A method for determining the content of sodium methyl mercaptide in the mother liquor of PPS slurry by high performance liquid chromatography

Abstract

The present invention discloses a method for determining the content of sodium methyl mercaptide in the mother liquor of PPS slurry by high performance liquid chromatography. The mobile phase used in the high performance liquid chromatography comprises mobile phase A: acetonitrile and mobile phase B: a mixed solution composed of a buffer solution of potassium dihydrogen phosphate and phosphoric acid; for mobile phase B, the pH of the buffer solution of potassium dihydrogen phosphate and phosphoric acid is 1.5 to 3.0; the elution program is as follows: isocratic elution is adopted from 0 to 10 min, and the volume fraction of mobile phase B in the mobile phase > 90%; gradient elution is adopted from 10 to 35 min until the volume fraction of mobile phase B in the mobile phase is not less than 60%; isocratic elution is adopted from 35 to 44 min; gradient elution is adopted from 44 to 45 min until the volume fraction of mobile phase B in the mobile phase > 90%. The method for determining the content of sodium methyl mercaptide in the mother liquor of PPS slurry disclosed by the present invention has the advantages of high detection precision, high accuracy and good stability, and is simple and rapid in testing.

Description

Technical Field

[0001] The present invention relates to the technical field of material analysis and detection, and particularly relates to a method for determining the content of sodium methyl mercaptide in the mother liquor of PPS slurry by high performance liquid chromatography. Background Art

[0002] Sodium methyl mercaptide, with the molecular formula CH3SNa, is a colorless and transparent liquid with an odor and is a strongly alkaline liquid. It can be used as a raw material for pesticides, pharmaceuticals, and dye intermediates.

[0003] Polyphenylene sulfide (PPS) is a new type of high-performance thermoplastic resin with high thermal stability, chemical corrosion resistance, and excellent electrical properties, and is widely used in the fields of electronics, automobiles, machinery, and chemical industry. During the PPS polymerization production reaction process, side reaction product sodium methyl mercaptide will be generated. The generation of sodium methyl mercaptide will not only consume the raw material sodium hydrosulfide in the PPS polymerization reaction, reduce the yield of the polymerization reaction, and cause the polymerization reaction to depolymerize; moreover, during the pickling process of producing PPS in the later stage, sodium methyl mercaptide will be converted into methyl mercaptan. The generation of methyl mercaptan increases the treatment cost of the three wastes in the later stage. At the same time, the unacidified sodium methyl mercaptide in the product affects the performance of the product and seriously reduces the quality of the product.

[0004] Therefore, it is very important to monitor the content of sodium methyl mercaptide in the mother liquor of PPS polymerization slurry. However, there is no unified test method and quality standard for the determination of the content of sodium methyl mercaptide. In order to explore the conversion rate of the polymerization reaction and ensure the production quality of PPS, it is necessary to control the quality of the content of sodium methyl mercaptide in the mother liquor of PPS polymerization slurry. Therefore, it is particularly important to develop a simple, effective, accurate, and rapid analysis method.

[0005] Currently, the analysis method of sodium methyl mercaptide mostly adopts the redox titration method. The main detection principle is: under alkaline conditions, sodium methyl mercaptide reacts with iodine in a redox reaction to generate disulfide ether. Therefore, the content of sodium methyl mercaptide can be determined by titrating with a standard iodine solution. The reaction principle is as follows:

[0006] 2CH3SH + I2 + 2NaOH → CH3SSCH3 + 2NaI + 2H2O

[0007] However, this analysis method is not applicable to the analysis of sodium methyl mercaptide in the mother liquor of PPS slurry because the test object of this method needs to meet the condition that under alkaline conditions, in addition to containing sodium methyl mercaptide, it cannot contain other components that react with I2. However, the components of the mother liquor of PPS slurry are complex, especially containing a large amount of sodium benzenethiolate and sodium p-chlorobenzenethiolate, and these substances will react with I2 in a redox reaction to generate diphenyl disulfide and 4,4'-dichlorodiphenyl disulfide. In addition, the titration method also has the common problems of cumbersome test process and poor test precision. Summary of the Invention

[0008] In view of the above problems existing in the prior art, the present invention discloses a method for determining the content of sodium methyl mercaptide in the mother liquor of PPS slurry, which has the advantages of high detection precision, high accuracy, good stability, and simple and rapid testing.

