A method for determining the content of zinc gluconate oral solution

Abstract

This application discloses a method for determining the content of zinc gluconate oral solution, belonging to the field of pharmaceutical quality testing technology. The method uses disodium ethylenediaminetetraacetate titration, adding ammonium fluoride and Eriochrome Black T indicator to an ammonium chloride buffer system. Titration continues until the solution changes from purple-red to blue-green and remains unchanged for 30 seconds. The zinc gluconate content is calculated based on the titration volume. This method eliminates interference from sample color and excipients, accurately determines the endpoint, and has demonstrated good specificity, precision, accuracy, and stability through experiments. It is suitable for determining the content of near-colorless samples, samples with deepened color, samples tested at high temperatures, and commercially available samples from different manufacturers. The method is simple to operate, low in cost, and can meet the routine quality control requirements of zinc gluconate oral solution.

Description

Technical Field

[0001] This application belongs to the field of pharmaceutical technology; specifically, it relates to a method for determining the content of zinc gluconate in oral solution. Background Technology

[0002] Zinc gluconate oral solution, a commonly used zinc supplement in clinical practice, is widely used to treat symptoms such as growth retardation and loss of appetite caused by zinc deficiency in children and adults. Accurate determination of its zinc content is a crucial aspect of quality control. Currently, the content determination of zinc gluconate oral solution primarily employs the EDTA complexometric titration method as described in the Pharmacopoeia of the People's Republic of China. This method uses an ammonia-ammonium chloride buffer to control the pH value and Chrome Black T as an indicator. The zinc content is determined by the color change at the titration endpoint. This method has advantages such as simple operation and high precision, and is a classic analytical method commonly used in pharmaceutical quality standards.

[0003] However, during actual production and stability studies, it was found that zinc gluconate oral solutions are mostly sugar-based formulations. With prolonged storage or exposure to high temperatures, the samples tend to gradually darken in color, changing from nearly colorless initially to pale yellow, significantly interfering with titration endpoint determination. When using existing pharmacopoeia methods, the indicator color overlaps with the sample background color, resulting in unclear endpoint color changes and difficulty in accurately identifying the transition from purplish-red to blue-green. Some commercially available samples even exhibit no obvious color change during titration and the endpoint cannot be determined due to interference from formulation components, severely affecting the accuracy and reproducibility of content determination results.

[0004] Furthermore, existing pharmacopoeia methods lack optimization for parameters such as sample volume, titrant concentration, and buffer system ratios, failing to address the needs of samples with deepening color, samples subjected to high temperatures, and differences in formulations from different manufacturers. This makes them unsuitable for detecting samples from multiple sources and in various states. While instrumental analysis methods such as ion chromatography can serve as alternatives, they suffer from drawbacks such as high equipment costs, cumbersome operation, and relatively large errors, failing to meet the requirements for rapid, routine, and high-volume sample detection.

[0005] Therefore, developing a method for determining the content of zinc gluconate oral solution that can eliminate sample color interference, clearly determine the endpoint, and has wider applicability is of great practical significance for improving the level of drug quality control and ensuring the safety and effectiveness of clinical drug use. Summary of the Invention

[0006] To address the technical problems of existing methods for determining the content of zinc gluconate oral solution, such as difficulty in accurately determining the titration endpoint and easy deviation of measurement results due to sample color deepening and interference from prescription ingredients, this application proposes a method for determining the content of zinc gluconate oral solution. By optimizing the sampling amount, buffer system, titrant concentration, and adding ammonium fluoride, the method effectively eliminates the interference of sample color and excipients, achieving clear and accurate determination of the titration endpoint. This solves the problem of increased difficulty in determining the endpoint for pharmacopoeia methods for samples with deepened color, samples tested at high temperatures, and some commercially available samples, thereby improving the accuracy, precision, and applicability of the content determination results.

