An analytical method for determining different tin and lead species in water samples by SPE-HPLC-ICP-MS coupling technology

Abstract

The present invention discloses an analytical method for determining different tin and lead species in water samples by SPE-HPLC-ICP-MS coupling technology. The method of the present invention proposes to simultaneously determine 7 species of tin and lead in water samples by using solid phase extraction-high performance liquid chromatography-inductively coupled plasma mass spectrometry coupling technology; the mobile phases used in the present invention are all aqueous phases, which conform to the concept of green chemistry; 7 different species of tin and lead can be detected simultaneously, with low detection limits, good precision and accuracy, and can be used for a large number of detection works; for the analysis of different tin and lead species in water samples, the sample spiked recovery rates are all higher than 90%, meeting the analysis requirements of actual samples; the present invention provides a practical method for the simultaneous analysis of different tin and lead species in water samples, filling the technical blank of the simultaneous detection of tin and lead species in water samples.

Description

Technical Field

[0001] The present invention relates to an analytical method for determining different tin and lead species in water samples by SPE-HPLC-ICP-MS coupling technology. Background Art

[0002] The toxicity, mobility and biological effects of tin and lead all depend on their chemical species. Therefore, it is very important to qualitatively and quantitatively analyze the species of tin and lead. In recent years, HPLC-ICP-MS has been widely used in the morphological analysis and detection of tin and lead due to its unique advantages such as simple coupling, easy operation, wide linear range and low detection limit. Since the concentrations of tin and lead species in water samples are often at relatively low levels, this method combines the current testing status of tin and lead species analysis, adds online solid-phase extraction technology (online-SPE), and through full research on the selection of determination methods and optimization of experimental conditions, an analytical method for determining tin and lead in water samples by solid-phase extraction-high performance liquid chromatography-inductively coupled plasma mass spectrometry (SPE-HPLC-ICP-MS) coupling technology has been established. The test quality technical indicators can meet the actual sample analysis requirements: the detection limit of tin species is lower than 0.008 ng L -1 , and the detection limit of lead is lower than 0.006 ng L -1 , the precision reaches within 5%, and the sample spike recovery rate is above 90%, providing technical support for the determination of tin and lead in water samples. Summary of the Invention

[0003] In order to overcome the defects of the prior art, the present invention first proposes an analytical method for determining tin and lead in water samples by solid-phase extraction-high performance liquid chromatography-inductively coupled plasma mass spectrometry (SPE-HPLC-ICP-MS) coupling technology and realizes simultaneous analysis.

[0004] The present invention provides a practical method for the morphological analysis of tin and lead in water samples. Among them, different tin species are trimethyltin (TMT), triethyltin (TET), tributyltin (TBT), triphenyltin (TPhT), and different lead species are inorganic lead (Pb(II)), trimethyllead (TML), triethyllead (TEL).

[0005] The technical solution of the present invention is as follows:

[0006] An analytical method for determining different tin and lead species in water samples by SPE-HPLC-ICP-MS coupling technology, comprising the following steps:

[0007] (1) Establish an analytical method for SPE-HPLC-ICP-MS coupling

[0008] Online SPE-HPLC-ICP-MS includes three processes: online solid-phase extraction (SPE), liquid-phase separation (HPLC), and ICP-MS detection. Among them, online solid-phase extraction includes three steps: column pre-equilibration, sample enrichment, and sample elution. After sample elution, liquid-phase separation of different tin and lead species is carried out, and then each tin and lead species enters the ICP-MS system for detection and analysis.

[0009] The conditions for online solid-phase extraction are as follows: enrichment column: GO@SiO2 (5 μm, 10 mm × 4.6 mm i.d.); pre-equilibration agent: 1.0 mM benzoic acid (BA), volume 8.0 mL; eluent: 4 mM sodium dodecylbenzenesulfonate (SDBS), pH 2.0; sample pH: 5.0 - 8.0; sample volume: 10 mL; enrichment flow rate: 10 mL min -1 ;

[0010] The conditions for liquid-phase separation are as follows: hydrophilic chromatographic column: Welch Amphion II (5 μm, 100 mm × 4.6 mm i.d.); mobile phase: 4 mM sodium dodecylbenzenesulfonate (SDBS), pH 2.0; flow rate: 1.5 mL min -1 ;

