“About” indicates a quantity within 10%.

If the measurement is stated to be “accurately measured” or “accurately weighed,” follow the statements in the general chapters Volumetric Apparatus 31 and Balances 41, respectively.

Percentages of alcohol, such as those under the heading Alcohol Content, refer to percentage by volume of C2H5OH at 15.56. Where a formula, test, or assay calls for alcohol, ethyl alcohol, or ethanol, the USP monograph article Alcohol shall be used. Where reference is made to “C2H5OH,” absolute (100 percent) ethanol is intended. Where a procedure calls for dehydrated alcohol, alcohol absolute, or anhydrous alcohol, the USP monograph article Dehydrated Alcohol shall be used.

Atomic weights used in computing molecular weights and the factors in the assays and elsewhere are those established by the IUPAC Commission on Atomic Weights and Isotopic Abundances.

Where it is directed that “any necessary correction” be made by a blank determination, the determination shall be conducted using the same quantities of the same reagents treated in the same manner as the solution or mixture containing the portion of the substance under assay or test, but with the substance itself omitted.

“Concomitantly” denotes that the determinations or measurements are to be performed in immediate succession.

The instruction “in a desiccator” indicates use of a tightly closed container of suitable size and design that maintains an atmosphere of low moisture content by means of a suitable desiccant such as anhydrous calcium chloride, magnesium perchlorate, phosphorus pentoxide, or silica gel. See also section 8.220, Vacuum Desiccator.

Logarithms are to the base 10.

A microbial strain cited and identified by its ATCC catalog number shall be used directly or, if subcultured, shall be used not more than five passages removed from the original strain.

“Negligible” indicates a quantity not exceeding 0.50 mg.

“NLT” means “not less than.” “NMT” means “not more than.”

“Odorless,” “practically odorless,” “a faint characteristic odor,” and variations thereof indicate evaluation of a suitable quantity of freshly opened material after exposure to the air for 15 minutes. An odor designation is descriptive only and should not be regarded as a standard of purity for a particular lot of an article.

“Percent” used without qualification means:

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.

Percentage concentrations are expressed as follows:

Pressure is determined by use of a suitable manometer or barometer calibrated in terms of the pressure exerted by a column of mercury of the stated height.

Reaction time is 5 minutes unless otherwise specified.

Specific gravity is the weight of a substance in air at 25 divided by the weight of an equal volume of water at the same temperature.

Temperatures are expressed in centigrade (Celsius) degrees, and all measurements are made at 25 unless otherwise indicated. Where moderate heat is specified, any temperature not higher than 45 (113 F) is indicated.

Unless otherwise specified, rounding rules, as described in section 7.20, Rounding Rules, apply to any time specified.

“Transfer” indicates a quantitative manipulation.

“Vacuum” denotes exposure to a pressure of less than 20 mm of mercury (2.67 kPas), unless otherwise indicated.

“Vacuum desiccator” indicates a desiccator that maintains a low-moisture atmosphere at a reduced pressure of not more than 20 mm of mercury (2.67 kPas) or at the pressure designated in the individual monograph.

In general, weights and measures are expressed in the International System of Units (SI) as established and revised by the Conférence générale des poids et mesures. For compendial purposes, the term “weight” is considered to be synonymous with “mass.”

Molality is designated by the symbol m preceded by a number that represents 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 represents the number of moles of the designated solute contained in an amount of the designated solvent that is sufficient to prepare 1 liter of solution.

Normality is designated by the symbol N preceded by a number that represents the number of equivalents of the designated solute contained in an amount of the designated solvent that is sufficient to prepare 1 liter of solution.

Chart of Symbols and Prefixes commonly employed for SI metric units and other units: