A quantitative detection method for the purity of sodium bis(oxalato)borate(III)

Abstract

The present invention provides a quantitative detection method for the purity of sodium bis(oxalato)borate, belonging to the field of purity analysis, which can solve the technical problems of the traditional content detection method of sodium bis(oxalato)borate, such as cumbersome operation process, large error, and inability to truly reflect the content of sodium bis(oxalato)borate. The detection method includes: first dissolving sodium bis(oxalato)borate in an organic solvent to prepare a solution to be detected, then establishing a standard curve using standard solutions of sodium bis(oxalato)borate ions with different concentrations, and finally determining the peak area of the solution to be detected by ion chromatography, and calculating the content of sodium bis(oxalato)borate in the solution to be detected according to the standard curve; wherein, a barrier solution is used for blocking when the solution to be detected is loaded. The quantitative detection method for the purity of sodium bis(oxalato)borate provided by the present invention has the characteristics of simple operation, high accuracy, short time consumption and high efficiency, and the present invention can be applied to the quantitative detection of sodium bis(oxalato)borate.

Description

Technical Field

[0001] The invention belongs to the field of purity analysis, and in particular relates to a quantitative detection method for the purity of sodium bis(oxalatoborate). Background Art

[0002] Sodium bis(oxalatoborate) is an important additive for sodium-ion batteries. It has the advantages of high ionic conductivity, wide electrochemical stability window, good thermal stability, good cycle stability, etc. It can improve the stability of the negative electrode SEI film, improve the electrochemical performance of the battery, high-temperature cycle performance, high safety performance, and has a very broad market prospect. The composition of the electrolyte is one of the key factors affecting the performance of sodium batteries. The development of high-performance electrolyte salts and additives is the key to the development of this type of battery. Important indicators of sodium-ion batteries such as storage capacity, electrochemical performance, and safety performance are closely related to the purity and impurities of electrolyte salts and additives. It can be seen that quantitative determination of battery additives is the key to evaluating / predicting the above-mentioned important indicators of sodium-ion batteries.

[0003] At present, the traditional method for detecting the content of sodium bis(oxalatoborate) is usually to measure the sodium content, boron content and oxalate content in the product separately. For example, the sodium content is measured by titration, the boron content is measured by titration, and the oxalate content is measured by titration. However, these detection methods not only have complicated pre-treatment steps, but also indirectly infer the content of sodium bis(oxalatoborate), and cannot directly and truly reflect the content of sodium bis(oxalatoborate). The errors of multiple test methods are superimposed, resulting in large errors.

[0004] It can be seen that there is an urgent need for a direct quantitative detection method for the purity of sodium bis(oxalatoborate) with high accuracy, short time consumption, convenient testing and high efficiency. Summary of the invention

[0005] Aiming at the technical problems that a traditional method for detecting the content of sodium bis(oxalatoborate) has complicated operation process, large error and inability to truly reflect the content of sodium bis(oxalatoborate), the invention proposes a quantitative detection method for the purity of sodium bis(oxalatoborate), which has the characteristics of simple operation, high accuracy, short time consumption and high efficiency.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A quantitative detection method for the purity of sodium bis(oxalatoborate), comprising the steps of first dissolving sodium bis(oxalatoborate) in an organic solvent to prepare a test solution, then using bis(oxalatoborate) ion standard solutions of different concentrations to establish a standard curve, finally using ion chromatography to determine the peak area of ​​the test solution, and calculating the sodium bis(oxalatoborate) content in the test solution according to the standard curve; wherein a barrier liquid is used for barrier when the test solution is sampled.

[0008] In one embodiment, the mass ratio of the sodium bis(oxalatoborate) to the organic solvent is 1:(500-1500).

[0009] In one embodiment, the organic solvent is selected from any one of methanol, ethylene glycol dimethyl ether, ethylene carbonate or propylene carbonate.

[0010] In one embodiment, the barrier fluid is selected from acetonitrile or dimethyl carbonate, and the acetonitrile is of chromatography grade with a content of >99.9%.

[0011] In one embodiment, the ion chromatography conditions are:

[0012] Detector: conductivity detector;

[0013] Column: Metrosep A Supp 7;

[0014] Column temperature: 35-40°C;

[0015] Flow rate: 0.7 mL / min;

[0016] Quantitative loop: 50 μL.

