Method for detecting raw materials, impurities and products in methylglycine trisodium diacetate reaction liquid

Abstract

The invention discloses a method for detecting raw materials, impurities and products in a methylglycine trisodium diacetate reaction solution. The method comprises the following steps: respectively preparing a lactic acid, iminodiacetic acid, dimer and MGDA mixed standard substance solution, a sodium 2-chloropropionate standard substance solution and a sample solution, determining the solutions by utilizing high performance liquid chromatography, and calculating the contents of iminodiacetic acid, dimer, lactic acid MGDA and 2-chloropropionic acid in the sample solution according to a single-point external standard method; the calculation formula is as follows. The detection method is high in analysis accuracy, can be applied to central control analysis of the MGDA synthesis process, can be used for tracking the reaction process and material balance of the synthesis process for preparing MGDA from 2-chloropropionic acid, and is of great significance to quality control of MGDA.

Description

Technical Field

[0001] This invention relates to the field of analytical testing technology, specifically to a method for detecting raw materials, impurities, and products in a trisodium methylglycine diacetate reaction solution. Background Technology

[0002] Trisodium methylglycine diacetate (MGDA-3Na) is a high-performance amino acid chelating agent developed by BASF. It boasts numerous advantages, including natural biodegradability, strong chelating ability, toxicological safety, and low detergent residue. It is widely used in cleaning agents, water treatment agents, papermaking auxiliaries, textile auxiliaries, personal care products, metal surface treatment, and industrial cleaning. MGDA meets EU requirements for environmentally friendly products and does not require hazard labeling within the EU. Therefore, in recent years, it has rapidly replaced traditional phosphorus-containing or recalcitrant chelating agents in the European detergent industry and is gradually entering other regions, especially the Asia-Pacific market, represented by China.

[0003] There are three main synthetic routes for MGDA: the Strecker method, the chloroacetic acid method, and the chloropropionic acid method. The Strecker method involves alanine, hydrogen cyanide (or sodium cyanide), and formaldehyde undergoing a Strecker reaction, followed by hydrolysis to obtain the product. Examples include patents WO1994029421A1 and US5817864A, which disclose methods for preparing glycine-N,N-diacetic acid derivatives, and CN106928077A, which discloses a method for preparing methylglycine diacetic acid. The chloroacetic acid method involves a one-step reaction of alanine and chloroacetic acid to obtain the product. Examples include patent CN112898169A, which discloses a method for preparing a biodegradable MGDA chelating agent, and CN109503402A, which discloses a method for preparing a green chelating agent. The 2-chloropropionic acid method involves a one-step reaction of 2-chloropropionic acid and iminodiacetic acid to obtain the product. For example, patent CN 106349093A discloses dicarboxymethylalanine and its synthetic method. The Strecker process suffers from two problems: highly toxic raw materials and the nephrotoxicity of the byproduct NTA, which is classified as a Group 2B carcinogen, posing environmental and safety risks. The p-chloroacetic acid process generates sodium glycolate, resulting in excessively viscous reaction solution that increases post-processing difficulty. Consequently, the p-chloroacetic acid process has high production costs and low product quality, with an effective content of only about 70%. The 2-chloropropionic acid process, with its mild reaction conditions, safe production process, and low energy consumption, shows promising application prospects. This route uses 2-chloropropionic acid and iminodiacetic acid as raw materials to synthesize MGDA-3Na. Besides the generated MGDA-3Na, the reaction solution also produces byproducts such as lactic acid and dimer impurities. Combined with unreacted raw materials, the reaction solution contains at least five substances, potentially affecting post-processing. Currently, no analytical method has been found for simultaneously determining the reaction monitoring of 2-chloropropionic acid, lactic acid, dimer, iminodiacetic acid, and MGDA.

