Method for quantifying key components and rapidly detecting water-reducing rate of polycarboxylate-type water reducer based on liquid chromatography

Abstract

The invention discloses a method for quantifying key components of a polycarboxylic acid water reducer and rapidly detecting the water reducing rate based on liquid chromatography, and belongs to the technical field of rapid detection of high-performance water reducers. On the basis of the molecular composition and action mechanism of the polycarboxylic acid water reducer, the characteristic that chemical components of the polycarboxylic acid water reducer are easily separated through polarity is utilized, and the rapid detection of the water reducing rate of the polycarboxylic acid water reducer is realized. The concentration of key chemical components such as macromonomers and triterpenoid saponin in the water reducing agent is quantitatively detected by adopting a liquid chromatography combined with an evaporative light scattering detection technology; by fitting a standard curve and establishing a regression equation of the key component concentration and the water-reducing rate, rapid calculation of the water-reducing rate of the water reducer is realized, quantitative detection and quality judgment of the key components of a product are completed, the detection period is shortened, a time-consuming and labor-consuming traditional concrete workability test is replaced, and the method is suitable for large-scale popularization and application. The component content reference can be established when the product enters the field for the first time, the daily monitoring of the quality of the water reducing agent is realized, and the detection efficiency and accuracy are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of rapid detection technology for high-performance water-reducing agents, and particularly relates to a rapid detection method for the quantification of key components and water reduction rate of polycarboxylate-based water-reducing agents based on liquid chromatography. Background Technology

[0002] Since the gradual promotion and application of naphthalene-based and melamine-based high-efficiency water-reducing agents in the 1960s, concrete production and construction technology has achieved leapfrog development, and the performance improvement of concrete materials is also deeply linked to the technological progress of water-reducing agents. With the continuous improvement of the performance requirements of engineering construction, new types of concrete such as high-performance concrete, self-compacting vibration-free concrete, fiber-reinforced concrete, and underwater non-dispersed concrete have been successfully developed and widely used in key projects such as the Three Gorges Dam, Hangzhou Bay Bridge, and Beijing-Shanghai High-Speed ​​Railway. The excellent performance of these new types of concrete is inseparable from the support of high-performance water-reducing agents.

[0003] Polycarboxylate-based high-performance water-reducing agents, as a rapidly developing new type of water-reducing agent in recent years, have significant advantages over traditional lignin-based and naphthalene-based water-reducing agents, including strong cement dispersibility, high water reduction rate, small slump loss over time, and wide cement adaptability. Their comprehensive performance far surpasses that of traditional water-reducing agents, and they are widely recognized as the third generation of water-reducing agents. This represents a historic breakthrough in the history of water-reducing agent development and has become the mainstream development direction for concrete water-reducing agents in the future. Currently, the development of polycarboxylate-based water-reducing agents in my country is still in its early stages. Related research began at the end of the 20th century, and engineering applications have only been limited to recent years. However, due to their excellent comprehensive performance, they have received widespread attention from the industry and have been successfully applied to various key projects. Even in Japan, a leader in research and application in this field, the development history of polycarboxylate-based water-reducing agents is only about twenty years, and they are still in a stage of continuous improvement and upgrading. The core component of polycarboxylate high-performance water-reducing agents is the macromonomer, which grafts various smaller monomers and materials onto long carbon chains such as acrylic acid.

[0004] Currently, researchers both domestically and internationally have conducted extensive research on the molecular structure, application performance, and mechanism of action of polycarboxylate superplasticizers. However, significant shortcomings and technological gaps remain in the field of product quality control. Existing testing standards primarily rely on performance testing, indirectly determining the quality of superplasticizers through cement paste and concrete performance tests, while also using solids content testing to preliminarily determine whether the polymer content meets standards. However, the quality of polycarboxylate superplasticizers depends not only on solids content and water reduction rate, but also on key indicators such as polymer content, specific component composition, and double bond saturation rate. These factors have a decisive impact on water reduction effect, concrete workability, and durability. Systematic studies on these key indicators are scarce both domestically and internationally, and related testing technologies are also lacking.

