An oral solution of alendronate sodium and a system for its detection and characterization

Abstract

The application relates to an oral alendronate sodium solution and a detection and characterization system thereof, and belongs to the fields of pharmaceutical preparations and analytical chemistry. The oral solution comprises an alendronate sodium active ingredient and specific excipients, and is characterized in that the contents of phosphate and phosphite are lower than 0.20 ug / mL, and the solution has an ultra-low impurity attribute. The application provides a robust preparation process, a high-precision ion chromatography-conductivity detection method, and a complete verification and characterization system. The method has strong specificity, high precision and a wide linear range, and overcomes the defects of inaccurate detection and unstable process in the prior art. The overall scheme realizes high batch consistency of the product, improves safety, meets the clinical needs of osteoporosis treatment, and has significant technical advantages and market competitiveness.

Description

Technical Field

[0001] This invention relates to the fields of pharmaceutical preparations and analytical chemistry, specifically to an alendronate sodium oral solution and its detection and characterization system. Background Technology

[0002] As an effective treatment for osteoporosis, the quality and safety of alendronate sodium oral solution are of paramount importance. Osteoporosis is a common metabolic bone disease, particularly prevalent among middle-aged and elderly individuals. Alendronate sodium exerts its therapeutic effect by inhibiting bone resorption, and its oral solution formulation has garnered significant attention due to its convenience and high bioavailability. Although this formulation has been marketed abroad, there are currently no products available in the domestic Chinese market, indicating a clear clinical need. Developing a high-quality, stable alendronate sodium oral solution would not only meet the treatment needs of domestic patients but also possess significant market value and social benefits.

[0003] In drug development, in addition to meeting legal quality standards, in-depth studies are typically conducted to comprehensively characterize the product's quality attributes and verify the robustness and consistency of the manufacturing process. These studies are crucial for demonstrating the scientific validity of high-quality standards, especially for generic drugs or new dosage forms. Phosphates and phosphites can serve as sensitive indicators for assessing the risk of introducing potential inorganic impurities during the manufacturing process. These trace components typically originate from raw materials, excipients, or the production environment, and their levels directly reflect the cleanliness and controllability of the process. Continuous monitoring of these components provides vital data support for process understanding, optimization, and validation, thereby ensuring batch-to-batch consistency and long-term safety of the product.

[0004] However, an analytical method for accurately and reliably determining such trace components in the oral solution is lacking in the art. Chinese Patent Publication No. CN120948651A discloses a high-performance liquid chromatography-electrospray ionization detector (HPLC-CAD) method for detecting phosphates and phosphites. However, this method suffers from technical deficiencies: poor precision, insufficient sensitivity, and a complex linear model, leading to large fluctuations and low reliability in the detection results. Using such an unrobust analytical tool makes it impossible to obtain high-quality, reproducible data in in-depth process studies and product characterization, thus hindering the scientific and reliable assessment of process capabilities and the establishment of a comprehensive and in-depth quality profile for the product.

[0005] Therefore, there is an urgent need in this field for a completely new solution that not only produces qualified products, but also provides a set of analytical techniques for in-depth characterization and research. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide an alendronate sodium oral solution, as well as a detection and characterization system that can determine its impurity content with high precision and reliability.

[0007] The technical solution adopted by the present invention to solve its technical problem is: an alendronate sodium oral solution, characterized in that the oral solution contains alendronate sodium as an active ingredient and excipients; the excipients include methylparaben, propylparaben, anhydrous citric acid, sodium citrate and sodium saccharin, and the content of phosphate and phosphite in the oral solution is both less than 0.20 μg / mL.

[0008] First, the active ingredient, alendronate sodium, ensures the efficacy in treating osteoporosis, while the excipient combination enhances the chemical stability of the solution and oral compliance, avoiding the introduction of impurities due to excipient interactions. The ultra-low impurity levels of phosphate and phosphite (below 0.20 μg / mL) reflect an extremely low risk of inorganic impurities being introduced during the manufacturing process and provide a clear standard for quality control.

[0009] Preferably, in the long-term stability test, the change in phosphate and phosphite content of the oral solution is less than 20% after being placed at room temperature for 37.5 hours.

[0010] A stability test at room temperature for 37.5 hours showed that the impurity content changed by less than 20%, indicating that the product maintains ultra-low impurity properties during storage and transportation, reducing the risk of degradation due to time or environmental factors. This stability not only ensures the product's quality reliability within its shelf life but also reduces warehousing and logistics costs, as it eliminates the need for stringent refrigeration conditions. From a clinical perspective, this characteristic ensures accurate patient dosage, avoids potential side effects from impurity accumulation, and thus enhances treatment safety and patient trust.

[0011] Specifically, the preparation method of the oral solution includes the following steps: (a) Add purified water to the mixing tank to prepare 70%~85% of the total volume; (b) Under the conditions of stirring frequency of 40~60Hz and temperature of 70℃~80℃, add the prescribed amounts of methylparaben and propylparaben, stir for 40min~60min until completely dissolved, and then cool to below 40℃; wherein the mass concentration of methylparaben is 0.01%~0.1% and the mass concentration of propylparaben is 0.01%~0.1%; (c) Adjust the stirring frequency to 30Hz~50Hz, add the prescribed amounts of sodium alendronate, anhydrous citric acid, sodium citrate, and sodium saccharin, and stir for 20min~40min until completely dissolved; wherein the mass concentration of sodium alendronate is 0.5%~1.5%, the mass concentration of anhydrous citric acid is 0.1%~0.5%, the mass concentration of sodium citrate is 0.5%~2.0%, and the mass concentration of sodium saccharin is 0.01%~0.1%; (d) Add purified water to the total volume, stir at a stirring frequency of 30Hz~50Hz for 20min~40min to mix evenly, and take a sample for intermediate product testing; (e) The drug solution is filtered through a 0.45μm polypropylene filter into a filling buffer tank, and then filled immediately after filtration to obtain the final oral solution.

[0012] A purified water volume range of 70%–85% avoids over-dilution or concentration. Frequent stirring and temperature control promote uniform dissolution and thermal stability of excipients, reducing impurity formation caused by localized overheating. The component concentration range is set based on pharmacokinetic requirements, ensuring efficacy while avoiding waste. A buffer system maintains the pH within an appropriate range (approximately 4.0–5.0), enhancing the chemical stability of the active ingredient. Intermediate testing and filtration steps further remove particulate impurities, ensuring the sterility and purity of the final product.

[0013] This method can stably output low-impurity products in large-scale production, reduce scrap rates, improve production efficiency, and provide clear guidelines for process validation, meeting GMP requirements.

[0014] A method for detecting the phosphate content in the above-mentioned alendronate sodium oral solution, employing ion chromatography-conductivity detection, includes the following steps: (1) Preparation of the test solution; (2) Inject the test solution into an ion chromatography system equipped with an anion exchange column; (3) Isocratic rinsing was performed using potassium hydroxide solution; (4) The phosphate content is detected by a conductivity detector and quantified based on the chromatographic peak area, wherein the anion exchange column is a Dionex RFIC IonPac AS11-HC 4mm x 250mm column.

[0015] Compared to existing HPLC-CAD techniques, ion chromatography-conductivity detection offers higher specificity, effectively eliminating interference from complex matrices in oral solutions and avoiding false positives. Isocratic elution simplifies the procedure and improves analytical efficiency, while the Dionex column ensures resolution, resulting in sharp phosphate peaks and stable retention times. This method maintains good linearity at the limit of quantitation (LOQ) of 0.20 μg / mL, with a precision RSD of less than 5%, significantly better than the volatility of existing techniques, providing reliable data support for process studies. Furthermore, this method is easy to standardize and transfer between different laboratories, reducing method validation time and accelerating product development cycles. It also enables real-time monitoring of trace impurities, facilitating early detection of process deviations and improving overall production robustness.

[0016] Preferably, the mass concentration of potassium hydroxide solution in the isocratic rinsing step (3) is in the range of 33 mmol / L to 37 mmol / L, and the rinsing time is maintained at 19 min to 22 min.