[0009] The specific technical solution is as follows:

[0010] A method for determining the content of sodium methyl mercaptide in the mother liquor of PPS slurry by high performance liquid chromatography, wherein the mobile phase used in the high performance liquid chromatography comprises mobile phase A and mobile phase B. Mobile phase A is selected from acetonitrile, and mobile phase B is selected from a mixed solution composed of a buffer solution of potassium dihydrogen phosphate and phosphoric acid;

[0011] For the mobile phase B, the pH of the buffer solution of potassium dihydrogen phosphate and phosphoric acid is 1.5 - 3.0;

[0012] The elution procedure is as follows:

[0013] Isocratic elution is used from 0 to 10 min, and the volume fraction of mobile phase B in the mobile phase > 90%;

[0014] Gradient elution is used from 10 to 35 min until the volume fraction of mobile phase B in the mobile phase is not less than 60%;

[0015] Isocratic elution is used from 35 to 44 min;

[0016] Gradient elution is used from 44 to 45 min until the volume fraction of mobile phase B in the mobile phase > 90%.

[0017] Preferably:

[0018] For the mobile phase B, the concentration of the buffer solution of potassium dihydrogen phosphate and phosphoric acid is 40 - 60 mmol / L; more preferably 50 mmol / L.

[0019] Preferably:

[0020] The flow rate of the mobile phase is 0.8 - 1.2 mL / min; more preferably 1.0 mL / min.

[0021] Preferably:

[0022] The chromatographic column used in the high performance liquid chromatography is selected from SB - AQ chromatographic column, and the column temperature is 15 - 25 °C; more preferably, the column temperature is 20 °C.

[0023] Preferably:

[0024] The detection wavelength is 205 - 210 nm; more preferably 208 nm.

[0025] Preferably:

[0026] The sample injection volume is 10 - 20 μL; more preferably 10 μL.

[0027] Even more preferably, the elution program is as follows:

[0028] At 0 min, the volume fraction of mobile phase A in the mobile phase is 2%, and the volume fraction of mobile phase B is 98%;

[0029] At 10 min, the volume fraction of mobile phase A in the mobile phase is 2%, and the volume fraction of mobile phase B is 98%;

[0030] At 35 min, the volume fraction of mobile phase A in the mobile phase is 40%, and the volume fraction of mobile phase B is 60%;

[0031] At 44 min, the volume fraction of mobile phase A in the mobile phase is 40%, and the volume fraction of mobile phase B is 60%;

[0032] At 45 min, the volume fraction of mobile phase A in the mobile phase is 2%, and the volume fraction of mobile phase B is 98%.

[0033] Most preferably, for mobile phase B, the pH of the buffer solution of potassium dihydrogen phosphate and phosphoric acid is 2.0; it has been found through experiments that when the pH of the buffer solution of potassium dihydrogen phosphate and phosphoric acid is 2.0 compared to a pH of 3.0, the detection limit for sodium methanethiol is lower and the responsiveness is higher.

[0034] Using the above chromatographic system, the method for determining the content of sodium methanethiol in the PPS slurry mother liquor by high performance liquid chromatography specifically includes:

[0035] (1) Prepare the sample solution: Mix the PPS slurry mother liquor with methanol solution A, and filter for later use;

[0036] (2) Prepare the reference solution: Weigh sodium methanethiol and mix it with methanol solution B, and prepare reference solutions with different concentrations of 20 - 125 mg / L respectively;

[0037] (3) Inject the sample for detection: Inject the sample solution or the reference solution respectively, perform chromatographic analysis under the above detection conditions, and calculate the content of sodium methanethiol in the sample solution based on the peak area by the external standard method.

[0038] In step (1), the volume concentration of methanol solution A is 40 - 60%; preferably 50%.

[0039] Preferably, the filtration is carried out using a 0.45 μm PTFE filter membrane.

[0040] In step (2), the volume concentration of methanol solution B is 40 - 60%; preferably 50%.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention discloses for the first time a high-performance liquid chromatography detection method for the content of sodium methanethiol in PPS slurry, making up for the limitation that the content of sodium methanethiol in the mother liquor of PPS slurry cannot be tested by redox titration due to the complex components in the mother liquor of PPS slurry and the presence of a large amount of interfering substances such as sodium benzenethiolate and sodium p-chlorobenzenethiolate.

