Identification method of AEC prepared by oxidation method and carboxymethylation method

Abstract

The invention belongs to the technical field of chemical analysis and detection, and particularly relates to a method for distinguishing fatty alcohol-polyoxyethylene ether carboxylic acid prepared by an oxidation method and fatty alcohol-polyoxyethylene ether carboxylic acid prepared by a carboxymethylation method. According to the principle, the fatty alcohol-polyoxyethylene ether carboxylic acid product prepared by using two methods has different residual impurities, and the content of monochloroacetic acid and chloride ion impurities is determined by using an ion chromatography so as to identify the fatty alcohol-polyoxyethylene ether carboxylic acid product. The method is easy and convenient to operate, high in accuracy and precision and good in repeatability, and reliable technical support is provided for quality control and application and popularization of fatty alcohol-polyoxyethylene ether carboxylic acid products.

Description

Technical Field

[0001] This invention belongs to the field of chemical analysis technology, specifically relating to an ion chromatography method for distinguishing between fatty alcohol polyoxyethylene ether carboxylic acid produced by oxidation and fatty alcohol polyoxyethylene ether carboxylic acid produced by carboxymethylation. Background Technology

[0002] Fatty alcohol polyoxyethylene ether carboxylic acid (AEC) is a high-performance green anionic surfactant that combines the mildness of nonionic surfactants with the high surface activity of anionic surfactants. It also has core advantages such as good biodegradability, low toxicity, wide pH range, and strong resistance to hard water. It has been widely used in high-tech fields such as daily cosmetics, pharmaceutical excipients, and electronic equipment cleaning.

[0003] Currently, the industrial processes for preparing AEC are mainly divided into two categories: oxidation and carboxymethylation. These two methods differ significantly in raw material selection, product residue characteristics, safety, and application suitability. The carboxymethylation method uses monochloroacetic acid or sodium monochloroacetate as the carboxylating agent. While it boasts advantages such as mature technology, low production cost, and ease of large-scale production, it inevitably produces residual impurities during the reaction. Specifically, these are incompletely converted monochloroacetic acid and chloride ions formed from the dissociation of the reaction byproduct sodium chloride. Monochloroacetic acid is extremely toxic, irritating, and corrosive; contact with the human body can cause acute skin or mucous membrane damage, and long-term exposure poses a potential carcinogenic risk. Excessive chloride ion residue can shorten the lifespan of medical devices and electronic equipment, reducing their operational stability and efficiency. Therefore, AEC prepared using this process has certain limitations. The oxidation method uses fatty alcohol polyoxyethylene ether as a starting material and produces AEC through a noble metal catalytic oxidation reaction. The preparation process does not require the use of chlorine-containing reagents, and the resulting product does not contain monochloroacetic acid or chloride ion residues. Its purity is significantly better than that of products produced by the carboxymethylation method, which can meet the high safety requirements of applications such as daily cosmetics, pharmaceutical excipients, and electronic industrial cleaning. However, this process requires precise control of the composition of the catalytic system and the oxidation reaction environment, and it also has problems such as complex process flow and high production costs, making it difficult to promote and apply on a large scale in low-cost civilian fields.

[0004] Currently, common methods for detecting AECs involve using high-performance liquid chromatography (HPLC), gas chromatography (GC), and liquid chromatography-mass spectrometry (LC-MS) to separate and identify homologues of fatty alcohol polyoxyethylene ether carboxylic acids (e.g., components with different carbon chain lengths), and then quantifying the main component and impurities through comparison with standards. For example, HPLC uses a C18 reversed-phase column with a methanol-water gradient elution mobile phase and an evaporative light scattering detector. However, existing methods have drawbacks: they cannot distinguish between AECs prepared by oxidation and carboxymethylation methods, and they suffer from insufficient sensitivity, low response intensity, poor separation, low accuracy and precision, and susceptibility to interference from fatty alcohol polyoxyethylene ethers and polyethylene glycol derivatives in AECs. These limitations significantly restrict their applicability to different types of AECs; furthermore, they consume a large amount of reagents, making it difficult to meet the needs of batch sample testing in industrial production scenarios. Summary of the Invention

[0005] The technical problem this invention aims to solve is to overcome the aforementioned deficiencies in existing technologies and provide an ion chromatography method for distinguishing between oxidative AEC and carboxymethylated AEC. This method offers high accuracy, good precision, low reagent consumption, and low cost.