[0007] This application discloses a method for determining the content of zinc gluconate in an oral solution, the method comprising the following steps: (1) Solution mixing: Accurately measure 20 mL of zinc gluconate oral solution (approximately equivalent to 0.07 g of zinc gluconate), add water and ammonia buffer, then add ammonium fluoride and indicator, and mix well to obtain a purple-red solution; (2) Titration: Use disodium ethylenediaminetetraacetate as the titrant and titrate it into the mixed solution of step (1) until the solution of step (1) changes from purple-red to blue-green and remains unchanged for 30 seconds. Stop the titration. (3) Calculation of zinc gluconate content: Calculate the zinc gluconate content based on the volume of titrant consumed in step (2).

[0008] Preferably, the ammonia buffer in step (1) is an ammonia-ammonium chloride buffer.

[0009] Preferably, the indicator in step (1) is Chrome Black T indicator.

[0010] Preferably, the amount of water added in step (1) is 90 mL.

[0011] Preferably, the amount of ammonia buffer added in step (1) is 2 mL.

[0012] Preferably, the amount of ammonium fluoride added in step (1) is 1g.

[0013] Preferably, in step (2), the role of disodium ethylenediaminetetraacetate is to react with Zn. 2+ Formation of ZnY 2- A colorless chelate, when titrated to the endpoint, ZnIn - In the solution, Eriochrome Black T is displaced by excess disodium ethylenediaminetetraacetate, forming a stable chelate ZnY. 2- Free Eriochrome Black T appears blue-green in solution, thus indicating the titration endpoint.

[0014] Preferably, the concentration of disodium ethylenediaminetetraacetate in step (2) is 0.01 mol / L.

[0015] Preferably, the pH of the ammonia-ammonium chloride buffer solution is 10.0 ± 0.2.

[0016] Preferably, the function of the chrome black T is to react with Zn 2+ Formation of stable purplish-red chelate ZnIn - .

[0017] This application uses an ammonia buffer solution to control the solution pH, and uses Eriochrome Black T (EBT, HIn) as the buffer. 2- The indicator ion (representing the indicator ion) is used as the indicator. After adding Eriochrome Black T, it first reacts with Zn. 2+ Forms a relatively stable purplish-red chelate (ZnIn) - Add EDTA dropwise to a zinc gluconate solution. EDTA reacts with Zn. 2+ Formation of ZnY 2- A colorless chelate, as shown in formula (1); at the titration endpoint, ZnIn - (lgK) 稳，ZnIn - In ZnY (=12.9), Chromium Black T is displaced by excess EDTA, forming a more stable chelate ZnY. 2- (lgK) 稳，ZnY 2- =16.4), free chrome black T (HIn) 2- It appears blue-green in the solution, thus indicating the titration endpoint as shown in equation (2); Equation (1): Zn 2+ + H2Y 2- → ZnY 2- + 2H + ; Equation (2): ZnIn - (Purple-red) + H2Y 2- → ZnY 2- + HIn 2- (Blue-green) + H + By reducing the sample volume and adjusting the amount of ammonia buffer solution to control the solution pH, and simultaneously titrating with a low concentration of disodium ethylenediaminetetraacetate (0.01 mol / L), color interference can be eliminated and the titration endpoint can be accurately determined. Each 1 mL of disodium ethylenediaminetetraacetate (0.01 mol / L) titrant is equivalent to 4.556 mg of C. 12 H 22 O 14 Zn.

[0018] The beneficial effects of the embodiments in this application are as follows: (1) By adding ammonium fluoride and optimizing the buffer system and titrant concentration, the sample color deepening and the interference of excipient components are eliminated. The titration endpoint changes from purple-red to blue-green and remains unchanged for 30 seconds. This solves the problem that the determination of the titration endpoint of samples with deepening color and samples under high temperature is more difficult by pharmacopoeia method, and makes the endpoint determination clear and accurate.

[0019] (2) Experiments have verified that this method has strong specificity and no interference from blank excipients; it has excellent repeatability, accuracy and solution stability, recovery rate close to 100%, low RSD value, and accurate and reproducible content determination results.

