Novel ion chromatography detection method

Abstract

Belonging to the technical field of ion analysis and detection, the invention discloses a novel ion chromatography detection method, which belongs to the technical field of ion analysis and detection, and the detection steps are as follows: adding ultrapure water into a lithium sulfate sample for complete dissolution, then conducting dilution and filtration, then adopting an SH-AP-1 type anion chromatographic column for exchange separation of anions in the solution, and finally conducting ion chromatography. F and Cl ions in the separated solution are detected by adopting a CIC-D120 type ion chromatograph, the retention time of different anions on a chromatographic column is detected in combination with an electrical conductivity detector and an inhibition type electrical conductivity detector in an auxiliary manner to carry out elemental qualitation, and quantification is carried out according to the peak height and the peak area. After the novel ion chromatography detection method is applied, high-sensitivity and high-precision detection of F and Cl ions in a lithium sulfate product is realized by optimizing chromatographic elution conditions and selecting a proper detector and a pretreatment technology.

Description

Technical Field

[0001] The invention relates to the technical field of ion analysis and detection, in particular to a novel ion chromatography detection method. Background Art

[0002] With the widespread application of lithium sulfate products in the fields of batteries, medicine, etc., its quality control has become the key. However, the quality control of lithium sulfate products is currently facing severe challenges, especially the frequent problems of excessive F and Cl ions. Due to the lack of standard experience procedures and equipment support, as well as the detection methods that are not clearly specified in the current national standards and industry specifications, it is difficult to quickly and accurately identify the source of defects in excessive F and Cl ions. It is impossible to meet the production line's demand for real-time data. Therefore, it is urgent to develop a new ion chromatography detection method to solve the above problems.

[0003] In response to the above problems and in combination with actual production needs, the applicant has developed a method for the accurate determination of trace fluorine (F) and chlorine (Cl) ions in lithium sulfate products. This method overcomes the limitations of existing technologies in terms of detection efficiency, accuracy and cost control, and provides strong technical support for the quality control of lithium sulfate products. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned background technical difficulties and provide a novel ion chromatography detection method with high sensitivity and high precision.

[0005] To achieve the above purpose, the technical scheme adopted is: a new ion chromatography detection method, the detection steps of which are to add ultrapure water to the lithium sulfate sample and completely dissolve it, then dilute and filter it, and then use an anion chromatography column to exchange and separate the anions in the solution, and then use an ion chromatograph to detect the F and Cl ions in the separated solution, and use a conductivity detector and a suppressed conductivity detector to assist in detecting the retention time of different anions on the chromatographic column to perform element qualitative analysis, and quantify it according to the peak height and peak area.

[0006] Furthermore, the chromatographic column is treated with SH series ion chromatography samples before use.

[0007] Furthermore, the anion chromatography column is an SH-AP-1 type hydroxide system anion chromatography column, the matrix of which is a polystyrene-divinylbenzene polymer with a cross-linking degree of 55%, and the ion chromatograph is a CIC-D120 type, which is an analysis system consisting of an ion chromatograph, an eluent generator, an injection system, and test software.