[0017] In one embodiment, the quantitative detection method of the purity of sodium bis(oxalatoborate) comprises the following steps:

[0018] Preparation of the test solution: dissolve the weighed sodium bis(oxalatoborate) in an organic solvent to prepare the test solution;

[0019] Establishment of standard curve: according to the content of sodium bis(oxalatoborate) in the solution to be tested, dilute the bis(oxalatoborate) ion standard solution into bis(oxalatoborate) ion standard solutions with different concentration gradients, and determine the peak area by ion chromatography, and establish a standard curve with concentration as the horizontal axis and the corresponding peak area as the vertical axis;

[0020] Quantitative determination of sodium bis(oxalatoborate): the test solution is determined by ion chromatography. After the test solution is sampled, a barrier liquid is used for barrier. Under the action of a high-concentration organic mobile phase, the peak area of ​​the test solution is measured. According to the standard curve, the content of sodium bis(oxalatoborate) in the test solution is calculated.

[0021] In one embodiment, the high concentration organic mobile phase is a (20.0-30.0) mmol / L sodium carbonate aqueous solution and 40% acetonitrile.

[0022] In one embodiment, the high concentration organic mobile phase is a 30.0 mmol / L aqueous solution of sodium carbonate and 40% acetonitrile.

[0023] Compared with the prior art, the advantages and positive effects of the present invention are:

[0024] 1. The present invention provides a quantitative detection method for the purity of sodium bis(oxalatoborate), which is a detection method that directly reflects the content of sodium bis(oxalatoborate). Sodium bis(oxalatoborate) is quantitatively detected by ion chromatography. At the same time, since sodium bis(oxalatoborate) has a low solubility in an organic solvent system commonly used in ion chromatography, a suitable organic solvent (methanol, ethylene glycol dimethyl ether, ethylene carbonate or propylene carbonate) is selected to dissolve sodium bis(oxalatoborate), which can fully dissolve sodium bis(oxalatoborate) without causing decomposition of bis(oxalatoborate); after the solution to be tested is sampled, a barrier liquid is used for barrier to prevent the decomposition of bis(oxalatoborate), thereby finally realizing accurate detection of the purity of sodium bis(oxalatoborate), thereby solving the technical problems that the conventional quantitative detection method of sodium bis(oxalatoborate) has a complicated operation process, large errors and cannot truly reflect the content of sodium bis(oxalatoborate);

[0025] 2. The present invention provides a quantitative detection method for the purity of sodium bis(oxalatoborate), which has the characteristics of simple operation, high accuracy, short time consumption and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the standard curve of the bis(oxalatoborate) ion standard solution provided in the embodiment of the present invention. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The embodiment of the present invention provides a quantitative detection method for the purity of sodium bis(oxalatoborate), wherein the sodium bis(oxalatoborate) is firstly dissolved in an organic solvent to prepare a test solution, and then a standard curve is established using standard solutions of bis(oxalatoborate) ions of different concentrations, and finally an ion chromatography is used to determine the peak area of ​​the test solution, and the sodium bis(oxalatoborate) content in the test solution is calculated according to the standard curve; wherein a barrier liquid is used for barrier when the test solution is loaded.

[0029] The above embodiment provides a quantitative detection method for the purity of sodium bis(oxalatoborate), and the detection object of the method is sodium bis(oxalatoborate), which is an important sodium ion battery additive, having the characteristics of high ionic conductivity, wide electrochemical stability window, good thermal stability, good cycle stability, etc. It can improve the stability of the negative electrode SEI film, improve the electrochemical performance of the battery, high temperature cycle performance, and high safety performance. Important indicators of sodium ion batteries such as storage capacity, electrochemical performance, and safety performance are closely related to the purity and impurities of electrolyte salts and additives. It can be seen that quantitative determination of battery additives is the key to evaluating / predicting the above important indicators of sodium ion batteries.

