Microscale Needles

Microfabricated needles Microhypodermic needles Microprojections Microscale needles Microtips and microspikes... 

For gas chromatography, the most suitable membrane extraction technique is MMLLE. The organic acceptor is better compatible with GC than with HPLC, as are the analytes that are best extracted in such a system, i.e., relatively hydrophobic compounds. A new development is the ESy instrument (ESyTech AB, Lund, Sweden) [76-78] where an MMLLE extraction in microscale (1 mL extracted into a volume ca 1 p,L) is automatically performed and the organic extract is directly injected into the GC by an injection needle, directly connected to the extraction cell. See Figure 12.7. 

A microscale SPE technique was developed in 1992 by Janusz Pawliszyn at the University of Waterloo, Ontario Canada. According to J. Berg of Varian Assoc., Walnut Creek, CA, the device shown in Figure 12-11, p. 135, "consists of a holder and a replaceable fiber assembly. The assembled unit looks much like a syringe, but in place of the hollow needle is a fiber inside a protective sheath. The fiber is attached to the holder plunger, so that it may be exposed by moving it out of the sheath. The fiber itself consists of a piece of fused silica rod coated with an adsorbent. 

Low-dimensional crystals such as epitaxial needles and solution-grown platelets of TPCOs act as a microscale gain medium. The self-cavity and self-waveguiding effects of these crystals result in ASE in the wavelength region of the fluorescence band where the self-absorption loss is minimized. Furthermore, the uniaxial orientation of the TPCO molecules in these low-dimensional crystals promotes the stimulated emission process and enhances the polarized ASE. 

Microscale external gas trap. (The inset shows an expanded view of an alternative fitting, using a syringe needle and a rubber septum.)... 

Attachment of polymer brushes to the surface with nanoscale and microscale features may provide additional level of control over the assembly of polymer brushes. For example, a two-layer structure was built from a rough polymer layer with needle-like structures of micrometer size and a layer formed by the nanoscopic self-assembled domains of a demixed polymer brush (carboxyl-terminated poly(styrene-co-2,3,4,5,6-pentafluorostyrene) and carboxyl-terminated poly(2-vinylpyridine)) irreversibly grafted onto the needles (Minko et al., 2003). The wettability of the surface can be altered by exposing the surface to solvents that are selective to one of the components of the brush. The microscale features amplify the response, allowing the surface enrichment by the favored component while the rest of the brush is collapsed and hidden within the microstructures of the film. 

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