[0017] The optimized range of potassium hydroxide concentration and rinsing time takes into account instrument fluctuations and operational errors, ensuring that the method remains stable even with minor parameter changes and avoiding detection failures due to harsh conditions.

[0018] A method for detecting the phosphite content in the above-mentioned alendronate sodium oral solution, characterized by employing ion chromatography-conductivity detection, the method comprising the following steps: preparing a test solution; injecting the test solution into an ion chromatography system equipped with an anion exchange column; performing gradient elution with potassium hydroxide solution, wherein the gradient program is as follows: within 0 to 20.0 min, the ratio of water to potassium hydroxide in the mobile phase linearly changes from 83:17 to 0:100, and maintains this ratio until 25.0 min, then returns to the initial ratio, and equilibrates until 45.0 min; detecting by a conductivity detector, and quantifying the phosphite content based on the chromatographic peak area, wherein the anion exchange column is a Dionex RFIC IonPacAS11-HC 4mm x 250mm column.

[0019] The gradient program effectively separates phosphite from coexisting ions, overcoming the co-elution problem that may occur with isocratic elution, thus improving the accuracy and specificity of detection. The total run time of 45.0 min, including the equilibration phase, ensures system reproducibility and avoids residual effects. It supports monitoring of process degradation products, such as providing early warning of impurity trends in accelerated stability tests, thereby improving product lifecycle management.

[0020] Preferably, the mass concentration of potassium hydroxide solution in the gradient rinsing is in the range of 48 mmol / L to 52 mmol / L.

[0021] This concentration range ensures the smoothness and repeatability of gradient elution, avoiding baseline noise caused by excessively high concentrations or incomplete separation caused by excessively low concentrations.

[0022] A method for verifying the ultra-low impurity properties of alendronate sodium oral solution, characterized in that the method comprises the following steps: (A) Provide the above-mentioned alendronate sodium oral solution; (B) The phosphate content was determined using the above-described ion chromatography method; (C) The phosphite content was determined using the above-described ion chromatography method; (D) Based on the measurement results, it was confirmed that the contents of phosphate and phosphite in the oral solution were both less than 0.20 μg / mL, thus verifying its ultra-low impurity properties.

[0023] This validation method demonstrates the systematic and scientific nature of the validation process. By organically combining oral solution, phosphate, and phosphite detection methods, a closed-loop validation system is formed, ensuring the traceability and objectivity of ultra-low impurity properties. This method can not only be used for routine quality control but also provide rapid evaluation during process changes or scale-up production, reducing validation cycles and costs.

[0024] A system for characterizing impurity levels in alendronate sodium oral solution, characterized in that the system comprises the following components: (I) The above-mentioned alendronate sodium oral solution; (II) The above-mentioned ion chromatography detection method used to define phosphate content; (III) The above-mentioned ion chromatography detection method for defining phosphite content; wherein the combined application of the system characterizes the impurity level of the oral solution and uses the determination results as the basis for evaluating process robustness and product quality.

[0025] This comprehensive characterization system enables all-round monitoring of product quality. The system seamlessly links the product entity (I) with high-precision testing methods (II and III), providing a complete data chain from production to testing, ensuring real-time visualization and historical traceability of impurity levels. This integrated design can quickly identify process weaknesses, such as predicting impurity sources through trend analysis, guiding process optimization. In supply chain management, it supports batch release and audit trails, reducing quality risks. Simultaneously, the system is easily scalable and adaptable to other impurity indicators, enhancing the versatility of the technology platform. It also strengthens product differentiation competitiveness, providing technical support for market promotion.

[0026] Preferably, the system further includes a data verification module for performing precision and accuracy analysis on the detection results, wherein the precision RSD is less than 5% and the accuracy recovery rate is in the range of 90% to 110%.

[0027] The data validation module enhances the reliability and compliance of the system. Strict standards, including a precision RSD of less than 5% and an accuracy recovery rate of 90%-110%, ensure the statistical significance of the test data and avoid misjudgments caused by random errors.

[0028] Compared with existing technologies, this invention has the following advantages: It successfully overcomes the shortcomings of existing HPLC-CAD methods in detecting trace inorganic impurities in alendronate sodium oral solution, such as poor precision, insufficient sensitivity, and complex linear models. By innovatively integrating ultra-low impurity oral solution products, robust preparation processes, high-precision ion chromatography-conductivity detection methods, and a complete characterization system, it achieves superior performance with phosphate and phosphite contents both below 0.20 μg / mL. This not only improves product safety and batch-to-batch consistency, reducing the risks of long-term use, but also ensures production robustness and reduces impurity introduction through process optimization. Simultaneously, the highly sensitive detection method provides reliable data support, accelerates the approval process, and meets the clinical needs of the domestic market. Overall, this invention constructs a closed-loop technical solution, setting a new standard for drug quality control, and possesses both practicality and commercial competitiveness. Attached Figure Description

[0029] Figure 1 Spectrum of blank excipient solution in phosphate method.

[0030] Figure 2 Phosphoric acid localization solution spectrum.

[0031] Figure 3 Spectrum of blank excipient solution in the phosphite method.

[0032] Figure 4 Spectrum of phosphorous acid reference solution.

[0033] Figure 5 Spectrum of phosphorous acid localization solution.

[0034] Figure 6 Phosphoric acid localization solution spectrum.

[0035] Figure 7 Trend graph of phosphoric acid linearity test.

[0036] Figure 8 Trend graph of linearity of phosphorous acid.

[0037] Figure 9 Chromatogram of phosphoric acid reference solution.

[0038] Figure 10 Chromatogram of a blank phosphate sample solution.

[0039] Figure 11 Chromatogram of solution recovery rate at the limit of quantitation of phosphate.

[0040] Figure 12 Chromatogram of a solution with 100% recovery of phosphoric acid.

[0041] Figure 13 Chromatogram of a phosphoric acid solution with 150% recovery.

[0042] Figure 14 Chromatogram of phosphorous acid reference solution.

[0043] Figure 15 Chromatogram of blank phosphite sample solution.

[0044] Figure 16 Chromatogram of solution recovery at the limit of quantitation of phosphorous acid.

[0045] Figure 17 Chromatogram of a solution with 100% recovery of phosphorous acid.

[0046] Figure 18 Chromatogram of a solution with 150% recovery of phosphorous acid.

[0047] Figure 19 Chromatogram of phosphate repeatability test solution.

[0048] Figure 20 Chromatogram of phosphate spiked repeatable test solution.

[0049] Figure 21 Chromatogram of the test solution for intermediate precision of phosphate.

[0050] Figure 22 Chromatogram of repeatable test solution of phosphite.

[0051] Figure 23 Chromatogram of repeatable test solution spiked with phosphite.

[0052] Figure 24 Chromatogram of the intermediate precision test solution for phosphite.

[0053] Figure 25 Chromatogram of stability of phosphate reference solution - 0h.

[0054] Figure 26 Chromatogram of the stability of phosphate reference solution - 25h.

[0055] Figure 27 Chromatogram of stability of phosphate reference stock solution - 0h.

[0056] Figure 28 Chromatogram of the stability of phosphate reference stock solution - 45.5h.

[0057] Figure 29 Chromatogram of the stability of the phosphate-spiked test solution - 0h.

[0058] Figure 30 Chromatogram of the stability of the phosphate-spiked test solution -37.5h.

[0059] Figure 31 Chromatogram of stability of phosphite reference solution - 0h.

[0060] Figure 32 Chromatogram of stability of phosphite reference solution - 43.5h.

[0061] Figure 33 Chromatogram of stability of phosphite reference stock solution - 0h.

[0062] Figure 34 Chromatogram of the stability of the phosphite reference standard stock solution - 46h.

[0063] Figure 35 Chromatogram of stability of phosphite test solution - 0h.

[0064] Figure 36 Chromatogram of the stability of the phosphite test solution - 40.5h.

[0065] Figure 37 Chromatogram of phosphate solution under durable chromatographic conditions - standard conditions.

[0066] Figure 38 Phosphate chromatography conditions durable for test solution chromatograms - standard conditions.

