During the primary drying phase of freeze drying (lyophilization), ice sublimes directly to vapor. The chamber pressure must be maintained:
Options:
(A) Well below the triple point of water ($611.65\text{ Pa}$ or $4.58\text{ Torr}$)
(B) At atmospheric pressure
(C) Above $10\text{ bar}$
(D) At critical point pressure ($22.06\text{ MPa}$)
Answer Key:
A
Step-by-Step Solution & Explanation
To prevent ice crystals from melting into liquid water, freeze drying must operate strictly below the water triple point pressure ($611.7\text{ Pa}$, $0.01^\circ\text{C}$), typically at $10-50\text{ Pa}$ ($0.1-0.5\text{ mbar}$).