[0004] Common methods for detecting MGDA-3Na include the iron complexation method and the Kjeldahl method (GB / T 2440 urea), which can only detect trisodium methylglycine diacetate or total nitrogen in the sample. These two methods cannot completely distinguish between components such as trisodium methylglycine diacetate and iminodiacetic acid, and fail to monitor the reduction of raw materials and the formation of products and impurities. They only monitor the endpoint of detection and are not suitable for determining the raw material 2-chloropropionic acid and related impurities in the reaction system. Patents CN115616118A and CN114235993A report a method for detecting polyhydroxy and carboxyl groups using high-performance liquid chromatography, but it is not fully applicable to the trisodium methylglycine diacetate reaction solution and has the following unresolved problems: separation of components, peak overlap, indistinguishability, especially poor retention of 2-chloropropionic acid. 2-Chloropropionic acid is highly polar and completely ionizes in alkaline systems. In aqueous solutions or alkaline reaction solutions, it exists almost entirely as a carboxyl group, leading to co-elution with polycarboxylic acid, iminodiacetic acid, and other polycarboxylic acid compounds. This results in peak tailing, peak overlap, and low response in chromatographic detection, severely affecting quantitative accuracy. Therefore, there is a need to develop an analytical method for the simultaneous determination of 2-chloropropionic acid, iminodiacetic acid, lactic acid, and MGDA in the reaction solution. Summary of the Invention

[0005] To address the aforementioned limitations of existing technologies, the present invention aims to provide a method for detecting raw materials, impurities, and products in a trisodium methylglycine diacetate reaction solution. This method offers high analytical accuracy and can be applied to the mid-process control analysis of MGDA synthesis. It can be used to track the reaction progress and material balance in the synthesis of MGDA from 2-chloropropionic acid, and is of significant importance for the quality control of MGDA.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for detecting raw materials, impurities, and products in a trisodium methylglycine diacetate reaction solution, comprising the following steps: (1) Preparation of mixed standard solution: Dissolve lactic acid, iminodiacetic acid, dimer and MGDA standard in water, mix evenly and filter through membrane to obtain mixed standard solution of lactic acid, iminodiacetic acid, dimer and MGDA; (2) 2-Chloropropionic acid standard solution: Dissolve 2-chloropropionic acid in anhydrous methanol and sodium methoxide solution, shake in a water bath, dilute with solvent, mix well and filter through a membrane to obtain sodium 2-chloropropionic acid standard solution. (3) Preparation of sample solution: Weigh the MGDA synthesis reaction solution, add acidic solution to adjust the pH value to 7-8, add methanol and evaporate to dryness in water bath, then add anhydrous methanol and sodium methoxide solution, shake in water bath, add solvent to dilute, mix evenly and filter membrane to obtain sample solution. (4) Determination of standard solutions: The mixed standard solution prepared in step (1) and the 2-chloropropionic acid standard solution prepared in step (2) were determined by high performance liquid chromatography, and the peak area of ​​each standard was recorded. (5) Determination of sample solution: The sample solution obtained in step (3) is subjected to high performance liquid chromatography under the chromatographic conditions in step (4), and the peak area of ​​the sample is recorded. (6) Calculate the content of components: Based on the results of step (4), calculate the content of iminodiacetic acid, dimer, lactic acid MGDA and 2-chloropropionic acid in the sample solution using the single-point external standard method according to the determination results of step (5); the calculation formula is as follows: ; Where: wi - mass fraction of 2-chloropropionic acid, iminodiacetic acid, dimer, lactic acid or MGDA in the sample, in %; Ai - peak area of ​​the sample; As - peak area of ​​the standard; mi - sample mass, in g; m s - Standard mass, in mg; Ps - Standard purity, in %.

[0007] Preferably, in step (1), the concentration of lactic acid in the mixed standard solution is 0.2 mg / mL to 3 mg / mL, the concentration of iminodiacetic acid is 0.2 mg / mL to 2 mg / mL, the concentration of dimer is 0.2 mg / mL to 3 mg / mL, and the concentration of MGDA is 0.2 mg / mL to 6 mg / mL.

[0008] Preferably, in step (2), the concentration of the sodium 2-chloropropionate standard solution is 0.2 mg / mL to 2 mg / mL.

[0009] Preferably, in steps (1) to (3), the filter membrane is a 0.45 μm filter membrane.

