Method for detecting content of tributyl phosphate in salt lake brine

Abstract

The invention discloses a method for detecting the content of tributyl phosphate in salt lake brine, and belongs to the field of environmental chemical analysis and detection. The method for detecting the tributyl phosphate in the salt lake brine specifically comprises the following steps: transferring the salt lake brine, adding water, diluting and uniformly mixing to obtain a sample solution; then loading the sample solution to an activated C18 solid-phase extraction column, leaching with water, discarding effluent, eluting with an acetone ethyl acetate solution, collecting eluant, blowing to be nearly dry, redissolving, and passing through a membrane to obtain a to-be-detected sample, determining by adopting GC / MS, and calculating to obtain the content of tributyl phosphate in the to-be-detected sample according to a standard curve model of an internal standard method. The method has good sensitivity, stability and repeatability, is suitable for accurate determination of tributyl phosphate in salt lake brine, and provides necessary technical support for detection and monitoring of salt lake brine pollutants.

Description

Technical Field

[0001] The invention relates to a method for detecting the content of tributyl phosphate in salt lake brine, belonging to the field of environmental chemical analysis and detection. Background Art

[0002] As a new energy metal, lithium plays an irreplaceable role in many fields, and the demand for lithium is also increasing every year. At present, the lithium ore extraction process is mature, and the lithium resources on the market mainly come from the extraction of lithium ore, but this process has high energy consumption and high mining costs. As the market demand for lithium increases year by year, people have turned their attention to salt lake brine with richer lithium resources, lower mining costs and lower energy consumption. Solvent extraction is one of the main production methods for extracting lithium from salt lake brine. Its principle is that an organic solvent extractant with high selectivity for lithium and no extraction effect on other solute ions extracts lithium from the aqueous phase into the organic phase, and then the lithium in the organic phase is eluted and separated from the extractant through the stripping process, so as to achieve efficient separation of lithium and other solute ions. The extraction method has broad application prospects and industrial production potential in the field of lithium extraction from salt lake brine due to its advantages such as low production cost and high lithium ion recovery rate.

[0003] The extraction system represented by tributyl phosphate is the main extraction system for lithium extraction from salt lake brine. This system is widely used due to its low cost and good extraction and separation effects. However, tributyl phosphate easily evaporates into the atmosphere and enters the organism through inhalation, dietary intake or skin contact, where it migrates and accumulates. Tributyl phosphate can destroy the cell morphology of phytoplankton, damage cell membrane structure and organelles such as mitochondria, and inhibit the growth of microalgae cells. The large-scale use of tributyl phosphate will pose a potential threat to human health and cause certain damage to the ecosystem. Therefore, it is of great significance to establish an efficient, convenient and rapid method for determining the content of tributyl phosphate in such a complex system as salt lake brine.

[0004] At present, the main detection methods for tributyl phosphate in water environment are: optical detection method, infrared spectroscopy detection method, gas chromatography, gas chromatography-mass spectrometry. Among them, the optical detection method is complicated to operate, and the qualitative and quantitative results are inaccurate; the infrared spectroscopy detection method is complicated to operate and has low sensitivity; the gas chromatography method is easily interfered by the matrix, and has problems such as inaccurate qualitative results and low sensitivity; the GC / MS method has the characteristics of less matrix interference and high method sensitivity. It comprehensively uses retention time, qualitative and quantitative ions to ensure the accuracy of the qualitative and quantitative results of the target analytes, and is currently a relatively efficient detection technology.

[0005] However, salt lake brine is different from ordinary water. It is rich in minerals and salt. Its main components include chloride, sulfate, carbonate, potassium, magnesium, sodium and other elements. Sodium chloride is the most important component in brine, accounting for the vast majority of the total salt. In addition, salt lake brine also contains some special elements such as lithium, rubidium, cesium, etc., as well as organic matter. The composition of salt lake brine is closely related to its geographical environment. The composition of different salt lakes is different, but the content of sodium chloride is very high. For this high-salt complex system, when separating and detecting the target object, matrix drift, difficulty in separating the target peak and impurity peak, peak tailing and other phenomena often occur, which leads to low sensitivity in detecting the target object.