[0043] The high-performance liquid chromatography detection method disclosed by the present invention has a simple and rapid operation process, and has the advantages of high sensitivity, high precision, high accuracy and good reproducibility for the content detection of sodium methanethiol in the mother liquor of PPS slurry, which has an important guiding role for monitoring the conversion rate of PPS polymerization reaction and ensuring the production quality of PPS. Description of the Drawings

[0044] Figure 1 It is the high-performance liquid chromatography diagram of the blank solution in Example 1;

[0045] Figure 2 It is the high-performance liquid chromatography diagram of the reference solution a in Example 1;

[0046] Figure 3 It is the high-performance liquid chromatography diagram of the sample solution a in Example 1;

[0047] Figure 4 It is the linear diagram of sodium methanethiol in Example 1;

[0048] Figure 5 It is the spectral absorption diagram of sodium methanethiol in Example 1;

[0049] Figure 6 It is the high-performance liquid chromatography diagram of the reference solution a in Comparative Example 1;

[0050] Figure 7 It is the high-performance liquid chromatography diagram of the reference solution a in Comparative Example 2;

[0051] Figure 8 It is the high-performance liquid chromatography diagram of the reference solution a in Comparative Example 3;

[0052] Figure 9 It is the high-performance liquid chromatography diagram of the sample solution a in Comparative Example 4;

[0053] Figure 10 It is the high-performance liquid chromatography diagram of the reference solution a in Comparative Example 5. Detailed Embodiments

[0054] In order to make the objectives, features, and advantages of the present invention more apparent, the following further lists embodiments to illustrate the present invention in detail. The following embodiments are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the principles described in the present invention all fall within the protection scope of the present invention.

[0055] The methanol used in the following embodiments, comparative examples, and various experiments is of HPLC grade, with the brand being Fisher. Potassium dihydrogen phosphate and phosphoric acid are both of chromatographic purity, and the water is ultrapure water to reduce baseline noise. The high-performance liquid chromatograph used is Thermo Fisher Ultimate 3000.

[0056] Example 1

[0057] 1. Chromatography system

[0058] Chromatographic column: Zorbax SB-AQ, 250×4.6 mm, 5 μm;

[0059] Mobile phase: Mobile phase A: acetonitrile; Mobile phase B: buffer solution of potassium dihydrogen phosphate and phosphoric acid;

[0060] Take 6.7988 g of potassium dihydrogen phosphate, accurately weigh it, add 900 mL of ultrapure water and stir to dissolve it. Adjust the pH to 2.0 with phosphoric acid, then transfer it to a 1 L volumetric flask and make up to the mark. After filtering through a 0.45 μm PTFE filter membrane, mobile phase B is obtained.

[0061] Flow rate: 1.0 mL / min;

[0062] Detection wavelength: 208 nm;

[0063] Column temperature: 20 °C;

[0064] Injection volume: 10 μL;

[0065] Elution program:

[0066]

[0067]

[0068] 2. Specific steps:

[0069] 2.1 Preparation of sample solution

[0070] Take 10.0687 g of the PPS slurry mother liquor, accurately weigh it, place it in a 100 mL volumetric flask, add a methanol solution (methanol and water are mixed at a volume ratio of 50:50, shake well to obtain, the same below) to dissolve and make up to the mark. After shaking well, filter through a 0.45 μm PTFE filter membrane to obtain sample solution a.

[0071] Take 3 portions of the PPS slurry mother liquor, approximately 5 g, 15 g, and 25 g respectively, place them in 50 mL volumetric flasks, add methanol solution to dissolve and make up to the mark. After shaking well, filter with a 0.45 μm PTFE filter membrane to obtain sample solutions b, c, and d respectively.

[0072] Take 6 portions of the PPS slurry mother liquor with masses of 10.0534 g, 10.0598 g, 10.0566 g, 10.0601 g, 10.0523 g, and 10.0574 g respectively. Weigh them accurately and place them in 50 mL volumetric flasks. Add methanol solution to dissolve and make up to the mark. After shaking well, filter with a 0.45 μm PTFE filter membrane to obtain sample solutions corresponding to numbers 1 - 6 in sequence.

[0073] 2.2 Preparation of reference solution

[0074] Take about 100 mg of the sodium methyl mercaptide reference substance, weigh it accurately, place it in a 100 mL volumetric flask, add methanol solution to dissolve, make up to the mark, and shake well. Accurately measure 5 mL of the above solution and place it in a 50 mL volumetric flask, then make up to the mark with methanol solution and shake well to obtain reference solution a (containing about 100 mg / L of sodium methyl mercaptide).