[0020] (3) It can be applied to near-colorless samples, samples with darker color, samples tested at high temperature, and samples sold by different manufacturers. It breaks through the limitation that the pharmacopoeia method is only applicable to light-colored freshly prepared samples and is suitable for the detection of samples from multiple sources and in multiple states. Attached Figure Description

[0021] Figure 1 This is a diagram of the titration process of a recently produced near-colorless sample, as shown in Example 6 of this application.

[0022] Figure 2 This is a diagram showing the titration process of the pale yellow sample used in the stability test of Example 6 of this application. Detailed Implementation

[0023] The technical solutions of this application will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0024] Example 1 Specificity test (1) Accurately measure 20 mL of the blank sample solution without zinc gluconate prepared according to the prescription process, place it in an Erlenmeyer flask, and add 90 mL of water; (2) Add 2 mL of ammonia-ammonium chloride buffer (pH 10.0), then add 1 g of ammonium fluoride and a small amount of Eriochrome Black T indicator. The solution turns blue-green and remains so for 30 seconds. (3) This demonstrates that the blank excipient solution does not interfere with this content determination method, that the method has good specificity, and that it can be accurately used for the content determination of zinc gluconate oral solution.

[0025] Example 2 Precision test (repeatability) (1) Accurately measure 20 mL of the oral solution of this product and place it in an Erlenmeyer flask. Prepare 6 portions at the same time and add 90 mL of water. (2) Add 2 mL of ammonia-ammonium chloride buffer (pH 10.0), then add 1 g of ammonium fluoride and a small amount of Eriochrome Black T indicator, and titrate with disodium ethylenediaminetetraacetate titrant (0.01 mol / L) until the solution changes from purple-red to blue-green and remains unchanged for 30 seconds; (3) The experimental data are shown in Table 1; Table 1: Results of Repeatability Tests

[0026] (4) Experimental results: As shown in Table 1, the relative standard deviation of the repeatability test of this experiment is no more than 0.2%, which proves that the repeatability of this method is good.

[0027] Example 3 Accuracy test (1) Accurately weigh three portions of zinc gluconate raw material (content: 98.6%, loss on drying: 9.0%), which are equivalent to 80%, 100%, and 120% of the amount of zinc gluconate in 20 mL of zinc gluconate oral solution, respectively, and place them in conical flasks; (2) Add 20 mL of blank sample solution without zinc gluconate prepared according to the prescription process, heat to dissolve, cool, add 90 mL of water, add 2 mL of ammonia-ammonium chloride buffer (pH 10.0), and add 1 g of ammonium fluoride and a small amount of chrome black T indicator. (3) Titrate with disodium ethylenediaminetetraacetate titrant (0.01 mol / L) until the solution changes from purple-red to blue-green and remains unchanged for 30 seconds. Each 1 mL of disodium ethylenediaminetetraacetate titrant (0.01 mol / L) is equivalent to 4.556 mg of C. 12 H 22 O 14 Zn; (4) The content of each component was determined and the recovery rate was calculated. The results are shown in Table 2. Table 2 Accuracy test results

[0028] (5) According to Table 2, the recovery rates at each concentration were between 99.7% and 100.3%, with an average recovery rate of 100.04%. The relative standard deviation of the nine recovery rate data was no greater than 0.1%, proving that the method is accurate and reliable and the error is within the allowable range.

[0029] Example 4 Solution stability test (1) Accurately measure 20 mL of the oral solution of this product and place it in an Erlenmeyer flask. At the same time, prepare 6 portions, add 90 mL of water, 2 mL of ammonia-ammonium chloride buffer (pH 10.0), 1 g of ammonium fluoride and a small amount of chrome black T indicator; (2) At 0, 1, 2, 4, 6 and 8 hours respectively, titrate with disodium ethylenediaminetetraacetate titrant (0.01 mol / L) until the solution changes from purple-red to blue-green and does not fade for 30 seconds; (3) The stability of the sample solution was examined by measuring the volume of titrant consumed. The results are shown in Table 3. Table 3 Results of solution stability test

[0030] (4) The results in Table 3 show that the relative standard deviation of the volume of titrant consumed within 8 hours is no greater than 0.2%, which proves that the solution has good stability within 8 hours.