[0006] Therefore, for the high-salt, complex-component salt lake brine system, establishing a highly sensitive detection method that can accurately measure tributyl phosphate has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the invention

[0007] In view of the defects and shortcomings of the prior art, the purpose of the present invention is to provide a method for detecting the content of tributyl phosphate in salt lake brine, which can efficiently and accurately determine the content of tributyl phosphate in salt lake brine, with short detection time, high accuracy and high sensitivity.

[0008] In order to achieve the above purpose, the technical solutions provided are as follows: A method for detecting the content of tributyl phosphate in salt lake brine, the method comprising the following steps: (1) Sample pretreatment After diluting the salt lake brine, a sample solution is obtained; then the sample solution is loaded onto an activated C18 solid phase extraction column, rinsed with water, the effluent is discarded, and then eluted with acetone ethyl acetate solution, the eluate is collected, blown to near dryness, redissolved, and passed through a membrane to obtain the sample to be tested; (2) Determination of tributyl phosphate content in the sample to be tested The sample obtained in step (1) is measured by GC / MS, and the content of tributyl phosphate in the sample is calculated based on the quantitative standard curve model constructed by the internal standard method.

[0009] In one embodiment, the dilution of the salt lake brine in step (1) refers to uniformly mixing the salt lake brine and water in a ratio of 1:1 to 2.

[0010] In one embodiment, the salt lake brine in step (1) refers to salt lake brine filtered through a 0.7 μm glass fiber filter membrane.

[0011] In one embodiment, the activated C18 solid phase extraction column in step (1) refers to a C18 solid phase extraction column that is activated by sequentially washing with acetonitrile and water.

[0012] In one embodiment, the amount of water used as the eluent in step (1) is 10-15 mL.

[0013] In one embodiment, the acetone ethyl acetate solution in step (1) is a mixed solution of acetone and ethyl acetate in a volume ratio of 1:1; the preparation process is: 200 mL of acetone is transferred and 200 mL of ethyl acetate is added to prepare.

[0014] In one embodiment, the re-dissolution in step (1) refers to re-dissolution using n-hexane.

[0015] In one embodiment, the membrane filter in step (1) refers to a 0.22 μm microporous filter membrane.

[0016] In one embodiment, the chromatographic conditions of the GC / MS in step (2) are: Agilent HP-5MS UI: 30m*0.25mm, 0.25μm; the column temperature is 50°C for 1 min, increased to 200°C at a heating rate of 20°C / min, maintained for 1 min, increased to 250°C at a heating rate of 10°C / min, maintained for 5 min; the flow rate is 1mL / min; the injection volume is 1μL; the injection mode is splitless injection; and the temperature of the injection port is 280°C.

[0017] In one embodiment, the mass spectrometry conditions of the GC / MS in step (2) are: EI ion source; detector temperature is 300°C; solvent delay time is 3 min; ionization energy is 70 eV; the measurement method is selected ion monitoring SIM, and the ion source temperature is 290°C.

[0018] Another object of the present invention is to provide an application of the above-mentioned method in the process of monitoring the tributyl phosphate content in salt lake brine.

