The problem of aligning multiple liquid chromatography mass spectrometry runs to a common reference time frame is solved to facilitate comparison among LC-MS runs. The device is characterized in that the venous reservoir is separated from the cardiotomy reservoir by a partition which includes a plurality of apertures. The decompression algorithm may be executed on a periodic basis, and the parameters used to select the data to be decompressed may be moved from the second memory to the first memory each time the decompression algorithm executes.