[0030] Furthermore, the traditional method for detecting the content of sodium bis(oxalatoborate) is usually to measure the sodium content, boron content and oxalate content in the product respectively. The specific method is as follows:

[0031] (1) Determination of sodium content: using the titration method, sodium bis(oxalatoborate) is roasted in a high-temperature furnace to completely decompose the oxalate. After cooling, the ignition residue is completely dissolved with water. Using methyl red-methylene blue as an indicator, the solution is titrated with hydrochloric acid standard solution until the solution changes from yellow-green to light purple, and the sodium content is calculated. (2) Determination of boron content: using the titration method, the test solution for determining the sodium content is heated to remove any residual carbon dioxide. All the boron is converted into boric acid. After strengthening the acidity with mannitol, phenolphthalein is used as an indicator. The solution is titrated with sodium hydroxide standard solution until the solution changes from yellow-green to light purple, and the boron content is calculated. (3) Determination of oxalate content: using the titration method, the sample is heated in a sulfuric acid-phosphoric acid solution medium. The oxalate reacts with excess potassium dichromate. Using sodium diphenylamine sulfonate as an indicator, the excess potassium dichromate is titrated with ammonium ferrous sulfate standard solution. The solution changes from purple to bright green as the indicated end point, and the oxalate content is calculated.

[0032] The pre-treatment operations of the above methods are too complicated, and they are all indirect inferences of the content of sodium bis(oxalatoborate), and cannot directly reflect the content of sodium bis(oxalatoborate). The absolute error of two parallel determinations of sodium content is about 0.1%, the absolute difference of two parallel determinations of oxalate content is about 0.5%, and the absolute difference of two parallel determinations of boron content is about 0.1%. The errors of multiple test methods are superimposed, and the errors are large.

[0033] In addition, the above methods all use titration, and the solution color changes from yellow-green to lavender or from purple to bright green based on human subjective judgment. The judgment of the result is highly artificial, and is not suitable for rapid quantitative detection of high-purity sodium bis(oxalyl)borate. Therefore, in view of the various defects of the traditional sodium bis(oxalyl)borate content detection method, it is urgent to develop a new direct quantitative detection method for the purity of sodium bis(oxalyl)borate with high accuracy, short time consumption, convenient testing and high efficiency.

[0034] Based on the above problems existing in the prior art, the present invention proposes a quantitative detection method for the purity of sodium bis(oxalate borate), which is a detection method that can directly and truly reflect the content of sodium bis(oxalate borate). Since ion chromatography has the characteristics of low detection limit, high sensitivity, high accuracy and good repeatability, it is suitable for the content determination of sodium bis(oxalate borate). Therefore, the present invention selects ion chromatography to quantitatively detect sodium bis(oxalate borate). However, when this method is applied to the quantitative detection of sodium bis(oxalate borate), it still faces many problems. For example, sodium bis(oxalate borate) has a low solubility in the organic solvent system commonly used in ion chromatography; when performing purity testing, the mobile phase is an aqueous phase, which can easily cause sodium bis(oxalate borate) to be easily decomposed into oxalate, resulting in inaccurate purity calculation in sample testing. Therefore, it is necessary to take effective measures to avoid the hydrolysis interference of the sample itself in order to achieve rapid and accurate detection. The above problems are the key to establishing a sodium bis(oxalate borate) purity detection method. In order to solve the above problems, the present invention is mainly improved from the following aspects:

[0035] (1) Select a suitable organic solvent to dissolve sodium bis(oxalatoborate), and the screening criteria are: it can fully dissolve sodium bis(oxalatoborate) and will not cause the decomposition of bis(oxalatoborate) to oxalate. Specifically, any one of methanol, ethylene glycol dimethyl ether, ethylene carbonate or propylene carbonate can be selected; (2) Since ion chromatography needs to be eluted in an aqueous phase eluent, after the test solution is injected, a barrier liquid (the barrier liquid is selected from acetonitrile or dimethyl carbonate, and the acetonitrile is chromatographic grade, with a content of >99.9%) is used for barrier method to prevent the decomposition of bis(oxalatoborate), and finally achieve accurate detection of the purity of sodium bis(oxalatoborate), solving the technical problems of the traditional quantitative detection method of sodium bis(oxalatoborate) that the operation process is cumbersome, the error is large, and the content of sodium bis(oxalatoborate) cannot be truly reflected. (Note: The screening criteria of the barrier liquid are: it has extremely low solubility in sodium bis(oxalatoborate) and is suitable for the solvent of the chromatographic system.)