[0011] The conditions for ICP-MS detection are as follows: plasma RF power 1200 W, cooling gas flow rate 13.02 L min -1 , auxiliary gas flow rate 0.75 L min -1 , nebulizer gas flow rate 0.85 L min -1 , and all gases are high-purity argon;

[0012] (2) Preparation of standard curves

[0013] Weigh standard samples of different tin and lead species, namely TMT, TET, TBT, TPhT, Pb (II), TML, and TEL, and prepare a mixed standard solution. Gradually dilute it to obtain a series of standard working solutions. Perform detection and analysis according to the method established in step (1). Using the concentration of each tin and lead species as the abscissa and the peak area in the HPLC-ICP-MS chromatogram as the ordinate, plot the standard curve.

[0014] (3) Detection of actual samples

[0015] Filter the water sample to be tested through a 0.45 μm aqueous filter membrane, perform detection and analysis according to the method established in step (1), and substitute the peak area in the obtained HPLC-ICP-MS chromatogram into the standard curve plotted in step (2) to obtain the content of different tin and lead species in the water sample.

[0016] Furthermore, the method for determining the RSD of the analysis method of the present invention is as follows: Prepare a mixed standard solution of 10.0 ng / L from standard samples of different tin and lead species, analyze the mixed standard according to the method established in the above step (1), perform parallel determination six times, and calculate the RSD based on the retention time, peak area, and peak height of each species, with RSD ≤ 5%.

[0017] Furthermore, the method for determining the detection limit and quantification limit of the analysis method of the present invention is as follows: Use the blank reagent of the standard sample, perform ten parallel determinations according to the method established in the above step (1), calculate the detection limit based on three times the standard deviation of the blank signal, and calculate the quantification limit based on ten times the standard deviation.

[0018] The technical solution of the present invention mainly has the following advantages:

[0019] (1) The present invention proposes a method for simultaneously analyzing the species of tin and lead in water samples by using the combined technology of high performance liquid chromatography - inductively coupled plasma mass spectrometry (HPLC - ICP - MS). This method can achieve the simultaneous separation of a total of 7 species including trimethyltin (TMT), triethyltin (TET), tributyltin (TBT), triphenyltin (TPhT), inorganic lead (Pb(II)), trimethyllead (TML), and triethyllead (TEL) at one time. After introducing the online solid phase extraction (online - SPE) technology, the simultaneous enrichment analysis of 7 species including TMT, TET, TBT, TPhT, Pb(II), TML, and TEL can be realized in one run. The correlation coefficient R of the standard working curve of the method of the present invention is > 0.993, the average recovery rate is between 89% - 104%, and the relative standard deviations of the peak area and retention time are both less than 3%, which can meet the simultaneous and rapid detection of trace tin and lead in environmental water samples.

[0020] (2) Compared with the HPLC - ICP - MS methods for analyzing single - metal species of tin or lead that have been developed, the present invention can simultaneously analyze 7 species of tin and lead in one run, and the mobile phases used are all green and environmentally friendly aqueous mobile phases without any organic solvents, meeting the concept of green environmental protection (Table 1).

[0021] Table 1 Comparison of the analytical performance of this method with other HPLC methods

[0022]

[0023]

[0024] (3) Compared with the developed invention of simultaneous analysis of tin and lead (a method for simultaneously determining the contents of different forms of tin and lead in tobacco), this method does not introduce any organic solvents, and the mobile phases used are all aqueous phases. Moreover, isocratic elution instead of gradient elution is used, and a complex gradient infusion pump is not required, which shortens the experimental time and reduces the consumption of reagents. In addition, the online solid-phase extraction technology is introduced in this invention, further reducing the detection limit to reach the pg L -1 level, enabling the detection of trace amounts of tin and lead in environmental water samples.

[0025] (4) Compared with other published single enrichment methods for tin and lead, the online solid-phase extraction technology introduced in this invention has the advantages of simple operation, high enrichment factor, low detection limit, and reusable adsorbent (Table 2). Moreover, the solid-phase extraction adsorbents used in this invention (C 18 , SCX, SAX, Amphion(II), GO@SiO2) all have good enrichment effects on various forms of tin and lead. Comparatively speaking, GO@SiO2 has the best enrichment effect, as shown in Table 6 specifically.