[0008] Furthermore, the detection steps are as follows: ① Prepare the solution to be tested: weigh lithium sulfate, dissolve it in ultrapure water and transfer it to a volumetric flask, dilute it with ultrapure water to obtain solution No. 1, then transfer 1 mL from solution No. 1 to a centrifuge tube, dilute it to 10 mL to obtain solution No. 2, use a syringe to transfer about 3-8 mL of solution No. 2, and filter it through a 0.25um filter to obtain the solution for the machine; ② Prepare a blank sample: Select deionized water with a resistivity of ≥18 MΩ·cm (25℃) and filtered through a 0.22 µm microporous filter membrane as the experimental water, and prepare the blank sample according to the method in step ①; ③Set the equipment parameters: select potassium hydroxide as the eluent, set the pump flow rate to 0.5-0.8mL / min, the temperature control pool temperature to 32-36℃, the column temperature to 30-35℃, the conductivity detector sampling frequency to 5Hz (zero before injection), the suppressed conductivity detector current to 90mA, and the quantitative loop volume to 25ul; ④ Prepare stock solution and draw standard curve: select fluoride ion standard stock solution (C=1000mg / L) and chloride ion standard stock solution (C=1000mg / L) as standard solution, transfer (0.3-0.8mL, 0.1-0.2mL) of fluoride ion solution standard substance (1000mg / L) in water, (3-5mL, 1-3mL) of chloride ion solution standard substance (1000mg / L) in water into a series of 100mL polytetrafluoroethylene volumetric flasks, and add ultrapure water to make up to volume. to 100mL, and obtain No. 5 and No. 4 standard solutions respectively; pipette No. 5 solution (5-10mL, 2-4mL, 0.5-1mL) into a series of 100mL polytetrafluoroethylene volumetric flasks, add ultrapure water to make up to 100mL, and obtain No. 3, No. 2, and No. 1 standard solutions; after shaking the standard solutions, verify whether the configuration is successful on the machine, and inject them into the ion chromatograph in the order of the configured standard curve concentration from low to high, and draw the standard curve with the mass concentration of each ion as the horizontal axis and the peak area as the vertical axis; ⑤Test baseline: Use 13mmol eluent concentration to stabilize the instrument state. After the instrument baseline noise meets the standard, perform sample information editing test. After the sample enters the chromatographic column from the injection system, it is eluted with eluents of different concentrations to remove the F - and Cl - Separate and enter the detector, the detector detects the signal strength, and obtains the test result through the standard curve conversion. After the test is completed, the test result is recorded and registered; ⑥Analyze the anion standard chromatogram.

[0009] Furthermore, the flow rate of the potassium hydroxide eluent is 0.5-0.9 mL / min.

[0010] Furthermore, the elution gradient of the potassium hydroxide eluent is: time 0.0 min, concentration 12.0-15.0 mM; time 9.0-10.0 min, concentration 12.0-15.0 mM; time 10.0-10.1 min, concentration 30.0-40.0 mM; time 18.0-20.0 min, concentration 30.0-40.0 mM; time 19.1-20.1 min, time 12.0-14.0 mM; time 25.0-30.0 min, concentration 12.0-14.0 mM.

[0011] Furthermore, the standard curve in step ④ is considered successful if its correlation coefficient is above 0.999.

[0012] Furthermore, it also includes a verification step, which includes stock solution standard test verification, lithium sulfate and lithium hydroxide method verification, optimal lithium sulfate dilution concentration verification and matrix recovery rate verification.

[0013] The beneficial effects of adopting the above scheme are: after the application of this new ion chromatography detection method, by optimizing the chromatographic elution conditions, selecting the appropriate detector and pre-treatment technology, high sensitivity and high precision detection of F and Cl ions in lithium sulfate products are achieved. Specific advantages include: 1. Use a high performance liquid chromatography column in combination with a conductivity detector or a suppressed conductivity detector to improve detection sensitivity.

[0014] 2. Develop standardized pre-treatment processes to reduce interference during sample preparation and ensure the accuracy of test results.

[0015] 3. Design and implement a complete method validation process, including the evaluation of parameters such as linear range, precision, and recovery rate, to ensure the reliability and applicability of the method, overcome the limitations of existing technologies in detection efficiency, accuracy, and cost control, and provide strong technical support for the quality control of lithium sulfate products. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the standard curve in Example 1.

[0017] Figure 2 This is the chromatogram in Example 1.

[0018] Figure 3 This is a diagram of the product batch number and sample weight in Example 3.

[0019] Figure 4 This is the standard curve diagram of Example 3 with a dilution factor of 1000.

[0020] Figure 5 This is the standard curve diagram of Example 3 with a dilution factor of 4000.

[0021] Figure 6 This is the standard curve diagram of Example 3 with a dilution factor of 10,000.

[0022] Figure 7 This is a standard curve diagram for the solid-to-liquid ratio of 10:1 in Example 4.

