Weighing Standard Ensures USP Compliance

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Mettler Toledo's global weighing standard, GWP, can help pharmaceutical manufacturers meet the new requirements of USP Chapter 41 and Chapter 1251.

Mettler Toledo’s global weighing standard, GWP, can help pharmaceutical manufacturers and suppliers meet the new requirements of United States Pharmacopeia’s (USP) revised Chapter 41 on balances and updates to the advisory Chapter 1251. The new revisions define modified balance test procedures for the US pharmaceutical industry and also apply to companies exporting to the US. The revised chapters become official on Dec. 1, 2013.

The revised General Chapter 41 details a relatively demanding balance assessment, outlining accuracy and repeatability tests for calibrated balances used to weigh analytes for quantitative measures. Since accuracy can only be gauged using weights that are at least 5% of an instrument’s capacity, test weight selection criteria have also been modified accordingly (weights smaller than 5% cannot assess systematic deviations sufficiently well enough).

General Chapter 1251 provides additional clarification on the new procedures and extends the scope to any balance used for an analytical procedure. It details that balance performance verification should be carried out using a risk-based approach. It is recommended to only weigh net samples that weigh sufficiently more than the minimum weight to account for fluctuations in the balance's performance due to varying influences from the environment and the balance operators. This requirement is clearly applied to the sample weight itself—and not to the tare vessel. Daily testing recommendations have been dropped, a change that is expected to provide significant time savings, according to a Mettler Toledo statement.


Mettler Toledo’s GWP Verification is standardized scientific methodology for secure selection, calibration and operation of weighing equipment. It provides the documented evidence for reproducible weighing results in harmony with all current quality standards in laboratory and manufacturing. Users can use GWP as the benchmark to select and calibrate their weighing equipment.

The company offers a free on-demand webinar that explains how balance quality management will be affected, focusing on the determination of minimum weight and execution of routine testing. A free white paper, video, and e-learning course are offered.