[0006] The present invention discloses an ion chromatography analysis method for distinguishing between oxidative AEC and carboxymethylated AEC. This method can differentiate between oxidative and carboxymethylated AEC products by detecting the presence of monochloroacetic acid and chloride ions in the AEC sample. Specifically, it includes the following steps:

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A method for identifying AEC prepared by oxidation and carboxymethylation methods, characterized by comprising the following steps:

[0009] (1) Sample solution preparation: Accurately weigh an appropriate amount of AEC, add ultrapure water and sonicate to prepare a sample solution with a concentration of 10~50 mg / mL;

[0010] (2) Sample solution processing: The sample solution described in step (1) is passed through a C18 solid phase extraction column after activation and equilibration treatment, and the effluent and eluent are collected; then the effluent and eluent are mixed and filtered through a 0.22-micron organic microporous filter membrane, and the filtrate is used as the sample solution to be tested;

[0011] (3) Establishing standard curves: Take monochloroacetic acid and sodium chloride and add ultrapure water to prepare reference stock solutions, and prepare a series of standard solutions with monochloroacetic acid and chloride ion mass concentrations of 1~50 μg / mL. Use ion chromatograph to determine and draw standard curves;

[0012] (4) Sample solution detection: The sample solution to be tested obtained in step (2) is detected using the same ion chromatograph parameters as in step (3), and the content of monochloroacetic acid and chloride ions in the sample is quantitatively obtained, thereby distinguishing AEC products prepared by different processes.

[0013] The parameters of the ion chromatograph are set as follows:

[0014] Anion guard column SH-GP-2;

[0015] Anion analysis column SH-AP-1;

[0016] Rinsing solution: 4-6 mmol / L potassium hydroxide solution;

[0017] Eluent flow rate: 0.6~0.8 mL / min;

[0018] Isocratic elution;

[0019] Column temperature: 35~40℃;

[0020] Conductivity cell temperature: 35~40℃;

[0021] Suppressor voltage: 10~12 V;

[0022] Column pressure: 15~20 MPa;

[0023] Injection volume: 25~50 μL;

[0024] Detection time: 20~30 min.

[0025] Preferably, in step (2), the sample solution is passed through the activated and equilibrated C18 solid-phase extraction column at a flow rate of 0.8~1.0 mL / min to obtain the effluent; after the sample solution has completely passed through the C18 solid-phase extraction column, the C18 solid-phase extraction column is rinsed with a 50% methanol-water solution to obtain the rinsing solution.

[0026] Preferably, in step (3), the concentrations of the monochloroacetic acid series standard solutions are 1 μg / mL, 5 μg / mL, 10 μg / mL, 25 μg / mL, and 50 μg / mL, respectively; the concentrations of the sodium chloride series standard solutions are 1 μg / mL, 5 μg / mL, 10 μg / mL, 25 μg / mL, and 50 μg / mL, respectively; and both the monochloroacetic acid series standard solutions and the sodium chloride series standard solutions are prepared fresh for each use.

[0027] Preferably, the structural formula of the AEC is: RO(CH2CH2O) n CH2COOH, where R represents C8~C 18Straight-chain or branched alkyl groups, where n ranges from 1 to 30.

[0028] Compared with the prior art, the beneficial effects of this invention are as follows:

[0029] Based on the characteristics of impurity content in AEC from different preparation methods, this invention proposes for the first time a method using ion chromatography to effectively distinguish and identify AEC prepared by oxidation and carboxymethylation methods. The technical challenge of identifying AEC by ion chromatography lies in the fact that trace amounts of monochloroacetic acid are easily masked by the matrix, overlap with similar impurities, and have low conductivity sensitivity, making stable and accurate detection difficult. To address this, this invention, through extensive optimization experiments, determined the optimal parameter settings for the ion chromatograph. The use of the SH-GP-2 anion guard column and the SH-AP-1 anion analyzer column is advantageous due to their high column efficiency and excellent separation performance for small molecule acids. The selection of 4-6 mmol / L potassium hydroxide solution as the eluent and a flow rate of 0.6-0.8 mL / min effectively shortens the analysis time while ensuring ion separation. Setting the column temperature and conductivity cell temperature to 35-40℃ stabilizes ion exchange, shortens retention time, and ensures separation efficiency and repeatability. The synergistic combination of these techniques successfully solves the industry problem of existing detection methods failing to effectively distinguish between AEC prepared by oxidation and carboxymethylation methods due to the ease with which trace monochloroacetic acid impurities are masked by the matrix, overlap with similar impurities, and low conductivity sensitivity.

[0030] Under the parameter settings of the ion chromatograph of this invention, the identification method of AEC prepared by oxidation and carboxymethylation methods of this invention is used to identify AEC from different preparation methods. Compared with the currently commonly used methods of separating and identifying AEC by high performance liquid chromatography, gas chromatography, and liquid chromatography-mass spectrometry, it has the following advantages:

[0031] (1) Good separation, the separation degree of target impurities such as chloride ion and monochloroacetate ion from other component peaks is greater than 1.5;

[0032] (2) High sensitivity: detection limit as low as 0.03 μg / mL, quantitation limit as low as 0.01 μg / mL;

[0033] (3) The method has high precision and accuracy; the recovery rate ranges from 93.0% to 98.4%, and the relative standard deviation ranges from 0.35% to 3.37%.

