The Impact of Sample Amounts on Potency Testing

This guest post is adapted from an article by our partner ARL Bio Pharma
Nora Talley, ARL Bio Pharma Analytical Associate Supervisor
Jessica Munson, M.S., ARL Bio Pharma Analytical Supervisor

Formulations require different sample amounts to allow for an accurate result representative of the compounded preparation. The table below is taken from ARL's Sample Submission Guidelines.

Potency (Per Requested Active Pharmaceutical Ingredient (API)

Raw Powders50 mg
Triturates/Granulations/Blend Powders1 g
Solid Dose Forms
5 units
Suspensions10 mL
Solutions2 mL
Semi-Solid Dose Forms
3 g


Raw powders require 50 mg to meet USP balance requirements and to allow for loss due to powder sticking to the container. Triturates, granulations, and blend powders differ from raw powders as they are a dilution of the active pharmaceutical ingredient (API). One (1) gram is requested for these sample types to allow for adequate API sampling and to reduce the effects of content uniformity.

Solid Dose Forms

Solid dosage forms such as capsules, suppositories, troches, pellets, tablets, and lozenges can be tested as single units for content uniformity assessment or by combining multiple units for a potency test. Combining multiple units collected throughout the batch is the best way to obtain an accurate potency result, which is representative of the overall batch, for solid dosage forms.


A minimum of 10 mL is requested for suspensions so proper mixing can occur. When the suspension is not mixed sufficiently to suspend the API, a test sample that truly represents the potency of the compounded preparation may not be obtained. This can cause both high- and low-test results.

Note: the container used for the sample (if not sent in the final package) should not be overly large, ideally not more than two times (2x) the size of the sample, as this can also cause sampling problems.


Solutions are by definition uniform and are simple to sample. 2 mL of solutions are requested so 1 mL can be collected accurately for the potency test. Exceptions can be made for highly priced drugs.

Semi-Solid Dose Forms

In semi-solid dosage forms such as creams, lotion, gels and ointments, it is essential that the ingredients of the semi solid compound are evenly distributed throughout the sample. To evenly distribute the API, three (3) grams need to be provided so that when necessary the sample can be mixed evenly with in its container with a spatula.

The amounts ARL requests are not minimum amounts required for a potency test. Instead, these are amounts that ARL recommends to provide a potency test result that truly represents the sample.

Learn more about best practices for laboratory testing on ARL Bio Pharma's website.

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