Monolithic materials: Promises, challenges, achievements
Nowadays, there is a lot of buzz in separations science about the porous materials known as monoliths. Monoliths are used mostly as separation media and supports, and each one can be roughly compared to a single porous ''particle''. Monoliths are an alternative to columns packed with particulate stationary phases, which chromatographers have used for >100 years. Although that technology is well developed, it is not flawless. Packed columns have rather large void volumes; this is an inevitable result of the particulate character of the packing. Even in a perfectly organized array of monodisperse spheres, {approx}30% of the volume is interstitial voids. In reality, the percentage is even larger. As a consequence, a significant part of the column volume is not used for separation. However, this is not the only problem. Consider what happens when a mobile phase is pumped through a column packed with a standard porous packing. The liquid flows readily through the interstitial voids between the particles, where resistance to its flow is the smallest (Figure 1a). In contrast, the liquid in the pores remains stagnant. If a sample is injected into the stream of the mobile phase, the compounds in the sample will also be carried through the voids. However, diffusion occurs because of the concentration gradient between the compounds in solution flowing through the interstices and the stagnant liquid within the pores of the packing, and transport of these compounds into the pores results. Once the concentration ''pulse'' has passed by the bead, the compounds diffuse back from the pores into the surrounding liquid; eventually, only the original stagnant phase remains within the pores.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Director. Office of Science. Biological andEnvironmental Research
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 917821
- Report Number(s):
- LBNL-61714; ANCHAM; R&D Project: 50MF50; TRN: US200817%%894
- Journal Information:
- Analytical Chemistry, Vol. 78, Issue 7; Related Information: Journal Publication Date: 04/01/2006; ISSN 0003-2700
- Country of Publication:
- United States
- Language:
- English
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