Biomedical Engineering Reference
In-Depth Information
Table 2. Parameters of the bilirubin adsorption isotherm on different adsorbent
(Annesini et al., 2005, 2008, submitted)
N
BIL
M
BIL
N
BIL
/M
BIL
Adsorbent Material
Eq.
Μ
mol/g
Μ
mol/g
Activated carbon
(05112, Fluka)
43.4±3.2
(33)
0.34±
0.13
Polymeric non-ionic resin
(Lewatit1064 MDPH, Bayer)
(30)
0.482±0.082
0.24±
0.03
A exp (−C
ALB
/C
∗
)
A = 48.9±3.4
C
∗
=
Anionic resin
(IRA 400, Sigma Aldric)
(30)
1245±
200 Μ
M
It is worth noting that the slope of the linear isotherm (33) is a decreasing function of
albumin concentration.
Since the free bilirubin adsorption isotherm from aqueous neutral solutions is not ex-
perimentally accessible (bilirubin is almost water insoluble at pH 7.4),
N
BIL
and
M
BIL
or, in
the case of linear isotherm, the ratio
N
BIL
/M
BIL
, may be considered as adjustable parameters
and determined by fitting of data obtained with albumin-containing solutions.
The experimental data of Annesini et al. (2005, 2008), showed that the chemical model
proposed is suitable to describe bilirubin adsorption isotherms onto activated carbon and
polymeric non-ionic resin (in the case of activated carbon, the linear form of the model (33)
can be used). On the other hand, for adsorption on anionic resin, Annesini et al. (submitted)
observed a clear reduction of the maximum bilirubin adsorbed amount as the concentration
of albumin in the solution was raised. Such a behavior, which is not predicted by the simple
chemical model presented here, suggests that, in this case, the effect of albumin on bilirubin
adsorption is not limited to binding in the liquid solution. Different other phenomena that
involve albumin and may cause the observed reduction of
N
BIL
can be hypothesized; in par-
ticular, albumin may compete with bilirubin for adsorption sites or cause steric hindrance to
its diffusion in the sorbent pores. Regardless of the phenomena actually involved, Annesini
et al. (submitted) accounted for these non-chemical effects of albumin with an empirical
relation between
N
BIL
and
C
ALB
. Tab. 2 reports a summary of the adsorption isotherm param-
eters for bilirubin on the different adsorptive media.
A comparison between bilirubin adsorption onto activated carbon and anionic resin at
constant albumin concentration (
120 Μ
mol/l) is reported in Fig. 4 (specific adsorption on
polymeric non-ionic resin is much lower and therefore not reported on the same plot). For
this albumin concentration, the slope of the bilirubin adsorption isotherm at
C
BIL
= 0
is 1.54,
0.36 and 0.012 l/g for anionic resin, activated carbon and polymeric resin, respectively. Fig.
4 clearly shows that the anionic resin is the best sorptive media for the bilirubin among
those tested.
Since the anionic resin showed the higher adsorption capacity for bilirubin, only this
adsorbent will be considered henceforth. In order to characterize bilirubin fixed-bed ad-