[0026] Table 2 Comparison of analytical performance with other methods

[0027]

[0028] Description of the Drawings

[0029] Figure 1 is the experimental flow chart of this invention.

[0030] Figure 2 is the chromatographic column screening diagram; where (a) mobile phase: 10 mM TBAH, pH = 2.0, chromatographic column: 1 cm C18; (b) mobile phase: 5 mM SHS + 10 mM TBAH, pH = 2.0, chromatographic column: 1 cm C8; (c) mobile phase: 10 mM HDBAC, pH = 2.5, chromatographic column: 1 cm SCX; (d) mobile phase: 5 mM DMPS, pH not adjusted, chromatographic column: 1 cm SAX; (e) mobile phase: 5 mM L-Cys + 10 mM HDBAC, pH = 2.5, chromatographic column: 1 cm Amphion II; the flow rate is 1.5 mL min -1 .

[0031] Figure 3 is the mobile phase concentration optimization diagram.

[0032] Figure 4 is the mobile phase pH optimization diagram.

[0033] Figure 5 It is the chromatogram for the separation of tin and lead.

[0034] Figure 6 It is the diagram for screening of adsorbent and pre - equilibration agent.

[0035] Figure 7 It is the diagram for screening of pre - equilibration agent concentration.

[0036] Figure 8 It is the diagram for screening of pre - equilibration agent volume.

[0037] Figure 9 It is the diagram for screening of eluent.

[0038] Figure 10 It is the diagram for screening of sample pH.

[0039] Figure 11 It is the diagram for screening of sample volume.

[0040] Figure 12 It is the diagram for screening of enrichment flow rate.

[0041] Figure 13 It is for 10 ng L -1 The standard chromatogram for the enrichment of tin and lead.

[0042] Figure 14 It is the diagram for the speciation analysis of tin and lead in environmental water samples.

[0043] Figure 15 It is the diagram for the speciation analysis of tin and lead in aquaculture pond water. Detailed implementation manners

[0044] The object of the present invention is to provide a detection method for different tin and lead species in water samples based on the combination of SPE - HPLC - ICP - MS, aiming at the deficiencies of the existing technology. This method selects a green aqueous mobile phase for simultaneous analysis of different tin and lead species.

[0045] The present invention will be further described below through specific embodiments, but the protection scope of the present invention is not limited thereto.

[0046] Example 1: Experimental process

[0047] Online SPE - HPLC - ICP - MS realizes the simultaneous enrichment analysis of tin and lead species mainly through the switching of six - port valve and fourteen - port valve. The experiment mainly includes three processes: online solid - phase extraction (SPE), liquid - phase separation (HPLC) and ICP - MS detection. The specific schematic diagram is as Figure 1 .

[0048] The online SPE program mainly includes three steps, namely: column pre - equilibration, sample enrichment and sample elution. The specific operations are as follows:

[0049] Column pre - equilibration: Both the high - pressure six - way valve (valve 1) and the high - pressure fourteen - way valve (valve 2) are in the "load" state. First, manually inject 8 mL of 1 mM BA pre - equilibration agent into the quantitative loop of valve 2. Switch the fourteen - way valve (valve 2) to the "inject" state, turn on the liquid - phase pump (pump 2), and use ultrapure water to carry the pre - equilibration agent BA into the GO@SiO2 enrichment column at a flow rate of 10 mL min -1 After 0.8 min, stop pump 2. Then switch valve 2 from "inject" to "load".

[0050] Sample enrichment: Manually inject 10 mL of the standard solution into the quantitative loop of valve 2. Switch valve 2 to "inject", turn on pump 2 to carry the solution into the GO@SiO2 enrichment column to achieve sample pre - enrichment. After 1 min, immediately switch valve 2 to the "load" state and turn off pump 2 at the same time. At this time, tin and lead species have been adsorbed on the GO@SiO2 enrichment column.

[0051] Sample elution: After the enrichment process is completed, switch valve 1 to "inject", turn on pump 1, and trigger the ICP - MS system to collect data. After the data collection is completed, turn off pump 1 and pump 2, and switch both valve 1 and valve 2 to the "load" state. The above process is shown in Table 3.

[0052] After the sample is eluted by the eluent, it enters a 10 - cm Amphion II chromatographic column for speciation separation, and then each species of Sn and Pb enters the ICP - MS system for detection and analysis.

[0053] Table 3 Enrichment procedures for tin and lead species

[0054]

[0055] Example 2: Optimization of liquid - chromatography separation conditions

[0056] 2.1 Selection of chromatographic column

[0057] Under the same instrument working conditions, five chromatographic columns, namely C 18 , C8, SCX, SAX, and Amphion II, were screened. The results are as Figure 2 , and as a preference, the hydrophilic chromatographic column Amphion II is used as the chromatographic column for subsequent experiments.

[0058] 2.2 Selection of mobile phase, its concentration, and pH value

[0059] In chromatographic analysis, in addition to the stationary phase playing a major role in separating the samples, the appropriate selection of the mobile phase also has an important auxiliary effect on improving the separation effect. In the preliminary experiment, the ion pair reagents had good elution effects on tin and lead species. Therefore, ion pair reagents such as sodium pentanesulfonate (SPS), sodium dodecylbenzenesulfonate (SDBS), hexadecyl dimethyl benzyl ammonium chloride (HDBAC), and tetrabutylammonium hydroxide (TBAH) were used as the mobile phase to complete the separation of different forms of tin and lead. The results showed that when SDBS was used as the mobile phase, different forms of tin and lead could be well separated. The best separation result is shown in Figure 5 .

[0060] This application investigated mobile phases with different concentrations. The concentration of the mobile phase mainly affected the peak elution speed, and the higher the concentration, the faster the peak elution. The separation of each species was investigated when the SDBS concentration ranged from 4.0 - 12.0 mM. The results are as shown in Figure 3 . As a preference, the concentration of the mobile phase is 4.0 mM.

[0061] This application also investigated mobile phases with different pH values. Different forms of tin and lead species have different ionization constants, and their retention times on the chromatographic column mainly change with the concentration and pH of the mobile phase. Under different pH conditions, the ionization degrees of each species are different, the interaction with the chromatographic column changes, and the retention times are different. The separation of each form was investigated when the SDBS concentration was 4.0 mM and the pH value ranged from 1.8 - 3.0. As shown in Figure 4 , when the SDBS concentration is 4.0 mM and the pH value is 2.0, the best separation effect can be obtained.

[0062] Example 3: Optimization of Enrichment Conditions

[0063] 3.1 Selection of Adsorbent and Pre - equilibration Agent

[0064] According to different adsorption and desorption mechanisms, five adsorbents, namely C 18 , SCX, SAX, Amphion II, and GO@SiO2, were screened. The results are as shown in Figure 6 . When GO@SiO2 was used as the adsorbent and benzoic acid (BA) was used as the pre - equilibration agent, the best enrichment effect for tin and lead species could be obtained.

[0065] 3.2 This application screened the concentration and volume of the pre - equilibration agent. The concentration and volume of the pre - equilibration agent will affect the enrichment effect to a certain extent. To obtain the best enrichment effect, the pre - equilibration agent BA with concentrations of 0.1 mM, 0.5 mM, 1.0 mM, and 5.0 mM was screened. The results are shown in Figure 7 . When the concentration of the pre - equilibration agent is 1.0 mM, the enrichment effect is better.

[0066] The enrichment effects of each species were investigated separately when the volume of the pre - equilibration agent was 2.0 mL, 4.0 mL, 6.0 mL, 8.0 mL, and 10.0 mL. The results are as follows Figure 8 shown. When the volume of BA was 8.0 mL, tin and lead could be enriched well.

[0067] 3.3 The types of eluents were also screened in this application. The types of eluents mainly affect the elution effects of each species. If the eluent effect is not good, the adsorbed species cannot be eluted from the enrichment column. Therefore, the enrichment effects were screened when using SDBS (5.0 mM, 10.0 mM), BA (20.0 mM), and the mobile phase (4.0 mM, pH 2.0) as internal eluents, as follows Figure 9 shown. When using the mobile phase as the internal eluent, better enrichment effects can be obtained.

[0068] 3.4 The sample pH was screened in this application. The sample pH values of 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, and 10.0 were screened. The results are as follows Figure 10 shown. When the pH range was 5.0 - 8.0, the enrichment effect was the best.