[0034] (4) It has strong specificity and is not affected by the fatty alcohol polyoxyethylene ether raw material and polyethylene glycol derivative by-product in AEC;

[0035] (5) The operation is simple and convenient, and the experimental reagents are consumed in small quantities. Attached Figure Description

[0036] Figure 1 This is an ion chromatogram of a standard solution of monochloroacetic acid ions.

[0037] Figure 2 This is the ion chromatogram of a chloride ion standard solution.

[0038] Figure 3 This is the ion chromatogram of AEC-9H obtained by carboxymethylation.

[0039] Figure 4 This is the ion chromatogram of AEC-9H obtained by oxidation.

[0040] Figure 5 This is the ion chromatogram of AEC-8H obtained by carboxymethylation.

[0041] Figure 6 This is the ion chromatogram of AEC-6H obtained by carboxymethylation.

[0042] Figure 7 This is the total ion chromatogram of a standard monochloroacetic acid solution.

[0043] Figure 8 This is the ultraviolet chromatogram of a standard solution of monochloroacetic acid. Detailed Implementation

[0044] The instruments and reagents used in the following embodiments of the present invention are as follows:

[0045] (a) Reagents: Monochloroacetic acid, chromatographic grade; sodium hydroxide, analytical grade; sodium chloride, analytical grade; ultrapure water.

[0046] (II) Instruments: Essentia IC-6 ion chromatograph, Shimadzu Corporation, Japan; CDD-10AVP conductivity detector, Shimadzu Corporation, Japan; SQP electronic balance, Sartorius Scientific Instruments GmbH, Germany; NY-1T Mini mixer, Changzhou Enpei Instrument Manufacturing Co., Ltd.; UPT-II-20T ultrapure water system, Sichuan Youpu Ultrasonic Technology Co., Ltd.; SH-GP-2 anion guard column (4.0 mm × 50 mm, 8 μm), Qingdao Shenghan Chromatography Technology Co., Ltd.; SH-AP-1 anion analyzer column (4.0 mm × 250 mm, 5.5 μm), Qingdao Shenghan Chromatography Technology Co., Ltd.; CNC ultrasonic cleaner, Kunshan Ultrasonic Instrument Co., Ltd.

[0047] The basic principle of ion chromatography in this invention is that AEC prepared by the carboxymethylation method inevitably contains incompletely converted chloroacetic acid and chloride ion impurities formed by the dissociation of sodium chloride, a byproduct of the reaction, due to the use of chloroacetic acid or sodium chloroacetate as the raw material. In contrast, AEC prepared by the oxidation method uses fatty alcohol polyoxyethylene ether as the starting material and does not introduce chlorine-containing reagents during the preparation process. Therefore, the product does not contain monochloroacetic acid or chloride ion residues, and its purity is significantly superior to that of the corresponding product prepared by the carboxymethylation method. Based on these significant differences, this invention proposes an ion chromatography analysis method that can accurately distinguish between AEC prepared by the oxidation method and AEC prepared by the carboxymethylation method, thereby achieving effective differentiation between AEC products prepared by the two processes.

[0048] To facilitate understanding of the technical solution of the present invention, the following detailed description is provided through specific embodiments.

[0049] Example 1

[0050] (a) Chromatographic column and mobile phase: An anion exchange guard column SH-GP-2 (4.0 mm × 50 mm, 8 μm) and an anion exchange analytical column SH-AP-1 (4.0 mm × 250 mm, 5.5 μm) were used, with 5 mmol / L potassium hydroxide eluent, and isocratic elution for 20 min. A conductivity detector was used for detection.

[0051] (II) Ion chromatographic analysis of AEC-9H by carboxymethylation method, the steps are as follows:

[0052] S1. Sample solution preparation: Accurately weigh an appropriate amount of carboxymethylated AEC-9H sample, place it in a container, add ultrapure water, and sonicate it at 25°C to ensure that the sample is fully dissolved. Make up the volume to prepare a sample solution with a concentration of 10 mg / mL.

[0053] S2. Sample Solution Processing: Take a C18 solid-phase extraction pretreatment column and perform activation and equilibration treatments on it sequentially, ensuring the packing material inside the column remains moist throughout the process. Pass the ultrasonically treated sample solution through the pretreated C18 solid-phase extraction column at a flow rate of 0.8 mL / min, collecting all sample eluent for later use. After the sample solution has completely passed through the C18 solid-phase extraction column, elute the column with a 50% (v / v) methanol-water solution, collecting all eluent for later use. Combine the collected sample eluent and eluent, and thoroughly mix the combined solution in a mixer. Then, filter the mixed solution through a 0.22-micron organic microporous membrane. The filtrate is used as the sample solution to be tested.