[0075] Take about 40 mg of the sodium methyl mercaptide reference substance, weigh it accurately, place it in a 100 mL volumetric flask, add methanol solution to dissolve, make up to the mark, and shake well. Accurately measure 2.5 mL, 5.0 mL, 7.5 mL, 10.0 mL, 12.5 mL, and 15 mL of the above solution respectively and place them in 50 mL volumetric flasks, then make up to the mark with methanol solution and shake well to obtain reference solutions of sodium methyl mercaptide with different concentrations, corresponding to reference solutions numbered 7 - 12 in sequence: 20.672 mg / L, 41.344 mg / L, 62.016 mg / L, 82.688 mg / L, 103.360 mg / L, 124.032 mg / L.

[0076] 2.3 Injection for detection

[0077] Inject the sample solution or reference solution respectively, and perform chromatographic analysis under the above detection conditions.

[0078] 3. Results of verification of detection method

[0079] 3.1 System suitability

[0080] In Example 1, the chromatogram of reference solution a is as Figure 2 shown. It can be seen from Figure 2 that the retention time (RT) of sodium methyl mercaptide is 5.573 min, the peak width (50%) is 0.097 min, the asymmetry factor is 1.18, the peak shape is good, and the number of theoretical plates is 18112.

[0081] The chromatogram of the blank solution (50% methanol solution) is as Figure 1 shown. By comparing Figure 1 and Figure 2 , it can be seen that there are no interfering peaks of sodium methanethiolate reference substance in the blank solution.

[0082] Take the reference substance solution a and inject it repeatedly 6 times. The results of the system suitability test are shown in Table 1:

[0083] Table 1

[0084]

[0085] According to Table 1, it can be seen that the RSD (relative standard deviation) of the retention time of the main peak of the 6 injections of the reference substance solution a is 0.03%, and the RSD of the peak area is 0.04%, indicating that the system suitability of the method of the present invention is good.

[0086] 3.2 Specificity

[0087] The chromatogram of the sample solution a is as Figure 3 shown. The retention time of sodium methanethiolate is 5.550 min, the peak width (50%) is 0.094 min, and the asymmetry factor is 1.18. By comparing Figure 1 and Figure 3 , it can be seen that there are no interfering peaks in the blank solution at the retention time of the main peak (sodium methanethiolate), and the resolution R between the main peak (sodium methanethiolate) of the sample solution and the adjacent peak is 2.94, and the resolution is greater than 1.5, indicating that the method has good specificity and is applicable to the analysis of sodium methanethiolate in the PPS slurry mother liquor.

[0088] 3.3 Linearity and range

[0089] The contents and peak areas of sodium methanethiolate in the reference substance solutions No. 7 - 12 are shown in Table 2.

[0090] Table 2

[0091]

[0092] Based on the data in Table 2, with the concentration of sodium methanethiolate as the abscissa and the peak area as the ordinate, linear regression is performed by the least - squares method. In the injection concentration range of 20 mg / L - 125 mg / L of sodium methanethiolate, the linear graph of sodium methanethiolate is as Figure 4 shown. The linear regression equation is: Y = 0.5197X - 2.6943, and the linear correlation coefficient R > 0.9998, indicating that the method of the invention has good linearity and can perform accurate quantitative detection.

[0093] 3.4 Method precision

[0094] The experimental results of the sample solutions No. 1 - 6 are shown in Table 3.

[0095] Table 3

[0096]

[0097]

[0098] It can be seen from Table 3 that the average content of sodium methyl mercaptide in the PPS slurry mother liquor is 191.5 ppm, and the RSD of the sodium methyl mercaptide content is 0.8%, indicating that this method has high precision.

[0099] The above 6 sample solutions were detected by different people, at different times and with different instruments. The results showed that the RSD of the sodium methyl mercaptide content < 1%. Compared with the sample solutions No. 1 - 6, among the 12 sample solutions, the RSD of the sodium methyl mercaptide content < 1%, indicating that the method has good reproducibility.

[0100] 3.5 Accuracy

[0101] Recovery analysis was carried out by adding sodium methyl mercaptide reference solutions with different concentrations to different sample solutions. Among them, the 7th reference solution was added to sample solution b, the 9th reference solution was added to sample solution c, and the 11th reference solution was added to sample solution d. Each spiked sample solution at each concentration was tested 3 times.

