Monitoring biomolecule separations by mass spectrometry is described. The mixture to be separated is introduced into a first fluidic stream, which then passes through a chromatography column. Small samples are periodically taken from the first fluidic stream as it leaves the chromatography column and injected into a first branch of a second fluidic stream. Low molecular weight components detrimental to the efficient operation of the mass spectrometer are removed by an in-line dialysis cell. A second fraction of the second fluidic stream acts as the dialysate. In a second and preferred system provided in accordance with the present teaching, the first fraction of the second fluidic stream is further split downstream of the sampling mechanism through the use of a three-way connector. Approximately 0.3 to 5 microliters per minute continues through the dialysis cell and thereafter to the electrospray emitter of the mass spectrometer.