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Drug Assay (Active Ingredients and Dosage Forms)

An assay is an investigative (analytic) procedure for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity of a target entity (the analyte).

Nelson Labs performs Assay tests to APIs and Finished Products using techniques as: HLPC, GC, Titrations, UV, IR, AA.

Study Outline

The testing is performed by the applicable technique best suitable for the test article. The concentration of the active ingredient termed assay is expressed in four commonly used terms:

As is Basis

The expression denotes analysis of the product as it is received. The sample is analyzed directly without any drying. For example, if 100 milligrams of material is found to contain 98% of API then its assay on as is basis is reported as 98%.

Dried Basis

The sample received is pulverized to a fine powder is dried before being weighed out to prepare the sample solution. This process is performed by heating to 105° to 120°C for specified time and drying in a desiccator to constant weight. Heat sensitive materials can be dried in a vacuum over a desiccant. The water removed is that which is absorbed from the environment and is not chemically bound to the material. Drying in the oven does not necessarily remove bound water or water of hydration.

Anhydrous Basis

Anhydrous basis implies that there is no water present in the material before analysis is performed. It means that the sample does not have any absorbed water or bound water such as hydrates.

The sample is weighed as received and residual moisture content, if any, is measured independently by methods such as Karl Fischer titration. At time of calculation of assay value, the water content is subtracted from the sample weight.

Testing Locations


If you have additional questions about Excipient Testing, or would like to consult with the experts at Nelson Labs, just send us a request or call our Fairfield, NJ facility  at +1 (973) 227-6882.