When Standards Outpace Practice: The Impact of Proposed USP <31> Revisions if Implemented
A Shift in Volumetric Measurement Expectations
Volumetric measurement is fundamental to analytical laboratories. From preparing standards to performing titrations, volumetric glassware—flasks, pipettes, and burettes—plays a central role in pharmaceutical quality control (QC).
For decades, USP General Chapter <31>, Volumetric Apparatus, has provided the framework for ensuring volumetric accuracy. In May 2025, the United States Pharmacopeia (USP) proposed revisions to this chapter in Pharmacopeial Forum 51(3), along with a companion chapter, <1331>, focused on calibration practices.
The intent of these revisions is clear:
- align USP with modern metrology
- harmonize with ISO and ASTM standards
- introduce traceability and risk-based calibration
However, the proposal represents more than an update—it introduces a fundamental shift in how volumetric measurement is expected to be managed.
The proposed revision introduces several key changes:
- Adoption of International Vocabulary of Metrology (VIM) terminology
- Alignment with ISO and ASTM standards
- Inclusion of piston-operated volumetric apparatus (POVA)
- Emphasis on risk-based calibration within Quality Management Systems
- Increased focus on traceability and measurement control
Together, these changes suggest that volumetric devices should be treated as traceable measurement instruments, rather than standardized laboratory tools.
The Pharmacopeial Forum comment period has now closed, and USP has been reviewing industry feedback, which will inform the final version of the chapter if approved.
In practice, most analytical laboratories rely on:
- Class A volumetric glassware
- Manufactured to ASTM or ISO tolerances
- Supported by manufacturer conformance documentation
In routine use:
- Glassware is not serialized
- Labs do not maintain device-level calibration records
- There is no apparatus-level traceability
Instead, accuracy is ensured through validated analytical methods, system suitability testing, and tightly controlled manufacturing tolerances.
Even when labeled as Class A, manufacturers often do not provide batch calibration certificates or traceability documentation. Laboratories typically receive catalog specifications and statements of compliance.
This means the current system is manufacturing-controlled, not calibration-controlled—and it has been effective for decades.
The proposed USP framework introduces expectations based on traceability, but this creates a gap between theory and practice.
Three structural realities drive this gap:
1. Unserialized Glassware – No unique identifiers prevent tracking calibration history.
2. Lack of Calibration Documentation – Manufacturers do not typically provide calibration certificates.
3. Limited Calibration Infrastructure – Most laboratories lack internal metrology systems.
Together, these factors create a traceability gap between what is expected and what is realistically achievable.
If interpreted as requiring apparatus-level traceability, the operational impact would be substantial.
A typical QC laboratory maintains hundreds to thousands of volumetric devices. Implementing traceability would require:
- assigning unique identifiers
- maintaining inventories
- implementing tracking systems
- developing new procedures
These changes would add administrative complexity and shift resources away from core analytical work.
Historically, regulators such as the FDA and EMA have accepted Class A glassware supported by manufacturer certification.
However, expectations are evolving toward traceability, data integrity, and risk-based systems. USP <1331>, although informational, may influence inspection expectations.
Laboratories may be asked to justify calibration strategies and reliance on manufacturer documentation.
The proposed revisions to USP <31>, in their current form, represent a significant and unnecessary departure from how Class A volumetric glassware is traditionally acquired, documented, and used in modern analytical laboratories. For decades, laboratories have relied on manufacturer-certified Class A glassware produced to ASTM or ISO tolerances, without device serialization or apparatus-level calibration programs—a model that has consistently demonstrated reliability and fitness for purpose.
The proposed framework introduces expectations for apparatus-level traceability that are misaligned with both current industry practice and the realities of laboratory infrastructure. Implementing such systems would require substantial changes to laboratory operations, including device-level identification, tracking, and documentation, adding complexity and administrative burden to routine analytical workflows without a clear corresponding benefit.
While the objective of improving measurement traceability is understandable, extending these principles to routine volumetric glassware represents an overextension of metrological control. In most analytical applications, volumetric uncertainty from Class A glassware is already well-controlled and does not represent a significant contributor to overall method variability. As such, the proposed changes risk introducing disproportionate operational burden while delivering limited, if any, meaningful improvement in analytical quality.