Reagents, Indicators, and Solutions
This section deals with the reagents and solutions required in conducting the Pharmacopeial and the National Formulary tests and assays.
As is stated in the General Notices, listing of reagents, indicators, and solutions in the Pharmacopeia in no way implies that they have therapeutic utility; thus, any reference to the USP in their labeling is to include the term “reagent” or “reagent grade.”
Reagents required in the tests and assays for the Pharmacopeial and National Formulary articles are listed in this section, generally with specifications appropriate to their intended uses. Exceptions to the latter include those reagents for which corresponding specifications are presented in the current edition of Reagent Chemicals, published by the American Chemical Society, and reagents for which specifications could not be drafted in time for inclusion here. Thus, where it is directed to “Use ACS reagent grade,” it is intended that a grade meeting the corresponding specifications of the current edition of ACS Reagent Chemicals shall be used. Where no such specifications exist, and where it is directed to “Use a suitable grade,” the intent is that a suitable reagent grade available commercially shall be used. Occasionally, additional test(s) augment the designation “suitable grade,” as indicated in the text. Listed also are some, but not all, reagents that are required only in determining the quality of other reagents. For those reagents that are not listed, satisfactory specifications are available in standard reference works.
In those instances in which a reagent required in a Pharmacopeial or National Formulary test or assay need not be of analytical reagent quality, it suffices to refer to the monograph for that article appearing in this Pharmacopeia or the National Formulary or the current edition of the Food Chemicals Codex (FCC). In such cases it is to be understood that the specifications are minimum requirements and that any substance meeting more rigid specifications for chemical purity is suitable.
Where the name of a reagent specified in a test or assay is the same as the title of a USP or NF article, and it does not appear among the following Reagent Specifications, a substance meeting the requirements of the USP or NF monograph is to be used (e.g., Benzocaine, USP; or Propylparaben, NF). However, reference is specifically made, under Reagent Specifications, to a reagent bearing the name of a USP or NF article: (1) where there are requirements for a reagent in addition to the USP or NF monograph requirements (e.g., Sodium Salicylate, USP; or Isopropyl Myristate, NF), (2) where a source other than the USP or NF monograph is specified (e.g., Lactose, ACS reagent; or Hydrochloric Acid, ACS reagent), (3) where complete reagent specifications differ from the USP or NF monograph standards (e.g., Calcium Lactate; or Thymol,) or (4) where a standard material is included among the reagent specifications (e.g., Calcium Carbonate, primary standard; or Sodium Carbonate, primary standard).
Reagents and solutions should be preserved in tight containers made of resistant glass or other suitable material. Directions for storage in light-resistant containers should be carefully observed.
Stoppers and stopcocks brought into contact with substances capable of attacking or penetrating their surfaces may be given a protective coating of a thin film of a suitable lubricant unless specifically interdicted.
Where a particular brand or source of a material or piece of equipment, or the name and address of a manufacturer, is mentioned, this identification is furnished solely for informational purposes as a matter of convenience, without implication of approval, endorsement, or certification.
Atomic absorption and flame photometry require the use of a number of metal-ion standard solutions. While the individual monographs usually provide directions for preparation of these solutions, use of commercially prepared standardized solutions of the appropriate ions is permissible, provided that the analyst confirms the suitability of the solutions and has data to support their use.
Reagents are substances used either as such or as constituents of solutions.
Indicators are reagents used to determine the specified end-point in a chemical reaction, to measure hydrogen-ion concentration (pH), or to indicate that a desired change in pH has been effected. They are listed together with indicator test papers.
Buffer Solutions are referred to separately.
Colorimetric Solutions, abbreviated “CS,” are solutions used in the preparation of colorimetric standards for comparison purposes.
Test Solutions, abbreviated “TS,” are solutions of reagents in such solvents and of such definite concentrations as to be suitable for the specified purposes.
Volumetric Solutions, abbreviated “VS” and known also as Standard Solutions, are solutions of reagents of known concentration intended primarily for use in quantitative determinations. Concentrations are usually expressed in terms of normality.
Water—As elsewhere in the Pharmacopeia, where “water,” without qualification, is mentioned in the tests for reagents or in directions for preparing test solutions, etc., Purified Water (USP monograph) is always to be used. Carbon dioxide-free water is Purified Water that has been boiled vigorously for 5 minutes or more and allowed to cool while protected from absorption of carbon dioxide from the atmosphere, or Purified Water that has a resistivity of not less than 18 Mohm-cm. Deaerated water, for purposes other than dissolution and drug release testing, is Purified Water that has been treated to reduce the content of dissolved air by suitable means, such as by boiling vigorously for 5 minutes and cooling or by the application of ultrasonic vibration. Particle-free water is water that has been passed through a 0.22-µm filter.
Chromatographic Solvents and Carrier Gases—The chromatographic procedures set forth in the Pharmacopeia may require use of solvents and gases that have been especially purified for such use. The purpose may be (a) to exclude certain impurities that interfere with the proper conduct of the test procedure, or (b) to extend the life of a column by reducing the build-up of impurities on the column. Where solvents and gases are called for in chromatographic procedures, it is the responsibility of the analyst to ensure the suitability of the solvent or gas for the specific use. Solvents and gases suitable for specific high-pressure or other chromatographic uses are available as specialty products from various reagent supply houses, although there is no assurance that similar products from different suppliers are of equivalent suitability in any given procedure. The reagent specifications provided herein are for general analytical uses of the solvents and gases and not for chromatographic uses for which the especially purified specialty products may be required.