[0067] Figure 39 Phosphate chromatography conditions durable blank excipient solution chromatogram - standard conditions.

[0068] Figure 40 Chromatogram of phosphate standard solution under durable chromatographic conditions - column temperature 25°C.

[0069] Figure 41 Phosphate chromatography conditions are durable. Chromatogram of test solution - column temperature 25℃.

[0070] Figure 42 Phosphate chromatography conditions durable blank excipient solution chromatogram - column temperature 25℃.

[0071] Figure 43 Chromatogram of phosphate standard solution under durable chromatographic conditions - column temperature 35℃.

[0072] Figure 44 Phosphate chromatography conditions are durable. Chromatogram of test solution - column temperature 35℃.

[0073] Figure 45 Phosphate chromatography conditions durable blank excipient solution chromatogram - column temperature 35℃.

[0074] Figure 46 Chromatogram of phosphate chromatographic condition durable reference solution - 33 mmol / L potassium hydroxide.

[0075] Figure 47 Phosphate chromatography conditions are durable. Chromatogram of test solution - 33 mmol / L potassium hydroxide.

[0076] Figure 48 Chromatogram of phosphate chromatographic conditions with durable blank excipient solution - 33 mmol / L potassium hydroxide.

[0077] Figure 49 Chromatogram of phosphate chromatographic condition durable reference solution - 37 mmol / L potassium hydroxide.

[0078] Figure 50 Phosphate chromatography conditions are durable. Chromatogram of test solution - 37 mmol / L potassium hydroxide.

[0079] Figure 51 Chromatogram of phosphate chromatographic conditions with durable blank excipient solution - 37 mmol / L potassium hydroxide.

[0080] Figure 52 Chromatogram of phosphite solution under durable chromatographic conditions - standard conditions.

[0081] Figure 53 Phosphite chromatography conditions durable chromatogram of test solution - standard conditions.

[0082] Figure 54 Chromatogram of phosphite solution under durable blank excipient solution - standard conditions.

[0083] Figure 55 Chromatogram of phosphite solution under durable chromatographic conditions - column temperature 25℃.

[0084] Figure 56 Phosphite chromatography conditions are durable. Chromatogram of test solution - column temperature 25℃.

[0085] Figure 57 Chromatographic conditions for phosphite: durable blank excipient solution chromatogram - column temperature 25℃.

[0086] Figure 58 Chromatogram of phosphite solution under durable chromatographic conditions - column temperature 35℃.

[0087] Figure 59 Phosphite chromatography conditions are durable. Chromatogram of test solution - column temperature 35℃.

[0088] Figure 60 Chromatographic conditions for phosphite: durable blank excipient solution chromatogram - column temperature 35℃.

[0089] Figure 61 Chromatogram of phosphite chromatographic condition durable reference solution - 48 mmol / L potassium hydroxide.

[0090] Figure 62 Phosphite chromatography conditions are durable. Chromatogram of test solution - 48 mmol / L potassium hydroxide.

[0091] Figure 63 Chromatogram of phosphite under durable blank excipient solution - 48 mmol / L potassium hydroxide.

[0092] Figure 64 Chromatogram of phosphite chromatographic condition durable reference solution - 52 mmol / L potassium hydroxide.

[0093] Figure 65 Phosphite chromatography conditions are durable. Chromatogram of test solution - 52 mmol / L potassium hydroxide.

[0094] Figure 66 Phosphite chromatography conditions durable blank excipient solution chromatogram - 52 mmol / L potassium hydroxide Detailed Implementation The technical effects of the present invention are described in detail below through specific embodiments and comparative experiments. In the experiments, "Comparative Example 1" uses the HPLC-CAD method described in the prior art (publication number CN120948651A) in the analytical method comparison section.

[0095] I. Preparation of the product of this invention Example 1: Preparation of 1L alendronate sodium oral solution The preparation method of the oral solution includes the following steps: (a) Add 0.7 L of purified water to the mixing tank; (b) Under the conditions of stirring frequency of 40 Hz and temperature of 70 °C, 0.1 g of methylparaben and 0.1 g of propylparaben were added respectively, and stirred for 40 min until completely dissolved, and then cooled to 39.9 °C; (c) Adjust the stirring frequency to 30Hz, add 5g sodium alendronate, 1g anhydrous citric acid, 5g sodium citrate and 1g sodium saccharin respectively, and stir for 20min until completely dissolved; (d) Add purified water to 1L, stir at 30Hz for 20min to mix evenly, and take a sample for intermediate product testing; (e) The drug solution was filtered through a 0.45 μm polypropylene filter into a filling buffer tank and filled immediately after filtration to obtain the final oral solution. The sample was recorded as S1.

[0096] Example 21: Preparation of L-Alendronate Sodium Oral Solution The preparation method of the oral solution includes the following steps: (a) Add 0.85 L of purified water to the mixing tank; (b) Under the conditions of stirring frequency of 60 Hz and temperature of 80 °C, add 1 g of methylparaben and 1 g of propylparaben respectively, stir for 60 min until completely dissolved, and then cool down to 35 °C. (c) Adjust the stirring frequency to 50Hz, add 15g sodium alendronate, 5g anhydrous citric acid, 20g sodium citrate and 1g sodium saccharin respectively, and stir for 40min until completely dissolved; (d) Add purified water to 1L, stir at 50Hz for 40min to mix evenly, and take a sample for intermediate product testing; (e) The drug solution was filtered through a 0.45 μm polypropylene filter into a filling buffer tank and filled immediately after filtration to obtain the final oral solution. The sample was recorded as S2.

[0097] Example 31: Preparation of L-Alendronate Sodium Oral Solution The preparation method of the oral solution includes the following steps: (a) Add 0.8 L of purified water to the mixing tank; (b) Under the conditions of stirring frequency of 50 Hz and temperature of 75 °C, add 0.5 g of methylparaben and 0.4 g of propylparaben respectively, stir for 50 min until completely dissolved, and then cool down to 38 °C; (c) Adjust the stirring frequency to 40Hz, add 10g sodium alendronate, 3g anhydrous citric acid, 10g sodium citrate and 0.5g sodium saccharin respectively, and stir for 30min until completely dissolved; (d) Add purified water to 1L, stir at 40Hz for 30min to mix evenly, and take a sample for intermediate product testing; (e) The drug solution was filtered through a 0.45 μm polypropylene filter into a filling buffer tank and filled immediately after filtration to obtain the final oral solution. The sample was recorded as S3.

[0098] II. Application and Comparison of the Characterization System of this Invention (Analytical Methods) 1. Exclusivity Experimental methods: To confirm the specificity of the method, blank excipient interference test and peak localization test were conducted respectively.

[0099] Blank excipient interference test: Prepare a blank excipient solution without active ingredients, inject and analyze it to examine whether there is interference at the retention time of the target analyte.

[0100] Peak localization test: Take the phosphate localization solution and the phosphite localization solution from the blank excipient interference test, mix them to prepare a mixed localization solution, and examine whether there is interference between phosphate and phosphite by comparing the retention times of phosphate and phosphite.

[0101] The method for measuring phosphate content, using ion chromatography-conductivity detection, includes the following steps: (1) Preparation of the test solution; (2) Inject the test solution into an ion chromatography system equipped with an anion exchange column; (3) Isocratic rinsing was performed using a potassium hydroxide solution with a mass concentration of 35 mmol / L for 20.0 min; (4) The phosphate content is detected by a conductivity detector and quantified based on the chromatographic peak area, wherein the anion exchange column is a Dionex RFIC IonPac AS11-HC 4mm x 250mm column.

[0102] The method for measuring phosphite content employs ion chromatography-conductivity detection, comprising the following steps: preparing a test solution; injecting the test solution into an ion chromatography system equipped with an anion exchange column; performing gradient elution with 50 mmol / L potassium hydroxide solution, wherein the gradient program is as follows: within 0 to 20.0 min, the ratio of water to potassium hydroxide in the mobile phase linearly changes from 83:17 to 0:100, and maintains this ratio until 25.0 min, then returns to the initial ratio, and equilibrates until 45.0 min; detecting the phosphite content using a conductivity detector, and quantifying the phosphite content based on the chromatographic peak area, wherein the anion exchange column is a Dionex RFIC IonPac AS11-HC 4mm x 250mm column.

[0103] Results and Discussion: Taking the product of Example 3 as an example, the test conditions are as follows: Blank excipient interference test (phosphate method validation): Blank excipient solution: Accurately measure 10 ml of blank excipient, place it in a 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0104] Phosphoric acid positioning solution: Accurately measure 1 ml of phosphate reference standard, place it in a 20 ml volumetric flask, dilute with water to the mark, and shake well.

[0105] Phosphoric acid reference solution: Take 100% solution from the linearity test.

[0106] Phosphorous acid positioning solution: Accurately measure 1 ml of phosphorous acid reference standard, place it in a 20 ml volumetric flask, dilute with water to the mark, and shake well.

[0107] Accurately measure 25 µl, inject it into the ion chromatograph, record the chromatogram, and the results are shown in Table 1. Figures 1-2 .

[0108] Table 1. Interference results of blank excipients Blank excipient interference test (validation of phosphite method): Blank excipient solution: Accurately measure 10 ml of blank excipient, place it in a 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0109] Phosphorous acid positioning solution: Take the stock solution from the linear term.

[0110] Phosphorous acid reference solution: Take 100% solution from the linearity test.

[0111] Phosphoric acid positioning solution: Accurately measure 0.5 ml of phosphoric acid reference standard, place it in a 10 ml volumetric flask, dilute with water to the mark, and shake well.

[0112] Accurately measure 25 µl, inject it into the ion chromatograph, record the chromatogram, and the results are shown in Table 2. Figures 3-4 .

[0113] Table 2. Interference Results of Blank Excipients The results showed that the blank excipient did not interfere with the detection of phosphate and phosphite.

[0114] Peak localization test (validation of phosphate method): Take 25 µl of the phosphoric acid localization solution and phosphorous acid localization solution from the blank excipient interference test, inject them into the ion chromatograph, record the chromatograms, and the results are shown in Table 3. Figure 5 .

[0115] Table 3. Peak localization results of phosphate and phosphite Take 25 µl of the phosphoric acid localization solution and phosphorous acid localization solution from the blank excipient interference test, inject them into the ion chromatograph, and record the chromatograms. The results are shown in Table 4. Figure 6 .

[0116] Table 4. Peak localization results of phosphate and phosphite The results showed that the retention time of the phosphorous acid peak relative to the phosphate peak was 0.47, which did not interfere with the phosphate determination; the retention time of the phosphate peak relative to the phosphorous acid peak was 1.84, which also did not interfere with the phosphite determination.

[0117] Comparative Example 1: The comparative document CN120948651A, in Example 2 of the specification, only describes that "the retention time of the target peak in the phosphoric acid and phosphorous acid positioning solutions is consistent with the retention time of the target peak in the spiked test sample solution." This document does not provide any data or chromatograms for blank excipient interference tests; therefore, whether its method can effectively eliminate excipient interference is an unverified risk.

[0118] Conclusion: This invention, through rigorous blank excipient interference testing, confirms the high specificity of the method in the complex matrix of alendronate sodium oral solution, effectively eliminating excipient interference and providing crucial assurance for accurate quantification. In contrast, the method in Comparative Example 1 lacks evidence regarding the elimination of excipient interference, and its specificity verification is insufficient.

[0119] 2. Linearity and Range Experimental method: Accurately weigh phosphate and phosphite reference standards, prepare a series of working solutions of different concentrations (covering the range from the limit of quantitation to 200% of the limit concentration), and inject them for analysis. Perform regression analysis on peak area (y) against concentration (x) to examine the linear relationship.

[0120] Results and Discussion: The sample from Example 3 was used for phosphate method verification: Linear stock solution: Accurately measure 1 ml of phosphate reference standard, place it in a 20 ml volumetric flask, dilute with water to the mark, and shake well.

[0121] Prepare linear solutions according to Table 5. Precisely measure 25 µl of both the limit of quantitation solution and the linear solution, inject them into the ion chromatograph, record the chromatograms, and plot peak area against concentration. Calculate the regression equation, correlation coefficient, and intercept using the least squares method. The results are shown in Tables 5-6. Figure 7 .

[0122] Table 5 Preparation of linear phosphate solutions Table 6 Results of Phosphate Linearity Test The results showed that within the range of quantitation limit to 200% of the limit concentration, the correlation coefficient r was greater than 0.990, indicating that the phosphate test method of this product had a good linear relationship.

[0123] Based on the results of linearity, precision, and accuracy tests, the validation range was determined to be from the limit of quantitation to 150% of the specified limit concentration.

[0124] Validation of the phosphite method: Linear stock solution: Accurately measure 1 ml of phosphorous acid reference standard, place it in a 20 ml volumetric flask, dilute with water to the mark, and shake well.

[0125] Prepare linear solutions according to Table 7. Precisely measure 25 µl of both the limit of quantitation (LOQ) solution and the linear solution, inject them into the ion chromatograph, record the chromatograms, and plot peak area against concentration. Calculate the regression equation, correlation coefficient, and intercept using the least squares method. The results are shown in Tables 7-8. Figure 8 .

[0126] Table 7 Preparation of linear solutions of phosphite Table 8 Results of the linearity test for phosphite The results showed that within the quantitation limit to limit concentration range of 200%, the correlation coefficient r was greater than 0.990, indicating that the linear relationship of the phosphite test method of this product was good.

[0127] Based on the results of linearity, precision, and accuracy tests, the validation range was determined to be from the limit of quantitation to 150% of the specified limit concentration.

[0128] In summary: for phosphate in the range of 0.2–4.0 μg / mL, the regression equation is y = 4.2211x - 0.2336, with a correlation coefficient (r) of 0.9997; for phosphite in the range of 0.2–4.0 μg / mL, the regression equation is y = 5.7121x - 0.7257, with a correlation coefficient (r) of 0.9989. This indicates that the present invention exhibits an excellent linear relationship between concentration and response value over a wide range of two orders of magnitude. The model is simple and clear, conforming to the conventions and requirements of conventional chromatographic quantitative analysis.

[0129] Comparative Example 1 For phosphate concentrations ranging from 0.2452 to 1.9618 μg / mL, the regression equation is y = 0.0812x. 2 +0.0436x +0.0119, the correlation coefficient (r) is 0.9980; for phosphite in the range of 0.2476~1.9804 μg / mL, the regression equation is y=0.0115x 2 +0.1369x -0.0055, the correlation coefficient (r) is 0.9993.

[0130] The methods in Comparative Example 1 all exhibit a quadratic (parabolic) relationship within the specified range. This indicates that the detector response exhibits significant nonlinear characteristics in this application scenario. Although the correlation coefficient is acceptable, the complex model introduces additional computational errors and uncertainties, and is less convenient, intuitive, and robust than a linear model in quantitative calculations.

[0131] in conclusion: 1) Linear Model Comparison: This invention employs a simple and stable linear model, while Comparative Example 1 relies on a more complex quadratic curve model. This reflects that the ion chromatography-conductivity detection system used in this invention has a more linear response mechanism than the HPLC-CAD system used in the other example when detecting such ions.

[0132] 2) Linearity range: The present invention maintains good linearity over a wider concentration range (0.2-4.0 μg / mL), indicating that the method has a wider applicability range.

[0133] 3) Method and effect: The linear model provided by this invention is better, more direct and more reliable. This is not only due to the difference in technical route, but also to the improvement of method simplicity and data reliability.

[0134] 3. Limit of Quantitation, Limit of Detection Test method: Validation of the phosphate method: Preparation of the limit of quantitation solution: Take the limit of quantitation solution under the linearity test.

[0135] Preparation of the limit of quantitation solution: Accurately measure 3 ml of the limit of quantitation solution, place it in a 10 ml volumetric flask, dilute with water to the mark, and shake well.

