Filtration in the microplate format allows high throughput sample preparation that is automatable with liquid-handling workstations. Generally, plasma samples are frozen before analysis and the freeze/thaw process can introduce or promote clot formation as the proteins separate from the water. The prevalence of clot formation and its magnitude become greater with repeated freeze/thaw cycles . These clots are capable of plugging pipettips and create pipetting errors with automated systems. Berna et al.  describe an application in which 20- |vm polypropylene filter plates (CaptivaTM; Varian Inc., Harbor City, California) were used as the source container for a set of plasma samples. The top of the filter plate is sealed, as well as the bottom. Prior to analysis, the filter plate containing frozen plasma samples is allowed to thaw; the bottom cover is removed and the filter plate is placed over a deep-well microplate to collect the plasma filtrate. The filter plate/collection plate combination can be placed into a centrifuge to complete the filtration process, if required, or a vacuum can be applied with a vacuum collar or manifold.
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