Heterogeneous separations electrostatic

A fluorescence-activated cell sorter (FACS) is a flow cytometry instrument used to separate and identify cells in a heterogeneous population. Cell mixtures to be sorted are first bound to fluorescent dyes such as fluorescein or phycoerythrin. The labeled cells are then pumped through the instrument and are excited by a laser beam. Cells that fluoresce are detected, and an electrostatic charge is applied. The charged cells are separated using voltage deflection. 

The results for the bulk centers in the alkaline-earth oxides show that, in principle, EPR spectra could be obtained for a pair of O" ions separated by R on the surface. However, there are no examples of well-resolved fine-structure spectra for such adsorbed species. The main reasons for this are expected to be as follows From the above formula, one would anticipate the spacings between the lines in the parallel and parpendicular directions to increase with decreasing distance R. It is therefore likely that with the heterogeneity of sites that has been discussed previously for isolated O species, the EPR spectrum would be difficult to observe. Electrostatic repulsion will favor the collinear orientation of the two trapped holes on opposite sides of the positive ion vacancy, as observed from the relaxation... 

In the following we discuss some types of catalytic processes where electrostatics plays a determining role. First we treat homogeneous catalysis in aqueous solution and then heterogeneous catalysis at gas-crystal surfaces and with the participation of porous materials will be discussed. A separate section is devoted to enzyme catalysis, which differs essentially from the previous processes. It is possible that further examples of electrostatic catalysis, not discussed in this work, will be found in the future. 

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