[0036] In a specific embodiment, the mass ratio of sodium bis(oxalatoborate) to the organic solvent is 1:(500-1500).

[0037] In one embodiment, the ion chromatography conditions are:

[0038] Detector: conductivity detector;

[0039] Column: Metrosep A Supp 7;

[0040] Column temperature: 35-40°C; column temperature preferably 35°C;

[0041] Flow rate: 0.7 mL / min;

[0042] Quantitative loop: 50 μL.

[0043] In a specific embodiment, the quantitative detection method of the purity of sodium bis(oxalatoborate) comprises the following steps:

[0044] S1. Preparation of a test solution: dissolving the weighed sodium bis(oxalatoborate) in an organic solvent to prepare a test solution;

[0045] S2. Establishment of standard curve: according to the content of sodium bis(oxalatoborate) in the solution to be tested, dilute the bis(oxalatoborate) ion standard solution into bis(oxalatoborate) ion standard solutions with different concentration gradients, and determine the peak area by ion chromatography, and establish a standard curve with concentration as the horizontal coordinate and the corresponding peak area as the vertical coordinate;

[0046] S3. Quantitative determination of sodium bis(oxalatoborate): The test solution is determined by ion chromatography. After the test solution is injected, it is blocked by a barrier liquid. Under the action of a high-concentration organic mobile phase, the peak area of ​​the test solution is measured. According to the standard curve, the content of sodium bis(oxalatoborate) in the test solution is calculated.

[0047] In the above step S3, the high concentration organic phase mobile phase is (20.0-30.0) mmol / L sodium carbonate aqueous solution, 40% acetonitrile, preferably 30.0 mmol / L sodium carbonate aqueous solution, 40% acetonitrile. It should also be noted that when using ion chromatography for quantitative detection of sodium bis(oxalatoborate), the regeneration liquid used is 0.7%-0.8% sulfuric acid aqueous solution.

[0048] In order to more clearly and in detail introduce a quantitative detection method for the purity of sodium bis(oxalatoborate) provided in an embodiment of the present invention, it will be described below in conjunction with a specific embodiment.

[0049] Comparative Example 1

[0050] This comparative example provides a quantitative detection method for the purity of sodium bis(oxalatoborate), specifically:

[0051] (1) Instruments, reagents and raw materials:

[0052] Ion chromatograph: Wantong 930; Sodium bis(oxalatoborate): content ≥99%, homemade; Sodium carbonate: high-grade pure, Sinopharm Chemical Reagent Co., Ltd.; Pure water: ultrapure water, deionized water with conductivity (25°C) not more than 0.0055mS / m, homemade.

[0053] (2) Detection method:

[0054] (2-1) Accurately weigh 0.1-0.2 g of the sodium bis(oxalatoborate) sample to be tested, dissolve it in ultrapure water to a volume of 100 mL, and mix thoroughly to obtain a test solution;

[0055] (2-2) Ion chromatography was used for testing, and the chromatographic conditions were:

[0056] Detector: conductivity detector;

[0057] Column: Metrosep A Supp 7;

[0058] Column temperature: 35 °C;

[0059] Flow rate: 0.7 mL / min;

[0060] Quantitative loop: 50 μL.

[0061] (3) Test results:

[0062] Through the analysis of the test results, it was found that due to the decomposition characteristics of sodium bis(oxalatoborate) in water, the test precision and repeatability of the purity of sodium bis(oxalatoborate) were poor; and sodium bis(oxalatoborate) was easily decomposed into oxalate, which was easily confused with the residual oxalate in the sample, resulting in errors in the purity calculation in the sample test.

[0063] Example 1

[0064] This embodiment provides a method for establishing a standard curve, which specifically includes the following steps:

[0065] (1) Using 1 mL of solution containing 1000 μg of bis(oxalate borate) as a bis(oxalate borate) standard solution (prepared on the spot), the bis(oxalate borate) standard solution was diluted in sequence to obtain a series of standard solutions;

[0066] (2) Use a suitable pipette to transfer 0.0 mL, 10.0 mL, 20.0 mL, 50.0 mL, and 100.0 mL of the bis(oxalatoborate) standard solution into five 100 mL volumetric flasks, dilute to the mark with water, and shake well;

[0067] (3) The ion chromatograph was adjusted to the optimal working state, and equal volumes of the working curve solution were injected and measured in sequence (the ion chromatography conditions were the same as those in Comparative Example 1), and a standard curve was drawn with the concentration of bis(oxalatoborate) in the working curve solution as the horizontal axis and the corresponding peak area as the vertical axis.