[0010] Preferably, in steps (2) and (3), the solvent is a mixture of phosphoric acid solution and acetonitrile; the volume ratio of phosphoric acid solution to acetonitrile is 1:1; and the mass concentration of phosphoric acid solution is 1%~2%.

[0011] Preferably, in steps (2) and (3), the volume ratio of anhydrous methanol to sodium methoxide methanol solution is 5~10:2~5; the sodium methoxide methanol solution is sodium methoxide solid diluted with anhydrous methanol; and the mass concentration of the sodium methoxide methanol solution is 15%~30%.

[0012] Preferably, in steps (2) and (3), the dilution is to dilute to 100 times the volume; the temperature of the water bath shaking is 60°C and the time is 10 min.

[0013] Preferably, in step (3), the acidic solution is a hydrochloric acid solution; the concentration of the hydrochloric acid solution is 0.1 mol / L to 1 mol / L.

[0014] Preferably, in step (3), the mass fraction of lactic acid in the MGDA synthesis reaction solution is 0.05% to 1%, the mass fraction of iminodiacetic acid is 0.05% to 10%, the mass fraction of dimer is 0.05% to 1%, the mass fraction of 2-chloropropionic acid is 0.05% to 10%, and the mass fraction of MGDA is 0.10% to 20%.

[0015] In a second aspect, the present invention provides the application of the above-described detection method in improving the accuracy and sensitivity of detecting MGDA content.

[0016] The beneficial effects of this invention are: (1) This invention introduces sodium methoxide solution during sample pretreatment to induce a derivatization reaction of 2-chloropropionic acid in the reaction solution, generating sodium 2-methoxypropionate. This derivatization reaction alters the molecular structure of 2-chloropropionic acid, transforming it from a highly polar, fully ionized sodium carboxylate salt into a less polar, partially molecularized etherified product. The hydrophobicity of the derivatized product is increased, enhancing its interaction with the chromatographic stationary phase and significantly prolonging its retention time. This method effectively avoids the problem of co-elution of 2-chloropropionic acid with polar substances such as lactic acid and iminodiacetic acid in conventional reversed-phase systems, while improving peak shape and signal response value. Experimental results show that after derivatization with sodium methoxide, the peak area and signal intensity of 2-chloropropionic acid increase by approximately 30%–50%, and the resolution improves from less than 1.0 to greater than 1.5, enabling accurate quantitative detection of 2-chloropropionic acid. Thus, this invention solves the long-standing analytical problems of peak tailing, separation difficulties, and low response values ​​of 2-chloropropionic acid in traditional systems through chemical derivatization, significantly improving detection resolution and quantitative accuracy.

[0017] (2) The XSelect HSS T3 column, a unique silica C18 column, was selected. Its reversed-phase retention capability for polar analytes, combined with a mobile phase system of acetonitrile and weakly acidic phosphate buffer (pH 6.0), established a chromatographic separation environment that combines polar interactions with ion balance. The bonded phase surface of the XSelect HSS T3 column contains amide groups, which enhance the retention of polar carboxylates through hydrogen bonding and dipole-dipole interactions, while avoiding the anion repulsion effect caused by residual silanol groups. This column type exhibits good separation capabilities for polycarboxylic acid, iminodiacetic acid, dimers, and MGDA, effectively maintaining peak symmetry and reducing tailing and forward tilting. Compared with traditional C18 columns, the XSelect HSS T3 column can simultaneously quantify five key components while maintaining resolution, with resolutions greater than 1.5 and good method repeatability (RSD < 2%). Therefore, the synergistic optimization of this column type and mobile phase system not only solves the problem of difficult retention of components in highly polar polyacid systems, but also significantly improves the accuracy, stability and column life of detection.

