White Paper

USP Chapter 41 Weighing Requirements

White Paper

Weighing in Pharmaceutical Quality Control According to U.S. Pharmacopeia Guidelines

USP Chapter 41 Weighing Requirements on Balances in Pharamceutical QC
USP Chapter 41 Weighing Requirements on Balances in Pharamceutical QC

USP Chapter <41> weighing requirements are mandatory in a Pharmaceutical Quality Control (QC) laboratory, where weighing is a fundamental step in almost every workflow. Typically, weighing a sample or standard is the first step in an analytical procedure, followed by dilution and subsequent analysis by techniques such as HPLC or qNMR. Any error in the weighing step has the potential to propagate through the whole analytical process, causing inaccuracies in the final result. To avoid this situation, the United States Pharmacopeia (USP) has set stringent requirements for balances that are used to weigh analytes for quantitative assessments. These requirements are designed to ensure that any uncertainty in weighing is small or even negligible within the analysis.

This white paper comprehensively explains the requirements of the 2019 versions of USP General Chapters <41> and <1251> and provides advice on how to put these requirements into practice. Weighing according to USP requirements will ensure that a consistently high quality of weighing results is achieved and is applicable to all pharmaceutical QC activities globally, not just those operating in the USA.

Ensure that your weighing processes are compliant with the current versions of USP General Chapters <41> and <1251>.

The mandatory General Chapter <41>, "Balances," describes three key requirements that a balance needs to fulfill when weighing analytes for quantitative measures: weighing should be performed on a calibrated balance that meets repeatability and accuracy requirements. This white paper will explain what that means and how to carry out acceptable repeatability and accuracy testing.

The informational General Chapter <1251>, "Weighing on an Analytical Balance," provides detailed guidance on the state-of-the-art strategy for the qualification and operation of balances. Disseminating all the information of General Chapter <1251> would go beyond the scope of this white paper, so focus is given to the dedicated topics of performance qualification and the safety factor. These topics are selected as they reflect user-routine testing of the equipment, which is crucial to ensuring that the instrument works continuously according to the requirements and is “fit for its intended purpose."



What are the important facts in USP General Chapters 41 and 1251?

  • Chapter 41 states that accurate weighing must be performed using a calibrated balance. A more demanding balance assessment is introduced. Repeatability and accuracy tests are defined with acceptance limits and permissible test weights. The white paper “Weighing According to US Pharmacopeia” explains the requirements in more detail. Standard operating procedures for balance testing are available to download for free.
  • Chapter 1251 revisions focus on balance qualification and operation, including the importance of "minimum weight." A daily balance check, typically performed in the pharmaceutical industry, is no longer mandatory. Instead, the type and frequency of testing should be based on the risk and process tolerance of the application. Performing the right tests at the right intervals ensures high-quality results and potentially saves time and money by eliminating unnecessary testing! Watch the video: Three Key Things about the USP Revisions on Weighing.
  • Chapter 1251 also introduces "gravimetric dosing," a state-of-the-art weighing methodology for analytical standard and sample preparation. This method involves weighing the sample and diluent, resulting in concentration units of mg/g.

How can METTLER TOLEDO support you?

Because the calibration of balances is a mandatory requirement of USP Chapter 41, METTLER TOLEDO offers the certificate USP General Chapter 41 "Balances."

Have a Look at the USP Sample Certificate

Who is affected by USP Chapter 41?"

The United States Pharmacopeia (USP) is the single reference work for the quality control of drugs in the United States. It is therefore also binding for pharmaceutical companies in other regions of the world who intend to export into the US market. As such, it has a similar legal status to the European Pharmacopoeia (Ph. Eur.) in Europe and is enforced by the Food and Drug Administration (FDA).

I am compliant with Ph. Eur.: do I also need a USP 41 Certificate?

Yes. Each certificate has dedicated statements to document compliance according to the specific pharmacopoeia. When references are made in customer documentation, they can be specifically related either to Ph. Eur. General Chapter 2.1.7. or to USP General Chapter 41.