[0023] Figure 8 This is a standard curve diagram for the solid-to-liquid ratio of 50:1 in Example 4.

[0024] Fig. 9 This is a standard curve diagram for the solid-to-liquid ratio of 20:1 in Example 4.

[0025] Fig.10 This is the standard curve diagram for the extraction time of 0.5h in Example 4.

[0026] Fig.11 This is a standard curve diagram for the extraction time of 2h in Example 4.

[0027] Fig.12 This is a standard curve diagram for the extraction time of 3h in Example 4. DETAILED DESCRIPTION

[0028] The technical scheme of the present invention is clearly and completely described below in conjunction with the specific embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, not all. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0029] Embodiment 1 A novel ion chromatography detection method, the detection steps of which are as follows: adding ultrapure water to a lithium sulfate sample to completely dissolve it, diluting and filtering it, then using an SH-AP-1 anion chromatography column to exchange and separate anions in the solution, using a CIC-D120 ion chromatograph to detect F and Cl ions in the separated solution, combining a conductivity detector and a suppressed conductivity detector to assist in detecting the retention time of different anions on the chromatographic column for elemental qualitative analysis, and performing quantitative analysis based on peak height and peak area. (In the above detection method, the CIC-D120 ion chromatograph is used: an analysis system consisting of an ion chromatograph, an eluent generator, an injection system, and a test software. An anion suppressor and a conductivity detector are also used, and the SH-AP-1 anion chromatographic column is a hydroxide system anion chromatographic column. The matrix is ​​a polystyrene-divinylbenzene polymer with a cross-linking degree of 55%, equipped with a vacuum filtration device with a filter membrane with a pore size of ≤0.22 µm, a disposable water-based microporous filter syringe filter with a pore size of 0.22 μm, and a disposable syringe of 1 ml~5 ml.) The detailed operation steps are as follows: ① Prepare the solution to be tested: weigh 1.0g±0.019 lithium sulfate, dissolve it in ultrapure water and transfer it to a 100mL volumetric flask, dilute it with ultrapure water to get solution No. 1, then transfer 1mL from solution No. 1 to a centrifuge tube, dilute it to 10mL to get solution No. 2, use a syringe to transfer about 5mL of solution No. 2, and filter it through a 0.25um filter to get the solution for the machine; ② Prepare a blank sample: Select deionized water with a resistivity of ≥18 MΩ·cm (25℃) and filtered through a 0.22 µm microporous filter membrane as the experimental water, and prepare the blank sample according to the method in step ①; ③ Set the equipment parameters: select potassium hydroxide as the eluent, set the pump flow rate to 0.7mL / min, the temperature control pool temperature to 35℃, the column temperature to 35℃, the conductivity detector sampling frequency to 5Hz (zeroed 25s before injection), the suppressed conductivity detector current to 90mA, and the quantitative loop volume to 25ul; ④ Prepare stock solutions and draw standard curves: Select fluoride ion standard stock solution (C=1000mg / L) and chloride ion standard stock solution (C=1000mg / L) as standard solutions, transfer (0.5mL, 0.1mL) of fluoride ion solution standard substance (1000mg / L) in water and (5mL, 2mL) of chloride ion solution standard substance (1000mg / L) in water into a series of 100mL polytetrafluoroethylene volumetric flasks, add ultrapure water to make up to 100mL, and obtain No. 5 and No. 4 standard solutions respectively; transfer No. 5 solution (10mL, 2mL, 1mL) into a series of 100mL polytetrafluoroethylene volumetric flasks, add ultrapure water to make up to 100mL, and obtain No. 3, No. 2, and No. 1 standard solutions; shake the standard solutions and verify whether the configuration is successful on the machine, and inject them into the ion chromatograph in the order of the configured standard curve concentration from low to high, and draw the standard curve with the mass concentration of each ion as the horizontal axis and the peak area as the vertical axis; ⑤Test baseline: Use 13mmol eluent concentration to stabilize the instrument state. After the instrument baseline noise meets the standard, perform sample information editing test. After the sample enters the chromatographic column from the injection system, it is eluted with eluents of different concentrations to remove the F - and Cl - Separate and enter the detector, the detector detects the signal strength, and obtains the test result through the standard curve conversion. After the test is completed, the test result is recorded and registered; ⑥Analyze the anion standard chromatogram.