[0102] The recovery test results of sample solution b, sample solution c, and sample solution d are shown in Table 4, Table 5, and Table 6 respectively. The results show that: the recoveries of the sample solutions are all between 95% and 105%, indicating that this method has good accuracy.

[0103] Table 4

[0104]

[0105] Table 5

[0106]

[0107] Table 6

[0108]

[0109] 3.6 Stability

[0110] The stabilities of the reference solution and the sample solution were investigated. The reference solution and the sample solution were taken respectively, sealed completely, and left standing at room temperature for 7 days, then injected for testing. The results showed that the relative deviation of the sodium methyl mercaptide content before and after standing of the sample < 0.1%, indicating that the reference solution and the sample solution have good stability.

[0111] 4 Wavelength Selection

[0112] The selection of the absorption wavelength for the test method of sodium methyl mercaptide in the PPS slurry mother liquor needs to consider multiple aspects. This is because on the one hand, the composition of the PPS slurry mother liquor is complex and the absorption wavelength range is wide. Therefore, when choosing a lower absorption wavelength, it is difficult for the baseline to be flat. On the other hand, when choosing a higher absorption wavelength, the sensitivity of sodium methyl mercaptide will be reduced. Combining Figure 5 with the spectral absorption diagram of sodium methyl mercaptide in

[0113] Example 2

[0114] The detection process is basically the same as that of Example 1, except that the flow rate of the mobile phase is replaced with 0.8 mL / min.

[0115] After testing, the asymmetry factor of the main peak (sodium methyl mercaptide) of the sample solution under this process is 1.20, the resolution from the adjacent peak is greater than 1.5, and the peak shape is good, indicating that this detection process is applicable to the analysis of sodium methyl mercaptide in the PPS slurry mother liquor.

[0116] Example 3

[0117] The detection process is basically the same as that of Example 1, except that the flow rate of the mobile phase is replaced with 1.2 mL / min.

[0118] After testing, the asymmetry factor of the main peak (sodium methyl mercaptide) of the sample solution under this process is 1.19, the resolution from the adjacent peak is greater than 1.5, and the peak shape is good, indicating that this detection process is applicable to the analysis of sodium methyl mercaptide in the PPS slurry mother liquor.

[0119] Comparative Example 1

[0120] The detection process is basically the same as that of Example 1, except that mobile phase B is replaced with water.

[0121] Figure 6 This is the chromatogram of reference solution a in this comparative example. It is observed that no chromatographic peak of sodium methyl mercaptide is detected, indicating that sodium methyl mercaptide cannot be detected by using the detection process in this comparative example.

[0122] Comparative Example 2

[0123] The detection process is basically the same as that of Example 1, except that mobile phase B is replaced with phosphoric acid aqueous solution (pH = 2.0).

[0124] Figure 7 This is the chromatogram of reference solution a in this comparative example. It is observed that no chromatographic peak of sodium methyl mercaptide is detected, indicating that sodium methyl mercaptide cannot be detected by using the detection process in this comparative example.

[0125] Comparative Example 3

[0126] The detection process is basically the same as that in Example 1, except that mobile phase B is replaced with potassium dihydrogen phosphate solution (50 mmol / L).

[0127] Figure 8 This is the chromatogram of reference solution a in this comparative example. It was observed that no chromatographic peak of sodium methanethiol was detected, indicating that sodium methanethiol could not be detected using the detection process in this comparative example.

[0128] Comparative Example 4

[0129] The detection process is basically the same as that in Example 1, except that the flow rate of the mobile phase is replaced with 1.5 mL / min.

[0130] Figure 9 This is the chromatogram of sample solution a in this comparative example. The retention time of sodium methanethiol was RT = 4.470 min, and the resolution R was 0.99, which could not meet the minimum resolution (minimum resolution R = 1.5) required for HPLC testing for complete separation of adjacent components. It shows that under the conditions of this detection process, it is not applicable to the analysis of sodium methanethiol in the PPS slurry mother liquor.

[0131] Comparative Example 5

[0132] The detection process is basically the same as that in Example 1, except that the chromatographic column is replaced with Zorbax SB-C18 (250×4.6 mm, 5 μm).

[0133] Figure 10 This is the chromatogram of reference solution a in this comparative example. It was observed that no chromatographic peak of sodium methanethiol was detected, indicating that sodium methanethiol could not be detected using the detection process in this comparative example.