[0054] S3. Establish a standard curve:

[0055] Step 1: Prepare standard curve solutions for monochloroacetic acid and chloride ions: Dilute monochloroacetic acid and chloride ion standard substances with different gradients to obtain a series of monochloroacetic acid standard solutions with concentrations of 1 μg / mL, 5 μg / mL, 10 μg / mL, 25 μg / mL, and 50 μg / mL, and a series of sodium chloride standard solutions with concentrations of 1 μg / mL, 5 μg / mL, 10 μg / mL, 25 μg / mL, and 50 μg / mL, respectively.

[0056] Step 2: Establish standard curves by using ion chromatography to prepare standard solutions of monochloroacetic acid and chloride ions at different concentrations.

[0057] Step 3: Detect the pretreated sample solution using the same ion chromatography parameters to obtain the concentrations of monochloroacetic acid and chloride ions. Calculate the content of monochloroacetic acid and chloride ions using the external standard method. The linear equation for monochloroacetic acid ions is y = 1.25 × 10⁻⁶. 4 x-5.12×10 3 R 2 The value is 0.9998; the linear equation for chloride ions is y = 3.87 × 10⁻⁶. 4 x-4.15×10 4 R 2 It is 0.9988.

[0058] Step 4, Standard Solution Detection: Inject 10 μg / mL monochloroacetic acid and chloride ion standard solutions separately for ion chromatography detection. Results are shown in [Figure number missing]. Figure 1 , Figure 2 .like Figure 1 As shown, the retention time t of monochloroacetic acid ions R1 =12.85 min; such as Figure 2 The retention time t of chloride ions is shown. R2 = 15.00 min.

[0059] S4. Sample Solution Detection: Inject the sample solution to be tested and perform ion chromatography. After blank background subtraction, the results are shown in [Figure 1]. Figure 3 .like Figure 3 As shown, the retention times of the characteristic peaks of monochloroacetic acid and chloride ions in the ion chromatogram of the carboxymethylated AEC-9H sample obtained by ion chromatography correspond to the retention times of the peaks of the two ion standard substances, indicating that the carboxymethylated AEC-9H contains monochloroacetic acid and chloride ion impurities. Using the external standard method, the content of monochloroacetic acid ions in AEC-9H can be calculated to be 0.0091%, and the content of chloride ions is 0.034%.

[0060] (iii) Negative blank test.

[0061] Blank spiking experiments were performed in negative blank AEC-9H samples at three spiking levels: low, medium, and high. Each spiking level was tested in six parallel runs. The average spiked recoveries and relative standard deviations (RSD) of monochloroacetic acid and chloride ions were calculated. Accuracy was expressed as average spiked recoveries, and precision was expressed as RSD. The results are shown in Table 1 below.

[0062] Table 1

[0063]

[0064] The results showed that the average recoveries of monochloroacetic acid and chloride ions in AEC-9H by carboxymethylation ranged from 93.0% to 98.4%, with RSDs of 1.06% to 3.37%. This method has good precision and high accuracy in determining monochloroacetic acid and chloride ions in AEC-9H by carboxymethylation.

[0065] (iv) Method reliability verification

[0066] The AEC-9H sample obtained by carboxymethylation was analyzed six times consecutively, and the results are shown in Table 2.

[0067] Table 2

[0068]

[0069] As shown in Table 2, the RSD of monochloroacetic acid ions is 4.40%, and the RSD of chloride ions is 2.14%. Both RSDs are less than 5%, indicating that the method has good repeatability in determining monochloroacetic acid and chloride ions in AEC-9H by carboxymethylation.

[0070] Example 2

[0071] (a) Chromatographic column and mobile phase: An anion exchange guard column SH-GP-2 (4.0 mm × 50 mm, 8 μm) and an anion exchange analytical column SH-AP-1 (4.0 mm × 250 mm, 5.5 μm) were used, with 5 mmol / L potassium hydroxide eluent, and isocratic elution for 20 min. A conductivity detector was used for detection.

[0072] (II) Ion chromatographic analysis of AEC-9H by oxidation method, the steps are as follows:

[0073] S1. Sample solution preparation: Accurately weigh an appropriate amount of AEC-9H sample from the oxidation method, place it in a container, add ultrapure water, and sonicate it at 25°C to ensure that the sample is fully dissolved. Make up the volume to prepare a sample solution with a concentration of 10 mg / mL.

[0074] S2. Sample Solution Processing: Take a C18 solid-phase extraction pretreatment column and perform activation and equilibration treatments on it sequentially, ensuring the packing material inside the column remains moist throughout the process. Pass the ultrasonically treated sample solution through the pretreated C18 solid-phase extraction column at a flow rate of 0.8 mL / min, collecting all sample eluent for later use. After the sample solution has completely passed through the C18 solid-phase extraction column, elute the column with a 50% (v / v) methanol-water solution, collecting all eluent for later use. Combine the collected sample eluent and eluent, and thoroughly mix the combined solution in a mixer. Then, filter the mixed solution through a 0.22-micron organic microporous membrane. The filtrate is used as the sample solution to be tested.

