Bead challenge test

The classic method of determining filter efficiency is by the bead challenge test, with a rating expressed as a beta ratio, thus a beta ratio > 75 specifies a filter efficiency of 98.6% or better relative to a particle size of x pm. 

In parallel libraries each compound is located in a defined reaction container, for example, one well of a 96-well plate. Because the molecular diversity of split-and-mix libraries usually exceeds that of parallel libraries, many more potential catalysts can be tested in split-and-mix libraries. Their screening is, however, a much greater challenge if the ensemble of all the beads is tested simultaneously. In contrast to parallel libraries, in which each potential catalyst is located in a defined reaction container, reactants and products are free to diffuse in the solvent that surrounds all the beads and leave the catalyst - naturally - unchanged. The challenge has been met by ... 

The process of orthogonal testing highlights one of the major technical challenges in solution-phase processes the separation of individual products from each other. In SPS, of course, products are, by definition, always attached to some kind of solid support, such as resin beads or pins. In solution-phase experiments, products are thoroughly mixed with each other. Even if one can identify which among all possible products are desirable, some way must he found to separate those products from those of no interest to the experimenter and from excess reagents that may he present in the reaction mixture. 

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