a card or insert having a plurality of recesses for a sample preparation device , the card containing cast - in - place composite and / or non - filled structures which are useful as sorptive or reactive media or for size - based separations . any particular card size or configuration can be used , and the inclusion of a large amount of adsorptive particles in polymer is achieved while still maintaining the membrane three dimensional structure . in a first preferred embodiment , the composite structures comprise particles entrapped within a porous polymeric substrate , and are cast in - place into a plurality of recesses in an insert for a multi - well sample preparation device , thereby providing an effective platform for high throughput micromass handling . with the appropriate selection of particle chemistry , virtually any separation or purification operation can be conducted in multiplicity , including selective bind / elute chromatography operations , on sample mass loads less than 1 microgram in volumes of a few microliters , as well as larger mass loads and volumes . manufacturing flexibility and high throughput is achieved . the card can be configured for direct analysis of bound sample without elution .