[0075] S3. Establish a standard curve:

[0076] Step 1: Prepare standard curve solutions for monochloroacetic acid and chloride ions: Dilute monochloroacetic acid and chloride ion standard substances with different gradients to obtain a series of monochloroacetic acid standard solutions with concentrations of 1 μg / mL, 5 μg / mL, 10 μg / mL, 25 μg / mL, and 50 μg / mL, and a series of sodium chloride standard solutions with concentrations of 1 μg / mL, 5 μg / mL, 10 μg / mL, 25 μg / mL, and 50 μg / mL, respectively.

[0077] Step 2: Establish standard curves by using ion chromatography to prepare standard solutions of monochloroacetic acid and chloride ions at different concentrations.

[0078] Step 3: Detect the pretreated sample solution using the same ion chromatography parameters to obtain the concentrations of monochloroacetic acid and chloride ions. Calculate the content of monochloroacetic acid and chloride ions using the external standard method. The linear equation for monochloroacetic acid ions is y = 1.25 × 10⁻⁶. 4 x-5.12×10 3 R 2 The value is 0.9998; the linear equation for chloride ions is y = 3.87 × 10⁻⁶. 4 x-4.15×10 4 R 2 It is 0.9988.

[0079] S4. Sample Solution Detection: Inject the sample solution to be tested and perform ion chromatography. After blank background subtraction, the results are shown in [Figure 1]. Figure 4 .like Figure 4 As shown, the ion chromatogram of the AEC-9H sample obtained by ion chromatography using the oxidation method did not show characteristic chromatographic peaks consistent with the retention times of monochloroacetic acid and chloride ions, indicating that the AEC-9H sample obtained by the oxidation method does not contain monochloroacetic acid and chloride ion impurities.

[0080] Example 3

[0081] (a) Chromatographic column and mobile phase: An anion exchange guard column SH-GP-2 (4.0 mm × 50 mm, 8 μm) and an anion exchange analytical column SH-AP-1 (4.0 mm × 250 mm, 5.5 μm) were used, with 5 mmol / L potassium hydroxide eluent, and isocratic elution for 20 min. A conductivity detector was used for detection.

[0082] (II) Ion chromatographic analysis of AEC-8H by carboxymethylation method, the steps are as follows:

[0083] S1. Sample solution preparation: Accurately weigh an appropriate amount of carboxymethylated AEC-8H sample, place it in a container, add ultrapure water, and sonicate it at 25°C to ensure that the sample is fully dissolved. Make up the volume to prepare a sample solution with a concentration of 20 mg / mL.

[0084] S2. Sample Solution Processing: Take a C18 solid-phase extraction pretreatment column and perform activation and equilibration treatments on it sequentially, ensuring the packing material inside the column remains moist throughout the process. Pass the ultrasonically treated sample solution through the pretreated C18 solid-phase extraction column at a flow rate of 0.8 mL / min, collecting all sample eluent for later use. After the sample solution has completely passed through the C18 solid-phase extraction column, elute the column with a 50% (v / v) methanol-water solution, collecting all eluent for later use. Combine the collected sample eluent and eluent, and thoroughly mix the combined solution in a mixer. Then, filter the mixed solution through a 0.22-micron organic microporous membrane. The filtrate is used as the sample solution to be tested.

[0085] S3. Establish a standard curve:

[0086] Step 1: Prepare standard curve solutions for monochloroacetic acid and chloride ions: Dilute monochloroacetic acid and chloride ion standard substances with different gradients to obtain a series of monochloroacetic acid standard solutions with concentrations of 1 μg / mL, 5 μg / mL, 10 μg / mL, 25 μg / mL, and 50 μg / mL, and a series of sodium chloride standard solutions with concentrations of 1 μg / mL, 5 μg / mL, 10 μg / mL, 25 μg / mL, and 50 μg / mL, respectively.

[0087] Step 2: Establish standard curves by using ion chromatography to prepare standard solutions of monochloroacetic acid and chloride ions at different concentrations.

[0088] Step 3: Detect the pretreated sample solution using the same ion chromatography parameters to obtain the concentrations of monochloroacetic acid and chloride ions. Calculate the content of monochloroacetic acid and chloride ions using the external standard method. The linear equation for monochloroacetic acid ions is y = 1.25 × 10⁻⁶. 4 x-5.12×10 3 R 2 The value is 0.9998; the linear equation for chloride ions is y = 3.87 × 10⁻⁶. 4 x-4.15×10 4 R 2 It is 0.9988.

[0089] Step 4, Standard Solution Detection: Inject 10 μg / mL monochloroacetic acid and chloride ion standard solutions separately for ion chromatography detection. Results are shown in [Figure number missing]. Figure 1 , Figure 2 .like Figure 1 As shown, the retention time of monochloroacetic acid ions is tR1 = 12.85 min; Figure 2 The retention time of chloride ions is shown to be tR2 = 15.00 min.