[0136] Accurately measure 25 µl of the solutions at the limit of quantitation and limit of detection, inject them into the ion chromatograph, and record the chromatograms. The results are shown in Tables 9 and 10.

[0137] Table 9 Results of Limits of Quantitation for Phosphate Table 10 Results of Phosphate Detection Limits The results showed that the signal-to-noise ratio of the phosphate limit solution was greater than 10, the signal-to-noise ratio of the detection limit solution was greater than 3, and the quantitation limit concentration was less than 50% of the specified limit, which met the acceptance criteria, indicating that the phosphate test method of this product has high sensitivity.

[0138] Validation of the phosphite method: Preparation of the limit of quantitation solution: Accurately measure 1 ml of the linear 2 solution under the linearity test, place it in a 10 ml volumetric flask, dilute with water to the mark, and shake well.

[0139] Preparation of the limit of quantitation solution: Accurately measure 3 ml of the limit of quantitation solution, place it in a 10 ml volumetric flask, dilute with water to the mark, and shake well.

[0140] Accurately measure 25 µl of the solutions at the limit of quantitation and limit of detection, inject them into the ion chromatograph, and record the chromatograms. The results are shown in Tables 11 and 12.

[0141] Table 11 Results of Limit of Quantitation for Phosphite Table 12 Results of Detection Limits for Phosphite The results showed that the signal-to-noise ratio of the limit of quantitation solution was greater than 10, the signal-to-noise ratio of the limit of detection solution was greater than 3, and the limit of quantitation concentration was less than 50% of the specified limit, which met the acceptance criteria, indicating that the phosphite testing method of this product has high sensitivity.

[0142] Results and Discussion: Table 13 Comparison of Limit of Quantitation and Limit of Detection Conclusion: 1. Sensitivity Comparison: The limits of quantitation and detection (LODs) of this invention for phosphates and phosphites are both lower than those of Comparative Example 1. This directly proves that the method of this invention has higher analytical sensitivity and can detect and quantify trace impurities in products earlier.

[0143] 2. Comparison of the rigor of method validation: Although Comparative Example 1 provides data for multiple LOQ solutions in its patent, the signal-to-noise ratio and peak area of ​​phosphate and phosphite solutions at the limit of quantitation level show significant fluctuations (phosphate s / n: 17-24, RSD=9%; phosphite s / n: 14-19, RSD=12%). This reflects the instability and poor reproducibility of its method near the sensitivity critical point. The dispersion of multiple data sets further confirms the technical defects of insufficient precision and narrow operating window in the low concentration region.

[0144] 4. Accuracy To assess the reliability of the data provided by the analytical method, we conducted a spiking recovery experiment to simulate the accuracy and precision of detection in a real sample matrix.

[0145] Test method: Validation of the phosphate method: Blank solution: Accurately measure 10 ml of this product and place it in a 25 ml volumetric flask. Dilute with water to the mark and shake well.

[0146] Recovery stock solution: Accurately measure 1 ml of phosphate reference standard, place it in a 20 ml volumetric flask, dilute with water to the mark, and shake well.

[0147] Limit of Quantitation (LOQ) Stock Solution: Accurately measure 1 ml of the recovery stock solution, place it in a 50 ml volumetric flask, dilute with water to the mark, and shake well.

[0148] Phosphoric acid reference solution: Accurately measure 1 ml of the recovery stock solution, place it in a 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0149] Prepare the recovery test solution according to Table 14. Accurately measure 25 µl each of the recovery test solution, reference solution, and blank solution, and inject them into the ion chromatograph separately, recording the chromatograms. Calculate the detection limit of phosphate using the external standard method, correcting with the blank solution, and calculate the recovery rate. The results are shown in Table 15. Figures 9-13 .

[0150] Table 14 Preparation of Phosphate Recovery Test Solutions Table 15 Results of Phosphate Recovery Test The results showed that the average recovery rate of phosphate was 106.40% and the RSD was 2.40% at the limit of quantitation concentration; at 100% and 150% concentrations, the average recovery rate of phosphate was 105.24% and the RSD was 4.87%, indicating that the method has high accuracy.

[0151] Validation of the phosphite method: Blank solution: Take the test sample solution from the repeatability test item.

[0152] Recovery rate stock solution: Take the linear stock solution under the linear term.

[0153] Limit of Quantitation (LOQ) Stock Solution: Accurately measure 1 ml of the recovery stock solution, place it in a 50 ml volumetric flask, dilute with water to the mark, and shake well.

[0154] Phosphorous acid reference solution: Take 100% solution from the linearity test.

[0155] Prepare the recovery test solution according to Table 16. Accurately measure 25 µl each of the recovery test solution, reference solution, and blank solution, and inject them into the ion chromatograph separately, recording the chromatograms. Calculate the detection amount of phosphorous acid using the external standard method, correcting with the blank solution, and calculate the recovery rate. The results are shown in Table 17. Figure 14 ~See Figure 18.

[0156] Table 16. Preparation of solutions for phosphite recovery rate test Table 17 Results of Phosphite Recovery Test The results showed that the average recovery rate of phosphite was 99.27% ​​and the RSD was 0.42% at the limit of quantitation concentration; at 100% and 150% concentrations, the average recovery rate of phosphite was 95.60% and the RSD was 4.15%, indicating that the method has high accuracy.

[0157] Comparative Example 1: At concentration levels of 50%, 100%, and 150%, the average recovery rate of phosphate was 101%, but the precision (RSD) was as high as 12%; the average recovery rate of phosphite was 107%, with an RSD of 4%.

[0158] Analysis and discussion: Accuracy, especially its accompanying precision, is the gold standard for measuring data reliability. Highly reliable data is the foundation for scientific decision-making in in-depth process research and product characterization.

[0159] 1) Precision determines data reliability: The method in Comparative Example 1 exhibited an RSD as high as 12% in phosphate detection, indicating significant fluctuations in its measurement results. This level of uncertainty renders any judgments made based on this data regarding process robustness or product consistency unreliable. In contrast, the method of this invention maintains an RSD below 5% across all concentration levels, providing a highly accurate and reproducible data foundation for process evaluation and product characterization.

[0160] 2) Reliability at low concentrations is crucial: Even at extremely low limits of quantitation, this invention maintains an excellent precision of 0.42% for the detection of phosphites, demonstrating its strong quantitative capability even at trace levels. This is of significant value for monitoring process fluctuations and product degradation trends, whereas the method in Comparative Example 1 did not provide precision data at low concentrations.

[0161] Conclusion: In terms of accuracy, the method of this invention demonstrates an overwhelming advantage. The data provided by the method in Comparative Example 1, due to its inherent instability, is unsuitable for tasks such as precise evaluation of production processes or rigorous characterization of ultra-low impurity properties of products. The method of this invention, however, is the preferred tool capable of providing scientific, robust, and reliable data support for the aforementioned research objectives.

[0162] 5. Precision Precision is a key indicator of an analytical method's ability to provide consistent results for homogeneous samples under defined conditions; its level directly determines the reliability and value of process research and product characterization data. This study comprehensively examined the variability of the method through repeatability and intermediate precision.

[0163] Test method: Validation of the phosphate method: 1) Repeatability of the test sample: Take the test sample, and personnel A shall perform six parallel determinations of phosphate according to the phosphate test method. Calculate the relative standard deviation of the six determinations. The results are shown in Table 18. Figure 19 .

[0164] Table 18 Results of Phosphate Repeatability Tests The results showed that phosphate in this product was not detected in six consecutive determinations, meeting the acceptance criteria and indicating that the method had good repeatability.

[0165] 2) Repeatability of spiked test samples Phosphate stock solution: Accurately measure 1 ml of phosphate reference standard, place it in a 20 ml volumetric flask, dilute with water to the mark, and shake well.

[0166] Blank solution: Take the test sample solution from the repeatability test item.

