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Standards of

What are they?

USP Reference Standards, which are integral components of monographs and other documents established by USP to help ensure the identity, potency, quality and purity of drugs and foods, are provided primarily for quality control in the performance of titrations and tests. USP Reference Standards are required to be used in pharmacopeial evaluations and testing of official standards publications, the United States Pharmacopeia – National Formulary (USP – NF), to ensure compliance with official USP – NF quality requirements, as enforced by the FDA.

USP Reference Standards also lend themselves to other applications, including measurements required to obtain accurate and reproducible results with modern chromatographic and spectrophotometric methods.

To fulfill their intended purpose, all USP Reference Standards must be stored, handled and used correctly.

Purity and Quality

USP Reference Standards are selected for their high purity, critical characteristics and suitability for their intended purpose. Unless a specific potency or content is stated on the label of the USP Reference Standard, it should be assumed that the USP Reference Standard is 100% pure for the USP purposes for which it was provided.

Heterogeneous substances of natural origin are also referred to as ”Reference Standards”. These are generally the equivalents of international standards.

USP Reference Standards are established through a rigorous testing, evaluation and quality control process. They are analyzed independently in three or more laboratories, including USP laboratories, and may include FDA and industrial laboratories in different parts of the world.

Reference Standards are issued under the authority of the USP Board of Trustees, after an Expert Committee of the USP Council of Experts approves the suitability of each batch for pharmacopeial use.

Reference Standard Categories

USP offers more than 3,000 Reference Standards for pharmaceuticals, excipients and dietary supplements.
The list of available USP Reference Standards includes:


  • Reference Standards required by the current official edition of USP – NF.
  • Required Reference Standards for Pending Monographs and Non-U.S. Monographs
  • Reference Standards not required in the current USP – NF, but for which there is still sufficient demand.
  • Reference Standards specified in the current edition of the Food Chemicals Codex.
  • Reference Standards for addictive substances, requested by analytical, clinical, pharmaceutical and research laboratories.

The distribution of controlled substances is subject to the regulations and licensing provisions of the Drug Enforcement Administration (DEA) of the U.S. Department of Justice.

USP also collaborates with the World Health Organization in the program to provide international biological standards and reference chemicals for antibiotics, biologics, and chemotherapeutic agents. Some USP Reference Standards are standardized in terms of the corresponding international standards.

Use of USP reference standards


Users should determine that the Reference Standards they use are from an official lot.

The suitability of the Reference Standards for applications and uses other than those specified in the USP- NF, Food Chemicals Codex or Dietary Supplements Compendium is at the sole risk and expense of the purchaser.


Ensure that USP Reference Standards are stored in their original covered containers and that special label directions are followed, away from heat and humidity and protected from light.


Ensure that the Reference Standards are accurately weighed (bearing in mind that relatively large errors can be made by weighing small masses) when it is indicated that a standard solution or standard preparation is to be prepared for a quantitative determination.

Please refer to the current official edition of USP – NF, General Chapters <41> Weights and Balances and <31> Volumetric Apparatus and General Notices in USP – NF, where you will find detailed information.


Use a clean, dry beaker as a drying beaker when the USP Reference Standard is required to dry before use. Never use the original container.

Make sure not to dry the sample repeatedly at temperatures above 25 degrees Celsius.

Comply with all special drying requirements specified on the label of the Reference Standards or in the specific sections of the USP or NF monographs. (Remember that any specific label or monograph instructions supersede the usual instructions in the Procedures described in “Tests and Ratings” of USP-NF General Notices).

Follow USP-NF Method I, General Chapter Water Determination, where volumetric determination of water is required when a Reference Standard is to be used. Instrumental or microanalytical methods are also accepted for this purpose. When using typical amounts (about 50 mg of Reference Standard), it is advisable to titrate with a one-quarter dilution of the reagent.