Biomedical Engineering Reference
In-Depth Information
2.4 Frontal affinity chromatography with inductively coupled plasma atomic emission
detection
This technique has been described in detail elsewhere (Williams and Rayson, 2003). Briefly,
the biomass packed column, having been exposed to 20 mL of 1.0M HCl to remove any
metals remaining on the biomaterial (effluent monitored by ICPAES), was exposed to 5 mL
of 16 M, distilled-deionized water. The influent was a metal-ion solution, 0.1mM-0.2mM,
made from the nitrate salt of Cd
2+
, Ni
2+
, or Zn
2+
. Initially, the influent metal ion
concentration increased as a step function.
Each influent was pumped through a column using a peristaltic pump (Rainin) at the rate of
~1.0 mL min
-1
to a cross-flow type nebulizer and Scott-type double-pass spray chamber of
the ICP-OES spectrometer (Jarrell-Ash, AtomComp700). The biomaterial in each column
was exposed to each metal solution for 50 minutes. The effluent was monitored and
resulting break-through curves were recorded for each metal ion (Figures 1A-C). Following
exposure to the column, bound metal ions were stripped from the column using each of two
exposures to a 1.0 M HCl solution. The first 150-second (~2.5 mL) exposure removed
approximately 98% of the metal ions on the column (Figure 1D). The second 20 minute (~20
mL) exposure removed the remaining 2%. This was followed by a 5 minute (~5 mL) rinse
with distilled deionized water to return the pH to f the biomaterial to that of the natural
water (~6.2). Influent pH was not buffered to a predetermined pH to more accurately
emulate conditions of a natural water supply within a remediation application.
With a three metal system there are six combinations that the metals can be sequentially
exposed to the biomaterial (CdZnNi, CdNiZn, NiCdZn, NiZnCd, ZnCdNi, and ZnNiCd)
and all six were performed on each column. Specifically, the ZnNiCd sequence involved
exposure of a column packed with a biosorbents to a 0.20 mM Zn
2+
solution for 50 minutes
(Figure 1A). The influent was changed to a 0.20 mM Ni
2+
solution for another 50 minutes
(Figure 1B). Similarly, a 0.20 mM Cd
2+
solution was pumped through the same column for
an additional 50 minutes (Figure 1C). The column was then exposed to 1.0 M HCl for 2.5
and 20 minutes to remove all bound metal ions (Figure 1D).
Simultaneous exposure of the three metals at the same molar concentration was also
undertaken for each column with both the native (Figure 2) and modified (not shown)
biomaterials. All determinations were performed in triplicate with three separate columns
packed with each individual biosorbent.
3. Results and discussion
3.1 Binding capacities of native and modified
d. innoxia
Figure 1 illustrates a sequential 50-mL exposure of 0.1mM Zn
2+
, Ni
2+
, and Cd
2+
to the native
D. innoxia
. Figure 2 shows the sequential 50-mL exposures of 0.2mM Zn
2+
, Ni
2+
, and Cd
2+
to
the modified biomaterial. Table 2 lists the observed binding capacities for the three metals to
the modified
D. innoxia
reported in moles metal bound per gram of biomaterial for each
replicate. The capacities reported are mass balance capacities, as the column effluent was
monitored.
Simple statistical analysis using a t-test confirms the binding capacity of each metal to the
biomaterial was decreased as expected. The position of the metal in the sequence was
similarly indicated as affecting capacities in both the native and the modified biomaterial
materials. Further statistical analysis indicated that not only the position in the sequence but