[0134] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for determining the content of sodium methyl mercaptide in the mother liquor of PPS slurry by high performance liquid chromatography, characterized in that, The mobile phase used in the high performance liquid chromatography method includes mobile phase A and mobile phase B. Mobile phase A is selected from acetonitrile, and mobile phase B is selected from a mixed solution composed of a buffer solution of potassium dihydrogen phosphate and phosphoric acid; For the said mobile phase B, the pH of the buffer solution of potassium dihydrogen phosphate and phosphoric acid is 1.5 - 3.0; The elution procedure is as follows: Isocratic elution is used from 0 to 10 min, and the volume fraction of mobile phase B in the mobile phase > 90%; Gradient elution is used from 10 to 35 min until the volume fraction of mobile phase B in the mobile phase is not less than 60%; Isocratic elution is used from 35 to 44 min; Gradient elution is used from 44 to 45 min until the volume fraction of mobile phase B in the mobile phase > 90%; The chromatographic column used in the high performance liquid chromatography method is selected from SB - AQ chromatographic column, and the column temperature is 15 - 25 °C; The detection wavelength is 205 - 210 nm.

2. The method for determining the content of sodium methyl mercaptide in the PPS slurry mother liquor by using high performance liquid chromatography according to claim 1, characterized in that: For the said mobile phase B, the concentration of the buffer solution of potassium dihydrogen phosphate and phosphoric acid is 40 - 60 mmol / L.

3. The method for determining the content of sodium methyl mercaptide in the PPS slurry mother liquor by using high performance liquid chromatography according to claim 1, characterized in that: The flow rate of the mobile phase is 0.8 - 1.2 mL / min.

4. The method for determining the content of sodium methyl mercaptide in the PPS slurry mother liquor by using high performance liquid chromatography according to claim 1, characterized in that: For the chromatographic column used in the high performance liquid chromatography method, the injection volume is 10 - 20 μL.

5. The method for determining the content of sodium methyl mercaptide in the PPS slurry mother liquor by using high performance liquid chromatography according to claim 1, characterized in that: The elution procedure is: At 0 min, the volume fraction of mobile phase A in the mobile phase is 2%, and the volume fraction of mobile phase B is 98%; At 10 min, the volume fraction of mobile phase A in the mobile phase is 2%, and the volume fraction of mobile phase B is 98%; At 35 min, the volume fraction of mobile phase A in the mobile phase is 40%, and the volume fraction of mobile phase B is 60%; At 44 min, the volume fraction of mobile phase A in the mobile phase is 40%, and the volume fraction of mobile phase B is 60%; At 45 min, the volume fraction of mobile phase A in the mobile phase is 2%, and the volume fraction of mobile phase B is 98%.

6. The method for determining the content of sodium methyl mercaptide in the PPS slurry mother liquor by using high performance liquid chromatography according to claim 5, characterized in that: For the said mobile phase B, the pH of the buffer solution of potassium dihydrogen phosphate and phosphoric acid is 2.0, and the concentration is 50 mmol / L.

7. The method for determining the content of sodium methyl mercaptide in the PPS slurry mother liquor by using high performance liquid chromatography according to claim 6, characterized in that: The flow rate of the mobile phase is 1.0 mL / min.

8. The method for determining the content of sodium methyl mercaptide in the PPS slurry mother liquor by using high performance liquid chromatography according to claim 7, characterized in that: The column temperature is 20 °C, the detection wavelength is 208 nm, and the injection volume is 10 μL.

9. The method for determining the content of sodium methyl mercaptide in the PPS slurry mother liquor by high performance liquid chromatography according to any one of claims 1 to 8, characterized in that, Specifically include: (1) Preparation of sample solution: Mix the PPS slurry mother liquor with methanol solution A, and reserve it after filtration; (2) Preparation of reference solution: Weigh sodium methanethiolate and mix it with methanol solution B, and prepare reference solutions with different concentrations ranging from 20 to 125 mg / L respectively; (3) Injection for detection: Inject the sample solution or the reference solution respectively, conduct chromatographic analysis, and calculate the content of sodium methanethiolate in the sample solution based on the peak area by the external standard method.

10. The method for determining the content of sodium methanethiolate in the PPS slurry mother liquor by high performance liquid chromatography according to claim 9, characterized in that: In step (1), the volume concentration of the methanol solution A is 40 - 60%; In step (2), the volume concentration of the methanol solution B is 40 - 60%.

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