[0031] In summary, based on Examples 1-4, the results of the content determination methodology validation are shown in Table 4.

[0032] Table 4. Validation results of the content determination methods in Examples 1-4

[0033] Example 5 Repeatability and stability tests of different batches (1) Test methods: In order to further verify the content determination method, we conducted repeatability and stability tests on samples recently produced by our company. The test methods were the same as those in Examples 2 and 4; the results are shown in Tables 5 and 6. Table 5. Results of Repeatability Tests on Recent Production Samples from Our Company

[0034] Table 6. Results of stability tests on sample solutions produced by our company recently.

[0035] (2) Test results: Table 5 shows that the relative standard deviation of the repeatability test of the recent production batch is no more than 0.2%, which proves that the repeatability of the method is good; Table 6 shows that the relative standard deviation of the volume of titrant consumed within 8 hours is no more than 0.2%, which proves that the solution is stable within 8 hours.

[0036] Example 6 Comparative test (our company's products) (1) Test method: The content determination method of zinc gluconate oral solution in the 2025 edition of the Chinese Pharmacopoeia, Part II, and the proposed new method were used to determine the content of the stability test sample and the sample recently produced by our company. The comparison of the determination results is shown in Table 7. Table 7 Comparison of Content Determination Results

[0037] (2) Experimental Results: As shown in Table 7, when using the method for determining the content of zinc gluconate oral solution in Part II of the 2025 edition of the Chinese Pharmacopoeia to determine the content of the stability test sample, the color of the stability test sample gradually deepened, interfering with the titration process and making it more difficult to determine the titration endpoint. The proposed new method for determining the content of the stability test sample can eliminate color interference and accurately determine the titration endpoint. The titration process is as follows: Figure 2 To determine the content in recently produced samples, the titration process is as follows: Figure 1 The content determination method for zinc gluconate oral solution in the 2025 edition of the Chinese Pharmacopoeia, Part II, and the proposed new method were used to determine the content of the stability test samples and the samples recently produced by our company. The content determination results were similar.

[0038] Example 7 Comparative test (commercially available products) (1) At room temperature: The content determination method of zinc gluconate oral solution in the 2025 edition of the Chinese Pharmacopoeia, Part II, and the proposed new method were used to determine the content of 5 commercially available samples produced by different companies. The results of the determination of the 5 samples are shown in Table 8. Table 8 Comparison of Content Determination Results of Commercially Available Samples

[0039] (2) When determining the content of zinc gluconate oral solution using the method for content determination in Part II of the 2025 edition of the Chinese Pharmacopoeia, ammonia-ammonium chloride buffer was added, and a precipitate formed in the solution. After shaking, the precipitate dissolved, and the solution turned pale yellow. During the titration, the solution did not change color, making it impossible to determine the titration endpoint and accurately determine the sample content. The reason may be that the components in the prescription interfere with the titration, preventing the excess EDTA from displacing Chrome Black T. The proposed new method can accurately determine the titration endpoint and determine the sample content. For other company samples, both the method for content determination in Part II of the 2025 edition of the Chinese Pharmacopoeia and the proposed new method can accurately determine the sample content, and the content determination results are similar. (3) High temperature test: We conducted a high temperature test (60℃) on commercially available samples from different companies. After 10 days, the color of each sample deepened to varying degrees. The content determination method of zinc gluconate oral solution in the 2025 edition of the Chinese Pharmacopoeia, Part II, and the proposed new method were used to determine the content of the above high temperature test samples. The comparison of the determination results is shown in Table 9. Table 9 Comparison of content determination results in high-temperature test (60℃) of commercially available samples

[0040] (4) As shown in Table 9, when using the method for determining the content of zinc gluconate oral solution in the 2025 edition of the Chinese Pharmacopoeia, Part II, to determine the content of samples tested at 60°C, the sample color deepens, interfering with the titration process and making it more difficult to determine the titration endpoint. The proposed new method for determining the content of samples tested at 60°C can eliminate color interference and accurately determine the titration endpoint. The content determination results of samples tested at 60°C using both the method for determining the content of zinc gluconate oral solution in the 2025 edition of the Chinese Pharmacopoeia, Part II, and the proposed new method are similar.