[0019] Beneficial effects: (1) The present invention uses solid phase extraction-gas phase mass spectrometry for the first time to detect the content of tributyl phosphate in salt lake brine, combining the advantages of solid phase extraction column purification with the high selectivity, high sensitivity monitoring capability and ability to provide relative molecular mass of gas phase mass spectrometry. By verifying that it is suitable for the detection of tributyl phosphate in the high-salt complex matrix of salt lake brine, not only can the qualitative analysis of tributyl phosphate be achieved, but also the content can be determined, thereby improving the sensitivity and accuracy of the detection; (2) The present invention dilutes the sample with water, purifies it with a solid phase extraction column, and combines it with a gas phase mass spectrometry method to effectively solve the problem that the high salt system of salt lake brine may affect the sensitivity of the instrument, removes interfering substances such as organic matter and inorganic salts in the salt lake brine, increases the detection sensitivity, realizes the qualitative and quantitative detection of tributyl phosphate, greatly shortens the analysis and detection time of tributyl phosphate, and improves the detection efficiency and accuracy; (3) The detection method provided by the present invention has good linearity, and the method has good sensitivity, stability and repeatability. It is suitable for the accurate determination of tributyl phosphate in salt lake brine, and provides necessary technical support for the ecological environment monitoring of salt lake brine. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The total ion current diagrams of the tributyl phosphate positive sample and the negative sample of the present invention, wherein (a) is the total ion current diagram of the positive sample, and (b) is the total ion current diagram of the negative sample; Figure 2 The data diagram is the effect of different injection port temperatures on the response of tributyl phosphate in Comparative Example 1; Figure 3 The data diagram is a graph showing the effect of different detector temperatures on the response of tributyl phosphate in Comparative Example 2; Figure 4 The data diagram is a graph showing the effect of different ion source temperatures on the response of tributyl phosphate in Comparative Example 3; Figure 5 This is a data graph showing the effect of different types of solid phase extraction columns on the recovery rate of tributyl phosphate in Comparative Example 4; Figure 6 The total ion current diagram of tributyl phosphate for different types of solid phase extraction columns in Comparative Example 4, wherein (a) is an NH2 solid phase extraction column, (b) is a Florisil solid phase extraction column, (c) is an HLB solid phase extraction column, and (d) is a C18 solid phase extraction column; Figure 7 The figure is a data diagram showing the effect of different elution solvents on the recovery rate of tributyl phosphate in Comparative Example 5; Figure 8 The figure is a data diagram showing the effect of the amount of elution solvent on the recovery rate of tributyl phosphate in Comparative Example 6; Fig. 9 These are the separation diagrams of tributyl phosphate using different chromatographic columns in Comparative Example 7, where (a) is an HP-5MS chromatographic column, (b) is a DB-5MS chromatographic column, and (c) is an HP-INNOWAX chromatographic column. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below with reference to examples so that those skilled in the art can implement the invention according to the description.

[0021] Source and preparation of the standard substances involved in the embodiments of the present invention: Tributyl phosphate (100 μg / mL) and tributyl phosphate-D27 (100 μg / mL) were purchased from Alta Technology Co., Ltd.; 1.0 mL of tributyl phosphate (100 μg / mL) and tributyl phosphate-D27 (100 μg / mL) were pipetted respectively, and the volume was adjusted to 10 mL with n-hexane to prepare a 10.0 μg / mL standard stock solution; Pipette 1.0 mL of tributyl phosphate (10.0 μg / mL) and tributyl phosphate-D27 (10.0 μg / mL) respectively, dilute to 10 mL with n-hexane, and prepare a 1.00 μg / mL standard intermediate solution; Standard working solution: Dilute the tributyl phosphate standard intermediate solution into different concentrations using n-hexane.

[0022] 7890B-5977B0 gas chromatograph-mass spectrometer (GC / MS), Agilent, USA; nitrogen blowdown instrument, Organomation, USA.