[0018] (3) The method of the present invention has high analytical accuracy and can be applied to the mid-control analysis of MGDA synthesis process. It can be used to track the reaction process and material balance of 2-chloropropionic acid to prepare MGDA, which is of great significance for the quality control of MGDA. Attached Figure Description

[0019] Figure 1 : Blank solvent chromatogram; Figure 2 : Chromatogram of mixed standard solution; Figure 3 Chromatogram of sodium 2-chloropropionate standard solution; Figure 4 : Chromatogram of the sample solution; Figure 5 Chromatogram of Comparative Example 1 sample; Figure 6 Chromatogram of Comparative Example 2. Detailed Implementation

[0020] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0021] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0022] Note: The preparation method of MGDA is based on the method disclosed in patent CN 106349093 A, "Dicarboxymethylalanine and its Synthesis Method", specifically as follows: Step 1: Mixed Reaction Iminodiacetic acid (133 g, 1 mol) and 2-chloropropionic acid (217 g, 2 mol) were added to a reaction flask, and the temperature was raised to 120 °C over 30 minutes. The reaction was carried out for 6 hours.

[0023] Step 2: Exhaust gas treatment: The exhaust gas is passed into a 20% sodium hydroxide solution for exhaust gas treatment and recovery to obtain the MGDA synthesis reaction solution.

[0024] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0025] Example 1 (1) Iminodiacetic acid (133 g, 1 mol) and 2-chloropropionic acid (217 g, 2 mol) were added to a reaction flask, and the temperature was raised to 120 °C in 30 minutes. The reaction was carried out for 6 hours. The tail gas was passed into a 20% sodium hydroxide solution for tail gas treatment and recovery to obtain the MGDA synthesis reaction solution.

[0026] (2) Weigh 100.35 mg lactic acid, 100.45 mg dimer, 50.21 mg iminodiacetic acid and 150.23 mg MGDA, dilute with water to 50 mL, shake well, filter through a 0.45 μm filter membrane, and prepare a mixed standard solution of 2.0070 mg / mL lactic acid, 2.0090 mg / mL dimer, 1.0042 mg / mL iminodiacetic acid and 3.0046 mg / mL MGDA.

[0027] Weigh 40.35 mg of 2-chloropropionic acid, dissolve it in 5 mL of anhydrous methanol and 3 mL of 15% sodium methoxide methanol solution, shake in a water bath at 60 °C for 10 min, then dilute to 50 mL with solvent (phosphoric acid solution: acetonitrile volume ratio = 1:1, phosphoric acid solution concentration is 1.5%), mix well and filter through a 0.45 μm filter membrane to obtain sodium 2-chloropropionic acid standard solution.

[0028] Weigh 1.0023g of the MGDA synthesis reaction solution prepared in step (1), adjust the pH value to 7-8 with 0.5mol / L hydrochloric acid solution, add 5mL of methanol, evaporate to dryness in a 90℃ water bath, then add 5mL of anhydrous methanol and 3mL of 15% sodium methoxide methanol solution, shake in a 60℃ water bath for 10min, add solvent (phosphoric acid solution: acetonitrile volume ratio = 1:1, phosphoric acid solution concentration is 1.5%) to dilute to 50mL, mix well and filter through a 0.45μm filter membrane to obtain the sample solution.

[0029] High performance liquid chromatography was used to determine the mixed standard solution, 2-chloropropionic acid standard solution and sample solution.

[0030] Instrumentation: Shimadzu LC-20AT high performance liquid chromatograph; Column: XSelect HSS T3 (250mm×4.6mm×5μm); Flow rate: 1.0 mL / min; Elution mode: gradient elution; Detector: UV detector; Detection wavelength: 215 nm; Column temperature: 35℃; Injection volume: 10 μL; Mobile phase A was a 10 mmol / L potassium dihydrogen phosphate solution (1.36 g of potassium dihydrogen phosphate was weighed into 1000 mL of water, 2.5 mL of ammonia was added, and the pH was adjusted to 6.0 with phosphoric acid). Mobile phase B was acetonitrile. Gradient elution was used for separation, and the gradient elution program is shown in Table 1.

[0031] Table 1 Gradient elution program 1.5% phosphoric acid solution + acetonitrile = 50 + 50 (V / V).

[0032] Under the chromatographic conditions described above, after the instrument baseline stabilized, inject 10 μL each of the solvent, mixed standard solution, 2-chloropropionic acid standard solution, and sample solution into the chromatograph, and record the chromatograms of the three components. The chromatogram of the standard solution is shown below. Figure 1 .