[0005] In practical engineering raw material quality control, relying solely on solid content and water reduction rate testing is insufficient to comprehensively, accurately, and efficiently determine the product quality of polycarboxylate superplasticizers. This can easily lead to substandard products entering the construction site, affecting the quality of concrete projects and the durability of structures. Furthermore, traditional concrete performance testing is time-consuming, labor-intensive, and has a long testing cycle, failing to meet the needs of rapid testing and daily monitoring of superplasticizer quality on construction sites. Based on the mechanism of action and molecular structure of polycarboxylate superplasticizers, their chemical components have the characteristic of being easily separated by polarity. Using precise analytical methods such as liquid chromatography, the quantitative detection of various chemical components can be achieved, thereby establishing a scientific and rapid quality testing system. This is of significant practical importance for improving the quality control technology of polycarboxylate superplasticizers and ensuring the quality of concrete projects. Summary of the Invention

[0006] (1) Technical problem to be solved: The purpose of this invention is to overcome the shortcomings of the existing technology, such as low efficiency of quality detection of polycarboxylate superplasticizers, single detection index, inability to comprehensively and accurately determine product quality, and lack of daily quality monitoring methods. It provides a rapid detection method for polycarboxylate superplasticizers, which uses liquid chromatography technology to realize the quantitative detection of key components of superplasticizers and rapid calculation of water reduction rate, shorten the detection cycle, improve the quality control system, and provide efficient and accurate technical support for the quality control of superplasticizers in engineering sites.

[0007] (2) The technical solution adopted in this invention is as follows: A rapid method for quantifying key components and detecting water reduction rate of polycarboxylate superplasticizers based on liquid chromatography includes the following steps: Step 1: Preparation of standard solution: Sugar, citric acid monohydrate, macromonomer, acrylic acid, triterpenoid saponins, sodium gluconate, sodium thiosulfate, sodium metabisulfite, and sodium bisulfite were selected as standard substances, and a series of mixed standard solutions with various concentrations were prepared. Step 2: Standard curve fitting: 2.1 Optimization of chromatographic conditions: Set the detection parameters for liquid chromatography, and use an evaporative light scattering detector to optimize the mobile phase ratio, flow rate, column temperature and detection wavelength; 2.2 Chromatographic detection and curve fitting: Using the optimized chromatographic conditions, the series of mixed standard solutions prepared in step 1 were analyzed one by one by chromatographic analysis. The peak area (y) of each target substance was used as the ordinate and the mass concentration (x) of the corresponding substance was used as the abscissa. The least squares method was used to fit the working curve to obtain the standard curve equation and linear range of each target substance. 2.3 Key curve confirmation: Confirm the standard curve equations for macromonomers, triterpenoid saponins, and white sugar, and ensure that their linear correlation coefficient R² ≥ 0.996, meeting the requirements for quantitative detection; Step 3: Quantitative detection of key components in water-reducing agent samples: 3.1 Sample pretreatment: Take the finished sample of polycarboxylate-based high-performance water-reducing agent, dilute and filter it to prepare a sample solution that meets the requirements of chromatographic detection; 3.2 Sample Chromatographic Detection: Under the same chromatographic conditions optimized in step 2, the sample solution was subjected to chromatographic detection to obtain the evaporative light scattering detector chromatogram of the finished water-reducing agent; 3.3 Component concentration calculation: Based on the elution time sequence in the chromatogram, determine the corresponding chromatographic peaks of macromonomers and triterpenoid saponins, read their peak areas, substitute the peak areas into the corresponding standard curve equation obtained in step 2, and calculate the mass concentration of macromonomers and triterpenoid saponins in the finished water-reducing agent. Step 4: Quick Calculation of Water Reduction Rate 4.1 Regression Equation Establishment: Based on the least squares method, the measured data of total concentrations of macromonomers and triterpenoid saponins and water reduction rates of multiple water-reducing agent samples were fitted to establish a regression equation between water reduction rate (Y) and total concentrations of macromonomers and triterpenoid saponins (X): Y = 1.098X + 6.8588 (R² = 0.9984), where Y is the water reduction rate (%) and X is the total concentration of macromonomers and triterpenoid saponins (%). 4.2 Water reduction rate calculation: Substitute the total concentration of macromonomers and triterpenoid saponins in the finished water-reducing agent calculated in step 3 into the above regression equation to quickly calculate the water reduction rate of the finished water-reducing agent; 4.3 Quality Judgment: Combining the quantitative detection results of macromonomers and triterpenoid saponins with the calculated water reduction rate, and referring to the component content and water reduction rate benchmark indicators established when the product first entered the market, the quality of the water-reducing agent product is quickly judged.

