Visual Comparison
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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)
The purpose of this test is to provide the details for the visual comparison of the color and/or turbidance of sample solutions of certain concentration to a standard solution or a series of standard solutions of known concentration. Where a color or turbidity comparison is directed, follow the procedures and conditions outlined below for performing these tests.
Comparison vessels: Color-comparison tubes matched as closely as possible in internal diameter, in depth of sample solution, and in all other respects should be used.
Viewing conditions for turbidity comparison: Tubes should be viewed horizontally against a dark background with the aid of a light source directed from the sides of the tubes.
Viewing conditions for color comparison: Tubes should be viewed downward against a white background. Most of the time, common room lighting is sufficient to perform the assessment. A light source directed from beneath the bottoms of the tubes may be used if needed and if the practice is consistent between the materials under comparison. (USP 1-May-2019)