[0167] Reference solution: Accurately measure 1 ml of the recovery stock solution, place it in a 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0168] Test solution: Accurately measure 10 ml of test solution and 1.0 ml of recovery stock solution, place them in the same 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0169] Accurately measure 25 µl each of the blank solution, test solution, and reference solution, and inject them separately into the ion chromatograph, recording the chromatograms. Calculate the phosphate detection limit using the external standard method, and calculate the relative standard deviation of the six determinations. The results are shown in Table 19. Figure 20 .

[0170] Table 19 Results of Phosphate Repeatability Tests The results showed that in six parallel determinations of the 100% recovery solution by personnel A, the average phosphate recovery rate was 103.94%, and the RSD was 1.76%, indicating that the phosphate test method of this product has good repeatability.

[0171] 3) Intermediate precision Take the same batch of test samples, and personnel B perform the determination on different dates and using different chromatographic systems, following the procedure described below.

[0172] Phosphate stock solution: Accurately measure 1 ml of phosphorous acid reference standard, place it in a 20 ml volumetric flask, dilute with water to the mark, and shake well.

[0173] Blank solution: Accurately measure 10 ml of this product and place it in a 25 ml volumetric flask. Dilute with water to the mark and shake well.

[0174] Reference solution: Accurately measure 1.0 ml of phosphate stock solution, place it in a 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0175] Test solution: Accurately measure 10 ml of test solution and 1.0 ml of phosphate stock solution, place them in the same 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0176] Accurately measure 25 µl each of the blank solution, test solution, and reference solution, and inject them separately into the ion chromatograph, recording the chromatograms. Calculate the phosphate detection limit using the external standard method, and calculate the relative standard deviations of the results from 6 measurements by personnel B and the 12 measurements by personnel A and B. The results are shown in Table 20. Figure 21 .

[0177] Table 20 Results of Phosphate Repeatability and Intermediate Precision Tests The results showed that personnel A and B, on different dates, using different instruments and different chromatographic systems, determined the 100% recovery rate solution six times consecutively. Personnel A showed repeatability results; Personnel B: the average phosphate recovery rate was 105.45%, and the RSD was 0.70%, indicating that the intermediate precision of the phosphate test method of this product was good.

[0178] Validation of the phosphite method: 1) Repeatability of the test sample Test solution: Accurately measure 10 ml of this product, place it in a 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0179] Take the test sample and perform six parallel determinations of phosphite according to the phosphite test method. Calculate the relative standard deviation of the six determinations. The results are shown in Table 21. Figure 22 .

[0180] Table 21 Results of repeatability tests for phosphite The results showed that the phosphite in this product was not detected in six consecutive determinations, indicating that the method has good repeatability.

[0181] 2) Repeatability of spiked test samples Phosphite stock solution: Take the linear stock solution from the linearity test.

[0182] Blank solution: Take the test sample solution from the repeatability test item.

[0183] Reference solution: Take the linear 2 solution from the linearity test.

[0184] Test solution: Accurately measure 10 ml of test solution and 1.0 ml of recovery stock solution, place them in the same 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0185] Accurately measure 25 µl each of the blank solution, test solution, and reference solution, and inject them separately into the ion chromatograph, recording the chromatograms. Calculate the detection limit of phosphite using the external standard method, and calculate the relative standard deviation of the six determinations. The results are shown in Table 22. Figure 23 .

[0186] Table 22 Results of repeatability tests for phosphite The results showed that in six parallel determinations of the 100% recovery solution by personnel A, the average recovery rate of phosphite was 92.79%, and the RSD was 2.0%, indicating that the phosphite test method of this product has good repeatability.

[0187] 3) Intermediate precision Take the same batch of test samples, and personnel B perform the determination on different dates and using different chromatographic systems, following the procedure described below.

[0188] Phosphite stock solution: Accurately measure 1 ml of phosphite reference standard, place it in a 20 ml volumetric flask, dilute with water to the mark, and shake well.

[0189] Blank solution: Accurately measure 10 ml of this product and place it in a 25 ml volumetric flask. Dilute with water to the mark and shake well.

[0190] Reference solution: Accurately measure 1.0 ml of phosphite stock solution, place it in a 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0191] Test solution: Accurately measure 10 ml of test stock solution and 1.0 ml of phosphorous acid stock solution, place them in the same 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0192] Accurately measure 25 µl each of the blank solution, test solution, and reference solution, and inject them separately into the ion chromatograph, recording the chromatograms. Calculate the detection limit of phosphite using the external standard method, and calculate the relative standard deviations of the results from 6 measurements by personnel B and the 12 measurements by personnel A and B. The results are shown in Table 23. Figure 24 .

[0193] Table 23 Results of repeatability and intermediate precision tests for phosphite The results showed that personnel A and B, on different dates, using different instruments and different chromatographic systems, determined the 100% recovery rate solution six times consecutively. Personnel A showed repeatability results; Personnel B: the average recovery rate of phosphite was 98.31%, and the RSD was 1.16%, indicating that the intermediate precision of the phosphite test method of this product was good.

[0194] Comparative Example 1: In the repeatability test of the spiked test sample, the average recovery rate of phosphate was 101% with an RSD of 5%, and the average recovery rate of phosphite was 107% with an RSD of 2%.

[0195] The intermediate precision test results showed that the RSD of phosphate recovery was as high as 10%, and the RSD of phosphite recovery was 6%.

[0196] Analysis and discussion: The comparison of precision reveals the fundamental differences between the two methods in terms of data reliability.

[0197] 1) Comprehensive leadership from within the laboratory to between laboratories: In terms of reproducibility: The phosphate RSD (5%) of the method in Comparative Example 1 in the laboratory (reproducibility) was more than 2.8 times that of the present invention (1.76%); its phosphite RSD (2%) was also comparable to that of the present invention (2.00%), but it did not show the same advantages as the present invention.

[0198] Intermediate precision level: When different personnel or dates are introduced, the variability of the method in Comparative Example 1 increases dramatically, with the RSD of phosphate reaching as high as 10% and the RSD of phosphite reaching 6%. This fully exposes the inherent instability of the method and its extremely high sensitivity to operating conditions.

[0199] In contrast, the precision of the method of this invention remains consistently at an extremely low level under different conditions (RSD is generally ≤2%). In particular, its intermediate precision performance is significantly better than that of Comparative Example 1, demonstrating its inherent characteristics as a reliable research tool and its strong anti-interference ability.

[0200] 2) Data reliability determines research depth: The intermediate precision of the method in Comparative Example 1, at 10% and 6%, means that a real process improvement or product difference must be large enough to be identified from the inherent "noise" of the method. This severely limits its application in fine-tuning processes or rigorously evaluating batch-to-batch consistency. Conversely, the extremely low variability of the method in this invention allows it to sensitively and reliably capture even minute changes, thus supporting deeper and more refined process research and product characterization.

[0201] Conclusion: The method of this invention demonstrates comprehensive and significant superiority in terms of precision, a core indicator. The method in Comparative Example 1, due to its poor precision, particularly intermediate precision, is unreliable for in-depth process understanding and rigorous product quality assessment. In contrast, the high-precision, high-reproducibility data provided by the method of this invention makes it an ideal analytical tool to support the development of alendronate sodium oral solution.

[0202] 6. Solution stability Solution stability is an important indicator for evaluating the convenience and reliability of analytical methods in actual operation. It determines the usability of samples and reagents after preparation and directly affects the flexibility of experimental arrangements.

[0203] Test method: Validation of the phosphate method: 1) Stability of the reference solution Take the reference solution from the recovery rate section, place it at room temperature under natural light, and accurately measure 25 μl at 0, 6, 17, and 25 hours, inject it into the ion chromatograph, record the chromatogram, and compare it with the value at 0 hours. Calculate the change in the phosphate peak area. The results are shown in Table 24. Figures 25-26 .

[0204] Table 24 Results of stability test of phosphate test standard solution The results showed that when the reference solution was placed at room temperature and under natural light for 25 hours, the maximum change in the peak area of ​​the main component was 2.99% < 5% compared with 0 hours, indicating that the reference solution was stable at room temperature and under natural light for 25 hours.

[0205] 2) Stability of the stock solution of phosphate reference standard Take the recovery stock solution from the recovery rate section, store it in a refrigerator (4℃), and accurately measure 25 μl at 0, 25, and 45.5 hours, inject it into the ion chromatograph, record the chromatogram, and compare it with the value at 0 hours. Calculate the change in the phosphate peak area. The results are shown in Table 25. Figures 27-28 .

[0206] Table 25 Results of stability tests on stock solutions of phosphoric acid reference standard The results showed that when the reference solution was placed at room temperature and under natural light for 25 hours, the maximum change in the peak area of ​​the main component was 2.99% < 5% compared with 0 hours, indicating that the reference solution was stable at room temperature and under natural light for 25 hours.

[0207] The results showed that when the phosphoric acid reference stock solution was placed in a refrigerator (4℃) for 45.5 h, the maximum change in the peak area of ​​phosphoric acid was 0.80% < 5% compared with 0 h, indicating that the phosphoric acid reference stock solution was stable in the refrigerator (4℃) for 45.5 hours.

[0208] 3) Stability of the spiked test solution Take the No. 1 test solution from the spiked repeatability test, place it at room temperature under natural light, and accurately measure 25 μl at 0, 6, 14, 24, and 37.5 hours, inject it into the ion chromatograph, record the chromatograms, and compare them with the values ​​at 0 hours. Calculate the change in phosphate content. The results are shown in Table 26. Figures 29-30 .

[0209] Table 26 Results of Phosphoric Acid Stability Test for Sample Solutions The results showed that after the test solution was placed at room temperature and under natural light for 37.5 hours, the maximum change in phosphate detection was 8.29% < 20% compared with 0 hours, indicating that the test solution was stable under room temperature and natural light for 37.5 hours.

[0210] Validation of the phosphite method: 1) Stability of the reference solution Take the linear solution 2 from the linearity test, place it at room temperature under natural light, and accurately measure 25 μl at 0, 3, 6, 18, and 43.5 hours, inject it into the ion chromatograph, record the chromatogram, and compare it with the value at 0 hours. Calculate the change in the peak area of ​​phosphorous acid. The results are shown in Table 27. Figures 31-32 .

[0211] Table 27 Results of stability test of phosphite test standard solution The results showed that after the reference solution was placed at room temperature and under natural light for 43.5 hours, the maximum change in the peak area of ​​the main component was 1.80% < 5% compared with 0 hours, indicating that the reference solution was stable at room temperature and under natural light for 43.5 hours.

[0212] 2) Stability of the stock solution of phosphorous acid reference standard Take the linear stock solution from the linearity test, store it in a refrigerator (4℃), and accurately measure 25 μl at 0, 24.5, and 46 hours, respectively, inject it into the ion chromatograph, record the chromatograms, and compare them with the values ​​at 0 hours. Calculate the change in the peak area of ​​phosphorous acid. The results are shown in Table 28. Figures 33-34 .

[0213] Table 28 Results of stability tests on stock solutions of phosphorous acid reference standard The results showed that when the phosphorous acid reference stock solution was placed in a refrigerator (4℃) for 46 hours, the maximum change in the peak area of ​​phosphorous acid was 1.19 < 5% compared with 0 hours, indicating that the phosphorous acid reference stock solution was stable within 46 hours under refrigerator (4℃) conditions.

[0214] 3) Stability of the spiked test solution Take the No. 3 test solution from the spiked repeatability test, place it at room temperature under natural light, and accurately measure 25 μl at 0, 3, 6, 16, and 40.5 hours, inject it into the ion chromatograph, record the chromatograms, and compare them with the values ​​at 0 hours. Calculate the change in phosphorous acid content. The results are shown in Table 29. Figures 35-36 .

[0215] Table 29 Results of stability tests on phosphorous acid test solutions The results showed that after the test solution was placed at room temperature and under natural light for 40.5 hours, the maximum change in the amount of phosphite detected was 12.91% < 20% compared with 0 hours, indicating that the test solution was stable under room temperature and natural light for 40.5 hours.

[0216] Comparative Example 1: The stability of the reference solutions of phosphate and phosphite at 5°C has been verified to be 22 hours; the stability of the spiked test solution at 5°C has been verified to be 16 hours.

[0217] Analysis and discussion: The results of the solution stability validation provide an objective comparison for evaluating the operating windows of different methods.

[0218] Validated stability window comparison: The method of this invention provides a longer validated stability window for critical solutions. For example, for spiked test solutions, the stability window validated by this invention at room temperature (≥37.5 hours) is more than twice as long as the window validated by Comparative Example 1 under refrigeration conditions (16 hours). This means that under the same validation criteria, using the method of this invention allows researchers more time to complete the detection of sample sequences, significantly reducing the risk of rushed operations or sequence interruptions due to time constraints.

[0219] Operational flexibility and fault tolerance: The longer, validated stability window, especially the stability achieved under more relaxed room temperature conditions, brings significant operational flexibility and system fault tolerance to this method. When conducting process studies requiring long-term operation or characterizing multiple batches of products, this invention provides greater flexibility in experimental planning, enabling more comfortable handling of practical situations such as instrument maintenance and sequence extension, thereby ensuring the integrity and consistency of data acquisition.

[0220] Conclusion: Regarding solution stability, the method of this invention exhibits a longer proven stability window and more relaxed storage conditions, making it more user-friendly and robust in complex process studies and product characterization applications. This further solidifies its position as an efficient and reliable analytical tool.

[0221] 7. Robustness of chromatographic conditions Robustness is used to assess the impact of small, intentional changes in chromatographic conditions on analytical results and is a key indicator of whether a method can be successfully transferred and reproduced across different instruments and laboratories.

[0222] Test method: Validation of the phosphate method: Based on the standard chromatographic conditions, the column temperature and the concentration of potassium hydroxide in the mobile phase were varied according to Table 30 to examine the robustness of the method.

[0223] Test solution: Accurately measure 10 ml of this product, place it in a 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0224] Reference solution: Accurately measure 1 ml of phosphate reference standard, place it in a 20 ml volumetric flask, dilute with water to the mark, and shake well; accurately measure 1 ml, place it in a 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0225] Blank excipient solution: Take the specificity item.

[0226] Accurately measure 25 μl of each of the above solutions and inject them into the ion chromatograph. Record the chromatograms. The results are shown in Table 31. Figures 37-51 .

[0227] Table 30 Robustness of Phosphate Test Methods Table 31 Results of Phosphate Test Durability Test The results showed that within a small range of column temperature (25℃, 30℃, 35℃) and mobile phase potassium hydroxide concentration (33, 35, 37 mmol / L), the samples were tested and all results showed "not detected". This was because the use of high-purity raw materials and a specific pH buffer system (citric acid / sodium citrate) effectively suppressed the generation of degradation impurities.

[0228] Validation of the phosphite method: Based on the standard chromatographic conditions, the column temperature and the concentration of potassium hydroxide in the mobile phase were varied according to Table 32 to examine the robustness of the method.

[0229] Test solution: Accurately measure 10 ml of this product, place it in a 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0230] Reference solution: Accurately measure 1 ml of phosphorous acid reference standard, place it in a 20 ml volumetric flask, dilute with water to the mark, and shake well; accurately measure 1 ml, place it in a 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0231] Blank excipient solution: Accurately measure 10 ml of blank excipient, place it in a 25 ml volumetric flask, dilute with water to the mark, and shake well.

[0232] Accurately measure 25 μl of each of the above solutions and inject them into the ion chromatograph. Record the chromatograms. The results are shown in Table 33. Figures 52-66 .

[0233] Table 32 Robustness of Phosphite Test Methods Table 33 Results of Phosphite Determination Durability Test The results showed that within a small range of column temperature (25℃, 30℃, 35℃) and mobile phase potassium hydroxide concentration (48, 50, 52 mmol / L), the detection result for the sample was also "not detected".

[0234] Comparative Example 11 In its durability test, the recovery rates of phosphate and phosphite fluctuated significantly when the column temperature, the initial ratio of organic phase and the flow rate were changed. The minimum range of change was 103% to 106%, and the maximum even drifted from 92% to 118%.