[0068] Results: The standard curve is as follows: Figure 1 As shown in the figure, within a certain range, the concentration of bis(oxalatoborate) ion and the corresponding peak area show a good linear relationship, and the correlation coefficient of the standard curve is R 2 >0.999.

[0069] Example 2

[0070] This example provides a quantitative detection method for the purity of sodium bis(oxalatoborate). The sodium bis(oxalatoborate) in samples 1-3 is measured, and each sample is prepared into 5 portions, specifically:

[0071] (1) Preparation of test solutions: accurately weigh 0.1-0.2 g of sample 1, sample 2, and sample 3, respectively, dissolve them in methanol to a volume of 100 mL, and mix thoroughly to obtain test solution A, test solution B, and test solution C, respectively;

[0072] (2) Establishing a standard curve: Establish a standard curve according to the method described in Example 1;

[0073] (3) Quantitative determination of sodium bis(oxalatoborate): ion chromatography was used to determine the test solution A, the test solution B and the test solution C (chromatographic conditions were the same as those in comparative example 1). After the test solution A, the test solution B and the test solution C were injected, they were blocked with a barrier liquid (acetonitrile, chromatographic grade, content>99.9%). Under the action of a high concentration organic mobile phase (30.0 mmol / L sodium carbonate aqueous solution, 40% acetonitrile), the peak area of ​​the test solution was measured. According to the standard curve, the content (ppm) of sodium bis(oxalatoborate) in the test solution A, the test solution B and the test solution C was calculated. According to the preparation method, the sodium bis(oxalatoborate) content (%) of each sample was calculated, and the sodium bis(oxalatoborate) content results in samples 1-3 were statistically analyzed as follows:

[0074] Table 1 Content of sodium bis(oxalatoborate) in samples 1-3

[0075] Parallel testing Sample 1 Sample 2 Sample 3 Parallel test 1 (%) 89.04 94.09 99.45 Parallel test 2 (%) 89.93 94.29 98.78 Parallel test 3 (%) 89.77 93.87 99.59 Parallel test 4 (%) 89.60 93.98 99.14 Parallel test 5 (%) 90.02 94.05 99.31 average value(%) 89.67 94.06 99.25 Standard Deviation (SD) 0.39 0.16 0.31 Relative standard deviation (RSD%) 0.43 0.17 0.32

[0076] By analyzing the data in Table 1, it can be seen that the contents of sodium bis(oxalatoborate) in the three samples selected in this embodiment are at low, medium and high levels, respectively, and their relative standard deviations are 0.43%, 0.16% and 0.32%, respectively, which are much lower than RSD less than 3%, and fully meet the error requirements, indicating that the method has high precision, indicating that the method of the present invention has high accuracy in testing the purity of sodium bis(oxalatoborate).

[0077] The calculation formulas for standard deviation and relative standard deviation are as follows:

[0078] In the above formula: ∑ represents the sum, represents the mean of xi, ^2 represents the quadratic, and Sqrt represents the square root.

[0079] Relative standard deviation (RSD) = standard deviation (SD) / arithmetic mean of results * 100%

[0080] Sodium bis(oxalatoborate) solvent screening test

[0081] Since sodium bis(oxalatoborate) itself has poor solubility, it is also very important to select a suitable solvent. Considering that sodium bis(oxalatoborate) has low solubility in organic solvent systems commonly used in ion chromatography, the purpose of this test is to screen a suitable organic solvent. The screening criteria are that the selected solvent can fully dissolve sodium bis(oxalatoborate) and will not cause the decomposition of bis(oxalatoborate) to oxalate. Based on the above content, the present invention selects several solvents including ultrapure water, ethanol, acetonitrile, methanol, ethylene glycol dimethyl ether, ethylene carbonate, and propylene carbonate for screening tests. The specific test methods and test results are as follows:

[0082] Test method:

