Lachman 评析 QC 实验室称量做法在 USP <41> 与 <1251> 修订下的可辩护性

Do you know if your QC laboratory weighing practices are defensible? They may not be if weighing controls are treated as routine rather than as a critical part of the analytical process. Because weighing underpins many test procedures and methods, unreliable balance data can compromise results throughout an assay.

Earlier this year (February 2026), the USP implemented significant updates to their primary chapters that address laboratory weighing: USP <41> Balances and USP <1251> Weighing on an Analytical Balance

Revised USP <41> requires a balance to be “calibrated over the operating range” and to meet the requirements for repeatability and accuracy. The laboratory must therefore define and justify the operating range for each balance rather than relying solely on the instrument’s nominal capacity.

USP <41> further states that calibration must include an assessment of the balance’s measurement uncertainty. Calibration should also be performed before and after any operation that could affect the balance’s performance. The laboratory should evaluate such operations through change management and document whether recalibration is required.

Revised USP <41> distinguishes between minimum weight and smallest net weight, both of which are considered in the balance’s repeatability assessment. The minimum weight is determined during the repeatability experiment. The smallest net weight is defined by the user based on the test procedures for which the balance will be used. USP <1251> recommends a safety factor to manage the relationship between these values: the user-defined smallest net weight should be at least twice the measured minimum weight.

USP <41> distinguishes calibration from the accuracy and repeatability checks used to verify suitable balance performance between calibrations. Calibration may include additional tests, such as eccentricity and linearity, to confirm overall performance and determine measurement uncertainty. For interim accuracy testing, the laboratory must define and justify the test weight with consideration of the balance’s operating range.

Informational chapter USP <1251> classifies balances as Group B instruments under USP <1058>. Accordingly, each balance must be qualified as fit for its intended use, and the laboratory must be able to defend the qualification approach applied to it. USP <1251> states:

“Because qualified instruments’ calibration measurement uncertainty propagates through validated analytical methods, they must be considered within the defined decision rule for the analytical target profile (ATP) in Analytical Procedure Life Cycle 〈1220〉 and when there are any changes in analytical procedures.”

The laboratory must proceduralize the frequency and scope of balance Performance Qualification, considering “the risk of the weighing application, as defined in the user’s quality management system.” Performance Qualification includes calibration and periodic performance checks, with the minimum requirements established in USP <41>.

The revisions to USP <41> and USP <1251> link the performance / capability of the balance to the method analytical target profile (ATP), where the user must ultimately defend and demonstrate that the Performance Qualification requirements for that balance support the method’s ATP and that a lifecycle approach is employed where the laboratory monitors the ongoing performance of the balance and confirms it is “fit for purpose”.

If you have any questions related to your laboratory balance controls, then please reach out to [email protected] for a conversation.

The post Are My QC Laboratory Weighing Practices Defensible? appeared first on Lachman Consultant Services, Inc..