[0033] Figure 1 The middle chromatogram shows the solvent chromatogram; the solvent does not interfere with the sample determination.

[0034] Figure 2 The retention times of lactic acid, dimer, iminodiacetic acid and MGDA were 4.362 min, 4.667 min, 14.764 min and 16.787 min, respectively, with peak areas of 225332, 299332, 393551 and 1524979, respectively. The resolution was greater than 3.0 for all of them, which met the baseline separation requirements.

[0035] Figure 3 The retention time of 2-chloropropionic acid, the product derived from methanol, was 6.00 min, and the peak area was 107032.

[0036] Figure 4In the process, the excess alkali in the sample solution was neutralized with a solvent, and the resolution of each component's chromatographic peak met the requirements. Since potassium dihydrogen phosphate buffer is an inorganic buffer system, it neither interferes with the sample determination nor damages the sample components, effectively protecting the chromatographic column and extending its service life.

[0037] The calculation formula is as follows: ; Where: wi - mass fraction of lactic acid, dimer, iminodiacetic acid, MGDA and 2-chloropropionic acid in the sample, in %; Ai - peak area of ​​the sample; As - peak area of ​​the standard; mi - mass of the sample, in g; ms - mass of the standard, in g; Ps - purity of the standard, in %.

[0038] 0.72%; 0.10%; 0.68%; 0.57%; 18.84%; According to the calculation formula, the content of lactic acid in the MGDA synthesis reaction solution is 0.72%, the content of dimer is 0.03%, the content of iminodiacetic acid is 0.68%, the content of MGDA is 18.84%, and the content of 2-chloropropionic acid is 0.57%.

[0039] Example 2 Weigh 10.35 mg lactic acid, 10.65 mg dimer, 10.78 mg iminodiacetic acid, and 10.74 mg MGDA, dilute with solvent to 50 mL, shake well, and filter through a 0.45 μm filter membrane to prepare a mixed standard solution of 0.2070 mg / mL lactic acid, 0.2130 mg / mL dimer, 0.2156 mg / mL iminodiacetic acid, and 0.2148 mg / mL MGDA.

[0040] Weigh 10.39 mg of 2-chloropropionic acid, dissolve it in 5 mL of anhydrous methanol and 2 mL of 15% sodium methoxide methanol solution, shake in a water bath at 60 °C for 10 min, dilute with solvent to 50 mL, mix well and filter through a 0.45 μm filter membrane to obtain sodium 2-chloropropionic acid standard solution. Weigh 0.5004g of the MGDA synthesis reaction solution prepared in step (1) of Example 1, adjust the pH value to 7-8 with 0.1mol / L hydrochloric acid, add 5mL of methanol, evaporate to dryness in an 80℃ water bath, add 5mL of anhydrous methanol and 2mL of 15% sodium methoxide methanol solution, shake in a 60℃ water bath for 10min, dilute to 50mL with solvent (phosphoric acid solution: acetonitrile volume ratio = 1:1, phosphoric acid solution concentration is 1.5%), mix well, and filter through a 0.45μm filter membrane to obtain the sample solution.

[0041] The Shimadzu LC-20AT high-performance liquid chromatograph and the XSelect HSS T3 column with specifications of 250 mm × 4.6 mm × 3 μm were used. Mobile phase A: 100 mmol / L dihydrogen phosphate solution (adjusted to pH 6.0 ± 1.0 with phosphoric acid solution); Mobile phase B: Acetonitrile; Solvent: 1% phosphoric acid solution + acetonitrile = 50 + 50 (V / V); The chromatographic conditions are shown in Table 2.

[0042] Table 2 Chromatographic conditions The determination method was the same as in Example 1, and the results are shown in Table 3.

[0043] Table 3 Durability Test Results The results showed that under various chromatographic conditions, there were no significant differences in the detection results of lactic acid, dimer, 2-chloropropionic acid, iminodiacetic acid, and MGDA, indicating that the method has good robustness.