[0083] Accurately weigh multiple portions of sodium bis(oxalatoborate) test samples, 0.1-0.2 g per portion, dissolve and dilute to 100 mL using ultrapure water, ethanol, acetonitrile, methanol, ethylene glycol dimethyl ether, ethylene carbonate and propylene carbonate, mix thoroughly to obtain different test solutions (named as test sample 1, test sample 2, test sample 3, test sample 4, test sample 5, test sample 6 and test sample 7, respectively), and test the solubility of the above-mentioned test solutions and whether the sodium bis(oxalatoborate) is decomposed into oxalate;

[0084] Test results:

[0085] Table 2 Sodium bis(oxalatoborate) solvent screening test results

[0086]

[0087]

[0088] By analyzing the results in the above table, it can be seen that sodium oxalate borate is insoluble in ethanol and acetonitrile, but is soluble in ultrapure water, methanol, ethylene glycol dimethyl ether, ethylene carbonate and propylene carbonate. Based on the solubility measurement results, the above five solvents that can dissolve sodium oxalate borate are first taken as candidate solvents, and then further analyzed whether sodium oxalate borate will decompose into oxalate in the above five solvents. Through relevant experiments, it is found that, except for ultrapure water, sodium oxalate borate will not decompose into oxalate in the four solvents of methanol, ethylene glycol dimethyl ether, ethylene carbonate and propylene carbonate. Therefore, the present invention uses these four solvents as the final solvents for quantitative detection of the purity of sodium disoxalate borate, and those skilled in the art can arbitrarily choose among the above four organic solvents according to actual needs.

Claims

1. A quantitative detection method for the purity of sodium bis(oxalato)borate, characterized in that, first dissolve sodium bis(oxalato)borate in an organic solvent to prepare a test solution, then establish a standard curve using standard solutions of sodium dioxalatoborate ions with different concentrations, and finally use ion chromatography to measure the peak area of the test solution, and calculate the content of sodium bis(oxalato)borate in the test solution according to the standard curve; wherein, a barrier solution is used for blocking when the test solution is loaded; the organic solvent is selected from any one of methanol, ethylene glycol dimethyl ether, ethylene carbonate or propylene carbonate; the barrier solution is acetonitrile, and the acetonitrile is of chromatographic grade with a content > 99.9%.

2. The quantitative detection method for the purity of sodium bis(oxalato)borate according to claim 1, characterized in that, the mass ratio of sodium bis(oxalato)borate to the organic solvent is 1:(500 - 1500).

3. The quantitative detection method for the purity of sodium bis(oxalato)borate according to claim 1, characterized in that, the ion chromatography conditions are as follows: Detector: Conductivity detector; Chromatographic column: Metrosep A Supp 7; Column temperature: 35 - 40 °C; Flow rate: 0.7 mL / min; Quantitative loop: 50 μL.

4. The quantitative detection method for the purity of sodium bis(oxalato)borate according to claim 1, characterized in that, comprises the following steps: Preparation of test solution: Weigh sodium bis(oxalato)borate and dissolve it in an organic solvent to obtain a test solution; Establishment of standard curve: According to the content of sodium bis(oxalato)borate in the test solution, dilute the standard solution of sodium dioxalatoborate ions into standard solutions of sodium dioxalatoborate ions with different concentration gradients, and use ion chromatography to measure the peak area, and establish a standard curve with the concentration as the abscissa and the corresponding peak area as the ordinate; Quantitative determination of sodium bis(oxalato)borate: Use ion chromatography to measure the test solution. After the test solution is injected, a barrier solution is used for blocking, and under the action of a high-concentration organic phase mobile phase, the peak area of the test solution is measured, and according to the standard curve, the content of sodium bis(oxalato)borate in the test solution is calculated.

5. The quantitative detection method for the purity of sodium bis(oxalato)borate according to claim 4, characterized in that, the high-concentration organic phase mobile phase is an aqueous solution of (20.0 - 30.0) mmol / L sodium carbonate and 40% acetonitrile.

6. The quantitative detection method for the purity of sodium bis(oxalato)borate according to claim 5, characterized in that, the high-concentration organic phase mobile phase is an aqueous solution of 30.0 mmol / L sodium carbonate and 40% acetonitrile.

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