[0090] S4. Sample Solution Detection: Inject the sample solution to be tested and perform ion chromatography. After blank background subtraction, the results are shown in [Figure 1]. Figure 5 .like Figure 5 As shown, the retention times of the characteristic peaks of monochloroacetic acid and chloride ions in the ion chromatogram of the carboxymethylated AEC-8H sample obtained by ion chromatography correspond to the retention times of the peaks of the two ion standard substances, indicating that the carboxymethylated AEC-8H contains monochloroacetic acid and chloride ion impurities. Using the external standard method, the content of monochloroacetic acid ions in AEC-8H can be calculated to be 0.017%, and the content of chloride ions is 0.17%.

[0091] (iii) Negative blank test

[0092] Blank spiking experiments were performed in negative blank AEC-8H samples at three spiking levels: low, medium, and high. Each spiking level was tested in six parallel runs. The average spiked recoveries and relative standard deviations (RSD) of monochloroacetic acid and chloride ions were calculated. Accuracy was expressed as average spiked recoveries, and precision was expressed as RSD. The results are shown in Table 3 below.

[0093] Table 3

[0094]

[0095] The results showed that the average recoveries of monochloroacetic acid and chloride ions in AEC-8H by carboxymethylation ranged from 94.5% to 97.3%, with RSDs of 0.35% to 2.88%. This method showed good precision and high accuracy in determining monochloroacetic acid and chloride ions in AEC-9H by carboxymethylation.

[0096] (iv) Method reliability verification

[0097] The AEC-8H sample obtained by carboxymethylation was analyzed six times consecutively, and the results are shown in Table 4.

[0098] Table 4

[0099]

[0100] As shown in Table 4, the RSD of monochloroacetic acid ions is 4.47%, and the RSD of chloride ions is 2.98%, both of which are less than 5%, indicating that this method has good repeatability in determining monochloroacetic acid and chloride ions in AEC-8H by carboxymethylation.

[0101] Example 4

[0102] (a) Chromatographic column and mobile phase: An anion exchange guard column SH-GP-2 (4.0 mm × 50 mm, 8 μm) and an anion exchange analytical column SH-AP-1 (4.0 mm × 250 mm, 5.5 μm) were used, with 5 mmol / L potassium hydroxide eluent, and isocratic elution for 20 min. A conductivity detector was used for detection.

[0103] (II) Ion chromatographic analysis of AEC-6H by carboxymethylation method, the steps are as follows:

[0104] S1. Sample solution preparation: Accurately weigh an appropriate amount of carboxymethylated AEC-6H sample, place it in a container, add ultrapure water, and sonicate it at 25°C to ensure that the sample is fully dissolved. Make up the volume to prepare a sample solution with a concentration of 20 mg / mL.

[0105] S2. Sample Solution Processing: Take a C18 solid-phase extraction pretreatment column and perform activation and equilibration treatments on it sequentially, ensuring the packing material inside the column remains moist throughout the process. Pass the ultrasonically treated sample solution through the pretreated C18 solid-phase extraction column at a flow rate of 0.8 mL / min, collecting all sample eluent for later use. After the sample solution has completely passed through the C18 solid-phase extraction column, elute the column with a 50% (v / v) methanol-water solution, collecting all eluent for later use. Combine the collected sample eluent and eluent, and thoroughly mix the combined solution in a mixer. Then, filter the mixed solution through a 0.22-micron organic microporous membrane. The filtrate is used as the sample solution to be tested.

[0106] S3. Establish a standard curve:

[0107] Step 1: Prepare standard curve solutions for monochloroacetic acid and chloride ions: Dilute monochloroacetic acid and chloride ion standard substances with different gradients to obtain a series of monochloroacetic acid standard solutions with concentrations of 1 μg / mL, 5 μg / mL, 10 μg / mL, 25 μg / mL, and 50 μg / mL, and a series of sodium chloride standard solutions with concentrations of 1 μg / mL, 5 μg / mL, 10 μg / mL, 25 μg / mL, and 50 μg / mL, respectively.

[0108] Step 2: Establish standard curves by using ion chromatography to prepare standard solutions of monochloroacetic acid and chloride ions at different concentrations.

[0109] Step 3: Detect the pretreated sample solution using the same ion chromatography parameters to obtain the concentrations of monochloroacetic acid and chloride ions. Calculate the content of monochloroacetic acid and chloride ions using the external standard method. The linear equation for monochloroacetic acid ions is y = 1.25 × 10⁻⁶. 4 x-5.12×10 3 R 2 The value is 0.9998; the linear equation for chloride ions is y = 3.87 × 10⁻⁶. 4 x-4.15×10 4 R 2 It is 0.9988.

[0110] Step 4, Standard Solution Detection: Inject 10 μg / mL monochloroacetic acid and chloride ion standard solutions separately for ion chromatography detection. Results are shown in [Figure number missing]. Figure 1 , Figure 2 .like Figure 1 As shown, the retention time t of monochloroacetic acid ions R1 =12.85 min; such as Figure 2 The retention time t of chloride ions is shown.R2 = 15.00 min.