[0069] 3.5 The sample volume and enrichment flow rate were also screened in this application. The enrichment effects were investigated when the sample volume was 2.0 mL, 4.0 mL, 6.0 mL, 8.0 mL, and 10.0 mL. The results are as follows Figure 11 shown. The enrichment factor increased with the increase of the sample volume. Therefore, the injection volume of 10.0 mL was selected in the subsequent experiments. And the effects of enrichment flow rates of 2.0 mL min -1 , 4.0 mL min -1 , 6.0 mL min -1 , 8.0 mL min -1 , 10.0 mL min -1 on the enrichment effect were investigated. As follows Figure 12 shown. The speed of the enrichment flow rate basically had no effect on the enrichment effect. In order to shorten the experimental time, the finally selected enrichment flow rate was 10.0 mLmin -1 .

[0070] Example 4: Index confirmation for the determination of different forms of tin and lead by SPE - HPLC - ICP - MS coupling technology

[0071] 4.1 Determination of the linear range of the coupling analysis method

[0072] Prepare standard samples of tin and lead forms into a mixed standard solution of tin and lead forms with concentrations of 10 mg L for TMT, TET, TBT, TPhT, Pb (II), TML, and TEL, and gradually dilute to the required concentration. The series of solution concentrations of the mixed standard of tin and lead forms are: 0.1, 1.0, 5.0, 10.0, 20.0, 50.0 ng L -1 ; According to the above instrument operating conditions, analyze the series of solutions of the mixed standard of tin and lead forms, measure the peak areas of the tin and lead forms, use the concentration as the abscissa and the peak area as the ordinate to draw a standard curve. The linear correlation coefficients are all better than 0.990. -1 ; According to the above instrument operating conditions, analyze the series of solutions of the mixed standard of tin and lead forms, measure the peak areas of the tin and lead forms, use the concentration as the abscissa and the peak area as the ordinate to draw a standard curve. The linear correlation coefficients are all better than 0.990.

[0073] 4.2 Determination of the detection limit and quantification limit of the combined analysis method

[0074] Using the blank reagent of the standard sample, according to the above instrument conditions, measure ten times on average, calculate the detection limit based on 3 times the standard deviation of the blank signal, and calculate the quantification limit based on 10 times the standard deviation.

[0075] 4.3 Determination of the precision of the combined analysis method

[0076] Use precision to investigate the reproducibility of the method. Prepare a mixed standard solution with a concentration of 10.0 ng L from the standard samples of tin and lead. According to the above working conditions, analyze the mixed standard of tin and lead, measure six times in parallel, and calculate the RSD based on the retention time, peak area, and peak height of each form. The results show that the RSDs are all less than 5%. The measurement results are shown in Table 4. -1 Use precision to investigate the reproducibility of the method. Prepare a mixed standard solution with a concentration of 10.0 ng L from the standard samples of tin and lead. According to the above working conditions, analyze the mixed standard of tin and lead, measure six times in parallel, and calculate the RSD based on the retention time, peak area, and peak height of each form. The results show that the RSDs are all less than 5%. The measurement results are shown in Table 4.

[0077] Table 4 Analytical performance of on-line SPE-HPLC-ICP-MS

[0078]

[0079] 4.4 Determination of the accuracy of the combined analysis method

[0080] In the present invention, the standard addition method is used to calculate the spike recovery rate to measure the accuracy of the method, that is, standard solutions of each form of tin and lead with known concentrations are added to the matrix sample, and after steps such as enrichment, separation, and detection, their concentrations are measured, and the percentage relationship between the actual concentration difference and the theoretical value is calculated, which is the spike recovery rate. From the measurement results, it can be seen that the spike recovery rates are all higher than 89%.

[0081] Example 5: Analysis of the mixed forms of tin and lead in water samples

[0082] Apply the established method to the analysis of the forms of tin and lead in water samples. The chromatogram is shown in Figure 14 - 15 , and the data are shown in Table 5.

