Lyophilization (Freeze-Drying) — Process Description

1. Process Overview

Lyophilization is a three-stage drying process that removes water from peptide solutions by sublimation and desorption under vacuum. The process preserves peptide structure and enables long-term stability.

2. Three-Stage Process

Stage	Purpose	Temperature	Pressure	Duration
Freezing	Solidify water	−40 °C	Atmospheric	2 – 4 h
Primary Drying	Sublime ice	−10 °C	0.05 – 0.1 mbar	12 – 36 h
Secondary Drying	Desorb bound water	+25 °C	<0.02 mbar	4 – 8 h

3. Critical Process Parameters

Parameter	Definition	Control Range
Eutectic Temperature (Te)	Temperature at which frozen solution melts	Must remain below Te during primary drying
Collapse Temperature (Tc)	Temperature above which cake structure collapses	≥ Tc + 2 °C margin
Glass Transition (Tg')	Temperature of amorphous phase transition	Typically −30 to −10 °C for peptides
Chamber Pressure	Pressure during primary drying	0.05 – 0.1 mbar

4. Residual Moisture Target

Application	Target Moisture	Method
Bulk peptide	≤1.0%	Karl Fischer titration
Lyophilized formulation	≤0.5%	Karl Fischer titration