One method for purifying a chitosan starting material includes contacting it
with at least one treatment agent selected from a protein-complexing agent, a metal-chelating
agent, and a metal-complexing agent under pH conditions effective for forming a
water insoluble chitosan precipitate and at least one water soluble material selected
from a water soluble protein complex, a water soluble metal chelate, and a water
soluble metal complex. Another variant involves solubilizing the chitosan starting
material in an aqueous solution to produce an intermediate chitosan material. The
intermediate chitosan material is contacted with a deproteinization agent and/or
a demetallization agent under pH conditions effective for forming a water insoluble
chitosan precipitate and at least one water soluble material that includes the
pre-existing impurity. In both methods, the water insoluble chitosan precipitate
and the water soluble material are separated resulting in a purified chitosan material.