[0030] The concentration gradient of the eluent potassium hydroxide is shown in Table 1: Table 1: Potassium hydroxide eluent gradient conditions The concentrations of the standard curve are shown in Table 2: Table 2: Concentrations of the standard curve According to the above steps, the standard curve of step ④ is finally drawn as follows Figure 1 As shown, the correlation coefficients of F and Cl curves can reach above 0.999.

[0031] The final chromatogram obtained in step 6 is as follows Figure 2 As shown, Figure 2 There are obvious peak positions and peak area sizes (the horizontal axis is the peak time, and the vertical axis is the signal intensity, based on the corresponding peak time), the elements can be qualitatively identified, and the content of the detected elements can be quantitatively analyzed based on the size of the peak area.

[0032] Embodiment 2 For the stock solution in Example 1, since the national standard samples were selected for testing, in order to verify the accuracy of the instrument test and to ensure the precision of the subsequent testing experiments, the applicant conducted a stock solution standard test verification before the experiment, which is also equivalent to the stock solution standard test verification. The verification steps are as follows: Use the national certified standard substance F single standard solution (concentration 1000 mg / L) to prepare a 0.5 mg / L solution (diluted with ultrapure water); use the cl single standard solution (concentration 1000 mg / L) to prepare a 5 mg / L solution (diluted with ultrapure water) and then test it on the machine; as shown in Table 3: Table 3: Standard sample test results Verified by standard solution, the deviation of F ion is less than 5%, which can meet the test requirements; the deviation of Cl ion is less than 10%, which can meet the test requirements. Verified by national standard substances, the test deviation is within the acceptable range, and the instrument test accuracy meets the standard.

[0033] Embodiment 3 At the same time, in order to ensure the service life of the instrument in Example 1, since the metal content in lithium sulfate is high, a small dilution factor is likely to damage the chromatographic column. Therefore, in order to test and verify the optimal dilution factor of lithium sulfate without affecting the experiment, the following experiment was conducted.

[0034] Lithium sulfate and lithium hydroxide method to verify the optimal lithium sulfate dilution concentration experiment: Lithium sulfate test method: Lithium sulfate can be dissolved in water, so the total F and Cl content can be measured. (Principle: Weigh a certain sample, dissolve all the F and Cl elements in the sample into water through water dissolution. Since the metal content in the sample is too high, the sample solution is diluted, and the F and Cl content in the sample can be obtained by testing on the machine) Test steps: weigh 1g lithium sulfate sample into a polytetrafluoroethylene beaker, add ultrapure water to dissolve, transfer all the solution to a 100mL volumetric flask after the sample is completely dissolved, add ultrapure water to the 100mL mark to obtain solution No. 1; transfer 1ml of solution from solution No. 1 to a 10mL centrifuge tube, add ultrapure water to the 10ml mark to obtain solution No. 2; then use a disposable syringe to transfer 4-5mL of solution, and filter to obtain the solution to be tested on the machine.

[0035] Lithium hydroxide test method: Lithium hydroxide can be dissolved in water, so the total F and Cl content can be measured. (Principle: Weigh a certain sample, dissolve all the F and Cl elements in the sample into water through water dissolution. Since the metal content in the sample is too high, the sample solution is diluted, and the F and Cl content in the sample can be obtained by testing on the machine) Test steps: weigh 1g lithium hydroxide sample into a polytetrafluoroethylene beaker, add ultrapure water to dissolve, transfer all the solution to a 100mL volumetric flask after the sample is completely dissolved, add ultrapure water to the 100mL mark to obtain solution No. 1: transfer 2mL of solution No. 1 to a 10mL centrifuge tube, add ultrapure water to the 10mL mark to obtain solution No. 2; then use a disposable syringe to transfer 4-5mL of solution, and filter to obtain the solution to be tested on the machine.

