Completeness of Solution
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
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The purpose of these methods is to verify that one or more materials are completely dissolved in a solution. These methods may be used to verify the descriptive solubility of a material according to the solubility table in General Notices, 5.30 Description and Solubility.
To verify the descriptive solubility, use the maximum amount of solvent specified for the descriptive solubility in the solubility table (see General Notices, 5.30 Description and Solubility). For example, for “soluble” use 30 parts of solvent. Into this amount of solvent, add 1 part of solute weighed accurately to 0.5%. Unless otherwise specified in the monograph, completeness of solution should be evaluated at 25°.
Evaluation of the completeness of solution, as described in this chapter, does not provide a precise measure of compound solubility. The descriptive solubility terms above should also not be confused with the terms “high solubility” and “low solubility” as applied to drug substances in the Biopharmaceutical Classification System.1,2 For more information on precise solubility measurements and biorelevant solubility determinations, see Solubility Measurements 〈1236〉.
Unless otherwise directed in the individual monograph, use Method I. (USP 1-Aug-2020)
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1 METHOD I (USP 1-AUG-2020)
Place the quantity of the substance specified in the individual monograph in a meticulously cleansed, glass-stoppered, 10-mL color- comparison tube. (USP 1-Aug-2020) Using the solvent that is specified in the monograph or on the label of the product, fill the color- comparison tube to the 10-mL mark. (USP 1-Aug-2020) Shake gently to dissolve: the solution is not less clear than an equal volume of the same solvent contained in a matched color-comparison tube (USP 1-Aug-2020) and examined similarly (see Visual Comparison 〈630〉, Viewing conditions for turbidity comparison). (USP 1-Aug-2020)
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2 METHOD II
Place the quantity of the substance specified in the individual monograph into a meticulously cleansed 10-mL flask. Add 10 mL of the solvent that is specified in the monograph or on the label of the product. Shake gently to dissolve. Transfer the solution to a suitable measurement tube and measure the turbidity of the prepared solution per Nephelometry and Turbidimetry 〈855〉. The acceptance criterion is that the turbidity of the sample preparation is NMT that of Reference suspension II in 〈855〉 , Table 1 [NMT 6 nephelometric turbidity units (NTU)]. (USP 1-Aug-2020)
1 US Food and Drug Administration. Guidance for industry. Waiver of in vivo bioavailability and bioequivalence studies for immediate-release solid oral dosage forms based on a biopharmaceutics classification system. Rockville, MD: US Food and Drug Administration; December 2017.
2 USP. Reagents and Reference Tables, Solutions, Buffer Solutions, 4. Standard Buffer Solutions, 4.1 Preparation. In: USP–NF. Rockville, MD: USP; 1 May 2018.