[0023] Example 1 A method for detecting the content of tributyl phosphate in salt lake brine comprises the following steps: (1) Sample pretreatment Accurately pipette 10 mL of salt lake brine and dilute it to 20 mL with water to obtain the sample solution; Activate the C18 solid phase extraction column with 6 mL acetonitrile and 6 mL water in turn; transfer all the above sample solutions to the C18 solid phase extraction column, rinse the solid phase extraction column with 15 mL water, discard the effluent, elute with 8 mL n-hexane ethyl acetate solution (mixed with 200 mL acetone and 200 mL ethyl acetate), collect the eluate and blow it to near dryness with nitrogen in a 40°C water bath, redissolve it in n-hexane and make it up to 1.0 mL, filter it through a 0.22 μm microporous filter membrane, and the filtrate is the sample to be tested; (2) Construction of quantitative relationship model The tributyl phosphate series standard working solutions were prepared into a series of standard solutions with the concentrations of 0 ng / mL, 5 ng / mL, 10 ng / mL, 30 ng / mL, 50 ng / mL, 100 ng / mL, and 200 ng / mL. The internal standard tributyl phosphate-D27 concentration was 20 ng / mL. GC / MS was used for determination and internal standard method was used for quantification. The mass concentration ratio of tributyl phosphate to tributyl phosphate-D27 was used as the abscissa (x), and the corresponding peak area ratio was used as the ordinate (y). A quantitative relationship model was constructed, as shown in Table 2. The results showed that the linear relationship was good within the mass concentration range of tributyl phosphate, and the correlation coefficient (r 2 ) were all greater than 0.999; the detection limit (LOD) and quantification limit (LOQ) of the method were determined by 3 times and 10 times the signal-to-noise ratio (S / N), respectively, as shown in Table 1; Table 1. Linear range, linear equation, correlation coefficient, detection limit and quantification limit of tributyl phosphate

[0024] The chromatographic conditions of GC / MS were as follows: Agilent HP-5MS UI: 30m*0.25mm, 0.25μm; the column temperature was 50°C for 1 min, then increased to 200°C at a heating rate of 20°C / min, then maintained for 1 min, then increased to 250°C at a heating rate of 10°C / min, then maintained for 5 min; the flow rate was 1mL / min; the injection volume was 1μL; the injection mode was splitless injection; the injection port temperature was 280°C; The mass spectrometry conditions of GC / MS were as follows: EI ion source; detector temperature was 300°C; solvent delay time was 3 min; ionization energy was 70 eV; the determination method was selected ion monitoring SIM, and the ion source temperature was 290°C; the retention time, quantitative ion, and qualitative ion of tributyl phosphate and tributyl phosphate-D27 are shown in Table 2; Table 2. Retention time and mass spectrometry parameters of tributyl phosphate and internal standard tributyl phosphate-D27 Project Name Retention time min Quantitative ion, m / z Qualifier ion, m / z Qualifier ion, m / z Tributyl phosphate 9.473 99.1 155 211 Tributyl phosphate-D27 9.340 103 167 231 (3) Determination of tributyl phosphate content in the sample The sample obtained in step (1) is measured by GC / MS, and the content of tributyl phosphate in the sample is calculated based on the quantitative relationship model constructed in step (2).

[0025] Example 2 Recovery and Precision Referring to the method of Example 1, appropriate amounts of tributyl phosphate standard solutions at three addition levels, low, medium and high, were added to the salt lake brine. Six parallel tests were conducted at each level to determine the recovery rate. The results are shown in Table 3.

[0026] Table 3. Spiked recovery test results

[0027] As shown in Table 3, the recoveries of tributyl phosphate at low, medium and high addition levels were 97.8%~109.5%, and the relative standard deviations were 5.4%~8.8%, which met the quantitative standard of the detection method. The results showed that the method had good accuracy and precision and was suitable for the determination of tributyl phosphate in salt lake brine.

[0028] Example 3 Referring to the method of Example 1, the content of tributyl phosphate in the actual salt lake brine sample was measured, and the results are shown in Table 4; Table 4. Determination results of tributyl phosphate in salt lake brine Salt Lake Brine Sample Source Tributyl phosphate content (μg / L) Emerald Lake Brine 1 ND Duck Lake Brine ND Totai Brine 1 ND Dry river brine 22.6 Koruk Brine 1 ND Totai Brine 2 ND Emerald Lake Brine 2 ND Dachaidan Brine ND Xiaochaidan Brine ND Koruk Brine 2 ND Dabson Brine ND Gahai Brine ND Dongtai brine ND Note: “ND” means not detected.

