Chemistry Reference
In-Depth Information
(a)
50
μ
m
1
Inlet frit
structures
2
3
3 mm
4
150
m
μ
Outlet frit
structures
5
5 mm
(b)
50
μ
m
Inlet frit
structures
Outlet frit
structures
ODS beads
(5
μ
m)
150
μ
m
50
μ
m
Figure 17.12
(a) Schematic of the PDMS microchip used for CEC and preconcentration: reservoirs:
(1) sample; (2) buffer; (3) sample waste; (4) bead introduction; (5) waste; expanded view of a bead chamber
and detailed structures of inlet and outlet frits. (b) Images of bead (5
m diameter)-packed chambers inlet and
outlet frit structures. Adapted from [123] with permission from Wiley-VCH Verlag GmbH & Co. KGaA © 2003.
m
photopolymerized frits for retaining beads in microfluidic channels for solid phase extraction. Although
intricate fabrication of methacrylate polymers has been previously performed, fabrication of the small frits
necessary for microfluidic frits was challenging. Several factors become critical to success in the
photopolymerization of these methyacrylate monomers. The first one was the purity of the monomers. The
second factor was the need for efficient cooling of the fluidic device during exposure. Cooling becomes
necessary to eliminate undesirable polymerization. The third and most important factor was the elimination
of localized fluid flow in the microchannels due to siphoning effects. These results in irregular, elongated
masses of polymer that is not appropriate for holding beads as it is shown in Figure 17.13(b). Once the frit
was in place, a simple procedure was used to pack the solid phase extraction column. Pulling slurry of beads
in acetonitrile through the frit produced a well packed column in a short period of time (10 s).