[0044] Example 3 Weigh 50.46 mg lactic acid, 50.79 mg dimer, 100.83 mg iminodiacetic acid, and 250.45 mg MGDA, dilute with water to 50 mL, shake well, filter through a 0.45 μm filter membrane, and prepare a mixed standard solution of 1.0092 mg / mL lactic acid, 1.0158 mg / mL dimer, 2.0166 mg / mL iminodiacetic acid, and 5.0090 mg / mL MGDA.

[0045] Weigh 50.68 mg of 2-chloropropionic acid, dissolve it in 10 mL of anhydrous methanol and 5 mL of 30% sodium methoxide methanol solution, shake in a water bath at 60 °C for 10 min, then dilute to 50 mL with solvent (phosphoric acid solution: acetonitrile volume ratio = 1:1, phosphoric acid solution concentration is 1.5%), mix well, and filter through a 0.45 μm filter membrane to obtain sodium 2-chloropropionic acid standard solution.

[0046] Weigh 2.0234g of the MGDA synthesis reaction solution prepared in step (1) of Example 1, adjust the pH value to 7-8 with 1mol / L hydrochloric acid, add 10mL of methanol, evaporate to dryness in a 95℃ water bath, add 10mL of anhydrous methanol and 5mL of 30% sodium methoxide methanol solution, shake in a 60℃ water bath for 10min, dilute to 50mL with solvent, mix well and filter through a 0.45μm filter membrane to obtain the sample solution; The high performance liquid chromatography parameter settings and determination methods are the same as in Example 1, and the results are shown in Table 4.

[0047] Table 4 Sample Inspection Results Example 4 Weigh 50.46 mg lactic acid, 50.79 mg dimer, 100.83 mg iminodiacetic acid, and 250.45 mg MGDA, dilute with water to 50 mL, shake well, filter through a 0.45 μm filter membrane, and prepare a mixed standard solution of 1.0092 mg / mL lactic acid, 1.0158 mg / mL dimer, 2.0166 mg / mL iminodiacetic acid, and 5.0090 mg / mL MGDA.

[0048] Weigh 50.68 mg of 2-chloropropionic acid, dissolve it in 10 mL of anhydrous methanol and 5 mL of 30% sodium methoxide methanol solution, shake in a water bath at 60 °C for 10 min, dilute with solvent to 50 mL, mix well and filter through a 0.45 μm filter membrane to obtain sodium 2-chloropropionic acid standard solution.

[0049] Instrumentation: Thermo Fisher Scientific U3000 high-performance liquid chromatograph Column: XSelect HSS T3 (250mm × 4.6mm, 5μm); The mobile phase was acetonitrile: 10 mmol / potassium dihydrogen phosphate solution (adjusted to pH 2.5 with phosphoric acid solution) = 5:95; Flow rate: 1.0 mL / min; Washing mode: isocratic elution; Detector: Ultraviolet detector Detection wavelength: 215 nm; Column temperature: 35℃; Injection volume: 10 μL.

[0050] The determination method is the same as in Example 1, and both the limit of quantitation test and the precision test are performed simultaneously. The specific methods are as follows: (1) Sensitivity test The mixed standard solution was diluted 1000 times to obtain the limit of quantitation solution, and the mixed standard solution was diluted 2000 times to obtain the limit of detection solution. The limit of detection and limit of quantitation of this method were investigated, and the results are shown in Table 5.

[0051] Table 5 Sensitivity Results As shown in Table 5, the detection limit of MGDA is as low as 0.11 μg / mL, indicating that the detection method of the present invention has high sensitivity and can be applied to the mid-control analysis of the MGDA synthesis process. It can be used to track the reaction process and material balance of the 2-chloropropionic acid to MGDA synthesis process, and promote the continuous production of MGDA.

[0052] (2) Precision test Weigh out 1.0341g, 1.0784g, 1.0123g, 1.0412g, 1.0374g, 1.0132g, and 1.1378g of the MGDA reaction solution prepared in step (1) of Example 1, respectively, dissolve and dilute to 100mL with sample solvent, shake well, filter through a 0.45μm filter membrane, prepare sample solution, and determine according to Example 1. The test results are shown in Table 6.