[0111] S4. Sample Solution Detection: Inject the sample solution to be tested and perform ion chromatography. After blank background subtraction, the results are shown in [Figure 1]. Figure 6 .like Figure 6 As shown, the retention times of the characteristic peaks of monochloroacetic acid and chloride ions in the ion chromatogram of the carboxymethylated AEC-6H sample obtained by ion chromatography correspond to the retention times of the peaks of the two ion standard substances, indicating that the carboxymethylated AEC-6H contains monochloroacetic acid and chloride ion impurities. Using the external standard method, the content of monochloroacetic acid ions in AEC-6H can be calculated to be 0.020%, and the content of chloride ions is 0.14%.

[0112] (iii) Negative blank test

[0113] Blank spiking experiments were performed in negative blank AEC-6H samples at three spiking levels: low, medium, and high. Each spiking level was tested in six parallel runs. The average spiked recoveries and relative standard deviations (RSD) of monochloroacetic acid and chloride ions were calculated. Accuracy was expressed as average spiked recoveries, and precision was expressed as RSD. The results are shown in Table 5 below.

[0114] Table 5

[0115]

[0116] The results showed that the average recoveries of monochloroacetic acid and chloride ions in AEC-6H by carboxymethylation ranged from 93.0% to 97.2%, with RSDs of 0.56% to 3.36%. This method has good precision and high accuracy in determining monochloroacetic acid and chloride ions in AEC-9H by carboxymethylation.

[0117] (iv) Method reliability verification

[0118] The AEC-6H sample obtained by carboxymethylation was analyzed six times consecutively, and the results are shown in Table 6.

[0119] Table 6

[0120]

[0121] As shown in Table 6, the RSD of monochloroacetic acid ions is 2.50%, and the RSD of chloride ions is 3.10%, both of which are less than 5%, indicating that this method has good repeatability in determining monochloroacetic acid and chloride ions in AEC-6H by carboxymethylation.

[0122] Comparative Example 1

[0123] The detection limitations of monochloroacetic acid were verified by using liquid chromatography-mass spectrometry (LC-MS).

[0124] The instruments and reagents used in Comparative Example 1 are as follows:

[0125] (a) Reagents: Monochloroacetic acid, chromatographic grade; methanol, chromatographic grade; formic acid, chromatographic grade; ultrapure water.

[0126] (II) Instruments: ACQUITY Arc-QDa high performance liquid chromatography-tandem mass spectrometry system, Waters Corporation, USA; SQP electronic balance, Sartorius Scientific Instruments GmbH, Germany; NY-1T Mini mixer, Changzhou Enpei Instrument Manufacturing Co., Ltd.; UPT-II-20T ultrapure water system, Sichuan Youpu Ultrasonic Technology Co., Ltd.; XBridge® C18 column (4.6 × 150mm, 3.5 μm), Waters Corporation, USA; CNC ultrasonic cleaner, Kunshan Ultrasonic Instrument Co., Ltd.

[0127] (III) Chromatographic and mass spectrometry conditions: Mobile phase: methanol-0.1% formic acid aqueous solution (8:2, V / V); isocratic elution for 30 min; flow rate: 1.0 mL / min; Waters XBridge® C18 column (4.6 × 150 mm, 3.5 μm); column temperature: 40℃; sample temperature: 15℃; full scan mode; scan range: 50~1000 Da; capillary voltage ±15 V; cone voltage ±0.8 kV; detection was performed using a mass spectrometer.

[0128] (iv) The analysis was performed using liquid chromatography-mass spectrometry (LC-MS), and the steps are as follows:

[0129] S1. Preparation of monochloroacetic acid standard solution: Accurately weigh an appropriate amount of monochloroacetic acid and prepare standard solutions with a concentration of 100 μg / mL.

[0130] S2. Detection of standard solution: The standard solution is detected using the chromatographic and mass spectrometric conditions described in (III).

[0131] S3. Test results: such as Figure 7 As shown, liquid chromatography-mass spectrometry (LC-MS) was used to detect the chromatographic peak of the monochloroacetic acid standard solution, which was not detected.

[0132] This comparative example shows that monochloroacetic acid cannot be detected using this liquid chromatography-mass spectrometry method, and it is even more impossible to distinguish between oxidative AEC and carboxymethylated AEC.

[0133] Comparative Example 2

[0134] High performance liquid chromatography-ultraviolet detection was used to detect monochloroacetic acid, and the detection limitations of this technique were verified.

[0135] The instruments and reagents used in Comparative Example 2 are as follows:

[0136] High performance liquid chromatography-ultraviolet detection was used to detect monochloroacetic acid, and the detection limitations of this technique were verified.

