The Latest Medical Gas USP Monographs

Since 2009, the Unites States Pharmacopeia (USP) has proposed revisions to the medical gas monographs. GAWDA and the Compressed Gas Association’s Medical Gas Committees have supported the efforts to modernize the antiquated and hazardous wet-chemical test procedures.
After a proposed new test procedure is developed and validated, the formal USP monograph revision process involves multiple comments and review periods. It is not unusual for a USP revision to take many years from proposal to finalization. The new Oxygen, USP and Medical Air monographs recently have been revised and published.

Summary of Significant Changes

  • The previous assay test methods for oxygen used an Orsat glassware and wet-chemistry: The new assay test method is “paramagnetic oxygen measurement.”
  • The assay test method for medical air used to be “electrochemical” oxygen analyzer. The new assay test method is “paramagnetic oxygen measurement.”
  • The calibration gas for oxygen, USP has been changed to 99.99% oxygen.
  • The calibration gas for medical air has been changed to 21% oxygen.

New Monographs
The charts below contain the details of the new USP monographs:

The recent changes to the USP monographs likely will not require much change in most GAWDA member operations. Be sure that you are using the correct span gas for the Servomex Oxygen Analyzer (certified 99.99% Oxygen).

What’s Next?
The other medical gas monographs (nitrogen, helium, nitrous oxide and carbon dioxide) are also being considered for revision by USP. However, there are no changes planned for the immediate future. We will let you know when the official test methods are revised. If you have any questions, contact me.

Gases and Welding Distributors Association
Thomas Badstubner Meet the Author
GAWDA’s FDA & Medical Gases Consultant Thomas L. Badstubner is president of AsteRisk LLC in Blackstone, Massachusetts. Members can reach him at 508-883-0927 and