Understanding water states is essential in formulation, stability, and lyophilization. Here’s the simplest breakdown:
Bound Water
- Tightly associated with molecules or surfaces
- Not easily removed (even on heating)
- Doesn’t freeze easily
- Contributes to structural stability
- Less available for reactions or microbial growth
Free Water
- Loosely held and easily removed
- Freezes and evaporates readily
- Drives chemical degradation & hydrolysis
- Supports microbial growth
- Major factor in stability issues
Why it matters?
The ratio of bound vs free water determines:
- Shelf-life
- Hygroscopicity
- Powder flow
- Degradation rate
- Lyophilization efficiency
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