MONITORING PURITY DURING MEDICAL GAS FILLING
MEDICAL GASES
Medical gases are defined as any gases used for the medical treatment of humans, and are regulated under the same rules as medicinal drugs.
These regulations are set out in an official publication known as a Pharmacopeia, which specifies – among other things – how each gas should be produced and validated, the acceptable level of purity and official measurement methods.
Although they share some of the same rules, the United States Pharmacopeia( USP) and European Pharmacopeia( EP) have different regulations, and the acceptable concentration levels often vary.
PROCESS MEASURING POINTS
Medical gas cylinders are filled either at a facility adjacent to an Air Separation Unit( ASU) or at specific cylinder filling plants. The gas composition is measured at the source of supply, while quality is measured before and / or after the bulk gas delivery.
Gases are delivered to the filling plant via pipeline from an ASU or a tanker, in a liquefied form which is stored in a cryogenic tank. For EP regulations, dedicated tankers do not need to be sampled after filling a cryogenic vessel if a certificate of analysis is provided with the delivery.
The liquefied gas is vaporized into gas and pumped to the filling manifold. The quality is usually high enough that no further purification is required.
There must be a dedicated manifold for each single gas, and a dedicated mixture manifold for two or more gases, with control procedures to prevent cross-contamination.
For multi-cylinder manifolds, the gas from at least one cylinder from each manifold filling cycle is tested for identity and assay each time the cylinders are changed on the manifold. For single gases filled one cylinder at a time, at least one cylinder per cycle is tested.
Air is classed as a single gas so long as it is not mixed using N 2 and O 2.
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