Biomedical Engineering Reference
In-Depth Information
Figure 10. Temperature dependencies of the rate constants,
k
, of the Weibull model for the
decomposition of
(
{
)
hexanoyl,
(
)
octanoyl,
(
U
)
decanoyl,
(
)
lauroyl, (
V
) myristoyl, and (
Z
)
palmitoyl ascorbates (a) in aqueous solution at pH 5 and (b) in air at 75% relative humidity.
Figure 11. Relationship between the activation energy,
E
, and the logarithm of the frequency factor,
A
,
for the rate constant,
k
. of the Weibull model for the decomposition of saturated acyl ascorbate in (
{
)
aqueous solution at pH 5 and (
) air at 75% relative humidity. The
A
value is in units of s
-1
.
relative humidity. At 12 and 44% relative humidity the rate of ascorbates increased as acyl
chains decreased. The decomposition kinetics of the acyl ascorbates were empirically
expressed by the Weibull equation (Eq. 3). The
k
values increased with increasing relative
humidity for all acyl ascorbates at 80ºC. The acyl chain length affected the
k
value at 44%
relative humidity, and the
k
value increased as acyl chain length decreased. The
n
value for