[0008] A further technical solution involves verifying the reliability of the detection method after step 3, including spike recovery tests and repeatability and stability tests. Spike recovery test: Different concentrations of standard substances were added to the finished water-reducing agent sample, and the samples were tested under the same chromatographic conditions. The spike recovery rate was calculated to verify the accuracy of the detection method. The spike recovery rate was required to be controlled between 90.2% and 110.8%. Repeatability and stability testing: On the same day and different working days, the same water-reducing agent sample is repeatedly tested under the same chromatographic conditions. The relative standard deviation (RSD) is calculated to verify the repeatability and stability of the test method. The relative standard deviation is required to be ≤3.6%.

[0009] A further technical solution is that the optimized liquid chromatography conditions in step 2 are as follows: a C18 reversed-phase column is used, the mobile phase is methanol-water solution, gradient elution is adopted, the flow rate is controlled at 0.8-1.2 mL / min, the column temperature is set at 30-35℃, the drift tube temperature of the evaporative light scattering detector is 80-90℃, and the carrier gas flow rate is 2.0-2.5 L / min.

[0010] A further technical solution is that the specific method for sample pretreatment in step 3 is as follows: take 1 mL of the finished water-reducing agent sample, dilute it with distilled water to 100 mL, shake it well, and then filter it through a 0.22 μm filter membrane to remove impurities before use.

[0011] A further technical solution is that the concentrations of the series of mixed standard solutions in step 1 are 5 mg / L, 25 mg / L, 50 mg / L, 100 mg / L, 250 mg / L, 625 mg / L, 1250 mg / L, and 2500 mg / L, respectively.

[0012] (3) Due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. Existing technologies only indirectly determine the quality of polycarboxylate superplasticizers through solid content and traditional concrete performance tests, without conducting quantitative detection of their key chemical components (macromonomers, triterpenoid saponins, etc.) or establishing a correlation between key components and water reduction rate. This invention, for the first time, utilizes the characteristic that the chemical components of polycarboxylate superplasticizers can be easily separated by polarity, combining liquid chromatography with evaporative light scattering detection technology to achieve quantitative detection of key components of the superplasticizer and rapid calculation of water reduction rate. This breaks through the limitations of traditional detection modes and fills the technical gap in accurate and rapid detection of polycarboxylate superplasticizers.

[0013] 2. This invention innovatively establishes standard curves and water reduction rate regression equations for macromonomers and triterpenoid saponins, integrating quantitative component detection with water reduction rate calculation to form a complete rapid detection system of "component detection - water reduction rate calculation - quality judgment". At the same time, through spiked recovery rate, repeatability and stability tests, the accuracy and reliability of the detection method are ensured, solving the problems of single indicators and insufficient accuracy of existing detection technologies.

[0014] 3. This invention completely replaces the time-consuming and labor-intensive traditional concrete workability test, shortening the water-reducing agent testing cycle from several hours or even days in the traditional method to about 20 minutes, significantly improving testing efficiency and adapting to the needs of rapid testing and batch testing on engineering sites; at the same time, it can establish the content of each component and water reduction rate benchmark when the product first arrives on site, realizing the daily and routine monitoring of water-reducing agent quality, changing the status quo of existing technology that can only conduct one-time testing upon arrival on site and cannot achieve full-process quality control.

[0015] 4. The testing method of this invention is simple to operate, accurate and efficient, and does not require complex large-scale equipment, making it suitable for various scenarios such as engineering sites and production enterprises. By accurately determining the quality of water-reducing agents, it can effectively prevent unqualified products from entering the project, ensuring the quality of concrete projects and the durability of structures. At the same time, it reduces the raw material loss and time costs caused by traditional testing, thereby reducing the cost of project quality control. In addition, the promotion and application of this invention can improve the quality control standards of polycarboxylate superplasticizers and promote the standardization and high-quality development of the water-reducing agent industry. Attached Figure Description

[0016] Figure 1 This is a fitted curve showing the relationship between the percentage of macromonomers and triterpenoid saponins in the polymer and the water reduction rate. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0018] like Figure 1 As shown.

