, respectively, covering the estimated concentration ranges of magnesium, calcium, and potassium in the macro-element diluted samples (magnesium 6-7 mg / L, calcium 1.9-2.3 mg / L, potassium 1.8-2.2 mg / L); prepare a set of trace element matching solutions with lead and cadmium concentrations of 0, 0.1, 0.5, 1, and 5 µg / L, respectively, covering the estimated concentration ranges of lead and cadmium in the trace element diluted samples.

[0095] Curve plotting: A set of constant element matching solutions and a set of trace element matching solutions were sequentially injected into the mass spectrometer, and response signal-element content standard curves were plotted. The correlation coefficients of the curves were all greater than 0.999. The plasma parameters included a radio frequency power of 1600W, a plasma gas flow rate of 16L / min, an auxiliary gas flow rate of 1.1L / min, and a carrier gas flow rate of 0.8L / min. The mass spectrometry parameters included a full scan mode, a scan mass number range of 5-250 amu, an ion lens voltage of 120V, and a detector voltage of 2000V.

[0096] Diluted samples of macroelements and microelements were injected into a mass spectrometer to measure the signal intensity of each element, and the element concentration was calculated using a standard curve.

[0097] Quality control: In the blank test, an ultrapure water blank sample is injected into the mass spectrometer to ensure that the measured values ​​of all elements are below the method detection limit. In the parallel sample determination, the relative deviation of the results of at least two parallel samples is less than 10%.

[0098] In the spiked recovery test, 100 mL of each of the above-mentioned macro-element dilution samples and trace element dilution samples were first taken as the spiked systems. For the macro-element dilution samples, a matrix-matched mixed standard stock solution of magnesium, calcium, and potassium (single element concentration of 100 mg / L) was used. 2.0 mL of this mixed standard solution was added to each sample using a pipette to make the theoretical spiking concentration of magnesium, calcium, and potassium in the system 2 mg / L. For the trace element dilution samples, a matrix-matched mixed standard stock solution of lead and cadmium (single element concentration of 100 µg / L) was used. 1.0 mL of this mixed standard solution was added to each sample to make the theoretical spiking concentration of lead and mercury in the system 1.0 µg / L.

[0099] After spiking, each sample was thoroughly mixed, using vortexing for 30 seconds followed by standing for 5 minutes to ensure uniform dispersion of the spiked element in the solution. Subsequently, the spiked and unspiked samples were measured under the same instrument parameters and conditions, and the response signals of each element were obtained and converted into measured concentrations. Based on the results, the recovery rate (%) was calculated using the formula: Recovery (%) = (Spiked sample concentration - Unspiked sample concentration) / Theoretical spiked concentration × 100%. The recoveries for magnesium, calcium, potassium, lead, and cadmium were calculated to evaluate the accuracy of the method for determining macro and trace elements under fractional dilution and matrix matching conditions.

[0100] In this experimental example, the mass spectrometer and the measured response signal-standard curve of constant element content are as follows: Figure 1 As shown, the response signal-trace element content standard curve is as follows: Figure 2 As shown, the recoveries of magnesium, calcium, and potassium spikes were 96%, 97%, and 93%, respectively, while the recoveries of lead and cadmium spikes were 104% and 107%, respectively.

[0101] Example 2

[0102] The steps and samples in Example 2 are basically the same as in Example 1, except that a separate set of element-matching solutions is prepared for each element. The response signal-constant element content standard curve is shown below. Figure 3 As shown, the response signal-trace element content standard curve is as follows: Figure 4 As shown.

[0103] Comparative Example 1

[0104] The procedures and samples for Comparative Example 1 were basically the same as those for Experimental Example 1. The difference was that 50 mL of the treated sample was diluted to 100 mL with ultrapure water and then passed through an exchange column packed with Chelex-100 chelating resin at a flow rate of 50 mL / h. This allowed lead and cadmium to be selectively adsorbed by the resin, while high concentrations of matrix ions such as potassium, magnesium, and calcium were discharged with the effluent. After adsorption, the resin column was rinsed three times with 20 mL of ultrapure water to remove residual matrix. Then, the resin was eluted with a 2 mol / L nitric acid solution containing 10 mL of high-purity nitric acid to desorb the enriched lead and cadmium. The eluent was collected and diluted to a final volume for subsequent ICP-MS determination. The response signal-macro-element content standard curve is shown below. Figure 5 As shown, the response signal-trace element content standard curve is as follows: Figure 6 As shown.

[0105] Comparative Example 2

[0106] The procedures and samples for Comparative Example 2 were basically the same as those for Experimental Example 1, except that 50 mL of the treated sample was diluted to 100 mL with ultrapure water and used directly for subsequent testing, without graded dilution or a matrix-matched process. Due to the lack of graded dilution, the instrument signal for macro-elements directly saturated, making accurate data measurement impossible. Without matrix-matched dilution, trace elements were suppressed by the high matrix effect of seawater, and ultra-trace elements could not be accurately measured due to excessively low signal values.

