NMR imaging has been used to investigate the in situ
swelling behavior of 2-hydroxypropylmethylcellulose (HPMC) tablets in a sample geometry chosen for the
simplicity of its diffusion behavior.
Preliminary 1H NMR spectroscopy experiments were
performed on equilibrated mixtures of HPMC and
water. From these, the dependence of the 1H
T
1 and T
2 relaxation
parameters of the water protons with
respect to HPMC weight percent were obtained. Further analysis of
the T
2 values and 1H
z-spectroscopic
data revealed that as the polymer concentration was increased from 10%
to 20% w/w HPMC, the polymer
mobility decreased substantially. One-dimensional NMR imaging of
1H in the swelling tablet system
was used to monitor the movement of water into the polymer and to
calculate the T
2 parameters across
the system. HPMC weight percents were calculated from these
T
2 values using the previously
determined
calibration. HPMC distributions were determined for two tablet
thicknesses. Similar swelling behavior
was observed for both thicknesses at early times prior to the thinner
tablet becoming completely hydrated.
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