OXYRED: BREATHABLE OXYGEN ANALYZER
DETECTION OF PPM AND MINOR CONTAMINANTS IN HIGH PURITY GASES
The Oxyred system is an FTIR automated laboratory sampling system studied for the analysis of compressed gases and capable of ppb contaminant detection in high purity gases, such as Oxygen moisture and its contaminants.
Oxyred is a customized system using an infrared spectrometer FTIR as detector and a long path cell (variable or fixed path) for the measurement at high sensitivity. The instrument is equipped with an integrated software with a touchscreen display.
Some parts of the pneumatic circuit are heated to reduce the possibility that moisture can condensate in large volumes. Heated parts are: long path cell, valves block and the transfer line. A pressure transducer with accuracy ±0.15% is controlling the pressure repeatability of the cell loading and unloading. The system includes:
- a controller box containing electronics and pneumatic valves,
- a pump,
- an heatable long path cell (variable or fixed path),
- a touch screen display.
We consider the FTIR measurement of substances in gaseous state gases and vapours. By gases we mean those compounds that at room temperature have a vapour pressure higher than one atmosphere, such as CO2, CO, NO2, NO, methane, dimethyl ether and arsine. By vapours we mean the gaseous phases of compounds that normally are liquids or solids (room temperature vapour pressure less than one atmosphere).
Long path cells are necessary for gas measurements mainly because of the low density of the gaseous samples.
A gas consists of fast-moving molecules that occupy a volume about one thousand times greater that the volume of a comparable mass of condensed phase material. Furthermore, a gas to be measured is frequently only a minor component in air, nitrogen, or another gaseous matrix material. The matrix gas may be totally transparent to infrared radiation, as in the case of dry air, or at least it is likely to be partially transparent.
The minor components thus may be measured by infrared absorption, providing that the optical path is long enough. All polyatomic molecules and hetero-nuclear diatomic molecules absorb infrared radiation. The absorption changes the molecular rotation and vibration. The pattern of absorption therefore depends on the physical properties of the molecule, such as the number and type of atoms, the bond angles and bond strengths. This means that each spectrum differs from all others and may be considered the molecular “signature”.