[0235] Analysis and discussion: The results of the durability test revealed a significant difference in the inherent robustness of the two analytical methods. At the same time, the results of this invention also indirectly verified the excellent performance of the product and process.

[0236] The consistency of "not detected" demonstrates the absolute robustness of the method: Even with minor variations in key parameters, the qualitative conclusion ("not detected") and quantitative result (response value below the limit of quantitation) of this invention remain highly consistent. This indicates that the method has a wide operating window and is insensitive to common variations. This inherent robustness ensures that the method consistently produces consistent and reliable results when transferred to different laboratories or operated by different analysts.

[0237] The stability of the results indirectly confirms the superior quality of the product and process: the consistent "not detected" results under different chromatographic conditions not only demonstrate the robustness of the analytical method but also strongly support the robustness of the preparation process described in this invention. This indicates that the extremely low impurity levels of the alendronate sodium oral solution produced by this process are an inherently consistent property, and will not produce conclusive differences due to minor legitimate fluctuations in detection conditions. This further strengthens the reliability of its "ultra-low impurity property."

[0238] The vulnerability of Comparative Example 1 highlights its application limitations: under parameter variations, the recovery rate of Comparative Example 1 fluctuated dramatically by as much as 26 percentage points (92%–118%), indicating that the method requires extremely stringent control of operating conditions. In practical applications, even unavoidable small parameter drifts can lead to significant distortion of detection results, making it difficult to provide reliable data support in rigorous research and development.

[0239] Conclusion: In terms of durability, the method of this invention not only demonstrates excellent robustness, but its stable test results also indirectly confirm the high purity of the product and the reliability of the preparation process. In contrast, the method of Comparative Example 1 exhibits significant fragility and uncertainty. This characteristic of the method of this invention provides a solid foundation for consistently, reliably, and reproducibly demonstrating the superior quality of the oral solution during complex and lengthy research and development cycles.

[0240] In summary, based on the comparative experiments of the above systems, the following conclusions can be drawn: The specific ion chromatography detection method provided by this invention comprehensively outperforms or surpasses the closest existing technology (HPLC-CAD method of Comparative Example 1) in all key performance indicators, including specificity, linearity and range, sensitivity, accuracy, precision, solution stability, and robustness. This method not only provides highly reliable, accurate, and stable analytical data but also exhibits excellent operability and reproducibility.

[0241] Most importantly, when this superior analytical method was applied to alendronate sodium oral solution produced using the specific preparation process of this invention, consistent and reliable "not detected" results were obtained. This not only positively validates the robustness of the analytical method, but also strongly confirms the robustness of the preparation process of this invention and the inherent high purity of the produced oral solution.

[0242] Therefore, the inventiveness of this invention lies not merely in a superior detection method or a conventional preparation process, but in the successful integration of a proven, robust process, the tangible product produced by this process, and a high-performance, dedicated characterization tool, forming a self-verifying, logically closed-loop "preparation and characterization system." This system can scientifically define, prepare, and verify a high-quality alendronate sodium oral solution with "ultra-low impurity properties," a complete and unified technical solution that cannot be directly obtained by those skilled in the art based on existing technologies.

[0243] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. An oral solution of alendronate sodium, characterized in that, The oral solution contains sodium alendronate as the active ingredient, as well as excipients; the excipients include methylparaben, propylparaben, anhydrous citric acid, sodium citrate, and sodium saccharin, and the content of phosphate and phosphite in the oral solution is less than 0.20 μg / mL.

2. The alendronate sodium oral solution according to claim 1, characterized in that, In the long-term stability test, the oral solution, after being placed at room temperature for 37.5 hours, showed a change of less than 20% in phosphate and phosphite content.

3. The alendronate sodium oral solution according to claim 1, characterized in that, The method for preparing the oral solution includes the following steps: (a) Add purified water to the mixing tank to prepare 70%~85% of the total volume; (b) Under the conditions of stirring frequency of 40~60Hz and temperature of 70℃~80℃, add the prescribed amounts of methylparaben and propylparaben, stir for 40min~60min until completely dissolved, and then cool to below 40℃; wherein the mass concentration of methylparaben is 0.01%~0.1% and the mass concentration of propylparaben is 0.01%~0.1%; (c) Adjust the stirring frequency to 30Hz~50Hz, add the prescribed amounts of sodium alendronate, anhydrous citric acid, sodium citrate, and sodium saccharin, and stir for 20min~40min until completely dissolved; wherein the mass concentration of sodium alendronate is 0.5%~1.5%, the mass concentration of anhydrous citric acid is 0.1%~0.5%, the mass concentration of sodium citrate is 0.5%~2.0%, and the mass concentration of sodium saccharin is 0.01%~0.1%; (d) Add purified water to the total volume, stir at a stirring frequency of 30Hz~50Hz for 20min~40min to mix evenly, and take a sample for intermediate product testing; (e) The drug solution is filtered through a 0.45μm polypropylene filter into a filling buffer tank, and then filled immediately after filtration to obtain the final oral solution.

4. A method for detecting the phosphate content in the alendronate sodium oral solution according to any one of claims 1 to 3, characterized in that, The method employs ion chromatography-conductivity detection, including the following steps: (1) Preparation of the test solution; (2) Inject the test solution into an ion chromatography system equipped with an anion exchange column; (3) Isocratic rinsing was performed using potassium hydroxide solution; (4) The phosphate content is detected by a conductivity detector and quantified based on the chromatographic peak area, wherein the anion exchange column is a Dionex RFIC IonPac AS11-HC 4mm×250mm column.

5. The method for detecting phosphate content in alendronate sodium oral solution according to claim 4, characterized in that, In step (3), the mass concentration of potassium hydroxide solution in the isocratic rinsing ranges from 33 mmol / L to 37 mmol / L, and the rinsing time is maintained at 19 min to 22 min.

6. A method for detecting the phosphite content in the alendronate sodium oral solution according to any one of claims 1 to 3, characterized in that, The method employs ion chromatography-conductivity detection and includes the following steps: A test solution was prepared; the test solution was injected into an ion chromatography system equipped with an anion exchange column; a gradient elution was performed using potassium hydroxide solution, wherein the gradient program was as follows: the ratio of water to potassium hydroxide in the mobile phase was linearly changed from 83:17 to 0:100 within 0 to 20.0 min, and this ratio was maintained until 25.0 min, then restored to the initial ratio, and equilibrated until 45.0 min; the phosphite content was detected by a conductivity detector and quantified based on the chromatographic peak area, wherein the anion exchange column was a Dionex RFIC IonPac AS11-HC 4 mm × 250 mm column.

7. The method for detecting phosphite content in alendronate sodium oral solution according to claim 6, characterized in that, The mass concentration of potassium hydroxide solution in the gradient rinsing is in the range of 48 mmol / L to 52 mmol / L.

8. A method for verifying the ultra-low impurity properties of alendronate sodium oral solution, characterized in that, The method includes the following steps: (A) Provide an oral solution of alendronate sodium according to any one of claims 1 to 3; (B) The phosphate content is determined using the ion chromatography detection method according to claim 4 or 5; (C) The phosphite content is determined using the ion chromatography detection method according to claim 6 or 7; (D) Based on the measurement results, it was confirmed that the contents of phosphate and phosphite in the oral solution were both less than 0.20 μg / mL, thus verifying its ultra-low impurity properties.

9. A characterization system for impurity levels in alendronate sodium oral solution, characterized in that, The system consists of the following parts: (I) The alendronate sodium oral solution according to any one of claims 1 to 3; (II) The ion chromatography detection method according to claim 4 or 5 used to define phosphate content; (III) The ion chromatography detection method according to claim 6 or 7 for defining the phosphite content; The combined application of the system characterizes the impurity levels of the oral solution, and the measurement results are used as the basis for evaluating process robustness and product quality.

10. The impurity level characterization system for alendronate sodium oral solution according to claim 9, characterized in that, The system also includes a data verification module for analyzing the precision and accuracy of the test results, wherein the precision RSD is less than 5% and the accuracy recovery rate is in the range of 90% to 110%.

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