ศิริวรรณ กันธิยะ. Pre-concentration of Cystine Using Monolithic Polymers. Master's Degree(Chemical Engineering). King Mongkut's University of Technology Thonburi. : King Mongkut's University of Technology Thonburi, 2006.
Pre-concentration of Cystine Using Monolithic Polymers
Abstract:
There has been an interest in developing a lab-on-a-chip system, a small device in micro and nano scales.
This type of device is especially useful for the analysis of humans biological fluid to provide medical
information for many diseases. Various functions can be connected together using micro-channels,
called microfluidics. The device can rapidly analyze a very small volume of sample by integrating
an on-chip sensor system. However, the limitation of this device is unreliable performance due to small
amount of sample volume, resulting in a very small amount of analytes to be measured. In this research,
poly(butyl methacrylate-co-ethylene dimethacrylate) (BUMA-EDMA) was used as monolithic polymers
to increase the concentration of a test compound in a microfluidic device. This device was fabricated
from poly(dimethylsiloxane) (PDMS) using the soft lithography technique and treated with oxygen
plasma to increase the hydrophilicity of the PDMS surface. The hydrophilicity of PDMS surface slightly
decreased after being exposed to air for 24 hours. Nonetheless, the surface was sufficiently hydrophilic
that solution could flow through without leaking. In the second part of this study, appropriate conditions
to in-situ polymerize monlith monomers and to operate the system were determined. Because of the difficulty
with polymerizing these monomers in our PDMS chip, this part of the study was conducted in capillary tubes.
Monomer concentrations of 12.5, 25, 50 and 75% by weight, and the polymerization time were varied to
investigate their effects on the structures, as well as the flow resistance of the monoliths. The monoliths
were first characterized using Scanning Electron Microscopy (SEM) and BET surface analysis. Higher
monomer concentration caused the decrease in small bead size, micropore size and void fraction while
increasing the surface area. Our results suggest that the adsorption efficiency would be higher for a high
monomer concentration monolith. Unfortunately, it would also result in tremendous back pressure and
possibly cause leaking. Therefore, 25% by weight monomer concentration monolith prepared by 3 hours
of UV exposure would be most appropriate for our application. Cystine was selected as a model compound
to verify the efficiency of this system. Cystine adsorption efficiency on this monolith was found to be 55%
by weight when the mixture was flowed through the system at 5 ?L/min. More importantly, cystine was
eluted using dilute HCl to yield 2.46 folds increase from its initial concentration.