[0107] A comparison of Examples 1 and 2 shows that both methods achieve good linear response relationships, with correlation coefficients for the standard curves of each element approaching 0.9999. In Example 1, standard curves were established using a matrix-matched solution with multiple elemental compositions, including the response signal-concentration curves for magnesium, calcium, potassium, lead, and cadmium. In Example 2, standard curves were established by preparing matching solutions for each element separately. This demonstrates that, under spiking recovery matching, using a multi-element mixed standard solution still maintains excellent linearity. Example 1 allows for the establishment of multiple elemental curves through a single preparation of a multi-element matching solution, which, compared to the method in Example 2 of preparing multiple sets of single-element solutions separately, reduces preparation steps and improves experimental efficiency.

[0108] A comparison of Example 1 and Comparative Example 1 shows that by using graded dilution and matrix matching to establish a standard curve, the sample matrix can be kept consistent with the standard solution, thus establishing a stable linear relationship between the response signal and concentration. Furthermore, Example 1 eliminates the need for complex steps such as resin adsorption, rinsing, and elution; sample pretreatment can be completed simply through dilution, significantly simplifying the experimental procedure.

[0109] In Comparative Example 2, the sample was simply diluted and then directly analyzed by ICP-MS, which failed to yield accurate data with a correlation coefficient of 0.999. In contrast, this method allows for the accurate determination of major and trace elements in seawater through simple operation.

[0110] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method for determining the content of an element in seawater, characterized by, Includes the following steps: (a) Sample preparation: The original sample is acidified and filtered to obtain the processed sample; (b) Stepwise dilution: The treated sample is diluted with ultrapure water at different ratios to obtain macro-element diluted samples and trace element diluted samples; wherein the ratio of the dilution factor of the macro-element diluted sample to the dilution factor of the trace element diluted sample is ≥10. (c) Matrix matching: Prepare multiple sets of macro-element matching solutions and multiple sets of trace element matching solutions; The constant element matching solution includes constant elements, and the content of the constant elements in multiple sets of constant element matching solutions covers the predicted content range of the constant elements in the constant element diluted sample. The trace element matching solution includes trace elements, and the content of the trace elements in multiple sets of trace element matching solutions covers the predicted content range of trace elements in the trace element diluted sample. (d) Curve plotting: Establish a response signal-constant element content standard curve based on the multiple sets of constant element matching solutions, and obtain the content of the constant element based on the response signal-constant element content standard curve and the constant element diluted sample; A response signal-trace element content standard curve is established based on the multiple sets of trace element matched solutions. The content of the trace element is obtained based on the response signal-trace element content standard curve and the trace element diluted sample.

2. The method of claim 1, wherein, The macroelements include at least one of sodium, magnesium, calcium, potassium, boron, and strontium, and the content of the macroelements in the multi-group macroelement matching solution is 0-500 µg / L; The trace elements include at least one of lead, mercury, cadmium, arsenic, copper, zinc, nickel, cobalt, manganese, and chromium, and the content of the trace elements in the multi-group trace element matching solution is 0-5 µg / L.

3. The method of claim 2, wherein, The dilution factor of the macro-element dilution sample is not less than 10 times relative to the treated sample, and the dilution factor of the trace element dilution sample is not more than 10 times.

4. The method according to any one of claims 1-3, characterized in that, The correlation coefficients of the response signal-constant element content standard curve and the response signal-trace element content standard curve are greater than 0.

999.

5. The method according to any one of claims 1-4, characterized in that, The pH value of the treated sample is less than 2, and it is stored at 4°C.

6. The method according to any one of claims 1-5, characterized in that, The filtration process uses a microporous filter membrane with a pore size of 0.2-1.0µm.

7. The method according to any one of claims 1-6, characterized in that, The original samples include at least one type of seawater collected at depths of 0.5m, 5m, and 10m below the sea surface.

8. The method according to any one of claims 1-7, characterized in that, The response signal was measured using inductively coupled plasma mass spectrometry (ICP-MS). The plasma parameters included a radio frequency power of 1550-1650 W, a plasma gas flow rate of 15-18 L / min, an auxiliary gas flow rate of 1.0-1.2 L / min, and a carrier gas flow rate of 0.7-1.0 L / min. The mass spectrometry parameters included a full scan mode, a scan mass number range of 5-250 amu, an ion lens voltage of 100-150 V, and a detector voltage of 1800-2200 V.

9. The method according to any one of claims 1-8, characterized in that, Step (d) is followed by at least one of a blank experiment, a spiked recovery experiment, and a parallel sample determination.

10. The method according to claim 9, characterized in that, If the difference in the spiked recoveries of multiple macroelements in the macroelement dilution sample is less than or equal to 5%, and the estimated range of the content of each macroelement differs by less than 10 times, then a set of macroelement matching solutions includes multiple macroelements. If the difference in the spiked recoveries of multiple trace elements in the diluted trace element sample is less than or equal to 5%, and the estimated range of the content of each trace element differs by less than 10 times, then a set of trace element matching solutions includes multiple trace elements.

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