[0137] The instruments and reagents used in Comparative Example 2 are as follows:

[0138] (a) Reagents: Monochloroacetic acid, chromatographic grade; methanol, chromatographic grade; ultrapure water.

[0139] (II) Instruments: ACQUITY Arc-2998 PDA high performance liquid chromatograph with UV detector, Waters Corporation, USA; SQP electronic balance, Sartorius Scientific Instruments GmbH, Germany; NY-1T Mini mixer, Changzhou Enpei Instrument Manufacturing Co., Ltd.; UPT-II-20T ultrapure water system, Sichuan Youpu Ultrasonic Technology Co., Ltd.; Kromasil-C18 column (4.6 × 250 mm, 5 μm), Nouryon GmbH, Netherlands; CNC ultrasonic cleaner, Kunshan Ultrasonic Instrument Co., Ltd.

[0140] (III) Chromatographic conditions: mobile phase: 80% methanol and 20% water; isocratic elution for 15 min; Waters XBridge® C18 column (4.6 × 150 mm, 3.5 μm); column temperature: 40℃; sample temperature: 15℃; wavelength range: 200~300nm; resolution: 1.2 nm; flow rate: 1.0 mL / min.

[0141] (iv) The analysis was performed using high performance liquid chromatography-ultraviolet detection, and the steps are as follows:

[0142] S1. Preparation of monochloroacetic acid standard solution: Accurately weigh an appropriate amount of monochloroacetic acid and prepare standard solutions with a concentration of 100 μg / mL.

[0143] S2. Standard solution detection: The standard solution is detected using the chromatographic element of (iii).

[0144] S3. Test results: such as Figure 8 As shown, the ultraviolet detector did not detect the chromatographic peak of the monochloroacetic acid standard solution.

[0145] This comparative example shows that monochloroacetic acid cannot be detected using high performance liquid chromatography-ultraviolet detection, and therefore cannot be used to distinguish between oxidative AEC and carboxymethylated AEC.

Claims

1. A method for identifying AEC prepared by oxidation and carboxymethylation methods, characterized in that... Includes the following steps: (1) Sample solution preparation: Accurately weigh an appropriate amount of AEC, add ultrapure water and sonicate to prepare a sample solution with a concentration of 10~50 mg / mL; (2) Sample solution processing: The sample solution described in step (1) is passed through a C18 solid phase extraction column after activation and equilibration treatment. The effluent and eluent are collected. The effluent and eluent are then mixed and filtered through a 0.22-micron organic microporous filter membrane. The filtrate is used as the sample solution to be tested. (3) Establishing standard curves: Take monochloroacetic acid and sodium chloride and add ultrapure water to prepare reference stock solutions, and prepare a series of standard solutions with monochloroacetic acid and chloride ion mass concentrations of 1~50 μg / mL. Use ion chromatograph to determine and draw standard curves; (4) Sample solution detection: The sample solution to be tested obtained in step (2) is detected using the same ion chromatography parameters as in step (3), and the content of monochloroacetic acid and chloride ions in the sample is quantitatively obtained, thereby distinguishing fatty alcohol polyoxyethylene ether carboxylic acid products prepared by different processes. The parameters of the ion chromatograph are set as follows: Anion guard column SH-GP-2; Anion analysis column SH-AP-1; Rinsing solution: 4-6 mmol / L potassium hydroxide solution; Eluent flow rate: 0.6~0.8 mL / min; Isocratic elution; Column temperature: 35~40℃; Conductivity cell temperature: 35~40℃; Suppressor voltage: 10~12 V; Column pressure: 15~20 MPa; Injection volume: 25~50 μL; Detection time: 20~30 min.

2. The method for identifying AEC prepared by oxidation and carboxymethylation as described in claim 1, characterized in that, In step (2), the sample solution is passed through the activated and equilibrated C18 solid-phase extraction column at a flow rate of 0.8~1.0 mL / min to obtain the effluent; after the sample solution has completely passed through the C18 solid-phase extraction column, the C18 solid-phase extraction column is rinsed with a 50% methanol-water solution to obtain the rinsing solution.

3. The method for identifying AEC prepared by oxidation and carboxymethylation as described in claim 1, characterized in that, In step (3), the concentrations of the monochloroacetic acid series standard solutions are 1 μg / mL, 5 μg / mL, 10 μg / mL, 25 μg / mL, and 50 μg / mL, respectively; the concentrations of the sodium chloride series standard solutions are 1 μg / mL, 5 μg / mL, 10 μg / mL, 25 μg / mL, and 50 μg / mL, respectively; and both the monochloroacetic acid series standard solutions and the sodium chloride series standard solutions are prepared fresh for each use.

4. A method for identifying AEC prepared by oxidation and carboxymethylation methods according to any one of claims 1 to 3, characterized in that, The structural formula of the aforementioned AEC is: RO(CH2CH2O) n CH2COOH; where: R represents C8~C 18 Straight-chain or branched alkyl groups, where n ranges from 1 to 30.

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