[0053] Table 6. Contents of MGDA, 2-chloropropionic acid, and iminodiacetic acid in the reaction solution As shown in Table 6, with the contents of lactic acid (0.21%), dimer (0.41%), 2-chloropropionic acid (2.23%), and iminodiacetic acid (3.02%) in the reaction solution, the RSD of six consecutive measurements was less than 5.0%; and with the content of MGDA (15.38%), the RSD of six consecutive measurements was less than 2.0%, indicating that the method of the present invention has good precision.

[0054] Weigh approximately 0.5g of the MGDA reaction solution prepared in step (1) of Example 1. Add lactic acid, dimer, 2-chloropropionic acid, iminodiacetic acid and MGDA standard solution to the weighed MGDA reaction solution at 50%, 100% and 150% of the content of each component in the sample, respectively. The determination method is the same as in Example 1. The spiked recovery rate is determined and the results are shown in Table 7.

[0055] Table 7 Results of spiked recovery tests As shown in Table 7, the spiked recoveries of lactic acid were 97.65%–102.39%, those of the dimer were 95.36%–105.24%, those of 2-chloropropionic acid were 97.34%–102.78%, those of iminodiacetic acid were 98.45%–101.32%, and those of MGDA were 98.79%–101.56%.

[0056] Comparative Example 1 The Thermo Fisher U3000 high-performance liquid chromatograph and a Spectrum Red RD-C18-AQ (250mm×4.6mm, 3μm) column were used.

[0057] Mobile phase: 10 mmol / L potassium dihydrogen phosphate solution (adjusted to pH 5.5 with phosphoric acid solution); Flow rate: 0.8 mL / min; Washing mode: isocratic elution; Detector: Ultraviolet detector; Detection wavelength: 215nm; Column temperature: 35℃; Injection volume: 5 μL.

[0058] Weigh 50.78 mg lactic acid, 50.95 mg dimer, 50.28 mg 2-chloropropionic acid, 100.83 mg iminodiacetic acid, and 250.45 mg MGDA, dilute with water to 50 mL, shake well, filter through a 0.45 μm filter membrane, and prepare a mixed standard solution of 1.0092 mg / mL lactic acid, 1.0158 mg / mL dimer, 2.0166 mg / mL iminodiacetic acid, and 5.0090 mg / mL MGDA.

[0059] Under the chromatographic conditions described above, after the instrument baseline stabilized, inject 5 μL of the standard solution into the chromatograph and record the chromatograms. See the sample chromatogram below. Figure 5 The results showed that lactic acid, 2-chloropropionic acid, and the dimer could not be separated, and MGDA and iminodiacetic acid were eluted together with the blank solvent, resulting in incomplete separation of the components. Therefore, the chromatographic conditions are not suitable for the detection of components such as MGDA, 2-chloropropionic acid, and iminodiacetic acid.

[0060] Comparative Example 2 Under the same conditions as in Example 1, the preparation of the sodium 2-chloropropionate standard solution in step (2) of Example 1 was performed, and the methanol / sodium methoxide used for derivatization was replaced with an equal amount of anhydrous ethanol / sodium ethoxide, while keeping other operating conditions consistent.

[0061] like Figure 6 As shown, after ethanol derivatization, 2-chloropropionic acid is converted into sodium 2-ethoxypropionate, which has a longer retention time than the methanol-derived product, but the derivatization conversion rate is significantly reduced (e.g., the peak area of ​​the derivatized product is about 70% of that of the methanol-derived product), and the peak shape shows slight broadening. The detection sensitivity and quantitative repeatability are both lower than those of the methanol-derived example.

[0062] Therefore, the use of methanol / sodium methoxide as the derivatization system in this invention has significant advantages in improving conversion rate, signal response and peak shape. Although sodium ethoxide ethanol solution can produce derivatized products, its effect is inferior to that of sodium methoxide methanol solution, and it cannot replace sodium methoxide methanol solution as the best implementation method.

