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Drug Assay (Active Ingredients and Dosage Forms)

Nelson Labs assay test being performed

What is a drug assay (test)?

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

Why are drug assays an important aspect of pharmaceutical testing?

Pharmaceutical manufacturers are required to follow strict regulatory guidelines and prove their products are high quality, safe, effective, and free of contamination and defects. Assays play an important role in this process by determining the concentration of a drug compared to its labeled amount.

What drug assay testing does Nelson Labs perform?

Nelson Labs performs assay tests on active pharmaceutical ingredients (APIs) and finished products, using techniques such as the following:

  • High Performance (or Ultra High Performance) Liquid Chromatography (HPLC or UHPLC)
  • Gas Chromatography (GC)
  • Titrations
  • Ultraviolet Light Absorption (UV)
  • Infrared Absorption (IR)
  • Atomic Absorption (AA)

Study Outline

The drug assay test is performed by the technique best suited for the test article. The concentration of the API, termed assay, is expressed in three commonly used terms:

As is Basis

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

Dried Basis

Dried basis assay implies that the assay results need to be corrected for the percentage of water that was determined lost through drying studies. At the time of calculation of assay value, the water content (percentage loss on drying) is subtracted from the sample weight.

Another method is to dry the sample before it is used. The sample is pulverized to a fine power and weighed to prepare the sample solution. This process is performed by drying the sample in a desiccator to a constant weight. Heat-sensitive materials can be dried in a vacuum over a desiccant. The water removed through drying is what was 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 the analysis is performed. This means that the sample does not have any absorbed water or bound water, such as hydrates.

The sample is weighed in the state that it was received and residual moisture content, if there is any, is measured independently by methods such as Karl Fischer titration. At the time the assay value is calculated, the water content is subtracted from the sample weight.

Testing Locations

  • Itasca, IL, USA

Learn more about our locations and their certifications.

Contact Us

If you have additional questions about pharmaceutical testing or would like to consult with experts at Nelson Labs, just send us a request or call us at +1 801-290-7500.