[0019] Example: 1. Preparation 1.1 Experimental Instruments and Reagents: Liquid chromatograph (equipped with evaporative light scattering detector), C18 reversed-phase column (4.6mm×250mm, 5μm), electronic balance (accuracy 0.0001g), ultrasonic cleaner, centrifuge, 0.22μm filter membrane; white sugar, citric acid monohydrate, macromonomer (polyethylene glycol monomethyl ether acrylate), acrylic acid, triterpenoid saponins, sodium gluconate, sodium thiosulfate, sodium metabisulfite, sodium bisulfite (all analytical grade), distilled water, and three sets of commercially available polycarboxylate-based high-performance water-reducing agent samples (numbered 1#, 2#, and 3#).

[0020] 1.2 Optimization of chromatographic conditions: The liquid chromatography parameters were set as follows: mobile phase was methanol-water solution (gradient elution: 0–5 min, methanol volume fraction 30%; 5–15 min, methanol volume fraction 30%–80%; 15–20 min, methanol volume fraction 80%–30%), flow rate was 1.0 mL / min, column temperature was 32℃, drift tube temperature of evaporative light scattering detector was 85℃, and carrier gas flow rate was 2.2 L / min, to ensure clear separation and no interference of chromatographic peaks of each standard substance.

[0021] Implementation steps 2.1 Preparation of standard solutions Accurately weigh each standard substance, dissolve and dilute with distilled water to prepare a series of mixed standard solutions with concentrations of 5 mg / L, 25 mg / L, 50 mg / L, 100 mg / L, 250 mg / L, 625 mg / L, 1250 mg / L and 2500 mg / L respectively. Shake well and let stand for 30 minutes for later use. 2.2 Standard Curve Fitting The prepared series of mixed standard solutions were injected one by one into the liquid chromatograph, and detected under optimized chromatographic conditions. The peak area of ​​each target substance was recorded. With peak area (y) as the ordinate and mass concentration (x) as the abscissa, the standard curve was fitted using the least squares method. The standard curve equation and linear range of the key substances are as follows: Large monomer: y=0.0922x+81.131, R²=0.9965, linear range 25mg / L~2500mg / L; Triterpenoid saponins: y=1.3515x+4.045, R²=0.9998, linear range 5mg / L~2500mg / L; White sugar: y=0.1028x-7.3411, R²=0.9999, linear range 50mg / L~1500mg / L.

[0022] The linear correlation coefficients of each standard curve all satisfy R² ≥ 0.996, and can be used for quantitative detection.

[0023] 2.3 Quantitative Detection of Key Components in Water-Reducing Agent Samples Twelve groups of polycarboxylate superplasticizer finished product samples were taken, 1 mL of each, diluted with distilled water to 100 mL, shaken well, and filtered through a 0.22 μm filter membrane to remove impurities. The treated sample solutions were injected into a liquid chromatograph and detected under the same chromatographic conditions. Based on the peak elution time, the peak areas corresponding to macromonomers and triterpenoid saponins were determined. Substituting these values ​​into the corresponding standard curve equation, the mass concentrations of macromonomers and triterpenoid saponins in each group of samples were calculated. The results are shown in Table 1 below. Table 1. Detection results of key component concentrations (mg / L) in each sample group Sample number Large monomer concentration Triterpenoid saponin concentration Total concentration 1# 850 120 970 2# 920 135 1055 3# 880 125 1005 4# 865 115 980 5# 825 130 955 6# 1105 145 1250 7# 1010 135 1145 8# 951 120 1071 9# 878 120 998 10# 882 130 1012 11# 829 125 954 12# 875 115 990 2.4 Reliability Verification of the Detection Method 2.4.1 Spike recovery test: Low, medium and high concentrations of macromonomers and triterpenoid saponin standards were added to sample #1, and the samples were detected under the same chromatographic conditions. The spike recovery rate was calculated. The results showed that the spike recovery rate was 90.2% to 110.8%, which met the accuracy requirements for quantitative detection. 2.4.2 Repeatability and stability tests: Repeatability tests (6 tests on the same day) and stability tests (1 test per day for 5 consecutive working days) were conducted on sample #2. The relative standard deviations were calculated. The results showed that the relative standard deviation of the repeatability test was 2.1% and the relative standard deviation of the stability test was 3.2%, both ≤3.6%, indicating that the repeatability and stability of the detection method are excellent.

