Biomedical Engineering Reference
In-Depth Information
further raised to 7.0 by incremental addition of the Na
2
SiO
3
solution. A gelatinous polymer
formed at pH 7.0. The solution was stirred an additional 30 minutes, covered and stored at
4°C overnight. The resulting aqueous layer was removed. Excess sulfate ions were removed
from the gel by successive washings with distilled deionized water until the aqueous phase
failed a sulfate test using a few drops of a 1.0% barium solution (as the nitrate salt). When no
precipitate was visible, one final wash with the distilled deionized water was performed to
ensure complete sulfate removal.
Remaining polymer was transferred to ceramic evaporating dishes and baked at
approximately 100 C until completely dry. The immobilized
D. innoxia
biomaterial was
then ground and sieved. The 40-60-mesh (423-635 μm) particle size fraction was collected.
Percent compositions of cell wall biomaterial were determined gravimetrically to be 64.6%
and 75.3% for the native and modified materials, respectively.
2.3 Biomaterial columns
The columns used have been described elsewhere (Williams and Rayson, 2003) and were
constructed in-house from Plexiglas
™
tubing (2.5 cm in length and 3 mm i.d.). Teflon
™
tubing (0.8-mm i.d.) was used for all column connections. Interface of the column to the ICP-
OES was accomplished by connecting the column outlet directly to the inlet of the cross-
flow type nebulizer using the minimum length of Teflon
™
tubing (15 cm). Column effluent
was monitored for each of 27 different metals simultaneously. Table 1 list the elements
observed and their respective emission wavelengths.
Element Wavelength/nm Element Wavelength/nm Element Wavelength/nm
Na 589.00 Mg 279.00 Al 396.15
Ca 317.90 Cr 267.70 Mn 257.60
Fe 259.90 Ni 231.60 Cu 324.70
Zn 213.80 Cd 228.80 Ag 328.00
Sn 189.90 Pb 220.30 Ba 493.40
Sr 421.50 U 409.00 Y 371.00
V 242.40 Mo 202.00 Co 228.60
Si 251.60 As 193.60 Se 196.00
Tb 350.97 Eu 381.97 Th 283.73
Table 1. Elements and the corresponding emission wavelength used during monitoring of
column effluents (elements of interests in this study indicated by boldface print).
Each column was packed with approximately 125 mg of the immobilized
D. innoxia
material
and flow tested using distilled deionized water. Once packed and tested for leaks, each
column was exposed to 20 mL of 1.0-M HCl using a peristaltic pump (Model Rabbit, Rainin)
(1.0 mL/min for 20 min) and the effluent monitored for metals released from the
biomaterial. Following the acid rinse, the columns were then exposed to 5 mL of distilled
deionized water (1.0 mL/min for five minutes) to reestablish an ambient pH influent
environment (~pH 6.2).
These studies involved, initially, the exposure of a small column (3.0 mm i.d., 10.0 mm in
length) to an equimolar mixture of metal ions, specifically, Cd
2+
, Zn
2+
, and Ni
2+
, and
exposure to solutions of each metal sequentially while continuously monitoring these (and
other) metal species in the column effluent.
