U.S. PHARMACOPEIA

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CONCENTRATIONS
Molal, molar, and normal solution concentrations are indicated throughout this Pharmacopeia for most chemical assay and test procedures (see also Volumetric Solutions in the section Reagents, Indicators, and Solutions). Molality is designated by the symbol m preceded by a number that is the number of moles of the designated solute contained in 1 kilogram of the designated solvent. Molarity is designated by the symbol M preceded by a number that is the number of moles of the designated solute contained in an amount of the designated solvent that is sufficient to prepare 1 L of solution. Normality is designated by the symbol N preceded by a number that is the number of equivalents of the designated solute contained in an amount of the designated solvent that is sufficient to prepare 1 L of solution.
Percentage Measurements— Percentage concentrations are expressed as follows:
Percent Weight in Weight— (w/w) expresses the number of g of a constituent in 100 g of solution or mixture.
Percent Weight in Volume— (w/v) expresses the number of g of a constituent in 100 mL of solution, and is used regardless of whether water or another liquid is the solvent.
Percent Volume in Volume— (v/v) expresses the number of mL of a constituent in 100 mL of solution.
The term percent used without qualification means, for mixtures of solids and semisolids, percent weight in weight; for solutions or suspensions of solids in liquids, percent weight in volume; for solutions of liquids in liquids, percent volume in volume; and for solutions of gases in liquids, percent weight in volume. For example, a 1 percent solution is prepared by dissolving 1 g of a solid or semisolid, or 1 mL of a liquid, in sufficient solvent to make 100 mL of the solution.
In the dispensing of prescription medications, slight changes in volume owing to variations in room temperatures may be disregarded.