Biomedical Engineering Reference
In-Depth Information
polymers can be made under strict experimental control or specii cations,
whereas chitosan requires careful selection as a starting material. Successful
commercialisation depends on reliable quality control and quality assess-
ment protocols, especially in the biomedical i led. h us, standardisation of
native chitosan on a global scale is warranted in order to promote its utility.
Chitosan polymers are typically analysed using a variety of spectroscopic
and analytical techniques.
In the analysis of chitosan and its derivatives, determining the degree
of deacetylation (DDA) is the main priority. h e DDA inl uences proper-
ties such as solubility and reactivity and the molecular weight af ects the
physico-chemical and biological properties of the compounds [19, 20].
Many dif erent techniques are available to determine the DDA where all
techniques having both advantages and disadvantages. h ere is no solitary
technique to determine DDA, a combination of techniques can be used
to coni rm the value obtained. h ese techniques also provide additional
information on the polymer such as incorporation of dif erent functional
groups onto the polymer backbone. Techniques available to determine
structural and physical properties include:
Size exclusion chromatography (SEC) - of ers the determination of the
number average molecular weight (M
n
) and the weight average molecu-
lar weight (M
w
) which can be used to calculate the polydispersity index
(M
w
/M
n
). American Standard Test Method (ASTM) Organisation utilizes
ASTM F2602-08e1 as the standard test method for determining the molar
mass of chitosan and chitosan salts by virtue of SEC coupled to Multi-angle
Light Scattering Detection (SEC-MALS).
Nuclear Magnetic Resonance Spectroscopy (NMR) -
1
H and
15
N-NMR
are used for samples in solution and
13
C NMR is used for solid samples.
Solution NMR is ideal when a suitable NMR solvent is available. However,
solid state NMR provides an opportunity to assign structure to insoluble
samples. h is quantitative analysis is preferred as it is simple, quick and
accurate. h e ASTM utilizes NMR as the method of choice to determine
the DDA of chitosan samples [20]. Kasaai
et al.
reviewed the various NMR
spectroscopy techniques in determining DDA and found that solution
1
H
NMR is by far the best method available. NMR can also be used to i nd the
degree of substitution of a chitosan derivative [21].
Viscometry - viscosity is related to the DDA where viscosity is a widely
used method to determine DDA [20]. h e intrinsic viscosity of a poly-
mer solution is related to the polymer molecular weight according to the
Mark-Houwink-Sakurada (MHS) equation, [η] = K(M
v
)
a
. Where [η] is the
intrinsic viscosity, M
v
the viscosity-average molecular weight, and K and a,
are the constants for a given solute-solvent system [22].