[0041] In summary, the method for determining the content of zinc gluconate oral solution provided in this application effectively solves the technical challenge of increased difficulty in determining the titration endpoint in pharmacopoeia methods for samples with deepened color, high-temperature testing samples, and some commercially available samples by optimizing the sampling amount, buffer system ratio, titrant concentration, and adding ammonium fluoride to eliminate interference. Methodological validation shows that this method has good specificity, with no interference from blank excipients; high precision, with a repeatability RSD ≤ 0.2%; excellent accuracy, with an average recovery rate of 100.04% and an RSD ≤ 0.1%; and good solution stability, with an RSD ≤ 0.2% within 8 hours. Comparison with the pharmacopoeia method shows no significant difference in the determination results for normal samples. For samples with deepened color or interference from prescription components, this method can clearly determine the endpoint and accurately determine the content, making it more applicable, simpler to operate, and less expensive. It can meet the quality control needs of routine, large-scale, and multi-state samples of zinc gluconate oral solution, providing reliable technical support for drug quality control and the safe and effective use of clinical medication.

[0042] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application. All equivalent changes and improvements made within the scope of this application shall still fall within the patent coverage of this application.

Claims

1. A method for determining the content of zinc gluconate in an oral solution, characterized in that, The method includes the following steps: (1) Solution mixing: Accurately measure 20 mL of zinc gluconate oral solution, which is approximately equivalent to 0.07 g of zinc gluconate. Add water and ammonia buffer solution, then add ammonium fluoride and indicator, and mix well to obtain a purple-red solution. (2) Titration: Use disodium ethylenediaminetetraacetate as the titrant and titrate it into the mixed solution of step (1) until the solution of step (1) changes from purple-red to blue-green and remains unchanged for 30 seconds. Stop the titration. (3) Calculation of zinc gluconate content: Calculate the zinc gluconate content based on the volume of titrant consumed in step (2).

2. The method for determining the content of zinc gluconate in an oral solution as described in claim 1, characterized in that, In step (1), the ammonia buffer solution is an ammonia-ammonium chloride buffer solution.

3. The method for determining the content of zinc gluconate oral solution as described in claim 1, characterized in that, The indicator used in step (1) is Chrome Black T indicator.

4. The method for determining the content of zinc gluconate in oral solution as described in claim 1, characterized in that, The amount of water added in step (1) is 90 mL.

5. The method for determining the content of zinc gluconate oral solution as described in claim 1, characterized in that, In step (1), the amount of ammonia buffer added is 2 mL.

6. The method for determining the content of zinc gluconate oral solution as described in claim 1, characterized in that, The amount of ammonium fluoride added in step (1) is 1g.

7. The method for determining the content of zinc gluconate oral solution as described in claim 1, characterized in that, In step (2), the role of disodium ethylenediaminetetraacetate is to react with Zn. 2+ Formation of ZnY 2- A colorless chelate, when titrated to the endpoint, ZnIn - In the solution, Eriochrome Black T is displaced by excess disodium ethylenediaminetetraacetate, forming a stable chelate ZnY. 2- Free Eriochrome Black T appears blue-green in solution, thus indicating the titration endpoint.

8. The method for determining the content of zinc gluconate oral solution as described in claim 1, characterized in that, In step (2), the concentration of disodium ethylenediaminetetraacetate is 0.01 mol / L.

9. The method for determining the content of zinc gluconate in an oral solution as described in claim 2, characterized in that, The pH of the ammonia-ammonium chloride buffer solution is 10.0 ± 0.

2.

10. The method for determining the content of zinc gluconate in an oral solution as described in claim 3, characterized in that, The function of the chrome black T is to react with Zn. 2+ Formation of stable purplish-red chelate ZnIn - .

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