[0036] The product batch numbers and sample quantities used in the experiment are as follows: Figure 3 The standard curve drawn from the experimental results is shown in Figure 4-6 As shown, (when the dilution multiples are 1000, 4000, and 10000 respectively).

[0037] After the test, it was found that both lithium sulfate and lithium hydroxide can be completely dissolved. From the analysis of the dilution multiple, the metal content in lithium sulfate is relatively high. If the dilution multiple is too small, it is easy to damage the chromatographic column. The dilution multiple of 10,000 times can meet the test requirements.

[0038] Embodiment 4 After the second and third embodiments, the above two embodiments are both for producing a product that can meet the detection requirements of the instrument and is not likely to reduce the service life of the chromatographic column.

[0039] The applicant also conducted a matrix recovery verification, which can also be called a precursor (nickel, cobalt, and manganese) test method: the precursor cannot be dissolved in water, and this method can only test the free F and Cl content in the sample. (Principle: add ultrapure water, place it on a pot mill for extraction, and fully dissolve the free F and Cl in the sample into water for 30 minutes, then take the filtrate after filtration to obtain a sample solution that can be put on the machine, and the F and Cl content in the sample can be obtained by testing on the machine) Test steps: weigh 10g of sample into a polyethylene can, add 100mL of ultrapure water, tighten the lid and place it on the canning machine, adjust the speed to 35r / min, and the canning time to 30min, so that the free F and C in the sample are fully dissolved in the water. Use medium-speed filter paper to filter out about 20mL of solution, and then use a disposable syringe to take 4-5mL of filtrate from the 20mL solution, and filter it through the plug to obtain the solution to be tested on the machine.

[0040] The solid-liquid ratio and extraction time during the test are shown in Table 4 below: Table 4: Matrix verification conditions table According to the above solid-liquid ratio conditions, three standard curves with different solid-liquid ratios were obtained after the machine was put into use. Figure 7-9 From the perspective of solid-liquid ratio, the Cl results obtained with a solid-liquid ratio of 50:1 are quite different and exceed the range of the standard curve; the test results with a solid-liquid ratio of 10:1 and 20:1 are slightly different, and the method spike recovery rate is 87% (80-120%), which verifies that the on-machine method in this application is feasible.

[0041] According to the above extraction time conditions, three standard curves with different extraction times were obtained after the machine was put into use. Figure 10-12 As shown in the figure, from the extraction time, the longer the extraction time, the smaller the difference in test results. Generally speaking, the extraction time of 0.5h can meet the test requirements, so the jar milling time of 0.5h can be adopted.

[0042] Embodiment 5 According to Examples 2 and 3, the applicant has developed a standardized pre-treatment process to reduce interference in the sample preparation process and ensure the accuracy of the test results. Example 4 verifies the feasibility of this solution. The applicant has designed and implemented a complete method validation process through this application, including the evaluation of parameters such as linear range, precision, and recovery rate, to ensure the reliability and applicability of the method, overcome the limitations of the prior art in detection efficiency, accuracy, and cost control, and provide strong technical support for the quality control of lithium sulfate products.

[0043] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0044] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A novel ion chromatography detection method, characterized in that: The detection steps are as follows: after the lithium sulfate sample is completely dissolved in ultrapure water, it is diluted and filtered, and then an anion chromatography column is used to separate the anions in the solution by exchange, and then an ion chromatograph is used to detect the F and Cl ions in the separated solution, and a conductivity detector and a suppressed conductivity detector are used to assist in detecting the retention time of different anions on the chromatographic column for elemental qualitative analysis, and quantitative analysis is performed based on the peak height and peak area.

2. The novel ion chromatography detection method according to claim 1, characterized in that: The chromatographic column is treated with SH series ion chromatography samples before use.

