Oxygen and PSA
What impurities are limited in Oxygen 93?
Which impurities does the Oxygen 93 monograph limit, such as CO, CO2 and water?
Short answer
The International Pharmacopoeia (13th edition, 2025) limits these impurities in Oxygen 93: carbon dioxide (maximum 300 ppm), carbon monoxide (5 ppm), NO plus NO2 (2 ppm in total), sulfur dioxide (1 ppm), oil (0.1 mg/m³) and water (67 ppm); Portugal's ACSS restates the same limits from the European Pharmacopoeia.
Portugal's ACSS specification ET 03/2006 (2024 revision) restates the European Pharmacopoeia limits for Oxygen 93:
| International Pharmacopoeia (2025), Oxygen 93% | European Pharmacopoeia, as restated by ACSS (2024) | |
|---|---|---|
| Oxygen | 90.0% to 96.0% (V/V) | 93% ± 3% (V/V) |
| Carbon dioxide | maximum 300 ppm (V/V) | ≤ 300 ml/m³ |
| Carbon monoxide | maximum 5 ppm (V/V) | ≤ 5 ml/m³ |
| Nitrogen oxides | NO and NO2: maximum 2 ppm (V/V) in total | NO/NO2 ≤ 2 ml/m³ |
| Sulfur dioxide | maximum 1 ppm (V/V) | ≤ 1 ml/m³ |
| Oil | maximum 0.1 mg/m³ | ≤ 0.1 mg/m³ (measured at ambient temperature and pressure) |
| Water | maximum 67 ppm (V/V) | water vapour ≤ 67 ml/m³ |
How the limits are checked
According to the EDQM history of the text, Ph. Eur. 2455 defines the quality of the gas delivered to the medical gas pipeline system, not at the terminal outlet, and since issue 12.3 it includes a section requiring a risk assessment for other impurities. The International Pharmacopoeia states that the oxygen content is continuously monitored during production.
AIGA 113/20, adopted from EIGA Doc 195, describes two oxygen analysers that continuously monitor and record the unit's output, and carbon monoxide, carbon dioxide and moisture analysers connected to the control and alarm systems, so that the main shut-off valve can close automatically when the oxygen or impurity levels leave the pharmacopoeia specification. Oil, nitric oxide, nitrogen dioxide and sulfur dioxide are tested at a sampling outlet, and the hospital's qualified personnel decide, through risk management, whether they are analysed continuously or periodically.
AIGA also names the quality of the intake air, including contamination with hydrocarbons, carbon monoxide, carbon dioxide, acid gases, nitrogen oxides, sulfur dioxide and particulate matter, as probably the major concern in selecting a site. The ACSS recommends permanent control with oxygen analysers, with the analyser and the shut-off valve upstream of the Oxygen 93 reservoir.
What the ULTRAOX datasheets state
The ULTRAOX SC and ST datasheets state "Oxygen quality in accordance with the European Pharmacopoeia". Their own values are listed in what the ULTRAOX datasheets state.
More questions
Where are the Ph. Eur. limits measured?
Ph. Eur. 2455 defines the quality of the gas delivered to the pipeline system, not at the terminal outlet, according to the EDQM history of the monograph.
Does the monograph cover other impurities?
Since issue 12.3, Ph. Eur. 2455 includes a section requiring a risk assessment for other impurities, according to EDQM.
Sources
- The International Pharmacopoeia, 13th edition (2025), Medicinal oxygen
- ACSS, ET 03/2006 v.2024, Especificações Técnicas para Gases Medicinais, section 4.2.1
- EDQM Knowledge database, Oxygen (93 per cent) 2455, monograph history
- AIGA 113/20 (adopted from EIGA Doc 195), On site generation of oxygen 93% for medicinal use, sections 4.3.1 and 6.2.1
- ULTRAOX SC datasheet, p. 3
- ULTRAOX ST datasheet, p. 3
Ultra Controlo figures come from its technical datasheets. Third-party facts were read at the source on the date shown.
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