The quality of fixation is influenced by pH and the type of ions present.
The choice of buffer is based on:
1. the buffering capacity in the desired pH range with the ability to maintain constant pH during fixation.
2. the side effects which vary with the tissue type:
a. suitable osmolarity so that cells and organelles neither swell nor shrink during fixation.
b. suitable ionic concentration so that materials are neither extracted nor precipitated during fixation.
c. the toxicity of the buffer.