[0083] Table 5 Morphological analysis of Sn and Pb in water samples (ng L –1 , n = 3)

[0084]

[0085]

[0086]

[0087]

[0088]

[0089] The results show that the content of inorganic lead in the aquaculture pond water is relatively high, and its concentration ranges from 0.29 to 8.73 ng L –1 , while the Pb(II) in seawater is only 0.64 - 3.20 ng L –1 . Compared with seawater, there are more organotin species in the aquaculture pond water, and their existing forms and concentration ranges are as follows: TMT: 0.03 - 0.13 ng L –1 , TBT: 0.03 - 0.18 ng L –1 , TET: 0.06 - 0.25 ng L –1 . And TBT is the only detected organotin form in seawater, with its content much lower than that in the aquaculture pond water, being 0.023 - 0.046 ng L –1 . TPhT, TML and TEL are not found in all water samples. And the species and contents in the influent water, pond water and effluent water of the aquaculture pond are also different. When detecting tin species, except that the total tin content of the influent water in Pond P3 in Jiaxing and Pond P6 in Pinghu is greater than that of the pond water and the effluent water, the maximum tin concentration exists in the effluent water in the rest of the aquaculture ponds. When detecting lead species, the total lead content in the influent water of Pond P4 and Pond P7 is the highest, while the total lead concentration in the effluent water is the highest in the rest of the aquaculture ponds. The reason for this phenomenon may be that the aquaculture feed contains trace amounts of tin and lead, and these tin and lead migrate in the aquaculture pond through fish predation, natural sedimentation and other biological activities, ultimately resulting in a higher content in the effluent water than in the influent water, and the lowest content in the pond water.

[0090] Example 6: The solid-phase extraction adsorbents (C 18 , SCX, SAX, Amphion(II), GO@SiO2) used in the present invention all have good enrichment effects on various forms of tin and lead. However, comparatively speaking, GO@SiO2 has the best enrichment effect, as shown in Table 6 specifically.

[0091] Table 6 Enrichment factors under different pretreatment conditions

[0092]

[0093]

Claims

1. An analytical method for determining different tin and lead species in water samples by SPE-HPLC-ICP-MS coupling technology, characterized in that, It includes the following steps: (1) Establish an analytical method for SPE-HPLC-ICP-MS coupling Online SPE-HPLC-ICP-MS includes three processes: online solid-phase extraction, liquid-phase separation, and ICP-MS detection; among them, online solid-phase extraction includes three steps: column pre-equilibration, sample enrichment, and sample elution; after sample elution, liquid-phase separation of different tin and lead species is carried out, and then each species of tin and lead enters the ICP-MS system for detection and analysis; The conditions for online solid-phase extraction are as follows: enrichment column: GO@SiO2 5μm, 10mm×4.6mm i.d.; pre-equilibrant: 1.0 mM benzoic acid, volume 8.0 mL; eluent: 4 mM sodium dodecylbenzenesulfonate, pH 2.0; sample pH: 5.0 - 8.0; sample volume: 10 mL; enrichment flow rate: 10 mL min -1 ; The conditions for liquid phase separation are as follows: hydrophilic chromatographic column: Welch Amphion II 5μm, 100mm×4.6mm i.d.; mobile phase: 4mM sodium dodecylbenzenesulfonate, pH 2.0; flow rate: 1.5mL min -1 ; (2) Preparation of standard curves Weigh standard samples of different tin and lead species, namely TMT, TET, TBT, TPhT, Pb(II), TML, and TEL, and prepare a mixed standard solution. Gradually dilute it to obtain a series of standard working solutions. Perform detection and analysis according to the method established in step (1). Using the concentration of each species of tin and lead as the abscissa and the peak area in the HPLC-ICP-MS chromatogram as the ordinate, plot the standard curves; (3) Detection of actual samples Filter the water sample to be tested through a 0.45μm aqueous filter membrane, perform detection and analysis according to the method established in step (1), and substitute the peak area in the obtained HPLC-ICP-MS chromatogram into the standard curves plotted in step (2) to further obtain the contents of different tin and lead species in the water sample.

2. The analytical method for determining different tin and lead species in water samples by SPE-HPLC-ICP-MS coupling technology according to claim 1, characterized in that, In step (1), the conditions for ICP-MS detection are as follows: plasma RF power is 1200 W, coolant gas flow rate is 13.02 L / min -1 , auxiliary gas flow rate is 0.75 L / min -1 , nebulizer gas flow rate is 0.85 L / min -1 , and all gases are high-purity argon gas.

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