Fa. Johnson et al., CHARACTERIZATION OF THE BLOCK STRUCTURE AND MOLECULAR-WEIGHT OF SODIUM ALGINATES, Journal of Pharmacy and Pharmacology, 49(7), 1997, pp. 639-643
Sodium alginates are widely used within the pharmaceutical sciences, y
et the molecular characteristics of these materials are frequently not
stated. In this study, a range of characterization techniques is appl
ied to five sodium alginate samples and the data compared, both betwee
n techniques and with the information obtained from the manufacturer.
The mannuronic acid to guluronic acid (MG) ratio and the distribution
of uronic acid residues of five sodium alginate samples have been meas
ured using circular dichroism and NMR, with circular dichroism yieldin
g MG ratios between 42.1 and 63.6%, depending on the grade of alginate
used. The MG ratios obtained from NMR studies were in broad agreement
with these values, and the technique also yielded information on the
distribution of uronic acid residues within each batch; this was again
found to vary considerably (NG > 1 values ranging from 6.9 to 17.5).
It was noted that samples with similar MG ratios could have markedly d
ifferent chain-distribution characteristics. The uronic acid ratio ran
ges obtained from the manufacturers were found to be in good agreement
with those found experimentally. Intrinsic viscosity measurements wer
e used to compare the molecular weights of the samples; values between
approximately 12000 and 180000 were obtained for the different batche
s. The study has enabled comparison of different methods for character
ization of sodium alginate samples, highlighting their relative merits
and the possible protocols that might be adopted. A critical discussi
on is given of the individual and combined use of these techniques and
the relevance of such studies to the rational design and quality cont
rol of alginate-based pharmaceutical systems.