A flow-through microsampling device that can be inserted in the column elution flow line of a chromatographic system has been developed. A sample drop (volume 2.2 nl) is ejected when a voltage pulse is applied to a piezo-electric transducer. The drops can be ejected with up to 70 Hz frequency, giving a sample flow range of 0-9 μl/min. Samples were collected on a moving agarose surface during elution of freshly prepared human serum. The precipitate pattern obtained after immunoelectrophoresis is similar to what would be obtained in a fused rocket electrophoresis of multiple samples from a fraction collector.