Medical Gas Testing Procedures

Recently we have seen the FDA concentrate its medical gas enforcement activity on medical gas testing procedures and documentation, with a particular focus on alternative test method validation. Whether this is related to the impending changes to the medical gas monographs is anybody’s guess, but a number of firms have been required to make significant changes in their testing procedures and analytical equipment due to an FDA inspection and enforcement actions. This article will examine current medical gas analytical practices, and hopefully help you avoid an unpleasant surprise during a future FDA inspection at your facility.

The current medical gas testing procedures and analytical equipment specified in the United States Pharmacopeia (USP) have been in place for nearly 40 years, and do not account for many newer analytical technologies. Most notable is the nearly universal use of the paramagnetic analyzer in our industry to analyze and identify Oxygen USP, even though the official method is the wet chemical Orsat process. Even though paramagnetic technology is ubiquitous in our industry, the FDA still requires firms to possess studies demonstrating that the paramagnetic analyzer is equivalent to the Orsat. The good news is that most popular analyzer manufacturers can provide either a copy of an appropriate validation study or a letter from the FDA accepting specific models as equivalent.

The same criterion applies to paramagnetic analyzers used to analyze Nitrogen NF and medical air. The official method to assay Nitrogen NF is the gas chromatograph, and the official method to assay medical air is the electro-chemical style analyzer. The paramagnetic analyzer, when used to analyze and identify Nitrogen NF and medical air, is considered an alternative test method. Firms that use paramagnetic analyzers to analyze these gases must have validation studies demonstrating the equivalency of the analyzer used. There are a few models of paramagnetic analyzers that have been validated and accepted by the FDA as equivalent to the official method for analyzing Nitrogen NF and medical air.

Firms that use gas chromatography (GC) units to analyze pure and mixed medical gases must make sure that the specifications of their GC conform to USP/NF requirements. An issue we have seen in numerous FDA enforcement actions involves the specific GC column dimensions stipulated in the medical gas monographs. USP stipulates GC metric column dimensions of either 3 or 6 meters in length with a 4 mm internal diameter, depending on the gas to be analyzed. Frequently, GCs sold in the United States arrive with column installed whose dimensions are expressed in feet and inches. If your GC is equipped with columns that do not conform to the specific USP requirements, you are required to validate the equivalency of your GC to the USP specifications. When it comes to GCs, unfortunately, there are no off-the-shelf validation studies that we are aware of.

The best way to ensure your firm is in compliance is to make a list of the analyzers you use to assay and ID your medical gases, and compare that to the official USP/NF medical gas monographs, which can be found in the online GAWDA FDA Compliance Manual. If your firm is not using the official method, the next step is to see if your model analyzer is a model accepted by the FDA as equivalent or one for which the manufacturer can provide an available validation study. If not, then you are faced with either validating your analyzer to the USP monographs, or switching to a new analyzer that is documented as a validated equivalent method.

Gases and Welding Distributors Association
Meet the Author
GAWDA Medical Gases Consultant J. Robert Yeoman is president & CEO of B&R Compliance Associates LLC in Lehigh Valley, Pennsylvania. Members can reach him at (610) 868-7183 and at