[0024] 2.5 Rapid Calculation of Water Reduction Rate Substituting the total concentrations (converted to mass fraction%) of macromonomers and triterpenoid saponins of each group of samples in Table 1 into the regression equation Y = 1.098X + 6.8588 (R² = 0.9984), the water reduction rate of each group of samples was calculated. Simultaneously, the actual water reduction rate of each group of samples was determined using traditional concrete workability tests for comparison and verification. The results are shown in Table 2 below. Table 2 Comparison of rapid calculation and actual measurement results of water reduction rate (%) Sample number Quickly calculate water reduction rate / % Actual measured water reduction rate / % deviation / % 1# 17.5 17.3 0.2 2# 18.4 18.7 -0.3 3# 17.9 18.0 -0.1 4# 17.6 17.4 0.2 5# 17.3 17.2 0.1 6# 20.6 20.9 -0.3 7# 19.4 19.1 0.3 8# 18.6 18.4 0.2 9# 17.8 17.7 0.1 10# 18.0 17.7 0.3 11# 17.3 17.5 -0.2 12# 17.7 17.8 -0.1 As shown in Table 2, the water reduction rate calculated by the present invention deviates very little from the traditional test results, both within ±0.3%, indicating that the rapid water reduction rate calculation method is accurate and reliable.

[0025] 2.6 Quality Judgment Based on sample #1, a quality judgment standard for this batch of water-reducing agent was established: macromonomer concentration 800-900 mg / L, triterpenoid saponin concentration 110-130 mg / L, and water reduction rate 17.0%-18.0%. According to this standard, the concentration of key components and water reduction rate of samples #2 and #3 are within the qualified range, and they are judged to be qualified products.

[0026] 3. Implementation Conclusions This embodiment demonstrates that the rapid detection method for polycarboxylate-based high-performance water-reducing agents of the present invention can complete the quantitative detection of key components and the calculation of water reduction rate in approximately 20 minutes. The spiked recovery rate is 90.2%–110.8%, the relative standard deviation is ≤3.6%, and the water reduction rate calculation deviation is ≤±0.2%. The accuracy and efficiency of the detection are significantly better than traditional detection methods. This method is simple to operate, highly practical, and can realize the daily monitoring of water-reducing agent quality, effectively ensuring the quality of concrete projects, reducing management and control costs, and can be widely applied to the production quality control of polycarboxylate-based high-performance water-reducing agents and the on-site raw material testing in engineering projects.

[0027] Once the concentration of macromonomers and triterpenoid saponins exceeds 22%-25%, it will no longer be applicable because the linear relationship is no longer valid. Currently, most polycarboxylate superplasticizers on the market have macromonomer and triterpenoid saponin concentrations below 22%-25%.

[0028] The above description is merely a preferred embodiment of the present invention.

