Oxygen in gases is determined using a paramagnetic analyser.
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. The measurement of oxygen concentration is dependent upon the pressure and temperature and, if the analyser is not automatically compensated for variations in temperature and pressure, it must be calibrated immediately prior to use. As the paramagnetic effect of oxygen is linear the instrument must have a suitable range with a readability of 0.1 per cent or better.
Calibration of the instrument. Make the setting in the following manner:
- set the zero by passing nitrogen R1 through the instrument at a suitable flow rate until a constant reading is obtained. It should be set to zero according to the manufacturer's instructions;
- set the appropriate limit by passing air (20.9 per cent V/V O2) through the instrument at a suitable flow rate until a constant reading is obtained. The limit should be set to 20.9 per cent V/V in accordance with the manufacturer's instructions.
Assay. Pass the gas to be examined through the instrument at a constant flow rate until a suitable reading is obtained.
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