3. The novel ion chromatography detection method according to claim 1, characterized in that: The anion chromatographic column is an SH-AP-1 type hydroxide system anion chromatographic column, the matrix of which is a polystyrene-divinylbenzene polymer with a cross-linking degree of 55%. The ion chromatograph is a CIC-D120 type, and the CIC-D120 type ion chromatograph is an analysis system consisting of an ion chromatograph, an eluent generator, an injection system, and test software.

4. The novel ion chromatography detection method according to claim 1 or 3, characterized in that: The detection steps are as follows: ① Prepare the solution to be tested: weigh lithium sulfate, dissolve it in ultrapure water and transfer it to a volumetric flask, dilute it with ultrapure water to obtain solution No. 1, then transfer 1 mL from solution No. 1 to a centrifuge tube, dilute it to 10 mL to obtain solution No. 2, use a syringe to transfer about 3-8 mL of solution No. 2, and filter it through a 0.25um filter to obtain the solution for the machine; ② Prepare a blank sample: Select deionized water with a resistivity of ≥18 MΩ·cm (25℃) and filtered through a 0.22 µm microporous filter membrane as the experimental water, and prepare the blank sample according to the method in step ①; ③Set the equipment parameters: select potassium hydroxide as the eluent, set the pump flow rate to 0.5-0.8mL / min, the temperature control pool temperature to 32-36℃, the column temperature to 30-35℃, the conductivity detector sampling frequency to 5Hz (zero before injection), the suppressed conductivity detector current to 90mA, and the quantitative loop volume to 25ul; ④ Prepare stock solution and draw standard curve: select fluoride ion standard stock solution (C=1000mg / L) and chloride ion standard stock solution (C=1000mg / L) as standard solution, transfer (0.3-0.8mL, 0.1-0.2mL) of fluoride ion solution standard substance (1000mg / L) in water, (3-5mL, 1-3mL) of chloride ion solution standard substance (1000mg / L) in water into a series of 100mL polytetrafluoroethylene volumetric flasks, and add ultrapure water to make up to volume. to 100mL, and obtain No. 5 and No. 4 standard solutions respectively; pipette No. 5 solution (5-10mL, 2-4mL, 0.5-1mL) into a series of 100mL polytetrafluoroethylene volumetric flasks, add ultrapure water to make up to 100mL, and obtain No. 3, No. 2, and No. 1 standard solutions; after shaking the standard solutions, verify whether the configuration is successful on the machine, and inject them into the ion chromatograph in the order of the configured standard curve concentration from low to high, and draw the standard curve with the mass concentration of each ion as the horizontal axis and the peak area as the vertical axis; ⑤Test baseline: Use 13mmol eluent concentration to stabilize the instrument state. After the instrument baseline noise meets the standard, perform sample information editing test. After the sample enters the chromatographic column from the injection system, it is eluted with eluents of different concentrations to remove the F - and Cl - Separate and enter the detector, the detector detects the signal strength, and obtains the test result through the standard curve conversion. After the test is completed, the test result is recorded and registered; ⑥Analyze the anion standard chromatogram.

5. The novel ion chromatography detection method according to claim 4, characterized in that: The flow rate of the potassium hydroxide eluent is 0.5-0.9 mL / min.

6. The novel ion chromatography detection method according to claim 4 or 5, characterized in that: The elution gradient of the potassium hydroxide eluent is as follows: time 0.0 min, concentration 12.0-15.0 mM; time 9.0-10.0 min, concentration 12.0-15.0 mM; time 10.0-10.1 min, concentration 30.0-40.0 mM; time 18.0-20.0 min, concentration 30.0-40.0 mM; time 19.1-20.1 min, time 12.0-14.0 mM; time 25.0-30.0 min, concentration 12.0-14.0 mM.

7. The novel ion chromatography detection method according to claim 4 is characterized in that: The standard curve in step ④ is considered successful if its correlation coefficient is above 0.

999.

8. The novel ion chromatography detection method according to claim 1, characterized in that: Also included are validation steps, which include stock solution standard test validation, lithium sulfate and lithium hydroxide method validation, optimal lithium sulfate dilution concentration validation, and matrix recovery validation.

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