Phosphorus pentoxide, freeze-drying desiccant

At the end of freeze-drying, the chamber is restored to atmospheric pressure with pure, dry nitrogen and the ampoules/vials are removed. The ampoules/vials are then stoppered and sealed/capped (see Section II.B.IO), or if required further desiccated over phosphorus pentoxide (see Section II.B.9). 

For materials where a very low residual moisture level is required which is not achievable by secondary drying during freeze-drying, further desiccation may be required. If this is so, the ampoules/vials are held at room temperature either in a series of tanks, or within the freeze-dryer, under vacuum with trays of phosphorus pentoxide for a period of 4 to 7 days. 

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