[0029] Comparative Example 1 Referring to the method of Example 1, the effect of six injection port temperatures of 200°C, 220°C, 240°C, 260°C, 280°C, and 300°C on the response of tributyl phosphate in a sample with a content of 40 ng / mL was investigated. The results are as follows: Figure 2 As shown: Depend on Figure 2 The results show that as the injection port temperature increases, the response of tributyl phosphate increases. When the injection port temperature rises to 280°C, the response of tributyl phosphate shows a stable trend, indicating that when the injection port temperature is 280°C, the response value of tributyl phosphate is relatively large, which is suitable for the detection of tributyl phosphate target.

[0030] Comparative Example 2 Referring to the method of Example 1, the response of tributyl phosphate in the sample with a content of 40 ng / mL at five detector temperatures of 270°C, 280°C, 290°C, 300°C, and 310°C was investigated. The results are as follows: Figure 3 As shown: Depend on Figure 3 The results show that as the detector temperature increases, the response of tributyl phosphate increases. When the detector temperature rises to 300°C, the response of tributyl phosphate shows a stable trend, indicating that when the detector temperature is 300°C, the response value of tributyl phosphate is relatively large, which is suitable for the detection of tributyl phosphate targets.

[0031] Comparative Example 3 Referring to the method of Example 1, the response of tributyl phosphate in the sample with a content of 40 ng / mL at five ion source temperatures of 230°C, 250°C, 270°C, 290°C, and 310°C was investigated. The results are as follows: Figure 4 As shown: Depend on Figure 4 The results show that as the ion source temperature increases, the response of tributyl phosphate increases. When the ion source temperature rises to 290°C, the response of tributyl phosphate shows a stable trend, indicating that when the ion source temperature is 290°C, the response value of tributyl phosphate is relatively large, which is suitable for the detection of tributyl phosphate targets.

[0032] Comparative Example 4 Referring to the method of Example 1, the effects of pretreatment with C18 solid phase extraction column, HLB solid phase extraction column, NH2 solid phase extraction column and Florisil solid phase extraction column on the recovery rate of tributyl phosphate in the sample with a content of 40 ng / mL were investigated. The results are as follows: Figure 5 As shown, the TIC total ion current diagram is as follows Figure 6 As shown: Depend on Figure 6It can be seen that the matrix interference of NH2 solid phase extraction column and Florisil solid phase extraction column is large, and there are more impurity peaks. C18 solid phase extraction column and HLB solid phase extraction column have no obvious matrix interference and fewer impurity peaks. Figure 5 The results show that the recovery rate of the C18 solid phase extraction column is higher than that of the HLB solid phase extraction column; the C18 solid phase extraction column was finally selected as the purification column of the present invention.

[0033] Comparative Example 5 Referring to the method of Example 1, the effects of six elution solvents, acetonitrile, methanol, acetone, ethyl acetate, acetone / n-hexane, and acetone / ethyl acetate, on the recovery rate of tributyl phosphate in a sample with a content of 40 ng / mL were investigated. The results are as follows: Figure 7 As shown: Depend on Figure 7 The results show that when acetone / ethyl acetate is used as the elution solvent, the recovery rate of the target is the highest. The elution time of the sample is shorter when acetone / ethyl acetate is used as the elution solvent, and the time required for nitrogen blowing is less than that of acetonitrile, so acetone / ethyl acetate is selected as the elution solvent.

[0034] Comparative Example 6 Referring to the method of Example 1, the effects of 4 mL, 8 mL, 12 mL, and 16 mL of acetone / ethyl acetate elution solvent on the recovery rate of tributyl phosphate in a sample with a content of 40 ng / mL were investigated. The results are as follows: Figure 8 As shown: Depend on Figure 8 The results show that as the amount of elution solvent increases, the recovery rate of the target compound tends to decrease. When 8mL acetone / ethyl acetate is used as the elution solvent, the recovery rate of the target compound is the highest, so 8mL acetone / ethyl acetate is selected as the elution solvent.

