Medical Air

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

Medical Air is a natural or synthetic mixture of gases consisting largely of nitrogen and oxygen. It contains NLT 19.5% and NMT 23.5%, by volume, of oxygen (O₂).

2 IDENTIFICATION

A. The paramagnetic signal exhibited by the Sample gas in the Assay confirms the presence of oxygen.

B. The Sample gas in the Assay meets the assay Acceptance criteria.

3 ASSAY

Procedure

The certified standards called for in the following test are listed in Reagents, Indicators, and Solutions.

Zero gas: Nitrogen certified standard

Span gas: 21% Oxygen certified standard. [Note—See Reagents, Indicators, and Solutions.]

Sample gas: Medical Air

Mode: Paramagnetic oxygen measurement (see Medical Gases Assay 〈415〉)

Analysis: Determine the concentration of oxygen in percentage by volume of Medical Air using a suitable paramagnetic analyzer.

Acceptance criteria: 19.5%–23.5% of oxygen by volume

4 IMPURITIES

Change to read:

See Impurities Testing in Medical Gases (ERR 1-Nov-2020) 〈413〉. The detector tubes called for in the following tests are listed in Reagents,

Indicators, and Solutions.

If the label indicates that Medical Air is a synthetic mixture of oxygen and nitrogen, and where oxygen complies to Oxygen USP and Nitrogen complies to Nitrogen NF, then the Impurities tests are not required.

Limit of Carbon Dioxide

Sample: Detector tube manufacturer's recommended volume ±5% of Medical Air

Analysis: Pass the Sample through a carbon dioxide detector tube at the rate specified for the tube by the detector tube manufacturer.

Acceptance criteria: NMT 500 ppm

Limit of Carbon Monoxide

Sample: Detector tube manufacturer's recommended volume ±5% of Medical Air

Analysis: Pass the Sample through a carbon monoxide detector tube at the rate specified for the tube by the detector tube manufacturer.

Acceptance criteria: NMT 10 ppm

Limit of Sulfur Dioxide

Sample: Detector tube manufacturer's recommended volume ±5% of Medical Air

Analysis: Pass the Sample through a sulfur dioxide detector tube at the rate specified for the tube by the detector tube manufacturer.

Acceptance criteria: NMT 5 ppm

Limit of Nitric Oxide and Nitrogen Dioxide

Sample: Detector tube manufacturer's recommended volume ±5% of Medical Air

Analysis: Pass the Sample through a nitric oxide–nitrogen dioxide detector tube at the rate specified for the tube by the detector tube manufacturer.

Acceptance criteria: NMT 2.5 ppm

Limit of Water and Oil

Analysis: Support one container in an inverted position (with the valve at the bottom) for 5 min. Cautiously open the valve slightly, maintaining the container in an inverted position. Vent the gas with a barely audible flow against a stainless steel mirror for a few seconds.

Acceptance criteria: No liquid is discernible on the mirror.

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in pressurized containers. Container connections shall be appropriate for air. Adaptors shall not be used to connect containers to patient use supply system piping or equipment.

Labeling: Label states if Medical Air is a synthetic mixture of Oxygen USP and Nitrogen NF. Where it is piped directly from the collecting tank to the patient point of use, label each outlet “Medical Air”.