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Medical Gas Analysis

Application: Medical Gas Analysis

Measuring oxygen in Medical Gas

USP37 Medical Gas requires a specific, selective and positive identification test using a paramagnetic signal

Regular analysis of medical gas is required to ensure that the oxygen concentration is NLT 99.0% volume. Following the appropriate United States Pharmacopeia standards, in this case specifically USP37, requires an analyzer which uses a paramagnetic based technology.  The Systech Illinois Paramagnetic Oxgyen Analyzer PM700 is perfectly suited for this medical gas analysis application.

USP -NF Standard:

  • Medical Oxygen contains not less than (NLT) 99.0% oxygen by volume.
  • Acceptance criteria: NLT 99.0% by volume USP37
  • Mode: paramagnetic oxygen measurement (see Medical Gases Assay 415)
  • Identification: the paramagnetic signal exhibited by the sample gas in the Assay confirms the presence of oxygen USP37.
  • Analysis: determine the percentage by volume of oxygen using a suitable paramagnetic analyzer.
  • The certified standards called for are listed under Reagents, Indicators and Solutions.
  • Zero gas: nitrogen certified standard
  • Span gas: oxygen certified standard

European Pharmacopeia 2.5.27 Oxygen in Gases

European Pharmacopeia 2.5.27 dictates that oxygen in gases be determined using a paramagnetic analyzer.


  • Oxygen in gases is determined using a paramagnetic analyzer.
  • The principle of the method is based on the high paramagnetic sensitivity of the oxygen molecule.
  • Oxygen exerts a strong interaction on magnetic fields, which is measured electronically, amplified and converted to a reading of oxygen concentration.
  • As the paramagnetic effect of oxygen is linear the instrument must have a suitable range with a readability of 0.1 percent or better.
  • The measurement of oxygen concentration is dependent upon the pressure and temperature so if the analyzer does not automatically compensate for variations it must be calibrated immediately prior to use.

Our PM700 Paramagnetic analyzer may be used for the following applications:

  • EP monograph of Argon – IDENTIFICATION A. “Verify that the gas is not oxygen using a paramagnetic analyzer (2.5.27).”
  • USP 37 Medical Air (19.5% to 23.5%)
  • USP 37 Oxygen NLT 99.0% by volume
  • Aviator’s Breathing Oxygen (ABO)
  • Breathable Air (BA)
  • Liquid Oxygen (LOX) Type II Grade A
  • CA OSHA 1910.134 CGA Grade D – for SCBA or Airline Respirators


Measuring moisture / water vapor in Medical gas

European Pharmacopeia 2.5.28 states that moisture in gases shall be determined using an electrolytic hygrometer


  • The measuring cell consists of a thin film of diphosphorus pentoxide between two coiled platinum wires acting as electrodes.
  • The water vapor / moisture in the gas to be examined is absorbed by the diphosphorus pentoxide creating phosphoric acid – an electrical conductor.
  • A continuous voltage applied across the electrodes electrolyzes the water while regenerating the diphosphorus pentoxide.
  • The resulting electric current is proportional to the water content.
  • This system is self-calibrating since it obeys Faraday’s law.

Systech Illinois Electrolytic P2O5 Moisture Analyzer MM510 is perfectly suited for this application.

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