[0063] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for detecting raw materials, impurities, and products in a trisodium methylglycine diacetate reaction solution, characterized in that, The method comprises the following steps: (1) Preparation of mixed standard solution: dissolve lactic acid, imino diacetic acid, dimer and MGDA standard in water, mix uniformly, and filter through a membrane to obtain a mixed standard solution of lactic acid, imino diacetic acid, dimer and MGDA; (2) Preparation of 2-chloropropionic acid standard solution: dissolve 2-chloropropionic acid in anhydrous methanol and sodium methoxide solution, oscillate in a water bath, dilute with a solvent, mix uniformly, and filter through a membrane to obtain a 2-chloropropionic acid sodium standard solution; (3) Preparation of sample solution: weigh the MGDA synthesis reaction solution, add an acidic solution to adjust the pH value to 7-8, evaporate to dryness in a water bath after adding methanol, then add anhydrous methanol and sodium methoxide solution, oscillate in a water bath, dilute with a solvent, mix uniformly, and filter through a membrane to obtain a sample solution; (4) Determination of standard solution: determine the mixed standard solution prepared in step (1) and the 2-chloropropionic acid standard solution prepared in step (2) by high performance liquid chromatography, and record the peak area of each standard; (5) Determination of sample solution: determine the sample solution obtained in step (3) by high performance liquid chromatography under the chromatographic conditions of step (4), and record the peak area of the sample; (6) Calculation of component content: calculate the content of imino diacetic acid, dimer, lactic acid, MGDA and 2-chloropropionic acid in the sample solution according to the single-point external standard method based on the determination results of step (5) and the results of step (4); the calculation formula is as follows: ； wherein: wi - mass fraction of 2-chloropropionic acid, iminodiacetic acid, dimer, lactic acid or MGDA in the sample, in %; Ai - sample peak area; As - standard peak area; mi - sample mass, in g; m s - standard mass, in mg; Ps-standard purity, unit: %.

2. The detection method according to claim 1, characterized in that, In step (1), the concentration of lactic acid in the mixed standard solution is 0.2 mg / mL-2 mg / mL, the concentration of imino diacetic acid is 0.2 mg / mL-2 mg / mL, the concentration of dimer is 0.2 mg / mL-2 mg / mL, and the concentration of MGDA is 0.2 mg / mL-5 mg / mL.

3. The method of claim 1, wherein In step (2), the concentration of the 2-chloropropionic acid sodium standard solution is 0.2 mg / mL-2 mg / mL.

4. The method of claim 1, wherein In steps (1)-(3), the filter membrane is a 0.45 μm filter membrane.

5. The method of claim 1, wherein In steps (2) and (3), the solvent is a mixture of phosphoric acid solution and acetonitrile; the volume ratio of the phosphoric acid solution to acetonitrile is 1:1; and the mass concentration of the phosphoric acid solution is 1%-2%.

6. The method of claim 1, wherein In steps (2) and (3), the volume ratio of the anhydrous methanol to the sodium methoxide methanol solution is 5-10:2-5; the sodium methoxide solution is prepared by dissolving sodium methoxide in methanol; and the mass concentration of the sodium methoxide solution is 15%-30%.

7. The method of claim 1, wherein, In steps (2) and (3), the dilution is diluted to 100 times by volume; and the water bath oscillation temperature is 60°C, and the time is 10 min.

8. The method of claim 1, wherein, In step (3), the acidic solution is a hydrochloric acid solution; and the concentration of the hydrochloric acid solution is 0.1 mol / L-1 mol / L.

9. The method of claim 1, wherein, In step (3), the mass fraction of lactic acid in the MGDA synthesis reaction solution is 0.05% to 1%, the mass fraction of iminodiacetic acid is 0.05% to 10%, the mass fraction of the dimer is 0.05% to 1%, the mass fraction of 2-chloropropionic acid is 0.05% to 10%, and the mass fraction of MGDA is 0.10% to 20%.

10. Use of the detection method according to any one of claims 1 to 9 to improve the accuracy and sensitivity of detection of the content of MGDA.

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