Claims

1. A rapid method for quantifying key components and detecting water reduction rate of polycarboxylate superplasticizers based on liquid chromatography, characterized in that, Includes the following steps: Step 1: Preparation of standard solutions: Select white sugar, citric acid monohydrate, macromonomer, acrylic acid, triterpenoid saponins, sodium gluconate, sodium thiosulfate, sodium metabisulfite, and sodium bisulfite as standard substances, and prepare a series of mixed standard solutions of various concentrations respectively. Step 2: Standard curve fitting: 2.1 Optimization of chromatographic conditions: Set the detection parameters for liquid chromatography, and use an evaporative light scattering detector to optimize the mobile phase ratio, flow rate, column temperature and detection wavelength; 2.2 Chromatographic detection and curve fitting: Using the optimized chromatographic conditions, the series of mixed standard solutions prepared in step 1 were analyzed one by one by chromatographic analysis. The peak area (y) of each target substance was used as the ordinate and the mass concentration (x) of the corresponding substance was used as the abscissa. The least squares method was used to fit the working curve to obtain the standard curve equation and linear range of each target substance. 2.3 Key curve confirmation: Confirm the standard curve equations for macromonomers, triterpenoid saponins, and white sugar, and ensure that their linear correlation coefficient R² ≥ 0.996, meeting the requirements for quantitative detection; Step 3: Quantitative detection of key components in water-reducing agent samples: 3.1 Sample pretreatment: Take the finished sample of polycarboxylate-based high-performance water-reducing agent, dilute and filter it to prepare a sample solution that meets the requirements of chromatographic detection; 3.2 Sample Chromatographic Detection: Under the same chromatographic conditions optimized in step 2, the sample solution was subjected to chromatographic detection to obtain the evaporative light scattering detector chromatogram of the finished water-reducing agent; 3.3 Component concentration calculation: Based on the elution time sequence in the chromatogram, determine the corresponding chromatographic peaks of macromonomers and triterpenoid saponins, read their peak areas, substitute the peak areas into the corresponding standard curve equation obtained in step 2, and calculate the mass concentration of macromonomers and triterpenoid saponins in the finished water-reducing agent. Step 4: Quick calculation of water reduction rate: 4.1 Regression Equation Establishment: Based on the least squares method, the measured data of macromonomers and total concentrations of triterpenoid saponins and water reduction rate of multiple water-reducing agent samples were fitted to establish a regression equation between water reduction rate (Y) and total concentrations of macromonomers and triterpenoid saponins (X): Y = 1.098X + 6.8588 (R² = 0.9984), where Y is the water reduction rate (%) and X is the total concentration of macromonomers and triterpenoid saponins (%). 4.2 Water reduction rate calculation: Substitute the total concentration of macromonomers and triterpenoid saponins in the finished water-reducing agent calculated in step 3 into the above regression equation to quickly calculate the water reduction rate of the finished water-reducing agent; 4.3 Quality Judgment: Combining the quantitative detection results of macromonomers and triterpenoid saponins with the calculated water reduction rate, and referring to the component content and water reduction rate benchmark indicators established when the product first entered the market, the quality of the water-reducing agent product is quickly judged.

2. The method for rapid detection of key components and water reduction rate of polycarboxylate superplasticizers based on liquid chromatography according to claim 1, characterized in that, After step 3, the reliability of the detection method is verified, including spike recovery tests and repeatability and stability tests. Spike recovery test: Different concentrations of standard substances were added to the finished water-reducing agent sample, and the samples were tested under the same chromatographic conditions. The spike recovery rate was calculated to verify the accuracy of the detection method. The spike recovery rate was required to be controlled between 90.2% and 110.8%. Repeatability and stability testing: On the same day and different working days, the same water-reducing agent sample is repeatedly tested under the same chromatographic conditions. The relative standard deviation (RSD) is calculated to verify the repeatability and stability of the test method. The relative standard deviation is required to be ≤3.6%.

3. The method for quantitative determination of key components and rapid detection of water reduction rate of polycarboxylate superplasticizer based on liquid chromatography according to claim 1, characterized in that, The optimized liquid chromatography conditions in step 2 are as follows: a C18 reversed-phase column is used, the mobile phase is methanol-water solution, gradient elution is used, the flow rate is controlled at 0.8-1.2 mL / min, the column temperature is set at 30-35℃, the drift tube temperature of the evaporative light scattering detector is 80-90℃, and the carrier gas flow rate is 2.0-2.5 L / min.

4. The method for quantitative determination of key components and rapid detection of water reduction rate of polycarboxylate superplasticizer based on liquid chromatography according to claim 1, characterized in that, The specific method for sample pretreatment in step 3 is as follows: Take 1 mL of the finished water-reducing agent sample, dilute it with distilled water to 100 mL, shake well, and then filter it through a 0.22 μm filter membrane to remove impurities before use.

5. The method for rapid detection of key components and water reduction rate of polycarboxylate superplasticizers based on liquid chromatography according to claim 1, characterized in that, The concentrations of the series of mixed standard solutions in step 1 are 5 mg / L, 25 mg / L, 50 mg / L, 100 mg / L, 250 mg / L, 625 mg / L, 1250 mg / L, and 2500 mg / L, respectively.

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