[0035] Comparative Example 7 Referring to the method of Example 1, the separation effect of chromatographic columns HP-5MS (30m×0.25mm×0.25μm), DB-5MS (30m×0.25mm×0.25μm), and HP-INNOWAX (30m×0.25mm×0.25μm) on tributyl phosphate in a sample with a content of 40ng / mL was investigated. The results are as follows: Fig. 9 As shown: Depend on Fig. 9 The results show that: DB-5MS has a low response to the target, the peak shape is asymmetric and slightly tailing, the separation effect is poor, and there are impurity peaks; HP-INNOWAX has a low response to the target, the peak shape is flat, and the separation effect is poor; HP-5MS column has a high response to the target, the peak shape is symmetrical and not tailing, and the separation effect is good, so the HP-5MS column was selected for separation and determination.

[0036] Comparative Example 8 With reference to the method of Example 1, the external standard method was used for quantitative determination, and the recovery and precision were measured. The results are shown in Table 5: Table 5. Spiked recovery test results - external standard method

[0037] From the results in Table 5, we can see that: under the three spike levels, the recovery rate of the target substance by the external standard method is significantly lower than that by the internal standard method, indicating that the internal standard method has a good recovery rate and better accuracy and precision; the relative standard deviation RSD of the external standard method is significantly greater than that of the internal standard method, indicating that the internal standard method is more stable, so the internal standard method is selected for quantification.

[0038] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for detecting the content of tributyl phosphate in salt lake brine, characterized in that: The method comprises the following steps: (1) Sample pretreatment After diluting the salt lake brine, a sample solution is obtained; then the sample solution is loaded onto an activated C18 solid phase extraction column, rinsed with water, the effluent is discarded, and then eluted with acetone ethyl acetate solution, the eluate is collected, blown to near dryness, redissolved, and passed through a membrane to obtain the sample to be tested; The acetone ethyl acetate solution is a mixed solution of acetone and ethyl acetate, with a volume ratio of 1:1; the preparation process is: take 200 mL of acetone and add 200 mL of ethyl acetate to prepare; (2) Determination of tributyl phosphate content in the sample to be tested The sample obtained in step (1) is measured by GC / MS, and the content of tributyl phosphate in the sample is calculated based on the quantitative standard curve model constructed by the internal standard method; The chromatographic conditions of the GC / MS are as follows: Agilent HP-5MS UI: 30m*0.25mm, 0.25μm; the temperature of the chromatographic column is 50°C for 1 min, then increased to 200°C at a heating rate of 20°C / min, then maintained for 1 min, then increased to 250°C at a heating rate of 10°C / min, then maintained for 5 min; the flow rate is 1mL / min; the injection volume is 1μL; the injection mode is splitless injection; the temperature of the injection port is 280°C; The mass spectrometry conditions of the GC / MS are as follows: EI ion source; detector temperature is 300°C; solvent delay time is 3 min; ionization energy is 70 eV; the determination method is selected ion monitoring method SIM, and the ion source temperature is 290°C.

2. The method according to claim 1, characterized in that: The dilution of the salt lake brine in step (1) refers to uniformly mixing the salt lake brine and water in a ratio of 1:1 to 2.

3. The method according to claim 1, characterized in that The salt lake brine in step (1) refers to the salt lake brine filtered through a 0.7 μm glass fiber filter membrane.

4. The method according to claim 1, characterized in that: The activated C18 solid phase extraction column in step (1) refers to a C18 solid phase extraction column that is activated by sequentially washing with acetonitrile and water.

5. The method according to claim 1, characterized in that The amount of water used as eluent in step (1) is 10-15 mL.

6. The method according to claim 1, characterized in that The re-dissolution in step (1) refers to re-dissolution using n-hexane.

7. Use of the method described in any one of claims 1 to 6 in monitoring the content of tributyl phosphate in salt lake brine.

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